Spectrally tunable nanoporous anodic alumina distributed Bragg reflectors (NAA-DBRs) are modified with titanium dioxide (TiO 2 ) coatings via atomic layer deposition and used as model optoelectronic platforms to harness slow light for photocatalysis under visible−NIR illumination. Photocatalytic breakdown of methylene blue (MB) with a visible absorbance band is used as a benchmark reaction to unveil the mechanism of slow light-enhanced photocatalysis in TiO 2 −NAA-DBRs with a tunable photonic stop band (PSB) and thickness of TiO 2 . Assessment of the optical arrangement between MB's absorbance band and the PSB of TiO 2 −NAA-DBRs is used to identify and quantify slow light contributions in driving this model photocatalytic breakdown reaction. Our findings reveal that photodegradation rates rely on both the spectral position of PSB and thickness of the semiconductor. The performance of these photocatalysts is the maximum when the red edge of the PSB is spectrally close to the red or blue boundary of the MB's absorbance band and to dramatically decrease within the absorbance maximum of MB due to light screening by dye molecules. It is also demonstrated that TiO 2 −NAA-DBRs featuring thicker photoactive TiO 2 layers can harvest more efficiently incident slow light by generating extra pairs of charge carriers on the semiconductor coating's surface. The crystallographic phase of TiO 2 in the functional coatings is found to be critical in determining the performance of these model photocatalyst platforms, where the anatase phase provides ∼69% higher performance over its amorphous TiO 2 form. This study provides opportunities toward the development of energy-efficient photocatalysts for environmental remediation and energy generation and other optoelectronic applications.

Photocatalysis comprises a variety of light-driven processes in which solar energy is converted into green chemical energy to drive reactions such as water splitting for hydrogen energy generation, degradation of environmental pollutants, CO2 reduction and NH3 production. Electrochemically engineered nanoporous materials are attractive photocatalyst platforms for a plethora of applications due to their large effective surface area, highly controllable and tuneable light-harvesting capabilities, efficient charge carrier separation and enhanced diffusion of reactive species. Such tailor-made nanoporous substrates with rational chemical and structural designs provide new exciting opportunities to develop advanced optical semiconductor structures capable of performing precise and versatile control over light–matter interactions to harness electromagnetic waves with unprecedented high efficiency and selectivity for photocatalysis. This review introduces fundamental developments and recent advances of electrochemically engineered nanoporous materials and their application as platforms for photocatalysis, with a final prospective outlook about this dynamic field.

ZnO field emitters on freely suspended inorganic nanomembranes were synthesized by catalyst-assisted metal organic chemical vapor deposition (MOCVD) using the precursors zinc acetylacetonate hydrate and oxygen. The morphology and the possibly involved growth mechanisms of the randomly distributed ZnO nanostructures were investigated by scanning electron microscopy (SEM) and by energy-dispersive x-ray spectroscopy (EDX). The findings indicate a growth process that involves the vapor-liquid-solid as well as the vapor-solid-solid mechanism. The field emission properties of such ZnO nanowire samples showed to be highly reproducible and independent of the investigated Si-based substrate types. Herein, a new type of flexible substrate for the MOCVD process has been introduced that allows for the direct growth of ZnO nanowires on free-standing membranes for potential field emission-based sensor applications. A turn-on field of 4.1 V µm-1 was detected for a macroscopic emission current density of 10 µA cm-2 and the stability test revealed fluctuations of only 9 % around the mean emission current over a duration of 3 h proving a reliable and stable operation of such devices. Moreover, approaches were identified to further enhance the field emission characteristics of the ZnO nanowires by variation of the synthesis parameters and by enlargement of the nanomembrane area.

One-dimensional zinc oxide nanostructures have aroused interest from scientists and engineers for electron field emission applications because of their experimentally accessible high aspect ratio in combination with their low work function. A comprehensive study of the vapor-solid growth of zinc oxide (ZnO) nanowhiskers by utilizing zinc acetylacetonate hydrate and oxygen at low temperature (580 °C) is reported herein. The nanowhiskers morphology was investigated by varying different growth parameters, such as temperature, substrate type and position, gas flow, precursor amount, and growth time. According to the obtained parameter dependences, the process was optimized to achieve homogenous crystalline nanowhiskers with high aspect ratios and clearly defined surface facets and tips. We show electron field emission measurements from tailor-made ZnO nanowhiskers grown on n-doped silicon, titanium thin films, and free-standing silicon nitride membranes, revealing field emission turn-on fields significantly lower compared to a perfect flat ZnO thin film. Especially the latter devices—ZnO nanowhiskers on a free-standing membrane—might pave the way into a novel nanomembrane detector unit in proteomics, which can significantly extend the mass range of current time-of-flight mass spectrometers.

We tested the growth of human iPSC-derived NPCs on nanowire arrays across a wide range of array characteristics. The proliferation, viability, and interaction with the nanowire arrays were mapped depending on the array pitch and nanowire length.