Patent Publication Number: US-9406481-B2

Title: Transmission electron microscope micro-grid

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201410269195.X, filed on Jun. 17, 2014, in the China Intellectual Property Office, the contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a transmission electron microscope micro-grid, especially relates to a transmission electron microscope micro-grid based on carbon nanotubes. 
     2. Description of Related Art 
     In a transmission electron microscope, a porous carbon supporting film (i.e., micro-grid) is used to carry powder samples to observe high resolution transmission electron microscopy images. With the development of nanotechnology, micro-grids are increasingly coming into widespread use in the field of electron microscopy. The micro-grids used in TEMs are usually manufactured using a layer of organic porous membrane covered on a metal mesh net, such as a copper mesh net or a nickel mesh net, and subsequently a layer of non-crystal carbon films are deposited thereon by evaporation. 
     Carbon nanotubes have special structures and excellent properties, and can form a carbon nanotube structure. The carbon nanotube structure can be used in the TEM micro-grids to reduce the interference non-crystal carbon films have on samples. However, the weight of the carbon nanotubes are light, therefore, the carbon nanotube structure is also light. If the carbon nanotube structure is used in the TEM micro-grids, the carbon nanotube structure floats, thereby affecting resolution transmission of the electron microscopy images and accuracy of measurement. 
     What is needed, therefore, is to provide a TEM micro-grid which can prevent the carbon nanotube structure from floating when the micro-grid is used in TEM. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. 
         FIG. 1  shows a schematic view of one embodiment of a method of making transmission electron microscope (TEM) micro-grid. 
         FIG. 2  shows a photographic of the TEM micro-grid in  FIG. 1 . 
         FIG. 3  shows a Scanning Electron Microscope (SEM) image of one embodiment of a carbon nanotube film. 
         FIG. 4  shows a SEM image of one embodiment of a carbon nanotube layer. 
         FIG. 5  is an exploded, isometric view of the TEM micro-grid of  FIG. 1 . 
         FIG. 6  shows a flowchart of one embodiment of a method of making transmission electron microscope micro-grid. 
         FIG. 7  shows a flowchart of one embodiment of an etching process in the method of  FIG. 6 . 
         FIG. 8  shows a flowchart of another embodiment of a method of making transmission electron microscope 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 “another,” “an,” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIGS. 1-2 , one embodiment of TEM micro-grid  10  comprises a carbon nanotube layer  110  sandwiched between a first metal layer  120  and a second metal layer  130 . 
     The carbon nanotube layer  110  comprises a first surface  111  and a second surface  113  opposite to each other. The carbon nanotube layer  110  comprises at least one carbon nanotube film. In one embodiment, the carbon nanotube layer  110  can comprises a plurality of carbon nanotube films stacked together. Referring to  FIG. 3 , each of the plurality of carbon nanotube films comprises a plurality of carbon nanotubes. The plurality of carbon nanotubes that can be arranged substantially parallel to a surface of the carbon nanotube film. A large number of the carbon nanotubes in the carbon nanotube film can be oriented along a preferred orientation, meaning that a large number 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 attractive force. A small number of the carbon nanotubes may be randomly arranged in the carbon nanotube film, and has a small if not negligible effect on the larger number of the carbon nanotubes in the carbon nanotube film arranged substantially along the same direction. The carbon nanotube film is capable of forming a free-standing structure. The term “free-standing structure” can be defined as a structure that does not have to be supported by a substrate. For example, a free standing structure can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. So, if the carbon nanotube film is placed between two separate supporters, a portion of the carbon nanotube film, not in contact with the two supporters, would be suspended between the two supporters and yet maintain film structural integrity. 
     Referring to  FIG. 4 , the carbon nanotube layer  110  comprises the plurality of carbon nanotube films. The plurality of carbon nanotubes in different carbon nanotube films can be intersected with each other. Thus the plurality of carbon nanotube films forms a network. A plurality of apertures  112  are defined in the carbon nanotube layer  110 . The plurality of apertures  112  are first through holes along the thickness of the carbon nanotube layer  110 . A size of each of the plurality of apertures  112  can range from about 1 nanometer to about 1 micrometer. In one embodiment, the thickness of the carbon nanotube layer  110  is smaller than 100 micrometers. Thus the first metal layer  120  and the second metal layer  130  can be easily penetrate the carbon nanotube layer  110  and combined together. 
     In one embodiment, the carbon nanotube layer  110  can include at least one carbon nanotube network. The carbon nanotube network is made by at least one carbon nanotube wire and defines a plurality of micropores. The effective diameters of the micropores can be from about 1 nm to about 1 μm. Each carbon nanotube wire can be composed of carbon nanotubes. 
     The carbon nanotube wire 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. The untwisted carbon nanotube wire includes a plurality of successive carbon nanotubes substantially oriented along an axis of the untwisted carbon nanotube wire and joined end-to-end by van der Waals attraction force therebetween. The untwisted carbon nanotube wire has a diameter ranging from about 0.5 nm to about 1 mm. 
     A twisted carbon nanotube wire is formed by twisting a carbon nanotube film by a mechanical force. The twisted carbon nanotube wire includes a plurality of carbon nanotubes oriented around an axis 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 nm to about 100 micrometers. The twisted carbon nanotube wire can be treated with an organic solvent before or after twisting. 
     The first metal layer  120  is attached on the first surface  111 . Furthermore, the first metal layer  120  connects to the first metal layer  110  via a plurality of dangling bonds on an outer surface of each of the carbon nanotubes in the carbon nanotube layer  110 . Thus the first metal layer  120  can be tightly attached on the first surface  111 . 
     Referring to  FIG. 5 , the first metal layer  120  is a continuous structure. The first metal layer  120  covers entire the first surface  111 . The first metal layer  120  comprises a first support edge  124 , and at least one first through hole  126  is defined in the first metal layer  120 . The first support edge  124  surround the at least one first through hole  126 . The first support edge  124  is configured to attach the carbon nanotube layer  110 . A shape of the first through hole  126  can be circle, square, hexagon, octagon, or oval. A thickness of the first metal layer  120  can range from about 1 micrometer to about 15 micrometer. In one embodiment, the thickness of the first metal layer  120  is about 1 micrometer. 
     In one embodiment, the first metal layer  120  is in a shape of circle with a plurality of first through holes. The first metal layer  120  forms a plurality of first grid  123  surrounded by the first support edge  124 . The first through hole  126  is defined in each of the plurality of first grid  123 . Furthermore, the first support edge  124  are integrated with the plurality of first grid  123  to form an continuous and integrated structure. A size of the first through hole  126  can range from about 10 micrometers to about 150 micrometers. The “size” of the first through hole  126  means the maximum span of the first through hole  126 . In one embodiment, the first through hole  126  is circular, and the diameter is about 15 micrometers. 
     The plurality of first grids  123  are connected with each other to form a network. The plurality of first through holes  126  can be aligned with a certain distance to form an array. The plurality of first through holes  126  can be aligned with a first distance along each column of the array. The plurality of first through holes  126  can be aligned with a second distance along each row of the array. The plurality of first through holes  126  can also be uniformly distributed in the first metal layer  120 . The distance between the adjacent two first through holes  126  is about 20 micrometers. A material of the first metal layer  120  can be copper, gold, silver, nickel, or molybdenum. The plurality of first grids  123  can be formed by etching the first metal layer  120 . In one embodiment, an outer diameter of the first support edge  124  can be about 3 micrometers, and the material of the first metal layer  120  is copper. 
     The first metal layer  120  can be formed on a first surface  111  of the carbon nanotube layer  110  via electroplating. The carbon nanotube layer  110  can partly covers the plurality of first through holes  126 . In one embodiment, the carbon nanotube layer  110  covers all the plurality of first through holes  126 . The first surface  111  can be exposed through the plurality of through holes  126 . The carbon nanotubes in the carbon nanotube layer  110  can be bonded with the plurality of grids  123 . 
     The structure of the second metal layer  130  can be same as the first metal layer  120 . Furthermore, because the carbon nanotube layer  110  defines the plurality of apertures  112 , the second metal layer  130  penetrates the carbon nanotube layer  110  and combines the first metal layer  120  through the plurality of apertures  112 . 
     The second metal layer  130  comprises a second support edge  134  and a plurality of second grids  133 . A second through hole  136  is defined in each of the plurality of second grids  133 . The second support edge  134  surrounds the plurality of second grids  133 . The carbon nanotube layer  120  is sandwiched between the first support edge  124  and the second support edge  134 . In detail, the edge of the carbon nanotube layer  110  is fixed between the first support edge  124  and the second support edge  134 . Furthermore, the first support edge  124  and the second support edge  134  are combined with the carbon nanotube layer  110  through the plurality of dangling bonds on the two opposite surfaces of the carbon nanotube  110 . The first metal layer  120  is in direct contact with the second metal layer  130  through the plurality of apertures  112 . 
     The distribution of the plurality of second grids  133  can be same as the distribution of the plurality of first grids  123 . The plurality of second grids  133  can also be mismatched with the plurality of first grids  123 . The carbon nanotube layer  110  can be partly sandwiched between the plurality of first grids  123  and the plurality of second grids  133 . Furthermore, the distribution of the plurality of first through holes  126  can also be same as the distribution of the plurality of second through holes  136 . The plurality of first through holes  126  and the plurality of second through holes  136  are opposite to each other. The plurality of first through holes  126  and the plurality of second through holes  136  can be distributed by one to one correspondence. The carbon nanotube layer  110  can be exposed through the plurality of first through holes  126  and the plurality of second through holes  136  at the same time. Thus a plurality of through channels are formed in the TEM micro-grids. A transmission portion can be defined by each pair of the first through hole  126  and the second through hole  136  at each of the plurality of through channels. The carbon nanotube layer  110  is suspended at the transmission portion. Thus a part of the carbon nanotube layer  110  is exposed and suspended, and the other part of the carbon nanotube layer  110  is sandwiched between the first metal layer  120  and the second metal layer  130 . 
     In use, the samples are deposited on the carbon nanotube layer  110  of the TEM micro-grid  10 , and the samples are observed through the plurality of transmission portion. 
     The TEM micro-grid  10  has following advantages. The first metal layer and the second metal layer are combined with the carbon nanotube layer through the plurality of dangling bonds, thus the carbon nanotube layer can be firmly fixed between the first metal layer and the second metal layer. The stability of the TEM micro-grid can be improved. The carbon nanotubes can be firmly fixed, and the floats of the carbon nanotubes and the pollution to the samples can be avoided. Furthermore, the samples can be tightly attracted and fixed by the carbon nanotubes through the transmission portion, thus the accuracy can be improved. 
     Referring to  FIG. 6 , one embodiment of a method of making transmission electron microscope micro-grid  10  comprises: 
     step (S 10 ), providing a carbon nanotube layer  110 , wherein the carbon nanotube layer  110  comprises a first surface  111  and a second surface  113  opposite to each other, and the carbon nanotube layer  110  comprises a plurality of carbon nanotubes; 
     step (S 11 ), forming a carbon nanotube composite layer  11  via electroplating a first metal layer  120  on the first surface  111  and electroplating a second metal layer  130  on the second surface  113 ; and 
     step (S 12 ), forming a plurality of first through holes  126  in the first metal layer  120  and a plurality of second through holes  136  in the second metal layer  130  by etching the first metal layer  120  and the second metal layer  130 , wherein the plurality of first through holes  126  and the plurality of second through holes  136  are opposite to each other. 
     In step (S 10 ), the carbon nanotube layer  110  can be located on a support (not shown). Furthermore, the carbon nanotube layer  110  can be suspended on a frame (not shown). The carbon nanotube layer  110  is a free-standing structure, and the carbon nanotube layer  110  can be suspended on the support or the frame. 
     The carbon nanotube layer  110  comprises a plurality of carbon nanotube films stacked together. Referring to  FIG. 3 , each of the plurality of carbon nanotube films comprises a plurality of carbon nanotubes. The plurality of carbon nanotubes that can be arranged substantially parallel to a surface of the carbon nanotube film. A large number of the carbon nanotubes in the carbon nanotube film can be oriented along a preferred orientation, meaning that a large number 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 attractive force. A small number of the carbon nanotubes may be randomly arranged in the carbon nanotube film, and has a small if not negligible effect on the larger number of the carbon nanotubes in the carbon nanotube film arranged substantially along the same direction. The carbon nanotube film is capable of forming a free-standing structure. The term “free-standing structure” can be defined as a structure that does not have to be supported by a substrate. For example, a free standing structure can sustain the weight of itself when it is hoisted by a portion thereof without any significant damage to its structural integrity. So, if the carbon nanotube film is placed between two separate supporters, a portion of the carbon nanotube film, not in contact with the two supporters, would be suspended between the two supporters and yet maintain film structural integrity. 
     The plurality of carbon nanotubes in different carbon nanotube films can be intersected with each other. Thus the plurality of carbon nanotube films forms a network. A plurality of apertures  112  are defined in the carbon nanotube layer  110 . The plurality of apertures  112  are first through holes along the thickness of the carbon nanotube layer  110 . In one embodiment, the carbon nanotube layer is suspended on the frame. 
     In step (S 11 ), the first metal layer  120  is deposited on the first surface  111  via electroplating method. The second metal layer  130  is deposited on the second surface  113 . The first metal layer  120  and the second metal layer  130  can be formed by: 
     step (S 111 ), providing a metal ions solution, wherein the metal ions solution comprises a plurality of metal ions; 
     step (S 112 ), immersing the carbon nanotube layer  110  into the metal ions solution, wherein the first surface  111  and the second surface  113  are exposed in the metal ions solution, and the carbon nanotube layer  110  is spaced from a electrode plate  140 ; and 
     step (S 113 ), applying a voltage between the carbon nanotube layer  110  and the electrode plate  140 , wherein the plurality of metal ions are reduced into metal particles and coated on the first surface  111  and the second surface  113 . 
     In step (S 111 ), the density of the plurality of metal ions can be selected according to the thickness of the first metal layer  120  and the second metal layer  130 . In one embodiment, the plurality of metal ions are formed by dissolving cooper sulfate into the water. 
     In step (S 112 ), the carbon nanotube layer  110  is spaced from the electrode plate  140 . A distance between the carbon nanotube layer  110  and the electrode plate  140  can range from about 0.5 millimeters to about 3 millimeters. The carbon nanotube layer  110  can be parallel with the electrode plate  140 . The material of the electrode plate  140  can be graphene, platinum, stainless steel, or carbon nanotube layer structure. The material of the electrode plated  140  can be inertia material in the metal ions solution. The size of the electrode plate  140  can be greater than the carbon nanotube layer. 
     The carbon nanotube layer  140  can be suspended in the metal ions solution. Furthermore, because the carbon nanotube layer  140  is fixed on the frame, the carbon nanotube layer  140  in the frame will be exposed in the metal ions solution. In one embodiment, the electrode plate  140  is copper plate, and the size of the copper plate is greater than the carbon nanotube layer  110 . 
     In step (S 113 ), a potential difference is applied between the carbon nanotube layer  110  and the electrode plate  140 . The electrode plate  140  is electrically connected to a positive electrode, and the carbon nanotube layer  110  is electrically connected to a negative electrode. Thus the metal ions will be reduced into metal particles, and the metal particles will be deposited on the carbon nanotube layer  110 . Furthermore, the metal particles are deposited on an outer surface of each of the plurality of carbon nanotubes. During the process of electroplating, a plurality of dangling bonds are formed on the outer surface of the plurality of carbon nanotubes, and the metal particles are tightly combined with the plurality of carbon nanotubes via the plurality of dangling bonds. Furthermore, the plurality of metal particles are connected with each other to form a continuous layered structure on the first surface  111  and the second surface  113 . Thus both the first metal layer  120  and the second metal layer  130  are continuously layered structure. In addition, the metal particles can be deposited on the outer surface of adjacent carbon nanotubes around each of the plurality of apertures  112 . Thus the first metal layer  120  and the second metal layer  130  are combined together to form an integrated structure. The carbon nanotube layer  110  is firmly sandwiched between the first metal layer  120  and the second metal layer  130 . 
     In one embodiment, a constant voltage is applied between the carbon nanotube layer  110  and the electrode plate  140 . The potential difference between the carbon nanotube layer  110  and the electrode plate  140  ranges from about 0.5 V to about 1.2 V, and an electroplating time range from about 0.5 hours to about 4 hours. 
     Furthermore, the first metal layer  120  and the second metal layer  130  can be formed one after another. In one embodiment, the second surface  113  can be attached on a substrate (not shown), and the first surface  111  is exposed in the metal ion solution. The first metal layer  120  can be formed on the first surface  111 . The carbon nanotube layer  110  with the first metal layer  120  is turned over, and the second surface  113  is exposed in the metal ion solution. The second metal layer  130  is formed on the second surface  113 . 
     Furthermore, during forming the second metal layer  130 , the metal particles can be deposited into the plurality of apertures  112 . Thus the second metal layer  130  can penetrate the carbon nanotube layer  110  and combined with the first metal layer  120  through the plurality of apertures  112 . The carbon nanotube layer  110  is sandwiched between the first metal layer  120  and the second metal layer  130 . 
     Furthermore, the carbon nanotube composite layer  11  can be washed to remove the impurity. Then the carbon nanotube composite layer  11  can be dried, and the first metal layer  120  and the second metal layer  130  can be tightly attached on the carbon nanotube layer  110 . 
     In step (S 12 ), the plurality of first through holes  126  and the plurality of second through holes  136  can be formed by physically etching or chemical etching. Referring to  FIG. 7 , the plurality of first through holes  126  and the plurality of second through holes  136  can be formed by: 
     step (S 121 ), providing a mask layer  150 , wherein the mask layer  150  defines a plurality of through holes  151 ; 
     step (S 122 ), applying the mask layer  150  on the second metal layer  130 , wherein the second metal layer  130  is exposed through the plurality of through holes  151 ; 
     step (S 123 ), forming the plurality of second through holes  136  and the plurality of first through holes  126  by etching the second metal layer  130  and the first metal layer  120  through the plurality of through holes  151 ; and 
     step (S 124 ), removing the mask layer  150 . 
     In step (S 121 ), the material of the mask layer  150  can be selected according to the material of the first metal layer  120  and the second metal layer  130  to ensure that the mask layer cannot be etched. In one embodiment, the material of the mask layer  150  can be photoresist. 
     In step (S 122 ), a first portion of the second metal layer  130  can be exposed through the plurality of through holes  151 , and a second portion of the second metal layer  130  is covered by the mask layer  150 . 
     In step (S 123 ), the second metal layer  130  and the first metal layer  120  can be etched through a acid solution. Thus the second mask layer  130  and the first metal layer  102  at the through hole  151  are etched to form the plurality of second through holes  136  and the plurality of first through holes  126 . The acid solution can be hydrochloric acid, sulfuric acid, or nitric acid. In one embodiment, the acidic solution of hydrochloric acid. 
     Because the carbon nanotube layer  110  has the plurality of apertures  112 , after the first portion of the second metal layer  130  are etched, the acid solution will penetrate the carbon nanotube layer  110  and continuously etch the first metal layer. Thus the plurality of first through holes  126  are formed in the first metal layer  120 , and the plurality of first through holes  126  and the plurality of second through holes  136  are opposite to each other one by one. 
     Furthermore, a second mask layer (not shown) can be applied on the first metal layer to protect the first mask layer. The second mask layer also defines a plurality of third through holes according the plurality of through holes  151  in the mask layer  150 . Thus the carbon nanotube layer  110  can be exposed through the plurality of third through holes and the plurality of through holes  151 . 
     The method of making transmission electron microscope micro-grid has following advantages. The first metal layer and the second metal layer are formed on the carbon nanotube layer via electroplating method, thus the first metal layer and the second metal layer can be bonded on the carbon nanotube layer, and the carbon nanotubes can be tightly combined with the metal layer. The stability of the transmission electron microscope micro-grid can be improved. Furthermore, the electron emitter can withstand a strong electric field force. 
     Referring to  FIG. 8 , another embodiment of a method of making transmission electron microscope micro-grid  10  comprises: 
     step (S 20 ), providing a first metal layer  120 ; 
     step (S 21 ), attaching a carbon nanotube layer  110  on the first metal layer  120 , wherein the carbon nanotube layer  110  comprises a first surface  111  and a second surface  113  opposite with each other, and the first surface  111  is attached to the first metal layer  120 ; 
     step (S 22 ), electroplating a second metal layer  130  on the second surface  113 ; and 
     step (S 23 ), forming a plurality of first through holes  126  and a plurality of second through holes  136  by etching the first metal layer  120  and the second metal layer  130 . 
     The method of making transmission electron microscope micro-grid  10  in this embodiment is similar with the method of making transmission electron microscope micro-grid  10  in the embodiment described above, except that the carbon nanotube layer  110  is firstly attached on the first metal layer  120 , and the second metal layer  130  is then electroplated on the carbon nanotube layer  110  and combined with the first metal layer  120 . 
     In step (S 21 ), the first metal layer  120  can be tightly combined with the carbon nanotube layer  110  and support the carbon nanotube layer  110 . In one embodiment, a thickness of the metal layer  120  is about 10 micrometers. Thus the first metal layer  120  has certain mechanical strength. 
     In step (S 22 ), during the process of the depositing the second metal layer  130 , the second metal layer  130  will be penetrate the carbon nanotube layer  110  through the plurality of apertures  112  in the carbon nanotube layer  110 . Thus the second metal layer  130  will be integrated with the first metal layer  120  to form an integrated structure. The carbon nanotube layer  110  is firmly sandwiched between the first metal layer  120  and the second metal layer  130 . 
     Depending on the embodiment, certain steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the 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. 
     Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the present disclosure. Variations may be made to the embodiments without departing from the spirit of the present disclosure as claimed. Elements associated with any of the above embodiments are envisioned to be associated with any other embodiments. The above-described embodiments illustrate the scope of the present disclosure but do not restrict the scope of the present disclosure.