Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-005031.pdf

Black Phosphorus Field-effect Transistors

Low-resistivity metal-semiconductor (M-S) contact is one of the urgent challenges in the research of 2D transition metal dichalcogenides (TMDs). Here, we report a chloride molecular doping technique which greatly reduces the contact resistance (Rc) in the few-layer WS2 and MoS2. After doping, the Rc of WS2 and MoS2 have been decreased to 0.7 kohm*um and 0.5 kohm*um, respectively. The significant reduction of the Rc is attributed to the achieved high electron doping density thus significant reduction of Schottky barrier width. As a proof-ofconcept, high-performance few-layer WS2 field-effect transistors (FETs) are demonstrated, exhibiting a high drain current of 380 uA/um, an on/off ratio of 4*106, and a peak field-effect mobility of 60 cm2/V*s. This doping technique provides a highly viable route to diminish the Rc in TMDs, paving the way for high-performance 2D nano-electronic devices.

Chloride Molecular Doping Technique on 2D Materials: WS2 and MoS2

Two-dimensional (2D) materials exhibit a wide range of atomic structures, compositions, and associated versatility of properties. Furthermore, for a given composition, a variety of different crystal structures (i.e., polymorphs) can be observed. Polymorphism in 2D materials presents a fertile landscape for designing novel architectures and imparting new functionalities. The objective of this Review is to identify the polymorphs of emerging 2D materials, describe their polymorph-dependent properties, and outline methods used for polymorph control. Since traditional 2D materials (e.g., graphene, hexagonal boron nitride, and transition metal dichalcogenides) have already been studied extensively, the focus here is on polymorphism in post-dichalcogenide 2D materials including group III, IV, and V elemental 2D materials, layered group III, IV, and V metal chalcogenides, and 2D transition metal halides. In addition to providing a comprehensive survey of recent experimental and theoretical literature, this Review identifies the most promising opportunities for future research including how 2D polymorph engineering can provide a pathway to materials by design.

Polymorphism in Post-Dichalcogenide Two-Dimensional Materials.

Manipulating the Light-Matter Interaction of PtS/MoS2 p–n Junctions for High Performance Broadband Photodetection

https://robots.iopscience.iop.org/article/10.1088/1361-6463/ac0269/pdf

Cold plasma treatment of catalytic materials: a review

Ising machines (IMs) are physical systems designed to find solutions to combinatorial optimization (CO) problems mapped onto the IM via the coupling strengths between its binary spins. Using its intrinsic dynamics and different annealing schemes, the IM relaxes over time to its lowest-energy state, which is the solution to the CO problem. IMs have been implemented on different platforms, and interacting nonlinear oscillators are particularly promising candidates. Here we demonstrate a pathway towards an oscillator-based IM using arrays of nanoconstriction spin Hall nano-oscillators (SHNOs). We show how SHNOs can be readily phase binarized and how their resulting microwave power corresponds to well-defined global phase states. To distinguish between degenerate states, we use phase-resolved Brillouin-light-scattering microscopy and directly observe the individual phase of each nanoconstriction. Micromagnetic simulations corroborate our experiments and confirm that our proposed IM platform can solve CO problems, showcased by how the phase states of a $2\ifmmode\times\else\texttimes\fi{}2$ SHNO array are solutions to a modified max-cut problem. Compared with the commercially available D-Wave ${\mathrm{Advantage}}^{\mathrm{TM}}$, our architecture holds significant promise for faster sampling, substantially reduced power consumption, and a dramatically smaller footprint. 

Phase-Binarized Spin Hall Nano-Oscillator Arrays: Towards Spin Hall Ising Machines

We report a novel strategy to stitch small WS2 flakes to form larger features in liquid-phase exfoliation. Owing to the initial granular size of the bulk WS2, which, is around 2 µm, the use of conventional liquid-based exfoliation techniques leads to small area nanoflakes with sizes around 1 μm. However, by joining smaller flakes through tin-oxide quantum dot (SnO2 QD) decoration during probe sonication, sheets up to 20 μm are achieved. The neighboring flakes could stitch together to form larger features through the Sn–S and Sn–O bonds at their lateral sides of their flakes and to realize mosaic arrangement of arbitrary shaped larger sheets. While the original WS2 flakes show n-type behavior, an interesting conversion into a p-channel behavior is observed upon addition of SnO2 QDs followed by additional SF6 plasma treatment process. Additionally, we have investigated the use of SF6 plasma treatment to enhance the carrier mobility and on-off ratio of the field effect transistors, yielding an effective field-effect-mobility of 80 cm2 V−1 s−1 and relatively high on/off current ratio of 105, indicating its superior electronic properties.

Mona Rajabali

Papers

Phase-Binarized Spin Hall Nano-Oscillator Arrays: Towards Spin Hall Ising Machines

High-performance large-area WS 2 -based transistors by a novel tin-oxide assisted liquid-phase exfoliation: doping adjustment by plasma treatment

High‐Performance Phosphorene‐Based Transistors Using a Novel Exfoliation‐Free Direct Crystallization on Silicon Substrates

Formation of Few- and Monolayered WS 2 Sheets Using Plasma-Treated Dimethyl-Sulfoxide Solvent-Based Exfoliation

Evolution of Phosphorene Sheets through Direct Crystallization of Thin-Film Red Phosphorus