The mechanical and optical properties generated due to the stacking of different atomically thin materials have made it possible to tune and engineer these materials for next-generation electronics. ...The understanding of the interlayer interactions in such stacked structures is of fundamental interest for structure and property correlation. Here, a combined approach of in situ Raman spectroscopy and mechanical straining along with molecular dynamics (MD) simulations has been used to probe one such interface, namely, the WS2/MoS2 heterostructure. Vertical heterostructures on poly(methyl methacrylate), when flexed, showed signs of decoupling at 1.2% strain. Theoretical calculations showed strain-induced stacking changes at 1.75% strain. The sliding characteristics of layers were also investigated using scanning probe microscopy based nanoscratch testing, and the results are further supported by MD simulations. The present study could be used to design future optoelectronic devices based on WS2/MoS2 heterostructures.
Hydrogen (H2) has attained significant benefits as an energy carrier due to its gross calorific value (GCV) and inherently clean operation. Thus, hydrogen as a fuel can lead to global sustainability. ...Conventional H2 production is predominantly through fossil fuels, and electrolysis is now identified to be most promising for H2 generation. This review describes the recent state of the art and challenges on ultra-pure H2 production through methanol electrolysis that incorporate polymer electrolyte membrane (PEM). It also discusses about the methanol electrochemical reforming catalysts as well as the impact of this process via PEM. The efficiency of H2 production depends on the different components of the PEM fuel cells, which are bipolar plates, current collector, and membrane electrode assembly. The efficiency also changes with the nature and type of the fuel, fuel/oxygen ratio, pressure, temperature, humidity, cell potential, and interfacial electronic level interaction between the redox levels of electrolyte and band gap edges of the semiconductor membranes. Diverse operating conditions such as concentration of methanol, cell temperature, catalyst loading, membrane thickness, and cell voltage that affect the performance are critically addressed. Comparison of various methanol electrolyzer systems are performed to validate the significance of methanol economy to match the future sustainable energy demands.
Metal–semiconductor contact has been a critical topic in the semiconductor industry because it influences device performance remarkably. Conventional metals have served as the major contact material ...in electronic and optoelectronic devices, but such a selection becomes increasingly inadequate for emerging novel materials such as two-dimensional (2D) materials. Deposited metals on semiconducting 2D channels usually form large resistance contacts due to the high Schottky barrier. A few approaches have been reported to reduce the contact resistance but they are not suitable for large-scale application or they cannot create a clean and sharp interface. In this study, a chemical vapor deposition (CVD) technique is introduced to produce large-area semiconducting 2D material (2H MoTe2) planarly contacted by its metallic phase (1T′ MoTe2). We demonstrate the phase-controllable synthesis and systematic characterization of large-area MoTe2 films, including pure 2H phase or 1T′ phase, and 2H/1T′ in-plane heterostructure. Theoretical simulation shows a lower Schottky barrier in 2H/1T′ junction than in Ti/2H contact, which is confirmed by electrical measurement. This one-step CVD method to synthesize large-area, seamless-bonding 2D lateral metal–semiconductor junction can improve the performance of 2D electronic and optoelectronic devices, paving the way for large-scale 2D integrated circuits.
A colloidal suspension containing a high concentration of metallic nanoparticles (NPs) finds potential applications in flexible electronic printing, nanofluids, healthcare, antifouling coating, and ...so on. Here, we demonstrate a generic, easily scalable, simple, and contamination-free cryogenic temperature grinding method, which can effectively be used to prepare pristine NPs that can be stabilized in polar liquids in high concentrations. These surfactant-free pristine NPs have been found to remain dispersed in different polar liquids (CH3OH, C2H5OH, glycol, etc.) for weeks. The long-term stability of the NPs in these liquids has been investigated using zeta potential, in situ Fourier transform infrared spectroscopy, indicating electrostatic stabilization for ultrapure, surfactant-free NPs. Furthermore, stabilization of the NPs has been probed with detailed calculations using the Derjaguin Landau Verwey Overbeek theory as well as atomistic molecular dynamics simulation (MD). Experimental measurements along with theoretical calculations categorically indicate that the electrostatic energy is helping these NPs to be stabilized in a polar liquid.
Composition and phase specific 2D transition metal dichalogenides (2D TMDs) with a controlled electronic and chemical structure are essential for future electronics. While alloying allows bandgap ...tunability, heterostructure formation creates atomically sharp electronic junctions. Herein, the formation of lateral heterostructures from quaternary 2D TMD alloys, by thermal annealing, is demonstrated. Phase separation is observed through photoluminescence and Raman spectroscopy, and the sharp interface of the lateral heterostructure is examined via scanning transmission electron microscopy. The composition‐dependent transformation is caused by existence of miscibility gap in the quaternary alloys. The phase diagram displaying the miscibility gap is obtained from the reciprocal solution model based on density functional theory and verified experimentally. The experiments show direct evidence of composition‐driven heterostructure formation in 2D atomic layer systems.
Phase separation in quaternary (MoxW1‐xS2ySe2(1‐y)) 2D transition metal dichalcogenide alloys via thermal annealing is demonstrated. The phase separation is shown to occur due to the existence of the miscibility gap in the quaternary alloy and results in the formation of a lateral W‐S‐Se/Mo‐S‐Se heterostructure. The technique provides a facile, one‐step process for heterostructure formation.
Under this study, a straightforward method for producing clay-modified silico-graphitic carbon (CGSGC) was developed and applied to create CGSGC/epoxy coatings for carbon steel (CS). The CGSGC was ...synthesized using a mixture of 25 % pond clay, and 75 % remnant agricultural biomass by mass via pyrolysis route. The aim was to evaluate the barrier and anti-corrosion properties of these coatings. The results demonstrated that adding 0.1 wt.% of CGSGC in the epoxy (EP) matrix enhanced its anti-corrosion inhibition capabilities by 99.8 % when compared with standard EP coating. The 0.1 wt.% CGSGC/EP mixed coating also exhibited robust hydrophobicity with WCA of 142.2° and thermal stability up to 250 °C with 2–3 % coating weight reduction. The microhardness of the optimized sample shows a 59.18 % improvement compared to standard EP coating. SEM images revealed improved EP compactness and reduction in microstructural defects (holes and cracks), with the incorporation of 0.1 wt.% CGSGC. 3D profilometry showed a smoother surface for the 0.1 wt.% CGSGC/EP coating. Similar such materials, while being abundantrly and renewably available, can be a safer alternative to conventional hazardous chemicals for protecting carbon steel from corrosion; not to mention the carbon credit benefits they entail.
The light-induced selective population of short-lived far-from-equilibrium vibration modes is a promising approach for controlling ultrafast and irreversible structural changes in functional ...nanomaterials. However, this requires a detailed understanding of the dynamics and evolution of these phonon modes and their coupling to the excited-state electronic structure. Here, we combine femtosecond mega-electronvolt electron diffraction experiments on a prototypical layered material, MoTe2, with non-adiabatic quantum molecular dynamics simulations and ab initio electronic structure calculations to show how non-radiative energy relaxation pathways for excited electrons can be tuned by controlling the optical excitation energy. We show how the dominant intravalley and intervalley scattering mechanisms for hot and band-edge electrons leads to markedly different transient phonon populations evident in electron diffraction patterns. This understanding of how tuning optical excitations affect phonon populations and atomic motion is critical for efficiently controlling light-induced structural transitions of optoelectronic devices.
Abstract
Photo-induced non-radiative energy dissipation is a potential pathway to induce structural-phase transitions in two-dimensional materials. For advancing this field, a quantitative ...understanding of real-time atomic motion and lattice temperature is required. However, this understanding has been incomplete due to a lack of suitable experimental techniques. Here, we use ultrafast electron diffraction to directly probe the subpicosecond conversion of photoenergy to lattice vibrations in a model bilayered semiconductor, molybdenum diselenide. We find that when creating a high charge carrier density, the energy is efficiently transferred to the lattice within one picosecond. First-principles nonadiabatic quantum molecular dynamics simulations reproduce the observed ultrafast increase in lattice temperature and the corresponding conversion of photoenergy to lattice vibrations. Nonadiabatic quantum simulations further suggest that a softening of vibrational modes in the excited state is involved in efficient and rapid energy transfer between the electronic system and the lattice.
A giant enhancement of nearly 100 times is seen in triethylamine response through Ti–Zr–Cr–V–Ni high-entropy alloy nanoparticle (HEA NP)-induced fermi energy control of two-dimensional molybdenum ...disulfide (MoS2) nanosheets. These Laves-phase HEA NP-decorated MoS2 samples are synthesized using cryomilling followed by 30 h of sonication. The prolonged sonication results in well-exfoliated MoS2 with fairly small (∼10–20 nm) HEA NPs anchored due to cryomilling confirmed by extensive microscopic and spectroscopic examinations. The presence of HEA NPs leads to reduction in edge oxidation of MoS2 as seen from X-ray photoelectron spectroscopy. Moreover, this edge state reduction causes strong Fermi level pinning, which is commonly observed in layered MoS2 with bulk metal electrodes. This leads to target gas-specific carrier-type response and selective oxidation of TEA vapors due to highly catalytically active metals. The resulting composite (MoS2 + NPs) exhibits high response (380% for 2000 ppm TEA vapors) along with selectivity toward TEA at 50 °C. The cross-sensitivity of the composite to other volatile organic compounds and NH3, CO, and H2 has been very minimal. Thus, the highly selective catalytic activity of metal alloy NPs and their Fermi energy control has been proposed as the prime factors for observed large sensitivity and selective response of MoS2 + NP nanocomposites.
Low-density nanostructured foams are often limited in applications due to their low mechanical and thermal stabilities. Here we report an approach of building the structural units of ...three-dimensional (3D) foams using hybrid two-dimensional (2D) atomic layers made of stacked graphene oxide layers reinforced with conformal hexagonal boron nitride (h-BN) platelets. The ultra-low density (1/400 times density of graphite) 3D porous structures are scalably synthesized using solution processing method. A layered 3D foam structure forms due to presence of h-BN and significant improvements in the mechanical properties are observed for the hybrid foam structures, over a range of temperatures, compared with pristine graphene oxide or reduced graphene oxide foams. It is found that domains of h-BN layers on the graphene oxide framework help to reinforce the 2D structural units, providing the observed improvement in mechanical integrity of the 3D foam structure.
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