Electrical Properties of Double-Sided Polymer Surface Nanostructures
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In this study, double-sided polymer surface nanostructures are fabricated using twice nanoimprint lithography and metal deposition technique. We perform electrical property measurement on these double-sided surface nanostructures. Open-circuit voltage and short-circuit current of the as-prepared samples with double-sided surface nanostructures and conductive electrode are recorded using an oscilloscope with applying different external force. The measurements are carried out at room temperature. We find that the intensity of open-circuit voltage and short-circuit current for the double-sided surface nanostructures depends strongly on the sizes, shapes, and arrangements of nanostructures and pressure force. The strongest electrical property can be observed in the hexagon nanopillar arrays with the diameter of about 400 nm containing sub-50-nm resolution sharp structures at the force of about 40 N. We discuss the physical mechanisms responsible for these interesting research findings. The experimental results we study are relevant to the applications of double-sided surface nanostructures such as a nanogenerator, pressure sensors, and nano-optoelectronic devices.
KeywordsDouble-sided nanostructures Nanoimprint lithography Electrical properties Open-circuit voltage Short-circuit current Pressure force
Indium tin oxide
Scanning electron microscopy
Surface-enhanced Raman scattering
Nanostructures on surfaces attract much interest as an efficient media for surface-enhanced Raman scattering (SERS), surface plasmon resonance, nonlinear optical and electrical response, and plasmonic excitation such as nanoparticles, nanograting, and nanopillars, especially metal surface nanostructures [1, 2, 3, 4, 5], which have potential applications as electronic, magnetic, photonic, optoelectronic, and sensor devices [6, 7, 8, 9, 10]. From a viewpoint of physics, the basic physical properties of surface nanostructures differ significantly from those of bulk materials with the same components. In particular, surface effects can be observed in the surface nanostructures. Therefore, surface nanostructures have been a major focus of research on surface materials which can be taken as a fundamental building block of nanotechnology and nanodevices. It should be noticed that polymer surface nanostructures have displayed unique optoelectronic and electrical properties due to the triboelectric effect that is electrostatic induction occurring within polymer materials [11, 12, 13]. Nanoscale structures increase surface roughness and the contact friction area to enhance the triboelectric effect, especially double-sided surface structures. The triboelectric effect in surface nanostructures can cause the generation of large electrical charges, which can obtain current by connecting electrodes and wires. The triboelectric effect in polymer surface nanostructures and related phenomena contributes greatly to their promising applications in nanogenerators, pressure and temperature sensors, and other electronic devices [14, 15, 16, 17]. The nanogenerators can transfer mechanical energy into electric energy, and the pressure or temperature sensors can transform different pressure or temperature to detectable electrical or optical signals.
As the rapid development of nanotechnology, it is now easy to fabricate periodic and complex unordered surface nanostructures, for example, photolithography, nanoimprint lithography (NIL), self-assembly, and interference lithography [18, 19, 20, 21, 22]. As one popular replication nanotechnology, NIL is simple, low-cost, high-resolution, and high-throughput, which is ideal for fabricating polymer nanostructures [23, 24, 25]. One major advantage to apply surface nanostructures as electronic devices is that the electrical response of the surface nanostructures can be tuned and modulated via varying structure parameters such as diameter, shape, and arrangement of nanostructures. Therefore, it is of importance and significance to examine basic electrical properties of surface nanostructures.
In this article, we present a detailed experimental study on the electrical properties of two kinds of double-sided surface nanostructures, such as grating and nanopillar arrays. The double-sided polymer surface nanostructures are fabricated using twice NIL process. Because the nanostructures on two side surfaces need not be aligned, the imprinting process is simple and low cost. The conductive electrode for measuring electrical signals is prepared by the metal deposition technique, such as indium tin oxide (ITO) or Ag film. We would like to research how these surface nanostructures can respond to external pressure, how their electrical properties depend on the sample’s parameters, and how the open-circuit voltage and short-circuit current of the as-prepared samples change.
When deformed by an external-touched mechanical pressure deformation provided by other materials, triboelectric charges are generated and distributed on the polymer surfaces. As soon as the deformation starts to be released, the external-touched materials become separated with the polymer surface. These triboelectric charges cannot be compensated, leading to induce opposite charges on the ITO electrode to drive free electrons to flow from the ITO electrode to the external circuit. This electrostatic induction process can give an output voltage/current signal.
Results and Discussion
The experimental results demonstrate that the external pressure force of about 40 N is an appropriate force for the hexagon nanopillar arrays to enhance electrical properties, because too much pressure force may destroy the nanostructure samples. This study can provide a basis for further investigation into other electrical or optical properties.
In this article, the samples with double-sided surface nanostructures are measured. The measuring mechanism of the electrical properties of surface nanostructures indicates that the double-sided surface nanostructures show better electrical performance.
In this study, double-sided polymer grating and nanopillar arrays have been fabricated using state-of-the-art nanotechnology. The electrical property measurements on these surface nanostructures have been carried out with applying external force at room temperature. We have found that the electrical signal of these samples depends strongly on force and structure arrangements and shapes. In particular, the strongest electrical signal can be observed in the hexagon nanopillar arrays with a diameter of about 400 nm containing sub-50-nm resolution sharp structures compared with other samples. And the appropriate force for measurement of electrical properties is about 40 N. These results indicate that the electrical properties can drive surface nanostructures for the applications in pressure sensor, nanogenerator, and electronic devices. We hope that the interesting experimental finding from this study can provide an in-depth understanding of electrical properties of grating and nanopillars with different arrangements.
This work was supported by the National Natural Science Foundation of China (NSFC) (Grant number 51703227, C0025053, 61605211, 61504147, and 61775213), Sichuan Science and Technology Program (Grant number 2017RZ0031, 2019YJ0014), the Instrument Development of Chinese Academy of Sciences, The National R&D Program of China (Grant number 2017YFC0804900), and Youth Innovation Promotion Association of Chinese Academy of Sciences. The authors thank their colleagues for their discussions and suggestions for this research.
ZM proposed the research work, coordinated the collaboration, and fabricated the nanostructures. XLP and DSH designed the experiment and experiment setup and carried out the analyses of the experimental results. CAX, SLF, and PH carried out the measurement and analyses. DCL participated in the experimental measurements, results, and discussions. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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