One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near-edge region can be fitted to a simple expression where the intercept gives the band gap and the fitting exponent identifies the electronic transition as direct or indirect. [See Tauc et al., Physica Status Solidi 15, 627 (1966); naturally, these are usually called “Tauc” plots.] In earlier work, we found that direct band gaps fitted using Tauc's method can be quite accurate, to ∼1% [see Viezbicke et al., Phys. Status Solidi B 252, 1700 (2015)]. Still, slopes of these Tauc plots are less frequently quantified, even though the slopes are directly rooted in key band-structure parameters. In this study, we examine the reproducibility of Tauc plot slopes for ZnO as a model direct-gap material and compare these experimental values with the theoretically derived slope. In contrast to the band gap accuracy, the experimental slope values varied by several orders of magnitude. The histogram of slope values was significantly more compact for Tauc plots exhibiting less Urbach tail contribution. In these cases, the Tauc slopes can provide an order-of-magnitude quantification of other key band characteristics such as carrier effective mass.

Assessing Tauc plot slope quantification: ZnO thin films as a model system

Transparent heat regulating (THR) materials and coatings for energy saving window applications: Impact of materials design, micro-structural, and interface quality on the THR performance

The sluggish kinetics of the oxygen evolution reaction (OER) is the bottleneck for the practical exploitation of water splitting. Here, the potential of a core–shell structure of hydrous NiMoO4 mic ...

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202101324

NiMoO4@Co3O4 Core–Shell Nanorods: In Situ Catalyst Reconstruction toward High Efficiency Oxygen Evolution Reaction

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges.

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Atomic layer deposition: an enabling technology for the growth of functional nanoscale semiconductors

Energy storage performances of Ni-based electrodes rely mainly on the peculiar nanomaterial design. In this work, a novel and low-cost approach to fabricate a promising core-shell battery-like electrode is presented. Ni(OH)2@Ni core-shell nanochains were obtained by an electrochemical oxidation of a 3D nanoporous Ni film grown by chemical bath deposition and thermal annealing. This innovative nanostructure demonstrated remarkable charge storage ability in terms of capacity (237 mAh g−1 at 1 A g−1) and rate capability (76% at 16 A g−1, 32% at 64 A g−1). The relationships between electrochemical properties and core-shell architecture were investigated and modelled. The high-conductivity Ni core provides low electrode resistance and excellent electron transport from Ni(OH)2 shell to the current collector, resulting in improved capacity and rate capability. The reported preparation method and unique electrochemical behaviour of Ni(OH)2@Ni core-shell nanochains show potential in many field, including hybrid supercapacitors, batteries, electrochemical (bio)sensing, gas sensing and photocatalysis.

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Ni(OH) 2 @Ni core-shell nanochains as low-cost high-rate performance electrode for energy storage applications

Robustness and electrical reliability of AZO/Ag/AZO thin film after bending stress

Earth-abundant materials for electrochemical water splitting typically show a lower efficiency than noble and rare metal electrocatalysts. Nanostructuring and appropriate material design can largely improve the performances of low-cost electrocatalysts, opening the route towards profitable mass production. Here, we report on a quantitative investigation of the oxygen evolution reaction (OER) on Ni-based nanowall (NW) electrodes. The NiO and Ni(OH)2 NW films (200 or 400 nm thick) are produced by chemical bath deposition followed by calcination at 350 °C. The morphology and the chemical arrangement of the NW were studied, before and after the OER, by scanning electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy. The OER electrocatalytic activity was investigated by electrochemical measurements under alkaline conditions (1 M KOH), demonstrating a stable overpotential of 345 mV at 10 mA cm−2, a Tafel slope of 48 mV dec−1 and an O2 turnover conversion frequency (TOF) of up to 0.18 s−1. The quantitative measurement of active electrocatalysts, through cross-correlation of the experimental data, shows nearly 100% material utilization in the 200 nm NiO NW. In thicker NiO or Ni(OH)2 NW films this fraction decreases below 60%, probably due to the decrease in the electric potential along the nanostructure, as revealed by numerical simulation. These data and discussion support the use of low-cost Ni-based nanostructures for high-efficiency and sustainable electrocatalysts.

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High intrinsic activity of the oxygen evolution reaction in low-cost NiO nanowall electrocatalysts

Ag cluster beam deposition for TCO/Ag/TCO multilayer

Undoped and Ti-doped ZnO (TZO) films were deposited by atomic layer deposition (ALD). Titanium was introduced by alternating consecutive ZnO cycles between each TiO2 single layer (Ti nominal concentration of 2%). The electrical, optical, morphological, and structural properties of the films (less than 80 nm thick) were tested as a function of the deposition temperature (from 120 to 240 °C). The TZO films deposited at 200 °C showed the lowest resistivity: 3.0 × 10−3 Ω cm. All the resulting TZO films were highly transparent, with an absorbance in the visible range of less than 3%. Thanks to an accurate investigation through transmission electron microscopy we ruled out the well-assessed explanation of an extrinsic doping mechanism of transparent conductive oxide (TCO), suggesting an alternative mechanism. These results demonstrate that the ALD is a promising technique to grow thin TZO films with remarkable electrical and optical properties.

Giacomo Torrisi

Papers

Ni(OH) 2 @Ni core-shell nanochains as low-cost high-rate performance electrode for energy storage applications

Robustness and electrical reliability of AZO/Ag/AZO thin film after bending stress

High intrinsic activity of the oxygen evolution reaction in low-cost NiO nanowall electrocatalysts

Ag cluster beam deposition for TCO/Ag/TCO multilayer

Atomic layer deposition of ZnO/TiO2 multilayers: towards the understanding of Ti-doping in ZnO thin films