Piezoresistive responses of nanoparticle thin-film strain sensors on flexible polyimide substrates were studied. Disordered interparticle tunneling introduces microscopic detour of charge conduction so as to reduce gauge factors. The disorder also results in large resistance change when current flows in the direction perpendicular to a unidirectional strain, reducing response anisotropy. For practical usages, stability and endurance of these strain sensors are confirmed with 7 × 104 bending cycles. Cracks form in devices under prolonged cyclic bending and slightly reduce gauge factor.

Gold nanoparticle (AuNP) films Stacked with individual AuNPs have been shown to exhibit novel electric, plasmonic, and photoelectric properties for wide applications. Here, we developed an efficient centrifugal method to assemble desirable large area monolayer, multilayer, and three-dimensional (3D) patterned AuNP films. The formation mechanism of AuNP films under different colloidal interactions was studied. The optimal energy barrier is about 10 k(B)T for assembling high quality monolayer AuNP films. The shift of localized surface plasmon resonance bands of the films follows a near-exponential distance decay with interparticle spacing s. A red-shift of about 190 nm reveals the strong near-field coupling at s similar to 0.9 nm. The electrical resistance exponentially increases with s, and exhibits Coulomb charging behavior at low temperature. Furthermore, patterning of AuNP films based on the lift-off technique was achieved and yielded 2D/3D complex structures with submicrometer critical dimension. This assembly method provides a feasible approach in developing future nanodevices and functional nanostructures

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How the interparticle tunnelling affects the charge conduction of self-assembled gold nanoparticles is studied by three means: tuning the tunnel barrier width by different molecule modification and by substrate bending, and tuning the barrier height by high-dose electron beam exposure. 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.