Since its first fabrication by exfoliation in 2014, phosphorene has been the focus of rapidly expanding research activities. The number of phosphorene publications has been increasing at a rate exceeding that of other two-dimensional materials. This tremendous level of excitement arises from the unique properties of phosphorene, including its puckered layer structure. With its widely tunable band gap, strong in-plane anisotropy, and high carrier mobility, phosphorene is at the center of numerous fundamental studies and applications spanning from electronic, optoelectronic, and spintronic devices to sensors, actuators, and thermoelectrics to energy conversion, and storage devices. Here, we review the most significant recent studies in the field of phosphorene research and technology. Our focus is on the synthesis and layer number determination, anisotropic properties, tuning of the band gap and related properties, strain engineering, and applications in electronics, thermoelectrics, and energy storage. The current needs and likely future research directions for phosphorene are also discussed. , there has been a quest for new two-dimensional (2D) materials aimed at fully exploring new fundamental phenomena stemming from quantum confinement and size effects. This quest has spurred new areas of research with rapid growth from both theoretical and experimental fronts aimed at technological advancements. Among recently discovered 2D materials, phosphorene is one of the most intriguing due to its exotic properties and numerous foreseeable applications.2 This review discusses recent advances in phosphorene research with special emphasis on: (i) fabrication and techniques for rapid identification of the number of layers; (ii) anisotropic behavior; (iii) band gap and property tuning; (iv) strain engineering and mechanical properties; (v) devices and applications; and (vi) future directions.2D materials composed of a single-atom-thick or a singlepolyhedral-thick layer can be grouped into diverse categories.

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We have developed a lithography free technique for the fabrication of two-dimensional material based devices for electrical characterization. We fabricated few-layer and multilayer WS2 devices using a transmission electron microscope (TEM) grid as a shadow mask, and its transport characteristics were studied by electrical measurements. WS2 samples were synthesized by first depositing WO3 followed by sulfurization and characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy. Each sample was exposed to hydrazine at varying pressures, and their electrical resistances were monitored during adsorption (exposing to hydrazine vapor) and subsequent desorption (by pumping). The WS2 sample consisting of two layers showed a decrease of resistance upon exposure to hydrazine vapor and showed complete reversibility upon pumping. The WS2 sample with three layers showed a decrease of resistance during exposure but showed only partial recovery during desorption. In contrast, the multilayered (12 layers) WS2 sample showed an initial decrease followed by a continued increase of the resistance upon exposure to hydrazine with little or no reversibility upon pumping. The charge transfer from N2H4 to WS2 is believed to be responsible for the decrease of the resistance. Trapping of N2H4 molecules within the multilayers of WS2 causing charge redistribution and possible chemical reactions may be responsible for the increase in resistance during the adsorption and complete irreversibility of resistance during desorption. The experimental results are explained with the help of computational calculations performed by employing the density functional theory (DFT) framework, as implemented in the Vienna Ab-initio Simulation Package (VASP).

supportive and kind to me throughout this journey. I got to learn a lot from his experience, his feedback has always been of great asset and I am honored that I got the opportunity to be under his worthy guidance and to be in his prestigious research team. The knowledge and skills that I learned from him, have played a huge role in the enhancement of my scientific career. Next, I want to thank all the teachers who have taught me courses during my Ph.D. course-work, particularly, Dr. Chakram S. Jayanthi, the Chair-person of Physics Department at the University of Louisville, and, Dr. Ming Yu, Professor in Physics who taught me some valuable courses. It was a delight to be their student and I feel honored to call myself their student. I would further like to thank Dr. Chris. L Davis who is my graduate program advisor, whose advice has been very fruitful for me right from choosing courses to important decision during my Ph.D. journey. Dr. Chris. L Davis is not only a great student advisor but also a great gentleman who is always nice, kind and polite to his students. I will always remain grateful for the kindness that he showed towards me. x 2.5.2 Scanning Electron Microscope .

We have demonstrated a simple and scalable fabrication process for defect-rich MoS2 directly from ammonium tetrathiomolybdate precursor using intense pulse light treatment in milliseconds durations. The formation of MoS2 from the precursor film after intense pulsed light exposure was confirmed with XPS, XRD, electron microscopy and Raman spectroscopy. The resulting material exhibited high activity for the hydrogen evolution reaction (HER) in acidic media, requiring merely 200 mV overpotential to reach a current density of 10 mA cm−2. Additionally, the catalyst remained highly active for HER over extended durability testing with the overpotential increasing by 28 mV following 1000 cycles. The roll-to-roll amenable fabrication of this highly-active material could be adapted for mass production of electrodes comprised of earth-abundant materials for water splitting applications.