A method for regulating the conductivity of carbon 60 single crystal and its application

Abstract

The present invention belongs to the technical field of semiconductor devices, and relates to a method for regulating the conductivity of single-crystalline C60 and its application. A substrate with a source electrode, a drain electrode, a gate electrode, and a channel reference electrode is provided. A strip-shaped single-crystalline C60 layer is laminated onto the substrate to prepare a four-probe air dielectric layer field effect transistor. An ionic liquid is injected into the gap between the strip-shaped single-crystalline C60 and the gate electrode. The conductivity of the single-crystalline C60 is regulated by adjusting the gate voltage and the radius of the cation in the ionic liquid, and the temperature during the regulation process is from 0 to the freezing temperature of the ionic liquid. The present invention regulates the conductivity of the C 60 single crystal and the insulating metal phase transition through the size of the dielectric layer ionic liquid.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices and relates to a method for regulating carbon 60 (C 60 ) Methods of single crystal conductivity and their applications. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] According to the inventor's research, at present, C 60 The conductivity and insulating metal phase transition of C are mainly regulated by chemical doping with alkali metal ions. For example, 1:1 doping can achieve the metallic phase, and 3:1 doping can achieve the transition from insulating to superconducting phase. However, alkali metal ion doping is an irreversible process and cannot continuously regulate C 60 The electronic state of the single crystal is poor in air stability after doping. In addition, alkali metal ion doping also destroys the C 60 The crystal structure of single crystals causes electronic disorder to a certain extent. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a method for regulating the conductivity of carbon 60 single crystal and its application, which can avoid the defects caused by alkali metal ion doping.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] On the one hand, a method for regulating the conductivity of a carbon 60 single crystal is provided. A substrate having a source electrode, a drain electrode, a gate electrode and a channel reference electrode is provided. A strip carbon 60 single crystal is laminated onto the substrate to prepare a four-probe air dielectric layer field effect transistor (FET). An ionic liquid is injected into the gap between the strip carbon 60 single crystal and the gate electrode. The conductivity of the carbon 60 single crystal is regulated by adjusting the gate voltage and the radius of the cations in the ionic liquid. The temperature range during the regulation process is from 0 to the solidification temperature of the ionic liquid.

[0007] The present invention has found through research that conductivity, electron mobility and double layer capacitance are all related to the radius of cations in ionic liquids. For cations with smaller radius, an obvious peak appears on the measured conductivity curve, and at 1e / C 60 The conductivity is almost completely suppressed near the charge density of 1.7 e / C, showing the characteristics of a Mott insulator. However, increasing the radius of the cation in the ionic liquid will sharply reduce the degree of suppression, which allows the method of the present invention to explore the 1.7 e / C 60The charge transfer of the device is greatly improved, and it exhibits band-like charge transfer, with a tendency to transform into a metallic phase at low temperatures.

[0008] On the other hand, an application of the above method for regulating the conductivity of carbon 60 single crystal is to regulate the insulating metal phase transition of carbon 60 single crystal.

[0009] Organic field effect transistors are used as driving circuits for the backplane, which are low-cost, flexible, and portable. They can be applied to 3D imaging projection and wearable three-dimensional technology, such as smart watches and ultra-thin / transparent / flexible electronic skins that can be used to monitor various functions of the body. However, the biggest problem with organic field effect transistors is how to achieve the largest possible charge density and conductivity at the lowest gate voltage. Due to the above method of the present invention, the charge density and conductivity can be adjusted by adjusting the gate voltage and the cation radius. Under a certain gate voltage, only the cation radius needs to be adjusted to adjust the charge density and conductivity. Therefore, the above method of the present invention can solve the above problem. Therefore, in the third aspect, a method for adjusting the conductivity of carbon 60 single crystals is used in the design and / or preparation of organic field effect transistors.

[0010] In a fourth aspect, a method for regulating the electrical conductivity of carbon 60 single crystal is used in the design and / or preparation of electronic devices.

[0011] When voltage is applied to the ionic liquid dielectric layer, positive and negative ions move toward the gate and semiconductor layer respectively, forming a positive and negative ion structure close to a single layer, and the electrolyte is electrically neutral inside, and the thickness of the single layer of positive and negative ions is only 1nm. Therefore, under the same dielectric constant, the charge density induced by the ionic liquid is two to three orders of magnitude higher than that of the traditional dielectric layer (>100nm, to prevent needle defects and large leakage currents in the dielectric layer). The large carrier concentration promotes the conductivity of some inorganic two-dimensional semiconductor materials to increase, from an insulator to a metal phase transition (MIT), which means that electronic devices run faster and have stronger storage capacity. At the same time, the insulator-metal transition induced by the ionic liquid gate can also support low-power microelectronic systems, that is, lower power is required to charge the electronic device, and the device operates with less power and a longer service life. Since the method provided by the present invention can adjust the charge density and conductivity by regulating the gate voltage and the cation radius, it can guide the design of electronic devices with lower power.

[0012] The beneficial effects of the present invention are:

[0013] The present invention studies C through organic semiconductor electric double layer transistor (EDLT) 60 Two-dimensional transport in single crystals at high surface charge densities, up to or exceeding 10 14 cm -2 or 1e / C 60The study showed that the method of the present invention enables clear evidence of strong ion-electron and electron-electron interactions in these systems, in particular, the C gate-regulated with two ionic liquids, DEME-TFSI and N4441-TFSI. 60 σ of single crystal s There is an obvious peak in the -n relationship. This peak is at the surface electron accumulation n = 0.5e / C 60 Nearby, and at n = 1e / C 60 The σ is completely suppressed near s Changing the ionic liquid to N8881-TFSI increases the cation radius, resulting in two major changes. First, σ s Obviously improved, and at n = 1e / C 60 σ s Secondly, it is possible to G Scan to a larger value, the electron accumulation exceeds 10 14 cm -2 In addition, and more importantly, increasing the cation radius of the ionic liquid weakens the C 60 The corrugated surface potential at the interface between the crystal and the ionic liquid achieves higher conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0015] Figure 1 Schematic diagram of the device structure prepared in the embodiment of the present invention.

[0016] Figure 2 C prepared in the embodiment of the present invention 60 Characterization of single crystal EDLTs; (a) C stacked along the

[111] direction 60 Crystal structure; (b) Out-of-plane XRD shows that the main crystal plane corresponds to the (111) close-packed plane; Inset: rocking curve of the (111) peak; (c) AFM height image of the (111) plane; Inset: AFM height curve along the dotted line direction (single molecule step height); (d) Molecular structures of three ionic liquids; (e) C 60 Schematic diagram of the cross section of a single crystal EDLT (top) and the corresponding top-down optical microscope image (bottom); the channel reference electrodes V1 and V2 used for four-probe testing can be clearly observed in the microscope image; the gap from the gate to the crystal is 5 μm; (f) At 215K, different ionic liquid dielectric layers C 60 σ of single crystal EDLTs s With the gate voltage V GThe scan rate is 20 mV·s -1 .

[0017] Figure 3 DEME-TFSI gate control C at 215K in the embodiment of the present invention 60 Electrical properties of single crystal EDLT; (a) conductivity σ s With V G The relationship between V G The maximum applied voltage is 2.5V and V D = 0.2 V; hysteresis is counterclockwise; inset: calculated four-probe mobility vs. V G relationship; (b) at different V G I at scan rate disp -V G Test;I disp -V G The area integral of C determines the charge density (n) induced by the ionic liquid, as shown in the shaded area; (c) C 60 I of single crystal EDLT D -V G and σ s -V G Characteristic curve, V G =4V; (d) The corresponding I disp -V G Test; solid and hollow circles represent the electron density n during charge and discharge, respectively; voltage scan rate is 20 mV·s -1 .

[0018] Figure 4 The gate control C of the ionic liquid with a larger cation radius at 215K in the embodiment of the present invention is 60 Performance of single-crystal EDLTs; (a) Semi-logarithmic I of EDLT controlled by N4441-TFSI gate D -V G Characteristic curve; V D =0.2V, maximum V G =4.5V; (b) The corresponding I disp -V G and nV G Curve; (c) Semi-logarithmic I of EDLT controlled by N8881-TFSI gate D -V G Curve; V D =0.2V, maximum V G =5.5V; (d) The corresponding I disp -V G and nV GCurve; V in all figures G The scan rate was 20 mV·s -1 .

[0019] Figure 5 The dielectric layers C of different ionic liquids in the embodiments of the present invention are 60 Single crystal EDLT performance; (a) Three ionic liquids (solid circles: N8881-TFSI; solid squares: N4441-TFSI; hollow squares: DEME-TFSI) gate-regulated C 60 σ of single crystal EDLTs s -n curve comparison; (b) V G =2.5V when μ and V T The relationship between the size of the cation radius and the error bars represent the standard deviation of at least eight devices tested for each ionic liquid; (c) C 60 Four-probe mobility versus temperature for single-crystal EDLTs; all devices were cooled to 215K and then slowly heated to 250K, with continuous measurements at 5K intervals; (d) different cation size / C 60 Schematic diagram of the surface electrostatic potential distribution at the interface. Smaller cations lead to C 60 The electrons in the crystal are strongly localized, presenting a narrow and sharp ripple-like potential distribution; large cations cause the Coulomb potential well to become shallower, the electron localization becomes weaker, and a relatively smooth potential distribution is presented. DETAILED DESCRIPTION

[0020] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0022] In view of the existing alkali metal ion doping C 60 The regulation of conductivity has problems such as irreversible process, inability to continuously regulate, poor air stability, and destruction of crystal structure. The present invention proposes a method for regulating C 60 Methods of single crystal conductivity and their applications.

[0023] A typical embodiment of the present invention provides a method for regulating C 60A method for single crystal conductivity is provided, wherein a substrate having a source electrode, a drain electrode, a gate electrode and a channel reference electrode is provided, and a strip C 60 The single crystal is laminated onto a substrate to prepare a four-probe air dielectric field effect transistor. 60 Ionic liquid is injected into the gap between the single crystal and the gate, and C is controlled by adjusting the gate voltage and the radius of the cations in the ionic liquid. 60 The single crystal conductivity is adjusted in the temperature range from 0 to the solidification temperature of the ionic liquid.

[0024] The present invention has found that conductivity, electron mobility and double-layer capacitance are all related to the radius of cations in the electrolyte. Under a constant gate voltage, the charge density and conductivity can be adjusted by adjusting the size of the cations in the ionic liquid, thereby adjusting its conductive properties.

[0025] Studies have shown that irreversible degradation will occur when the adjustment process is carried out at room temperature, so the temperature during the adjustment process needs to be controlled between 0 and the solidification temperature of the ionic liquid.

[0026] In some embodiments, the temperature of the ionic liquid injection process is 265-272 K. Injecting the ionic liquid under an inert atmosphere can more quickly reduce the temperature of the adjustment process to the target temperature to prevent degradation.

[0027] The radius of the cation in the ionic liquid is mainly adjusted by the type of ionic liquid. In some embodiments, the chemical formula of the ionic liquid is as follows:

[0028]

[0029] Among them, n1, n2, n3 are all natural numbers, R 1 CH 3 OCH 2 -, methoxy or methyl.

[0030] The cationic radius of the ionic liquid can be adjusted by adjusting n1, n2, and n3.

[0031] Specifically, the ionic liquid is selected from diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, tributylmethylammonium bis(trifluoromethylsulfonyl)imide, and trioctylmethylammonium bis(trifluoromethylsulfonyl)imide.

[0032] In some embodiments, the ionic liquid is injected through a capillary tube, and the capillary action of the capillary tube can better fill the ionic liquid between the strip carbon 60 single crystal and the gate.

[0033] In some embodiments, the source electrode is composed of a chromium layer and a gold layer, and the thickness ratio of the chromium layer to the gold layer is 2-4:15-25, nm:nm.

[0034] In some embodiments, the drain electrode is composed of a chromium layer and a gold layer, and the thickness ratio of the chromium layer to the gold layer is 2-4:15-25, nm:nm.

[0035] In some embodiments, the gate is composed of a chromium layer and a gold layer, and the thickness ratio of the chromium layer to the gold layer is 2-4:15-25, nm:nm.

[0036] In some embodiments, the distance between the source and the drain is 250-350 μm.

[0037] In some embodiments, C 60 The single crystals were obtained by physical vapor transport (PVT).

[0038] In some embodiments, the gate and C 60 The gap between single crystals is 4 to 6 μm.

[0039] Since the above method has a tendency to transform into a metal phase at low temperature, another embodiment of the present invention provides an application of the above method for regulating the conductivity of carbon 60 single crystal in regulating the insulating metal phase transformation of carbon 60 single crystal.

[0040] The third embodiment of the present invention provides an application of the above method for regulating the conductivity of carbon 60 single crystal in the design and / or preparation of organic field effect transistors. Under the condition of a certain gate voltage, the above method only needs to adjust the cation radius to achieve the regulation of charge density and conductivity, thus solving the problem of achieving the maximum possible charge density and conductivity under the minimum gate voltage.

[0041] A fourth embodiment of the present invention provides an application of the above method for regulating the conductivity of carbon 60 single crystals in the design and / or preparation of electronic devices. Since the method provided by the present invention can adjust the charge density and conductivity by adjusting the gate voltage and the cation radius, it can guide the design of electronic devices with lower power.

[0042] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0043] Example

[0044] Experimental part:

[0045] Device preparation and testing:

[0046] C 60 Purchased from Sigma-Aldrich. C was grown in a glove box for 6 days by physical vapor transport (PVT). 60The single crystal growth device is a horizontal tube, and the high temperature zone is heated and sublimated. The sublimation temperature is 615℃. 60 The molecular vapor is deposited and crystallized in the low temperature region due to supersaturation, and the deposition temperature is 510-390°C. 60 The single crystal was laminated onto a prefabricated gold-coated PDMS substrate with source, drain, gate and channel reference electrodes to make a four-probe air dielectric field effect transistor. All contact electrodes consisted of a chromium (3nm) / gold (20nm) bilayer film. The distance between the source and drain electrodes was 300 microns, and the distance between the reference electrodes (V1 and V2) was 150 microns. The gate-to-crystal gap for all devices was 5 microns, as shown in Figure 2. Figure 1 EDLT is based on a four-probe air dielectric layer, where ionic liquid is filled into the C 60 The gap between the single crystal and the gate is constructed. The ionic liquid was purchased from Merck KGaA. The IV characteristics of the device were measured in a N-filled 2 The variable temperature test was performed in the dark with a low temperature probe station at 10 -4 The displacement current was recorded using a Keithley 2612 sourcemeter measurement device that sweeps the voltage between the gate and the shorted source and drain contacts while measuring the current.

[0047] Characterization:

[0048] High-resolution X-ray diffraction (XRD) was measured using a Philips Panalytical X'Pert Pro diffractometer, monochromatic Cu Kα radiation (wavelength 0.154 nm), X-ray photon capability of 45 kV and 40 mA. Surface potential maps were measured using a Nanoscope V multimode atomic force microscope from Bruker Instruments and a conductive probe (NSC18, Pt coating, resonance frequency 60-90 kHz, k = 2-5.5 N / m) from Mikromasch, USA.

[0049] Results and Discussion

[0050] The lath-shaped C was grown by physical vapor transport (PVT) under an inert atmosphere. 60 single crystals and were characterized by X-ray diffraction and atomic force microscopy, as Figure 2 ac. The main crystal plane corresponds to the tightly packed (111) plane and is very smooth with a suitable molecular step density (<2 steps / 10 μm). The crystal was tested for four-probe field effect transmission using an air dielectric field effect transistor with gold source and drain contacts. The electron mobility is related to the gate voltage and is as high as 2.5 cm 2 / Vs, through the test of nearly 30 devices, the average mobility is ~1cm 2 / Vs. A drop of ionic liquid was then transferred to C 60 Near the gap between the crystal and the recessed gate, e.g. Figure 2 As shown in e. Under the capillary force, the ionic liquid automatically fills into C 60 The gap below the crystal forms an ionic liquid dielectric layer. The transfer of the ionic liquid was done on a probe station at 270K under an inert atmosphere. After the ionic liquid was inserted into the gap, the platform temperature immediately dropped to ~215K, just above the freezing point of the ionic liquid. Assembly and operation at well below room temperature are necessary to obtain reproducible devices; this is because the narrow electrochemical window of the ionic liquid leads to irreversible degradation when EDLTs operate at room temperature.

[0051] In C 60 Three different ionic liquids were used in single crystal EDLTs, DEME-TFSI [diethylmethyl (2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) imide], N4441-TFSI [tributylmethyl ammonium bis (trifluoromethylsulfonyl) imide], and N8881-TFSI [trioctylmethyl ammonium bis (trifluoromethylsulfonyl) imide]; their chemical structures are shown in Figure 2. Figure 2 d. The TFSI anion is the same in each case. These ionic liquid electrolytes are all ammonium salts, in which the positive charge is located on the core N atom and the alkyl chain provides a steric barrier to the positive charge and to the neighboring ions or interfacial C 60 The molecules separate to form a delocalized and non-clustered charge distribution. A cation radius can be estimated using the ionic liquid density and computer simulation (ChemBio3D). Based on the two-dimensional projected area A of the ionic liquid at the interface cation With a single C 60 The projected area of ​​the molecule (A C60 ) are compared, as shown in Table 1, the interface area occupied by the N8881 cation is much larger than that of a C 60 molecules, while DEME and N4441 cations are smaller than C 60 .

[0052] Table 1. C of different ionic liquid dielectric layers 60 Comparison of single crystal EDLT parameters.

[0053]

[0054]

[0055] a) σ S and n is at V G = extracted at +2.5V; b)Capacitance is in nV G The linear region of the graph is given by the formula

[0056] Figure 2 f shows the C based on three different ionic liquid dielectric layers 60 Typical four-probe conductivity (σ) of single crystal EDLTs at 215K s ) and gate voltage (V G ) due to the low temperature and the corresponding slow ion transport, which delays the formation and annihilation of the double layer, a hysteresis in the retrace is observed in all scans. At 215K, σ s -V G The behavior is reproducible and at positive gate voltage, the EDLTs using N8881-TFSI ionic liquid are always higher than those using N4441-TFSI and DEME-TFSI devices. s The transistor turns on at a positive gate voltage consistent with electron accumulation. The low voltage required reflects the very large capacitance of the ionic liquid (≥5 μF cm -2 ).

[0057] Figure 3 The dielectric layer C using DEME-TFSI ionic liquid is shown 60 Complete data of single-crystal EDLTs. Figure 3 a shows the voltage at 215K at 20 mV s -1 The scan rate is 50 times continuously at V G = Conductivity σ in the range of -0.5V to +2.5V s The conductivity did not decay, indicating that the ionic liquid dielectric layer C 60 Single crystal EDLTs devices have good stability. Figure 3 b shows the gate displacement current I of the same device at different scan rates disp With V G These curves reveal that V G The cycle from the negative threshold voltage to +2.5V and then back to below the threshold voltage corresponds to the process of electron accumulation and depletion. In the case of ionic liquid as the dielectric layer, the onset voltage of the channel opening and closing is clearly seen, and V G Only +1V, that is, a very small voltage can drive the device to work normally. disp -V G The curve fit (see shaded area) gives a reliable charge measurement, which is the total gate-induced charge in the semiconductor channel. It increases with V G The capacitance of the DEME-TFSI double layer is calculated to be 7.8 μF cm -2, which is nearly three orders of magnitude higher than silicon wafers (Table 1). G = +2.5V, electron density n = 5.2x 10 13 cm -2 , which is equivalent to nearly 0.5e / C 60 molecular.

[0058] Figure 3 c shows a larger gate voltage (V G = +4V), the drain current I D and conductivity σ s With V G At a larger V G In the range, significant behavior is observed: V G = +2.65V in the forward scan, I D and σ s A clear peak appears. This peak is also obvious in the reverse scan, moving about 0.7V in the negative direction. D and σ s Obviously suppressed; C 60 The two-dimensional conductivity of the surface is basically closed. Figure 3 Semi-logarithm of c I D -V G In the figure, we can see that the peak current is V G = 10 of the current at +4V 3 times. Figure 3 d shows the same V G The corresponding displacement current (I disp ). It can be clearly observed that I disp There is also an obvious peak. disp Fitting, correspondingly nV G The slope of the curve is relatively gentle (solid circle curve), which is unusual and unprecedented for EDLTs. Because the accumulated electron density reflects the two-dimensional electron state density (DOS) on the crystal surface, I disp -V G The peak in the figure indicates that an electronic subband is filled. disp To V G = +4V integral produces maximum charge density n = 8.5x10 13 cm -2 or ~0.8e / C 60 .also, Figure 3 c s The peak value and I disp The peak value (vertical gray dashed line) is consistent with that of n = 0.5e / C 60 σ s Peak value and I dispThe corresponding relationship of the peak value can be explained by the band filling theory. The conductivity peak appears near the maximum value of DOS, that is, at 0.5e / C 60 The maximum conductivity is at 1e / C 60 The conductance is completely turned off below 0.05. By testing the metal-semiconductor contact resistance and different scan rates, it can be clearly concluded that the current suppression is independent of the contact resistance or scan rate.

[0059] Figure 4 It is a C using N4441-TFSI and N8881-TFSI dielectric layers. 60 Single crystal EDLTs test data. Figure 4 a and 4b show the logarithmic I of EDLTs using N4441-TFSI D -V G and Linear I disp -V G Characteristics. In the forward sweep V G = +2.85V, I D The peak value also corresponds to n~0.5e / C 60 I disp -V G The curve of I disp The maximum value of I D The total induced charge is n = 0.8e / C 60 =9x10 13 cm -2 It reaches a peak again. G The linear region of the relationship is 6.5 μF cm -2 (See Table 1), which is slightly lower than DEME-TFSI, which may be due to the difference in cation radius. In general, the results of N4441-TFSI device and DEME-TFSI device are very similar.

[0060] When using N8881-TFSI for C 60 When the crystal was gated, a distinctly different behavior was observed. Figure 4 c shows the index I D -V G In the forward scan of the curve, at V G =Two weak peaks appeared at +3V and +5V. Figure 4 I in d disp -V G The trajectory is also quite different; there is no clear peak, but a "box-shaped" trajectory, indicating a very ideal charge accumulation and depletion behavior. disp -V G The integral curve of V does not show a platform, but n increases with VG Approximately linear increase until V G = +5.5V, corresponding to a very large total electron accumulation n = 1.9x10 14 cm -2 =1.7e / C 60 and double layer capacitance 5.8 μF cm -2 (Table 1) The double layer capacitance of N8881-TFSI is lower than that of DEME-TFSI and N4441-TFSI, which is consistent with the increase in cation size, but the use of N8881-TFSI ionic liquid can scan to a higher V G The charge accumulation of DEME-TFSI and N4441-TFSI is about twice as high as that of DEME-TFSI and N4441-TFSI (Table 1). disp To V G = +3V integration again shows that I D The first weak peak appears at 0.5e / C 60 , as with the other two types of EDLT. However, with V G There is no sharp drop in conductance and no evidence of any subband filling. D At 1e / C 60 After being partially suppressed at 1.6x10 14 cm -2 =1.5e / C 60 (V G =5V) a second peak appeared.

[0061] Figure 5 a shows three different ionic liquid dielectric layers C 60 The electrical conductivity σ of single-crystal EDLTs s Relationship with n. All EDLTs are within 0.5e / C 60 The conductivity near the maximum value appears, and it is all at 1e / C 60 There is a minimum value near . In the case of EDLTs with smaller cations (DEME and N4441), σ s At n = 1e / C 60 In contrast, for the N8881 device, σ s There is a soft band gap, that is, at n = 1e / C 60 When σ is not completely suppressed s , and at 1.5e / C 60 At higher charge densities near σ s Another peak appears.

[0062] Figure 5 b shows another important result. V G = +2.5V, through the formula μ = σ s / ne is used to calculate the electron mobility μ of each EDLT and its temperature dependence is tested in a limited temperature range of 215-~250K. Figure 5 As can be seen in b, the mobility of the DEME and N4441 devices decreases with decreasing temperature, indicating thermally activated charge transport. However, for the N8881 EDLTs, the mobility increases with decreasing temperature, showing band-like charge transport performance. This distinct temperature dependence is consistent with the strong carrier localization in the DEME and N4441 gate-controlled devices and the delocalization in the N8881. The four-probe mobilities in all EDLTs are lower than those of the air dielectric field-effect devices, a phenomenon that is mainly attributed to the strong localization effect discussed below, as well as the known relationship between mobility and the dielectric constant of the gate insulator.

[0063] Different conductivity and charge transport properties are caused by the cations and C 60 The interaction between charge carriers and C 60 Its inherent properties. Face-centered cubic C 60 The LUMO (conduction band) of the crystal is quite narrow, about 0.5 eV, so the Coulomb interaction between electrons and cations and the interaction between electrons and electrons are considered to be very important, especially at very high interfacial charge density. Experimental data show that the migration of charge is related to the cation radius - a large cation radius has a high σ s , mobility and a smaller threshold voltage V T ,like Figure 5 c, and when n = 1e / C 60 This is consistent with the Coulomb interaction.

[0064] In the case of DEME and N4441, the conductivity is n = 0.5e / C 60 It reaches its maximum value when n=1e / C 60 This can be explained by assuming that the electrons in C 60 The strong localization on the crystal surface can be explained by Figure 5 d. An important reason for localization is the Coulomb attraction between electrons and cations. This attraction is particularly strong for EDLT with DEME or N4441 cations because the cation radius r cation <r C60 This attraction is calculated to be as high as 0.5 eV, comparable to the LUMO bandwidth. This interaction may break the neutral C 60 The crystal LUMO is usually a triply degenerate state. Assuming that each electron is fixed to a single C 60 In terms of molecules, when half of the C 60 When the molecule is charged, the conductivity is maximum, e.g. Figure 5d, which corresponds to a 1 / 4 filling of the nondegenerate LUMO band. Similarly, when all C 60 When all molecules are charged, 1 / 2 of the LUMO is filled and the conductivity will reach a minimum, because at C 60 The Coulomb loss of the two electrons exceeds the LUMO bandwidth. According to the Mott-Hubbard model (the most common model used to study the electron repulsion effect in solid materials), each site (a C 60 The presence of an integer number of conduction electrons in the molecule leads to a "strongly correlated" phase. Figure 5 In d, it is assumed that the Coulomb repulsion (Hubbard U) opens a Mott-Hubbard-like gap and splits the nondegenerate LUMO band into two upper and lower subbands. disp -V G The data confirm the existence of the subband. Figure 3 d and Figure 4 I in b disp -V G The curve is the embodiment of the two-dimensional state density of the interface. 60 σ s and I disp The decrease in is consistent with a 1 / 2 band charge filling, i.e., a complete filling of the subband. Importantly, the traditional Mott-Hubbard model only involves electron-electron interactions, while ignoring electron-ion interactions. However, the electron-ion interaction is obviously important in σ s and I disp Therefore, the simple Mott model cannot fully describe C 60 Electronic structure and transport in single-crystalline EDLTs; a detailed description must also consider the effects of interfacial cations on charge distribution and transport, and further theoretical and experimental confirmation is needed. The cations are predicted to generate an inhibition potential at the crystal / ionic liquid interface, with disorder or order depending on the accumulated interfacial charge. This potential will be significant for smaller cations (DEME and N4441), and this potential, combined with the Hubbard electron-electron interaction, leads to 1e / C 60 The explanation of a strong insulating state nearby is plausible.

[0065] When the cation radius of N8881-based EDLTs increases, the physical properties change significantly. The increase in carrier mobility indicates that the accumulated electrons are distributed toward a delocalized state, which means that the cation-induced ripple potential is significantly weakened. This situation provides a better opportunity to observe the effects of electron-electron interactions. Our data measured near 215K show that compared with DEME and N4441 EDLTs, at n = 1e / C 60Complete suppression of conductivity no longer occurs. Instead, Figure 5 a shows the existence of a soft band gap, which may be caused by the Hubble gap being comparable to thermal energy. Additional low-temperature tests are needed to confirm that at n = 1e / C 60 Time s However, at 1e / C 60 The weak suppression of conductivity near , strongly supports the involvement of electron correlation physics. In the Mott-Hubbard model, another maximum of conductivity may occur at n = 1.5e / C 60 , which is exactly what is observed in the present example in EDLTs gated with N8881-TFSI, corresponding to half filling of the upper level band and 3 / 4 filling of the entire LUMO band.

[0066] in conclusion

[0067] In summary, this example uses EDLTs to study C 60 Two-dimensional transport in single crystals at very large surface charge densities exceeding 10 14 cm -2 or 1e / C 60 The above data indicate that strong ion-electron and electron-electron interactions are involved in these systems, especially in the C gated by the two ionic liquids DEME-TFSI and N4441-TFSI. 60 σ of single crystal s There is a clear peak in the -n relationship. This peak occurs at C 60 The surface electron density near the interface between molecules and ionic liquid is n = 0.5e / C 60 At n=1e / C 60 The σ is completely suppressed near s Changing the ionic liquid to N8881-TFSI increases the cation radius, resulting in two major changes. First, σ s Significantly improved, and at n=1e / C 60 σ s Secondly, C 60 The electron accumulation at the interface between molecules and ionic liquid exceeds 10 14 cm -2 In this case, two conductivity peaks appear, one centered at n = 0.5 e / C 60 , and the other one is close to n=1.5e / C 60 In addition, the correlation between carrier mobility and cation radius indicates that C 60 The importance of carrier-ion interactions in single-crystalline EDLTs. 60 σ in single crystal EDLTs sThe -n characteristics are influenced by Mott physics and the corrugated surface potential induced by the cations in the ionic liquid. The presence of the corrugated surface potential is a key difference from the traditional Mott model. Importantly, the corrugated surface potential decreases as the cation radius of the ionic liquid increases, achieving higher conductivity and revealing a soft band gap at 215K.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for regulating the conductivity of carbon 60 single crystal, characterized in that: A substrate having a source electrode, a drain electrode, a gate electrode and a channel reference electrode is provided, a strip carbon 60 single crystal is laminated onto the substrate to prepare a four-probe air dielectric layer field effect transistor, an ionic liquid is injected into the gap between the strip carbon 60 single crystal and the gate electrode, and the conductivity of the carbon 60 single crystal is regulated by adjusting the gate voltage and the radius of the cation in the ionic liquid, and the temperature during the regulation process is from 0 to the solidification temperature of the ionic liquid; The ionic liquid is selected from diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, tributylmethylammonium bis(trifluoromethylsulfonyl)imide, and trioctylmethylammonium bis(trifluoromethylsulfonyl)imide.

2. The method for regulating the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The temperature during the injection of ionic liquid is 265~272 K.

3. The method for regulating the conductivity of carbon 60 single crystal according to claim 2, characterized in that: The ionic liquid was injected under an inert atmosphere.

4. The method for regulating the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The ionic liquid is injected through the capillary.

5. The method for regulating the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The source electrode consists of chromium and gold layers.

6. The method for regulating the conductivity of carbon 60 single crystal according to claim 5, characterized in that: The thickness ratio of the chromium layer and the gold layer is 2~4:15~25, nm:nm.

7. The method for regulating the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The drain electrode consists of chromium and gold layers.

8. The method for regulating the conductivity of carbon 60 single crystal according to claim 7, characterized in that: The thickness ratio of the chromium layer and the gold layer is 2~4:15~25, nm:nm.

9. The method for regulating the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The gate is made of layers of chromium and gold.

10. The method for controlling the electrical conductivity of carbon 60 single crystal according to claim 9, characterized in that: The thickness ratio of the chromium layer and the gold layer is 2~4:15~25, nm:nm.

11. The method for controlling the conductivity of carbon 60 single crystal according to claim 1, characterized in that: Carbon 60 single crystals were obtained by physical vapor transport method.

12. The method for controlling the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The gap between the gate and the carbon 60 single crystal is 4~6μm.

13. The method for controlling the conductivity of carbon 60 single crystal according to claim 1, characterized in that: The distance between the source and drain is 250~350 μm.

14. Use of the method for regulating the electrical conductivity of a carbon 60 single crystal according to any one of claims 1 to 13 in regulating the insulating metallic phase transition of a carbon 60 single crystal.

15. Use of the method for regulating the conductivity of a carbon 60 single crystal according to any one of claims 1 to 13 in designing and / or preparing an organic field effect transistor.

16. Use of the method for regulating the electrical conductivity of carbon 60 single crystal according to any one of claims 1 to 13 in designing and / or preparing electronic devices.

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