Patent Publication Number: US-9429515-B2

Title: Optical microscopy vapor-condensation-assisted device

Description:
RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 201410034580.6 filed on Jan. 25, 2014 in the China Intellectual Property Office, the contents of which are incorporated by reference herein. 
     FIELD 
     The subject matter herein generally relates to an optical microscopy system and method for imaging nanostructures with the optical microscopy system. 
     BACKGROUND 
     An accurate and efficient imaging of nanostructures can significantly deepen our understanding of the microscopic world and shed light on prospective applications. Compared with scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), scanning tunneling microscope (STM), etc., it is very easy to operate an optical microscope and quite convenient to integrate it with other facilities. However, nanomaterials or nanostructures such as carbon nanotubes (CNTs) cannot be directly observed by optical microscope, because their nanoscale dimensions are much smaller than the wavelength of visible light. 
     Therefore the visualization of nanomaterials, especially of CNTs by optical microscopy is highly desirable and has long been attempted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present optical microscopy system can be better understood with references to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present optical microscopy system. 
         FIG. 1  is a schematic view of an optical microscopy system in accordance with an embodiment. 
         FIG. 2  is an exploded view of a vapor-condensation-assisted device in accordance with one embodiment. 
         FIG. 3  is a schematic view of the vapor-condensation-assisted device in accordance with  FIG. 2 . 
         FIG. 4  shows a schematic view of a vapor-condensation-assisted device in accordance with one embodiment. 
         FIG. 5  is a schematic view of an optical microscopy system in accordance with an embodiment. 
         FIG. 6  is a schematic view of carbon nanotubes on a substrate. 
         FIG. 7  is an optical microscopy image of the carbon nanotubes on the substrate by the optical microscopy system of one embodiment. 
         FIG. 8  is a Scanning Electron Microscope (SEM) image of the carbon nanotubes in  FIG. 7 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one present embodiment of optical microscopy system and method using the same, in at least one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. 
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant feature being described. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features. The description is not to be considered as limiting the scope of the embodiments described herein. 
     Several definitions that apply throughout this disclosure will now be presented. 
     The term “coupled” is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The term “outside” refers to a region that is beyond the outermost confines of a physical object. The term “inside” indicates that at least a portion of a region is partially contained within a boundary formed by the object. The term “substantially” is defined to be essentially conforming to the particular dimension, shape or other word that substantially modifies, such that the component need not be exact. For example, substantially cylindrical means that the object resembles a cylinder, but can have one or more deviations from a true cylinder. The term “comprising” means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in a so-described combination, group, series and the like. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     References will now be made to the drawings to describe, in detail, various embodiments of the present epitaxial structures and methods for making the same. 
     Referring to  FIG. 1 , an optical microscopy system  100  is provided according to one embodiment. The optical microscopy system  100  comprises an optical microscope  10  and a vapor-condensation-assisted device  20 . The optical microscope  10  can be one of various optical microscopes in existing technology. The vapor-condensation-assisted device  20  is used to provide vapor. 
     In one embodiment, the optical microscope  10  comprises stage  110 , objective lenses  120 , eyepiece  130 , and an image collecting system  140 , a light source system  150  and focus adjusting system  160 . 
     The stage  110  is a platform below the objective lenses  120  which supports the specimen being viewed. The objective  120  is usually in a cylinder housing containing a glass single or multi-element compound lens. The optical microscope  10  can comprises one or more objective lenses  120  that collect light from the specimen. In one embodiment, there are around three objective lenses  120  screwed into a circular nose piece which may be rotated to select the required objective lens  120 . These arrangements are designed to be par focal, which means that when one changes from one lens to another on a microscope, the specimen stays in focus. The image collecting system  140  comprises a computer  144  and a camera  142 . The focus adjusting system  160  comprises focus knobs to move the stage  110  up and down with separate adjustment for coarse and fine focusing. Many sources of light can be used as the light source system  150 . At its simplest, daylight is directed via a mirror. 
     Referring to  FIG. 2 , the vapor-condensation-assisted device  20  comprises an air blowing device  210 , a vapor producing device  220  and a guide pipe  230 . The air blowing device  210  is connected to the vapor producing device  220  and can blow air to the vapor producing device  220 . The vapor producing device  220  is connected to the guide pipe  230 . The air can blow from the air blowing device  210  into the vapor producing device  220  and out of the guide pipe  230 . The vapor produced the in vapor producing device  220  can be blew to the specimen on the stage  110  by the blowing air from the air blowing device  210 . 
     The air blowing device  210  can be a flexible bulb can inhale or exhale the air by pressing. The air bowling device  210  is connected to the vapor producing device  220 . The air can blow into the vapor producing device  220  by the air blowing device  210 . In one embodiment, the air blowing device  210  is a rubber suction bulb. 
     The vapor producing device  220  comprises a liquid absorbing material  222 , a hollow tube  224 , and heating layer  226  and a power source  228 . The liquid absorbing material  222  is located in the hollow tube  224 , but does not affect the ventilation performance of the hollow tube  224 . A liquid material is absorbed by the liquid absorbing material  222 . The heating layer  226  is surrounded the out surface of the hollow tube  224  and electrical connected to the power source  228 . The heating layer  226  is used to heat the liquid absorbing material  222  located in the hollow tube  224 . The liquid material turns into vapor when the liquid absorbing material  222  is heated. 
     A material of the hollow tube  224  is not limited, and can be soft or hard materials. The hard material can be ceramic, glass, or quartz. The soft material can be resin, rubber, plastic or flexible fiber. The cross section shape of the hollow tube  224  is also unlimited, and can be round, arc, or rectangle. In one embodiment, this example, the hollow tube  224  is a hollow ceramic tube with a circular cross section. 
     The liquid absorbing material  222  has good absorption performance. The liquid absorbing material  222  can be cotton, non-woven fabrics and high absorbent resin. In one embodiment, the liquid absorbing material  222  is attached to the inner surface of the hollow tube  224 . 
     The heating layer  226  is disposed on an outer surface of the hollow tube  224 . The heating layer  226  comprises a carbon nanotube structure. The carbon nanotube structure includes a plurality of carbon nanotubes uniformly distributed therein, and the carbon nanotubes therein can be combined by van der Waals attractive force therebetween. The carbon nanotube structure can be a substantially pure structure of the carbon nanotubes, with few impurities. The carbon nanotubes can be used to form many different structures and provide a large specific surface area. The heat capacity per unit area of the carbon nanotube structure can be less than 2×10 −4  J/m 2 ·K. Typically, the heat capacity per unit area of the carbon nanotube structure is less than 1.7×10 −6  J/m 2 ·K. As the heat capacity of the carbon nanotube structure is very low, and the temperature of the heating element  16  can rise and fall quickly, which makes the heating layer  226  have a high heating efficiency and accuracy. As the carbon nanotube structure can be substantially pure, the carbon nanotubes are not easily oxidized and the life of the heating layer  226  will be relatively long. Further, the carbon nanotubes have a low density, about 1.35 g/cm 3 , so the heating layer  226  is light. As the heat capacity of the carbon nanotube structure is very low, the heating layer  226  has a high response heating speed. As the carbon nanotube has large specific surface area, the carbon nanotube structure with a plurality of carbon nanotubes has large specific surface area. When the specific surface of the carbon nanotube structure is large enough, the carbon nanotube structure is adhesive and can be directly applied to the surface outer surface of the hollow tube  224 . 
     The carbon nanotubes in the carbon nanotube structure can be arranged orderly or disorderly. The term ‘disordered carbon nanotube structure’ refers to a structure where the carbon nanotubes are arranged along many different directions, and the aligning directions of the carbon nanotubes are random. The number of the carbon nanotubes arranged along each different direction can be almost the same (e.g. uniformly disordered). The disordered carbon nanotube structure can be isotropic. The carbon nanotubes in the disordered carbon nanotube structure can be entangled with each other. 
     The carbon nanotube structure including ordered carbon nanotubes is an ordered carbon nanotube structure. The term ‘ordered carbon nanotube structure’ refers to a structure where the carbon nanotubes are arranged in a consistently systematic manner, e.g., the carbon nanotubes are arranged approximately along a same direction and/or have two or more sections within each of which the carbon nanotubes are arranged approximately along a same direction (different sections can have different directions). The carbon nanotubes in the carbon nanotube structure can be selected from a group consisting of single-walled, double-walled, and/or multi-walled carbon nanotubes. 
     The carbon nanotube structure can be a carbon nanotube film structure with a thickness ranging from about 0.5 nanometers to about 1 millimeter. The carbon nanotube film structure can include at least one carbon nanotube film. The carbon nanotube structure can also be a linear carbon nanotube structure with a diameter ranging from about 0.5 nanometers to about 1 millimeter. The carbon nanotube structure can also be a combination of the carbon nanotube film structure and the linear carbon nanotube structure. It is understood that any carbon nanotube structure described can be used with all embodiments. It is also understood that any carbon nanotube structure may or may not employ the use of a support structure. 
     In one embodiment, the carbon nanotube structure includes at least one drawn carbon nanotube film. A film can be drawn from a carbon nanotube array, to form a drawn carbon nanotube film. The drawn carbon nanotube film includes a plurality of successive and oriented carbon nanotubes joined end-to-end by van der Waals attractive force therebetween. The drawn carbon nanotube film is a free-standing film. Each drawn carbon nanotube film includes a plurality of successively oriented carbon nanotube segments joined end-to-end by van der Waals attractive force therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes parallel to each other, and combined by van der Waals attractive force therebetween. As can be seen in  FIG. 3 , some variations can occur in the drawn carbon nanotube film. The carbon nanotubes  145  in the drawn carbon nanotube film are oriented along a preferred orientation. The carbon nanotube film can be treated with an organic solvent to increase the mechanical strength and toughness of the carbon nanotube film and reduce the coefficient of friction of the carbon nanotube film. A thickness of the carbon nanotube film can range from about 0.5 nanometers to about 100 micrometers. 
     The vapor producing device  220  further comprises two electrodes  221  located on and electrically connected to the heating layer  226 . Furthermore, it is imperative that the two spaced electrodes  221  are separated from each other to prevent short circuiting of the electrodes. The two electrodes  221  can be directly electrically attached to the heating layer  226  by, for example, a conductive adhesive (not shown), such as silver adhesive. Because, some of the carbon nanotube structures have large specific surface area and are adhesive in nature, in some embodiments, the two electrodes  221  can be adhered directly to heating layer  226 . It should be noted that any other bonding ways may be adopted as long as the two electrodes  221  are electrically connected to the heating layer  226 . The shape of the two electrodes  221  are not limited and can be lamellar, rod, wire, and block among other shapes. 
     The two electrodes  221  can be conductive films. A material of the two electrodes  221  can be metal, alloy, indium tin oxide (ITO), antimony tin oxide (ATO), conductive silver glue, conductive polymers or conductive carbon nanotubes. The metal or alloy materials can be aluminum, copper, tungsten, molybdenum, gold, titanium, neodymium, palladium, cesium or any combination of the alloy. In one embodiment, the electrode  221  is a palladium film with a thickness of 20 nanometers. 
     The power source  228  can be AC or DC power. The power source  228  is electrically connected to the two electrodes  221 . When a voltage is applied to heating layer  226  via the two electrodes  221 , the carbon nanotube structure of the heating layer  226  radiates heat at a certain wavelength. The temperature of the heating layer  226  ranges from 50° C. to 500° C., the liquid material in the liquid absorbing material  222  turns to vapor. 
     The vapor producing device  220  can further comprises a protecting layer  202  attached to the exposed surface of the heating layer  226 . The protecting layer  202  can protect the heating layer  226  from the environment. A material of the protecting layer  202  can be an insulated material, such as resin, plastic or rubber. A thickness of the protecting layer  202  can range from about 0.5 μm to about 2 mm. 
     The guide pipe  230  comprises a first opening  231  and a second opening  235  opposite to the first opening  231 . The diameter of the first opening  231  is smaller than the diameter of the second opening  235 . Air can flow from the first opening  231  to the second opening through the guide pipe  230 . The second opening  235  is sealed connected to the vapor producing device  220 . The material of the guide pipe  230  is not limited, and can be soft or hard materials. The hard material can be ceramic, glass, or quartz. The soft material can be resin, rubber, plastic or flexible fiber. The cross section shape of the hollow tube  224  is also unlimited, and can be round, arc, or rectangle. In one embodiment, this example, the guide pipe  230  is a hollow ceramic tube with a circular cross section. 
     The air blowing device  210 , the vapor producing device  220  and the guide pipe  230  are integrated with each other. The air blowing device  210  can push the air through the vapor producing device  220  and the guide pipe  230 , from the first opening  231  to the sample on the stage  110 . 
     Referring to  FIG. 3 , the vapor-condensation-assisted device  20  can further comprises an additional pipe  240 . The additional pipe  240  is located between the vapor producing device  220  and the air blowing device  210 . The vapor producing device  220  is connected to the air blowing device  210  via the additional pipe  240 . The material of the additional pipe  240  is not limited, and can be soft or hard materials. The hard material can be ceramic, glass, or quartz. The soft material can be resin, rubber, plastic or flexible fiber. The stability of air flow can be enhanced by the additional pipe  240 . In one embodiment, the additional pipe  240  is made of rubber, and 50 centimeters long. 
     Referring to  FIG. 4 , a vapor-condensation-assisted device  40  according to another embodiment is provided. 
     The vapor-condensation-assisted device  40  comprises an air blowing device  410  a vapor producing device  420  and a guide pipe  230 . The air blowing device  410  comprises blowing machine  412  and a first connecting pipe  414 . First end of the first connecting pipe  414  is connected to the blowing device  410  and used to exhaust the air blowing from the air blowing device  410 . Second end of the first connecting pipe  414  is connected to the vapor producing device  420 . 
     The vapor producing device  420  comprises a three neck flask  427  and a second connecting pipe  429 . The three neck flask  427  comprises an air inlet  423 , an outlet  425  and a liquid inlet  428 . A liquid is held in the three neck flask  427 . First end of the first connecting pipe  414  is connected to the blowing device  410  and used to exhaust the air blowing from the air blowing device  410 . Second end of the first connecting pipe  414  is inserted in the three neck flask  427  through the air inlet  423 . Another end of the first connecting pipe  414  is under the liquid surface contained in the three neck flask  427 . First end of the second connecting pipe  429  is inserted into the three neck flask  427  through the outlet  425 , and is above the liquid surface contained in the three neck flask  427 . Second end of the second connecting pipe  429  is sealed connected to the second opening  235  of the guide pipe  230 . The liquid inlet  428  is used to pour liquid into the three neck flask  427 . When the air is blew into the three neck flask  427  under the liquid surface, liquid particles would get into the second connecting pipe  429  with the air into the second connecting pipe  429 . Thus, vapor can be delivered to the stage  110 . 
     Further, the vapor-condensation-assisted device  40  can comprise a heating device  426  to heat the three neck flask  427 . In one embodiment, the heating device  426  is a spirit lamp. 
     Referring to  FIG. 5 , an optical microscopy system  200  is provided according to one embodiment. The optical microscopy system  200  comprises an optical microscope  30  and a vapor-condensation-assisted device  20 . 
     The optical microscope  30  comprises an observing device  320 , an image processing device  360 , a support frame  330  and a stage  310 . The guide pipe  230  of the vapor-condensation-assisted device  20 , the observing device  320 , and an image processing device  360  are fixed on the support frame  330 . The observing device  320  integrated eyepieces, objective lenses, focus knobs, and charge-coupled device (CCD). An image caught by the observing device  320  can be send to the image processing device  360 , and display on the screen of the image processing device  360 . The optical microscopy system  200  is simple and very low-cost. 
     A method for observing nanostructures by the optical microscopy system  100 ,  200  according to the embodiments is provided. The method comprises the steps of:
         S1, providing a sample  60  with a nanostructure;   S2, locating the sample  60  on the stage  110 ,  310  of the optical microscopy system  100 ,  200 ; and   S3, applying a vapor to the sample  60  to observe the sample  60  via the optical microscopy system  100 ,  200 .       

     In S1, the sample can be any patterns with nanostructures on a substrate. In one embodiment, the sample  60  comprises carbon nanotubes  610  horizontally aligned on a substrate  600  as shown in  FIG. 6 . The carbon nanotubes  610  are parallel to the surface of the substrate  600 . The substrate  600  is a silicon substrate. 
     In S2, the sample  60  can be located on a slide first and then the slide is put on the stage  110 ,  310 . The substrate  600  can be observed by adjusting the focusing mechanism of the optical microscopy system  100 ,  200 . The sample  60  can not be observed by the optical microscopy system  100 ,  200 , when the vapor is not induced to the surface of the sample  60 . 
     In S3, when the vapor-condensation-assisted device  20  is applied, the first opening  231  of the guide pipe  230  can be immersed into liquid and inhale some liquid into the vapor producing device  220 . The liquid inhaled in the vapor producing device  220  is absorbed by the liquid absorbing material  222 . When the vapor producing device  220  is heated by the heating layer  226 , vapor is obtained and can flow with the air flow from the air bowling device  210  to the first opening  231 . The vapor is induced to the surface of the sample  60 . The liquid can be water or alcohol. In one embodiment, the liquid is water, the vapor is water vapor. When the vapor of water reaching the sample  60 , the vapor of water would condense into micro-droplets on the condensation nuclei attached to the sample  60 . Under oblique illuminating light, the micro-droplets of water will act as scattering centers, appearing as bright dots under a dark-field optical microscope. Thus, the sample  60  is observed by the optical microscopy system  100 ,  200 . 
     Referring to  FIG. 7 , an optical microscopy image of carbon nanotubes  610  on the substrate  600  is taken by the above method via the optical microscopy system  100 . The orientation of the carbon nanotubes is clearly shown in  FIG. 7 . As a comparison, a SEM image of the carbon nanotubes  610  taken by a Scanning Electron Microscope is provided in  FIG. 8 .  FIGS. 7 and 8  compare the optical microscopy image and the SEM image of the carbon nanotubes  610  on the same area of the substrate  600 . It is evident that the optical microscopy image exactly shows the location and the morphology of the carbon nanotubes  610 . In fact, there is a carbon nanotube visible in the optical microscopy image (indicated by the white arrow in  FIG. 7 ), but invisible in the SEM image (where the white arrow locates in  FIG. 8 ). This may be due to the special contrast mechanism of SEM. 
     In another embodiment, a method for observing nanostructures by an optical microscopy is provided. The method comprises the steps of:
         S10, providing a sample  60  with a nanostructure;   S20, applying a cold source on the stage  110  of the optical microscope  10 ; and   S30, locating the sample  60  on the cold source to observe the sample  60  via the optical microscope  10  in an environment with vapor.       

     In S30, the cold source is used to decrease the temperature of the sample  60 . The temperature of the sample  60  is lower than the temperature of environment. The vapor in the environment could condense on the surface of the sample  60 , because the temperature of the sample  60  is lower than the temperature of environment. Therefore, the sample  60  can be observed by the optical microscope  10 . 
     A method for observing nanostructures by an optical microscopy are provided according to one embodiment is provided. The method comprises steps of:
         S100, providing a sample  60  with a nanostructure;   S200, applying a cold source on the stage  110  of the optical microscope  10 ;   S300, locating the sample  60  on the cold source; and   S400, applying a vapor to the sample  60  to observe the sample  60  via the optical microscope  10 .       

     In S400, because the sample is located on the cold source, the temperature of the sample  60  is much lower than the temperature of the vapor. The vapor is easy to condense on the surface of the sample  60 . The sample  60  can be easily observed by the optical microscope  10 . 
     A technique to observe nanostructures by optical microscopy is developed with the help of water vapor condensation. Essentially, we do not directly observe the nanostructures themselves, but the condensation nuclei on them. The difference in the density and the type of the sub-nanometer condensation nuclei leads to different contrast under an optical microscope. In fact, the vapor molecule is not restricted to water. Any other vapor that meets the following conditions is acceptable. T his simple, low-cost, and efficient optical microscopy system is applicable to a variety of nanostructures, even to functional groups, and does not induce any impurities to the specimens, which will pave the way for widespread applications. 
     Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure. 
     It is also to be understood that the above description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.