This study investigates bipolar and nonpolar resistive-switching of HfO 2 with various metal electrodes. Supported by convincing physical and electrical evidence, it is our contention that the composition of conducting filaments in HfO 2 strongly depends upon the metal electrodes. Nonpolar resistive-switching with the Ni electrode is attributed to the migration of metal cations and the corresponding electrochemical metallization. Conversely, oxygen-deficient filaments induced by anion migration are responsible for bipolar resistive-switching. It was also found that the characteristic nature of the conducting filaments influences many aspects of switching characteristics, including the switching power, cycling variations, and retention at elevated temperatures. V
A two‐tier nanostructure comprising a 20‐nm‐diameter “nanograss” on 100‐nm‐diameter nanopillars exhibits robust and near‐perfect superhydrophobicity, that is, water contact angles close to 180° and sliding angles close to 0°. Although the solid fraction was very low (∼0.02%), this surface could support a drop of water under a pressure of 234 Pa.
In this paper, sub-20 nm ferroelectric PVDF–TrFE
copolymer nanograss structures with aspect ratios up to 8.9 were developed.
This study demonstrated sub-20 nm PVDF–TrFE nanograss structures
that are nanoimprinted using a silicon nanograss mold in a single
step. Vertically oriented PVDF–TrFE nanopillars were poled
using the developed flip-stacking poling method. According to the
PFM measurements, the piezoelectricity of flat thin films fabricated
in this work reaches 14.0 pm/V. The maximum output voltage of the
single PVDF–TrFE nanopillar was 526 mV, and the maximum piezoelectricity
of the single PVDF–TrFE nanopillar was 210.4 pm/V. The piezoelectricity
of the developed PVDF–TrFE nanograss structures was 5.19 times
larger than that of the PVDF–TrFE flat thin films. The developed
technique is simple, economical, and easy to fabricate. The developed
ferroelectric PVDF–TrFE copolymer nanograss structures, which
showed enhanced piezoelectricity compared to the PVDF–TrFE
flat thin films, have potential applications in nanotip-based protein
biosensors, nanotip-based tactile sensors, and power nanogenerators.
In this paper, we report the optical constants (refractive index, extinction coefficient) of self-assembled hollow gold nanoparticle (HGN) monolayers determined through spectroscopic ellipsometry (SE). We prepared a series of HGNs exhibiting various morphologies and surface plasmon resonance (SPR) properties. The extinction coefficient (k) curves of the HGN monolayers exhibited strong SPR peaks located at wavelengths that followed similar trends to those of the SPR positions of the HGNs in solution. The refractive index (n) curves exhibited an abnormal dispersion that was due to the strong SPR extinction. The values of Δn and k
max both correlated linearly with the particle number densities. From a comparison of the optical constant values of HGNs with those of solid Au nanoparticles (NPs), we used SE measurements to demonstrate a highly sensitive Si-based chemical sensor. HGNs display a slightly lower value of k at the SPR peak but a much higher sensitivity to changes in the surrounding medium than do solid Au NPs.
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