Intrinsic defect engineering of CVD grown monolayer MoS2_2 for tuneable functional nanodevices

Defects in atomically thin materials can drive new functionalities and expand applications to multifunctional systems that are monolithically integrated. An ability to control formation of defects during the synthesis process is an important capability to create practical deployment opportunities. Molybdenum disulfide (MoS$_2$), a two-dimensional (2D) semiconducting material harbors intrinsic defects that can be harnessed to achieve tuneable electronic, optoelectronic, and electrochemical devices. However, achieving precise control over defect formation within monolayer MoS$_2$, while maintaining the structural integrity of the crystals remains a notable challenge. Here, we present a one-step, in-situ defect engineering approach for monolayer MoS$_2$ using a pressure dependent chemical vapour deposition (CVD) process. Monolayer MoS$_2$ grown in low-pressure CVD conditions (LP-MoS$_2$) produces sulfur vacancy (Vs) induced defect rich crystals primarily attributed to the kinetics of the growth conditions. Conversely, atmospheric pressure CVD grown MoS$_2$ (AP-MoS$_2$) passivates these Vs defects with oxygen. This disparity in defect profiles profoundly impacts crucial functional properties and device performance. AP-MoS$_2$ shows a drastically enhanced photoluminescence, which is significantly quenched in LP-MoS$_2$ attributed to in-gap electron donor states induced by the Vs defects. However, the n-doping induced by the Vs defects in LP-MoS$_2$ generates enhanced photoresponsivity and detectivity in our fabricated photodetectors compared to the AP-MoS$_2$ based devices. Defect-rich LP-MoS$_2$ outperforms AP-MoS$_2$ as channel layers of field-effect transistors (FETs), as well as electrocatalytic material for hydrogen evolution reaction (HER). This work presents a single-step CVD approach for in-situ defect engineering in monolayer MoS$_2$ and presents a pathway to control defects in other monolayer material systems.Comment: 29 pages, 5 figure

Hybrid crystalline-ITO/metal nanowire mesh transparent electrodes and their application for highly flexible perovskite solar cells

Here, we propose crystalline indium tin oxide/metal nanowire composite electrode (c-ITO/metal NW-GFRHybrimer) films as a robust platform for flexible optoelectronic devices. A very thin c-ITO overcoating layer was introduced to the surface-embedded metal nanowire (NW) network. The c-ITO/metal NW-GFRHybrimer films exhibited outstanding mechanical flexibility, excellent optoelectrical properties and thermal/chemical robustness. Highly flexible and efficient metal halide perovskite solar cells were fabricated on the films. The devices on the c-ITO/AgNW- and c-ITO/CuNW-GFRHybrimer films exhibited power conversion efficiency values of 14.15% and 12.95%, respectively. A synergetic combination of the thin c-ITO layer and the metal NW mesh transparent conducting electrode will be beneficial for use in flexible optoelectronic applications

LSPR-Induced Catalytic Enhancement Using Bimetallic Copper Fabrics Prepared by Galvanic Replacement Reactions

A simple galvanic replacement (GR) reaction-based strategy to create copper-based bimetallic fabrics for photoreductive catalysis is reported. It is shown that a nanostructured Cu@Fabric can be easily converted into bimetallic Cu-Au@Fabric and Cu-Ag@Fabric through a spontaneous electroless process that involves simple exposure of copper fabrics to the aqueous solutions of gold and silver ions. The nanoscale hierarchical ordering of cotton fabrics combined with their high porosity and wettability make them outstanding supports for catalyst recovery and reusability. The deposition of miniscule quantities of expensive noble metals on readily available Cu not only reduces the overall catalyst cost, but also plays a major role in improving the catalyst stability and reusability over several cycles through minimizing Cu oxidation. The synergistic effects of the localized surface plasmon resonance (LSPR) properties of Cu, Au, and Ag allow these bimetallic fabrics into highly active visible light photocatalysts. Mechanistic investigation of the photocatalytic activity provides in-depth information on the electron transfer processes occurring at the catalyst/ reactant interface, revealing electron transport as the rate-limiting step, which could be overcome under visible light photoillumination conditions. The outcomes enhance the understanding of template-supported bimetallic nanostructures for LSPR-induced photocatalysis applications, offering new potential to design multifunctional fabrics for various applications

SURFACE RESIDUAL STRESSES AND MICROMECHANISMS OF WEAR ASSESSED ON RETRIEVED CERAMIC FEMORAL HEADS

e experimental determination of residual stress fields on the surface of retrieved femoral heads represents a fundamental step in understanding their wear degradation behavior and the tribological mechanisms, which are operative on the femoral joint during its working life time. In this work, the surface of retrieved alumina and zirconia (Al2O3 and ZrO2) femoral heads were investigated by piezo-spectroscopic tecniques based both on photoluminescence and Raman effects. The high spatial resolution of the laser, impinging on the investigated surface (typically about 1 micron of lateral resolution), enabled us estimating patterns and magnitude of residual stress in extremely narrow zones, comparable with the grain size of the material. Four retrieved ceramic femoral heads were analyzed

Broadband light active MTCNQ-based metalorganic semiconducting hybrids for enhanced redox catalysis

Efficient harvesting of solar light is highly desirable for a wide range of applications, including photocatalysis and energy conversion. However, traditional semiconducting metal oxide photocatalysts are typically effective only under UV irradiation while metalmetal oxide hybrids can utilize the UV as well as the visible component of the solar light. In this article, we fabricate hybrids of metal7,7,8,8-tetracyanoquinodimethane (TCNQ) on cotton fibres as a supporting three-dimensional (3D) template for photo-reductive catalysis. These materials extend the absorption of light from the visible to infrared region, thereby allowing the use of over 95% of solar irradiation. We demonstrate the ability of these materials to harvest light across a broad wavelength range by utilizing them as highly active materials for reductive photocatalysis. The mechanism of the underlying charge-transfer phenomena under different photo-excitation conditions reveals a photo-illumination induced redox process at the catalyst/reactant interface resulting in superior catalytic efficiency