CN113604779B - Ordered chiral molecular chain preparation method and SiC device substrate - Google Patents
Ordered chiral molecular chain preparation method and SiC device substrate Download PDFInfo
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Abstract
The invention provides a preparation method of an ordered chiral molecular chain and a SiC device substrate, which comprises the following steps: cleaning the SiC monocrystalline substrate to remove impurities on the surface of the SiC monocrystalline substrate; placing SiC single crystal substrate under vacuum degree of 1.0X10 × ‑10 mbar～3.0×10 ‑10 Heating and degassing the SiC monocrystal substrate in a preparation cavity of mbar in a direct current heating mode; then, the SiC monocrystal substrate is circularly heated for 90min at 900 ℃ and 1400 ℃; then cutting off direct current heating to cool the SiC monocrystalline substrate to room temperature, so that double-layer graphene is uniformly formed on the surface of the SiC monocrystalline substrate; evaporating 2,2 '-diphenyl ethynyl-4, 4' -dibromobiphenyl molecules in the preparation cavity to make chiral separation and self-assembly on the surface of double-layer graphene of a low-temperature SiC single crystal substrate, and increasing the vacuum degree in the preparation cavity to 1.0X10 ‑9 mbar～3.0×10 ‑9 At mbar, molecules begin to deposit, and after a period of time, large-area ordered chiral molecular chains can be prepared.
Description
Technical Field
The invention relates to the technical field of chiral molecular separation and preparation, in particular to a preparation method of ordered chiral molecular chains based on 2,2 '-diphenyl ethynyl-4, 4' -dibromobiphenyl and a SiC device substrate.
Background
In the chemical field, there is a large class of molecules in which chiral isomers exist that look like left and right hands, but do not overlap, and are referred to as "chiral molecules". Chiral molecules play a very important role from microscopic to macroscopic, for example, chiral molecules in some drugs have significant differences in biological activity, metabolic processes, toxicity, etc., and even differences such as "disease treatment" and "pathogenicity" exist in the world. In recent years, chiral separation has attracted attention because of its application to thin film transistors, heterogeneous catalytic chemistry and pharmaceutical engineering, and therefore, how to separate the "left and right hands" of chiral molecules more economically, efficiently and conveniently has become an important subject.
In the prior art, chiral separation generally adopts crystallization resolution, chemical resolution, enzyme resolution, membrane resolution, extraction resolution, chromatography resolution and other methods, for example, the crystallization resolution is based on the formation of diastereomeric salts or covalent derivatives from enantiomers and pure chiral substances, separation is carried out by utilizing the property difference of diastereomers, and the derivatives are reduced to pure enantiomers. Chemical resolution is the conversion of two enantiomers to diastereomers by resolution reagents, which are then separated by differences in their physical and chemical properties. The extraction and resolution method is a method for resolution by utilizing the difference of affinity forces or chemical action differences of chiral extractant and two enantiomers in prochiral molecules.
The chiral separation methods described above in the prior art have a number of disadvantages: for example, the crystallization resolution method has the disadvantages of time consumption, labor consumption and large deviation from expectations, the chemical resolution method has the disadvantages of low yield, low purity of products, few enantiomer types suitable for chiral resolution and the like, and the enzyme resolution method has the disadvantages of limited enzyme preparation variety and high preparation price, so that the technical scheme has the disadvantages of complex operation steps, poor separation effect, incapability of separating and preparing chiral molecular long chains, and incapability of chiral separation under the condition that the original chiral separation is not carried out or the chiral separation is difficult to be carried out in solution, 2' -diphenylethynyl-4, 4' -dibromobiphenyl needs to be prepared in solution, the prepared 2,2' -diphenylethynyl-4, 4' -dibromobiphenyl has chiral isomers, and referring to fig. 1, the chemical structural formula of two enantiomers of 2,2' -diphenylethynyl-4, 4' -dibromobiphenyl molecules is shown in a 2D plane, but the two enantiomers of the 2,2' -diphenylethynyl-4, 4' -dibromobiphenyl molecules are randomly mixed together in solution to form ordered chiral separation, and the prepared 2, 4' -dibromobiphenyl molecule cannot be separated in the existing method by chiral separation.
Disclosure of Invention
The invention provides a preparation method of an ordered chiral molecular chain and a SiC device substrate, and aims to solve the problems that two enantiomers of a 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecule in the prior art are randomly mixed together in a solution and cannot form an ordered chiral long chain, and the prepared 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecule is difficult to carry out chiral separation in the solution by the existing method.
In order to achieve the above object, the embodiment of the present invention provides a method for preparing an ordered chiral molecular chain, including: cleaning a SiC monocrystalline substrate, and removing impurities on the surface of the SiC monocrystalline substrate; heating and degassing the SiC monocrystal substrate in a direct current heating mode; then, the SiC monocrystal substrate is circularly heated for 90min at 900 ℃ and 1400 ℃; then cutting off direct current heating to cool the SiC monocrystalline substrate to room temperature, so that double-layer graphene is uniformly formed on the surface of the SiC monocrystalline substrate; placing SiC single crystal substrate under vacuum degree of 1.0X10 × -10 mbar～3.0×10 -10 In a preparation cavity of mbar, the temperature of a SiC monocrystal substrate is lower than room temperature, 2 '-diphenyl ethynyl-4, 4' -dibromobiphenyl molecules are thermally evaporated in the preparation cavity, chiral separation and self-assembly are carried out on the surface of double-layer graphene of the SiC monocrystal substrate, and when the vacuum degree in the preparation cavity is increased to 1.0x10 -9 mbar～3.0×10 -9 At mbar, molecules begin to be deposited, and after a period of time, large-area ordered chiral molecular chains are prepared.
Optionally, the SiC single crystal substrate is circularly heated at 900 ℃ and 1400 ℃ for 90min specifically: heating the SiC monocrystal substrate at 900 ℃ for 15min, heating the SiC monocrystal substrate to 1400 ℃ for 15min to heat the SiC monocrystal substrate for the first round, and repeating the steps until the third round of heating is finished.
Optionally, the preparation cavity is an ultrahigh vacuum preparation cavity of a scanning tunnel microscope.
Optionally, heating the SiC single crystal substrate to 600-650 ℃ and continuously heating for 4-8 hours to heat and degas the SiC single crystal substrate.
Optionally, the thermal evaporation temperature of the thermal evaporation 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecule is 140-150 ℃ and the deposition time is 10-20 min.
Alternatively, the thermal evaporation temperature of the thermally evaporated 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 143 ℃, the temperature of the SiC single crystal substrate is lower than 0 ℃, and the deposition time is 15min.
Alternatively, the thermal evaporation temperature of the thermally evaporated 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 145 ℃, the temperature of the SiC single crystal substrate is lower than 0 ℃, and the deposition time is 10min.
Optionally, the thermal evaporation temperature of the thermally evaporated 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 145 ℃, the temperature of the SiC single crystal substrate is lower than 0 ℃, and the deposition time is 15min
Alternatively, the SiC single crystal is a 4H-SiC (0001) or 6H-SiC (0001) single crystal.
The embodiment of the invention also provides a SiC device substrate, which comprises: the SiC single crystal substrate is uniformly formed with double-layer grapheme and ordered chiral molecular chains uniformly distributed on the surface of the double-layer grapheme by the preparation method of the ordered chiral molecular chains.
In summary, the beneficial effects of the invention are as follows:
the embodiment of the invention provides a preparation method of ordered chiral molecular chains and a SiC device substrate, which have excellent chiral separation effect on 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules, wherein uniform double-layer graphene is formed on the surface of a SiC single crystal substrate, and then the 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules are subjected to chiral separation and self-assembly on the surface of the double-layer graphene through thermal evaporation, so that large-area ordered chiral molecular chains are finally obtained on the surface of the double-layer graphene of the SiC single crystal substrate, and the double-layer graphene on the surface of the SiC single crystal substrate is modified, thereby providing conditions for preparing corresponding SiC chiral devices by subsequently utilizing the SiC single crystal substrate with the modified double-layer graphene.
In addition, by changing parameters such as thermal evaporation temperature, reaction time, degassing temperature, degassing time and the like, ordered chiral molecular chains with different chain lengths and different densities can be obtained on the surface of double-layer graphene of the SiC single crystal substrate, and the embodiment of the invention can well control parameters such as average chain length, average width, coverage and the like of the finally generated ordered chiral molecular chains, thereby providing a simple and flexible solution for subsequent large-scale preparation of SiC chiral devices with different characteristics.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments, as illustrated in the accompanying drawings.
Drawings
FIG. 1 shows the chemical structural formula of two enantiomers of a 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecule of an embodiment of the invention in the 2D plane;
FIG. 2 shows chemical structural formulas of two chiral molecular chains prepared in the examples of the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples for the purpose of facilitating understanding to those skilled in the art.
The embodiment of the invention firstly provides a preparation method of ordered chiral molecular chains, which is used for separating two enantiomers shown in figure 1 and preparing corresponding chiral molecular long chains.
In a first embodiment of the present invention, a method for preparing an ordered chiral molecular chain is performed according to the following steps:
step one: the SiC single crystal substrate is cleaned to remove surface impurities, wherein the SiC single crystal can be 4H-SiC (0001) or 6H-SiC (0001).
Specifically, cleaning the SiC single crystal substrate to remove surface impurities thereof may include the steps of: doping n-type nitrogen with doping concentration of 1.3X10 18 cm -3 The size is 2X 12mm 2 The SiC single crystal substrate of (C) was rinsed with deionized water, then sonicated in deionized water and ethanol for 15min, respectively, and then nipped from ethanol with tweezers, followed by high purity N 2 And drying the surface of the SiC monocrystal substrate.
The size, doping concentration and doping type of the SiC single crystal substrate are only one example of the preparation method of the ordered chiral molecular chain provided by the embodiment of the present invention, and a person skilled in the art can select SiC single crystal substrates with different sizes, different doping concentrations and different doping types to prepare large-area ordered chiral molecular chains according to needs, and the technical schemes of adopting SiC single crystal substrates with different sizes, doping concentrations and doping types belong to the protection scope of the present invention, so that the description is omitted herein.
The first step of the embodiment of the invention is mainly to clean the SiC monocrystalline substrate before the SiC monocrystalline substrate is placed in the preparation cavity, remove impurities such as organic matters adsorbed on the surface of the SiC monocrystalline substrate, so as to avoid affecting the growth of subsequent graphene and enable the purity of the ordered chiral molecules generated subsequently to be higher.
Step two: placing SiC single crystal substrate under vacuum degree of 1.0X10 × -10 mbar～3.0×10 -10 In the preparation cavity of mbar, the SiC monocrystal substrate is heated and degassed in a direct current heating mode, and in the embodiment, the heating and degassing temperature range is 600-650 ℃, and the heating and degassing time is 4-8 hours; then, the SiC monocrystal substrate is circularly heated for 90min at 900 ℃ and 1400 ℃; and then cutting off direct current for heating, so that the temperature of the SiC monocrystalline substrate is reduced to the room temperature, and the surface of the SiC monocrystalline substrate uniformly forms double-layer graphene, so that the SiC monocrystalline substrate has better flatness in space compared with single-layer graphene.
The preparation cavity can be an ultrahigh vacuum preparation cavity of a scanning tunnel microscope, and the SiC single crystal substrate needs to be firstly fixed on a direct current heating sample rack matched with a heating table of the ultrahigh vacuum preparation cavity of the scanning tunnel microscope, si is upwards, then the SiC single crystal substrate is firstly placed in a rapid sample injection cavity connected with the ultrahigh vacuum preparation cavity, and then the vacuum is pumped to 5.0x10 -7 And (3) when the valve between the rapid sample injection cavity and the preparation cavity is opened, conveying the SiC single crystal substrate to a direct current heating table in the ultrahigh vacuum preparation cavity of the scanning tunnel microscope, heating the ultrahigh vacuum preparation cavity to 600-650 ℃, heating for 4-8 hours, and degassing the SiC single crystal substrate.
Wherein the cyclic heating of the SiC monocrystal substrate at 900 ℃ and 1400 ℃ for 90min comprises the following steps: heating the SiC monocrystal substrate at 900 ℃ for 15min, heating the SiC monocrystal substrate to 1400 ℃ for 15min to obtain first round heating, and repeating the steps until the third round heating is finished. Through the cyclic heating step at 900 ℃ and 1400 ℃, the flatness of the double-layer graphene on the surface of the SiC monocrystal substrate is improved, so that the chiral separation effect of the subsequent 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is greatly improved, the separation difficulty of the 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is greatly reduced, and the problem that the 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules cannot be subjected to chiral separation in a solution is solved.
When the ultra-high vacuum preparation cavity of the scanning tunnel microscope is selected as the preparation cavity, after direct current heating is cut off and the temperature of the SiC single crystal substrate is reduced to room temperature, the SiC single crystal substrate can be placed in an analysis cavity with the temperature of 77K of the scanning tunnel microscope, and double-layer graphene appearing on the surface of the SiC single crystal substrate is confirmed by the scanning tunnel microscope, and the double-layer graphene is uniformly distributed on the whole SiC single crystal substrate.
The second step of the embodiment of the invention is mainly to uniformly distribute double-layer graphene on the whole SiC single crystal substrate.
Step three:
placing SiC single crystal substrate with temperature lower than room temperature under vacuum degree of 1.0X10 -10 mbar～3.0×10 -10 The preparation cavity of mbar; thermally evaporating 2,2 '-diphenyl ethynyl-4, 4' -dibromobiphenyl molecules in a preparation cavity to enable the molecules to be chiral separated and self-assembled on the surface of double-layer graphene of the SiC single crystal substrate, and increasing the vacuum degree in the preparation cavity to 1.0 multiplied by 10 -9 mbar～3.0×10 -9 At mbar, molecules begin to be deposited, and after a period of time, large-area ordered chiral molecular chains are prepared.
Referring to fig. 2, chemical structural formulas of two chiral molecular chains prepared in the embodiment of the present invention correspond to a left-handed molecular chain formed by self-assembling a left-handed enantiomer (L) and a right-handed molecular chain formed by self-assembling a right-handed enantiomer (R), respectively.
The SiC single crystal substrate of the double-layer graphene appearing on the surface can be moved from the temperature of 77K of the analysis chamber of the scanning tunnel microscope to a sample stage at room temperature in the preparation chamber, and then 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules are immediately evaporated into the preparation chamber by thermal evaporation and deposited on the surface of the low-temperature SiC single crystal substrate.
In the first embodiment of the present invention, the SiC single crystal substrate has a temperature lower than 0 ℃ and a thermal evaporation temperature of 143 ℃ for thermally evaporating 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules, and the vacuum degree in the preparation chamber is increased to 1.0X10 -9 mbar～3.0×10 -9 And starting to deposit molecules at mbar, wherein the deposition time is 10min, and closing a molecular thermal evaporation power supply after the deposition is finished, so that the deposition process is finished.
After the deposition process is finished, the SiC monocrystal substrate can be conveyed to an analysis cavity, and the analysis cavity is observed by a low-temperature scanning tunnel microscope, so that a left-handed molecular chain formed by self-assembly of a left-handed enantiomer (L) and a right-handed molecular chain formed by self-assembly of a right-handed enantiomer (R) can be uniformly and orderly distributed on the surface of the double-layer graphene.
In the first embodiment of the invention, the chain lengths of the left-handed molecular chains and the right-handed molecular chains are distributed between 97nm and 105nm, the average chain length is 100nm, the chiral molecular chain width is distributed between 1.9nm and 2.0nm, the average width is 1.95nm, and the compactness is 60%, wherein the compactness is the coverage density of ordered chiral molecules on the surface of the double-layer graphene.
The second embodiment of the present invention is different from the first embodiment in that: in the third step, the evaporation temperature was 145℃and the deposition time was 10min, and other steps and parameters were the same as those in the first embodiment of the present invention. In the second step, the double-layer graphene appearing on the surface of the SiC monocrystal substrate is confirmed by a scanning tunnel microscope, the temperature of an analysis cavity of the scanning tunnel microscope is 77K, so that the temperature of the SiC monocrystal substrate is always lower than room temperature and even lower than 283K, the chain length of chiral molecules prepared by the second embodiment of the invention is distributed between 153nm and 168nm, the average length is 160nm, the width of chiral molecule chains is distributed between 1.9nm and 2.0nm, the average width is 1.95nm, and the compactness is 68%.
In the second embodiment of the invention, in order to prepare ordered chiral chain molecules with longer average chain length and higher coverage density on the surface of the double-layer graphene compared with the first embodiment of the invention, the evaporation temperature is correspondingly increased in the third step, so that the separation and self-assembly of 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules to generate long chains are facilitated.
The third embodiment of the present invention is different from the first and second embodiments in that: the evaporation temperature in the third step is 145 ℃, the deposition time is 15min, and other steps and parameters are the same as those in the first and second embodiments of the invention. The chiral molecule chain length prepared by the third embodiment of the invention is distributed between 195nm and 214nm, the average length is 200nm, the chiral molecule chain width is distributed between 1.9nm and 2.0nm, the average width is 1.95nm, and the chiral molecule chain length is uniformly distributed on the surface of the SiC single crystal substrate, and the compactness is 75%.
In the third embodiment of the invention, in order to prepare the ordered chiral molecular chain with longer average chain length and higher coverage rate compared with the second embodiment of the invention, the deposition time is correspondingly increased in the third step, so that the 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules are more favorable for separating and self-assembling into long chains on the SiC single crystal substrate.
According to the preparation method of the ordered chiral molecular chain, provided by the embodiment of the invention, the parameters of different chain lengths and different densities of the ordered chiral molecular chain are finally obtained on the surface of the double-layer graphene of the SiC single crystal substrate by adjusting the degassing heating temperature, the heating time, the evaporating temperature, the deposition time and the temperature of the SiC single crystal substrate, so that the average chain length, the average width, the coverage of the ordered chiral molecular chain are better controlled, and the like.
In summary, the preparation method of the ordered chiral molecular chain provided by the embodiment of the invention has simple process, can prepare a large-area ordered chiral molecular long chain on the surface of the SiC monocrystal, greatly improves the controllability, the high efficiency, the repeatability and the high purity of the corresponding chiral molecular in the preparation process, and enables the preparation of the corresponding ordered chiral molecular chain through the 2,2 '-diphenyl ethynyl-4, 4' -dibromobiphenyl molecule controllably, efficiently and high purity to be possible to realize industrialized application.
The embodiment of the invention also provides a SiC device substrate, which comprises a SiC single crystal substrate, wherein double-layer grapheme and ordered chiral molecular chains uniformly distributed on the surface of the double-layer grapheme are uniformly formed on the surface of the SiC single crystal substrate by the ordered chiral molecular chain preparation method, so that the double-layer grapheme on the surface of the SiC single crystal substrate is modified, and conditions are provided for preparing corresponding SiC chiral devices by using the modified double-layer grapheme in the follow-up SiC device substrate.
The SiC device substrate provided by the embodiment of the invention has double-layer graphene and the structure of ordered chiral molecular chains on the double-layer graphene, and parameters such as average chain length, average width, coverage and the like of the ordered chiral molecular chains can be adjusted by changing preparation process parameters, so that a simple and flexible solution is provided for subsequent large-scale preparation of SiC chiral devices with different characteristics.
Finally, any modification or equivalent replacement of some or all of the technical features by means of the structure of the device according to the invention and the technical solutions of the examples described, the resulting nature of which does not deviate from the corresponding technical solutions of the invention, falls within the scope of the structure of the device according to the invention and the patent claims of the embodiments described.
Claims (9)
1. A method for preparing an ordered chiral molecular chain, comprising the steps of:
cleaning a SiC monocrystalline substrate, and removing impurities on the surface of the SiC monocrystalline substrate;
heating and degassing the SiC monocrystal substrate in a direct current heating mode; heating the SiC monocrystalline substrate at 900 ℃ for 15min, heating the SiC monocrystalline substrate to 1400 ℃ for 15min to perform first round heating, and repeating the steps until the third round heating is finished; then cutting off direct current heating to cool the SiC monocrystalline substrate to room temperature, so that double-layer graphene is uniformly formed on the surface of the SiC monocrystalline substrate;
placing SiC single crystal substrate under vacuum degree of 1.0X10 × -10 mbar～3.0×10 -10 The preparation cavity of mbar, siC monocrystal substrate temperature is lower than room temperature, 2 '-diphenyl ethynyl-4, 4' -dibromobiphenyl molecule is thermally evaporated in the preparation cavity, chiral separation and self-assembly are carried out on the double-layer graphene surface of the SiC monocrystal substrate, and when the vacuum degree in the preparation cavity is increased to 1.0x10 -9 mbar～3.0×10 -9 At mbar, deposition of molecules begins, producing ordered chiral molecular chains.
2. The method for preparing ordered chiral molecular chains according to claim 1, wherein the preparation chamber is an ultra-high vacuum preparation chamber of a scanning tunneling microscope.
3. The method for producing an ordered chiral molecular chain according to claim 1, wherein the SiC single crystal substrate is heated to 600 to 650 ℃ and the heating is continued for 4 to 8 hours to heat and degas the SiC single crystal substrate.
4. The method for preparing ordered chiral molecular chains according to claim 1, wherein the thermal evaporation temperature of the thermally evaporated 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 140-150 ℃ and the deposition time is 10-20 min.
5. The method for preparing ordered chiral molecular chains according to claim 1, wherein the thermal evaporation temperature of thermally evaporating 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 145 ℃, the temperature of SiC single crystal substrate is lower than zero, and the deposition time is 10min.
6. The method for preparing ordered chiral molecular chains according to claim 1, wherein the thermal evaporation temperature of thermally evaporating 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 143 ℃, the temperature of SiC single crystal substrate is lower than zero, and the deposition time is 10min.
7. The method for preparing ordered chiral molecular chains according to claim 1, wherein the thermal evaporation temperature of thermally evaporating 2,2 '-diphenylethynyl-4, 4' -dibromobiphenyl molecules is 145 ℃, the temperature of SiC single crystal substrate is lower than zero, and the deposition time is 15min.
8. The method for producing an ordered chiral molecular chain according to claim 1, wherein the SiC single crystal is 4H-SiC (0001) or 6H-SiC (0001).
9. A SiC device substrate, comprising: a SiC single crystal substrate on the surface of which double-layer graphene and ordered chiral molecular chains uniformly arranged on the surface of the double-layer graphene are uniformly formed by the ordered chiral molecular chain preparation method according to any one of claims 1 to 8.
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