Abstract:
Disclosed is an electrical-mechanical complex sensor for nanomaterials, including: a detector having a piezoelectric film therein, for measuring a mechanical property of a nanomaterial when a bending or tensile load is applied to the nanomaterial; a first detection film formed at an end of the detector to measure the mechanical property and an electrical property of the nanomaterial) in real time at the same time, when the nanomaterial contacts the first detection film; and a support to which one end of the detector is integrally connected, for supporting the detector.

Description:
TECHNICAL FIELD 
     The present invention relates to an electrical-mechanical complex sensor for nanomaterials, and more particularly, to an electro-mechanical complex sensor for nanomaterials which can measure electrical-mechanical properties at the same time. 
     BACKGROUND ART 
     The twenty first century may well be called an era of nanotechnology. For the last several decades, studies on nanotechnology have achieved excellent results, and more study results on and developments of nanotechnology are being expected. 
     Generally, nanomaterials refer to nanowires and nanorods having diameters ranging from less than 10 nm to several hundred nm. 
     Reliability evaluation methods and technologies for nanomaterials are necessarily required in an aspect of applications of nanotechnology, and accordingly a systematic mechanical property measuring and analyzing technology for nanomaterials needs to be developed. 
     As shown in  FIG. 7 , a mechanical property measuring apparatus for nanomaterials includes an electron microscope  100  for observing and controlling a nano material  35 , a nano-manipulator  60  mounted within the electron microscope  100  to control the nanomaterial  35  and perform a mechanical property test, and a force sensor  1  having a cantilever shape and controlled by the nano-manipulator  60 . Load values can be obtained by using the force sensor  1  during a mechanical property test, and the results are numericalized by a computer. 
     The nano-manipulator  60  is installed within a scanning electron microscope  100  to be driven in a vacuum state, in which a feed through for data communication between an interior of a vacuum chamber and the outside is installed to maintain a vacuum state. 
     Further, the nano-manipulator  60  realizes 3-axis control at a minimum resolution of 10 nm for a smooth experiment for the nanomaterial  35 , and since the nano-manipulator  60  needs to be precisely driven along the axes, a motor which can be minutely driven while not generating electromagnetic fields, that is, a piezoelectric nanomotor is mounted to the nano-manipulator to perform precise control such as minute manipulation in nano unit. 
     As shown in  FIG. 7 , the nano-manipulator  60  is configured to linearly moved along the X, Y, and Z axes, and the force sensor  1  and a tungsten tip may be replaced in a sensor holder  2  connected to the Z axis. 
     The nano-manipulator  60  is mounted at an upper portion of an interior of a chamber of the electron microscope  100  so that a body or an attachment of the nano-manipulator  60  cannot cover a detector in charge of an image of the electron microscope  100  to badly influence the image. 
     Further, the nano-manipulator  60  is controlled by a keyboard of a computer or a joystick through a control box called network control (NWC). 
     Then, a maximum movement distance of the nano-manipulator  60  along the axes is 20 mm. 
     The force sensor  1  serves to measure a load applied to the nanomaterial  35  when a bending or tensile load is applied to the nanomaterial  35  to measure a mechanical property of the nanomaterial  35 . 
     As shown in  FIG. 7 , the force sensor  1  is of a cantilever type having a shape similar to that of an AFM tip, and it is easy to bond the nanomaterial  35  to the body of the sensor by using an electron beam of the electron microscope  100  during a tension test. 
     The body of the force sensor  1  is formed of SiO 2  and a piezoelectric material such as ZnO is applied on a SiO 2  surface, so that an infinitesimal force is applied from the outside, an electrical change due to compression or tension applied to a thin film while the cantilever is bent is converted into a mechanical value. 
     Then, an accurate load value can be obtained during a mechanical property test for the nanomaterial  35  by inputting a natural spring constant K of SiO 2  to perform a calibration. 
     As shown in  FIG. 8 , a natural spring constant of SiO 2  varies according to a thickness of SiO 2 , a resolution of the force sensor  1  depends on the K value, an average resolution of the force sensor  1  is 100 nN or less, and a maximum of several mN can be measured. 
       FIG. 9  is a flowchart showing a method of testing a nano property according to a generally known mechanical property test procedure. First, the nanomaterial  35  in a powder state is dispersed, and then the nanomaterial  35  dispersed for a mechanical property test is selected by using the tungsten tip or the force sensor  1  and a location of the nanomaterial  35  is controlled. 
     If the nanomaterial  35  to be tested is determined, a tension or bending test is performed on the nanomaterial  35  after the nanomaterial  35  is gripped between the tungsten tip and the force sensor  1 . 
     An electron beam of the electron microscope  100  is used to grip the nanomaterial  35  between the tungsten tip and the force sensor  1 . 
     If the electron beam is scanned to a contact portion between the nano material  35  and the tungsten tip, carbon molecules and hydrocarbon molecules existing within the electron microscope  100  are deposited so that the nanomaterial  35  is gripped by the tungsten tip. 
     Then, if a gripping degree of the nanomaterial  35  is evaluated to be normal, tension and bending tests are performed, while if determined to be inferior, the nanomaterial  35  is wasted. 
       FIG. 10  is a picture showing an example of a tension/bending test for nanomaterials. 
     In order to perform a tension test for the nanomaterial  35 , the nanomaterial  35  is made horizontal to an end of the force sensor  1  by vertically gripping the nanomaterial  35  by the tungsten tip or a rigid body and rotating the holder  2  of the electron microscope  100 . 
     After the force sensor  1  and the nanomaterial  35  are horizontally positioned for an accurate measurement during the tension test, the force sensor  1  and an end of the nanomaterial  35  are gripped by using an electron beam of the electron microscope  100  and a tension test is performed on the nanomaterial  35 . 
     According to the tension test method, the nano-manipulator  60  is adjusted by using a joystick, a tensile force is applied to the nanomaterial  35  gripped by an end of the force sensor  1  if the force sensor  1  is pulled by using the nano-manipulator  60 , and the force sensor  1  converts an electrical change due to a tension applied to a piezoelectric material into a mechanical value. 
     Further, a mechanical property is evaluated by using a spring constant K of the force sensor  1 . 
     The force sensor  1  is positioned on the right side of the nanomaterial  35  to perform a bending test on the nanomaterial  35 , and the force sensor  1  and the nanomaterial are positioned perpendicular to each other for an accurate measurement. 
     Then, the nanomaterial  35  and the force sensor  1  are not gripped but a bending test is performed after a position of the force sensor  1  is determined. 
     According to the bending test method, the nano-manipulator  60  is adjusted by using a joystick, and the nanomaterial is deflected by moving the force sensor  1  by using the nano-manipulator  60 . 
     The bending test is performed not until the nanomaterial  35  is fractured and within a range where a nonlinear section is not generated as the force sensor  1  and the nanomaterial  35  are slid with respect to each other. 
     If tests of mechanical properties, that is, tension and bending tests are performed on the nanomaterial  35  by using the nano-manipulator  60  and the force sensor  1  in this way, a displacement-load graph of  FIG. 11  is obtained, a strain-stress graph can be obtained from  FIG. 11 , a modulus of elasticity of the nanomaterial  35  can be obtained from the strain-stress graph, and a tensile strength and a percentage of elongation of the nanomaterial  35  can be obtained 
     Thus, reliability of nanomaterials  35  can be evaluated and reliability of nano and micromaterials can be predicted by comprehending characteristics of nanomaterials  35  through mechanical property test using the nano-manipulator  40  and the force sensor  1  and creating a database for mechanical property test results on the nanomaterials  35 , allowing mechanical property test services for various nanomaterials  35 . 
     However, since only measurement of mechanical properties of nanomaterials  35  is given undue stress to the force sensor  1  according to the related art, a sensor capable of measuring a mechanical property and an electrical property at the same time is required. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
     Therefore, the present invention has been made in view of the above-mentioned problems, and an aspect of the present invention is to provide an electrical-mechanical complex sensor which can measure mechanical and electrical properties in real time at the same time when a load is applied to a nanomaterial such as a carbon nanotube to measure and evaluate a correlation between mechanical characteristics and electrical characteristics, thereby improving an evaluation of reliability of a nanomaterial. 
     Technical Solution 
     In accordance with an aspect of the present invention, there is provided an electrical-mechanical complex sensor for nanomaterials for measuring mechanical and electrical properties at the same time as compared with an existing force sensor for measuring only a mechanical property of a nanomaterial, wherein a detector has a lamination structure of SiO 2 /an Au layer/a piezoelectric film (ZnO)/an Au layer/SiO 2  so that a load applied to the nanomaterial is measured by using a piezoelectric phenomenon of a piezoelectric film generated when a tensile load is applied by bringing a first detection film formed at an end of a detector to apply a bending load or grip the nanomaterial. 
     Advantageous Effects 
     The advantage of the electrical-mechanical complex sensor for nanomaterials according to the present invention is as follows. 
     A first detection film formed at an end of a detector and a second detection film formed at an end of an electrode for measuring electrical characteristics are connected to each other through a carbon nanotube yarns and an end of the detector contacts a nanomaterial or is gripped, so that electrical and mechanical properties of a nanomaterial can be measured at the same time while a bending load or a tensile load is applied to the nanomaterial, thereby making it possible to measure and evaluate a correlation between mechanical characteristics and electrical characteristics and improving an evaluation of reliability of the nanomaterial. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing an electrical-mechanical complex sensor according to an embodiment of the present invention. 
         FIG. 2  is a partial view of  FIG. 1 . 
         FIG. 3  is a partial perspective view of  FIG. 1 . 
         FIG. 4  is a schematic view showing an electrical-mechanical complex sensor for nanomaterials according to the embodiment of the present invention. 
         FIG. 5  is a graph depicting a change in resistance according to a displacement of a nanomaterial. 
         FIG. 6  is a graph depicting a change in force (load) according to a displacement of a nanomaterial. 
         FIG. 7  is a picture representing a system for testing and measuring a mechanical property of a nanomaterial. 
         FIG. 8  is a graph depicting a relationship between a spring constant and a thickness of a force sensor according to the related art. 
         FIG. 9  is a flowchart of a mechanical property test for a nanomaterial. 
         FIG. 10  is a picture representing examples of tension and bending tests for nanomaterials. 
         FIG. 11  is a picture representing sample data of a mechanical property test for a nanomaterial. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS FOR MAIN PARTS 
       10 : Support  11 : First electrode 
       12 : Second electrode  13 : Third electrode 
       14 : Fourth electrode  15 : Fifth electrode 
       20 : Detector  21 : Detection film 
       22 : Silicon oxide film (SiO 2 ) 
       23 : Au layer 
       24 : Piezoelectric film (ZnO) 
       25 : Pt 
       30 : Carbon nanotube yarns 
       35 : Nano material 
       40 : Complex sensor 
       50 : Tungsten tip 
       51 : Stage 
       60 : Nano-manipulator 
       70 : Multi-meter 
       80 : Voltage source 
       90 : Computer 
       100 : Electron Microscope 
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a plan view showing an electrical-mechanical complex sensor according to an embodiment of the present invention.  FIG. 2  is a partial view of  FIG. 1 .  FIG. 3  is a partial perspective view of  FIG. 1 .  FIG. 4  is a schematic view showing an electrical-mechanical complex sensor for nanomaterials according to the embodiment of the present invention. 
     The present invention can measure electrical-mechanical complex properties of a nanomaterial  35  in real time at the same time to measure and evaluate correlations between mechanical characteristics and electrical characteristics and improve evaluation of a reliability of the nanomaterial  35 . 
     The electrical-mechanical complex sensor  40  for nanomaterials according to the embodiment of the present invention includes a support  10  and a detector  20 . 
     The support  10  supports the detector  20  in the form of a cantilever and at least five electrodes are formed on an upper surface of the support  10 . Among the electrodes, the first to fourth electrodes  11  to  14  from the bottom are used as a Wheatstone bridge circuit for measuring a tension and a bending load corresponding to mechanical properties from the detector  20 , ends of the four electrodes, that is, the first to fourth electrodes  11  to  14  are electrically connected to the detector  20 , and electrode terminals are formed at opposite ends of the four electrodes  11  to  14 . 
     Then, the electrode terminals are connected to an external voltage source  80  to receive electric power. 
     The detector  20  is formed in the form of a cantilever one end of which is supported by the support  10 , and a silicon oxide film (SiO 2 )  22 , an Au layer  23 , a piezoelectric film (ZnO)  24 , an Au layer  23 , and a silicon oxide film (SiO 2 )  22  are laminated in the detector  20  from the bottom. 
     Then, if an infinitesimal force is applied from the outside, a tensile or compressing force is applied to the piezoelectric film  24  while the detector  20  in the form of a cantilever is defected so that an electrical change can be converted to a mechanical value. 
     Then, the mechanical value is calibrated by inputting K which is a spring constant of the silicon oxide film (SiO 2 ) to obtain an accurate load value during a mechanical property test of the nanomaterial  35 . 
     Here, the fifth electrode  15  which is the remaining one of the electrodes is used as an electrode for measuring electrical characteristics. 
     A first detection film  21   a  of Au is formed at an end of the detector  20 , a second detection film  21   b  of Au is formed in the fifth electrode  15  of the support  10 , and opposite ends of a carbon nanotube yarns  30  are attached to the first detection film  21   a  and the second detection film  21   b  such that a current flows through the carbon nanotube yarns  30 , making it possible to measure an electrical property of the nanomaterial  35 . 
     Then, in order to increase electrical conductivities between the carbon nanotube yarns  30  and the first and second detection films  21   a  and  21   b , Pt  25  is deposited by using a focused ion beam (FIB) or carbon molecules or hydrocarbon molecules are deposited by using an electron beam on the first and second detectors  21   a  and  21   b  to which opposite ends of the carbon nanotube yarns  30  are attached. 
     If the electron beam is scanned to contact portions between the carbon nanotube yarns  30  and the first detection film  21   a , and between the carbon nanotube yarns  30  and the second detection film  21   b , the carbon molecules or hydrocarbon molecules in the interior of the electron microscope  100  are deposited and the carbon nanotube yarns  30  is gripped by the first and second detection films  21   a  and  21   b.    
     An omni probe or a tungsten tip  50  is used to attach or control the carbon nanotube yarns  30 , and the omni probe or the tungsten tip  50  may be controlled by using the FIB or the nano-manipulator  60  attached within the electron microscope  100 . 
     The complex property measuring apparatus using the electrical-mechanical complex sensor  40  according to the embodiment of the present invention includes a complex sensor  40 , a tungsten tip  50 , a nano-manipulator  60 , a computer  90 , a multi-meter  70 , and a voltage source  80 . 
     The complex sensor  40  serves to measure mechanical and electrical characteristics of the nanomaterial  35  at the same time. 
     The tungsten tip  50  serves to attach or control the carbon nanotube yarns  30  between the first detection film  21   a  formed at an end of the detector  20  of the complex sensor  40  and the second detection film  21   b  of the fifth electrode  15 , or grip the nanomaterial  35  to control the nanomaterial  35  during the tension or bending tests. 
     Then, the tungsten tip  50  is configured to be moved upward, downward, leftward, and rightward in the stage  51 . 
     The nano-manipulator  60  is mounted within a scanning electron microscope  100  to serve to control the complex sensor  40  and is driven in a vacuum state, and a feed through for data communications between an interior and an exterior of the vacuum chamber is installed to maintain a vacuum state. 
     The nano-manipulator  60  is configured to be linearly moved along the X, Y, and Z axes at a resolution of a minimum of 10 nm for a smooth test of the nanomaterial  35 . 
     The nano-manipulator  60  is required to be precisely driven along the axes, in which case electromagnetic fields generated in the drive motor should not badly influence an image of the electron microscope  100 . 
     Thus, according to the present invention, a piezoelectric nanomotor as a motor which can be minutely driven while not generating electromagnetic fields may be mounted for a precise control such as a minute manipulation in nano unit. 
     The nano-manipulator  60  is mounted at an upper portion of an interior of the chamber of the electron microscope  100 , and the body or attachments of the nano-manipulator  60  is mounted not to cover a detector in charge of an image of the electron microscope  100 , not badly influencing the image. 
     Further, the nano-manipulator  60  is configured to be precisely controlled by a keyboard of a computer or a joystick through a control box called a network control. 
     The voltage source  80  is electrically connected to the nano-manipulator  60  and the stage  51  to apply electric power necessary for measuring electrical-mechanical characteristics to an electrode of the complex sensor  40 . 
     The multi-meter  70  measured a voltage, a current, and a resistance of the voltage source  80 . 
     Hereinafter, a method of measuring a tension and a bending load by using the electrical-mechanical complex sensor  40  according to the embodiment of the present invention, and measuring varying electrical characteristics (voltage, current, and resistance) at the same time will be described. 
     For an electrical-mechanical property test of the nanomaterial  35 , a suitable nanomaterial  35  is first selected. 
     That is, the nanomaterial  35  in the form of powder is dispersed, the nanomaterial  35  dispersed for a mechanical property test is selected by using the tungsten tip  50  or the complex sensor  40 , and a position of the nanomaterial  35  is controlled. 
     If the nanomaterial  35  to be tested is determined, the nanomaterial  35  is gripped. 
     After the nanomaterial  35  is gripped between the tungsten tip  50  and the complex sensor  40 , tension and bending tests are performed. 
     The tests are performed at room temperature, and 6 or more hours of stabilization time is required for stabilization after the complex sensor  40  and the material are installed. Further, since the manipulation in nano unit is influenced even by minute vibrations, vibrations are removed by using an anti-vibration pad, and an action or equipment which may cause vibrations is prohibited. 
     An electron beam of the electron microscope  100  is used to grip the nanomaterial  35 . If the electron beam is scanned to a contact portion between the nanomaterial  35  and the tungsten tip  50 , the carbon molecules or hydrocarbon molecules in the electron microscope  100  are deposited to allow the nanomaterial  35  to be gripped by the tungsten tip  50 . 
     Then, in order to evaluate a gripping degree of the nanomaterial  35 , after the tungsten tip  50  is electrically connected to the nano multi-meter  70  through the feed screw within the electron microscope  100  and is brought into contact with the nanomaterial  35  and the tungsten tip  50 , a resistance of a current flowing through the nanomaterial  35  and the tungsten tip  50  is measured by the multi-meter  70  in the gripping step by irradiating an electron beam to the contact portion in a vacuum atmosphere. 
     It is determined while performing the gripping whether an initially measured resistance is lowered by a set rate within a predetermined lapse of time in measuring an electrical resistance. 
     If the resistance is lowered by the set rate, it may be determined that the gripping is normal and tension and bending tests may be performed, and otherwise, it is determined that the nanomaterial is inferior and the nanomaterial is wasted. 
     Next, a tension test is performed. 
     In order to perform the tension test, an end of the complex sensor  40  is made horizontal to the nanomaterial  35  by adjusting the nano-manipulator  60 . 
     The nano-manipulator  60  is adjusted by a joystick of the computer, and since the nano-manipulator  60  can be moved only along three axes during the measurement, the nano-manipulator  60  is positioned on the right side of the nanomaterial  35  and the complex sensor  40  and the nanomaterial  35  are disposed horizontally. 
     Thereafter, a tension test for nanomaterials  35  is performed while the first detection film  21   a  of the complex sensor  40  and an end of the nanomaterial  35  are gripped by using an electron beam of the electron microscope  100 . 
     The tension test is performed in a displacement control method by using a network control, a tensile load applied to the nanomaterial  35  is measured through the detector  20  of the complex sensor  40  every 2 nm while tension speed is 10 nm/s. 
     Further, electrical characteristics (voltage, current, and resistance) changed at the same time when the tensile load is applied to the nanomaterial  35  are measured by the second detection film  21   b  connected to the first detection film  21   a  of the detector  20  through the carbon nanotube yarns  30 . 
     In more detail, a current is allowed to flow to the electrodes by turning on the computer  90  and applying a voltage to the nano-manipulator  60  and an electrode of the complex sensor  40 . 
     Here, when a voltage is applied to the first to fourth electrodes  11  to  14  constituting the Wheatstone bridge circuit and a voltage is applied to the detector  20  electrically connected to the first to fourth electrodes  11  to  14  and the first detection film  21   a  at an end of the detector  20 , a current of the first detection film  21   a  flows to the second detection film  21   b  formed at an end of the fifth electrode  15  of the support  10  through the carbon nanotube yarns  30 . 
     Then, if a voltage is applied to the piezoelectric film  24  of the detector  20 , the piezoelectric film  24  is prolonged in a direction in which a voltage is applied, and according to the characteristics of the piezoelectric material contracted in a direction perpendicular to a direction in which the voltage is applied, if a tensile load is applied to the nanomaterial  35 , an electrical change is converted to a mechanical change by using the piezoelectric phenomenon, making it possible to calculate the applied tensile load. 
     Further, since the electrical characteristics of the nanomaterial  35  vary as a bending load and a tensile load are applied to the nanomaterial  35 , a difference between electrical signals flowing through the fifth electrode  15  due to electrical characteristics of the nanomaterial  35  before the tensile load is applied and electrical characteristics of the nanomaterial  35  after the tensile load is applied is measured so that the electrical characteristics of the nanomaterial  35  can be recognized while a current applied to the first detection film  21   a  of the detector  20  flows to the second detection film  21   b  of the fifth electrode  15  through the carbon nanotube yarns  30 . 
     For a bending test for nanomaterials  35 , a cantilever bending test is performed. 
     The complex sensor  40  is positioned on the right side of the nanomaterial  35 , and the complex sensor  40  and the nanomaterial  35  are positioned perpendicular to each other for an accurate measurement. 
     The nanomaterial  35  and the complex sensor  40  are not gripped, and the bending test is performed after a position of the complex sensor  40  is determined. 
     The bending test is performed not until the nanomaterial  35  is fractured and within a range where a nonlinear section is not generated as the complex sensor  40  and the nanomaterial  35  are slid with respect to each other. During the bending test, a method of measuring a bending load and electrical characteristics is the same as the tension test. 
     Here,  FIG. 5  is a graph depicting a change in resistance according to a displacement of a nanomaterial  35 .  FIG. 6  is a graph depicting a change in force (load) according to a displacement of a nanomaterial  35 . 
     By performing a tension or bending test on the nanomaterial  35 , the displacement-load (mechanical property) or displacement-resistance (electrical property) graph as in  FIGS. 5 and 6  can be obtained, correlations between mechanical characteristics and electrical characteristics can be measured and evaluated, and evaluation of a reliability of the nanomaterial  35  can be improved.