CN112779597A - Method for producing van der waals two-dimensional layered single crystal - Google Patents
Method for producing van der waals two-dimensional layered single crystal Download PDFInfo
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- CN112779597A CN112779597A CN201911093004.8A CN201911093004A CN112779597A CN 112779597 A CN112779597 A CN 112779597A CN 201911093004 A CN201911093004 A CN 201911093004A CN 112779597 A CN112779597 A CN 112779597A
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- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
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- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
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- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
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Abstract
The invention provides a method for preparing van der Waals two-dimensional layered single crystal, which comprises the following steps: (1) placing raw materials and a transmission medium at one end of a quartz tube, and then vacuumizing; wherein, one end for placing the raw material and the transmission medium is called a raw material end, and the other end of the quartz tube is called a nucleation end; (2) the temperature of the raw material end of the quartz tube is T2, the temperature of the nucleation end is the growth temperature T1 of the material, the temperature T2 of the raw material end is higher than the temperature T1 of the nucleation end, and the temperature difference delta T between the temperature T2 of the raw material end and the temperature T1 of the nucleation end is controlled21Is 30-100 ℃; (3) synchronously regulating and controlling the temperature T2 of the raw material end and the temperature T1 of the nucleation end at the same cooling rate and heating rate to realize the cooling amplitude and the heating amplitude within the range of 1-30 ℃, thereby preparing the van der Waals two-dimensional layered single crystal. The method of the invention solves the problems of slow single crystal growth existing in the traditional CVT technology,the technical problems of more growth defects and unstable quality are solved, and the growth of the single crystal with controllable appearance and quality at lower temperature is realized.
Description
Technical Field
The invention belongs to the technical field of intermetallic compound single crystal preparation. In particular, the present invention relates to a method for producing van der waals two-dimensional layered single crystals. More particularly, the present invention relates to a method for preparing a single crystal of transition metal chalcogenide and transition metal halogen compound using an oscillating temperature field based on the principle of Chemical Vapor Transport (CVT).
Background
Layered compounds of transition metal chalcogenides or transition metal halogen compounds have a layered structure similar to graphite, and are bonded between layers within the crystal by van der waals forces. Single or few layer films of such materials have recently renewed a great deal of interest in the materials and physics community due to their excellent magnetic, magnetoelectric transport and optical properties. It is worth pointing out that the highest quality single or few layer films are obtained by mechanically peeling single crystals, and chemical vapor transport is the main method for synthesizing single crystals of such compounds.
Chemical Vapor Transport (CVT) refers to a technology in which a precursor and a transport medium undergo a reversible reaction in a closed container to form a gaseous intermediate product, chemical equilibrium is shifted by using a temperature gradient inside the container, a raw material is decomposed in a certain temperature region and diffuses to another temperature region, and then nucleation and crystallization are performed.
Chemical vapor transport is a natural phenomenon that originally exists in nature. The early German chemist's book discovered that hematite (Fe) in the study of volcanic eruptions2O3) Is related to volcanic gas activity. The high-temperature gas near the crater contains a large amount of hydrogen chloride. They react with molten iron oxide in the slurry and generate water vapor and ferric chloride vapor. When the gases containing the reactants drifted away from the crater, the ferric chloride reacted with water vapor to regenerate hematite when cooled.
One of the earliest cases in which chemical vapor transport was used was the purification of metallic zirconium. A sealed iodine-containing vessel was inserted with a low purity zirconium wire and heated by passing through an upper electrode. The red hot zirconium wire reacts with iodine vapor to generate a gasified compound, the gasified compound is diffused to the wall of the container with lower temperature, and the reverse reaction is generated to deposit high-purity metal zirconium. The invention of halogen lamps is also a similar principle, except that the reaction of tungsten and iodine is exothermic. When the sublimed tungsten reacts with iodine during use, the resultant tungsten iodide is subjected to reverse reaction decomposition at a high temperature, so that the metal tungsten is re-deposited on the tungsten filament, and the service life of the filament is greatly prolonged.
The German chemist Schafer firstly studied the chemical vapor transport systematically by means of thermodynamic methods and explored the great potential of the method in terms of crystal growth. Chemical vapor transport has become a versatile single crystal growth technique for growing single crystals of various intermetallic compounds, halogen compounds, oxides, sulfides, and the like.
A typical chemical vapor transport method in a laboratory is to pump a quartz tube filled with precursors and transport media (such as halogens, hydrogen chloride, water vapor and the like) to high vacuum, seal the quartz tube, and place the quartz tube into a high-temperature furnace. The precursor and the transmission medium are subjected to reversible reaction to generate gaseous products, and the concentrations of the gaseous products are different at different temperatures due to different chemical balances in an equilibrium state. Diffusion processes are caused by concentration gradients inside the quartz tube, and diffusion tends to smooth out concentration differences, causing actual gaseous components at different temperatures to deviate from equilibrium. The gaseous products at the feed end are in an unsaturated state and continue to decompose. The gaseous product at the nucleation end is in a supersaturated state, and reverse reaction occurs to realize nucleation and growth of the single crystal.
When a traditional CVT is used for growing crystals, a constant temperature is used, and the temperature of a raw material end and the temperature of a nucleation end are kept unchanged in the crystal growth process and are in a thermodynamic equilibrium state (refer to fig. 1 a). The farther the difference between the equilibrium states of the raw material end and the nucleation end is, the larger the concentration difference is, the diffusion rate is increased, and further the driving force of crystal growth is also large. In order to configure suitable growth conditions, two methods can be used in the ideal case: 1. the average temperature of growth is changed so that the change in gibbs free energy of reaction at the average temperature is as close to zero as possible. At this time, the slope of the solubility-temperature curve is the largest, and the nucleation end/raw material end can enter a supersaturated zone/unsaturated zone by a small temperature difference (refer to fig. 1 b); 2. the temperature difference between the growing end and the raw end is increased to make the nucleation end/raw end enter the supersaturated/unsaturated zone (refer to fig. 1 c). The conventional CVT has the following disadvantages: on the one hand, too high a growth temperature increases crystal thermal defects; on the other hand, too large temperature difference makes the nucleation points dense and difficult to control, and crystals adjacent to the nucleation points are connected into one piece. That is, the desired reaction temperature may be higher than the use temperature of the single crystal furnace. And the excessive growth temperature causes the increase of crystal thermal defects. The blind increase of the temperature difference can lead to uncontrollable nucleation density, so that the crystal morphology is poor. Therefore, it is very important to develop a technology capable of controllable growth at low temperature.
Disclosure of Invention
The present invention aims to provide a method for producing high-quality single crystals of transition metal chalcogenides and transition metal halides at low temperatures with high efficiency.
The above object of the present invention is achieved by the following means.
The invention provides a method for preparing van der Waals two-dimensional layered single crystal, which comprises the following steps:
(1) placing raw materials and a transmission medium at one end of a quartz tube, and then vacuumizing; wherein, one end for placing the raw material and the transmission medium is called a raw material end, and the other end of the quartz tube is called a nucleation end;
(2) the temperature of the raw material end of the quartz tube is T2, the temperature of the nucleation end is the growth temperature T1 of the material, the temperature T2 of the raw material end is higher than the temperature T1 of the nucleation end, and the temperature difference delta T between the temperature T2 of the raw material end and the temperature T1 of the nucleation end is controlled21Is 30-100 ℃;
(3) synchronously regulating and controlling the temperature T2 of the raw material end and the temperature T1 of the nucleation end at the same cooling rate and heating rate to realize the cooling amplitude and the heating amplitude within the range of 1-30 ℃, thereby preparing the van der Waals two-dimensional layered single crystal.
Preferably, in the method of the present invention, the raw material is a polycrystalline powder used for producing a transition metal chalcogenide single crystal or a transition metal halogen compound single crystal.
Preferably, in the method of the present invention, the transition metal elements of the transition metal chalcogenide and the transition metal halogen compound are selected from one or more of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Pt, Pd; the chalcogen element of the transition metal chalcogenide is selected from one or more of S, Se and Te; the halogen of the transition metal halogen compound is selected from one or more of F, Cl, Br and I.
Preferably, in the method of the present invention, the transmission medium is selected from solid state I2Liquid Br2Gaseous Cl2One or more of them.
Preferably, in the method of the present invention, the temperature decrease rate and the temperature increase rate are 1 to 40 ℃/min.
Preferably, in the method of the present invention, the temperature increase rate is greater than the temperature decrease rate, which is more favorable for single crystal growth.
Preferably, in the method of the present invention, the synchronously controlling the temperature decreasing rate and the temperature increasing rate of the raw material end temperature T2 and the nucleation end temperature T1 is performed by a method comprising the following steps:
the raw material end temperature T2 and the nucleation end temperature T1 are cooled at the same cooling rate and the same cooling time, then are kept for 0-1h at the temperature after being cooled, and then are heated at the same heating rate and the same heating time, and are kept for 0-1h at the temperature after being heated; the above process is repeated so that the raw material end temperature T2 and the nucleation end temperature T1 oscillate in waveform.
Preferably, in the method of the present invention, when the transition metal chalcogenide is NbSe2、MoS2、MoSe2Or MoTe2And the transition metal halide compound is CrI3Or CrBr3When the temperature of the raw material end T2 is 600-650 ℃, the temperature of the nucleation end T1 is 550-600 ℃; the cooling rate is 1-10 ℃/min, and the heating rate is 12-40 ℃/min; the temperature reduction amplitude and the temperature rise amplitude are within the range of 5-30 ℃.
Preferably, in the method of the present invention, it further comprises a reverse temperature control step after the step (1) and before the step (2), the reverse temperature control step comprising the steps of:
heating the raw material end of the quartz tube to the growth temperature T1 of the material, heating the nucleation end to T3 so that the temperature T3 of the nucleation end is higher than the temperature T1 of the raw material end, and controlling the temperature difference delta T between the temperature T3 of the nucleation end and the temperature T1 of the raw material end31Is 100-200 ℃.
In the invention, the reverse temperature control step is added, which has the following advantages: and cleaning impurities and raw material powder attached to the nucleation end to reduce the nucleation points which can appear during forward temperature control growth and ensure that each nucleation point can develop into a single crystal with a perfect appearance.
Preferably, in the method of the present invention, when the transition metal chalcogenide is NbSe2、MoS2、MoSe2Or MoTe2And the transition metal halide compound is CrI3Or CrBr3The reverse temperature control step is carried out under the following conditions: the material end temperature T1 is 550-600 ℃, and the nucleation end temperature T3 is 750-800 ℃.
Preferably, in the method of the present invention, the method further comprises a step of sequentially ultrasonically cleaning the quartz tube with acetone or diluted hydrochloric acid and absolute ethyl alcohol before the step (1).
Preferably, in the method of the present invention, the evacuation in the step (1) is performed by a method comprising the steps of: connecting quartz tube to vacuum system, repeatedly cleaning with protective gas for more than three times, and pumping to vacuum degree of 10-5To 10-4Pa。
Preferably, in the method of the invention, the protective gas is selected from argon and/or nitrogen.
The invention has the following beneficial effects:
the method of the invention solves the defects of slow single crystal growth, more growth defects and unstable quality of the traditional CVT technology, and realizes the synthesis of high-quality single crystals at lower temperature.
The method realizes the synthesis of the single crystal at lower temperature, which is 200 ℃ lower than that of the traditional method, and the low temperature in the method can reduce the thermal defect, while the oscillation temperature field in the method can accelerate the momentum and mass transmission.
Drawings
Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:
FIG. 1a is a schematic diagram illustrating a conventional chemical vapor transport single crystal growth principle;
FIG. 1b is a schematic diagram of a conventional chemical vapor transport single crystal growth with a changed equilibrium position;
FIG. 1c is a schematic diagram of the temperature difference increase in the conventional chemical vapor transport single crystal growth;
FIG. 2a is a schematic diagram illustrating the growth principle of a constant temperature gradient in a conventional chemical vapor transport;
FIG. 2b is a schematic diagram of the growth principle of an oscillating temperature field according to an embodiment of the present invention;
FIG. 3a is a schematic diagram of a method of growing an oscillating temperature field according to an embodiment of the present invention;
FIG. 3b is a schematic temperature curve of a method of growing with an oscillating temperature field according to an embodiment of the present invention;
FIG. 4a is a single crystal plot of a crystal produced by examples 1-4 of the present invention;
FIG. 4b is an XRD spectrum of a single crystal prepared in example 1 of the present invention;
FIG. 4c is a single crystal of comparative example 1 of the present invention;
FIG. 4d is a single crystal plot of example 1 of the present invention;
FIG. 5a is a schematic diagram of the side structure of a single crystal produced in example 1 of the present invention;
FIG. 5b is a schematic representation of the ab-plane structure of a single crystal prepared in example 1 of the present invention;
FIG. 5c is an SEM image of the (001) direction of a single crystal prepared in example 1 of the present invention;
FIG. 5d is an SEM of (111) direction of a single crystal prepared in example 1 of the present invention;
FIG. 6 is a temperature change resistance curve of single crystals prepared in examples 1-4 of the present invention;
FIG. 7 shows CrI prepared in example 5 of the present invention3Single crystal diagram.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 2a, for the conventional growth method (endothermic reaction) with constant temperature gradient, the raw material end of the quartz tube should be in a high temperature region T2, corresponding to the point q in the solubility-temperature diagram, and the gaseous components are in a supersaturated state, and crystals are precipitated. The quartz tube-shaped core end is positioned in a low-temperature zone T1, corresponding to the point n in the figure, the gaseous components are in an unsaturated state, and the raw materials are decomposed to supplement the consumption of the core end, so that the whole quartz tube is in dynamic balance.
Referring to fig. 2b, the temperature difference T2-T1 between the feedstock end T2 and the nucleation end T1 is kept constant, and T1 and T2 are simultaneously raised and lowered to realize the change of the supersaturation state. Thereby remarkably improving the crystal growth without increasing the nucleation density of the crystal.
As shown in fig. 2b, the a-b process: t1 and T2 are heated simultaneously. The supersaturation degree of the nucleation end is reduced, and the crystal growth is inhibited; the raw material end enters an unsaturated zone, and the raw material is decomposed in an accelerated way. c-d process: and the temperature of T1 and T2 is reduced simultaneously. The supersaturation degree of the nucleation end is increased, and the crystal growth is promoted; decomposition of the feedstock end is temporarily inhibited. e-b-c-d-e forms a circulation process, and the supersaturation degree of crystal growth at the nucleation end is controlled by setting different cooling rates. Crystal growth with high degree of supersaturation can be achieved even at low growth temperatures. The method can control the appearance and quality of crystal growth, widen the growth temperature zone, avoid impurity phase and realize high-quality single crystal growth.
In a specific embodiment of the invention, when preparing NbSe2Single crystal or CrI3When the single crystal is used, the method comprising the following steps can be adopted:
(1) in an argon glove box, loading the precursor and a transmission medium into a quartz tube with the inner diameter of 16mm multiplied by the length of 200mm and sealing;
(2) connecting the prepared quartz tube on a vacuum system, repeatedly cleaning with argon gas for three times, and pumping to high vacuum (<10-4Pa)；
(3) Heating and sealing the quartz tube by using a flame gun at a proper length of the quartz tube;
(4) pre-calibrating the temperature distribution of the double-temperature-zone tube furnace, and placing a quartz tube between two temperature zones;
(5) heating the temperature close to the raw material end to 550-600 ℃ at the speed of 5-10 ℃/min, heating the temperature close to the nucleation end to 750-800 ℃, and maintaining for 1-2 days;
(6) the temperature of the raw material end is synchronously controlled to be raised to 600-650 ℃ at the speed of 5-10 ℃/min, and the temperature close to the nucleation end is lowered to 550-600 ℃. After the temperature is stabilized for 1-2 hours, the two temperature zones are synchronously reduced by 5-30 ℃ at the speed of 1-10 ℃ per hour and then heated by 5-30 ℃ at the speed of 12-40 ℃ per hour. Repeating the above processes to oscillate the temperature waveforms of the raw material end and the nucleation end;
(7) after 7-14 days of growth, directly taking out the quartz tube, and immersing the raw material end in water for cooling.
(8) Breaking the quartz tube in a fume hood, repeatedly cleaning the single crystal with absolute ethyl alcohol, and then putting the single crystal into a vacuum oven for drying.
Example 1
Preparation of NbSe2(Single Crystal)
(1) And ultrasonically cleaning the inner wall of a quartz tube with the inner diameter of 16mm multiplied by the length of 200mm and the closed end for 10 minutes by using acetone and absolute ethyl alcohol in sequence, washing the quartz tube with deionized water for twice, and finally drying the quartz tube with a blast drying oven.
(2) Nb and Se powders (purity 4N or more) in an amount of 1g in total mass were mixed in a glove box at a ratio of 1:2, and 5mg/cm3The iodine (purity: 3N or more) was mixed and charged into a quartz tube and sealed.
(3) Filling quartz fiber cotton into the open end of the quartz tube, connecting to a busbar of a vacuum system, and vacuumizing until the vacuum degree reaches 10-4And (Pa), heating and sealing the quartz tube by a flame gun at the position of 10cm away from the bottom of the quartz tube.
(4) The fused quartz tube was placed in a horizontal dual temperature zone tube furnace with pre-calibrated temperature distribution as shown in fig. 3 a.
(5) Electrifying the tube furnace, heating the raw material end to 550 ℃ at the speed of 8 ℃/min, heating the temperature close to the nucleation end to 750 ℃, and keeping the temperature for 1-2 days to clean the raw material powder possibly attached to the nucleation end.
(6) The temperature of the raw material end is controlled to be increased to 600 ℃ at the speed of 10 ℃/min, and the temperature close to the nucleation end is reduced to 550 ℃. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 12 ℃ at the rate of 1 ℃/hour, then the temperature is increased by 24 ℃ at the rate of 12 ℃/hour, and then the temperature is reduced by 24 ℃ at the rate of 1 ℃/hour. The process of "further raising the temperature at a rate of 12 ℃/hour by 24 ℃ and further lowering the temperature at a rate of 1 ℃/hour by 24 ℃" was repeated to oscillate the waveform of the temperatures of the raw material end and the nucleation end at 550 ℃.
(7) After the growth is finished for 10 days, directly taking out the quartz tube, and dipping the raw material end in water for cooling;
(8) breaking the quartz tube in a fume hood, repeatedly cleaning the single crystal with absolute ethyl alcohol, and then putting the single crystal into a vacuum oven for drying.
FIG. 3a shows the placement of the fused-on quartz tube into a horizontal dual-temperature zone tube furnace with a pre-calibrated temperature profile.
FIG. 3b shows the temperature-time setting curves, S, for the feedstock side and the nucleation side1Is the rate of temperature rise, S2Is the rate of temperature decrease.
FIG. 4b shows 2H-NbSe prepared by the present embodiment2The result of X-ray diffraction of (1). The single crystal X-ray diffraction proves that the 2H-NbSe prepared by the embodiment2Is 2H structure single crystal without impurity phase.
FIG. 4d shows NbSe prepared in this example2The single crystal has smooth surface and regular shape, some of the single crystals are hexagonal and have typical two-dimensional growth characteristics.
HRTEM of FIGS. 5 a-5 d shows the NbSe of 2H phase more clearly2The atomic arrangement of (a).
Example 2
The parameters of the technical features of all the steps are the same as those of the embodiment 1, except that the synchronous cooling rate in the step (6) in the embodiment 1 is changed, namely, the step (6) in the embodiment 1 is modified as follows: the temperature of the raw material end is controlled to be increased to 600 ℃ at the speed of 10 ℃/min, and the temperature close to the nucleation end is reduced to 550 ℃. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 12 ℃ at the rate of 3 ℃/hour, then the temperature is increased by 24 ℃ at the rate of 12 ℃/hour, and then the temperature is reduced by 24 ℃ at the rate of 3 ℃/hour. The process of "further raising the temperature at a rate of 12 ℃/hour by 24 ℃ and further lowering the temperature at a rate of 3 ℃/hour by 24 ℃" was repeated to oscillate the waveform of the temperatures of the raw material end and the nucleation end at 550 ℃.
Fig. 4a shows a single crystal plot prepared in this example.
Example 3
The parameters of the technical features of all the steps are the same as those of the embodiment 1, except that the synchronous cooling rate in the step (6) in the embodiment 1 is changed, namely, the step (6) in the embodiment 1 is modified as follows: the temperature of the raw material end is controlled to be increased to 600 ℃ at the speed of 10 ℃/min, and the temperature close to the nucleation end is reduced to 550 ℃. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 12 ℃ at the rate of 4 ℃/hour, then the temperature is increased by 24 ℃ at the rate of 12 ℃/hour, and then the temperature is reduced by 24 ℃ at the rate of 4 ℃/hour. The process of "further raising the temperature at a rate of 12 ℃/hour by 24 ℃ and further lowering the temperature at a rate of 4 ℃/hour by 24 ℃" was repeated to oscillate the waveform of the temperatures of the raw material end and the nucleation end at 550 ℃.
Fig. 4a shows a single crystal plot prepared in this example.
Example 4
The parameters of the technical features of all the steps are the same as those of the embodiment 1, except that the synchronous cooling rate in the step (6) in the embodiment 1 is changed, namely, the step (6) in the embodiment 1 is modified as follows: the temperature of the raw material end is controlled to be increased to 600 ℃ at the speed of 10 ℃/min, and the temperature close to the nucleation end is reduced to 550 ℃. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 30 ℃ at the speed of 5 ℃/hour, then heated by 60 ℃ at the speed of 15 ℃/hour, and then reduced by 60 ℃ at the speed of 5 ℃/hour. The process of "raising the temperature at a rate of 15 ℃/hour again to 60 ℃ and then lowering the temperature at a rate of 5 ℃/hour to 60 ℃ is repeated, so that the temperatures of the raw material end and the nucleation end oscillate in a waveform at 550 ℃.
Fig. 4a shows a single crystal plot prepared in this example.
FIG. 4a shows NbSe grown at different ramp rates2The appearance of the single crystal is regular as the cooling rate is increased and the number of screw dislocation is reduced.
FIG. 6 is a temperature change resistance curve of single crystals prepared in examples 1-4 of the present invention. FIG. 6 shows NbSe grown at different ramp rates2Comparison of the electrotransport properties. FIG. 6 shows that as the temperature decrease rate increases, the single crystal residual resistivity increases and the superconducting transition temperature increases, indicating that the crystal quality becomes higher。S2Is the ramp down rate and RRR is the residual resistivity. FIG. 6 shows characteristic peaks of electronic structure phase transition near 33K (-240 ℃ C.) and 7.2K (-265.8 ℃ C.), corresponding to occurrence of charge density wave phase transition and superconducting transition, respectively, also demonstrating 2H-NbSe2. The measured phase transition critical point is very close to the literature standard data, which indicates that the prepared sample is high-quality 2H-NbSe with less defect density2And (3) single crystal.
Example 5
CrI3Preparation of
(1) And ultrasonically cleaning the inner wall of a quartz tube with the inner diameter of 16mm multiplied by the length of 200mm and the closed end for 10 minutes by using acetone and absolute ethyl alcohol in sequence, washing the quartz tube with deionized water for twice, and finally drying the quartz tube with a blast drying oven.
(2) Cr and I, which were 0.3g in total mass (purity 4N or more), were mixed in a glove box at a ratio of 1:3, and the mixture was charged into a quartz tube and sealed.
(3) Filling quartz fiber cotton into the open end of the quartz tube, connecting to a busbar of a vacuum system, and vacuumizing until the vacuum degree reaches 10-4And when Pa, heating and sealing the quartz tube by using a flame gun at the position of 8-10cm away from the bottom of the quartz tube.
(4) And putting the fused and sealed quartz tube into a horizontal double-temperature-zone tube furnace with the temperature distribution calibrated in advance.
(5) And electrifying the tube furnace, heating the raw material end to 600 ℃ at the speed of 8 ℃/min, heating the temperature close to the nucleation end to 700 ℃, and keeping the temperature for 1 day to clean the raw material powder possibly attached to the nucleation end.
(6) Keeping the temperature of the raw material end to be 600 ℃ at the speed of 10 ℃/min, and reducing the temperature close to the nucleation end to be 550 ℃. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 12 ℃ at the rate of 4 ℃/hour, then are heated by 24 ℃ at the rate of 12 ℃/hour, and are reduced by 24 ℃ at the rate of 4 ℃/hour. The process of "further raising the temperature at a rate of 12 ℃/hour by 24 ℃ and then lowering the temperature at a rate of 4 ℃/hour by 24 ℃" was repeated to oscillate the temperatures of the feedstock end and the nucleation end in a 550 ℃ waveform.
(7) After the growth is finished for about 7 days, directly taking out the quartz tube, and dipping the raw material end in water for cooling;
(8) breaking the quartz tube in a glove box, taking out the single crystal, and sealing and storing.
FIG. 7 shows CrI prepared in this example3And (3) single crystal.
Example 6
CrI3Preparation of
(1) And ultrasonically cleaning the inner wall of a quartz tube with the inner diameter of 16mm multiplied by the length of 200mm and the closed end for 10 minutes by using acetone and absolute ethyl alcohol in sequence, washing the quartz tube with deionized water for twice, and finally drying the quartz tube with a blast drying oven.
(2) Cr and I, which were 0.3g in total mass (purity 4N or more), were mixed in a glove box at a ratio of 1:3, and the mixture was charged into a quartz tube and sealed.
(3) Filling quartz fiber cotton into the open end of the quartz tube, connecting to a busbar of a vacuum system, and vacuumizing until the vacuum degree reaches 10-4And (Pa), heating and sealing the quartz tube by using a flame gun at the position of 9cm away from the bottom of the quartz tube.
(4) And putting the fused and sealed quartz tube into a horizontal double-temperature-zone tube furnace with the temperature distribution calibrated in advance.
(5) And electrifying the tube furnace, heating the raw material end to 600 ℃ at the speed of 8 ℃/min, heating the temperature close to the nucleation end to 700 ℃, and keeping the temperature for 1 day to clean the raw material powder possibly attached to the nucleation end.
(6) The temperature of the feedstock end was reduced to 580 c at a rate of 10 c/min and the temperature near the nucleation end to 550 c. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 12 ℃ at the rate of 4 ℃/hour, then are heated by 24 ℃ at the rate of 12 ℃/hour, and are reduced by 24 ℃ at the rate of 4 ℃/hour. The process of "further raising the temperature at a rate of 12 ℃/hour by 24 ℃ and then lowering the temperature at a rate of 4 ℃/hour by 24 ℃" was repeated to oscillate the temperatures of the feedstock end and the nucleation end in a 550 ℃ waveform.
(7) After the growth is finished for about 7 days, directly taking out the quartz tube, and dipping the raw material end in water for cooling;
(8) breaking the quartz tube in a glove box, taking out the single crystal, and sealing and storing.
CrI prepared in this example3Single crystal andexample 5 is similar.
Example 7
CrI3Preparation of
(1) And ultrasonically cleaning the inner wall of a quartz tube with the inner diameter of 16mm multiplied by the length of 200mm and the closed end for 10 minutes by using acetone and absolute ethyl alcohol in sequence, washing the quartz tube with deionized water for twice, and finally drying the quartz tube with a blast drying oven.
(2) Cr and I, which were 0.3g in total mass (purity 4N or more), were mixed in a glove box at a ratio of 1:3, and the mixture was charged into a quartz tube and sealed.
(3) Filling quartz fiber cotton into the open end of the quartz tube, connecting to a busbar of a vacuum system, and vacuumizing until the vacuum degree reaches 10-5And (Pa), heating and sealing the quartz tube by using a flame gun at the position of 9cm away from the bottom of the quartz tube.
(4) And putting the fused and sealed quartz tube into a horizontal double-temperature-zone tube furnace with the temperature distribution calibrated in advance.
(5) And electrifying the tube furnace, heating the raw material end to 600 ℃ at the speed of 8 ℃/min, heating the temperature close to the nucleation end to 700 ℃, and keeping the temperature for 1 day to clean the raw material powder possibly attached to the nucleation end.
(6) The temperature of the feedstock end was raised to 650 ℃ at a rate of 10 ℃/min and the temperature near the nucleation end was lowered to 550 ℃. After the temperature is stabilized for 2 hours, the two temperature zones are synchronously reduced by 12 ℃ at the rate of 4 ℃/hour, then are heated by 24 ℃ at the rate of 12 ℃/hour, and are reduced by 24 ℃ at the rate of 4 ℃/hour. The process of "further raising the temperature at a rate of 12 ℃/hour by 24 ℃ and then lowering the temperature at a rate of 4 ℃/hour by 24 ℃" was repeated to oscillate the temperatures of the feedstock end and the nucleation end in a 550 ℃ waveform.
(7) After the growth is finished for about 7 days, directly taking out the quartz tube, and dipping the raw material end in water for cooling;
(8) breaking the quartz tube in a glove box, taking out the single crystal, and sealing and storing.
CrI prepared in this example3The single crystal was similar to example 5.
Comparative example 1
The parameters of the technical characteristics of all the steps are the same as those of example 1, except that the single crystal growth is carried out by using a constant temperature gradient in the conventional chemical vapor transport, that is, the temperature of the nucleation end is controlled at 550 ℃, and the temperature of the raw material end is controlled at 730 ℃.
Fig. 4c shows a single crystal plot of the present comparative example preparation. FIG. 4c shows that the temperature difference required for conventional single crystal growth is large, and the grown crystals agglomerate.
Claims (10)
1. A method for preparing van der waals two-dimensional layered single crystal, comprising the steps of:
(1) placing raw materials and a transmission medium at one end of a quartz tube, and then vacuumizing; wherein, one end for placing the raw material and the transmission medium is called a raw material end, and the other end of the quartz tube is called a nucleation end;
(2) the temperature of the raw material end of the quartz tube is T2, the temperature of the nucleation end is the growth temperature T1 of the material, the temperature T2 of the raw material end is higher than the temperature T1 of the nucleation end, and the temperature difference delta T between the temperature T2 of the raw material end and the temperature T1 of the nucleation end is controlled21Is 30-100 ℃;
(3) synchronously regulating and controlling the temperature T2 of the raw material end and the temperature T1 of the nucleation end at the same cooling rate and heating rate to realize the cooling amplitude and the heating amplitude within the range of 1-30 ℃, thereby preparing the van der Waals two-dimensional layered single crystal.
2. The method according to claim 1, wherein the raw material is elemental or polycrystalline powder of an element used for producing a transition metal chalcogenide single crystal or a transition metal halogen compound single crystal;
preferably, the transition metal elements of the transition metal chalcogenide and the transition metal halogen compound are selected from one or more of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Ni, Pt and Pd; the chalcogen element of the transition metal chalcogenide is selected from one or more of S, Se and Te; the halogen of the transition metal halogen compound is selected from one or more of F, Cl, Br and I;
preferably, the transmission medium is selected from solid state I2Liquid Br2Gaseous Cl2One or more of them.
3. The method of claim 1, wherein the cooling rate and the warming rate are 1-40 ℃/min;
preferably, the rate of temperature rise is greater than the rate of temperature fall.
4. The method of claim 1, wherein the synchronously regulating the temperature decrease rate and the temperature increase rate of the feedstock end temperature T2 and the nucleation end temperature T1 is performed by a method comprising:
the raw material end temperature T2 and the nucleation end temperature T1 are cooled at the same cooling rate and the same cooling time, then are kept for 0-1h at the temperature after being cooled, and then are heated at the same heating rate and the same heating time, and are kept for 0-1h at the temperature after being heated; the above process is repeated so that the raw material end temperature T2 and the nucleation end temperature T1 oscillate in waveform.
5. The method of claim 4, wherein when the transition metal chalcogenide is NbSe2、MoS2、MoSe2Or MoTe2And the transition metal halide compound is CrI3Or CrBr3When the temperature of the raw material end T2 is 600-650 ℃, the temperature of the nucleation end T1 is 550-600 ℃; the cooling rate is 1-10 ℃/min, and the heating rate is 12-40 ℃/min; the temperature reduction amplitude and the temperature rise amplitude are within the range of 5-30 ℃.
6. The method according to claim 1, further comprising a reverse temperature control step after said step (1) and before step (2), the reverse temperature control step comprising the steps of:
heating the raw material end of the quartz tube to the growth temperature T1 of the material, heating the nucleation end to T3 so that the temperature T3 of the nucleation end is higher than the temperature T1 of the raw material end, and controlling the temperature difference delta T between the temperature T3 of the nucleation end and the temperature T1 of the raw material end31Is 100-200 ℃.
7. The method of claim 6, wherein,when the transition metal chalcogenide is NbSe2、MoS2、MoSe2Or MoTe2And the transition metal halide compound is CrI3Or CrBr3The reverse temperature control step is carried out under the following conditions: the material end temperature T1 is 550-600 ℃, and the nucleation end temperature T3 is 750-800 ℃.
8. The method of claim 1, further comprising the step of sequentially ultrasonically cleaning the quartz tube with acetone or diluted hydrochloric acid and absolute ethanol before the step (1).
9. The method according to claim 1, wherein the evacuating in step (1) is performed by a method comprising the steps of: connecting quartz tube to vacuum system, repeatedly cleaning with protective gas for more than three times, and pumping to vacuum degree of 10-5To 10-4Pa。
10. The method of claim 9, wherein the protective gas is selected from argon and/or nitrogen.
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| CN113373511A (en) * | 2021-05-12 | 2021-09-10 | 南京理工大学 | Large-size CrI3Method for producing single crystal |
| CN113501505A (en) * | 2021-08-19 | 2021-10-15 | 河北大学 | Two-dimensional tungsten selenide nano material and preparation method thereof |
| CN114735751A (en) * | 2022-03-17 | 2022-07-12 | 西北工业大学 | Single-layer CrI prepared based on chemical vapor transport3Sheet and method |
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| CN1061057A (en) * | 1990-10-30 | 1992-05-13 | 四川大学 | The preparation method of mercury iodide monocrystal |
| CN110144624A (en) * | 2018-02-11 | 2019-08-20 | 中国科学院理化技术研究所 | A kind of growing method of selenium germanium gallium barium polycrystalline synthetic method and selenium germanium gallium barium monocrystalline |
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| CN113373511A (en) * | 2021-05-12 | 2021-09-10 | 南京理工大学 | Large-size CrI3Method for producing single crystal |
| CN113373511B (en) * | 2021-05-12 | 2022-09-09 | 南京理工大学 | Large-size CrI 3 Method for producing single crystal |
| CN113501505A (en) * | 2021-08-19 | 2021-10-15 | 河北大学 | Two-dimensional tungsten selenide nano material and preparation method thereof |
| CN114735751A (en) * | 2022-03-17 | 2022-07-12 | 西北工业大学 | Single-layer CrI prepared based on chemical vapor transport3Sheet and method |
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