CN103094478B - Unimolecule negative differential resistance device based on silicon-molecule compound system and preparation method - Google Patents
Unimolecule negative differential resistance device based on silicon-molecule compound system and preparation method Download PDFInfo
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Abstract
The invention discloses a unimolecule negative differential resistance effect device based on a silicon-molecule compound system. The unimolecue negative differential resistance device is a unimolecule device prepared by utilizing of resonance between state density of a bivalent cobalt ion dz2 rail in a cobalt- phthalocyanine molecule and an S1 surface state of R3-silver/ silicon surface. The unimolecule negative differential resistance device comprises a source electrode, a drain electrode, a grid electrode, the cobalt- phthalocyanine molecule and a tunneling layer. The single cobalt- phthalocyanine molecule is arranged between the source electrode and the drain electrode. The surface of the cobalt- phthalocyanine molecule is perpendicular to a connecting line between the source electrode and the drain electrode. Cobalt ions in the cobalt- phthalocyanine molecule are contacted with the source electrode. The tunneling layer is arranged between the drain electrode and the cobalt- phthalocyanine molecule. The invention further provides a method for preparing the unimolecule negative differential resistance effect device. The negative differential resistance effect of the molecule device is very stable and has nothing to do with doping kinds and doping density of the substrate. The unimolecule negative differential resistance device based on silicon-molecule compound system is small in size, high in property, capable of being widely applied to an electronic circuit based on nanometer materials in the future.
Description
Technical field
The present invention relates to technical field of electronic devices, especially a kind of unimolecule negative differential resistance effect (NDR based on silicon-molecular complex system, Negative Differential Resistance) device and preparation method thereof, can be used for the switching oscillator and frequency locking circuit etc. of high frequency.
Background technology
Nearly decades, semiconductor device was developed to current large scale integrated circuit by electron tube the earliest.But along with people are to high speed, the high power capacity demand of information processing, traditional semiconductor device has been difficult to meet these demands.Therefore, searching renewal, more stable, more powerful electronic device have become electronic information technology in the urgent need to the problem considered and solve.Research in recent years also finds that some have and determines that the large molecule of space structure and electronic structure has special Electric transport properties, and the appearance of this kind of device will make up the deficiency of the device gone out designed by based semiconductor material greatly, be expected to become the main components for high-performance electronic circuit of future generation.
The kind of molecular device is a lot, comprising the molecular device with switching effect or rectifying effect.Although the performance of molecular device is well embodied experimentally in recent years, the application that distance is actual also has a lot of bottlenecks, is mainly included in the difficulty in industry preparation, and how to develop that performance is more, the better functional molecule apparatus of stability.The molecular device obtained by assembling organic molecular configuration at silicon face in the last few years has a lot of excellent character (see document D.Vuillaume, Molecular Nanoelectronics.Proceedings of the IEEE, 2010,98,2111-2123), but this eka-silicon-molecular device current is by considering separately the device manufactured designed by the physical property of silicon substrate or binding molecule, the stability of its performance is subject to extraneous interference.And the physical property of the two be combined with each other developed by molecular device involved in the present invention just.
The molecular device made based on negative differential resistance effect is that more representational one is (see document N.P.Guisinger et a1.Room Temperature Negative DifferentialResistance through Individual Organic Molecules on Silicon Surfaces.NanoLetters, 2004,4,55-59).Negative differential resistance is find (see document L.Esaki in heavily doped p-n junction the earliest, New Phenomenon in Narrow Germanium p-n Junctions.Phys.Rev.1958,109,603-604), when its I-V curve shows as and adds forward voltage, electric current reduces along with the increase of voltage.In decades subsequently, people have gone out a series of nano-device with negative differential resistance effect with the Materials based on multi-layer nano membrane structure.And along with the development of technique of scan tunnel microscope, people can study the negative differential resistance effect of individual molecule or cluster under atom or molecular scale.Negative differential resistance mainly produces in single tunnel layer and two tunnel layer system.In single tunnel layer system, negative differential resistance Producing reason mainly exists caused by the very sharp-pointed local density of state in the needle point of scanning tunnel microscope and sample, and the sharp-pointed state on needle point can be realized (see document P.Bedrossian et al.Demonstration of the tunnel-diodeeffect on an atomic scale by binding molecule or cluster, Nature, 1989,342,258-260).And two tunnel layer system is comparatively complicated, need to make needle point and sample and between sample and substrate, all there is tunnel layer just to cause negative differential resistance effect (see document T.Rakshit et al.Silicon-based MolecularElectronics Nano Letters, 2004,4,1803-1807), and molecular device involved in the present invention utilize the second negative differential resistance just mechanism of production designed by.
When making this molecular device, need to carry out Passivation Treatment to exposed silicon face.
(being called for short R3-silver/silicon face) is wherein a kind of, and it is in chemically inert to binding molecule.There are three surface state S1 in R3-silver/silicon face, S2, S3 are (see document H.Aizawa et al.Asymmetric structure of the near Fermi surface
surface, Surface Science, 1999,429, L509-L514).The bottom of S1 band is positioned at below Fermi surface 0.3eV, its doping type with block and doping content are identical, and Fermi surface is disperse with upper part, generally can be filled with electrons, so at space-charge layer (SCL, Space-Charge Layer) in can be bent upwards, as shown in Fig. 2 (a) by band in body.S2/S3 band is positioned at below Fermi surface 1.1eV, and wherein S1 band and S2/S3 exist the band gap of a 0.7eV between being with.Because the physical efficiency band of general S2/S3 surface state and space-charge layer influences each other, exposed R3-silver/silicon face can observe obvious negative differential resistance effect.But the appearance of this negative differential resistance affects very large by extraneous factor, as the doping content of silicon substrate, the temperature etc. of measurement, if directly utilize this substrate, is difficult to the negative differential resistance that preparation is stable.And after R3-silver/silicon face deposit cobalt Phthalocyanine, utilize the S1 state on surface and the d of cobalt ions
z 2orbit resonance, can produce negative differential resistance effect clearly, utilizes this point the present invention to design a kind of hybrid silicon-molecular device with negative differential resistance effect had nothing to do with doping content and the doping type of substrate just.
Summary of the invention
In order to solve above-mentioned prior art Problems existing, main purpose of the present invention is the principle utilizing negative differential resistance, provides a kind of unimolecule negative differential resistance effect device based on silicon-molecular complex system and preparation method thereof.
According to an aspect of the present invention, a kind of unimolecule negative differential resistance effect device based on silicon-molecular complex system is provided, comprises: source electrode 1, drain electrode 2, grid 3, cobalt Phthalocyanine 4 and tunnel layer 5, wherein:
Single cobalt Phthalocyanine 4 is between described source electrode 1 and described drain electrode 2, and the plane of described cobalt Phthalocyanine 4 is vertical with the line between described source electrode 1 and described drain electrode 2, and the cobalt ions in described cobalt Phthalocyanine 4 contacts with described source electrode 1;
Tunnel layer 5 is provided with between described drain electrode 2 and described cobalt Phthalocyanine 4.
According to a further aspect in the invention, also provide a kind of preparation method of the unimolecule negative differential resistance effect device based on silicon-molecular complex system, the method comprises:
Step S1, preparation R3-silver/silicon face substrate is as the source electrode of described unimolecule negative differential resistance effect device;
Step S2, the described R3-silver/silicon face prepared evaporates a small amount of cobalt Phthalocyanine, obtains cobalt phthalocyanine-R3-silver/silicon face;
Step S3, cobalt phthalocyanine-R3-silver/silicon face that described step S2 obtains evaporates ground floor oxide, forms oxide layer a;
Step S4, the oxide layer a that described step S3 obtains evaporates second layer oxide, forms the oxide layer b with pore space structure;
Step S5, preparation drain electrode on described oxide layer a and described oxide layer b;
Step S8, etches the hole for making grid on the comparatively ideal single cobalt Phthalocyanine both sides of Electric transport properties, and prepare grid in described hole, thus finally obtain unimolecule negative differential resistance effect device.
The negative differential resistance effect of the above-mentioned unimolecule negative differential resistance effect device based on silicon-molecular complex system provided by the present invention is very stable, has nothing to do with the dopant species of substrate and doping content.This kind of single molecules apparatus volume with negative differential resistance characteristic produced due to the present invention is little, and performance is high, can be widely used in from now on based in the electronic circuit of nano material.
Accompanying drawing explanation
Fig. 1 is the principle schematic of the unimolecule negative differential resistance effect device that the present invention is based on silicon-molecular complex system;
The energy diagram of single molecules apparatus of the present invention when Fig. 2 a is equilbrium position;
Fig. 2 b is the energy diagram of single molecules apparatus of the present invention under negative voltage;
Fig. 2 c is the energy diagram of single molecules apparatus of the present invention under higher negative voltage;
Fig. 3 is preparation method's flow chart of single molecules apparatus of the present invention;
Fig. 4 is the vertical stratification schematic diagram at each position of molecular device after actual assembled of the present invention;
Fig. 5 is the planar structure schematic diagram at each position of molecular device after actual assembled of the present invention;
Fig. 6 a is at the shape appearance figure of scanning tunnel microscope of the cobalt Phthalocyanine of R3-silver/silicon face and the structural representation of molecule, and the lower left corner is shape appearance figure and the structural representation of the R3-silver/silicon face amplified;
Fig. 6 b is that the single cobalt Phthalocyanine that scanning tunnel microscope is measured is composed at the I-V of R3-silver/silicon face.
Embodiment
For making the object, technical solutions and advantages of the present invention clearly understand, below in conjunction with specific embodiment, and with reference to accompanying drawing, the present invention is described in more detail.
According to an aspect of the present invention, a kind of unimolecule negative differential resistance effect device based on silicon-molecular complex system is provided, as shown in Figure 1, unimolecule negative differential resistance effect device based on silicon-molecular complex system provided by the invention comprises: source electrode 1, drain electrode 2, grid 3, cobalt Phthalocyanine 4 and tunnel layer 5, wherein:
Described source electrode 1 uses R3-silver/silicon face;
Described drain electrode 2 uses gold as electrode;
Single cobalt Phthalocyanine 4 is between described source electrode 1 and described drain electrode 2, and the plane of described cobalt Phthalocyanine 4 is vertical with the line between described source electrode 1 and described drain electrode 2, and the cobalt ions in described cobalt Phthalocyanine 4 contacts with described source electrode 1;
Tunnel layer 5 is provided with between described drain electrode 2 and described cobalt Phthalocyanine 4;
Separate by the oxide layer of high-k between four lobes of described grid 3 and described cobalt Phthalocyanine 4.
In described unimolecule negative differential resistance effect device, described cobalt Phthalocyanine 4 is between described source electrode 1 and described drain electrode 2, when adding negative voltage, for general molecular device, also can correspondingly be increased by the electric current on molecule or tunnelling current along with the voltage between source electrode and drain electrode increases it.But for this unimolecule negative differential resistance effect device of the present invention, tunnelling current can reduce along with the increase of absolute value of voltage in a specific voltage, and this characteristic is identical with the effect that negative differential resistance of the prior art shows.
Utilize following model can occur that the mechanism of negative differential effect makes an explanation on unimolecule negative differential resistance effect device of the present invention, can see that the density of states of hydrogen atom on this surperficial empty phthalocyanine is without fluctuating according to the density of states of R3-silver/silicon face, and the d of divalent cobalt ion
z 2the density of states of track but has comparatively macrorelief.And the cobalt Phthalocyanine be adsorbed on different equilbrium position, the d of its divalent cobalt ion
z 2the density of states of track also has certain change, as shown in Fig. 2 (a).Because experiment test of the present invention is all generally at the above 0.08-0.12eV of drain electrode Fermi surface, in order to simplify, the d of cobalt Phthalocyanine
z 2the density of states of track generally selects the energy at the above 0.1eV of drain electrode Fermi surface.
(the voltage V=V when applying a negative voltage between source electrode and drain electrode
gap+ V
sCL+ V
inter, wherein, V
gapfor the voltage drop between drain electrode Fermi surface and cobalt Phthalocyanine band gap, V
sCLfor the voltage drop of space charge layer, i.e. the Fermi surface of R3-silver/silicon face and the d of cobalt Phthalocyanine divalent cobalt ion
z 2voltage drop between the density of states of track, V
intervoltage drop for interface between cobalt Phthalocyanine and R3-silver/silicon face), cause V
gap/ V becomes large, V
sCL/ V diminishes, the d of center divalent cobalt ion
z 2the density of states of track will move down.As voltage drop V
interwhen arriving 0.1eV, the d of divalent cobalt ion
z 2the density of states of track is alignd being with S1 rapidly, as shown in dotted line in Fig. 2 (b), now can cause the d of divalent cobalt ion
z 2produce between the density of states of track and S1 are with and resonate, thus occur a peak value on the negative voltage of I-V curve.When continuing to increase voltage, d
z 2rail moving enters between the band gap of S1 and S2/S3, and as shown in Fig. 2 (c), the now resonance of molecular orbit and S1 is destroyed, and causes tunnelling current to decline.When molecular orbit is between the energy gap of S1 and S2/S3, tunelling electrons is mainly from the valence band that the S2/S3 of R3-silver/silicon face is with.Because the surface state of S2/S3 is below needle point Fermi surface, therefore these states can not have contribution to negative differential resistance again.Due to the d of cobalt ions
z 2track is more than Fermi surface, and therefore it can only be with S1 and align under negative voltage.
That is, the negative differential resistance effect of described unimolecule negative differential resistance effect device utilizes the divalent cobalt ion d in described cobalt Phthalocyanine (4)
z 2resonance between the density of states of track and the S1 surface state of described R3-silver/silicon face produces.
Above model simply describes the general principle that unimolecule negative differential resistance effect device of the present invention produces negative differential resistance effect.Also find in further studying, the negative differential resistance effect of unimolecule negative differential resistance effect device of the present invention is very stable.First the substrate of this unimolecule negative differential resistance effect device has nothing to do with the kind of doping and doping content, and it is based on the surface state of substrate, and the carrier concentration of the size of surface state and doping type and block is without contacting directly.In addition, the difference of temperature is also very little on negative differential resistance impact.This is also for the application of unimolecule negative differential resistance effect device of the present invention provides important foundation.
Further, if need the voltage location to negative differential resistance occurs to regulate, then grid voltage V can be added on described unimolecule negative differential resistance effect device
gregulate and control, described grid 3, mainly by regulating the chemical potential of cobalt Phthalocyanine, regulating and controlling electronics in cobalt Phthalocyanine and filling most high level and MO relative position, the especially d of divalent cobalt ion
z 2the relative position of track and Fermi surface, this change that will negative differential resistance caused in I-V curve to occur position, thus apply more widely for the application of unimolecule negative differential resistance effect device of the present invention provides.
According to a further aspect in the invention, a kind of preparation method of the unimolecule negative differential resistance effect device based on silicon-molecular complex system is also provided.The manufacture method of traditional point sub-electrode mainly utilizes electromigration to be prepared, and namely first utilizes the method for general electron beam lithography to prepare gold nano band, and makes nanoribbons break to form two electrodes of gold by big current.But in unimolecule negative differential resistance effect device of the present invention, because one of them electrode is R3-silver/silicon face, and cobalt Phthalocyanine must lie low at R3-silver/silicon face, therefore, when preparing unimolecule negative differential resistance effect device of the present invention, difficult point mainly comprises two aspects, and one is how to prepare the source electrode of the R3-silver/silicon face substrate with complete structure and have the drain electrode of micro-nano structure, and two is how to select suitable molecular device and carry out suitable grid preparation.
Fig. 3 is preparation method's flow chart of unimolecule negative differential resistance effect device of the present invention, and the method comprises the following steps:
Step S1, preparation R3-silver/silicon face substrate is as the source electrode of described unimolecule negative differential resistance effect device;
The step of described preparation R3-silver/silicon face substrate is further comprising the steps:
Step S11, prepares Si (111)-7 × 7 reconstructing surface, and this reconstructing surface can use general Si (111)-7 × 7 reconstruction processing method to obtain under the environment of ultra high vacuum;
Step S12, Si (111)-7 × 7 reconstructing surface prepared evaporates the silver atoms of a small amount of (about 0.3 individual layer) and carries out annealing in process (annealing temperature about 300 degree), thus forms R3-silver/silicon face substrate.
Wherein, the generation situation of reconstructing surface can be detected by the equipment such as scanning tunnel microscope or low energy electron diffraction, as the display of Fig. 6 (a) lower left corner be exactly utilize scanning tunnel microscope to as described in the reconstruct of R3-silver/silicon face substrate detect the shape appearance figure obtained.
Step S2, the described R3-silver/silicon face substrate prepared evaporates a small amount of cobalt Phthalocyanine, obtains cobalt phthalocyanine-R3-silver/silicon face;
During evaporation, vacuum pressure is less than 10 as far as possible
-9mbar is namely under the environment of ultra high vacuum, and the coverage of described cobalt Phthalocyanine is approximately below 0.1 individual layer, and in addition, during evaporation, described R3-silver/silicon face substrate can keep at low temperatures.In evaporation process, can be detected the pattern of single cobalt Phthalocyanine by scanning tunnel microscope, be exactly the detection shape appearance figure of the single cobalt Phthalocyanine of R3-silver/silicon face utilizing scanning tunnel microscope to obtain as shown in Fig. 6 (a).
Step S3, cobalt phthalocyanine-R3-silver/silicon face that described step S2 obtains evaporates ground floor oxide, forms oxide layer a as tunnel layer;
Described oxide layer a is used for as the tunnel layer 5 between the drain electrode 2 shown in Fig. 1 and cobalt Phthalocyanine 4.Described oxide layer a generally can select the materials such as alundum (Al2O3), also can use thiol molecule.In order to obtain fine and close oxide layer, the preparation of described oxide layer a should keep low temperature environment; Epitaxial device or pulsed laser deposition equipment is belonged to make this oxide layer by general molecule.
In general, the thickness of described oxide layer a is approximately a few nanometer.The described oxide layer a obtained after above-mentioned evaporation can be detected by atomic force microscope.If unimolecule negative differential resistance effect device of the present invention needs to increase grid, then described oxide layer a just needs the material that use dielectric constant is larger, as hafnium oxide etc.
Because described oxide layer a can protect the cobalt Phthalocyanine after R3-silver/silicon face and evaporation not by extraneous destruction well, the step therefore after described step S3 all can be carried out in the environment outside ultra high vacuum.
Step S4, the oxide layer a that described step S3 obtains evaporates second layer oxide, formed and have the oxide layer b of pore space structure, the object that this oxide layer b makes hole is to allow prepared drain electrode in following step S5 can directly touch described oxide layer a.As shown in Figure 4,5.Its making step is as follows:
S41, first on the cobalt phthalocyanine-R3-silver/silicon face of described oxide layer a, spin coating one deck electron beam bears etching glue, and thickness is about about 70nm;
S42, utilizes general electron beam lithography to expose the figure making hole;
S43, after the figure of etching hole, utilize general magnetron sputtering technique or technique for atomic layer deposition obtain described in there is the oxide layer b of pore space structure.The thickness of described oxide layer b is greatly about more than 50nm, and described oxide layer b can select poorly conductive but the smaller material of dielectric constant.
Step S5, on described oxide layer a and described oxide layer b, preparation drain electrode, because the area of drain electrode is less, therefore can adopt general electron beam lithography to prepare drain electrode;
The material of described drain electrode generally selects gold.
The step of described preparation drain electrode is further comprising the steps:
Step S51, spin coating one deck electron beam lithography glue on the cobalt phthalocyanine-R3-silver/silicon face with described oxide layer a and described oxide layer b, this glue is positive glue, and material is polymethyl methacrylate (PMMA), and thickness is about 200nm;
Step S52, utilizes general electron beam lithography to expose the electrode pattern making drain electrode 2 in Fig. 1, as shown in Figure 5;
Step S53, evaporates titanium/gold atom after etching the electrode pattern of described drain electrode 2, obtains described drain electrode 2, and wherein, the thickness of evaporation is about: titanium atom layer is 5nm, and gold atom layer is 100nm.
In the process of preparation drain electrode, the area of drain electrode is little as far as possible, and the size of described drain electrode and the direct contact portion of described oxide layer a is greatly about about 30 ~ 50nm, and this size is close to the limit of general electron beam lithography.
In Fig. 5, described drain electrode limit trapezoidal portions is mainly draws electric level a, use for being connected with the extraction electrode b that following step S6 prepares, the general size of the electric level a of described extraction is at about 80 ~ 100nm, because described extraction electrode a only directly contacts with described oxide layer b, therefore can not work to the Electric transport properties of molecule.
In addition, by multiple for disposable for the electrode pattern of described drain electrode exposure, multiple drain electrode can be prepared, thus strengthen the probability of the single cobalt Phthalocyanine of described drain contact.
Step S6, described oxide layer b is prepared extraction electrode b, shows for connecting test source;
The Main Function of described extraction electrode b is that described extraction electrode a is connected use with external measuring circuit, and the preparation of described extraction electrode b needs to reuse electron beam lithography, and etched features as shown in Figure 5.The condition of described electron beam lithography is with identical above, and etching glue is positive glue.And after the described extraction electrode b figure of etching, evaporate titanium/gold atom.
Step S7, by described extraction electrode b and R3-silver/silicon face substrate and test source list catenation;
By after completing in steps above, the one end in test source table is connected extraction electrode b, the other end connects on R3-silver/silicon face substrate.By changing measuring voltage V
dSmeasure the change of electric current I, thus obtain I-V curve.Due to the existence of described tunnel layer 5, the size of electric current is receiving peace magnitude, therefore needs to add preamplifier when measuring electric current.
As mentioned above, in step s 5, in order to strengthen the contact probability of drain electrode and single cobalt Phthalocyanine, the electrode pattern of drain electrode is disposable expose multiple, and according to result involved in hereafter feasibility study display, when not adding grid, negative differential resistance should appear at the position of about-0.7V.Can select according to this standard and have molecular device that the is functional and drain electrode of character repetition, the grid preparation involved by following step S8 provides performance effective sample.
Step S8, etches the hole for making grid on the comparatively ideal single cobalt Phthalocyanine both sides of Electric transport properties, and prepare grid in described hole, thus finally obtain unimolecule negative differential resistance effect device.
The preparation of described grid is more difficult, mainly because single cobalt Phthalocyanine is perpendicular to source-drain electrode, therefore grid can only add from the side of single cobalt Phthalocyanine, certainly which increases the complexity of unimolecule negative differential resistance effect device preparation technology of the present invention.In addition, also there is due to R3-silver/silicon face substrate the band gap in surface state and body, the Fermi surface of R3-silver/silicon face substrate may be made to regulate and control when regulating and controlling single cobalt Phthalocyanine energy level, therefore grid can not with described source and drain two electrode contact when applying.The present invention proposes following scheme to prepare the grid of unimolecule negative differential resistance effect device of the present invention:
Step S81, use electron beam lithography, the hole for making grid is etched on the comparatively ideal single cobalt Phthalocyanine both sides of Electric transport properties, the size of this hole should control at 50 ~ 100nm, the degree of depth is about about 100nm (thickness of described etching should be greater than the thickness of described oxide layer b), and wherein, positive glue selected by electron beam lithography glue, after stripping etching glue, the sample after described etching is put into ion bean etcher and etches.
Step S82, etches in the region that obtains in step S81 and prepares an oxide layer c, and the region evaporation gate electrode at oxide layer c place, thus prepare grid;
After etching, the R3-silver that step S1 obtains/silicon face substrate partial denudation, if now directly evaporation gate electrode can make to be short-circuited between grid and the substrate of drain electrode, therefore need to etch in the region that obtains in step S81 to prepare an oxide layer c to prevent from puncturing between grid and described R3-silver/silicon face substrate.The thickness of described oxide layer c, greatly about about 50nm, realizes by technique for atomic layer deposition.
After preparing described oxide layer c, again by the regional exposure gate electrode of electron beam lithography to oxide layer c place, positive etching glue is used during exposure, then evaporation gate electrode after exposition, thus obtaining final unimolecule negative differential resistance effect device, after actual assembled of the present invention, the structural representation at each position of molecular device is as shown in Figure 5.
Above-mentioned preparation method except for the preparation of unimolecule negative differential resistance effect device of the present invention, is also applicable to a series of electronic transport device with individual molecule on complete structure substrate and cluster of preparation.
In order to verify the feasibility of unimolecule negative differential resistance effect device of the present invention, test based on unimolecule negative differential resistance effect device of the present invention, in experiment, the I-V characteristic (as described in Fig. 6 (b)) of unimolecule negative differential resistance effect device of the present invention obtains on the low-temperature scanning tunneling microscope of Omicron company, and experiment is carried out respectively at the temperature of 5K and 77K.In this experiment, needle point is equivalent to the drain electrode prepared in step S5, and the vacuum tunnel layer between needle point and single cobalt Phthalocyanine is equivalent to the oxide layer a prepared in step S3.For the measurement that single cobalt Phthalocyanine is composed at the I-V of R3-silver/silicon in scanning tunnel microscope, unimolecule negative differential resistance effect device of the present invention occurs that the position of negative differential resistance is mainly at-0.7eV at present, in Fig. 6 (b), abscissa is for being spectrum bias voltage V, ordinate is tunnelling current I, as can be seen from Figure, do spectrum bias voltage for-0.7V time spectral line table reveal obvious negative differential resistance effect.
In previous a lot of experimental studies, negative differential resistance effect may be caused by the special electronic state of some of needle point or the molecule be adsorbed on needle point.In this case negative differential resistance effect can be strongly depend on the tunnelling condition of needle point.But in experiment of the present invention, negative differential resistance effect does not also rely on the change of needle point.Find after having changed several different needle point in experiment, negative differential resistance and needle point are without any dependence.After using sky Phthalocyanine instead, the phenyl ring on molecule lobe does not observe any negative differential resistance effect.Therefore this may be relevant with the special electronic state of divalent cobalt ion in cobalt Phthalocyanine.Further research also proves on single cobalt Phthalocyanine and other substrate, and I-V spectrum does not find negative differential resistance effect.Therefore the interface between cobalt Phthalocyanine and substrate, the correlation namely between cobalt Phthalocyanine energy level and substrate surface state is the key causing negative differential resistance effect.
This kind of single molecules apparatus volume with negative differential resistance characteristic produced due to the present invention is little, and performance is high, can be widely used in from now on based in the electronic circuit of nano material.Such as resonant tunneling diode can be widely used in, resonance tunneling transistor at the electronic component of existing negative differential resistance characteristic, resonant interband tunnel device, high-frequency generator, gate, in the manufacture of the devices such as single electron switch.Therefore along with the microminiaturization of electronic device, intelligent, this single molecules apparatus will be applied in device production from now on more and more.
Above-described specific embodiment; object of the present invention, technical scheme and beneficial effect are further described; be understood that; the foregoing is only specific embodiments of the invention; be not limited to the present invention; within the spirit and principles in the present invention all, any amendment made, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (13)
1. the unimolecule negative differential resistance effect device based on silicon-molecular complex system, it is characterized in that, this unimolecule negative differential resistance effect device comprises: source electrode (1), drain electrode (2), grid (3), single cobalt Phthalocyanine (4) and tunnel layer (5), wherein:
Described cobalt Phthalocyanine (4) is positioned between described source electrode (1) and described drain electrode (2), the planes of molecules of described cobalt Phthalocyanine (4) is vertical with the line of described drain electrode (2) with described source electrode (1), and the cobalt ions in described cobalt Phthalocyanine (4) contacts with described source electrode (1);
Be provided with tunnel layer (5) between described drain electrode (2) and described cobalt Phthalocyanine (4), described tunnel layer (5) is oxide layer, and its thickness is in nanometer scale.
2. unimolecule negative differential resistance effect device according to claim 1, is characterized in that, described source electrode (1) uses silicon
silver surface.
3. unimolecule negative differential resistance effect device according to claim 2, is characterized in that, the negative differential resistance effect of described unimolecule negative differential resistance effect device utilizes the divalent cobalt ion d in described cobalt Phthalocyanine (4)
z 2the density of states of track and described silicon
resonance between the S1 surface state of silver surface produces.
4. unimolecule negative differential resistance effect device according to claim 1, is characterized in that, described drain electrode (2) uses gold as electrode.
5. unimolecule negative differential resistance effect device according to claim 1, is characterized in that, separates between four lobes of described grid (3) and described cobalt Phthalocyanine (4) by the oxide layer obtained by hafnium oxide.
6., based on a preparation method for the unimolecule negative differential resistance effect device of silicon-molecular complex system, it is characterized in that, the method comprises:
Step S1, prepares silicon
silver surface is as the source electrode of described unimolecule negative differential resistance effect device;
Step S2, is less than 10 in vacuum pressure
-9under the environment of mbar, the described silicon prepared
silver surface substrate evaporates the cobalt Phthalocyanine of below 0.1 individual layer, obtain cobalt phthalocyanine-silicon
silver surface;
Step S3, at cobalt phthalocyanine-silicon that described step S2 obtains
silver surface evaporates ground floor oxide, form oxide layer a;
Step S4, the oxide layer a that described step S3 obtains evaporates second layer oxide, forms the oxide layer b with pore space structure;
Step S5, preparation drain electrode on described oxide layer a and described oxide layer b;
Step S8, etches the hole for making grid on the single cobalt Phthalocyanine both sides that Electric transport properties is desirable, and prepare grid in described hole, thus finally obtain unimolecule negative differential resistance effect device.
7. method according to claim 6, is characterized in that, described step S1 is further comprising the steps:
Step S11, prepares Si (111)-7 × 7 reconstructing surface under the environment of ultra high vacuum;
Step S12, Si (111)-7 × 7 reconstructing surface prepared evaporates the silver atoms of 0.3 individual layer and carries out annealing in process, thus forms silicon
silver surface substrate.
8. method according to claim 6, is characterized in that, the thickness of described oxide layer a in nanometer scale, and should keep low temperature environment when preparing described oxide layer a.
9. method according to claim 6, is characterized in that, in described step S4, the step preparing described oxide layer b is further comprising the steps:
S41, has the cobalt phthalocyanine-silicon of described oxide layer a
on silver surface, spin coating one deck electron beam bears etching glue;
S42, uses the exposure of electron beam lithography machine to make the figure of hole;
S43, after the figure of etching described hole, utilize magnetron sputtering technique or technique for atomic layer deposition obtain described in there is the oxide layer b of pore space structure.
10. method according to claim 6, is characterized in that, the step of described preparation drain electrode is further comprising the steps:
Step S51, has the cobalt phthalocyanine-silicon of described oxide layer a and described oxide layer b
the positive etching glue of spin coating one deck electron beam on silver surface;
Step S52, utilizes electron beam lithography machine to expose the electrode pattern making drain electrode;
Step S53, evaporates titanium/gold atom after etching the electrode pattern of described drain electrode, obtains described drain electrode.
11. methods according to claim 10, is characterized in that, prepare multiple drain electrode according to described step S51-step S53, to strengthen the probability of the single cobalt Phthalocyanine of described drain contact.
12. methods according to claim 6, is characterized in that, the step preparing grid in described step S8 comprises further:
Step S81, using electron beam lithography, etching the hole for making grid on the single cobalt Phthalocyanine both sides that Electric transport properties is desirable;
Step S82, etches in the region that obtains in step S81 and prepares an oxide layer c, and the region evaporation gate electrode at oxide layer c place, thus prepare grid.
13. methods according to claim 6, is characterized in that, described unimolecule negative differential resistance effect device can be applied in the electronic circuit based on nano material.
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