A method for preparing a metal nanomaterial surface protrusion

Abstract

The application discloses a preparation method of metal nanometer material surface protrusions and belongs to the field of nanoelectronics. In the application, metal nanometer wires or nanometer strips are first prepared into two-end devices, the metal nanometer wires are annealed by using Joule heat, and the initial morphology of the surface of the nanometer wires is stabilized through electrical preparation operation, then a semiconductor parameter analyzer and a matched probe station are used to perform current-voltage (I-V) scanning on the metal nanometer wires, the three-dimensional metal protrusions on the surface of the nanometer wires are regulated to the required morphology and height by monitoring the transient slope of the R-V curve of the nanometer wires and the amplitude of the resistance increase.

Description

Technical Field

[0001] This invention belongs to the field of nanoelectronics and is a method for preparing three-dimensional protrusions on the surface of metal nanomaterials. Background Technology

[0002] Three-dimensional nanoscale metal structures have important application value in the field of nanoelectronics, and can be applied to at least the following aspects: (1) Microscopic characterization tools: using three-dimensional nanoscale conductive structures to construct the tip of a probe microscope; (2) Nanoscale or atomic scale devices: constructing nanoscale or atomic scale point contact or junction devices to realize electrical or thermal transport; (3) Three-dimensional interconnection between nanoelectronic devices: using three-dimensional nanoscale metal structures to realize the interconnection of nanoelectronic devices or circuits between different layers.

[0003] Common techniques for fabricating three-dimensional nanoscale protrusions on the surface of metal conductors include: (1) Electron beam lithography, metal deposition, and lift-off techniques: Electron beam lithography is used to pattern photoresist on the surface of an insulating substrate, and then metal protrusion structures are obtained through metal deposition and lift-off; (2) Electron beam lithography and metal etching techniques: Electron beam lithography is used to pattern metal thin films on a smooth and flat surface of a metal conductor, and then etching techniques are used to form three-dimensional structures; (3) Focused ion beam (FIB) and other techniques are used to directly etch the metal surface to form three-dimensional structures. These techniques can fabricate three-dimensional conductive structures on a large scale. The shape and height of the three-dimensional structure can be pre-designed by photolithography, and its height can be changed by metal deposition or etching techniques, resulting in high processing efficiency. However, there are two problems: First, the morphology and size of this structure are usually designed and determined in advance, and the height of different protrusions is controlled by metal deposition or etching processes. Once the fabrication is completed, the morphology and height of the protrusions are fixed, and the morphology and size cannot be fine-tuned and corrected using this technology. Second, the above technology is difficult to fabricate three-dimensional nanoscale protrusions on a single metal nanowire, and it is difficult to control the shape of the tip of the three-dimensional protrusion and the height of the protrusion. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing metal protrusions on the surface of metal nanomaterials. This method can be used to control the three-dimensional metal protrusions on the surface of nanowires to the desired morphology and height.

[0005] The technical solution provided by this invention is as follows:

[0006] A method for preparing protrusions on the surface of a metal nanomaterial, comprising the following steps:

[0007] (1) Preparation of metal nanowires or nanoribbons: Nanowires or nanoribbons are prepared on a substrate. The substrate can be silicon dioxide, glass, plastic and mica, etc., and the materials of the metal nanowires or nanoribbons include, but are not limited to, metals such as gold, silver, palladium, platinum, aluminum, tantalum and indium.

[0008] Nanowire or nanoribbon fabrication: Fabrication of metallic nanoribbons (e.g., on a substrate) Figure 1 The fabrication process can involve patterning with a mask followed by metal deposition-lifting, or directly patterning the metal layer without a mask. If mask patterning is used, the methods include, but are not limited to, ultraviolet lithography, electron beam lithography, imprinting, or pattern transfer processes; the metal layer fabrication methods include, but are not limited to, electron beam evaporation deposition, thermal evaporation deposition, magnetron sputtering, electroplating, atomic layer deposition, and epitaxial growth. If patterning is performed directly on the metal layer without a mask, methods such as gallium ion focused ion beam (FIB) etching, helium ion etching, and plasma etching can be used to directly etch metal nanoribbon patterns onto the metal layer; or methods such as focused ion beam etching and self-assembly can be used to perform local deposition or growth on the substrate to directly obtain the metal nanoribbon structure. The width of the metal nanoribbons ranges from 50 nm to 500 nm, and the thickness ranges from 10 nm to 100 nm.

[0009] (2) Atomic force microscopy and image analysis software were used to characterize the initial morphology and height of the samples;

[0010] (3) Place the metal nanowire or nanoribbon sample on the probe stage surface. The probe stage can be a commercially available system or a custom-built system. The nanowire or nanoribbon should have its two ends connected to two electrode plates, which in turn contact the probe (e.g., ...). Figure 1 The two probes are connected to the two ports of the semiconductor parameter analyzer via wires, ensuring a good electrical connection. The semiconductor parameter analyzer can be a commercial instrument or a self-designed and manufactured scientific instrument, but it should ensure good voltage and current accuracy. The voltage output and measurement accuracy should be no less than 1mV, the maximum voltage no less than 10V, the current measurement accuracy no less than 1nA, and the maximum current no less than 1mA.

[0011] (4) Annealing of nanowires or nanoribbons: Metal nanowires or nanoribbons are annealed using Joule heating. A scanning voltage is applied to the original sample at a rate of 1mV / s-100mV / s using a semiconductor parameter analyzer. When the resistance-voltage (RV) curve rises approximately linearly and the resistance reaches a saturation plateau or tends to decrease after the plateau, the voltage is stopped, and the morphology of the annealed nanowires or nanoribbons is characterized using an atomic force microscope.

[0012] (5) Electrical preparation operation before the formation of metal protrusions: Perform 3-10 IV scans, monitor the RV curve platform simultaneously, and stop the electrical preparation operation when the RV curve no longer continues to decline. The main purpose of this preparation operation is to prevent the surface height fluctuation of metal nanowires or nanoribbons from increasing or the roughness from increasing significantly, and to gradually stabilize the morphology of their surfaces.

[0013] (6) Control of the morphology and height of the metal protrusions: Apply one or more IV scan voltages to the sample using a semiconductor parameter analyzer. The voltage increase rate is in the range of 1mV / s-100mV / s to obtain three-dimensional metal protrusions perpendicular to the nanowire direction.

[0014] This invention allows for the control of the morphology and height of metal protrusions by monitoring the transient slope and the magnitude of the resistance increase in the continuously increasing RV curve. The magnitude of the resistance increase in the metal nanowires or nanoribbons after a single IV scan is controlled within 1%-10% (based on the resistance value at 0.1V). The sample morphology is characterized immediately after each single IV scan using atomic force microscopy.

[0015] The morphology of a metal protrusion refers to its three-dimensional morphology, or it can refer to the two-dimensional cross-sectional shape perpendicular to or along the direction of the nanowire (or nanoribbon); the height refers to the three-dimensional height relative to the substrate.

[0016] If the morphology and height of the metal protrusion meet the preset or design requirements, the IV scan is stopped; if the requirements are not met, the IV scan is performed again, and the transient slope and resistance increase of the RV curve of the nanowire or nanoribbon are monitored to adjust the morphology and height of the metal protrusion until they meet the preset or design requirements.

[0017] The morphology of metallic protrusions includes, but is not limited to, the following:

[0018] Needle-shaped metal protrusion structure: After 1 to 3 manipulation operations in step (6) above, at least one needle-shaped metal protrusion will be generated on the surface of the nanowire or nanoribbon. After each manipulation operation, the height of the highest point of the protrusion will increase by 1-10 nm (based on the substrate).

[0019] Saddle-shaped metal protrusion structure: After 2-10 adjustments in step (6) above, the metal protrusion will exhibit a saddle-shaped structure. After each adjustment, the height of the highest point of each protrusion will increase by 0-5 nm.

[0020] Hemispherical metal protrusion structure: After at least three adjustment operations in step (6), the metal protrusion will exhibit a hemispherical structure. After a single adjustment operation, the height of the highest point of the protrusion will increase by 0-3 nm.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention prefabricates metal nanowires or nanoribbons into devices at both ends. The metal nanowires are first annealed using Joule heating and then the initial morphology of the nanowire surface is stabilized through electrical preparatory operations. A semiconductor parameter analyzer and a matching probe station are used to perform current-voltage (IV) scanning on the metal nanowires (i.e., gradually increasing the voltage from zero at a certain rate). Then, by monitoring the transient slope of the RV curve of the nanowires and the magnitude of the increase in resistance, the three-dimensional metal protrusions on the surface of the nanowires are adjusted to the desired morphology and height. Attached Figure Description

[0023] Figure 1 Schematic diagram of metal nanowires and peripheral circuitry;

[0024] Figure 2 In a specific embodiment of the present invention, the resistance-voltage (RV) curves of the nanowires during the electrical preparatory operation stage before the formation of the metal protrusion are shown, wherein: lines 1 to 4 are the RV curves corresponding to the sequentially performed current-voltage (IV) scans; as the number of scans increases, the RV curves gradually shift downwards as a whole;

[0025] Figure 3 Atomic force microscope images of metal nanowires in a specific embodiment of the present invention; wherein: Figure (a) shows the initial morphology of the nanowires, and Figures (b)-(e) show the corresponding morphology. Figure 2 Atomic force microscopy (AFM) images after IV scans 1 to 4.

[0026] Figure 4 In a specific embodiment of the present invention, the RV curves for the control operation stage of the morphology and height of the metal protrusion are shown; wherein: curves 1 to 4 are the RV curves corresponding to the first to fourth current-voltage (IV) scans respectively; as the number of scans increases, the RV curves shift upwards overall.

[0027] Figure 5 Two-dimensional (2D) and three-dimensional (3D) atomic force microscopy (AFM) images of the metal protrusions in a specific embodiment of the present invention. Among them, (a) is a two-dimensional (2D) AFM image of the sample after the first test in the control operation stage, and (b)-(d) are respectively the areas corresponding to the white dashed boxes in Figure (a), showing that the protrusions have needle-like, saddle-shaped and spherical morphologies;

[0028] Figure 6 A height distribution diagram of different shapes of metal protrusions in a specific embodiment of the present invention; wherein, the three curves respectively correspond to Figure 5 (b)~(d) along Figure 5 (a) Height distribution curve of the white dotted line. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] (1) Fabrication of gold (Au) nanowires: Nanowire devices were fabricated on a silicon dioxide substrate. The material of the nanowire devices was gold (Au). Electron beam lithography, electron beam metal deposition, and lift-off processes were used. The narrowest point of the Au nanowires was 100 nm wide, 10 nm thick, and 450 nm long.

[0031] (2) Atomic force microscopy was used to characterize the initial morphology of the samples;

[0032] (3) Place the Au nanowire device sample to be regulated on the probe stage surface. An MPI TS150 probe stage is used. A pair of electrode plates are led out from the substrate for the positive and negative electrodes of the nanowire device, and a pair of probes are brought into contact with them respectively. The probes are connected to the port of the semiconductor parameter analyzer via wires, ensuring a good electrical connection. A KeySight B1500A semiconductor analyzer is used.

[0033] (4) Au nanowire annealing: Au nanowires were annealed using Joule heating generated by electric current for 70 seconds. This operation increased the nanowire grain size and made the structure more compact. A scanning voltage of 20 mV / s was applied to the original sample using a semiconductor parameter analyzer. When the resistance-voltage (RV) curve rose and a plateau trend of resistance saturation appeared, the voltage was manually stopped, and the morphology of the annealed nanowire sample was characterized using an atomic force microscope.

[0034] (5) Electrical preparatory procedures before the formation of metallic protrusions: Perform four IV cycle scans, simultaneously monitoring the RV curve, with each RV curve decreasing compared to the previous one (e.g., ...). Figure 2 As testing progressed, the height variation on the nanowire surface ceased to increase, the roughness no longer increased significantly, the RV curve plateau and descent phase disappeared, and the surface morphology gradually stabilized. (e.g.) Figure 3 (a)).

[0035] (6) A scanning voltage of 20 mV / s was applied to the original sample using a parameter analyzer to obtain Au three-dimensional metal protrusions perpendicular to the nanowire direction.

[0036] (7) Adjustment of Au protrusion morphology and height: A scanning voltage of 20 mV / s is applied to the original sample using a parametric analyzer. The voltage is stopped when the transient slope of the RV curve continuously increases and the resistance value rises by 3% (based on the resistance value at 0.1 V). The sample morphology is characterized using an atomic force microscope. Repeating the above process and performing different adjustments yields metal protrusions with different morphologies and heights (e.g., Au protrusions). Figure 5 As shown in (b) to (d), this figure is along Figure 5 (a) is a three-dimensional atomic force microscope image within the white dashed box.

[0037] (7) Needle-like protrusion structure: Perform one adjustment operation, i.e. Figure 4 The first voltage scan was performed. A voltage was applied from 0V to 2.31V at a rate of 20mV / s, and a bulge appeared near the anode of the nanowire. Its height distribution along the direction parallel to the nanowire was needle-like (e.g., ...). Figure 5 (b)), see reference Figure 6 Its peak height is approximately 23.9 nanometers.

[0038] (8) Saddle-shaped protrusion structure: Then, two adjustment operations are performed, namely Figure 4 The second and third voltage scans were performed. Voltages were applied at a rate of 20 mV / s from 0 V to 1.87 V and from 0 V to 1.516 V, respectively. The height distribution of the metal protrusions along the direction parallel to the nanowires changed from a needle-like shape to a saddle-shaped structure (e.g., Figure 5 (c)), see reference Figure 6 The highest point of the protrusion is 24.8 nanometers.

[0039] (9) Hemispherical protrusion structure: Perform another adjustment operation, namely Figure 4 The fourth test was conducted. A voltage was applied at a rate of 20 mV / s from 0 V to 1.78 V, and the height distribution of the metal protrusions along the direction parallel to the nanowires changed from a saddle-shaped structure to a hemispherical structure (e.g., ...). Figure 5 (d)). Reference Figure 6 After testing, the height of the highest point of the protrusion was 27.4 nanometers.

[0040] The embodiments described above are not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention is defined by the scope of the claims.

Claims

1. A method for preparing protrusions on the surface of a metal nanomaterial, comprising the following steps: 1) Fabrication of metal nanowires or nanoribbons on a substrate; 2) Atomic force microscopy and image analysis software were used to characterize the initial morphology and height of the metal nanowires or nanoribbons; 3) Place the metal nanowire or nanoribbon sample on the probe stage surface. Connect the two ends of the nanowire or nanoribbon to two electrode plates respectively. The electrode plates then contact the probes. The two probes are connected to the two ports of the semiconductor parameter analyzer through wires to ensure good electrical connection. 4) Anneal the metal nanowires or nanoribbons using Joule heating. Apply a scanning voltage to the original sample at a rate of 1mV / s-100mV / s using a semiconductor parameter analyzer. When the resistance-voltage (RV) curve rises approximately linearly and the resistance reaches a saturation plateau or tends to decrease after the plateau, stop applying the voltage and characterize the morphology of the annealed nanowires or nanoribbons using atomic force microscopy. Then perform 3-10 IV scans, simultaneously monitoring the RV curve plateau, and stop the electrical preparation operation when the RV curve no longer continues to decrease. 5) Apply a single or multiple IV scan voltage to the sample using a semiconductor parameter analyzer, with the voltage increasing at a rate in the range of 1 mV / s to 100 mV / s; immediately after each IV scan, characterize the sample morphology using an atomic force microscope to obtain two-dimensional metal protrusions perpendicular to or along the nanowire direction.

2. The method for preparing surface protrusions of metal nanomaterials as described in claim 1, characterized in that, The substrate is silicon dioxide, glass, plastic or mica, and the metal nanowires or nanoribbons are made of gold, silver, palladium, platinum, aluminum, tantalum or indium.

3. The method for preparing surface protrusions of metal nanomaterials as described in claim 1, characterized in that, Step 1) Prepare metal nanowires or nanoribbons by patterning with a mask and then completing the process through metal deposition-exfoliation; or by directly patterning the metal layer without using a mask. The width of the metal nanoribbons ranges from 50 nm to 500 nm, and the thickness ranges from 10 nm to 100 nm.

4. The method for preparing surface protrusions of metal nanomaterials as described in claim 1, characterized in that, The semiconductor parameter analyzer uses commercial instruments or self-designed and manufactured scientific research instruments, requiring voltage output and measurement accuracy of not less than 1mV, maximum voltage of not less than 10V, current measurement accuracy of not less than 1nA, and maximum current of not less than 1mA.

5. The method for preparing surface protrusions of metal nanomaterials as described in claim 1, characterized in that, In step 6), the morphology of the metal protrusion is controlled by monitoring the transient slope of the continuously increasing RV curve and the magnitude of the resistance rise. The magnitude of the resistance rise after a single IV scan is controlled between 1% and 10%.

6. The method for preparing surface protrusions of metal nanomaterials as described in claim 5, characterized in that, After 1 to 3 control operations, the metal protrusions on the surface of the nanowire or nanobelt become needle-like, and the height of the highest point of the protrusion increases by 1-10 nm after each control operation.

7. The method for preparing surface protrusions of metal nanomaterials as described in claim 5, characterized in that, After 2-10 adjustment operations, the metal protrusions exhibit a saddle-shaped structure. After each adjustment operation, the height of the highest point of the protrusions increases by 0-5nm.

8. The method for preparing surface protrusions of metal nanomaterials as described in claim 5, characterized in that, After at least three adjustment operations, the metal protrusion exhibits a hemispherical structure. After each adjustment operation, the height of the highest point of the protrusion increases by 0-3 nm.

Images