Double-layer heterostructure device, design method and application in spin thermoelectric conversion

Abstract

The invention discloses a double-layer heterostructure device, a design method and application in spin thermoelectric conversion, and belongs to the technical field of nanoelectronics. The design method comprises the following steps: cutting two-dimensional C2N into single-layer C2NNR; based on a single-layer C2NNR, considering the alignment condition of different atoms between an upper layer and a lower layer in a transport period, and constructing b-C2NNR van der Waals heterostructures with different stacking modes; the bl-C2NNR van der Waals heterostructures in different stacking modes are used for respectively building a double-layer heterostructure device; under the condition of zero bias, the temperature of the left electrode and the right electrode of the double-layer heterostructure device and the temperature difference of the left electrode and the right electrode are changed to cause the double-layer heterostructure device to generate thermal driving current, it can be calculated that charge current Ic is restrained, at the moment, the double-layer heterostructure device can conduct spinning thermoelectric conversion, and therefore the material library of low-dimensional nano-electronic devices is expanded. The material has the potential to become one of excellent reserve materials of spinning thermoelectric nano devices.

Description

Technical Field

[0001] The present invention belongs to the field of nanoelectronics technology, and particularly relates to a bilayer heterostructure device, a design method thereof, and an application in spin thermoelectric conversion. Background Art

[0002] Spintronics originated in the 1980s and has developed with the in-depth study of the spin properties of electrons. The development of this field benefits from the progress of semiconductor materials, magnetic materials, and nanotechnology. In particular, the discovery of phenomena such as the giant magnetoresistance effect has shown broad application prospects for spintronics in data storage and logic devices. Spintronics realizes more efficient data storage and logical operations by manipulating the spin state. The advantages of spintronic devices include lower energy consumption, higher storage density, and faster data processing speed. Common spintronic devices include spin rectifiers, spin filters, spin valves, tunnel magnetoresistance devices, etc., which are widely used in magnetic storage, sensors, and quantum computing. In 2004, a major scientific breakthrough in the field of materials science - Geim and Novoselov successfully prepared the first two-dimensional single-layer material graphene by mechanical exfoliation of three-dimensional graphite with tape. The discovery of graphene has set off a wave of research on low-dimensional new materials.

[0003] Recently, through a simple bottom-up wet chemical reaction, a two-dimensional material C2N-h2D with a highly ordered pore structure has been synthesized. This new material, like porous graphene, has uniformly distributed hexagonal pores, uniformly distributed nitrogen atoms and holes. The presence of pores makes it easier to adsorb metal particles, showing excellent optical, thermal, and electronic properties.

[0004] However, at present, there are few types of materials that can effectively achieve the spin Seebeck effect and complete thermoelectric conversion, and there are significant differences in performance. The performance of many materials is not ideal at high temperatures, which limits their use in practical applications; the intensity of the spin Seebeck effect usually changes with temperature, which affects the stability and predictability in different working environments. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a bilayer heterostructure device, a design method thereof, and an application in spin thermoelectric conversion, which solves the problems in the prior art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A design method for a bilayer heterostructure device, comprising the following steps:

[0008] Cut two-dimensional C2N into single-layer C2NNR;

[0009] Based on single-layer C2NNR, considering the alignment of different atoms between the upper and lower layers within a transport cycle, build bl-C2NNR van der Waals heterostructures with different stacking patterns;

[0010] Use bl-C2NNR van der Waals heterostructures with different stacking patterns to build bilayer heterostructure devices respectively.

[0011] Furthermore, the single-layer C2NNR is denoted as 4ZCC, with a width of 1, and is symmetric up and down and in a zigzag shape terminated by carbon atoms.

[0012] Furthermore, the bl-C2NNR van der Waals heterostructure includes two stacking patterns:

[0013] The atomic positions in the first layer completely coincide with those in the second layer, denoted as: 4ZCC_AA;

[0014] The atoms in the second layer are located in the gaps between the atoms in the first layer, denoted as: 4ZCC_AB.

[0015] Furthermore, considering different stacking patterns under the alignment of different atoms between the upper and lower layers within a transport cycle, the atomic positions in the upper layer remain fixed, and the atoms in the lower layer move to the right within one cycle to make the alignment of the upper and lower layer atoms different, denoted as move_n_AA / AB, where n is the number of times the atoms in the lower layer move to the right.

[0016] Furthermore, the bilayer heterostructure device is a nanoelectronic device composed of a left electrode, a central scattering region, and a right electrode.

[0017] The bilayer heterostructure device is designed using the above design method for bilayer heterostructure devices.

[0018] The above bilayer heterostructure device is applied in spin thermoelectric conversion.

[0019] Furthermore, the application includes: under zero bias voltage conditions, changing the temperatures of the left and right electrodes of the bilayer heterostructure device, the temperature difference between the left and right electrodes causes a thermally driven current to be generated, and the spin-up current I ↑ and the spin-down current I ↓ The charge current I obtained by adding them together c is suppressed, and the bilayer heterostructure device can perform spin thermoelectric conversion.

[0020] Furthermore, the temperature T of the left electrode of the bilayer heterostructure device L = 500K, and the temperature difference ΔT between the left and right electrodes = 60K.

[0021] A method for spin thermoelectric conversion using the double - layer heterostructure device described above, the method being: under zero - bias conditions, applying different temperatures to the left and right electrodes of the double - layer heterostructure device to make its charge current I c be suppressed.

[0022] Advantages of the present invention:

[0023] 1. The present invention uses the bl - C2NNR van der Waals heterostructure in the stacked case to build a double - layer heterostructure device. Due to its spin thermoelectric conversion effect, the double - layer heterostructure device expands the material library of low - dimensional nano - electronic devices and has the potential to become one of the excellent reserve materials for spin thermoelectric nano - devices.

[0024] 2. The single - layer C2NNR in the intrinsic state shows metallic properties. Through the stacking method, the inter - layer coupling effect will cause the conduction band and valence band to split, forming two sub - bands, upper and lower. The van der Waals heterostructure obtains a larger spin current while maintaining the original spin - resolved current property, suppresses the charge current, realizes the spin Seebeck effect, and completes the thermoelectric conversion.

[0025] 3. The present invention uses double - layer stacking to drive the spin - electron movement by using the temperature difference. In the ferromagnetic state, a larger spin current can be formed and the applicable temperature range is relatively wide. It effectively utilizes waste heat to complete thermoelectric conversion and reduces energy waste. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 is the unit cell (C2NNR) and energy - band structure diagram of the single - layer C2N nanoribbon;

[0028] Figure 2 is the AA - and AB - stacked double - layer C2N (bl - C2NNR) van der Waals heterostructure and energy - band structure diagram;

[0029] Figure 3 is ten stacking methods in which the atoms of the upper - layer C2NNR remain stationary and all the atoms of the lower - layer move one period to the right along the z - direction;

[0030] Figure 4 is that after the lower - layer atoms complete the periodic movement, there are five configurations with non - zero magnetic moments and their corresponding energy - band structures

[0031] Figure 5 is the electronic device structures in six cases of the single - layer C2NNR and five configurations with non - zero magnetic moments;

[0032] Figure 6 Transmission spectra of six cases for single-layer C2NNR and five configurations with non-zero magnetic moments;

[0033] Figure 7 It is the eigenstate of the single layer and 4ZCC_AB stacking structure at the Fermi level;

[0034] Figure 8 Spin-resolved current, spin current and charge current under single layer and 4ZCC_AB. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Example 1

[0037] The design method of a double-layer heterostructure device comprises the following steps:

[0038] S1, the 2D C2N is cut into a zigzag single-layer C2N nanoribbon unit cell (C2NNR) with a width of 1 and symmetric top and bottom with carbon atoms as the terminal, denoted as 4ZCC;

[0039] The structure and band structure of single-layer C2NNR are shown in Figure 1 As shown in (a) and (b) in the figure, a zigzag monolayer C2NNR with a width of 1 and a symmetric carbon atom as the terminal is constructed. The edge of the nanoribbon is terminated by hydrogen (H) atoms to eliminate dangling bonds. The vacuum layer in the x and y directions must be greater than The cell structure is optimized by using density functional theory and non-equilibrium Green's function method with the calculation software Quantum ATK. During the optimization, the lattice constant in the z direction is fixed so that the forces between atoms are less than The K-space grid was set to 1×1×15, the cutoff energy was set to 80 Hartree, the band structures in the ferromagnetic and antiferromagnetic states were calculated, and the electronic properties of the single-layer C2NNR were analyzed.

[0040] Figure 1 As can be seen from (b) in the figure, the two cross bands with spin up and spin down are split at the Fermi level and are separated above and below the Fermi level. At the same time, only one of the two cross bands passes through the Fermi level, and the single-layer C2NNR exhibits metallic properties.

[0041] S2. Based on the primitive cell of monolayer C2N nanoribbon, considering the alignment of different atoms between the upper and lower layers within a transport cycle, construct bilayer C2NNR (bl-C2NNR) van der Waals heterostructures with different stacking patterns;

[0042] Considering different stacking patterns (AA-: the atomic positions in the first layer coincide exactly with those in the second layer; AB-: the atoms in the second layer are located in the gaps between the atoms in the first layer) under the alignment of different atoms between the upper and lower layers within a transport cycle, use Quantum ATK software for optimization, and the forces between atoms are all less than And introduce the interlayer van der Waals force, set as DFT-D3, calculate the band structures in the ferromagnetic state and the intra-layer and inter-layer antiferromagnetic states. Due to the interlayer charge transfer in the bilayer van der Waals heterojunction, the strong coupling between layers leads to a magnetic moment of 0 for some configurations, and all states merge into a non-magnetic state, which is not conducive to the study of spin-polarized transport. Therefore, only focus on the ferromagnetic state that can be stabilized by the magnetic field, and perform electronic property analysis on the primitive cells of five bl-C2NNR heterostructures with non-zero magnetic moments and different stacking patterns;

[0043] Calculate the total energy E in the ferromagnetic state for five bl-C2NNR structures with non-zero magnetic moments total , and investigate the stability of all configurations, as shown in Table 1; during the process of keeping the upper-layer atomic positions fixed and moving the lower-layer atoms to the right within the period, the energy of the bilayer structure approximately shows a gradually decreasing trend, and the structural stability gradually increases.

[0044] Table 1 Total energies of bl-C2NNR structures under different stacking conditions

[0045] <![CDATA[E total (eV)]]> 4ZCC_AB -14868.18725 move_4_AB -14868.86481 move_5_AA -14868.66868 move_6_AB -14868.89211 move_8_AB -14868.91670

[0046] Figure 2 (a) in is the bl-C2NNR van der Waals heterostructure under AA stacking, denoted as 4ZCC_AA, where the upper one is the top view and the lower one is the side view; Figure 2 (b) in shows the band structure of 4ZCC_AA; it can be seen that: the bands of 4ZCC_AA are spin-degenerate and the total magnetic moment is 0.

[0047] Figure 2 (c) in is the bl-C2NNR van der Waals heterostructure under AB stacking, denoted as 4ZCC_AB, where the upper one is the top view and the lower one is the side view; Figure 2 (d) in shows the band structure of 4ZCC_AB; it can be seen that: through the stacking method, the interlayer coupling effect will cause the conduction band and valence band to split, forming two sub-bands above and below. Therefore, 4ZCC_AB has 4 crossing bands, and 3 bands respectively cross the Fermi level, showing metallic characteristics.

[0048] Consider different stacking methods under the alignment of different atoms between the upper and lower layers within a transport cycle. The positions of the upper-layer C2NNR atoms remain fixed, and the lower-layer atoms move to the right within one cycle, resulting in different alignments between the upper and lower layers, denoted as move_n_AA / AB, where n represents the number of times the lower-layer atoms move to the right;

[0049] Figure 3 It shows ten stacking methods where the upper-layer C2NNR atoms remain fixed and the lower-layer atoms move to the right along the z direction within one cycle.

[0050] Figure 4 In (a)-(e), it respectively represents that the lower-layer atoms complete the periodic movement, and there are five configurations with non-zero magnetic moments, namely: 4ZCC_AB, move_4_AB, move_5_AA, move_6_AB, move_8_AB; Figure 4 In (f)-(j), it respectively represents the band structures corresponding to these five configurations with non-zero magnetic moments; it can be seen that: the band structures of these configurations are similar to that of 4ZCC_AB, all having 4 crossing bands and presenting metallic characteristics.

[0051] S3. Use bl-C2NNR van der Waals heterostructures with different stacking methods to separately construct bilayer heterostructure devices;

[0052] Select bl-C2NNR van der Waals heterostructures under different stackings to construct nanoelectronic devices (bilayer heterostructure devices) composed of a left electrode - central scattering region - right electrode, with the transport direction along the z direction.

[0053] Figure 5 In (a), it is the structural diagram of the nanoelectronic device constructed by a single-layer C2NNR; Figure 5 In (b)-(f), they are the structural diagrams of the nanoelectronic devices constructed by five configurations with non-zero magnetic moments; it can be seen that the green regions are respectively the left and right electrodes of the device, and the white region is the central scattering region of the device.

[0054] Calculate and analyze their transmission spectra through the transmission coefficient formula, and observe the electron transport differences from the single-layer C2N-h2D nanoribbon device; the transmission coefficient formula is:

[0055]

[0056] where τ ↑ / ↓ (E) is the spin-resolved transmission coefficient, which includes: τ ↑ (E) and τ ↓ (E) are respectively the spin-up and spin-down transmission coefficients; G R (E) and G A (E) are respectively the retarded and advanced Green's functions of the scattering region, and ΓL and Γ R are the coupling matrices of the left and right electrodes, respectively.

[0057] The transmission spectra of the nanoelectronic devices constructed by single-layer C2NNR and the electronic devices constructed by five configurations with non-zero magnetic moments are as shown in (a)-(f) of Figure 6 . It can be seen from the figure that, compared with single-layer C2NNR, the transmission coefficients at the Fermi level for all configurations have increased. Corresponding to Figure 4 , in the band structures of the three configurations of 4ZCC_AB, move_5_AA, and move_6_AA, three bands cross the Fermi level among the four crossing bands. Therefore, the transmission coefficient of the nanoelectronic devices constructed by these three configurations at the Fermi level is 3. Similarly, in the band structures of the two configurations of move_4_AB and move_8_AB, two bands cross the Fermi level. Therefore, the transmission coefficient of the nanoelectronic devices constructed at the Fermi level is 2.

[0058] The eigenstates of single-layer C2NNR and the 4ZCC_AB stacking structure at the Fermi level are as shown in Figure 7 . It can be seen that the transmission coefficient of the nanoelectronic device constructed by single-layer C2NNR at the Fermi level is 1, so there is only 1 transmission channel. Further calculating the transport eigenstates of the 4ZCC_AB configuration at the Fermi level, it can be clearly observed that due to the charge transfer between the interlayer atoms, the originally split 2 transmission channels become three. The transmission coefficient of the nanoelectronic device constructed by 4ZCC_AB at the Fermi level is 3, so there are 3 transmission channels. Consistent with the law of the band structure after stacking, the interlayer coupling effect will cause the conduction band and valence band to split, resulting in the accumulation of the transmission coefficient at the Fermi level being greater than or equal to 2, further enhancing the thermoelectric effect of the device.

[0059] Example 2

[0060] In this example, the application of the double-layer heterostructure device designed in Example 1 in spin thermoelectric conversion is introduced;

[0061] For the double-layer heterostructure device designed in Example 1, under zero bias voltage conditions, by changing the temperatures of the left and right electrodes, with the left electrode as the high-temperature region (temperature T L ), and the right electrode as the low-temperature region (temperature T R ), a temperature difference ΔT = T L - T R is formed in the system. This temperature difference causes different carrier concentrations at both ends of the device, forming different Fermi-Dirac distributions at both ends (the formula is where k B is the Boltzmann constant, and the Fermi-Dirac distribution is determined by the energy E and temperature T). Then, the spin-polarized current I formed by the thermal drive in the device↑ / ↓ It can be calculated by the Landauer-Büttiker formula:

[0062]

[0063] where e represents the electron charge and h represents the Planck constant; f L and f R represent the Fermi-Dirac distributions of the left and right electrodes in the non-equilibrium state respectively, and τ ↑ / ↓ is the spin transmission coefficient for spin-up and spin-down.

[0064] The spin-polarized current I ↑ / ↓ includes the spin-up current I ↑ and the spin-down current I ↓ ; the spin current I ↑ / ↓ and the charge current I s are calculated through the spin-polarized current I c ; the generated spin current passes through I s = I ↑ - I ↓ to calculate, and the charge current is calculated by I c = I ↑ + I ↓ to calculate.

[0065] For the nanoelectronic device built with monolayer C2NNR, its spin-polarized current I ↑ / ↓ and the corresponding spin current I s , charge current I c results are shown in (a) and (c) of Figure 8 respectively; for the bilayer heterostructure device (with the stacking structure of 4ZCC_AB), its spin-polarized current I ↑ / ↓ and the corresponding spin current I s , charge current I c results are shown in (b) and (d) of Figure 8 respectively;

[0066] It can be seen from (b) and (d) of Figure 8 that: compared with the monolayer structure, the spin-up current I ↑ and the spin-down current I ↓ show opposite signs and comparable magnitudes, thus forming a huge spin current I s , while the charge current I c is almost completely suppressed, generating a significant spin-dependent Seebeck effect. Therefore, the bl-C2NNR van der Waals heterostructure can become an effective thermoelectric conversion electronic device in the ferromagnetic state.

[0067] An increase in the temperature of the left electrode or an increase in the temperature difference can both lead to a larger spin current. Moreover, the spin current in this embodiment reaches a maximum value of 267.31 nA under the conditions of T L = 500 K and ΔT = 60 K.

[0068] In the description of this specification, the descriptions with reference to the terms "one embodiment", "example", "specific example", etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0069] The foregoing shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification is only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements fall within the scope of the present invention claimed.

Claims

1. A design method for a bilayer heterostructure device, characterized in that, The following steps are involved: Cut the 2D C2N into a single-layer C2NNR; Based on a single-layer C2NNR, the alignment of different atoms between the upper and lower layers in a transport cycle is considered to build bl-C2NNR van der Waals heterostructures with different stacking modes; Double-layer heterostructure devices were constructed using bl-C2NNR van der Waals heterostructures with different stacking methods.

2. The design method of the bilayer heterostructure device according to claim 1, wherein The single-layer C2NNR is denoted as 4ZCC, has a width of 1, and is in a zigzag shape that is symmetrical up and down and terminated with carbon atoms.

3. The design method of the double-layer heterostructure device according to claim 2, characterized in that, There are two stacking modes of bl-C2NNR van der Waals heterostructures: The atomic positions of the first layer completely coincide with those of the second layer, denoted as: 4ZCC_AA; The atoms in the second layer are located in the gaps between the atoms in the first layer, denoted as: 4ZCC_AB.

4. The design method of the double-layer heterostructure device according to claim 3, characterized in that, Consider different stacking methods under the condition of different atomic alignment between the upper and lower layers in a transport cycle. The upper atomic position remains stationary, and the lower atomic moves to the right in a cycle, making the upper and lower atomic alignment different, denoted as move_n_AA / AB, where n is the number of times the lower atomic moves to the right.

5. The design method of the double-layer heterostructure device according to claim 1, wherein The double-layer heterostructure device is a nanoelectronic device consisting of a left electrode, a central scattering region and a right electrode.

6. Double-layer heterostructure device, characterized in that, The device is designed using the design method for a double-layer heterostructure device according to any one of claims 1 to 5.

7. Application of the double-layer heterostructure device according to claim 6 in spin thermoelectric conversion.

8. The application according to claim 7, wherein The application includes: under zero bias conditions, changing the temperature of the left and right electrodes of the double-layer heterostructure device, the temperature difference between the left and right electrodes causes it to generate a thermal driving current, and the spin-up current I of the thermal driving current ↑ and the spin-down current I ↓ The charge current I obtained by adding c is suppressed, and the double-layer heterostructure device is capable of spin thermoelectric conversion.

9. The application according to claim 8, wherein The temperature T of the left electrode of the double-layer heterostructure device L = 500 K, and the temperature difference ΔT between the left and right electrodes is 60 K.

10. A method for spin thermoelectric conversion using the double-layer heterostructure device according to claim 6, characterized in that, Under zero bias conditions, different temperatures are applied to the left and right electrodes of the double-layer heterostructure device to suppress its charge current I c from being generated.

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