Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond

2D transition metal dichalcogenides (TMDCs) are among the most exciting materials of today. Their layered crystal structures result in unique and useful electronic, optical, catalytic, and quantum properties. To realize the technological potential of TMDCs, methods depositing uniform films of controlled thickness at low temperatures in a highly controllable, scalable, and repeatable manner are needed. Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method capable of meeting these challenges. In this review, the applications evaluated for ALD TMDCs are systematically examined, including electronics and optoelectonics, electrocatalysis and photocatalysis, energy storage, lubrication, plasmonics, solar cells, and photonics. This review focuses on understanding the interplay between ALD precursors and deposition conditions, the resulting film characteristics such as thickness, crystallinity, and morphology, and ultimately device performance. Through rational choice of precursors and conditions, ALD is observed to exhibit potential to meet the varying requirements of widely different applications. Beyond the current state of ALD TMDCs, the future prospects, opportunities, and challenges in different applications are discussed. The authors hope that the review aids in bringing together experts in the fields of ALD, TMDCs, and various applications to eventually realize industrial applications of ALD TMDCs.Peer reviewe

Large-format X-ray reflection grating operated in an echelle-like mounting

We report on resolving power measurements of an X-ray reflection grating designed for use in an astronomical soft X-ray spectrograph. The grating was patterned via electron-beam lithography (EBL) to have fanned grooves to match the convergence of an illuminating beam. Grating measurements were conducted in an echelle-like mounting, which yields access to high diffraction orders in the soft X-ray bandpass (0.2–2.0 keV). By comparing the zeroth-order line-spread function to the telescope focus, we find evidence for minimal broadening (<1'') introduced by the figure of the grating. In addition, we fit for the spectral resolution (R = λ/Δλ) intrinsic to this grating using a Bayesian Markov Chain Monte Carlo approach. Using an ensemble fitting technique, we find that the grating resolution R exceeds 2200 (3σ lower bound). This current grating resolution meets the performance required for a notional soft X-ray grating spectroscopy mission measuring hot baryonic material in the extended halos of galaxies. Using ray-trace simulations, we identify a geometric aberration resulting from path length differences across the width of the grating as a limiting factor in assessing the resolution of these gratings and discuss methods for placing better constraints on the inherent resolution of X-ray astronomical reflection gratings fabricated using EBL

Reducing parasitic effects of actuation and sensing schemes for piezoelectric microelectromechanical resonators

International audienceThe co-integration of piezoelectric actuation and sensing capabilities on microelectromechanical system-based resonators can be a source of electrical cross-talk that, if not properly taken into account, may dramatically affect the interpretation of the device's output. In this paper, we identify three parasitic electrical effects pertaining to the most commonly used piezoelectric actuation and sensing schemes. To further investigate the impact of such parasitic effects, microcantilevers, bridges and membranes integrating a layer of sol-gel lead zirconate titanate (PZT) were fabricated and electrically characterized. Experimental results on the resonant characteristics were compared with simulations of the studied resonators' equivalent electrical models. Methods for reducing the design-dependent parasitic electrical effects such as mutual capacitances of less than 10fF, electrical wiring or static capacitance mismatches of less than 20% of the integrated piezoelectric films are discussed

Thickness characterization of atomically-thin WSe2 on epitaxial graphene by low-energy electron reflectivity oscillations

In this work, low-energy electron microscopy is employed to probe structural as well as electronic information in few-layer WSe2 on epitaxial graphene on SiC. The emergence of unoccupied states in the WSe2–graphene heterostructures are studied using spectroscopic low-energy electron reflectivity. Reflectivity minima corresponding to specific WSe2 states that are localized between the monolayers of each vertical heterostructure are shown to reveal the number of layers for each point on the surface. A theory for the origin of these states is developed and utilized to explain the experimentally observed featured in the WSe2 electron reflectivity. This method allows for unambiguous counting of WSe2 layers, and furthermore may be applied to other 2D transition metal dichalcogenide materials.</p

Tunnel junction abruptness, source random dopant fluctuation and PBTI induced variability analysis of GaAs_0.4Sb_0.6/In_0.65Ga_0.35As heterojunction tunnel FETs

We present reliability analysis of the two most critical interfaces in III-V Heterojunction Tunnel FET (HTFET) design: (1) Tunnel Heterojunction is characterized in three-dimensional atomic scale resolution using Atom Probe Tomography. We explore the impact of tunnel junction abruptness and source dopant fluctuations on HTFET performance; (2) Extremely scaled Hi-K gate dielectric (sub-0.8 nm EOT: HfO2, HfO2-ZrO2 bilayer and ZrO2)/III-V channel interface is evaluated using Positive Bias Temperature Instability (PBTI) measurements. HfO2 based HTFET exhibits superior PBTI performance over ZrO2 based HTFET and shows lifetime improvement over III-V FinFET