Strain Modulation of Optoelectronic Properties in Nanolayered Black Phosphorus: Implications for Strain-Engineered 2D Material Systems

Strain engineering is an exciting direct approach to control the key intrinsic properties of two-dimensional (2D) materials. However, fabrication complexities arising from weak van der Waals interaction-induced slippage, coupled with mechanical breakdown of metal electrodes, have prevented fundamental investigations into strain effects on electrical and optoelectronic characteristics of these material systems. To overcome this limitation, we report a simple prestretch fabrication technique that allowed us to demonstrate a functional multilayer black phosphorus (BP)-based device on a stretchable elastomeric platform. By applying a uniaxial compressive strain of up to 10%, we reveal that mechanical strain can be effectively used to modulate the electronic and optical properties of nanolayered BP. This simple strategy can be extended well-beyond BP to other 2D materials, creating opportunities for fundamental investigations into strain effects in 2D material systems and potential applications in strain-engineered sensors for optical synapse applications

Gold Sunflower Microelectrode Arrays with Dendritic Nanostructures on the Lateral Surfaces for Antireflection and Surface-Enhanced Raman Scattering

A facile method is presented for uniform electrochemical growth of dendritic gold nanostructures selectively at the lateral surfaces of conductor–dielectric disc arrays to obtain gold sunflower microelectrode arrays (SMA). The electrical anisotropicity of Au–SiO2 disc arrays is leveraged to restrain the electrochemical growth to the lateral surfaces, while the enhanced electric field on the lateral surfaces due to the fringe effect facilitates growth of highly dendritic nanostructures in unprecedented growth regimes. Electrochemical growth of gold dendrites is performed on 200 nm thick gold lateral surfaces of Au–SiO2 disc arrays with a disc diameter of 5 μm, a 50 nm SiO2 thickness, and dendrite sizes controlled from 150 to 1400 nm in length. The fabricated SMA exhibit broadband antireflection characteristics for visible radiation, tunable photonic–plasmonic hybrid modes in the near-infrared region, strong electromagnetic (EM) field enhancements, and a high density of EM hotspots useful for surface-enhanced Raman scattering (SERS). The efficacy of developed gold SMA is demonstrated for SERS-based detection of an important Raman label 4-aminothiophenol (4-ATP), which is widely used for binding and detection of different biomarkers. The optimized SERS substrate exhibits an impressive limit of detection of 0.5 nM for 4-ATP with a relative standard deviation of only 6.74% and could be reused multiple times following the surface regeneration process

Vanadium Dioxide-Based Miniaturized Thermal Sensors: Humidity Effects on Phase Change and Sensitivity

With rapid advancements in technology in the electronics sector, demand for the miniaturization of devices while retaining their functionality is on the rise. Metal oxide-based thermal sensors are desired, owing to their enhanced sensing capabilities and low cost of operation. Highly sensitive metal oxide sensors can enable stable, accurate, and miniaturized thermal sensors tailored to different operational ranges. However, the influence of humidity and how it affects the sensitivity of the material by interacting with the material surface has not been extensively studied. In this work, we report a vanadium dioxide (VO2)-based thin film thermal sensor studied under the influence of varying humidity conditions. The effect of different humidity levels on the overall thermal sensing behavior and the insulator-to-metal transition (IMT) phenomenon was investigated. Further, density functional theory (DFT) studies were conducted to understand the thermal sensing mechanism under changing humidity conditions. The developed sensor exhibited a good response over a broad temperature range of −100 to 100 °C, with a TCR of −0.00243%, high sensitivity, and cyclic repeatability. Wireless measurement capabilities were also demonstrated. Such sensors could potentially be used in environmental sensing applications

Vanadium Dioxide-Based Miniaturized Thermal Sensors: Humidity Effects on Phase Change and Sensitivity

With rapid advancements in technology in the electronics sector, demand for the miniaturization of devices while retaining their functionality is on the rise. Metal oxide-based thermal sensors are desired, owing to their enhanced sensing capabilities and low cost of operation. Highly sensitive metal oxide sensors can enable stable, accurate, and miniaturized thermal sensors tailored to different operational ranges. However, the influence of humidity and how it affects the sensitivity of the material by interacting with the material surface has not been extensively studied. In this work, we report a vanadium dioxide (VO2)-based thin film thermal sensor studied under the influence of varying humidity conditions. The effect of different humidity levels on the overall thermal sensing behavior and the insulator-to-metal transition (IMT) phenomenon was investigated. Further, density functional theory (DFT) studies were conducted to understand the thermal sensing mechanism under changing humidity conditions. The developed sensor exhibited a good response over a broad temperature range of −100 to 100 °C, with a TCR of −0.00243%, high sensitivity, and cyclic repeatability. Wireless measurement capabilities were also demonstrated. Such sensors could potentially be used in environmental sensing applications

The Acoustophotoelectric Effect: Efficient Phonon–Photon–Electron Coupling in Zero-Voltage-Biased 2D SnS₂ for Broad-Band Photodetection

Two-dimensional (2D) layered metal dichalcogenides constitute a promising class of materials for photodetector applications due to their excellent optoelectronic properties. The most common photodetectors, which work on the principle of photoconductive or photovoltaic effects, however, require either the application of external voltage biases or built-in electric fields, which makes it challenging to simultaneously achieve high responsivities across broad-band wavelength excitationespecially beyond the material’s nominal band gapwhile producing low dark currents. In this work, we report the discovery of an intricate phonon–photon–electron couplingwhich we term the acoustophotoelectric effectin SnS2 that facilitates efficient photodetection through the application of 100 MHz order propagating surface acoustic waves (SAWs). This effect not only reduces the band gap of SnS2 but also provides the requisite momentum for indirect band gap transition of the photoexcited charge carriers, to enable broad-band photodetection beyond the visible light range, while maintaining pA-order dark currents without the need for any external voltage bias. More specifically, we show in the infrared excitation range that it is possible to achieve up to 8 orders of magnitude improvement in the material’s photoresponsivity compared to that previously reported for SnS2-based photodetectors, in addition to exhibiting superior performance compared to most other 2D materials reported to date for photodetection

Black Phosphorus-Diketopyrrolopyrrole Polymer Semiconductor Hybrid for Enhanced Charge Transfer and Photodetection

Black Phosphorus-Diketopyrrolopyrrole Polymer Semiconductor Hybrid for Enhanced Charge Transfer and Photodetectio

High‑<i>k</i> 2D Sb₂O₃ Made Using a Substrate-Independent and Low-Temperature Liquid-Metal-Based Process

High dielectric constant (high-k) ultrathin films are required as insulating gate materials. The well-known high-k dielectrics, including HfO2, ZrO2, and SrTiO3, feature three-dimensional lattice structures and are thus not easily obtained in the form of distinct ultrathin sheets. Therefore, their deposition as ultrathin layers still imposes challenges for electronic industries. Consequently, new high-k nanomaterials with k in the range of 40 to 100 and a band gap exceeding 4 eV are highly sought after. Antimony oxide nanosheets appear as a potential candidate that could fulfill these characteristics. Here, we report on the stoichiometric cubic polymorph of 2D antimony oxide (Sb2O3) as an ideal high-k dielectric sheet that can be synthesized via a low-temperature, substrate-independent, and silicon-industry-compatible liquid metal synthesis technique. A bismuth–antimony alloy was produced during the growth process. Preferential oxidation caused the surface of the melt to be dominated by α-Sb2O3. This ultrathin α-Sb2O3 was then deposited onto desired surfaces via a liquid metal print transfer. A tunable sheet thickness between ∼1.5 and ∼3 nm was achieved, while the lateral dimensions were within the millimeter range. The obtained α-Sb2O3 exhibited high crystallinity and a wide band gap of ∼4.4 eV. The relative permittivity assessment revealed a maximum k of 84, while a breakdown electric field of ∼10 MV/cm was observed. The isolated 2D α-Sb2O3 nanosheets were utilized in top-gated field-effect transistors that featured low leakage currents, highlighting that the obtained material is a promising gate oxide for conventional and van der Waals heterostructure-based electronics

Vacuum-Free Liquid-Metal-Printed 2D Semiconducting Tin Dioxide: The Effect of Annealing

Thin film transistors (TFTs) offer unparalleled opportunities for the fabrication of multifunctional electronic and optoelectronic devices. In this work, we report a vacuum-free liquid metal exfoliation technique for rapidly printing ∼2 nm-thick layer of oxide from molten tin. We explore the effect of rapid thermal annealing at 450 °C on the stoichiometry, morphology, and crystal structure of the resulting tin oxide nanosheets. The annealed samples exhibit a dominant SnO2 phase and a high degree of transparency (>99%) in the visible spectra. Field-effect transistors based on the two-dimensional (2D) SnO2 films show typical n-channel conduction with a field-effect mobility of ∼7.5 cm2 V–1 s–1. Photodetectors utilizing annealed tin dioxide demonstrate significant improvement in photoresponsivity reaching a value of 5.2 × 103 A W–1 compared to that found in an unannealed sample at an ultraviolet wavelength of 285 nm. We demonstrate that the improvement in device performance is due to nanocrystalline changes within the oxide layers during the annealing process. This work offers a straightforward and ambient air-compatible method for depositing ultrathin, large-area semiconducting oxides as potential candidates for enabling emerging applications in transparent nanoelectronics and optoelectronics