Abstract:
A transmission electron microscope (TEM) micro-grid includes a grid and a carbon nanotube composite film covered thereon. The carbon nanotube composite film includes a carbon nanotube film and a layer of nano-materials coated thereon. The carbon nanotube composite film covers a surface of the grid. The nano-material layer is coated on a surface of each of the plurality of carbon nanotubes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201110092686.8, filed on 2011 Apr. 14, in the China Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to transmission electron microscope micro-grids, and particularly to a transmission electron microscope micro-grid based on carbon nanotubes. 
     2. Description of Related Art 
     With the development of nanotechnology, micro-grids are becoming ubiquitous in the field of electron microscopy. The current transmission electron microscopy (TEM) micro-grid includes a metal mesh net and a carbon nanotube film located on a surface of the metal mesh net. In use, the sample is adhered to a surface of the carbon nanotube film and the background noise from the amorphous carbon film is avoided. However, because the specimen is directly supported by the carbon nanotube, when the TEM micro-grid is used to observe the carbon nanotube samples, the carbon nanotube samples and the carbon nanotubes in the micro-gird are indistinguishable. Thus, the current transmission electron microscopy micro-grid cannot be effectively used to directly observe the carbon nanotube samples. 
     What is needed, therefore, is to provide a transmission electron microscopy micro-grid that can be used to directly observe the carbon nanotube samples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference 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 embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic view of one embodiment of a transmission electron microscope (TEM) micro-grid. 
         FIG. 2  is a schematic view of one embodiment of a carbon nanotube composite film. 
         FIG. 3  is a Scanning Electron Microscope (SEM) image of one embodiment of a carbon nanotube composite film. 
         FIG. 4  is an SEM image of one embodiment of a carbon nanotube film. 
         FIG. 5  is a schematic view of one embodiment of a carbon nanotube segment of the carbon nanotube film in  FIG. 4 . 
         FIG. 6  is an SEM image of a carbon nanotube film structure including two stacked carbon nanotube films of  FIG. 4 , aligned along different directions. 
         FIG. 7  is a schematic view of one embodiment of a TEM micro-grid. 
         FIG. 8  is a schematic view of one embodiment of a carbon nanotube composite film. 
         FIG. 9  is an SEM image of an untwisted carbon nanotube wire of one embodiment of a TEM micro-grid. 
         FIG. 10  is an SEM image of a twisted carbon nanotube wire of one embodiment of a TEM micro-grid. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. 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. 
     Referring to  FIGS. 1 and 2 , one embodiment of a TEM micro-grid  100  includes a support  110  and a carbon nanotube composite film  120  stacked with each other. The carbon nanotube composite film  120  includes a plurality of carbon nanotubes  124  and a nano-material layer  126  coated on a surface of the carbon nanotubes  124 . The plurality of the carbon nanotubes  124  is interconnected with each other to form a carbon nanotube film structure. The carbon nanotube composite film  120  defines a plurality of micropores  122 . 
     Further referring to  FIG. 3 , the carbon nanotube composite film  120  includes the plurality of carbon nanotubes  124  crossed with each other. The carbon nanotubes  124  can be orderly or disorderly aligned. If the carbon nanotubes  124  are disorderly aligned, the carbon nanotubes  124  can be curved and entangled with each other. If the carbon nanotubes  124  are orderly aligned, the carbon nanotubes  124  can be aligned along one or more directions, with some variation. 
     The carbon nanotube composite film  120  can be a freestanding structure. The term “freestanding structure” means that the carbon nanotube composite film  120  can sustain the weight of itself when hoisted by a portion thereof without any significant damage to its structural integrity. For example, if the carbon nanotube composite film  120  is placed between two separate supports, a portion of the carbon nanotube composite film  120  not in contact with the two supports would be suspended between the two supports and maintain its structural integrity. 
     The carbon nanotube film structure of the carbon nanotube composite film  120  is also a freestanding structure. The carbon nanotube film structure is not functionalized by chemical treatment and can be a pure carbon nanotube film structure without any functional group. 
     The carbon nanotube film structure includes at least one carbon nanotube film. The carbon nanotube film structure can include 2 to 10 carbon nanotube films stacked with each other. In one embodiment, the carbon nanotube film structure includes 2 to 4 carbon nanotube films. 
     The carbon nanotube film can be a drawn carbon nanotube film which is a freestanding structure composed of a plurality of carbon nanotubes. The carbon nanotubes are arranged substantially parallel to a surface of the drawn carbon nanotube film. A large majority of the carbon nanotubes in the drawn carbon nanotube film can be oriented along a preferred orientation, meaning that a majority of the carbon nanotubes in the carbon nanotube film are arranged substantially along the same direction. An end of one carbon nanotube is joined to another end of an adjacent carbon nanotube arranged substantially along the same direction by van der Waals force. 
     Some variations can occur in the orientation of the carbon nanotubes in the drawn carbon nanotube film. Microscopically, the carbon nanotubes oriented substantially along the same direction may not be perfectly aligned in a straight line, and some curved portions may exist. It can be understood that a contact between some carbon nanotubes located substantially side by side and oriented along the same direction cannot be totally excluded. 
     Referring to  FIG. 4  and  FIG. 5 , the drawn carbon nanotube film can include a plurality of successively oriented carbon nanotube segments  123  joined end-to-end by van der Waals force therebetween. Each carbon nanotube segment  123  includes a plurality of carbon nanotubes  124  substantially parallel to each other, and joined by van der Waals force therebetween. The carbon nanotubes  124  are oriented substantially along the same direction. The drawn carbon nanotube film can be drawn from a carbon nanotube array. The carbon nanotube segments  123  can vary in width, thickness, uniformity, and shape. The carbon nanotubes in the drawn carbon nanotube film are also substantially oriented along a preferred orientation. A thickness of the carbon nanotube film can range from about 1 nanometer to about 100 micrometers. In one embodiment, the thickness of the carbon nanotube film ranges from about 100 nanometers to about 10 micrometers. A width of the carbon nanotube film relates to the carbon nanotube array from which the drawn carbon nanotube film is drawn. In each carbon nanotube segment  123 , a plurality of gaps exists between the two adjacent carbon nanotubes. The width of each of the gaps is less than 10 micrometers. Examples of a carbon nanotube film are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang et al. 
     Referring to  FIG. 6 , in one embodiment, the carbon nanotube composite film  120  includes at least two carbon nanotube films stacked with each other. An angle between the aligned directions of the carbon nanotubes in the two adjacent carbon nanotube films can range from about 0 degrees to about 90 degrees (0°≦a≦90°. In another embodiment, the carbon nanotube composite film  120  includes two carbon nanotube films stacked together at an angle of about 90 degrees, thus the two adjacent carbon nanotube films are substantially perpendicular to each other. 
     The nano-material layer  126  includes a plurality of nano particles forming a continuous layer structure. The nano-material layer  126  is coated on the surface of the carbon nanotubes  124 . The nano-material layer  126  and the carbon nanotubes  124  can form a plurality of carbon nanotube composite fibers. The carbon nanotube composite film  120  includes a plurality of carbon nanotube composite fibers forming a mesh. The nano-material layer  126  at the intersection of two adjacent carbon nanotubes  124  is an integral structure. Thus, the stability of the carbon nanotube composite film  120  is improved. In one embodiment, the nano-material layer  126  is coated on the surface of each of the carbon nanotubes  124  continuously. 
     The material of the nano-material layer  126  has a chemical stability and includes DLC (Diamond-Like Carbon), diamond, silicon, silicon carbide, silicon dioxide, boron nitride and/or silicon nitride, etc. In one embodiment, the material of the nano-material layer  126  is an amorphous nano-material. The amorphous nano-material can reduce the effect of the lattice structure of the nano-material layer  126  during observation of the sample. The thickness of the nano-material layer  126  can range from about 1 nanometer to about 500 nanometers. In one embodiment, the thickness of the nano-material layer  126  ranges from about 20 nanometers to about 200 nanometers. The nano-material layer  126  is filled into the gaps between two adjacent carbon nanotubes  124 . The inner walls of the gaps are coated with the nano-material layer  126 . The nano-material layer  126  should be thin enough such that the gaps cannot be fully filled. Thus, the carbon nanotube composite film  120  still defines a plurality of micropores  122 . 
     The size of the micropores  122  is smaller than the size of the gaps. The size of the micropores  122  can range from about 0.5 nanometers to about 1 micrometer. Among the plurality of micropores  122 , at least 60% of the plurality of micropores  122  has a size smaller than 50 nanometers, and at least 80% of the plurality of micropores  122  has a size smaller than 100 nanometers. In one embodiment, at least 80% of the plurality of micropores  122  has a size smaller than 50 nanometers, and at least 90% of the plurality of micropores  122  has a size smaller than 100 nanometers. In one embodiment, the shape of the micropores  122  of the carbon nanotube composite film  120  is rectangular. The nano-material layer  126  can be deposited on the surface of the carbon nanotubes  124  by CVD (chemical vapor deposition) or PVD (physical vapor deposition) method. The TEM micro-grid  100  is suitable to observe the distribution of the nano particles with a size smaller than 100 nanometers. 
     In one embodiment, the material of the nano-material layer  126  is DLC. The surface of the carbon nanotubes  124  is completely coated by the DLC. The thickness of the DLC is about 1 nanometer to 100 nanometers. The DLC can improve the self-supporting property and wear resistance of the carbon nanotube composite film  120 . In one embodiment, two layers of carbon nanotube films are stacked with each other and suspended in a reaction chamber, and the aligned direction of the carbon nanotubes in the two layers of carbon nanotube films are perpendicular to each other. The DLC is deposited on the surface of the carbon nanotubes  124  by the PECVD (Plasma Enhanced CVD) method. 
     The support  110  defines at least one through hole  112 . The support  110  can be a grid structure or a metal sheet which defines at least one through hole  112 . The support  110  can also be a metallic grid used in a typical TEM. The material of the metallic grid can be copper or any other metal materials which is suitable. The support  110  can also be a nonmetallic grid. The material of the nonmetallic grid can be ceramic, glass, or quartz. A surface of the support  110  is covered with the carbon nanotube composite film  120 , thereby suspending portions of the carbon nanotube composite film  120  across the through holes  112 . In one embodiment, both the size and the shape of the support  110  are the same as that of the carbon nanotube composite film  120 . All the though holes  112  are covered by the carbon nanotube composite film  120 . Furthermore, the diameter of the through hole  112  is larger than the size of the micropores  122 . In one embodiment, the diameter of the through hole  112  ranges from about 10 micrometers to about 2 millimeters. 
     In one application of the TEM micro-grid  100 , the sample is located on the surface of the TEM micro-grid  100 . In detail, the sample is suspended on the micropores  122  of the carbon nanotube composite film  120  and contacts with the surface of the nano-material layer  126 . The sample can be nano-scaled particles, such as nano-wires, nanotubes, or nano-balls. The material of the sample can be carbon, metal, ceramic, or semiconductive material. The size of the sample can be smaller than 1 micrometer. In one embodiment, the size of the sample is smaller than 100 nanometers. 
     Referring to  FIG. 7  and  FIG. 8 , another embodiment of a TEM micro-grid  200  includes a support  110  and a carbon nanotube composite film  220  stacked together. The TEM micro-grid  200  is similar to the TEM micro-grid  100 , except that the carbon nanotube composite film  220  includes a plurality of carbon nanotube wires  224  coated with nano-material layer  226 . The plurality of carbon nanotube wires  224  forms a carbon nanotube film structure. The carbon nanotube film structure is a freestanding structure. The nano-material layer  226  is coated on the surface of the carbon nanotube wires  224 . The carbon nanotube composite film  220  defines a plurality of micropores  222 . 
     The carbon nanotube composite film  220  includes a plurality of carbon nanotube wires  224  intersecting with each other. In one embodiment, the carbon nanotube composite film  220  includes two layers of carbon nanotube wires  224  intersecting with each other and forming a plurality of micropores  222 . The carbon nanotube wires  224  in the same layer are substantially parallel to each other. The aligned direction of the carbon nanotube wires  224  in different layers is substantially perpendicular to each other. 
     The carbon nanotube wire  224  can be an untwisted carbon nanotube wire or a twisted carbon nanotube wire. An untwisted carbon nanotube wire is formed by treating a carbon nanotube film with an organic solvent. Referring to  FIG. 9 , the untwisted carbon nanotube wire includes a plurality of successive carbon nanotubes, which are substantially oriented along the linear direction of the untwisted carbon nanotube wire and joined end-to-end by the van der Waals force therebetween. The untwisted carbon nanotube wire can have a diameter ranging from about 0.5 nanometers to about 100 micrometers. Examples of an untwisted carbon nanotube wire are taught by U.S. Pat. No. 7,045,108 to Jiang et al., and U.S. Pat. No. 7,704,480 to Jiang et al. 
     A twisted carbon nanotube wire is formed by twisting a carbon nanotube film by using a mechanical force. Referring to  FIG. 10 , the twisted carbon nanotube wire includes a plurality of carbon nanotubes oriented around an axial direction of the twisted carbon nanotube wire. The length of the twisted carbon nanotube wire can be set as desired and the diameter of the carbon nanotube wire can range from about 0.5 nanometers to about 100 micrometers. The twisted carbon nanotube wire can be treated with an organic solvent before or after twisting. 
     The nano-material layer  226  is a continuous layer structure including a plurality of nano particles. The plurality of nano particles is coated on the surface of the carbon nanotube wire  224 . At the intersection of two adjacent carbon nanotube wires  224 , the nano particles of the nano material layer  226  on the surface of each carbon nanotube wire  224  are combined together to form an integral structure. Thus, the stability of the carbon nanotube composite film  220  is improved. The nano-material layer  226  can be deposited on the surface of the carbon nanotube wire  224 . In one embodiment, a composite carbon nanotube wire can be fabricated by twisting the carbon nanotube composite film  120  described above with a mechanical force or with an organic solvent treatment. Thus the nano-material layer  226  is coated on the surface of each carbon nanotube. In one embodiment, the material nano-material layer  226  is DLC. 
     According to the above descriptions, the TEM micro-grid of the present disclosure has the following advantages. First, the carbon nanotube of the TEM micro-grid is coated with a layer of nano-material made from carbon nanotubes. Thus, the TEM micro-grid can be used to observe the carbon nanotube sample. Furthermore, the accuracy of a TEM adopting the TEM micro-grid can be improved. Second, the nano-material layer is integrated at the intersection of the two adjacent carbon nanotube layers, so the stability of the whole carbon nanotube composite film is improved. Third, because the carbon nanotube is coated with a nano-material layer, the micropores among the carbon nanotube film are relatively small, so the TEM micro-grid is suitable to observe the nano particles with a size smaller than 100 nanometers. 
     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. It is understood that any element of any one embodiment is considered to be disclosed to be incorporated with any other embodiment. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.