Mirror-backed Dark Alumina: A Nearly Perfect Absorber for Thermoelectronics and Thermophotovotaics.

We present here a broadband, wide-angle, and polarization-independent nearly perfect absorber consisting of mirror-backed nanoporous alumina. By electrochemically anodizing the disordered multicomponent aluminum and properly tailoring the thickness and air-filling fraction of nanoporous alumina, according to the Maxwell-Garnet mixture theory, a large-area dark alumina can be made with excellent photothermal properties and absorption larger than 93% over a wide wavelength range spanning from near-infrared to ultraviolet light, i.e. 250 nm-2500 nm. The measured absorption is orders of magnitude greater than other reported anodized porous alumina, typically semi-transparent at similar wavelengths. This simple yet effective approach, however, does not require any lithography, nano-mixture deposition, pre- and post-treatment. Here, we also envisage and theoretically investigate the practical use of proposed absorbers and/or photothermal converters in integrated thermoelectronic and/or thermophotovoltaic energy conversion devices, which make efficient use of the entire spectrum of ambient visible to near-infrared radiation.

Paradox of low field enhancement factor for field emission nanodiodes in relation to quantum screening effects.

We put forward the quantum screening effect in field emission [FE] nanodiodes, explaining relatively low field enhancement factors due to the increased potential barrier that impedes the electron Fowler-Nordheim tunneling, which is usually observed in nanoscale FE experiments. We illustratively show this effect from the energy band diagram and experimentally verify it by performing the nanomanipulation FE measurement for a single P-silicon nanotip emitter (Φ = 4.94eV), with a scanning tungsten-probe anode (work function, Φ = 4.5eV) that constitutes a 75-nm vacuum nanogap. A macroscopic FE measurement for the arrays of emitters with a 17-µm vacuum microgap was also performed for a fair comparison.

Plasmonic metallic nanostructures by direct nanoimprinting of gold nanoparticles.

We demonstrated the plasmonic metallic nanostructure fabricated by direct nanoimprinting of gold nanoparticles (AuNPs). This approach combines the patterning and lift-off processes into a simple one-step process without the need for expensive patterning lithographies and the stringent requirement of the lift-off process for nanostructures. Good imprinting integrity was accomplished with a negligible residual layer. The dynamic optical responses of the imprinted gold pillars from AuNPs to the bulk material during the annealing process were investigated. The localized surface plasmon resonance (LSPR) properties of AuNPs or gold pillar arrays can be controlled and tuned during the annealing process. The sensitivity of the gold pillar array in terms of the wavelength shift per refractive index unit (RIU) reached 259 nm/RIU. The size of the imprinted gold pillars is highly scalable in our process. The corresponding resonance wavelengths can be widely tuned from the visible to infrared region by changing the size of the gold pillars, thus providing a wide range of sensing capability.

Sandwiched long-period fiber grating filter based on periodic SU8-thick photoresist technique.

A loss-tunable sandwiched long-period fiber grating (SLPFG) filter is proposed in this Letter. This SLPFG utilized thick SU8 photoresist layers to induce refractive index modulations, and ultrahigh period precision was hence achieved. The external force required to tune this SLPFG filter is about 0.3942 N with the deepest loss attenuation 31.29 dB at 1534 nm wavelength. This process not only improves the overall performance of traditional long period fiber grating but also cuts down the facility cost by 50%. The proposed SLPFG has great potential for low-cost and compact force transducer applications.

Coupled acidification and ultrasound with iron enhances nitrate reduction.

Contaminated soils, especially when pollutant concentrations are high, pose potentially serious threats to surface and groundwater quality, when there are spills, discharges, or leaking storage tanks. For in situ remediation of nitrate in groundwater, the use of zero-valent iron (Fe(0)) is suggested. The formation of passivating scales on Fe(0) over time may limit the long-term reduction potential of Fe(0). The aim of this study was to investigate the effect of ultrasound and pH on the destruction of passive oxide film. Batch tests were conducted in a specially designed protocol using ultrasound, and changing iron (commercial iron powder of micro-scale grain size) loading and pH. The results showed deactivation of the degradation process by Fe(0) with combined ultrasound/iron system and with ultrasound alone. However, the degradation rate increases with decrease in pH. The degradation rate was 45% for pH 2 and 20% for pH 4. The combination of iron, acidification, and ultrasound showed excellent degradation efficiency, and the degradation rate was 99%. Acidification could destroy passive oxide film and activate iron, thus, hastening the reaction between Fe(0) and nitrate. Ultrasound was helpful in destroying or preventing the formation of passive oxide film under acidification.