Preparation method and application of supramolecular device

Abstract

The invention belongs to the field of molecular electronic devices, and discloses a preparation method and application of a supramolecular device. Comprising the following steps: S1, obtaining a hydrogen bond self-assembled gold nanorod assembly solution; s2, cleaning and hydrophilizing the surface of a chip, dropwise adding the gold nanorod assembly solution to the surface of the chip, standing and depositing, washing with deionized water, and blow-drying in an inert atmosphere to obtain a gold nanorod supramolecular junction; and S3, determining the position of the gold nanorod supramolecular junction which is complete in structure and can be used for connection on the chip by using a scanning electron microscope, and performing overlay connection on the gold nanorod supramolecular junction and an external circuit. According to the invention, by combining a bottom-to-top self-assembly method and a top-to-bottom micro-nano processing method, high-yield and stable molecular device construction with a controllable structure is realized.

Description

Technical Field

[0001] This invention belongs to the field of molecular electronic devices, specifically relating to a method for preparing and applying supramolecular devices. Background Technology

[0002] The trend of continuous miniaturization of semiconductor devices, predicted by Moore's Law, has slowed significantly due to approaching physical limits. Current main semiconductor device process nodes have reached 3-5 nm, and their corresponding channel lengths are insufficient to meet the demand for further miniaturization of the source-drain nanometer gap to the single-molecule scale. In the post-Moore era, molecular electronics is booming, aiming to further reduce the size of electronic devices. How to stably and precisely position molecules within the nanoelectrode gap has become a core challenge in the fabrication of next-generation ultra-small, high-performance electronic components. While existing micro / nano-fabrication-based fixed electrode methods can directly construct nanometer gaps, they struggle to achieve precise sub-nanometer gap control and suffer from low molecular junction formation rates. Mechanically controlled fracture techniques can control nanometer gaps in real time and achieve high junction formation rates, but their molecular junction lifetimes are short, and they lack structural information on the morphology of metal contacts near the molecules. Therefore, achieving highly stable, high-yield, and controllable nanometer gap construction remains a critical problem that urgently needs to be solved. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for fabricating supramolecular devices and their applications. By combining bottom-up self-assembly and top-down micro / nano fabrication methods, high-yield, stable, and structurally controllable molecular device construction is achieved.

[0004] The objective of this invention is achieved through the following technical solution: This invention provides a method for preparing supramolecular devices, comprising the following steps: S1, obtain a solution of hydrogen-bonded self-assembled gold nanorod assembly, wherein the gold nanorod assembly is a supramolecular junction structure formed by gold nanorods connected end to end through hydrogen bonding. S2. After cleaning and hydrophilizing the chip surface, the gold nanorod assembly solution is dropped onto the chip surface. After static deposition, the gold nanorod assemblies are dispersed on the chip surface. Unassembled or aggregated nanoparticles are removed by rinsing with deionized water and dried under an inert atmosphere to form isolated and structurally complete gold nanorod supramolecular junctions on the chip. S3. Using a scanning electron microscope, the location of a structurally complete gold nanorod supramolecular junction on the chip that can be used for connection is determined. A metal electrode is formed on the chip through a patterning process and is overlaid and connected to both ends of the gold nanorod supramolecular junction. One end of the metal electrode is connected to the end of the gold nanorod supramolecular junction, and the other end is connected to an external circuit electrode on the chip, so that the gold nanorod supramolecular junction serves as a conductive channel connected to the external circuit.

[0005] In some embodiments, in step S1, the hydrogen-bonded self-assembled gold nanorod assembly solution is obtained by adding assembly molecules capable of forming hydrogen bonds to the gold nanorod solution for assembly to obtain the hydrogen-bonded self-assembled gold nanorod assembly solution.

[0006] Furthermore, the assembling molecule capable of forming hydrogen bonds is at least one of HS-(CH2)2-NH2, HS-(CH2)3-NH2, and HS-(CH2)4-NH2.

[0007] Furthermore, the length of the gold nanorod is 72.10 ± 0.32 nm; the diameter of the gold nanorod is 10.49 ± 0.04 nm.

[0008] In some embodiments, in step S2, the cleaning and hydrophilization treatment is performed using an inductively coupled plasma etching device to perform oxygen plasma treatment.

[0009] In some embodiments, the settling time in step S2 is 5-10 minutes.

[0010] In some embodiments, in step S2, the amount of the gold nanorod assembly solution dropped onto the chip is 3 μL.

[0011] In some embodiments, in step S3, the structurally complete, connectable gold nanorod supramolecular junction is a structurally complete gold nanorod dimer after being dropped onto the chip.

[0012] In some embodiments, in step S3, the overlay connection is performed as follows: First, the coordinates and orientation of the structurally complete gold nanorod assembly relative to the gold identification mark are determined by SEM electron microscopy; then, the electron microscope image is imported into electron beam exposure design software to complete the design of the matching electrical contact pattern; next, PMMA photoresist is spin-coated on the chip surface, and overlay exposure is performed using an electron beam exposure system to make the metal lead pattern accurately extend to both ends of the gold nanorod assembly, thereby realizing its electrical connection with the source and drain electrodes.

[0013] This invention also provides the application of the molecular devices prepared by the above-described preparation method in testing the electrical transport properties of hydrogen-bonded molecular systems.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) The supramolecular device preparation method provided by the present invention has a high success rate of device construction, long lifespan, and can achieve long-term stable testing: the supramolecular structure has already been formed in the solution before being connected to the external circuit, ensuring the existence of the supramolecular assembly from the source, and the atomic-level controllable construction of the molecular-electrode interface can be achieved by controlling the stoichiometry of the self-assembled monolayer; at the same time, the device prepared by this method is very stable under appropriate bias scanning mode and the current level has not changed significantly after being stored for several months. The molecular junction has an extremely long lifespan and can be used for subsequent high-throughput stable electrical testing. (2) The supramolecular device preparation method provided by the present invention reduces the device preparation cost and simplifies the process: the coupling of gold nanorod dimers is achieved by utilizing hydrogen bonding forces in the solution, which can efficiently complete the construction of molecular structures; the gold nanorods and molecular solutions are mixed evenly and stirred in a centrifuge tube without any additional complex operations, and the molecular-electrode surface can be controlled to be constructed; the method is simple, has extremely low cost, and has a high preparation yield. Attached Figure Description

[0015] Figure 1 The morphology and size of the gold nanorods in the gold nanorod stock solution obtained in Example 1 are shown. Figure 2 These are TEM images of the gold nanorod assemblies obtained in Examples 1-3; Figure 3 The electron microscope images of the gold nanorod assembly deposited on the chip in Example 1 are as follows: (a) no assembly; (b) dimer structure; (c) trimer structure; (d) chain network structure. Figure 4 The images show electron microscopy (EM) images of the gold nanorod assembly deposited on the chip substrate obtained in Example 1 before and after overlay, where (a) is before overlay and (b) is after overlay. Figure 5 A schematic diagram of the chip structure in Example 1 (a); a two-dimensional AFM image after overlay (b); a three-dimensional AFM image after overlay (c). Figure 6 The supramolecular devices obtained in Examples 1-3 were subjected to 300 consecutive scans. I - V Test diagrams: (a) Example 1; (b) Example 2; (c) Example 3; (d) Comparison of current magnitudes among the three (shaded areas represent standard deviations), where C2 represents Example 1, C3 represents Example 2, and C4 represents Example 3; Figure 7 Electron microscopy characterization images of 20 molecular devices successfully prepared by all methods in Example 1; Figure 8 Electron microscopy images of 20 molecular devices successfully prepared by all methods in Example 2; Figure 9Electron microscopy characterization images of 20 molecular devices successfully prepared by all methods in Example 3; Figure 10 The 60 supramolecular devices obtained in Examples 1-3 I - V Test images: (a) Example 1; (b) Example 2; (c) Example 3; Figure 11 (a) shows the conductivity statistical distribution of the supramolecular devices obtained in Examples 1-3, where C2 represents Example 1, C3 represents Example 2, and C4 represents Example 3; (b) shows the electron transmission calculation curves, where n=2 represents Example 1, n=3 represents Example 2, and n=4 represents Example 3; (c) shows the gate voltage modulation obtained in Example 1. I - V Line graph. Detailed Implementation

[0016] This invention provides a method for fabricating supramolecular devices, comprising the following steps: S1. A solution of gold nanorods with a length of 72.10±0.32 nm and a diameter of 10.49±0.04 nm is mixed with a solution of assembly molecules that can form hydrogen bonds to obtain a solution of gold nanorods that are self-assembled by hydrogen bonds. The assembly molecules that can form hydrogen bonds are at least one of HS-(CH2)2-NH2, HS-(CH2)3-NH2, and HS-(CH2)4-NH2.

[0017] S2. After cleaning and hydrophilizing the chip surface with oxygen plasma using an inductively coupled plasma etching device, the specific conditions are: O2 flow rate 100 mL / min, RF power 200 W, and processing time 60 seconds. The gold nanorod assembly solution is then dropped onto the chip surface. After standing for 5-10 minutes, it is rinsed with deionized water and dried under an inert atmosphere to obtain gold nanorod supramolecular junctions. S3. Using a field emission scanning electron microscope (FET), the location of the structurally complete, connectable gold nanorod supramolecular junction on the chip is determined. The electron microscope image is then imported into electron beam lithography design software to complete the design of the corresponding electrical contact patterns. After spin-coating PMMA photoresist onto the chip, an electron beam lithography system is used to perform overlay lithography, precisely extending the metal leads of the designed pattern and connecting them to both ends of the gold nanorod assembly. This achieves electrical connection between the assembly and the source and drain electrodes, completing the overlay connection of the gold nanorod supramolecular junction to the external circuitry.

[0018] It should be noted that the chip contains four sets of electrodes, each containing 10 pairs of independent, individually testable source / drain electrodes. Each electrode pair is equipped with two sets of high-precision gold identification markers to ensure accurate alignment of subsequent nanostructures. To avoid electrical short circuits between gold nanorods during the photoresist baking process, electron beam photoresist (PMMA) is spin-coated onto the chip surface immediately after assembly deposition, and the sample is placed in a nitrogen atmosphere overnight to allow residual solvents to evaporate fully.

[0019] The embodiments of the present invention also provide the application of the molecular devices prepared by the above-described preparation method in testing the electrical transport properties of hydrogen-bonded molecular systems.

[0020] The present invention will be further described in detail with reference to specific embodiments. The following embodiments can enable those skilled in the art to have a more comprehensive understanding of the present invention, but do not limit the present invention in any way.

[0021] Example 1: This embodiment provides a method for fabricating supramolecular devices, including the following steps: Preparation of the gold seed: First, 12 μL of chloroauric acid aqueous solution (0.2 mol / L) was added to 5 mL of CTAB solution (0.1 mol / L) and mixed. Then, under vigorous stirring, 600 μL of ice-cold sodium borohydride solution (0.01 mol / L) was rapidly added to this mixture. The solution immediately changed from yellow to dark brown, indicating the formation of the gold seed.

[0022] Growth of gold nanorods: 50 μL of a 0.1 mol / L gold seed solution was added to 500 mL of a 0.1 mol / L CTAB aqueous solution. Subsequently, under stirring, 7.5 mL of a 1 mol / L NaOH solution was added sequentially to provide an alkaline environment, 150 μL of a 0.01 mol / L silver nitrate solution was added as a morphology directing agent, and 500 μL of a 0.1 mol / L hydroquinone as a mild reducing agent. After the addition of the reducing agent, the system color gradually changed from deep yellow to colorless, indicating that the gold precursor had undergone a pre-reduction reaction. The CTAB-coated gold seed will undergo anisotropic growth in the solution to form gold nanorods. The solution was allowed to stand overnight to obtain the gold nanorod stock solution.

[0023] Assembly of gold nanorods: First, take 40 μL of gold nanorod stock solution diluted to 1 nM and transfer it to a centrifuge tube. Then, add 3 μL of 2mM HS-(CH2)2-NH2 aqueous solution (the assembly molecule is HS-(CH2)2-NH2) and mix it with a mixer for 10 seconds. Repeat twice to obtain the gold nanorod assembly solution. The absorbance of the diluted gold rod was measured by ultraviolet spectroscopy, and the concentration c was calculated according to the absorption formula A=lg(1 / T)=Kbc, where A is the absorbance, T is the transmittance, K is the molar absorptivity, and b is the thickness of the absorption layer.

[0024] Deposition of gold nanorod assembly solution onto chip substrate: First, the chip surface was cleaned and hydrophilized using inductively coupled plasma etching (ICP-C). Specific conditions were: O2 flow rate 100 mL / min, RF power 200 W, and processing time 60 seconds. Then, 3 μL of gold nanorod assembly solution was rapidly dropped onto the chip surface and allowed to settle for 5-10 minutes. After deposition, the surface was gently rinsed with deionized water and dried with nitrogen gas to obtain supramolecular junctions deposited on the chip substrate.

[0025] Overlay connection of gold nanorod supramolecular junctions with external circuitry: First, structurally complete gold nanorod assemblies suitable for subsequent connection were selected using electron microscopy, and their coordinates and orientation relative to the gold identification markers were precisely determined. Then, the electron microscopy images were imported into electron beam lithography design software to complete the design of the corresponding electrical contact patterns. After spin-coating PMMA photoresist onto the chip, overlay lithography was performed using an electron beam lithography system to precisely extend and connect the designed metal leads to both ends of the gold nanorod assembly, achieving electrical connection with the source and drain electrodes.

[0026] Example 2: This embodiment provides a method for preparing supramolecular devices. Compared with Example 1, 3 μL of 5mM HS-(CH2)3-NH2 aqueous solution is added to 40 μL of gold nanorod stock solution diluted to 1 nM, and the assembled molecule is HS-(CH2)3-NH2, while other conditions remain the same.

[0027] Example 3: This embodiment provides a method for preparing supramolecular devices. Compared with Example 1, 4 μL of 4mM HS-(CH2)4-NH2 aqueous solution is added to 40 μL of gold nanorod stock solution diluted to 1 nM, and the assembled molecule is HS-(CH2)4-NH2, while other conditions remain the same.

[0028] The morphology and size of the gold nanorods in the gold nanorod stock solution obtained in Example 1 were characterized and tested. The results are as follows: Figure 1As shown, the obtained gold nanorods exhibited uniform morphology, with a length of 72.10 ± 0.32 nm and a diameter of 10.49 ± 0.04 nm. Morphological characterization of the gold nanorod assemblies obtained in Examples 1-3 was performed: 10 μL of the gold nanorod assembly solution was dropped onto a 300-mesh copper grid, allowed to stand for 5-10 minutes to allow the assemblies to deposit, and then the copper grid was washed with water to complete the gold nanorod assembly, followed by overnight standing. Finally, transmission electron microscopy (TEM, JEOL JEM-2100plus) was used to observe the surface morphology of the samples to analyze the distribution and assembly state of the gold nanorod assemblies. The results are as follows: Figure 2 As shown, in addition to the common gold nanorod dimer structure, a few polymer structures also exist. This is because both tips of the gold nanorod have been modified with molecules, causing them to gradually evolve into longer polymer structures such as trimers and tetramers. In other words, there are more supramolecular junctions in a single assembly structure, which can be selected for subsequent overlay connection with external circuits.

[0029] Morphological characterization results of the supramolecular junctions deposited on the chip substrate obtained in Example 1 ( Figure 3 The study revealed that the deposited structure was predominantly dimer. A small number of isolated gold nanorods were also observed, presumably due to incomplete assembly or detachment during the experimental process. Trimers, tetramers, and other chain structures were also observed. These polymeric nanostructures do not affect subsequent overlay processes; any complete dimer region within their chain segments can be selected as a processing unit.

[0030] Morphological characterization results of gold nanorod supramolecular junctions and external circuits before and after overlay in Example 1 ( Figure 4 The results show that the gold nanorod assembly has been successfully connected to the external circuit metal electrodes of the chip, forming a true source and drain structure. To further reveal the back gate structure at the bottom of the device, atomic force microscopy (AFM, Dimension FastScan) was used for two-dimensional and three-dimensional morphology measurements. The test results (…) Figure 5 The external circuitry includes a bottom back gate, and the overall structure forms a typical source-drain-gate three-terminal device, providing a reliable foundation for subsequent electrical transport testing of molecular devices. The gate dielectric is deposited as 20 nm Al₂O₃ using atomic layer deposition (ALD), and the bottom back gate is composed of 3 nm Cr and 30 nm Au deposited by electron beam evaporation.

[0031] To evaluate the electronic transport characteristics of the device, a semiconductor probe station and a semiconductor parameter analyzer were used to perform the following tests: I - V Tests were conducted, and 300 cyclic scans were performed at 298 K on three different chain lengths of HS-(CH2)n-NH2 (n=2,3,4) hydrogen-bonded supramolecular devices. The test results are as follows. Figure 6As shown, the device prepared by this method has excellent stability and repeatability, and the current level changes very little after being stored for several months.

[0032] In addition, 60 devices were obtained according to the preparation methods of Examples 1-3 (20 devices were prepared in each example). Figure 7-9 The aforementioned molecular device chip was placed in a vacuum probe stage and subjected to low-temperature testing at 70K. I - V Test, test results are as follows Figure 10 As shown.

[0033] By Figure 10 The current value under a +300 mV bias voltage was converted into conductance and statistically distributed. G 0 represents quantum conductance, which is equal to 2e 2 / h, approximately 77.6 μS ( e The amount of electron charge. h (where is Planck's constant). The outermost s orbital of a gold atom contains only one electron, therefore its conductivity is 1 when a single atomic point is formed. G 0. The results show that the conductivity decreases exponentially with increasing methylene chain length, consistent with the physical laws of the tunneling transport model. Further analysis using density functional theory (DFT) and non-equilibrium Green's function (NEGF) to calculate and analyze the electron transmission spectra of the three supramolecular junctions yielded the following results: Figure 11 As shown, the calculated transmission peak positions and conductivity trends are highly consistent with the experimental results. The device conductivity distribution spans several orders of magnitude, which is related to the atomic-level differences in the electrode surfaces and molecular anchoring configurations of different gold nanorod assemblies. This is an inherent phenomenon commonly found in molecular devices, and its accuracy can be further improved through large-scale statistical analysis in the future. Furthermore, thanks to the 20 nm Al₂O₃ high-dielectric-constant gate dielectric, the molecular energy levels can be effectively tuned in the range of >1 eV. Figure 11 c shows the three-terminal gate control behavior of the device at 70 K. A significant current enhancement is observed at higher bias voltages, indicating that the molecular junction has high conductivity when the molecular energy level falls into the electrode Fermi window.

[0034] In summary, the results demonstrate that the self-assembled supramolecular devices prepared by this process exhibit good repeatability and high stability in both room-temperature and low-temperature electrical tests. Each step of the experimental process achieves a high success rate, and the device yield is significantly higher than that achievable using traditional methods. These results provide promising proof of principle for the controllable and high-yield construction of bottom-up molecular devices.

[0035] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for fabricating a supramolecular device, characterized in that, Includes the following steps: S1, obtain a solution of hydrogen-bonded self-assembled gold nanorod assembly, wherein the gold nanorod assembly is a supramolecular junction structure formed by gold nanorods connected end to end through hydrogen bonding. S2. After cleaning and hydrophilizing the chip surface, the gold nanorod assembly solution is dropped onto the chip surface. After static deposition, the gold nanorod assemblies are dispersed on the chip surface. Unassembled or aggregated nanoparticles are removed by rinsing with deionized water and dried under an inert atmosphere to form isolated and structurally complete gold nanorod supramolecular junctions on the chip. S3. Using a scanning electron microscope, the location of a structurally complete gold nanorod supramolecular junction on the chip that can be used for connection is determined. A metal electrode is formed on the chip through a patterning process and is overlaid and connected to both ends of the gold nanorod supramolecular junction. One end of the metal electrode is connected to the end of the gold nanorod supramolecular junction, and the other end is connected to an external circuit electrode on the chip, so that the gold nanorod supramolecular junction serves as a conductive channel connected to the external circuit.

2. The preparation method according to claim 1, characterized in that, In step S1, the hydrogen-bonded self-assembled gold nanorod assembly solution is obtained by adding hydrogen-bonded assembly molecules to the gold nanorod solution and assembling them to obtain the hydrogen-bonded self-assembled gold nanorod assembly solution.

3. The preparation method according to claim 2, characterized in that, The assembly molecule capable of forming hydrogen bonds is at least one of HS-(CH2)2-NH2, HS-(CH2)3-NH2, and HS-(CH2)4-NH2.

4. The preparation method according to claim 2, characterized in that, The length of the gold nanorod is 72.10±0.32 nm; the diameter of the gold nanorod is 10.49±0.04 nm.

5. The preparation method according to claim 1, characterized in that, In step S2, the cleaning and hydrophilization treatment method is to perform oxygen plasma treatment using an inductively coupled plasma etching device.

6. The preparation method according to claim 1, characterized in that, In step S2, the settling time is 5-10 minutes.

7. The preparation method according to claim 1, characterized in that, In step S2, the amount of the gold nanorod assembly solution dropped onto the chip is 3 μL.

8. The preparation method according to claim 1, characterized in that, In step S3, the structurally complete and connectable gold nanorod supramolecular junction is a structurally complete gold nanorod dimer after being dropped onto the chip.

9. The preparation method according to claim 1, characterized in that, In step S3, the overlay connection is performed by first determining the coordinates and orientation of the structurally complete gold nanorod assembly relative to the gold identification mark using a scanning electron microscope. The electron microscope images were then imported into electron beam exposure design software to complete the design of the corresponding electrical contact patterns. Next, PMMA photoresist was spin-coated onto the chip surface, and electron beam exposure system was used for overlay exposure to precisely extend the metal lead pattern to both ends of the gold nanorod assembly, realizing its electrical connection with the source and drain electrodes.

10. The application of a molecular device prepared by the preparation method according to any one of claims 1-9 in testing the electrotransport properties of hydrogen-bonded molecular systems.

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