CN113533397B - Device and method for in-situ research on low-temperature crystal structure of two-dimensional material - Google Patents
Device and method for in-situ research on low-temperature crystal structure of two-dimensional material Download PDFInfo
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Abstract
The invention provides a device and a method for in-situ research of a two-dimensional material low-temperature crystal structure. The system comprises a low-temperature control system, a RHEED system, a substrate table lifter, a hollow Z-axis driver and a vacuum system. The relative distance between the substrate table and the heat exchange device is adjusted to switch between the low-temperature working mode and the high-temperature working mode. And (3) a low-temperature working mode: the back of the substrate table is completely contacted with the bottom end of the heat exchange device, and the device is suitable for low-temperature crystal structure test of two-dimensional materials and preparation of low-melting-point metal films; and (3) high-temperature working mode: the heat exchange device is far away from the substrate table, and the high vacuum environment ensures minimum gas convection heat leakage. The invention integrates a low-temperature control system in the RHEED system, and provides a low-temperature environment for the crystal structure test of the two-dimensional material. The invention has the beneficial effects that: simple structure, convenient operation is fit for the low temperature crystal structure analysis of normal position two-dimensional material and does not destroy the sample structure.
Description
Technical Field
The invention relates to the technical field of spintronics, in particular to a device and a method for in-situ research of a two-dimensional material low-temperature crystal structure.
Background
With the miniaturization trend of electronic products such as smart phones and notebook computers, the conventional electronic devices face many challenges such as power consumption increase and manufacturing cost increase in the continuous miniaturization process. In recent years, the two-dimensional material has a thickness of only a few atomic layers, presents a plurality of excellent properties different from the traditional bulk material, and is expected to become a core material of a novel electronic device, namely a spintronic device, with small volume and low power consumption. However, many of the novel properties of two-dimensional materials are exhibited at low temperatures. Considering that the crystal structure of the material has an important influence on the performance of the material, the research on the crystal structure of the two-dimensional material at different temperatures, particularly at low temperature, is of great significance for understanding the structure-performance relationship of the material and exploring a spintronic device with excellent performance.
Currently, the main techniques for studying the crystal structure of materials at low temperatures are low temperature XRD (X-ray diffraction) and low temperature TEM (transmission electron microscope). The low-temperature XRD technology utilizes X-rays as a detection light source and realizes temperature control through a low-temperature accessory, but is limited by the intensity of the X-rays and is not suitable for the crystal structure analysis of a two-dimensional material with the thickness of only a few atomic layers. The low-temperature TEM technology utilizes transmission electron beams as a detection light source, and realizes temperature control through a special low-temperature sample rod. Because the penetration force of the electron beam is weak, the observed area of the sample must be thinned to be less than 100nm for TEM observation. The sample preparation process is complicated, time-consuming, and can cause deformation and contamination of the sample. Considering that a two-dimensional material is only a few atomic layers thick and has a high specific surface area, the surface of the two-dimensional material is sensitive to surface adsorption and the external environment. The low-temperature XRD and low-temperature TEM technologies both need to transfer a sample to be tested from preparation equipment to test equipment and cannot be carried out in situ. The inevitable surface adsorption of the sample during the transfer process is likely to cause great changes to the structure and properties of the two-dimensional material. Therefore, in-situ testing is critical to whether the intrinsic structure and properties of a two-dimensional material can be obtained.
RHEED (reflection type high energy electron diffractometer) is a technique for obtaining surface information (surface sensitivity of 1-4 nm) of a sample by using reflection of high energy electrons. Different from XRD, the RHEED technology adopts high-energy electron beams instead of X rays as a detection light source, has high light source intensity and can realize the crystal structure analysis of a two-dimensional material; unlike TEM, RHEED technology uses the reflection of an electron beam rather than the transmission of an electron beam to obtain crystal structure information, so that the sample does not need to be specially thinned, and non-destructive crystal structure analysis can be achieved. And the RHEED technology is usually arranged in a film preparation system, so that the real-time monitoring of the growth condition of the epitaxial film and the in-situ test of the crystal structure can be realized. However, the existing RHEED technology can be performed only at normal temperature or high temperature, and cannot be used for crystal structure analysis at low temperature. Therefore, there is a need to develop a cryo-crystal structure analysis technique that is suitable for two-dimensional materials in situ, simple and does not destroy the structure of the sample.
Disclosure of Invention
In order to solve the technical problems, the invention discloses a device and a method for in-situ research of a two-dimensional material low-temperature crystal structure, and the technical scheme of the invention is implemented as follows:
a device for researching a two-dimensional material cryogenic crystal structure in situ comprises a cryogenic control system, a RHEED system, a substrate table lifter, a hollow Z-axis driver and a vacuum system;
the low-temperature control system is positioned on the vacuum system and connected with the vacuum system, the RHEED system is arranged on the side edge of the vacuum system, the substrate table is arranged below the low-temperature control system, the hollow Z-axis driver is positioned at the joint of the low-temperature control system and the vacuum system and controls the low-temperature control system, and the substrate table lifter is arranged on the upper side of the hollow Z-axis driver and controls the substrate table; the height of the substrate table may be individually controlled by a substrate table lift so that the relative distance between the substrate table and the heat exchanging device may be adjusted.
The substrate table is provided with a substrate at the bottom; the substrate stage is integrated with a temperature feedback control system consisting of a heater, a thermometer and a feedback temperature control element;
the low-temperature control system comprises a closed-cycle refrigerator, an air extraction device, a gas transmission device, a mass flow controller and a heat exchange device; the circulation refrigerator is positioned at the upper part of the low-temperature control system, the air extraction device is connected with the gas transmission device and positioned at the side edge of the closed circulation refrigerator, the mass flow controller is positioned on a connecting pipeline between the gas transmission device and the closed circulation refrigerator, and the heat exchange device is connected and positioned below the closed circulation refrigerator.
Preferably, the vacuum system comprises a vacuum preparation chamber, a vacuum pump and a vacuum interface; the vacuum pump is arranged on the lower side wall of the vacuum preparation cavity, the vacuum interface is positioned at the top of the vacuum preparation cavity, and the heat exchange device extends into the vacuum preparation cavity through the vacuum interface.
Preferably, the RHEED system includes a RHEED electron gun and a RHEED phosphor screen; the RHEED electron gun is positioned at one side of the vacuum preparation cavity, and the RHEED fluorescent screen is positioned at the other side of the vacuum preparation cavity.
Preferably, the closed-cycle refrigerator comprises a refrigeration head, a compressor and a gas delivery conduit; the refrigerating head extends into the heat exchange device and is connected with the compressor through a gas conveying pipeline.
Preferably, the outer surface of the substrate table is made of a high thermal conductivity oxygen-free copper.
Preferably, the vacuum preparation chamber is a thin film deposition chamber.
Preferably, the heat exchange device is provided with a protective cover; the protective cover wraps the surface of the heat exchange device.
Preferably, the protection cover is made of austenitic stainless steel and is of a long-strip tubular structure.
Preferably, the types of closed cycle refrigerators include pulse tube refrigerators and gifford-mcmahon refrigerators; the refrigerant gas in the closed-cycle refrigerator is selected from one of helium 3 and helium 4.
A method for in-situ research of a two-dimensional material low-temperature crystal structure comprises a low-temperature working mode and a high-temperature working mode;
in a low-temperature working mode, the substrate table lifter lifts the substrate table to enable the back surface of the substrate table to be in full contact with the bottom end of the heat exchange device, the mass flow controller accurately controls the balance between the flow of the refrigerating gas and the heating power of a heater of the substrate table, and meanwhile, the hollow Z-axis driver adjusts the overall height of the substrate table and the heat exchange device, so that an electron beam emitted by the RHEED electron gun glazes to the surface of the substrate table, and the electron beam with crystal structure information reflected by the surface of the substrate is presented to the RHEED fluorescent screen;
in a high-temperature working mode, the substrate table is lowered through the substrate table lifter so that the substrate table is far away from the heat exchange device, temperature control is achieved through a temperature feedback control system integrated in the substrate table to meet the requirement of thin film preparation on the temperature of the substrate, and meanwhile, the overall height of the substrate table and the heat exchange device is adjusted through the hollow Z-axis driver to meet the requirement of the thin film preparation on the height of the substrate.
The low-temperature control system provides a low-temperature environment and an accurate temperature control condition for testing, realizes the accurate control of the temperature of the substrate table and the large-range temperature change test of the two-dimensional material crystal structure by accurately controlling the flow of low-temperature refrigerating gas and the balance of the heating power of the substrate table heater, and solves the problem that the existing RHEED technology cannot test the low-temperature crystal structure;
the RHEED technology ensures the in-situ test of the two-dimensional material crystal structure because of being compatible with a plurality of film preparation systems such as a pulse laser deposition system and a molecular beam epitaxy system, thereby avoiding the surface adsorption influence in the sample transfer process related to other crystal structure analysis technologies including XRD and TEM technologies;
compared with the traditional low-temperature TEM technology, the low-temperature RHEED technology has the advantages of no need of special sample preparation and no damage to the sample structure, and has the characteristics of high light source intensity and suitability for the crystal structure analysis of two-dimensional materials compared with the traditional low-temperature XRD technology.
The low-temperature control system not only provides a low-temperature test condition for the RHED system, but also provides a low-temperature preparation condition for the film preparation system, expands the functions of film preparation, and is particularly suitable for preparing low-melting-point metal films.
The invention can realize the preparation of two-dimensional materials and the large-range variable temperature test analysis of the crystal structure by using a set of device, thereby greatly improving the space utilization rate of the device.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below, it is obvious that the drawings in the following description are only one embodiment of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
In which like parts are designated by like reference numerals. It should be noted that the terms "front," "back," "left," "right," "upper" and "lower" used in the following description refer to directions in the drawings, and the terms "bottom" and "top," "inner" and "outer" refer to directions toward and away from, respectively, the geometric center of a particular component.
Fig. 1 is a schematic structural view of the apparatus of embodiment 1.
In the above drawings, the reference numerals denote:
1, a compressor
2, air extraction equipment
3, gas transmission equipment
4, mass flow controller
5, refrigeration head
6, heat exchange device
7, vacuum interface
8, substrate table lifter
9, hollow Z-axis driver
10,rheed electron gun
11,rheed fluorescent screen
12, vacuum pump
13, vacuum preparation chamber
14, substrate table
15, substrate
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples
In a specific embodiment, as shown in fig. 1, an apparatus for in-situ study of a two-dimensional material cryo-crystalline structure comprises a cryo-control system, a RHEED system, a substrate table 14, a substrate table lift 8, a hollow Z-axis actuator 9, and a vacuum system;
the low-temperature control system is positioned on the vacuum system and connected with the vacuum system, the RHEED system is installed on the side edge of the vacuum system, the substrate table 14 is installed below the low-temperature control system, the hollow Z-axis driver is positioned at the joint of the low-temperature control system and the vacuum system and controls the low-temperature control system, the substrate table lifter 8 is installed on the upper side of the hollow Z-axis driver and controls the substrate table 14, and the substrate table 14 can move by controlling the hollow Z-axis driver; the height of the substrate table 14 can be individually controlled by the substrate table lift 8, so that the relative distance between the substrate table 14 and the heat exchanging device 6 can be adjusted.
The substrate stage 14 is provided with a substrate 15 at the bottom; the substrate 15 is stuck to the surface center position of the substrate stage 14 through a binder which has good heat conduction and high and low temperature resistance; the substrate stage 14 integrates a temperature feedback control system consisting of heaters, thermometers and feedback temperature control elements;
the low-temperature control system comprises a closed-cycle refrigerator, an air extraction device 2, a gas transmission device 3, a mass flow controller 4 and a heat exchange device 6; the circulating refrigerator is positioned on the upper part of the low-temperature control system, the air extraction device 2 is connected with the gas transmission device 3 and positioned on the side edge of the closed circulating refrigerator, the mass flow controller 4 is positioned on a connecting pipeline between the gas transmission device 3 and the closed circulating refrigerator, and the heat exchange device 6 is connected and positioned below the closed circulating refrigerator.
The vacuum system comprises a vacuum preparation cavity 13, a vacuum pump 12 and a vacuum interface 7; the vacuum pump 12 is installed on the lower side wall of the vacuum preparation cavity 13 so as to vacuumize the vacuum preparation cavity 13, the vacuum interface 7 is located at the top of the vacuum preparation cavity 13, and the heat exchange device 6 extends into the vacuum preparation cavity 13 through the vacuum interface 7 to refrigerate a sample.
The RHEED system includes a RHEED electron gun 10 and a RHEED phosphor screen 11; the RHEED electron gun 10 is positioned at one side of the vacuum preparation cavity 13, and the RHEED fluorescent screen 11 is positioned at the other side of the vacuum preparation cavity 13 and is used for real-time monitoring and in-situ analysis of a crystal structure in the film growth process.
The closed-cycle refrigerator comprises a refrigerating head 5, a compressor 1 and a gas conveying pipeline; the refrigerating head 5 extends into the heat exchange device 6, and the refrigerating head 5 is connected with the compressor 1 through a gas conveying pipeline.
In this embodiment, the gas transmission device 3, the mass flow controller 4, the heat exchanger 6, and the gas extraction device 2 are connected in sequence via a gas transmission pipe. The gas transport device 3 transports the refrigerant gas into the pipeline. The mass flow controller 4 is used to precisely control the flow rate of the refrigerant gas. The heat exchange device 6 can be filled with refrigerating gas as a cooling medium, and can be further cooled by arranging a throttle valve, a liquid helium tank and the like in the heat exchange device. The air extraction device 2 is used for providing a low-pressure environment for the pipeline so that refrigeration can be continuously carried out. Other cryogenic control techniques known in the art may also be used to similar effect.
The operation modes of the present embodiment include a low-temperature operation mode and a high-temperature operation mode;
the low-temperature mode is used for in-situ testing of the crystal structure of the two-dimensional material at low temperature and can also be used for preparing a low-melting-point metal film needing low-temperature conditions, and the temperature of the substrate table 14 in the low-temperature mode is lower than the room temperature; the second is a high temperature mode of operation, which is also typically self-contained in the thin film fabrication system, in which the substrate stage 14 is at a temperature greater than or equal to room temperature.
In the low-temperature operation mode, the substrate stage 14 is lifted by the substrate stage lifter 8, the back surface of the substrate stage 14 and the bottom end of the heat exchanging device 6 are completely contacted to realize heat conduction, and the balance between the flow rate of the refrigerating gas and the heating power of the heater of the substrate stage 14 is accurately controlled by the mass flow controller 4, so that the temperature of the substrate stage 14 is accurately controlled. Meanwhile, the overall height of the substrate stage 14 and the heat exchange device 6 is adjusted through the hollow Z-axis driver 9, so that the electron beam emitted by the RHEED electron gun 10 can glace to the surface of the substrate 15, and the electron beam with the crystal structure information reflected by the surface of the substrate 15 is presented to the RHEED fluorescent screen 11.
In the high temperature operation mode, the substrate stage 14 is lowered by the substrate stage lift 8 so that the substrate stage 14 is away from the heat exchanging device 6 to reduce the heat radiation of the substrate stage 14. Meanwhile, the high vacuum environment ensures minimum gas convection heat leakage. The temperature control of the high temperature zone is achieved by a temperature feedback control system integrated in the substrate stage 14 to meet the temperature requirements of the substrate 15 for thin film fabrication. The highest temperature that can be achieved in the high temperature mode of operation of the present invention depends on the substrate stage 14 itself of the thin film fabrication system.
In a preferred embodiment, the outer surface of the substrate table 14 is made of high thermal conductivity oxygen-free copper.
In this embodiment, for making the bottom of substrate table 14 and heat transfer device 6 realize good heat-conduction and for guaranteeing that the temperature in sample region is even, substrate table 14 surface adopts high thermal conductivity oxygen-free copper to make and forms, certainly, this patent is not only limited to high thermal conductivity oxygen-free copper, chooses other good materials of heat conduction for use and also can make, can obtain according to economy and raw and other materials and select to replace after considering comprehensively in a plurality of aspects.
In a preferred embodiment, the vacuum preparation chamber 13 is a thin film deposition chamber.
In the present embodiment, the vacuum preparation chamber 13 may be a thin film deposition chamber of a pulsed laser deposition system, a molecular beam epitaxy system, or other thin film preparation system compatible with the RHEED system. The substrate stage 14 of the thin film fabrication system itself can typically be controlled from room temperature to high temperatures.
In a preferred embodiment, the heat exchange means 6 are provided with a protective cover; the protective cover wraps the surface of the heat exchange device 6. The protection casing material is austenite stainless steel, and the protection casing is rectangular tubular structure.
In this embodiment, the heat exchanger 6 is isolated from the low-temperature environment and the vacuum environment therein by a shield. The protective cover can be made of common materials suitable for vacuum sealing, such as austenitic stainless steel but not limited to the material. The shape and structure of the protective cover are generally long-strip tubular, so that the protective cover can conveniently go deep into the vacuum cavity to refrigerate a sample.
In a preferred embodiment, the types of closed cycle refrigerators include pulse tube refrigerators and gifford-mcmahon refrigerators; the refrigerant gas in the closed cycle refrigerator is selected from one of helium 3 and helium 4.
In the present embodiment, the types of the closed-cycle refrigerator include a pulse tube refrigerator, a gifford-mcmahon refrigerator, and an improved refrigerator based on these principles, and a more suitable refrigerator may be selected according to actual needs as long as the required requirements can be met. The refrigerant gas may be helium 3, helium 4, or other refrigerant gas. The type of refrigerator and the choice of refrigerant gas depend on the specific refrigeration requirements.
The low-temperature control system of the embodiment provides a low-temperature environment and an accurate temperature control condition for testing, realizes the accurate control of the temperature of the substrate table 14 and the large-scale temperature change test of the two-dimensional material crystal structure by accurately controlling the flow of the low-temperature refrigerating gas and the balance of the heating power of the heater of the substrate table 14, and solves the problem that the existing RHEED technology cannot test the low-temperature crystal structure
In this embodiment, the outer surface of the substrate table 14 is made of high thermal conductivity oxygen-free copper or other materials with good thermal conductivity to ensure good thermal conductivity of the substrate table 14 and the bottom end of the heat exchange device 6 of the low temperature control system and uniform temperature of the sample area, and meanwhile, the temperature of the substrate table 14 is accurately controllable by accurately controlling the flow rate of the cooling gas and the balance of the heater power of the substrate table 14, so that the large-range temperature change test of the two-dimensional material crystal structure is realized
The substrate stage lift 8 of the present embodiment can control the height of the substrate stage 14 individually, and can switch between the low-temperature and high-temperature operation modes by adjusting the relative distance between the substrate stage 14 and the heat exchanging device 6. In the low-temperature working mode, the back surface of the substrate stage 14 is completely contacted with the bottom end of the heat exchange device 6, and the method is suitable for low-temperature crystal structure test of two-dimensional materials and preparation of low-melting-point metal films; in the high temperature mode of operation, the heat exchange device 6 is located away from the substrate stage 14, and the high vacuum environment ensures minimal convective heat leakage from the gas.
The RHEED technology ensures the in-situ test of the two-dimensional material crystal structure because of being compatible with a plurality of film preparation systems such as a pulse laser deposition system and a molecular beam epitaxy system, thereby avoiding the surface adsorption influence in the sample transfer process related to other crystal structure analysis technologies including XRD and TEM technologies;
compared with the traditional low-temperature TEM technology, the low-temperature RHEED technology of the embodiment has the advantages of no need of special sample preparation and no damage to the structure of the sample, and has the characteristics of high light source intensity and suitability for the crystal structure analysis of two-dimensional materials compared with the traditional low-temperature XRD technology.
The low-temperature control system of the embodiment provides a low-temperature test condition for the RHED system, also provides a low-temperature preparation condition for the film preparation system, expands the function of film preparation, and is particularly suitable for preparing low-melting-point metal films;
according to the embodiment, the preparation of the two-dimensional material and the large-range variable temperature test analysis of the crystal structure can be realized by using one set of device, and the space utilization rate of the device is greatly improved. It should be understood that the above-described embodiments are merely exemplary of the present invention, and are not intended to limit the present invention, and that any modification, equivalent replacement, or improvement made without departing from the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (7)
1. The device for researching the low-temperature crystal structure of the two-dimensional material in situ is characterized in that: the system comprises a low-temperature control system, a RHEED system, a substrate table lifter, a hollow Z-axis driver and a vacuum system; the low-temperature control system comprises a closed-cycle refrigerator, an air extraction device, a gas transmission device, a mass flow controller and a heat exchange device; the low-temperature control system is positioned on the vacuum system and connected with the vacuum system, the RHEED system is installed on the side edge of the vacuum system, the substrate table is installed below the low-temperature control system, the hollow Z-axis driver is positioned at the joint of the low-temperature control system and the vacuum system and controls the overall height of the substrate table and the heat exchange device, and the substrate table lifter is installed on the upper side of the hollow Z-axis driver and controls the substrate table; the substrate table is provided with a substrate at the bottom; the substrate stage is integrated with a temperature feedback control system consisting of a heater, a thermometer and a feedback temperature control element; the closed-cycle refrigerator comprises a refrigerating head, a compressor and a gas conveying pipeline; the refrigerating head extends into the heat exchange device and is connected with the compressor through a gas conveying pipeline; the closed-cycle refrigerator is positioned at the upper part of the low-temperature control system, the air extraction equipment is connected with the gas transmission equipment and is positioned at the side edge of the closed-cycle refrigerator, the gas transmission equipment is connected with the heat exchange device through a connecting pipeline, the mass flow controller is positioned on the connecting pipeline, and the heat exchange device is connected with and positioned below the closed-cycle refrigerator; the vacuum system comprises a vacuum preparation cavity, a vacuum pump and a vacuum interface; the vacuum pump is arranged on the lower side wall of the vacuum preparation cavity, the vacuum interface is positioned at the top of the vacuum preparation cavity, and the heat exchange device extends into the vacuum preparation cavity through the vacuum interface; the RHEED system comprises an RHEED electron gun and an RHEED fluorescent screen; the RHEED electron gun is positioned at one side of the vacuum preparation cavity, and the RHEED fluorescent screen is positioned at the other side of the vacuum preparation cavity.
2. The apparatus of claim 1, wherein the apparatus comprises: the outer surface of the substrate table is made of high thermal conductivity oxygen-free copper.
3. The apparatus of claim 2, wherein the apparatus comprises: the vacuum preparation cavity is a film deposition cavity.
4. The apparatus according to claim 3, wherein the apparatus comprises: the heat exchange device is provided with a protective cover; the protective cover wraps the surface of the heat exchange device.
5. The apparatus according to claim 4, wherein the apparatus comprises: the protection casing material is the austenitic stainless steel, the protection casing is rectangular tubular structure.
6. The apparatus according to claim 5, wherein the apparatus comprises: the types of the closed-cycle refrigerator comprise a pulse tube refrigerator and a Giford-Membrahong refrigerator; the refrigerant gas in the closed cycle refrigerator comprises one of helium 3 or helium 4.
7. A method for researching a two-dimensional material low-temperature crystal structure in situ is characterized by comprising the following steps: the device for researching the two-dimensional material cryocrystal structure in situ according to claim 6 comprises a low temperature operation mode and a high temperature operation mode; in a low-temperature working mode, the substrate table lifter lifts the substrate table to enable the back surface of the substrate table to be in full contact with the bottom end of the heat exchange device, the balance between the flow of the refrigerating gas and the heating power of a heater of the substrate table is accurately controlled, meanwhile, the overall height of the substrate table and the heat exchange device is adjusted through the hollow Z-axis driver, so that an electron beam emitted by the RHEED electron gun glazes onto the surface of the substrate, and the electron beam with crystal structure information reflected by the surface of the substrate is presented on the RHEED fluorescent screen; in a high-temperature working mode, the substrate table is lowered through the substrate table lifter so that the substrate table is far away from the heat exchange device, temperature control is achieved through a temperature feedback control system integrated in the substrate table to meet the requirement of thin film preparation on the temperature of the substrate, and meanwhile, the overall height of the substrate table and the heat exchange device is adjusted through the hollow Z-axis driver to meet the requirement of the thin film preparation on the height of the substrate.
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