CN101252073A - A Thermally Driven Deformable Transmission Electron Microscope Grid and One-Dimensional Nanomaterial Deformation Method - Google Patents

Abstract

The invention relates to a heat-driven deformation transmission electron microscope grid and a one-dimensional nanometer material deformation method, which belong to the field of nanometer devices and in-situ nanometer material deformation methods in transmission electron microscopes. The existing grid can only be deformed by electron beam irradiation, and the stress provided is limited. The carrying net of the present invention evaporates metal thin films A and B on the supporting film of the existing carrying net, and the thermal expansion coefficient of the metal thin film A is greater than that of the metal thin film B. The carrying net of the present invention is to the deformation method of one-dimensional nanometer material: after metal thin film A and B are scratched, one-dimensional nanometer material is dispersed on it, put into transmission electron microscope and heat, the two-layer thin film of rupture is due to the expansion coefficient difference Different curling occurs, thereby providing the driving force for deforming one-dimensional nanomaterials and realizing the deformation of one-dimensional materials. The carrier grid of the present invention can realize large-angle tilting in X and Y directions, realize in-situ deformation operation of one-dimensional nanomaterials, has the characteristics of reliable performance, convenient installation and simple structure, and expands the function of transmission electron microscope.

Description

A Thermally Driven Deformable Transmission Electron Microscope Grid and One-Dimensional Nanomaterial Deformation Method

technical field

The invention belongs to the field of in-situ nano material deformation methods in nano devices and transmission electron microscopes, and in particular relates to a heat-driven deformation transmission electron microscope grid and a one-dimensional nano material deformation method.

Background technique

Due to the extremely high resolution of the transmission electron microscope, it can provide information at the nanoscale or even the atomic scale. It is a powerful tool for studying the microstructure of substances. It has a wide range of applications in physics, chemistry, material science, life science and other fields, especially in the current The rapidly developing field of nanoscience and technology is one of the most powerful research tools. The transmission electron microscope grid is used to support the sample to be tested. The skeleton of the most commonly used transmission electron microscope grid is generally a copper grid, and the copper grid is covered with an amorphous carbon support film. Generally speaking, these grids can only carry the samples to be tested, and the transmission electron microscope can only observe the static tissue structure of the samples distributed on these grids, and cannot use these grids to manipulate samples and perform dynamic in-situ detection. With the development of micro-electromechanical systems (MEMS, micro electromechanical system) and nano-electromechanical systems (NEMS, nano electromechanical system), it is particularly urgent to study the mechanical properties of a single nanowire or film under external force. The structure of the wire or thin film is small and difficult to manipulate. How to fix and in-situ deform a single nanowire or nano-film sample in the transmission electron microscope reveals the deformation mechanism of nanomaterials under the action of external force at the nanoscale and atomic level, and the size effect becomes problem facing researchers. At present, due to the extremely limited space between the sample stage and the pole piece in the transmission electron microscope, generally 1 to 3 mm, it is very difficult to manipulate a single nanowire or nanofilm and directly measure the mechanical properties at an atomic scale resolution. There are mainly three methods that have been reported.

One is the method reported in "Applied physics letters" 2002, volume 80, No. 21. The main principle is to use a specially deposited piezoelectric ceramic film (PZT) as a grid, and deposit the researched film on the surface of the piezoelectric ceramic. Use the TEM sample rod that can be energized to put the grid and the sample into the TEM. Under the action of the electric field, the deformation of the piezoelectric ceramic realizes the stretching and compression of the film, and at the same time, the TEM imaging system is used to record the fatigue of the film. Fracture change process. The sample preparation process of this method is more complicated. Due to the limitation of the tilting angle of the sample rod (generally only single-axis tilting or biaxial tilting ±5°), the original sample cannot be performed at the best resolution (high-resolution atomic scale). It is impossible to understand its deformation mechanism fundamentally.

Another method was reported in "Physics Review Letters" 2005, Volume 94, page 236802 and "Nature" 2006, Volume 439, page 281. The main principle is to put the scanning tunneling microscope probe into the transmission electron microscope, and use external The system controls the movement of the probe to manipulate a single carbon nanotube to achieve stretching and deformation of the carbon nanotube. The conductive probe is used to stretch the carbon nanotube while electrifying. Deformation behavior and fracture mechanism of superplasticity at high temperature. Although this method can achieve atomic resolution for well-designed samples and simultaneously perform tensile and energized measurements, due to the relatively complicated mechanical structure placed in the sample chamber of the transmission electron microscope, the sample stage can only be tilted at a small angle (±5° ) or can only be tilted on a single axis (no more than ±20°), which still limits its application range and is not conducive to popularization.

The third method is reported on page 236802 of Volume 94 of "Nano Letters" in 2007 and page 281 of Volume 439 of "Advanced Materials" in 2006. It mainly uses a special carbon film and uses electron beam irradiation to induce cracked carbon. The film curls to achieve bending and stretching of the one-dimensional nanomaterials dispersed on it. This method can achieve large-angle biaxial tilting, so that high-resolution images in situ during deformation can be obtained, and the experimental process is simple and convenient. The cost is not high. However, the controllability of the curling of the carbon film induced by electron beam irradiation is poor, the application of stress and the strain rate are difficult to control, and the stress provided is limited, and it is difficult to deform some materials with high strength.

In the above-mentioned in-situ nanomaterial mechanical property test by transmission electron microscope, neither the first two sample consoles nor the carrier grid can achieve large-angle double-tilt. For most nanomaterials that require real-time observation of structural changes under the action of external forces , its application is limited. The third method is less controllable and provides limited stress, and many materials are not suitable for this method.

Contents of the invention

The object of the present invention is to solve the problems in the prior art, and provide a thermally driven deformation transmission electron microscope carrier grid capable of large-angle tilting and strong controllability and a method for deforming one-dimensional nanomaterials.

The carrier net provided by the present invention comprises a skeleton (1) and a supporting film (2) vapor-deposited on the skeleton (1), and is characterized in that it also includes a metal film A (3) (also known as an active layer) and a metal film B(4) (also known as passive layer); wherein, the metal film A(3) is evaporated on the support film (2), the metal film B(4) is evaporated on the metal film A(3), and the metal The thermal expansion coefficient of the thin film A (3) is greater than that of the metal thin film B (4).

Wherein, the thickness of the metal thin films A (3) and B (4) is 20-50 nm. In order to ensure greater bending deformation at lower temperatures, the specific bending of the two metal films A(3) and B(4) is greater than 10/10 ^-6 °C ^-1 , such as some commercial bimetallic sheet materials, Metal film A (3) can be Mn75Ni15 or Ni20Mn6Fe74 or Mn72Ni10Cu18, etc.; metal film B (4) can be Ni36Fe64 or Ni42Fe58, etc.

The carrying net provided by the present invention is made through the following steps: adopting the physical evaporation coating process, on the upper surface of the support film (2) of the conventional transmission electron microscope carrying net (commonly used carrying net is generally based on copper mesh as the skeleton, evaporated on the copper mesh) carbon coating), vapor-deposit two layers of metal films A(3) and B(4) with large differences in expansion coefficient.

The method for deforming one-dimensional nanomaterials by the carrier grid provided by the present invention comprises the following steps:

1) Prefabrication of micro-cracks (5) on the metal films A(3) and B(4) of the grid (the film can be gently scratched by a blade or other suitable methods);

2) After ultrasonically dispersing the one-dimensional nanomaterial, drop it onto the metal film B (4) on the transmission electron microscope grid;

3) Fixing the thermally deformed transmission electron microscope carrier grid on the heatable transmission electron microscope sample rod, and putting it into the transmission electron microscope;

4) Find the place where a one-dimensional nanomaterial exists at the microcrack (5) of the metal film B (4) for observation, and fix the sample by electron beam welding, and then use the heating rod to heat the grid;

5) The deformation process and lattice structure changes of the nanowires were recorded in situ in real time through the high-resolution atomic images of the transmission electron microscope.

As the temperature rises, due to the different thermal expansion coefficients of the metal films A (3) and B (4), curling occurs at the microcrack (5), thereby stretching or bending the one-dimensional nanomaterial fixed thereon. Through the comparative analysis of real-time high-resolution images of the microstructural changes of one-dimensional nanomaterials before and after deformation, the characteristics of elastic-plastic deformation of one-dimensional nanomaterials, the size effect of deformation, and the generation of dislocations during deformation can be revealed at the atomic level. And the microstructure that reflects the mechanical properties of materials such as the expansion of cracks.

The present invention has the following advantages:

1. The heat-driven deformable transmission electron microscope grid provided by the present invention can realize the thermal deformation of the grid film, and the outer dimensions of the grid are completely consistent with those of the prior art grid, and can be easily loaded into a high-resolution transmission electron microscope. Large-angle tilting in both X and Y directions (currently commercial double-tilt heating tables can reach ±30°/±60°).

2. The heat-driven deformation transmission electron microscope carrying grid of the present invention realizes the in-situ deformation operation of one-dimensional nanomaterials, has the characteristics of reliable performance, convenient installation, and simple structure, and expands the functions of transmission electron microscopy.

Description of drawings

Fig. 1. Schematic diagram of the cross-sectional structure of thermally driven deformable transmission electron microscope grid.

Fig. 2. TEM photo of thermally driven deformed TEM grid.

Fig. 3. Transmission electron micrographs of crimped and stretched Si nanowires of metal films A (3) and B (4) after heating.

Detailed ways

Example

Using the conventional physical evaporation coating process, the thermally driven deformable transmission electron microscope grid is produced. As shown in Figure 1, the support film (2) (carbon film) is arranged on the skeleton (1) (copper grid), and the upper support film (2) Metal film A (3) and metal film B (4) are vapor-deposited on the surface in sequence; wherein, metal film A (3) is made of Mn72Ni10Cu18 alloy, metal film B (4) is made of Ni36Fe64 alloy, and metal film A (3) is made of Mn72Ni10Cu18 alloy. The thickness is 30 nm, and the thickness of the metal thin film B (4) is 30 nm.

Deformation of one-dimensional nanomaterials using thermally driven deformable TEM grids:

1) Prefabricate some microcracks (5) on the metal films A(3) and B(4) carrying the grid with a blade, as shown in Figure 2, the black area is the skeleton (1) (copper grid), and the gray round hole area is Support film (2) (carbon film), metal film A (3) and metal film B (4), the blank space is microcrack (5);

2) Drop the Si nanowires dispersed by ultrasonic vibration (in absolute ethanol) onto the grid metal film B (4);

3) Fix the carrier grid on the heated sample rod of the transmission electron microscope;

4) Heating the grid, using a transmission electron microscope to observe the deformation of a nanowire and record the process at the nanoscale or atomic scale.

Through observation, it is found that Si nanowires exhibit large strain plasticity during deformation, which is different from the brittleness of their bulk materials, and Si exhibits a different deformation mode from bulk materials at the nanoscale, as shown in Figure 3.

Finally, it should be noted that: the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; Those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced; and all technical solutions and improvements that do not depart from the spirit and scope of the invention should be covered by the claims of the present invention.

Claims (5)

1. A heat-driven deformable transmission electron microscope grid, comprising a skeleton (1) and a supporting film (2) evaporated on the skeleton (1), is characterized in that, also includes a metal film A (3) and a metal film B ( 4); wherein, the metal film A (3) is evaporated on the support film (2), the metal film B (4) is evaporated on the metal film A (3), and the thermal expansion coefficient of the metal film A (3) It should be greater than the thermal expansion coefficient of the metal film B(4). 2. carrier net according to claim 1, is characterized in that, the thickness of described metal thin film A (3) is 20～50nm. 3. carrier net according to claim 1, is characterized in that, the thickness of described metal thin film B (4) is 20～50nm. 4. The carrier grid according to claim 1, characterized in that the specific bending of the metal films A (3) and B (4) is greater than 10/10 ^-6 ·°C ^-1 . 5. A one-dimensional nanomaterial deformation method, is characterized in that, comprises the following steps: 1) prefabricating microcracks (5) on the metal thin films A (3) and B (4) of the transmission electron microscope grid; 2) Dispersing the one-dimensional nanomaterials on the metal thin film B (4) of the radio mirror grid; 3) Then fix the radio microscope grid carrying the one-dimensional nanomaterial on the sample heating rod of the transmission electron microscope; 4) The grid is heated by the heating rod, so that the metal films A (3) and B (4) are curled, and the one-dimensional nanomaterial is deformed.

Images