Characterization of epitaxial CVD graphene on Ir(111)/α-Al2O3(0001) by photoelectron momentum microscopy

We characterized CVD-grown graphene with high single-crystallinity on Ir(111)/α-Al2O3(0001) by photoelectron momentum microscopy. A multi-functional photoelectron momentum microscope (PMM), which is installed with element-specific valence band photoelectron spectroscopy and X-ray absorption spectroscopy, is a complementary characterization tool to conventional methods, such as Raman spectroscopy and atomic force microscopy, for comprehensive and quantitative characterization of graphene/Ir(111). Using PMM, we characterized the properties of CVD-grown graphene including the single-crystallinity, number of layers, crystal orientation, and degree of interaction between graphene and Ir(111) and clarified the relationship between these properties and the CVD growth conditions.

Optimisation of processing conditions during CVD growth of 2D WS2 films from a chloride precursor

Monolayer tungsten disulphide (WS2) is a direct band gap semiconductor which holds promise for a wide range of optoelectronic applications. The large-area growth of WS2 has previously been successfully achieved using a W(CO)6 precursor, however, this is flammable and a potent source of carbon monoxide (CO) upon decomposition. To address this issue, we have developed a process for the wafer-scale growth of monolayer WS2 from a tungsten hexachloride (WCl6) precursor in a commercial cold-wall CVD reactor. In comparison to W(CO)6, WCl6 is less toxic and less reactive and so lends itself better to the large-scale CVD growth of 2D layers. We demonstrate that a post-growth H2S anneal can lead to a dramatic improvement in the optical quality of our films as confirmed by photoluminescence (PL) and Raman measurements. Optimised films exhibit PL exciton emission peaks with full width at half maximum of 51 ± 2 meV, comparable to other state-of-the-art methods. We demonstrate that our WS2 films can be readily transferred from the sapphire growth substrate to a Si/SiO2 target substrate with no detectable degradation in quality using a polystyrene support layer. Our approach represents a promising step towards the industrial-scale fabrication of p-n junctions, photodetectors and transistors based on monolayer WS2.

Tungsten(VI) selenide tetrachloride, WSeCl4 - synthesis, properties, coordination complexes and application of [WSeCl4(SenBu2)] for CVD growth of WSe2 thin films

WSeCl4 was obtained in good yield by heating WCl6 and Sb2Se3 in vacuo. Green crystals grown by sublimation were shown by an X-ray structure analysis to contain square pyramidal monomers...

Synthesis of layered vs planar Mo2C: role of Mo diffusion

Chemical Vapor Deposition (CVD) growth of Metal Carbides is of great interest as this method provides large area growth of MXenes. This growth is mainly done using a melted diffusion-based process; however, different morphologies in growth process is not well understood. In this work, we report deterministic synthesis of layered (non-uniform c-axis growth) and planar (uniform c-axis growth) of Molybdenum Carbide (Mo2C) using a diffusion-mediated growth. Mo-diffusion limited growth mechanism is proposed where the competition between Mo and C adatoms determines the morphology of grown crystals. Difference in thickness of catalyst at the edge and center lead to enhanced Mo diffusion which plays a vital role in determining the structure of Mo2C. The layered structures exhibit an expansion in the lattice confirmed by the presence of strain. Density Functional Theory (DFT) shows consistent presence of strain which is dependent upon Mo diffusion during growth. This work demonstrates the importance of precise control of diffusion through the catalyst in determining the structure of Mo2C and contributes to broader understanding of metal diffusion in growth of MXenes.

Computational synthesis of 2D materials grown by chemical vapor deposition

The exotic properties of 2D materials made them ideal candidates for applications in quantum computing, flexible electronics, and energy technologies. A major barrier to their adaptation for industrial applications is their controllable and reproducible growth at a large scale. A significant effort has been devoted to the chemical vapor deposition (CVD) growth of wafer-scale highly crystalline monolayer materials through exhaustive trial-and-error experimentations. However, major challenges remain as the final morphology and growth quality of the 2D materials may significantly change upon subtle variation in growth conditions. Here, we introduced a multiscale/multiphysics model based on coupling continuum fluid mechanics and phase-field models for CVD growth of 2D materials. It connects the macroscale experimentally controllable parameters, such as inlet velocity and temperature, and mesoscale growth parameters such as surface diffusion and deposition rates, to morphology of the as-grown 2D materials. We considered WSe2 as our model material and established a relationship between the macroscale growth parameters and the growth coverage. Our model can guide the CVD growth of monolayer materials and paves the way to their synthesis-by-design. Graphic abstract

Review of Si-Based GeSn CVD Growth and Optoelectronic Applications

GeSn alloys have already attracted extensive attention due to their excellent properties and wide-ranging electronic and optoelectronic applications. Both theoretical and experimental results have shown that direct bandgap GeSn alloys are preferable for Si-based, high-efficiency light source applications. For the abovementioned purposes, molecular beam epitaxy (MBE), physical vapour deposition (PVD), and chemical vapor deposition (CVD) technologies have been extensively explored to grow high-quality GeSn alloys. However, CVD is the dominant growth method in the industry, and it is therefore more easily transferred. This review is focused on the recent progress in GeSn CVD growth (including ion implantation, in situ doping technology, and ohmic contacts), GeSn detectors, GeSn lasers, and GeSn transistors. These review results will provide huge advancements for the research and development of high-performance electronic and optoelectronic devices.