Electronic device comprising nanogap electrodes and nanoparticle

Abstract

An electronic device includes a substrate and at least two electrodes spaced by a nanogap, wherein the at least two electrodes are bridged by at least one nanoparticle and wherein the at least one nanoparticle has an overlap area with the at least two electrodes higher than 2% of the area of the at least one nanoparticle. A method of manufacturing of the electronic device and the use of the electronic device in photodetector, transistor, phototransistor, optical modulator, electrical diode, photovoltaic cell or electroluminescent component are also described.

Claims

1. An electronic device comprising: a substrate; and at least two electrodes spaced by a nanogap having a size ranging from 0.1 nanometer to less than 1000 nanometers, wherein the at least two electrodes are bridged by at least one nanoparticle, the at least one nanoparticle is not a carbon based nanoparticle and wherein the at least one nanoparticle has an overlap area with the at least two electrodes higher than 2% of the projected surface of the at least one nanoparticle, and each of the at least one nanoparticle is a nanorod, a nanoplatelet, a nanoplate, a nanowall, a nanodisk, a nanotube, a nanoribbon, a nanobelt or a nanowire.

2. The electronic device according to claim 1, wherein the at least one nanoparticle has an overlap area with each of the at least two electrodes higher than 1% of the projected surface of the at least one nanoparticle.

3. The electronic device according to claim 1, wherein the nanogap has a size ranging from 1 nanometer to 100 nanometers.

4. The electronic device according to claim 1, wherein the nanogap has a length ranging from 1 nanometer to 10 millimeters.

5. The electronic device according to claim 1, wherein the at least one nanoplatelet is a semiconductor nanoplatelet.

6. The electronic device according to claim 1, further comprising an electrolyte on the at least one nanoparticle.

7. The electronic device according to claim 1, wherein a pn junction is formed between the at least two electrodes.

8. An apparatus comprising: an electronic device comprising a substrate and at least two electrodes spaced by a nanogap having a size ranging from 0.1 nanometer to less than 1000 nanometers, wherein the at least two electrodes are bridged by at least one nanoparticle, the at least one nanoparticle is not a carbon based nanoparticle, the at least one nanoparticle having an overlap area with the at least two electrodes higher than 2% of the projected surface of the at least one nanoparticle, wherein the apparatus is one of a photodetector comprising the at least two electrodes bridged by the at least one nanoparticle, a transistor comprising the at least two electrodes bridged by the at least one nanoparticle, a phototransistor comprising the at least two electrodes bridged by the at least one nanoparticle, an optical modulator comprising the at least two electrodes bridged by the at least one nanoparticle, an electrical diode comprising the at least two electrodes bridged by the at least one nanoparticle, a photovoltaic solar cell comprising the at least two electrodes bridged by the at least one nanoparticle, and an electroluminescent component comprising the at least two electrodes bridged by the at least one nanoparticle, and each of the at least one nanoparticle is a nanorod, a nanoplatelet, a nanoplate, a nanowall, a nanodisk, a nanotube, a nanoribbon, a nanobelt or a nanowire.

9. The electronic device according to claim 1, wherein the nanogap has a size ranging from 10 nanometers to 80 nanometers.

10. The electronic device according to claim 1, wherein the nanogap has a length ranging from 5 nanometers to 1 millimeter.

11. The electronic device according to claim 1, wherein the nanogap has a length ranging from 10 nanometers to 100 micrometers.

12. The electronic device according to claim 1, wherein the nanogap has a length ranging from 50 nanometers to 10 micrometers.

13. A method of manufacturing an electronic device according to claim 1, the method comprising the steps of: a) forming on a substrate at least two electrodes spaced by a nanogap ranging from 0.1 nanometer to less than 1000 nanometers; b) preparing at least one nanoparticle, each of the at least one nanoparticle being a nanorod, a nanoplatelet, a nanoplate, a nanowall, a nanodisk, a nanotube, a nanoribbon, a nanobelt or a nanowire; c) optionally causing a nanoparticle ligand exchange procedure to occur; d) depositing of the at least one nanoparticle onto the nanogap, wherein the at least one nanoparticle is not a carbon based nanoparticle, the at least one nanoparticle having an overlap area with the at least two electrodes spaced by a nanogap higher than 2% of the projected surface of the at least one nanoparticle; e) causing a nanoparticle ligand exchange procedure to occur if the nanoparticle ligand exchange procedure is not performed at step c); and f) optionally depositing an electrolyte.

14. The method of manufacturing an electronic device according to claim 13, wherein forming the at least two electrodes on the substrate spaced by a nanogap is selected from electromigration, electrodeposition, mechanically controlled break junctions, e-beam lithography, self-alignment methods, lift-off methods, shadowing methods, on-wire lithography, and nanotube masks.

15. The method of manufacturing an electronic device according to claim 13, wherein depositing the at least one nanoparticle onto the nanogap is selected from drop casting, spin coating, dip coating, spray casting, screen printing, inkjet printing, sputtering techniques, evaporation techniques, electrophoretic deposition, gravure printing, flexographic printing, and vacuum methods.

16. The method of manufacturing an electronic device according to claim 13, wherein the at least one nanoparticle is a semiconductor nanoplatelet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scheme of the electronic device according to one embodiment of the present invention.

(2) FIG. 2 is a scanning electron microscopy picture of nanogaps at three different scales.

(3) FIG. 3 is a scanning electron microscopy picture of nanogaps coated with CdTe nanoplatelets at three different scales.

(4) FIG. 4 shows the current as a function of time under a constant drain-source bias in the electronic device according to one embodiment of the present invention wherein the nanogap electrodes are bridged with CdSe/CdS nanoplatelets. The square response corresponds to light illumination. The response time of the electronic device is faster than 0.1 second.

(5) FIG. 5 shows the current as a function of drain bias under incident light power in the electronic device according to one embodiment of the present invention wherein the nanogap electrodes are bridged with CdSe/CdS nanoplatelets.

(6) FIG. 6 shows the current as a function of gate bias under incident light power in the electronic device according to one embodiment of the present invention wherein the nanogap electrodes are bridged with CdSe/CdS nanoplatelets. The gating is made by LiClO.sub.4 in PEG as electrolyte.

(7) FIG. 7a is a scheme of the energy diagram of the electronic device according to one embodiment of the present invention under zero drain bias for conduction and valence band.

(8) FIG. 7b is a scheme of the conduction band diagram of the electronic device according to one embodiment of the present invention under different drain bias.

(9) FIG. 8 shows nanostructures of the present invention.

(10) FIG. 9 shows additional nanostructures of the present invention.

(11) FIG. 10 shows devices formed from the nanostructures of the present invention.

REFERENCES

(12) N Nanoparticle(s) E Electrode(s) d Inter-electrode distance L Length of the electrode

EXAMPLES

(13) The present invention is further illustrated by the following examples.

(14) Nanoparticle Synthesis:

(15) CdSe Nanoplatelets

(16) In a first step Cadmium myristate (Cd(Myr).sub.2) is prepared. In a typical synthesis 240 mg of Cd(Myr).sub.2, 25 mg Se powder are mixed in 30 ml of ODE, the solution degassed under vacuum for 20 minutes at room temperature. Then the atmosphere is switch to Argon and the temperature is set to 240 C. At 204 C. 40 mg of Cd(OAc).sub.2 are quickly added. The reaction is performed 12 minutes at 240 C. After this, the solution is cooled down. The precipitation of the nanoplatelets is done by adding ethanol. After centrifugation the obtained solid is redispersed in hexane. The cleaning procedure is repeated three times.

(17) CdTe Nanoplatelets

(18) In a first step Cadmium propanoate (Cd(Prop).sub.2) is prepared by mixing 1.036 g of CdO in 10 ml of propionic acid under Argon for 1 hour. Then the flask is open to air and the temperature risen to 140 C. up to the point the volume get divided by a factor two. The whitish solution is precipitated by addition of acetone. After centrifugation the solid is dried under vacuum for 24 hours. In the glove box 1M TOPTe is prepared by stirring 2.55 g of Te pellets in 20 ml of TOP for four days at room temperature. In a three necks flask 0.13 g of Cd(Prop).sub.2, 160 m of oleic acid and 10 ml ODE are degassed for 90 minutes at 95 C. Then the atmosphere is switched to Argon and the temperature risen to 210 C. 0.2 mL of 1M TOPTe is quickly injected in the flask. After 20 minutes the reaction is quenched by adding 1 mL of oleic acid and cooling down the flask at room temperature. The cleaning process is done by adding Ethanol to precipitate the CdTe nanoplatelets. The solid obtained after centrifugation is redispersed in hexane. This procedure is repeated three times.

(19) CdSe/CdS Nanoplatelets

(20) Two procedures can be performed to obtain a CdS shell on CdSe core. In a first procedure 30 mg of NaSH are mixed in 4 ml of N methyl formamide (NMFA) in a 20 mL vial up to dissolution. Then 500 L of the CdSe core in solution in hexane are added in the vial. The solution is stirred until a complete transfer of the nanoparticles in the NMFA phase. Then 500 l of 0.2 M cadmium acetate in NMFA are added in the vial. The reaction is performed for 1 hour at room temperature under stirring. Precipitation is ensured by addition of ethanol. After centrifugation the obtained solid is dispersed in NMFA. The cleaning step is repeated a second time. As an alternative procedure to grow the shell it is possible to dissolve 30 mg of Na.sub.2S are mixed in 2 ml of NMFA in a 4 mL vial up to dissolution. The core are then precipitated by addition of acetonitrile to remove the excess of sulfide and redispersed in NMFA. Then 500 l of 0.2 M cadmium acetate in NMFA are added in the vial. After the almost immediate reaction the excess of precursors is removed by precipitation of the nanocrystals with a mixture of toluene and acetonitrile (5:1). The solid obtained by centrifugation is redissolved in NMFA. The procedure is repeated 3.5 times. The final nanoparticles are stored in NMFA.

(21) Spherical CdSe Quantum Dots

(22) In a three necks flask, 8 ml of ODE, 1.5 g of TOPO and 0.75 ml of Cd(OA).sub.2 at 0.5 M in oleic acid are degassed for 30 minutes under vacuum. Then under argon flow, the temperature is set at 280 C. and a mixture of 3 ml of oleylamine and 4 ml of TOPSe at 1 M in TOP are quickly injected at 300 C. while the temperature is set at 280 C. After 8 minutes, the reaction is stopped and the quantum dots are precipitated twice with ethanol and resuspended in hexane.

(23) PbS Spherical Quantum Dots

(24) In a three necks flask, we introduce 0.9 g lead oxide and 40 mL of oleic acid. The mixture is degassed for 1 h at 100 C. under vacuum and then heated under Argon at 150 C. for three hours. In the glove box 0.4 mL of Bis(trimethylsilyl)sulfide (TMSS) are mixed in 20 mL of octadecene (ODE). In a 100 mL three necks flask, 12 ml of the lead oleate (PbOA) mixture previously prepared are quickly degassed at 100 C. and then heated at 150 C. under Argon. 6 mL of the solution of TMSS in ODE are quickly injected to the flask and the reaction performed for 3 minutes. Finally the solution is quickly cooled to room temperature. The solution is precipitated by adding ethanol and centrifuged for 5 minutes at 3000 rpm. The solid is redispersed in toluene. The cleaning step is repeated a second time. At the third cleaning, selective precipitation is performed to separate the different size.

(25) HgTe Spherical Quantum Dots

(26) In the glove box a 1 M solution of trioctylphosphine telluride (TOPTe) is prepared by a slow stirring of Te powder in trioctylphosphine (TOP). In a three neck flask 135 mg of HgCl.sub.2 and 7.4 g of octadecylamine are degassed under vacuum for 1 hour at 120 C. The atmosphere is then switch to Argon and the solution heated at 80 C. 0.5 ml of the 1 M TOPTe are quickly injected and the reaction is performed at the same temperature for 5 minutes. The solution is quenched by a quick addition of dodecanthiol. Finally the flask is cooled down to room temperature. The obtained dark solution is then split between two centrifuge tubes filled with a 10% in volume mixture of dodecanthiol (DDT) in tetrachloroethylene (TCE) and a droplet of TOP. The solution is precipitated by addition of methanol. After centrifugation the solid is dried and redispersed in chloroform. The cleaning is step is repeated three times.

(27) CdS Nanorods

(28) In the glove box, 0.18 g of sulfur powder are stirred in 20 ml of TOP up to dissolution and formation of trioctylphosphine sulfide (TOPS). The final solution is reddish. In a 100 ml three necks flask, 0.23 g of CdO, 0.83 g of n-tetradecylphosphonic acid (nTDPA) and 7 g of trioctylphosphine oxide (TOPO) are degassed under vacuum for two hours at 80 C. Then the flask is switch under Argon and the temperature risen up to 340 C. Above 300 C. the solution turns colorless. After 5 minutes the flask is cooled to 300 C., every two minutes 0.4 ml of the TOPS mixture is injected. The color of the solution turn yellowish after 30 minutes and this color will increase up to the end. Once all the TOPS have been injected the heating mantle is removed and the flask quickly cooled down. Around 70 C. some toluene is added to avoid the TOPO solidification. The cleaning process is repeating three times by precipitating the rods by adding ethanol and redispersing them in toluene.

(29) Nanogap Fabrication:

(30) Self-Aligned Method

(31) On a Si/SiO.sub.2 wafer, a first electrode is prepared either using standard optical lithography or electron beam lithography. In a typical preparation AZ 5214-E resist is deposit by spin coating on the wafer. The wafer is then baked for 90 s at 110 C. A first UV exposure using the lithography mask is performed for a couple second. Then the film is further bake at 125 C. for 2 minutes. Finally we process to metal deposition. The electrodes are made of a layer of Ti (2 nm), a layer of gold (30 nm) and a layer of Cr (30 nm). Lift off process is then made to remove the resist by dipping the wafer in acetone. The wafer is then cleaned using isopropanol and a plasma O.sub.2 etching is conducted for 5 minutes. The electrodes are cooked in air at 250 C. for 30 minutes in order to convert the Cr into chromium oxide. In a second step a second electrodes is prepared using the same lithography method in a geometry which allow an overlap with the first electrode. For metal deposition we evaporate a Ti layer (2 nm) and a gold layer (30 nm). The chromium oxide layer acts as a shadow mask and a nanometer size gap is formed between the two electrodes. After a lift off step and a cleaning step, the top chromium oxide layer of the first electrodes is etched using a chromium etchant solution. A final step of cleaning with acetone and isopropanol is performed.

(32) E-Beam Lithography Method

(33) On a Si/SiO.sub.2 wafer, a polymethyl metacrylate polymer is deposited and cooked at 165 C. to remove the excess of solvent. Using electron beam lithography, two electrodes are designed and allows in a second step the evaporation of metals (typically 3 nm of Cr and 30 nm of gold). After a lift off procedure the nanogap is formed.

(34) Tilted Evaporation Method

(35) On a Si/SiO.sub.2 wafer, a first electrode is prepared either using standard optical lithography or electron beam lithography. In a typical preparation AZ 5214 E resist is deposit by spin coating on the wafer. The wafer is then baked for 90 s at 110 C. A first UV exposure using the lithography mask is performed for a couple second. Then the film is further bake at 125 C. for 2 minutes. We then process to metal deposition by evaporating Ti (2 nm) and a layer of gold (30 nm). A second pattern is prepared using the same lithography procedure. The second metallic evaporation is made while the sample is tilted in order that the first electrode shadows some part of the second pattern. This shadow effect allows the formation of nanogap at the scale of a few tenth nanometers.

(36) Nanoparticle Depositions for Photodetection1.sup.st Strategy

(37) The nanoparticles initially dispersed in a non-polar solvent can be spincoated onto the nanogap in a glove box. The film is then heated on a hot plate to remove the excess of solvent at 90 C. The device is then dipped into a solution of short ligand such as ethanedithiol ou 1.4 diaminobutane at 1% in ethanol for 1 minute. The film is then rinsed in pure ethanol for 20 s and finally dried under nitrogen flow.

(38) Nanoparticle Depositions for Photodetection2.sup.nd Strategy

(39) The nanoparticles initially dispersed in a non-polar solvent are mixed with a solution of Na.sub.2S in N-methyl formamide (1% in weight). After strong sonication the particle switch of phase and are transferred in the polar phase. The initial and now clear non polar phase is discarded. The polar phase is then cleaned two other times by adding hexane. The nanoparticles are precipitated by addition of an alcohol. The obtained pellet is redispersed in fresh N-methyl formamide. This solution is then dropcasted onto the nanogap on a hot plate at 100 C. The heating is performed until a complete removal of the solvent.

(40) Electrolyte Preparation

(41) The electrolyte is a mixture of polyethylene glycol (PEG) or polyethylene oxide (PEO) with a given molar weight and ions. The molar ratio between the cation and the oxygen is taken equal to 16. For a typical electrolyte 50 mg of LiClO.sub.4 and 230 mg of PEG (MW=6000 g.Math.mo.sup.1) are heated together at 150 C. on a hot plate in the glove box. For higher PEG/PEO molar weight the mixture is heated at 200 C. Processing the electrolyte in air has not lead to any noticeable change. The electrolyte can then be brushed on the at least one nanoparticle onto the nanogap by softening it at 90 C.

(42) Responsivity:

(43) A nanogap where CdSe/CdS nanoplatelets coated with S.sup.2 capping ligands have been bridged is characterized at room temperature under primary vacuum. The applied drain source is 2 V. The sample is illuminated using a 405 nm with a power between 1 and 50 mW corresponding to a flux into the nanogap of 1 to 50 nW. The obtained photoresponse is 3 kA.Math.W.sup.1.

(44) Pn Junction Formation

(45) HgTe quantum dots are capped using S.sup.2 ligands, using a phase transfer method using Na.sub.2S precursor dissolved in N-methyl formamide. The nanoparticle solution is dropcasted on nanogap electrodes. Electroltrolyte made of LiClO.sub.4 dissolved in PEG (M.sub.W=6000 g.Math.mol.sup.1) is brushed on the nanoparticle film, while the electrolyte has been soften at 90 C. A gate electrode is deposited on the electrolyte and grounded. A source bias of 2V compared to the gate is applied and a drain bias of 2V compared to the gate is also applied while using a two channel sourcemeter. The whole system is frozen by cooling the system to a temperature below the freezing point of the electrolyte. Then a stable pn junction is formed showing a current-voltage characteristic of a diode.

(46) Measurement Conditions in View of FIGS. 4-7

(47) The samples are characterized under vacuum. A drain source bias between 0 and 5 V is 20 applied. Light illumination results from a 405 nm laser source operated with a power ranging from 0.15 mW and 50 mW. All measurements are made at room temperature. FIG. 4 shows the current as a function of time under a constant drain-source bias in the electronic device wherein the nanogap electrodes are bridged with CdSe/CdS nanoplatelets. The square response corresponds to light illumination. The response time of the electronic device is faster than 0.1 second. FIG. 5 shows the current as a function of drain bias under incident light power in the electronic device wherein the nanogap electrodes are bridged with CdSe/CdS nanoplatelets. FIG. 6 shows the current as a function of gate bias under incident light power in the electronic device wherein the nanogap electrodes are bridged with CdSe/CdS nanoplatelets. The gating is made by LiClO4 in PEG as electrolyte. FIG. 7a is a scheme of the energy diagram of the electronic device under zero drain bias for conduction and valence band. FIG. 7b is a scheme of the conduction band diagram of the electronic device under different drain bias.