Scanning Probe Lithography Patterning of Monolayer Semiconductors and Application in Quantifying Edge Recombination.

Scanning probe lithography is used to directly pattern monolayer transition metal dichalcogenides (TMDs) without the use of a sacrificial resist. Using an atomic-force microscope, a negatively biased tip is brought close to the TMD surface. By inducing a water bridge between the tip and the TMD surface, controllable oxidation is achieved at the sub-100 nm resolution.

Susceptibility tensor imaging and tractography of collagen fibrils in the articular cartilage.

Purpose: To investigate the B orientation-dependent magnetic susceptibility of collagen fibrils within the articular cartilage and to determine whether susceptibility tensor imaging (STI) can detect the 3D collagen network within cartilage.

Methods: Multiecho gradient echo datasets (100-μm isotropic resolution) were acquired from fixed porcine articular cartilage specimens at 9.4 T.

Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring.

Flexible pressure sensors have many potential applications in wearable electronics, robotics, health monitoring, and more. In particular, liquid-metal-based sensors are especially promising as they can undergo strains of over 200% without failure. However, current liquid-metal-based strain sensors are incapable of resolving small pressure changes in the few kPa range, making them unsuitable for applications such as heart-rate monitoring, which require a much lower pressure detection resolution.

Measuring the Edge Recombination Velocity of Monolayer Semiconductors.

Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on the material's optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ, as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination.

General Thermal Texturization Process of MoS2 for Efficient Electrocatalytic Hydrogen Evolution Reaction.

Molybdenum disulfide (MoS2) has been widely examined as a catalyst containing no precious metals for the hydrogen evolution reaction (HER); however, these examinations have utilized synthesized MoS2 because the pristine MoS2 mineral is known to be a poor catalyst. The fundamental challenge with pristine MoS2 is the inert HER activity of the predominant (0001) basal surface plane. In order to achieve high HER performance with pristine MoS2, it is essential to activate the basal plane.

High Luminescence Efficiency in MoS2 Grown by Chemical Vapor Deposition.

One of the major challenges facing the rapidly growing field of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is the development of growth techniques to enable large-area synthesis of high-quality materials. Chemical vapor deposition (CVD) is one of the leading techniques for the synthesis of TMDCs; however, the quality of the material produced is limited by defects formed during the growth process. A very useful nondestructive technique that can be utilized to probe defects in semiconductors is the room-temperature photoluminescence (PL) quantum yield (QY).

Dual-gated MoS2/WSe2 van der Waals tunnel diodes and transistors.

Two-dimensional layered semiconductors present a promising material platform for band-to-band-tunneling devices given their homogeneous band edge steepness due to their atomically flat thickness. Here, we experimentally demonstrate interlayer band-to-band tunneling in vertical MoS2/WSe2 van der Waals (vdW) heterostructures using a dual-gate device architecture. The electric potential and carrier concentration of MoS2 and WSe2 layers are independently controlled by the two symmetric gates.

Air stable p-doping of WSe2 by covalent functionalization.

Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-stable chemical doping. Specifically, p-doping of WSe(2) via NOx chemisorption at 150 °C is explored, with the hole concentration tuned by reaction time. Synchrotron based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) depict the formation of various WSe(2-x-y)O(x)N(y) species both on the surface and interface between layers upon chemisorption reaction.

Design of surfactant-substrate interactions for roll-to-roll assembly of carbon nanotubes for thin-film transistors.

Controlled assembly of single-walled carbon nanotube (SWCNT) networks with high density and deposition rate is critical for many practical applications, including large-area electronics. In this regard, surfactant chemistry plays a critical role as it facilitates the substrate-nanotube interactions. Despite its importance, detailed understanding of the subject up until now has been lacking, especially toward tuning the controllability of SWCNT assembly for thin-film transistors.

Air-stable surface charge transfer doping of MoS₂ by benzyl viologen.

Air-stable doping of transition metal dichalcogenides is of fundamental importance to enable a wide range of optoelectronic and electronic devices while exploring their basic material properties. Here we demonstrate the use of benzyl viologen (BV), which has one of the highest reduction potentials of all electron-donor organic compounds, as a surface charge transfer donor for MoS2 flakes. The n-doped samples exhibit excellent stability in both ambient air and vacuum.