Patent Description:
This invention was made with Government support under (DE-FG02-07ER84812) awarded by the Department of Energy. The Government has certain rights in this invention.

The present disclosure relates to a micron scale heating stage configured for conducting mechanical property testing on a sub-micron scale. In particular, the present disclosure relates to sub-micron scale heating and mechanical testing of a test subject.

Document <CIT> shows a force sensor fabricated in a micro machined process, for use in for instance a nanoindentation setup, wherein said force sensor comprises: a membrane movable in relation to a bulk structure; at least one detection element in a detection structure in connection with the bulk structure; and connectors for connecting said force sensor to electronics, wherein said membrane is attached to said bulk structure through at least one spring and said membrane includes a probe holding structure, wherein said at least one spring provides said membrane with movement capabilities for said membrane in at least one direction with respect to said bulk structure, and wherein said movement is measured using said at least one detection element. Thus, <CIT> discloses a micron scale stage configured for conducting mechanical property testing on a sub-micron scale comprising: a base interface configured for coupling with a holder base of a sub-micron scale mechanical property testing instrument and electro-mechanical transducer assembly.

Document <CIT> shows high resolution observation of a sample at a high temperature above <NUM>° C. This is accomplished by suppressing sample drift by heating over a short time and with small electric current. A heater envelope made of a ceramic having a carbon coating on the.

surface is attached around a heater surrounding the sample. The heater envelope is rotatable around pivot screws, and has an outer frame portion of a holder individually having slots capable of letting a focused ion beam (FIB) enter so that the sample mounting on the holder, as it is, may be milled with the FIB.

Nanoindentation is a method to quantitatively measure mechanical properties, such as elastic modulus and hardness, of materials at nanometer length scale using depth sensing indentation technique. In nanoindentation, a nanoindenter capable of determining the loading force and displacement is used. Typically, a force employed in nanoindentation is less than <NUM> mN, with a typical displacement range being smaller than <NUM>, and with a noise level typically being better than <NUM> rms. The force and displacement data are used to determine a sample's mechanical properties. For sample property estimation a nanoindenter is integrated with a characterized indenter tip which has known geometry and known mechanical properties.

One of the emerging nanomechanical characterization techniques is quantitative transmission electron microscopy (TEM) in-situ mechanical testing. This testing method enables monitoring of the deformation of a sample in real time while measuring the quantitative mechanical data. Coupling a nanomechanical system with TEM imaging allows researchers to study structure property correlation and the influence of pre-existing defects on the mechanical response of materials. In addition to imaging, selected-area diffraction can be used to determine sample orientation and loading direction influence on mechanical response. Moreover, with in-situ mechanical testing, the deformation can be viewed in real-time rather than "post mortem". Performing TEM in-situ nanomechanical testing can provide unambiguous differentiation between the many possible causes of force or displacement transients which may include dislocation bursts, phase transformations, shear banding or fracture onset. Nanomechanical testing at elevated temperature is an important part of material characterization for materials having phase changes or variant mechanical properties as the temperature increases. Some of the applications of the high temperature nanomechanical test are glass transition temperature identification of polymeric and rubber materials, phase transformations of low temperature metals and shape memory alloys, study of biological samples at body temperature, simulated and accelerated thermal aging studies, accelerated material creep studies, and time-temperature-superposition curve plotting of polymers.

It relates to a micron scale heating stage as defined in independent claim <NUM>. It also relates to a method of sub-micron scale heating and mechanical testing of a test subject as defined in independent claim <NUM>. Advantageous embodiments of the present invention can be found in the dependent claims and in the following description and the figures.

In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration how specific embodiments of the present disclosure may be practiced. In this regard, directional terminology, such as "top," "bottom," "front," "back," "leading," "trailing," etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present disclosure can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. These embodiments are described in sufficient detail to enable those skilled in the art to practice aspects of this disclosure, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

According to embodiments described herein, a system and method are provided for mechanically testing small test subjects at the nano and micro scales (i.e., sub-micron scale), including, but not limited to, nanostructures, thin films and the like. Such testing is performed, in one example, to determine the mechanical properties of the materials composing the subjects. A TEM holder modification for nanomechanical testing instrumentation provides a small space constrained by the front end portion of the holder and the pole gap of a TEM electron beam. Developing a TEM in-situ nanomechanical test instrument with an integrated heater is therefore a great challenge requiring a new design and instrumentation approach. According to one embodiment, as will be described in greater detail herein, the system described herein includes a micromachined or microelectro-mechanical (MEMS) based heater including heating and sensing elements. The heater enables the use of a nanoindenter or other instrument which provides a high precision actuation force, corresponding indenting or other deformation (e.g., indenting, scratching, pulling, compressing and the like), and high resolution displacement sensing on at least a nanometer or micrometer scale.

<FIG> is a schematic block diagram illustrating an example of a nanomechanical test system <NUM> employing a MEMS based heater <NUM> (referred to hereafter as MEMS heater <NUM>) for heating and sensing the temperature of a small test sample (or test subject) <NUM>. In addition to the MEMS heater <NUM>, the nanomechanical test system <NUM> (e.g., sub-micron) includes an electro-mechanical (EM) transducer <NUM> having a displaceable probe <NUM>, an actuator <NUM> to displace the displaceable probe <NUM>, a displacement sensor <NUM>, a computer <NUM>, a coarse positioner <NUM>, a fine positioner <NUM>, and a controller <NUM>. The EM transducer <NUM> includes, but is not limited to, indentation, compression, tensile, fatigue, tribology, fracture instruments and the like.

The nanomechanical test system <NUM> further includes a test subject holder <NUM> including a sample stage (or micron scale heating stage) <NUM> and having a base portion (or holder base) <NUM>. The MEMS heater <NUM> is positioned on the sample stage <NUM> (e.g., within or along the subject holder), and the holder is detachably mounted to the nanomechanical test system <NUM>. According to one embodiment, and described in greater detail below, the MEMS heater <NUM> is micromachined or MEMS based so as to fit into a small, restricted space such as for in-situ nanomechanical testing application within a quantitative transmission electron microscope (TEM), for example.

According to one embodiment, the controller <NUM> includes an input/output module <NUM>, a transducer control circuit <NUM>, a heater control circuit <NUM>, a first <NUM>. processor <NUM>, such as microprocessor or digital signal processor (DSP) and/or field programmable gate array (FPGA), for example, and a first memory system (or memory) <NUM>. According to one embodiment, the first memory system <NUM> includes a displacement module <NUM>, a force module <NUM>, a temperature sensing module <NUM>, and a heating module <NUM>. According to another embodiment, the input/output module <NUM> further includes a D/A converter <NUM>, and an A/D converter <NUM>.

In one example, the computer <NUM> includes a second processor <NUM> and a second memory system (or memory) <NUM> that stores an application module <NUM>. The computer <NUM> may access and communicate with the controller <NUM> via an interface <NUM> (e.g. a USB interface). <FIG> shows the computer <NUM> and controller <NUM> as separate entities. In other examples, computer <NUM> and controller <NUM> are combined as part of a single processing and control system.

According to one embodiment, the application module <NUM>, displacement module <NUM>, and force module <NUM> each include instructions respectively stored in memories <NUM>, <NUM> and which are accessible and executable by first processor <NUM>. Memories <NUM>, <NUM> include, but are not limited to, any number of volatile or non-volatile storage devices such as RAM, flash memory, hard disk drives, CD-ROM drives, DVD drives and the like. In other embodiments, the displacement module <NUM>, force module <NUM>, temperature sensing module <NUM>, and heating module <NUM> include any combination of hardware and software components configured to perform functions described herein. The software component of the displacement module <NUM> and the force module <NUM>, the temperature sensing module <NUM>, and the heating module <NUM> are each stored on a medium separate from the first processor <NUM> prior to being stored in first memory system <NUM>, in one example. Examples of such media include a hard disk drive, a flash memory device, a compact disc (e.g. a CD-ROM, CD-R, or CD-RW), and a digital video disc (e.g. a DVD, DVD-R, and DVD-RW), for example.

According to one embodiment, the coarse positioner <NUM> and the fine positioner <NUM> enable <NUM>-dimensional positioning (i.e. x-, y-, and z-axes in <FIG>) of the EM transducer <NUM> and displaceable probe <NUM> in the millimeter range with a sub-nanometer resolution. According to one embodiment, final positioning and movement of the displaceable probe <NUM> is performed by the actuator <NUM> via the application module <NUM> on the computer <NUM> and the controller <NUM>. According to one embodiment, the controller <NUM> is configured to control and monitor the movement of displaceable probe <NUM> and to provide data representative of a displacement of the displaceable probe <NUM> (from the displacement sensor <NUM>) to the computer <NUM> through the interface <NUM>. According to one embodiment, controller <NUM> is configured to determine and adjust a force applied to the test sample <NUM> by the displaceable probe <NUM>.

According to one embodiment, the controller <NUM> is configured to control and monitor the temperature of the MEMS heater <NUM> and the test subject <NUM> and to provide data representative of a temperature of the MEMS heater <NUM> and the test subject <NUM> to the computer <NUM> via interface <NUM>. In one example, the controller <NUM> is configured to determine and adjust a heating power <NUM> applied to the MEMS heater <NUM> and the test subject <NUM> to achieve a desired test subject temperature (and heater temperature) for testing and observation of the test subject.

In operation, a user can program the controller <NUM> with the computer <NUM> through the application module <NUM>. According to one embodiment, the controller <NUM>, through the force module <NUM>, provides an input or force signal (or actuation force) <NUM> to the actuator <NUM> representative of a desired force for application to the test sample <NUM> by the displaceable probe <NUM>. In response to the input or force signal <NUM>, the actuator <NUM> drives the displaceable probe <NUM> toward the sample stage <NUM> (e.g. along the z-axis in <FIG>). The displaceable probe <NUM> contacts and applies the desired force to the test subject <NUM>. The D/A converter <NUM> converts the input or force signal provided by the force module <NUM> from digital to analog form which, in turn, is amplified to generate the actuation force <NUM> by transducer control circuit <NUM> as provided to actuator <NUM>.

The displacement sensor <NUM> comprises a transducer (e.g. a capacitive transducer) which detects movement of displaceable probe <NUM> at least along the z-axis, and provides a displacement signal <NUM> to controller <NUM> representing measurement of the movement of the displaceable probe <NUM>. In other embodiments, in addition to movement along the z-axis, the displacement sensor <NUM> detects and provides indication of other types of movement of displaceable probe <NUM>, such as displacement along the x- and/or y-axes or rotational movement about the x- and/or y-axes. The transducer control circuit <NUM> conditions the displacement signal <NUM> from the displacement sensor <NUM> and sends the displacement signal <NUM> to the A/D converter <NUM>. The A/D converter <NUM> converts the displacement signal <NUM> from an analog form, as received from the transducer control circuit <NUM>, to a digital form for processing by the displacement module <NUM>. The displacement module <NUM>, according to one embodiment, communicates measurement of the movement of the displaceable probe <NUM> to the force module <NUM> (e.g. for force calculations) and computer <NUM> (via interface <NUM>).

According to one embodiment, controller <NUM> is further configured to control movement or displacement of displaceable probe <NUM> in the x- and y-directions relative to sample stage <NUM>, such as by moving EM transducer <NUM> relative to sample stage <NUM> or by moving sample stage <NUM> relative to EM transducer <NUM>. According to one embodiment, the nanomechanical test system <NUM> further includes an imaging device <NUM> comprising an instrument/device such as an electron microscope, an optical microscope, or a scanning probe microscope (SPM) (e.g., an atomic force microscope (AFM)) configured to provide images of a test sample <NUM> mounted to sample stage <NUM>, including images of the test subject before, during and after mechanical testing such as indentation, compression, fatigue and fracture testing and the like and video of the same.

Examples of nanomechanical test systems suitable to be configured for use with a MEMS heater <NUM> according to embodiments of the present disclosure are described in <CIT> and <CIT>, both of which are assigned to the same assignee as the present disclosure. For instance, test systems suitable for configuration with the MEMS heater <NUM> include, but are not limited to, optical microscopes, scanning probe microscopes (SPM), electron microscopes and the like. In each of these examples, ex-situ or in-situ heating is performed with the MEMS heater <NUM>. Another test system suitable for configuration with the MEMS heater <NUM> is an electron microscopy (e.g. transmission electron (TEM) and/or scanning electron(SEM)) in-situ nanomechanical tester commercially available under the trade name PicoIndenter from Hysitron, Incorporated, of Minneapolis, Minnesota, USA.

During a temperature controlled mechanical testing, as will be described in greater detail below, MEMS heater <NUM> is controlled so as to heat and maintain the test subject <NUM> at the desired temperature. The MEMS heater <NUM> is operated with at least one of open loop control or closed loop control. For more accurate temperature regulation in a changing thermal environment, the closed loop control system utilizing the temperature signal <NUM> as the feedback is used. When the sample temperature reaches the desired temperature, EM transducer <NUM> is operated to apply a force with the displaceable probe <NUM> to the test subject <NUM>. According to one embodiment, the temperature of the test subject <NUM> is measured by the MEMS heater <NUM> and the force applied and a displacement of the indented material of the test subject <NUM> are measured by nanomechanical test system <NUM>. The nanomechanical test system <NUM> measures these parameters through the actuator <NUM> and the displacement sensor <NUM> of EM transducer <NUM> while being synchronously imaged via imaging device <NUM>. The force and displacement data and images of the corresponding indentation are substantially simultaneously measured in real-time and observed by a combination of the actuator <NUM>, the displacement sensor <NUM> and the imaging device <NUM> (e.g., an electron microscope). Stated another way, examination of the test subject - through the above described measuring and imaging techniques - at a specified testing temperature is thereby performed without any appreciable pause between measurement, imaging or heating. Phenomena including elastic/plastic deformation and the like that alter the shape of the indentation over time after application of the indentation force have minimal effect on the measurement and imaging of the indentation. Additionally, elastic/plastic deformation and the like are observable and measurable for a time period starting immediately after indentation. That is to say, because the nanomechanical test system <NUM> with the MEMS heater <NUM> is able to perform the indentation testing, and measure and observe the material surrounding the indentation at substantially the same time, changes in the material over a period of time are similarly observable at the time of and immediately after the indentation. Observation of these parameters and phenomena at or immediately after indentation are sometimes critical in the accurate assessment and determination of corresponding material properties.

<FIG>, B show the MEMS heater <NUM> designed for nanomechanical testing at a selected elevated temperature. The MEMS heater <NUM>, for instance, in the sample stage <NUM>, is coupled with the base portion <NUM> as described above and further described below. As shown in <FIG>, in one example, the sample stage <NUM> includes a base interface <NUM> for coupling with the base portion <NUM> (i.e., the holder base, further described below) to form the test subject holder <NUM>. The sample stage <NUM> further includes a test subject stage <NUM>. For nanomechanical tests at elevated temperature, the MEMS heater <NUM> mounts a test subject <NUM> (shown in <FIG>) at the test subject stage <NUM> for interaction with the displaceable probe <NUM>. As an example, a thin film subject is attached to the MEMS heater <NUM> (e.g., the test subject stage <NUM>) along a stage subject surface <NUM> and positioned perpendicular to the Z-axis for a nanoindentation experiment. For proper sample mounting, the stage subject surface <NUM> should be flat and perpendicular to the Z-axis. As described in further detail below the stage subject surface <NUM> is coupled with a stage plate <NUM>. The stage plate <NUM> braces the stage subject surface <NUM> providing mechanical stiffness and minimizes deflection of the stage subject surface during mechanical testing of a sample.

The heating element <NUM> and the sensing element <NUM> are thin film resistors within a substrate <NUM> of the MEMS heater <NUM>. As shown in <FIG>, the heating and sensing elements <NUM>, <NUM> are on the test subject stage <NUM> adjacent to the stage subject surface <NUM>. Stated another way, relative to the base portion <NUM> (<FIG>) and the base interface <NUM>, the heating element <NUM> and sensing element <NUM> are immediately adjacent to the stage subject surface <NUM> to ensure heat is generated and temperature is measured at a test subject and not transmitted through large portions of the sample stage <NUM> to a test subject <NUM>. As described below, minimizing the distance heat is transmitted through the sample stage <NUM> to the test subject correspondingly minimizes mechanical drift and thermal expansion. Similarly, positioning of the heating element <NUM> remotely from the base portion <NUM>, as shown in <FIG>, thermally isolates the heated test subject stage <NUM> from the remainder of the test subject holder <NUM> and further minimizes drift and expansion. Referring to <FIG>, positioning the heating element <NUM> adjacent to the stage subject surface <NUM> on the test subject stage <NUM> and away from the base interface <NUM> (coupled to the base portion <NUM> shown in <FIG>) remotely positions the heating element from the rest of the test subject holder <NUM>.

The heating element <NUM> is heated by generating heating power using current flow. The sensing element <NUM> senses temperature in the substrate <NUM> by corresponding resistance variation with temperature changes. As heating element <NUM> and sensing element <NUM> materials, metal or ceramic thin films are used. The heating element <NUM> and the sensing element <NUM> are connected to the base portion <NUM> of the sample stage <NUM> using four thin-film leads <NUM>, <NUM>, <NUM>, <NUM>. The thin film leads <NUM>, <NUM>, <NUM>, <NUM> include one or more of metal materials, ceramic materials and the like. The thin-film leads <NUM>, <NUM>, <NUM>, <NUM> have relatively low electrical resistance because the heating element <NUM> and the sensing element <NUM> should be the dominant resistance source. By using low electrical resistivity materials (e.g., gold), thin film leads <NUM>, <NUM>, <NUM>, <NUM> have correspondingly low resistance. The low resistance of the first and second thin-film leads <NUM> and <NUM> prevents heat generation on the leads. Similarly, the low resistance of the third and fourth thin-film leads <NUM> and <NUM> prevents the addition of undesirable resistance corresponding to locations on the sample stage remote from the stage subject surface <NUM> and the heating element <NUM> for temperature measurements of the MEMS heater <NUM>.

The control voltage is provided by the D/A converter <NUM> to control the current flow though the heater control circuit <NUM> and the sensing element <NUM>. The heater control circuit <NUM> uses either DC or AC circuitry for the resistance measurement of the sensing element <NUM>. Since the sensing element <NUM> temperature change is detected by a change in resistance, for resistance detection, a Wheatstone Bridge is used for the sensing circuitry in one example. Nanomechanical testing at elevated temperature experiences thermal expansion and drift proportional to the volume and length of the materials involved (the test sample <NUM> as well as the sample stage <NUM>). Since mechanical testing relies on measured force and displacement data, thermal expansion and mechanical drift cause undesirable change in the displacement measurement data (and force calculation) and distort the mechanical properties calculated from the measured data. To minimize thermal expansion and mechanical drift, a material with low coefficient of thermal expansion and a large thermal resistance from the heating element <NUM> of the sample stage <NUM> to the base portion <NUM> of the test subject holder <NUM> are required. The MEMS heater <NUM> is designed to create a large temperature drop through the heating element <NUM> to the base portion <NUM> (see <FIG>) to minimize thermal expansion and drift within the components. To have an enhanced temperature drop from the heating element <NUM> to the base portion <NUM>, the MEMS heater <NUM> includes the exemplary geometry shown in <FIG> and the materials described herein having a large thermal resistance between the heating element <NUM> and the base portion <NUM>. Additionally, the materials of the sample stage <NUM> and at least the two support columns <NUM>, <NUM> have low coefficients of thermal expansion, and any thermal drift and expansion because of heating are thereby minimized within the sample stage <NUM>.

With the large temperature drop in the MEMS heater <NUM> from the heating element <NUM> to the base portion <NUM>, the heated volume is limited to the portion of the MEMS heater close to heating element <NUM> (e.g., the stage subject surface <NUM> and to a much smaller extent the support columns <NUM>, <NUM> shown in <FIG>). The heated volume is thereby minimized and the associated thermal expansion and drift is thereby minimized throughout the test subject holder <NUM> including the sample stage <NUM> and the base portion <NUM> (see <FIG>). Minimizing the heated volume of the MEMS heater <NUM> also minimizes power used to heat the test sample <NUM> to a desired temperature since heat conduction and convection are limited to a smaller heating volume (i.e., the test subject stage <NUM> including the stage subject surface <NUM> and the stage plate <NUM> and to a lesser degree the support columns <NUM>, <NUM> and the base interface <NUM>). Concentrating the application of heat to the test subject stage <NUM> including the stage subject surface <NUM> also causes less thermal expansion and drift since less energy is involved in the heating process. That is to say, the geometry of the sample stage <NUM>, the materials used therein and the location of the heating element <NUM> alone or together localize heating within the sample stage to the test subject stage <NUM>. Stated another way, the materials and geometry of the sample stage <NUM> and the MEMS heater <NUM> (e.g., the support columns <NUM>, <NUM>) throttle heat transfer from the sample stage <NUM> into larger components of the test subject holder <NUM> (see <FIG>) and even the base interface <NUM> otherwise capable, at elevated temperatures, of greater expansion and thermal drift because of their relatively large volume and dimensions compared to the test subject stage <NUM> of the sample stage <NUM>.

To increase the thermal resistance and correspondingly decrease heat transfer through the test subject holder <NUM>, the sample stage <NUM> includes a material having low thermal conductivity and a minimized cross-sectional area (an area perpendicular to the Z-axis and the direction of heat transfer in the example shown in <FIG>, <FIG>). The thermal resistance of the material is inversely proportional to both the material thermal conductivity and the cross-sectional surface area perpendicular to a heat flux direction (e.g., the direction of heat transfer along the support columns <NUM>, <NUM> from the MEMS heater <NUM> toward the base portion <NUM>). The MEMS heater <NUM> shown in <FIG> employs two voids <NUM>, <NUM> with the support columns <NUM>, <NUM> having minimal cross sectional area relative to the area of the test subject stage <NUM> to reduce the cross-sectional area perpendicular to the Z-axis and enhance the thermal resistance along the Z-axis. The increased thermal resistance enhances the temperature drop from the heating element <NUM> through the sample stage <NUM> when the MEMS heater <NUM> is operated.

Use of low thermal conductivity material for the sample stage <NUM>, the geometry of the stage (e.g., columns and voids), and the location of the heating element <NUM> adjacent to the stage subject surface <NUM> ensures heating of a test sample occurs at the test sample, and heat energy is minimally transmitted through the remainder of the sample stage <NUM> and into the test subject holder, such as the holder base <NUM>. Because heat is generated at the test subject stage <NUM> adjacent to a test sample on the stage subject surface <NUM> heat energy must travel through the minimally thermal conductive material of the test subject stage <NUM> and the minimal cross sectional area of the support columns <NUM>, <NUM> to reach portions of the test subject holder <NUM> having larger volumes and correspondingly capable of large mechanical drift and thermal expansion. Further, only minimal radiant heat from the test subject stage <NUM> can cross the voids <NUM>, <NUM> relative to conductive heat transfer through the columns <NUM>, <NUM>. The voids <NUM>, <NUM> thereby cooperate with the other resistive heat transfer features of the sample stage <NUM> to throttle heat transfer away from the test subject stage <NUM>. These features alone or in combination thermally isolate (e.g., substantially or extensively thermally insulate) the test subject stage <NUM> and substantially contain heat generated therein relative to the holder base <NUM> and the remainder of the test subject holder <NUM> to minimize mechanical drift and thermal expansion through heating of the heating element <NUM>. A minimal amount of heat is transferred to portions of the test subject holder <NUM> (as described below by example). In one example, the holder base <NUM> and the base interface <NUM> (<FIG> and <FIG>) are at a temperature of around <NUM> degrees Celsius or less (e.g., around <NUM> degrees Celsius) while the test subject stage <NUM> is heated to around <NUM> degrees Celsius. While complete thermal isolation is not achieved, heat transferred to the base interface <NUM>, the holder base <NUM> and the remainder of the test subject holder <NUM> from the heated test subject stage <NUM> is minimal and mechanical drift and thermal expansion are correspondingly minimal. Samples (e.g., test sample <NUM>) on the stage subject surface <NUM> are thereby held substantially static during heating, mechanical testing and observation, for instance, with a transmission electron microscope. Stated another way, observation of a micron or nanometer size discrete portion of the tested sample that is mechanically tested - as opposed to the remainder of the sample - is thereby performed prior to, during and immediately after testing because drift and expansion in components thermally isolated from the test subject stage <NUM> are minimized.

Since the MEMS heater <NUM> is used in nanomechanical testing, the mechanical compliance of the MEMS heater <NUM> is critical in one example. The enhanced stiffness (in contrast to mechanical compliance) of the sample stage <NUM>, including the MEMS heater <NUM>, minimizes deflection of the sample stage and correspondingly minimizes false additional displacement measured by the displaceable probe <NUM> over the true actual penetration depth of the probe into the test sample <NUM>. The stage plate <NUM> reinforces the stage subject surface <NUM> and enhances the stiffness of the sample stage <NUM>. The material of the substrate <NUM> including the stage plate <NUM> is sufficiently stiff to not add its compliance to the mechanical data of the sample. For instance, the stage plate <NUM> and the substrate <NUM> include materials with high Young's modulus, flexural modulus and the like, such as fused quartz or Zerodur. The stage plate <NUM> braces the stage subject surface <NUM> to substantially minimize deflection of the stage subject surface <NUM>, for instance, during mechanical testing and observation. In another example, the support columns <NUM>, <NUM> underlie and brace the stage subject surface <NUM> to enhance the stiffness of the stage subject surface. In contrast to the stiffness (the minimal mechanical compliance) of the MEMS heater <NUM>, other heaters use membrane structures with enhanced mechanical compliance that permit mechanical deflection of the membranes and preclude use of the heaters for accurate mechanical testing. Optionally, the stage plate <NUM> is an integral part of the sample stage <NUM>. For instance, the stage plate <NUM> and the test subject stage <NUM> (including the stage subject surface <NUM>) are formed as a single piece of the sample stage <NUM> with the MEMS heater <NUM> disposed thereon. In another option, the stage plate <NUM> is coupled to the sample stage <NUM> to supplement the stiffness of the test subject stage <NUM> and the stage subject surface <NUM>.

One of the important applications of the MEMS heater is electron microscopy in-situ nano-mechanical testing. Since electron microscopy uses a vacuum environment, the MEMS heater should be made of vacuum compatible materials which do not outgas in vacuum.

Fused quartz is an example of materials having low thermal expansion, low thermal conductivity, and low mechanical compliance with no out gassing in high vacuum. Fused quartz has coefficient of thermal expansion of <NUM>/m·K, thermal conductivity of <NUM> W/m·K, and Young's modulus of <NUM> GPa. Those thermal and mechanical properties can provide satisfactory performance as the substrate <NUM> material.

The four holes <NUM>, <NUM>, <NUM>, <NUM> are designed for mechanical and electrical integration of the MEMS heater <NUM> with the base portion <NUM> of the test subject holder <NUM>. The holes <NUM>, <NUM>, <NUM>, <NUM> are sized and shaped for receipt of conductive fixtures (eg. conductive screws) to mechanically fix the MEMS heater <NUM> to the base portion <NUM> of the test subject holder <NUM>. The conductive fixtures also can make electrical connections by contacting thin-film leads <NUM>, <NUM>, <NUM>, <NUM> and the connectors on the base portion <NUM> of the test subject holder <NUM>. The mechanical and electrical connections as described above are useful for TEM in-situ nanomechanical testing where minimal space is available for connection.

Since electron microscopy uses an electron beam for imaging, the test sample <NUM> accumulates the electrons if electrically isolated. An electron charged test sample <NUM> causes electrostatic force between a displaceable probe <NUM> and the test sample <NUM> and may cause a jump-to-contact as the displaceable probe <NUM> approaches the test sample <NUM>. This electrostatic attraction by the accumulated electrons is undesirable for applications, such as indentation, because it distorts the measurement data, for instance the indentation loading/unloading curve. Discharging the electrons in the test sample <NUM> by electrically grounding the test sample improves the quantitative accuracy of mechanical measurements in electron microscopy in-situ mechanical testing.

Referring now to <FIG>, for discharging purpose, the bottom side of the MEMS heater <NUM> has a conductive thin film (e.g., metal or ceramic thin film) pattern <NUM>. This conductive thin film pattern <NUM> layer discharges electrons on the test sample <NUM> (See <FIG>). The conductive thin film pattern <NUM> is electrically coupled with the test sample <NUM> by applying a conductive adhesive, epoxy, or paste between the test sample <NUM> and the conductive thin film pattern <NUM>. The conductive thin film pattern <NUM> is electrically coupled with an electron microscopy ground to prevent any charge accumulation and electrostatic attraction between the test sample <NUM> and the displaceable probe <NUM> because of differing electrical potential.

The test sample <NUM> is mounted directly on the stage subject surface <NUM> of the MEMS heater <NUM>, in one example. As shown in <FIG>, for TEM in-situ nanomechanical testing, the test sample <NUM> is exposed to the electron beam and the beam is transmitted through the test sample <NUM>. To make a thin test sample <NUM> along the electron beam <NUM> direction, the sample is deposited or attached on a sharp wedge-shaped sample mount <NUM> as shown in <FIG>. The sample mount <NUM> includes a first side <NUM> including a sharp edge <NUM> along the wedge shape <NUM> for reception of the test sample <NUM>. A MEMS fabrication process is used to make the micro or nano scale sharp edge <NUM>. The MEMS fabrication process includes, but is not limited to, deposition processes, focused ion beam lithography and milling, laser machining, photolithography and etching (dry or wet) and the like. With the configuration shown in <FIG>, the test sample <NUM> and sample mount <NUM> are heated to the desired temperature using the MEMS heater <NUM>. After the test sample reaches the desired temperature, the EM transducer <NUM> (See <FIG>) actuates the displaceable probe <NUM> to test the test sample <NUM>. In one example, while the displaceable probe <NUM> indents the test sample <NUM>, the mechanical data and the sample image are recorded simultaneously in real time by the displacement sensor <NUM> and the imaging device <NUM>, respectively.

Because the stage subject surface <NUM> is parallel to the electron beam and positions the test sample <NUM> on the sample mount <NUM> within the beam, electron transparency is maintained through the test sample <NUM>. Stated another way, the stage subject surface <NUM> and the sample mount <NUM> are positioned outside of the electron beam and do not underlie the beam emitter. The electron beam is thereby able to pass through the sample without distortion from underlying materials. Further, the sample stage <NUM> is braced by the stage plate <NUM> (described above and shown in <FIG>, <FIG>). The stage plate <NUM> underlies the stage subject surface <NUM> and is also outside of the electron beam. Transparency of the test sample <NUM> is thereby maintained while also providing a rigid test subject stage <NUM> with a stage subject surface <NUM>. Stated another way, transmission electron microscopy is effectively performed on the test sample <NUM> while at the same time mechanical testing (indentation, fracture, tension and the like) is permitted with negligible deformation of the underlying stage subject surface <NUM>.

Referring to <FIG> and <FIG>, a second side <NUM> of the sample mount <NUM> is usually planar and perpendicular to the Z-axis. The planar second side <NUM> is coupled with the stage subject surface <NUM> of the MEMS heater <NUM>. The front wall is similarly flat and perpendicular to the Z-axis for a flush coupling. An example of a sample mount <NUM> including a MEMS fabricated silicon wedge shape <NUM> having a sharp edge <NUM> for mounting of a sample is shown in <FIG>. The sample mount <NUM> has a wedge shape <NUM> fabricated on the first side <NUM> of a silicon wafer. The planar second side <NUM> is on the other side of the sample mount <NUM> (e.g., a silicon wafer). Use of a heavily doped silicon wafer for the sample mount <NUM> fabrication makes the sample mount <NUM> conductive. By connecting the sample mount <NUM> to the TEM ground, electrons on the test sample <NUM> are discharged to substantially prevent electrostatic attraction during imaging.

To evaluate the performance of the MEMS heater <NUM>, finite element analysis (FEA) was performed using the commercially available finite element analysis software COSMOSWorks®. For the simulation, a model of the PicoIndenter <NUM> for the Hitachi TEM model H <NUM> and HF <NUM> was used. <FIG>, B show the model of the PicoIndenter including the test subject holder <NUM>, the sample mount <NUM>, the MEMS heater <NUM> and its coupling using four fasteners <NUM>, <NUM>, <NUM>, <NUM> (e.g., brass screws). <NUM>,<NUM> triangular elements were generated for this simulation. Exemplary components of the tested MEMS heater <NUM>, the test subject holder <NUM> and the other components shown in <FIG> are described herein. The sample mount <NUM> has a thermal conductivity of <NUM> W/m·K, a specific heat of <NUM> J/kg·K and a mass density of <NUM>/m<NUM>. A fused quartz material is used in the substrate <NUM> of the sample stage <NUM> and has a thermal conductivity of <NUM> W/m·K, a specific heat of <NUM> J/kg·K and a mass density of <NUM>/m<NUM>. The fasteners <NUM>, <NUM>, <NUM>, <NUM> are brass screws and have a thermal conductivity of <NUM> W/m·K, a specific heat of <NUM> J/kg·K and a mass density <NUM>,<NUM>/m<NUM>. For the PicoIndenter <NUM>, a titanium outer tube <NUM> is specified having a thermal conductivity of <NUM> W/m·K, a specific heat of <NUM> J/kg·K and a mass density of <NUM>/m<NUM>. The front end <NUM> of the test subject holder <NUM> includes a co-fired ceramic having a thermal conductivity of <NUM> W/m·K, a specific heat of <NUM> J/kg·K and a mass density of <NUM>/m<NUM>. The ball tip <NUM> is constructed with sapphire and has a thermal conductivity of <NUM> W/m·K, a specific heat of <NUM> J/kg·K and a mass density of <NUM>/m<NUM>. Thermal conductivity generally decreases and the specific heat generally increases as the material temperature rises. For evaluation purposes those properties are assumed constant. Steady state analysis and transient analysis were performed to investigate the temperature distribution, heating time and heating power.

For the steady state analysis, as boundary conditions, the heating element <NUM> was assumed to maintain a temperature of <NUM> and the outer tube surface <NUM> with the largest diameter and ball tip <NUM>. were assumed to maintain a temperature of <NUM>. The outer tube surface <NUM> with the largest diameter is the portion of the PicoIndenter <NUM> that makes contact with the TEM main body and heat transfers through this contact from the PicoIndenter to the TEM main body. <FIG> shows points of interest examined for both analyses (steady state and transient). At steady state, the estimated temperature at Point A (the stage subject surface <NUM>) was <NUM>, at Point B (between the base interface <NUM> and the stage subject surface <NUM>) it was <NUM>, at Point C (the base interface <NUM>) it was <NUM>, at Point D it was <NUM>, and at Point E it was <NUM>. There was a large temperature drop from the heating element <NUM> to the front end <NUM> of the test subject holder <NUM> including the holder base <NUM>. As described above, the substantial temperature drop is desirable to minimize heating power needed to achieve a specified sample temperature with less thermal drift. As shown with the estimated temperatures, most of the temperature drop occurred at the substrate <NUM> of the sample stage <NUM> indicating a minimal amount of heat transfer to the other components of the test subject holder <NUM> (e.g., larger components, such as the base portion <NUM> with corresponding larger thermal drift if heated). This result indicates that the same calibration constant of the sample stage <NUM> with the MEMS heater <NUM> can be used for different PicoIndenter holders. Stated another way, because substantially all of the heat generated within the sample stage <NUM> at the heating element <NUM> (See <FIG>, <FIG>) is retained within the sample stage (i.e., not transmitted to the holder of the PicoIndenter), the sample stage is adaptable for coupling with different PicoIndenters without separate individual calibrations.

For transient thermal analysis, as boundary conditions, the heating element <NUM> is heated with <NUM> mW and the outer tube surface <NUM> with the largest diameter and ball tip <NUM> as shown in <FIG>. were assumed to have a convection coefficient of <NUM> W/m<NUM>·K. The larger convection coefficient is employed to model fast heat transfer through the outer tube and the ball tip <NUM>. All the components are assumed to have a <NUM> temperature at the initial. Transient analysis was done over <NUM> seconds of heating at <NUM> second increments for points A, B and C (See <FIG>). <FIG> shows the estimated temperature variation through the <NUM> second period. After a steep temperature rise for points A and B during the first <NUM> seconds, heat transfer slows. After <NUM> seconds of heating, the temperatures at points A and B are stabilized. Advantageously, because the MEMS heater <NUM> has an integrated temperature sensor (sensing element <NUM>), heating of the sample stage <NUM> is rapid, quantitative and accurate with a closed loop control scheme. In contrast, other methods associate a particular voltage with a temperature observed with an optical device, and use the observed relationship as a generalized calibration that is less accurate and subject to differences caused by a variety of factors (the sample material, differences in mass and volume of the stage and sample heated from those used for calibration, and the like).

Additionally, with the closed loop scheme and the sensing element <NUM>, higher heating power is initially used while raising the test sample <NUM> temperature and lower heating power is gradually used as the test sample <NUM> temperature approaches the desired temperature (e.g., <NUM>). Although the testing data here includes a desired temperature of <NUM>, the sample stage <NUM> including the MEMS heater <NUM> is configured, in one example, for heating to at least <NUM> or more.

A sample stage <NUM> including the MEMS heater <NUM> was fabricated using metal deposition techniques and laser machining. As substrate <NUM> material, fused quartz is chosen. Fused quartz has a <NUM> W/m·K thermal conductivity which is about <NUM> times lower than that of silicon. The fused quartz also has low coefficient of thermal expansion (<NUM>/m·K) which helps to reduce the thermal expansion and drift during heating with the MEMS heater <NUM>. The high Young's modulus (i.e., stiffness) of fused quartz minimizes compliance to the applied force used for mechanical test and thereby mitigates the inclusion of deflection of the sample stage in displacement measurements and force calculations. The structural dimensions are determined based on the MEMS fabrication capability. The heating element <NUM> and sensing element <NUM> include platinum materials. Platinum is used up to <NUM> without degradation and has a linear temperature-resistance relation. As the heating element <NUM>, a platinum thin film is deposited on <NUM>-nm thick titanium adhesive layer. The dimension of the heating element <NUM> is <NUM>-long, <NUM>-µm wide, and <NUM> thick. Considering the resistivity of platinum, <NUM>µΩ·cm, the resistance of the heating element was designed as <NUM>Ω. With this resistance, the heating element has a much larger resistance than other resistance sources such as contact and lead resistances ensuring heating occurs at the heating element <NUM> and minimizing heating of the contacts and leads. The heater resistance also permits current flow resolution with <NUM> mA current flow to generate the <NUM> mW required heating power to raise the test sample <NUM> temperature to <NUM>. A resistance value closer to the resistance value of the contacts and leads allows the contacts and leads to undesirably heat other portions of the sample stage <NUM>. A higher resistance may decrease the temperature resolution because of a large heating power variation to the current flow resolution. For comparison, Hysitron's <NUM> heating stage manufactured for the TriboIndenter uses <NUM> mA current flow and <NUM> W heating power.

As the sensing element <NUM>, a platinum thin film is deposited on a <NUM>-nm thick titanium adhesive layer. The dimension of the sensing element <NUM> is <NUM>-long, <NUM>-µm wide, and <NUM> thick. Considering the resistivity of platinum, the resistance of the sensing element <NUM> as described is <NUM>,<NUM>Ω. The resistance of the sensor resistor is determined as <NUM>,<NUM>Ω. As the nominal resistance increases, resistance variation to the temperature change also increases. Accordingly, making the resistance of sensing element <NUM> higher provides increased temperature sensing resolution. As the electrical leads from the heating and sensing elements to the sample stage, gold film is deposited on the titanium adhesive layer. <FIG>, B show the fabricated sample stage <NUM> and MEMS heater <NUM> with the brass screw connections coupled with a test structure. The heating and sensing elements are electrically connected to the front end <NUM> using the gold leads patterned on the MEMS heater <NUM> of the sample stage <NUM> and the fasteners (e.g. four brass screws). The fasteners also mechanically fix the MEMS heater <NUM> and the sample stage <NUM> on the base portion <NUM>.

Microscope images in <FIG>, B show the top (<FIG>) and bottom (<FIG>) sides of the fabricated MEMS heater <NUM>. The top side image shows the platinum heating and sensing elements and the gold leads patterns. The metallization is well done. However, there was resistance difference between the designed value and the measured value. The measured heater and sensor resistance at room temperature is about <NUM>Ω and <NUM> kΩ respectively. Those values are about <NUM> times higher than the designed value. This difference does not cause performance degradation since the driving electrical circuit can be adjusted for those resistances. Fabrication errors occur during micromachining fabrication processes. Such processes include, but are not limited to deposition processes, focused ion beam lithography and milling, laser machining, photolithography and etching (dry or wet). The front side of the MEMS heater wall is diced using a dicing saw to separate each individual heater from the fused quartz substrate wafer. Dicing creates a planar front side wall. The plane of the front side wall is essential for consistently attaching a silicon wedge to the MEMS heater <NUM>. The bottom side platinum lead <NUM> is patterned to discharge the electrons on the sample during the experiment inside TEM. This platinum lead <NUM> connects the TEM ground and the sample mount <NUM>. By discharging the electrons on the test sample <NUM>, undesirable electrostatic interaction between the displaceable probe <NUM> and test sample <NUM> during the electron microscopy in-situ nanomechanical test is prevented.

The fabricated MEMS heater <NUM> was annealed at <NUM> for <NUM> minutes. This annealing process causes inter-metallic diffusion which changes the heater and sensor characteristics. By annealing the MEMS heater at the temperature higher than the operating temperature, the heating element <NUM> and sensing element <NUM> can maintain the same characteristics within the operation temperature range (room temperature to <NUM>). After the annealing, the sensing element <NUM> showed repeatable and linear temperature-resistance characteristic. <FIG> is the measured sensing element <NUM> resistance at different temperatures. Resistance of the sensing element <NUM> is measured from <NUM> to <NUM> with <NUM> interval. The resistance changes at <NUM>Ω/°C within the measured temperature range. From the measured data, the thermal coefficient of the sensing element <NUM> is estimated as α=<NUM>-<NUM> which indicates <NUM>% resistance change per <NUM> temperature change compared to the nominal resistance at <NUM>.

For testing purposes, the fabricated sample stage <NUM> including the MEMS heater <NUM> was integrated with the emulated PicoIndenter front end <NUM> and heating circuit <NUM> as shown in <FIG>. The coupling by way of the fasteners does not mechanically damage the MEMS heater <NUM> and sample stage <NUM> and it secures electrical connections well. The contact resistance between the fasteners and the patterned gold lead (shown in <FIG>) is measured to be less than <NUM>Ω. This low contact resistance is negligibly smaller than the heater and the sensor resistances. Because of the low contact resistance, the contact area between the front end <NUM> and the sample stage <NUM> is not heated by current flow and does not thereby distort the sensor reading.

<FIG> shows the heating experiment images under microscope. Current flow was applied to the heater to check the heating element performance. The glowing light from the heater shows the heater is heated well above <NUM> and the glowing intensity change by heating power change shows that the heater is responding properly.

<FIG> shows a schematic view of one example of a test subject holder <NUM>. The test subject holder <NUM> includes a holder base <NUM> coupled with a means for holding a test subject <NUM>. As described herein, in some examples, the means for holding the test subject <NUM> includes a test subject stage including a sample stage and a base interface (See <FIG>, <FIG>). The means for holding the test subject <NUM> includes a subject surface <NUM> configured to position a sample <NUM> within an electron beam <NUM> of a transmission electron microscope. As shown in <FIG>, the subject surface <NUM> includes a surface projection <NUM>, for instance a wedge shaped projection, that receives the sample <NUM>. When installed in the transmission electron microscope, the means for holding the test subject <NUM> and the subject surface <NUM> position the sample within the electron beam <NUM>.

The test subject holder <NUM> further includes a means for heating <NUM>. In one example, the means for heating <NUM> includes a resistive MEMS heating element on the means for holding the test subject <NUM>. As previously described herein, the means for heating <NUM> heats a portion of the means for holding the test subject <NUM> (e.g., a test subject stage <NUM>) and the sample <NUM> to a specified temperature, for instance, <NUM> degrees Celsius or greater. The test subject holder <NUM> with the means for heating are configured for use in ex-situ and in-situ heating and observation with optical, scanning probe and electron microscopes.

Also shown in <FIG> is an electro-mechanical transducer <NUM> with a probe <NUM>. The electro-mechanical transducer <NUM> performs mechanical testing and measurement of the sample <NUM> on the subject surface <NUM>. For instance, the electro-mechanical transducer <NUM> performs indentation, tensile, compression, fracture, fatigue, tribology testing and the like.

As shown in <FIG>, the means for heating <NUM> is positioned adjacent to the subject surface <NUM> and the sample <NUM>. Heating of the sample <NUM> is thereby performed at the sample <NUM> and not otherwise transmitted from a heating feature remote from the sample and the subject surface <NUM>. For instance, the means for heating <NUM>, such as a resistive heating element, is located adjacent to the sample <NUM> according to an adjacent spacing <NUM> of approximately <NUM> millimeters As previously described in other examples and discussed again here, the means for heating <NUM> is configured to heat a portion of the means for holding the test subject <NUM>. For example, the means for heating <NUM> is configured to heat a minimal volume of the means for holding the test subject1304 compared to the holder base <NUM> and the remainder of the means for holding coupled with the holder base. By limiting the volume heated the means for heating <NUM> is able to quickly heat the portion of the means for holding with the sample <NUM> thereon and use less heating energy. By maintaining the means for heating <NUM> adjacent to both the sample <NUM> and the subject surface <NUM> rapid heating with less energy expenditure is possible because there is minimal transmission of heat energy through other portions of the means for holding the test subject <NUM>. As described above, positioning the means for heating <NUM> according to an adjacent spacing <NUM> of around <NUM> millimeters locates the means for heating <NUM> adjacent (e.g., immediately adjacent) to the sample <NUM> and the subject surface <NUM>. As further discussed below, the volume heated by the means for heating <NUM> is in some examples limited by features such as voids, columns and a material of the means for holding the test subject <NUM>. These features alone or in combination cooperate with the placement of the means for heating adjacent to the subject surface <NUM> to substantially limit the volume of the means for holding the test subject <NUM> heated by the means for heating <NUM>.

As described in other examples herein, the means for holding a test subject <NUM> includes in some examples voids, supports and thermally resistive materials configured to contain heat energy within a smaller volume of the means for holding a test subject <NUM> relative to the remainder of the means for holding and the holder base buood <NUM>. These features and materials are described herein and are applicable to the means for holding the test subject <NUM>. Referring to the sample stage <NUM> in <FIG> and <FIG>, for example, the support columns <NUM>, <NUM> extending from the base interface <NUM> to the test subject stage <NUM> throttle heat transfer from a first portion of the sample stage <NUM> (e.g., a means for holding a test subject <NUM>) to the base interface <NUM>. The support columns <NUM>, <NUM> have a smaller cross sectional area along a plane parallel to the plane defined by the test subject stage <NUM>. A smaller cross sectional area in the support columns <NUM>, <NUM> relative to the test subject stage <NUM> throttles heat transfer from the test subject stage <NUM> toward the base interface <NUM> as well as the holder base <NUM> shown in <FIG>.

Additionally, one or more voids <NUM>, <NUM> shown in <FIG> and <FIG>, space the test subject stage <NUM> from the base interface <NUM> and the juncture between the base interface <NUM> and the holder base <NUM>. Transmission of heat energy across the voids <NUM>, <NUM> is difficult compared to conduction of heat energy through the material of the test subject stage <NUM>. Additionally, in a vacuum (common in electron microscopes) transmission across the voids <NUM>, <NUM> is only possible by minimal radiative heat transfer and not by relatively enhanced heat transfer through convection. The voids <NUM>, <NUM> thereby throttle heat transfer from the test subject stage <NUM> to the remainder of the sample stage <NUM> including the base interface <NUM>. The support columns <NUM>, <NUM> (and the voids <NUM>, <NUM> therebetween) position the test subject stage <NUM> (e.g., the subject surface <NUM> including a sample <NUM>) remotely relative to the remainder of the sample stage <NUM> (means for holding a test subject <NUM>). The voids <NUM>, <NUM> and support columns <NUM>, <NUM> shown in <FIG>, B thereby thermally isolate the subject surface <NUM> (e.g., test subject stage) of the means for holding the test subject <NUM> shown in <FIG> from the remainder of the means for holding and the holder base <NUM>.

While the test subject stage <NUM> (e.g., the subject surface <NUM>) is not completely thermally isolated from the remainder of the means for holding coupled with the holder base <NUM>, heat transfer from the test subject stage <NUM> to the holder base <NUM> and base interface <NUM> is substantially minimized. For instance, in one example where a sample and the test subject stage <NUM> (e.g., sample <NUM> and subject surface <NUM>) are heated to a temperature of around <NUM> or greater the remainder of the sample stage <NUM> adjacent to the holder base <NUM> is maintained at a temperature of around <NUM> or less.

Moreover, the means for holding a test subject <NUM> is constructed with a thermally resistive material configured to resist conductive heat transfer from the subject surface <NUM> to the holder base <NUM> and a remainder of the means for holding the test subject <NUM> (including for instance the base interface <NUM> as shown in <FIG>). For example, the means for holding the test subject <NUM> is constructed with fused quartz. Fused quartz has a coefficient of thermal expansion of around <NUM>/m·K and a thermal conductivity of around <NUM> W/m·K. With this minimal thermal conductivity the fused quartz substantially retards the transmission of heat from the subject surface <NUM> to the holder base <NUM>. Further fused quartz experiences minimal thermal expansion at the heated subject surface <NUM> because of its low coefficient of thermal expansion.

These features described immediately above and herein including the columns <NUM>, <NUM>, voids <NUM>, <NUM> as well as the materials of the means for holding the test subject <NUM> operate alone or together to thermally isolate and thereby substantially retard heat transfer from the subject surface <NUM> to the remainder of the means for holding a test subject <NUM> and the holder base <NUM>. These features either alone or in combination ensure that heating through the means for heating <NUM> of the sample <NUM> is substantially contained adjacent to the subject surface <NUM> to provide rapid heating of the sample <NUM> with relatively low amounts of heat energy. Stated another way, because of the thermal isolation of the subject surface <NUM> and sample <NUM>, the means for heating <NUM> substantially heats the subject surface <NUM> and the sample <NUM> while only minimally transmitting heat from the subject surface to the remainder of the means for holding the test subject <NUM> (including for example, the base interface <NUM> and the holder base <NUM> shown in <FIG>).

Because heating of the subject surface <NUM> is substantially localized at the subject surface and the sample <NUM> with only minimal heat transferred to the remainder of the means for holding the test subject <NUM>, mechanical drift and thermal expansion of the material of the means for holding the test subject <NUM> as well as the holder base <NUM> are substantially minimized. Mechanical drift and thermal expansion of the materials comprising the holder base <NUM> and the means for holding the test subject <NUM> are proportional to the dimensions and volume of the materials of each of those elements heated during operation of the means for heating <NUM>. Because the volume heated by the means for heating <NUM> is substantially limited to the subject surface <NUM> and the sample <NUM> mechanical drift and thermal expansion are thereby minimized. For example, with the minimal heat transfer through the support columns <NUM>, <NUM> and across the voids <NUM>, <NUM> along with the thermally resistive material of the means for holding, the remainder of the means for holding and the holder base <NUM> experience minimal heating and thereby experience minimal mechanical drift and thermal expansion. In another example, the sample surface <NUM> is constructed with a material, such as fused quartz, having a low coefficient of thermal expansion. Heating of the sample surface <NUM> thereby results in minimal thermal expansion of the surface.

A portion of the sample <NUM> observed, for instance, through transmission electron microscopy is thereby held substantially static during heating with the means for heating <NUM>. The sample <NUM> including the portion observed, is further held statically for both mechanical testing with the electro-mechanical transducer <NUM> and observation by the electron beam <NUM> of a transmission electron microscope. That is to say, a portion of the sample <NUM> at a micron or less scale (e.g., nano-scale) is observable by a transmission electron microscope during heating as well as mechanical deformation and testing and thereafter. Mechanical properties of the material making up the sample <NUM> are thereby observable before heating, during heating, during mechanical testing and immediately thereafter by observation of one discrete portion of the sample throughout testing.

Additionally, as described herein, the means for holding a test subject <NUM> in other examples includes a support, such as a stage plate <NUM> shown in <FIG>. The support braces the subject surface <NUM> of the means for holding the test subject <NUM>. The support (e.g., the stage plate <NUM>) braces the subject surface <NUM> and the sample and minimizes deflection of the subject surface during mechanical testing with the electro-mechanical transducer <NUM>. Observation of the sample <NUM> and accurate assessment of the sample properties are thereby possible through a transmission electron microscope without the distortion caused by deflection of the subject surface.

As described above, the subject surface <NUM> with the support provides a robust surface for positioning and observation of the sample <NUM>. Because the sample <NUM> is positioned on the subject surface <NUM> and because the surface is positioned outside of the electron beam <NUM> electron transparency is maintained through the sample <NUM> thereby providing distortion free observation of the sample <NUM>. Stated another way, the subject surface <NUM> supports the sample <NUM> during mechanical testing with the electro-mechanical transducer <NUM> and minimizes deflection of the surface and the sample while also maintaining electron transparency of the sample <NUM>. For instance, as shown in <FIG>, the subject surface <NUM> is oriented parallel to the electron beam <NUM> with the surface projection <NUM> presenting the sample <NUM> and extending toward the electron beam <NUM>. Because the sample <NUM> is provided along the edge of the surface projection <NUM> the sample itself as opposed to the subject surface <NUM> is positioned within the electron beam <NUM> to maintain electron transparency.

In contrast, in some examples sample stages provide deflectable membranes and wires underlying the sample. These features, such as wires and membranes, allow for electron transparency but they are not sufficiently robust to brace against deflection from mechanical testing, such as nano-indentation. In other examples, where a sample is positioned on a robust surface capable of providing support against mechanical testing, electron transparency is not maintained because the support is positioned within the electron beam axis. The means for holding a test subject <NUM> described herein addresses both of these issues by providing a robust support in the subject surface <NUM> (e.g., a stage plate <NUM>) as well as an electron transparent sample <NUM> through positioning of the subject surface <NUM> outside of the electron beam <NUM>.

Referring now to <FIG> and <FIG>, one example of a prior art test subject holder <NUM> is shown. The test subject holder <NUM> includes a specimen cradle <NUM> movably positioned within the test subject holder. The specimen cradle <NUM> includes a specimen area <NUM> configured to receive a specimen for observation under a transmission electron microscope. The specimen area <NUM> is surrounded by a heating element <NUM> configured to heat the specimen area <NUM> and the specimen. In the example shown, the heating element <NUM> includes a heating element extending through the periphery of the specimen cradle <NUM> and substantially surrounding the specimen area <NUM>.

Referring now to <FIG>, the test subject holder <NUM> including the specimen cradle <NUM> is shown in a cross sectional view. The heating element <NUM> extends into and out of the page and around the periphery of the specimen cradle <NUM> to surround the specimen area <NUM>. As shown in <FIG>, the specimen area <NUM> is remotely spaced according to a remote spacing <NUM> from the heating element <NUM>. In one example, the heating element <NUM> is positioned away from the specimen area <NUM> around <NUM> millimeters. The heating element is positioned away from the specimen area <NUM> (e.g., a membrane) to maintain electron transparency through the specimen area <NUM>. Stated another way, the heating element <NUM> is positioned peripherally away from the specimen area <NUM> to allow observation of a specimen on the specimen area <NUM> through transmission electron microscopy. Because the heating element <NUM> is positioned remotely relative to the specimen area <NUM> a significant amount of heat energy is needed to heat the specimen area <NUM> to a specified temperature. Further, because the heating element <NUM> is positioned within the specimen cradle <NUM> surrounding the specimen area <NUM> heating of the heating element <NUM> not only must heat the specimen area <NUM> it must also heat the remainder of the specimen cradle <NUM> to achieve the specified temperature on the specimen area <NUM>.

In one example, the heated volume of the specimen cradle <NUM> in the specimen area <NUM> is greater than a volume of the test subject stage <NUM> shown in <FIG>, <FIG>. Because the specimen area <NUM> is not thermally isolated from the specimen cradle <NUM> heat energy from the heating element <NUM> is transmitted within the specimen cradle <NUM> as well as the specimen area <NUM>. In some examples, it thereby requires additional heat energy and time to heat the specimen area <NUM> to a specified temperature. Further it requires additional heat energy to maintain the specimen area <NUM> at the desired temperature.

In contrast to the test subject holder <NUM> shown in <FIG>, <FIG>, the test subject holder <NUM> shown in <FIG> includes the subject surface <NUM> having the means for heating <NUM>, such as a heating element, positioned adjacent to the subject surface and sample <NUM>. As previously described, for example, the means for heating <NUM> is positioned adjacently according to an adjacent spacing <NUM> to the sample <NUM>. For instance, the adjacent spacing <NUM> is around <NUM> millimeters compared to the remote spacing in the example shown in <FIG> of around <NUM> millimeters. At a micron or nanoscale the difference in spacing between the sample and the heating element in the test subject holders <NUM> and <NUM> provides significant differences in the amount of heat energy needed to elevate the temperature of a sample to high specified temperatures. Stated another way, the adjacent spacing <NUM> positions the means for heating <NUM> immediately adjacent to the sample <NUM> (with the above described heating benefits) when compared to the remote spacing <NUM> of the specimen cradle <NUM>.

Furthermore, because there is a difference in the spacing of the heating elements relative to the samples the volume of the specimen cradle <NUM> heated by the heating element <NUM> is much greater than the volume of the subject surface <NUM> heated by the means for heating <NUM>. In one example, the heated volume of the specimen cradle <NUM> is exponentially larger (e.g., an exponent of <NUM>) because of the cubed relationship of dimensions such as radius, depth, and circumference to volume. Stated another way, where the remote spacing <NUM> of the specimen cradle <NUM> is greater than the adjacent spacing <NUM> of the means for heating <NUM> relative to the sample <NUM> the heated volume of the specimen cradle <NUM> is exponentially larger than that of the means for holding the test subject <NUM> thereby requiring additional heat energy to achieve and maintain a specified temperature of a sample.

In one example, because of the remote spacing <NUM> of the heating element <NUM> from the specimen area <NUM> and the corresponding greater volume of the specimen cradle <NUM>, mechanical drift and thermal expansion of the specimen cradle <NUM> is greater than corresponding drift and expansion in the means for holding the test subject <NUM> shown in <FIG> as well as the other examples of sample stages shown herein. As previously described, heating a larger volume of material correspondingly produces greater mechanical drift and thermal expansion relative to heating of a smaller volume, such as a volume of material equivalent to the test subject stage <NUM> shown in <FIG> and the subject surface <NUM> shown in <FIG>. By thermally isolating the subject surface <NUM> relative to the remainder of the sample stage as well as the holder base <NUM> with the features described herein (e.g., support columns, voids thermally resistive materials and the like) corresponding mechanical drift and thermal expansion are minimized. Stated another way, because the holder base 1302and the remainder of the means for holding the test subject <NUM>, (e.g., the base interface <NUM>), are thermally isolated only a small fraction of the heat within the subject surface <NUM> (test subject stage <NUM>) is transmitted into those features.

As previously described, holder base <NUM> and the remainder of the means for holding the test subject <NUM> (e.g., base interface <NUM>) have a larger volume relative to the subject surface <NUM> and the sample <NUM>. Because this large volume is not substantially heated due to the thermal isolation mechanical drift and thermal expansion of these features is minimized. In contrast, the specimen cradle <NUM> shown in <FIG>, B includes the heating element <NUM> in the ring surrounding the specimen area <NUM>. Heating of the specimen area <NUM> correspondingly heats the entirety of the specimen cradle <NUM> and causes mechanical drift and thermal expansion throughout the specimen cradle <NUM>. As previously described, mechanical drift and thermal expansion of the test subject holder such as test subject holder <NUM> moves the sample including a discrete portion of a sample observed through transmission electron microscopy. Because in some examples, the specimen cradle <NUM> fails to minimize the mechanical drift and thermal expansion of the cradle, consistent observation of a discrete portion of the specimen area <NUM> is difficult.

Referring again to <FIG> and <FIG>, the specimen area <NUM> extends across the specimen cradle <NUM>. The specimen area <NUM> is electron transparent to permit the transmission of electrons through the specimen area including the sample for observation during transmission electron microscopy. Because the specimen area <NUM> is transparent the specimen area <NUM> is capable of deflection when subjected to mechanical testing such as fatigue, indentation, tensile, fracture testing and the like. Observation of mechanical properties of the sample on the specimen area <NUM>, for instance, at or near the time of mechanical testing through transmission electron microscopy is thereby difficult as the mechanical properties of the sample are distorted through undesired deflection of the specimen area <NUM>. In contrast, the subject surface <NUM> shown in <FIG> is positioned outside of the electron beam <NUM> and positions the sample <NUM> within the electron beam. A robust support, such as a stage plate <NUM> (shown in <FIG>, <FIG>) braces the sample and the subject surface <NUM> during mechanical testing, for example, testing with the electro-mechanical transducer <NUM>. Mechanical properties of the sample <NUM> are readily observed throughout heating, mechanical testing and afterward as the electron beam is directed through the sample <NUM> because of minimal deflection of the sample <NUM> and minimized mechanical drift and thermal expansion.

<FIG> shows one example of a method <NUM> of sub-micron scale heating and mechanical testing of a test subject. Reference is made in the description of method <NUM> to features and elements previously described herein. Where convenient, reference numerals previously described are included in the description of the method <NUM>. The references are not intended to be limiting. For instance, where a single reference numeral is provided it is also implied reference is made to all similar features as well as their equivalents.

At <NUM>, a test subject such as a sample is coupled along a stage subject surface <NUM> of a test subject stage <NUM>. The test subject stage <NUM> is coupled with a holder base, such as holder base <NUM> shown in <FIG>. In one example, coupling of the test subject along the stage subject surface <NUM> includes mounting of a sample on a sample mount <NUM> as shown in <FIG> and <FIG>. The test subject stage <NUM> includes the stage subject surface <NUM> underlying the sample mount <NUM>. In another example, the stage subject surface includes the first side <NUM>, sharp edge <NUM> and wedge shape <NUM> of the sample mount <NUM>. Stated another way, the sample mount <NUM> is included as a part of the test subject stage <NUM> and the stage subject surface <NUM>.

At <NUM>, the holder base <NUM> is coupled within a submicron mechanical testing instrument and electro-mechanical transducer assembly, such as the electro-mechanical transducer <NUM> shown in <FIG>. As shown in <FIG>, the test subject stage, including the MEMS heater <NUM> and the sample mount <NUM> is positioned outside an electron beam <NUM> axis of the electro-mechanical transducer assembly when installed in a transmission electron microscope. The test subject stage <NUM> positions a sample, such as a test sample <NUM> shown in <FIG>, within the electron beam (see electron beam <NUM> in <FIG>). Stated another way, the MEMS heater <NUM> including the test subject stage <NUM> positions the test sample <NUM> within the electron beam axis while the test subject stage <NUM> is positioned outside of the electron beam to provide electron transparency through the test sample <NUM>.

At <NUM>, the test subject is heated to a specified temperature through heat generated at the test subject stage <NUM> adjacent to the test subject with a heating element, such as heating element <NUM> shown in <FIG>. In one example, the heating element <NUM> is positioned immediately adjacent to the stage subject surface <NUM> of the test subject stage <NUM>. That is to say, the heating element <NUM> is not remotely positioned relative to the stage subject surface, and heat transfer to the stage subject surface as well as the sample positioned on the stage subject surface is localized to the volume of the test subject stage <NUM> containing the stage subject surface <NUM>. As previously described, by localizing the generation of heat to the area adjacent to the stage subject surface <NUM> mechanical drift and thermal expansion of materials of the remainder of the sample stage <NUM> and the holder base <NUM> are substantially minimized.

At <NUM>, the test subject is mechanically tested on a micron or less scale. Mechanical testing of the test subject includes, but is not limited to, testing with the electro-mechanical transducer <NUM>. Mechanical testing with the electro-mechanical transducer <NUM> includes, but is not limited to, indentation, compression, tensile, fatigue, tribology, fracture testing and the like. As previously described herein, testing of a sample on the test subject stage <NUM> on the sample stage <NUM> is performed with little or no distortion due to deflection of the test subject stage <NUM> because of the stage plate <NUM> coupled along the test subject stage <NUM>. In one example, the stage plate <NUM> is formed integrally with the test subject stage <NUM> and the sample stage <NUM>. The stage plate braces the test subject stage <NUM> and the sample thereon against deflection caused by mechanical testing from the instruments on the electro-mechanical transducer <NUM>. Observation of the test subject on the test subject stage <NUM> is thereby performed with minimal distortion from deflection of the test subject stage <NUM> compared to distortion caused by mechanical testing of samples on other substrates including membranes and wires. As discussed above, mechanical testing as described in <NUM> is performed on a sample positioned within an electron beam axis that provides electron transparency while still providing a robust test subject stage <NUM> capable of absorbing and minimizing deflection caused by the mechanical testing.

At <NUM>, the test subject (e.g., the test sample <NUM> as shown in <FIG>) is statically held against thermal mechanical drift and expansion from heating by throttling heat transfer from the test subject stage <NUM> to the holder base <NUM> as well as the base interface <NUM> of the sample stage. In one example, throttling of heat transfer includes throttling heat transfer out of the test subject stage <NUM> through one or more supports <NUM>, <NUM> coupling the test subject stage with the remainder of the sample stage <NUM> and the holder base <NUM> (See <FIG>, <FIG>). For instance, the one or more supports <NUM>, <NUM> have a smaller cross-sectional area along a direction of heat transfer from the test subject stage <NUM> to the holder base <NUM> and the base interface <NUM>. The cross-sectional area is smaller compared to a test subject stage cross-sectional area in the same direction. Stated another way, because the supports have a smaller cross-sectional area than the test subject stage <NUM> the supports <NUM>, <NUM> effectively provide a narrow passage for conduction of heat into the remainder of the sample stage <NUM> and the holder base <NUM>.

In another example, the test subject stage <NUM> has a first thermal resistance greater than a second thermal resistance of the holder base <NUM>. That is to say, because the first thermal resistance of the test subject stage <NUM> and the sample stage <NUM> is greater than that of the holder base <NUM>, heat transfer from the test subject stage <NUM> through the support columns <NUM>, <NUM> as well as the base interface <NUM> is effectively retarded by the material prior to reaching the holder base <NUM>.

In still another example, the sample stage <NUM> includes one or more voids <NUM>, <NUM> as shown in <FIG>. The voids <NUM>, <NUM> are formed between the support columns <NUM>, <NUM> and provide gaps between the test subject stage <NUM> and the base interface <NUM> of the sample stage <NUM>. Radiant heat transfer across the voids <NUM>, <NUM> is minimal compared to conductive heat transfer. In the case where the atmosphere around the sample stage <NUM> and the holder base <NUM> is a vacuum (e.g., for instance during heating, testing and observation) the vacuum ensures that only radiant heat transfer across the voids is possible while conductive heat transfer through the support columns <NUM>, <NUM> is minimized as described herein. Radiant heat transfer across the voids <NUM>, <NUM> is minimal compared to the already small amount of heat transfer possible through the support columns <NUM>, <NUM> and thermally isolates the test subject stage <NUM> from the remainder of the sample stage <NUM> and the holder base <NUM>.

As discussed above, by throttling the heat transfer from the test subject stage <NUM> to the base interface <NUM> coupled with the holder base <NUM> mechanical drift and thermal expansion of features other than the test subject stage <NUM> and the test sample <NUM> on the test subject stage <NUM> are minimal. For instance, where a heating element is positioned remotely relative to a specimen membrane heating of the heating element must also heat the volume of the specimen cradle surrounding the membrane as well as the membrane itself causing thermal expansion and mechanical drift of the specimen cradle and the membrane. In contrast, because the heating element <NUM> of the sample stage <NUM> is localized to the area adjacent to the test subject stage <NUM> and the sample on the stage subject surface <NUM> (e.g., immediately adjacent relative to the remote spacing of the heating element <NUM> relative to the specimen membrane <NUM> of the prior art shown in <FIG>, <FIG>) drift and thermal expansion are minimized. Heating of a small portion of the sample stage <NUM>, such as the test subject stage <NUM>, is performed without corresponding significant heating of the remainder of the sample stage <NUM> and the holder base <NUM>. Throttling of heat transfer from the test subject stage <NUM> substantially minimizes the heating of these other components and thereby minimizes their corresponding thermal mechanical drift and expansion.

At <NUM>, a parameter of the test subject is simultaneously measured while mechanically testing and holding the test subject statically. Stated another way, because the sample stage <NUM> is capable of heating a sample on the test subject stage <NUM> with little or no thermal mechanical drift and thermal expansion as described above, mechanical testing is performed on the sample and the electron beam of a transmission electron microscope is able to observe the sample before, during and immediately after the testing. Simultaneous measurement of the parameter of the test subject includes observation and testing at substantially the same time as well as synchronously observing the test subject prior to mechanical testing, during testing and then immediately after mechanical testing. Because of the minimization of thermal mechanical drift and expansion due to the throttling of heat transfer from the test subject stage <NUM> a portion of the test sample, for instance, at a micron or nano-scale is observed throughout heating, testing and the time immediately after testing. Difficult to observe features as well as measurements of properties of the test sample <NUM> are thereby observable throughout the method <NUM>.

Several options for the method <NUM> follow. In one example, the coupling of the test subject along the stage subject surface <NUM> includes mounting the test subject on a sample mount such as sample mount <NUM>. Heating of the test subject includes equally distributing heat throughout the sample mount <NUM>. For instance, where the sample mount <NUM> includes a material having a greater thermal conductivity than the sample stage <NUM> heat transferred into the sample mount <NUM> is readily transmitted throughout the sample mount to evenly heat the entire sample mount. In another example, the method <NUM> includes sensing the temperature of the test subject stage <NUM> with a sensing element <NUM> positioned at the test subject stage. As shown in <FIG>, the sensing element <NUM> is positioned adjacent to the heating element <NUM> as well as the stage subject surface <NUM>. Positioning of the sensing element <NUM> adjacent to these features enables the sensing element <NUM> to accurately determine the temperature of the test subject stage <NUM> throughout heating of the test sample <NUM>. In still another example, the method <NUM> includes controlling heating of the test subject with a closed or open loop control system including the heating element <NUM> and the sensing element <NUM> at the test subject stage <NUM>.

In another example, heating the test subject to the specified temperature includes heating only a test subject stage <NUM> volume and the test subject. Stated another way, heat transfer is effectively throttled into the remainder of the sample stage <NUM> including the base interface <NUM> as well as the holder base <NUM>. Corresponding heat transfer to the remainder of the sample stage <NUM> and the holder base <NUM> is thereby minimal with heating of the sample stage <NUM> limited to the test subject stage <NUM> volume as well as the test subject on the test subject stage <NUM>. For instance, heating of only the test subject stage volume as well as the test subject includes maintaining the holder base <NUM> (as well as the junction between the base interface <NUM> and the holder base <NUM>) at around50° C or less while the test subject stage <NUM> is heated to around <NUM>° C or greater. In still another example, simultaneously measuring the parameter of the test subject includes simultaneously imaging the test subject, for instance with a transmission electron microscope, along with mechanical testing and holding of the test subject statically. In still another example, mechanical testing, holding the test subject statically and simultaneously measuring the parameter of the test subject are performed within a test subject holder <NUM> housed in an imaging device <NUM>. One example of a test subject holder <NUM> is shown in <FIG> and <FIG>.

Referring now to <FIG> and <FIG>, one example of an instrument assembly <NUM> not falling under the claimed invention is shown, including a tip heater assembly <NUM>. The instrument assembly <NUM> includes a tip assembly <NUM> having the tip heater assembly <NUM>, a tip <NUM>, such as a diamond tip, and an extension shaft <NUM>. In one example, the extension shaft <NUM> includes, but is not limited to, a quartz tip extension having a minimal coefficient of thermal expansion and a minimal thermal conductivity. The instrument assembly <NUM> further includes a transducer assembly <NUM> including two or more capacitor plates <NUM> configured to measure movement of the tip assembly <NUM> (e.g., the tip <NUM>) and also perform mechanical testing on a sub-micron scale (e.g., nano-scale) such as indentation, scratching and the like. In another example, the instrument assembly <NUM> includes instruments to measure tension, compression, fracture testing and the like. The transducer assembly <NUM> measures movement of the tip <NUM> and also is capable of moving the tip <NUM> for mechanical testing (such as indentation). The tip assembly <NUM> is coupled with the transducer assembly <NUM> by an interconnect <NUM> extending therebetween. In one example, the interconnect <NUM> is constructed with, but not limited to, materials including MACOR®, ZERODUR® and the like. As with the extension shaft <NUM>, the interconnect <NUM> is constructed with materials having low coefficients of thermal expansion and minimal thermal conductivities. The instrument assembly <NUM> further includes a tip base <NUM> (e.g., heat sink) sized and shaped to couple with an instrument including, but not limited to, scanning microscopes, electron microscopes, optical microscopes and the like.

Referring again to <FIG>, the extension shaft <NUM> is shown extending through a heat shield orifice <NUM> of a heat shield <NUM>. As shown, the extension shaft <NUM> as well as the interconnect <NUM> are positioned within a heat shield cavity <NUM> of the instrument assembly <NUM>. In one example, the heat shield <NUM> is a convective heat shield including inlet and outlet ports for transmission of refrigerant fluids including chilled water, glycol, ammonia and the like. In another example, the heat shield <NUM> is constructed with materials having low coefficients of thermal expansion and minimal thermal conductivities. In still another example, the heat shield <NUM> is coupled with a heat sink that forms the tip base <NUM>. The tip base is constructed with similar materials (with low thermal conductivities and coefficients of thermal expansion) to substantially prevent heat transfer from the instrument assembly <NUM> to a coupled instrument, such as a microscope. The heat shield <NUM> minimizes convective and radiative heat transfer from the tip heater assembly <NUM> as well as the MEMS heater <NUM> as previously described herein. Throttling of heat transfer from the tip heater assembly <NUM> as well as the MEMS heater <NUM> into the instrument assembly <NUM> including the transducer assembly <NUM> substantially minimizes any thermal expansion and drift of the transducer assembly <NUM> and the extension shaft <NUM>.

Referring now to <FIG>, the tip heater assembly <NUM> is shown in detail. The tip heater assembly <NUM> includes a heating element and a sensor positioned immediately adjacent to the tip <NUM>. In one example, the heating element and the sensor are resistive heating and sensing elements. Positioning of the heating element and sensor immediately adjacent to the tip <NUM> localizes heating of the tip assembly <NUM> to the volume immediately adjacent to the tip <NUM>. The tip <NUM> as well as the tip heater assembly <NUM> are positioned remotely from the remainder of the extension shaft <NUM> by voids <NUM> interposed between the tip heater assembly <NUM> and the remainder of the shaft. The voids <NUM>, as shown in <FIG>, are bounded by support columns <NUM> extending between along the extension shaft <NUM> to the tip heater assembly <NUM>. Sensor leads <NUM> and heating element leads <NUM>, in one example, extend through the extension shaft <NUM> including the support columns <NUM> for electrical coupling with the tip heater assembly <NUM>.

In a similar manner to the MEMS heater <NUM>, the instrument assembly <NUM> including the tip heater assembly <NUM> heats the tip <NUM> locally without undesirable significant heat transfer through the remainder of the extension shaft <NUM> and transducer assembly <NUM>. The tip heater assembly <NUM> is remotely positioned relative to the remainder of instrument assembly <NUM> and is immediately adjacent to the tip <NUM>. Further, because the tip heater assembly <NUM> and tip <NUM> are isolated from the remainder of the extension shaft <NUM> by the voids <NUM> and the support columns <NUM> heat transfer from the tip heater assembly <NUM> is substantially throttled into the remainder of the extension shaft <NUM>. The support columns <NUM> minimize conductive heat transfer through minimal cross-sectional area into the portion of the extension shaft <NUM> coupled with the interconnect <NUM> and the transducer assembly <NUM> (see <FIG>). Additionally, the voids <NUM> prevent any conduction of heat across the voids and substantially retard heat transfer by only allowing convective heat transfer (a minimal form of heat transfer relative to conductive heat transfer) and radiative heat transfer. In one example, where the instrument assembly <NUM> is retained within a vacuum the voids <NUM> substantially prevent any convective heat transfer from the tip heater assembly <NUM> to the remainder of the extension shaft <NUM> and only allow minimal radiative heat transfer across the voids. Additionally, because the extension shaft <NUM> is constructed with materials having low coefficients of thermal expansion and minimal thermal conductivity heat transfer from the tip heater assembly <NUM> to the remainder of the instrument assembly <NUM> is minimized and corresponding thermal expansion and thermal drift of those components (the transducer assembly <NUM> and a majority of the extension shaft <NUM>) are correspondingly minimized as well.

By localizing heating of the tip <NUM> at the tip heater assembly <NUM> only a small volume of the extension shaft <NUM> relative to the entire extension shaft is heated with minimal heating power. Stated another way, minimal power is needed to heat the small volume of the tip heater assembly <NUM>, the portion of the extension shaft <NUM> adjacent to the tip heater assembly <NUM> and the tip <NUM> relative to the larger volume of the remainder of the extension shaft <NUM> and the transducer assembly <NUM>. The low volume and minimal heating power facilitate rapid thermal stabilization and minimize the thermal drift during mechanical testing and observation. Further, because the extension shaft <NUM> positions the tip <NUM> remotely relative to the transducer assembly <NUM> as well as the tip base <NUM> thermal drift of the transducer assembly <NUM> and the tip base <NUM> is substantially minimized through use of the materials of the extension shaft, the geometry of the tip assembly <NUM> as well as the heat shield <NUM>. Moreover, the geometry of the shaft including the support columns <NUM> and the volume of the extension shaft <NUM> including the tip heater assembly <NUM> supports the tip <NUM> and provides rigid support to ensure accurate transmission of forces from the transducer and measurement of movement of the tip <NUM>.

In an example where the instrument assembly <NUM>, including the tip heater assembly <NUM>, is incorporated into a system having a sample heating stage, such as the MEMS heater <NUM> described herein, the tip <NUM> is heated to a temperature identical (or nearly identical) to the temperature of the sample stage having the MEMS heater and the sample thereon. Undesirable heat transfer from the heated sample to an otherwise cool tip is thereby substantially prevented. Stated another way, by substantially equalizing the temperatures of the tip <NUM>, the sample and the sample stage heat transfer between the tip <NUM> and the sample is substantially prevented. Correspondingly, distortion of the sample and the mechanical properties measured from the sample are substantially prevented. In other devices, contact between an unheated tip and a heated sample transfers heat from the heated sample into the tip causing distortions (thermal expansion, drift and the like) in one or more of the sample and the tip thereby distorting the properties and measurements collected by the tip.

In one example, the tip heater assembly <NUM> is constructed with fabrication processes including MEMS processes. For instance, the instrument assembly <NUM> is constructed with but not limited to, focused ion beam lithography and milling, laser machining, photo lithography and etching (dry or wet) and the like. In another example, the instrument assembly <NUM> including the tip heater assembly <NUM> is provided together with the MEMS heater examples previously described herein. In still another example, the instrument assembly <NUM> is provided separately from the heated test subject stage described herein.

The sample stage including the MEMS heater described herein and shown in the Figures mounts a small test sample and substantially statically holds the test sample in place when the temperature of the sample and the sample stage are raised and the sample is indented or compressed for material testing. The sample stage includes materials having high thermal resistances and low coefficients of thermal expansion that focus heating of the sample stage near the test sample and arrest heating of other portions of the stage and the test subject holder mounting the sample stage. Undesirable thermal expansion and drift of the sample stage are thereby minimized. Further thermal expansion and drift of the test subject holder are minimized because heat transfer is throttled from the sample stage toward the test subject holder. The test subject holder is substantially larger than the sample stage and because of the arresting of heat transfer corresponding large amounts of thermal expansion and drift are prevented. Similarly, because the sample stage is relatively small compared to the test subject holder heating focused in the sample stage causes corresponding negligible drift in components that already have low coefficients of thermal expansion.

Further, the sample stage (e.g., including the stage plate separately or integrally formed with the sample stage) provides a stiff brace against deflection from testing indentations and compression and thereby ensures displacement and force measurements from indentation or compression do not include errors from deflection of the stage as opposed to indentation of the test sample. In contrast to heaters including membrane features, the sample stage described herein provides a solid and robust support for the test sample. At elevated temperatures (around <NUM> degrees Celsius) the sample stage braces the test sample and is substantially free of deflection inaccuracies in nano-mechanical tests due to mechanical compliance in the stage. A combination of geometry of the sample stage - including the support columns and the robust front face - along with materials having stiffness (e.g., high Young's modulus, flexural modulus and the like) ensures the sample stage is resistant to deflection over a range of operating temperatures for the MEMS heater.

Claim 1:
A micron scale heating stage (<NUM>) configured for conducting mechanical property testing on a sub-micron scale comprising:
a base interface (<NUM>) configured for coupling with a holder base (<NUM>) of a sub-micron scale mechanical property testing instrument and electro-mechanical transducer assembly; and
a microelectromechanical (MEMS) heater (<NUM>) including:
- a test subject stage (<NUM>), wherein the test subject stage (<NUM>) includes
a stage subject surface (<NUM>), and
a stage plate (<NUM>) underlying the stage subject surface (<NUM>), wherein the stage plate (<NUM>) braces the stage subject surface (<NUM>); and
- a heating element (<NUM>) on the test subject stage (<NUM>) and adjacent to the stage subject surface (<NUM>) and away from the base interface (<NUM>), such that when the base interface (<NUM>) is coupled with the holder base (<NUM>), the holder base (<NUM>) is thermally isolated from the heating element (<NUM>).