| Summary: | 博士 === 國立中興大學 === 物理學系所 === 102 === Gold nanoparticle (AuNP) films stacked with individual AuNPs have been shown to exhibit novel electric, plasmonic, and photoelectric properties for wide applications. In this thesis, we developed an efficient centrifugal method to assemble desirable large area monolayer, multilayer, and three-dimensional (3D) patterned AuNP films with the nanolithography techniques as AuNP devices. For this devices, we studied the electronic transport of the 2D NPs films, the NP strain device assembled on the flexible substrate and the application of surface enhanced Raman spectroscopy (SERS) device with the patterned NPs film.
For the electronic transport of the 2D NPs films, studied by three means: tuning the tunnel barrier width by different molecule modification(the length of the molecules from 0.9nm to 1.88nm) and by substrate bending, and tuning the barrier height by high-dose electron beam(e-beam) exposure. The resistance of AuNPs film changed with 2-7 order of magnitude after the exposure, the property can be tuned from insulator to metal. All approaches indicate that the metal–Mott insulator transition is governed predominantly by the interparticle coupling strength, which can be quantified by the room temperature sheet resistance. The Hubbard gap, following the prediction of quantum fluctuation theory, reduces to zero rapidly as the sheet resistance decreases to the quantum resistance. At very low temperature, the fate of devices near the Mott transition depends on the strength of disorder. The charge conduction is from nearest-neighbour hopping to co-tunnelling between nanoparticles in Mott insulators whereas it is from variable-range hopping through charge puddles in Anderson insulators. When the two-dimensional nanoparticle network is under a unidirectional strain, the interparticle coupling becomes anisotropic so the average sheet resistance is required to describe the charge conduction. When the AuNPs device prepared near the metal-insulator transition. The insulating devices demonstrated single-charge tunneling and resonant tunneling at mK temperatures. A magnetic field perpendicular to the substrate could suppress the Coulomb oscillations, suggesting that the charge interactions were due to dynamical charge inhomogeneities, rather than single-nanoparticle charging effects.
In addition to electronic transport of the NP films, a concise and economical way to build nanoparticle thin-film strain sensors of high gauge factors on flexible polyimide substrate is developed. The gauge factor, which quantifies a strain sensor’s performance, can reach as high as 100, much larger than many other competing sensors. However, their gauge factors may be reduced by disorder because of microscopic detour of charge conduction. The disorder also results in large resistance change when the current flows in the direction perpendicular to a unidirectional strain, reducing the response anisotropy a typical strain sensor would have. The stability and endurance of the strain sensors are confirmed with 70000 bending cycles. In some of the device, we found out the device showed a hysteresis loop in a bending cycle in a certain range of strain. Moreover, the application as SERS devices are made by the patterned NPs films because of their surface plasmon resonance. The Raman spectrum mapping(with 633nm excitation laser) shows that a smaller NP film produces a stronger light reflection intensity. There are “hot spots”, exhibiting enhanced light reflections and Raman signals at the edge of these NPs films. By designing the shape and size of the patterned NP film, one can get “hot spots” for SERS signal, allowing wide applications.
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