Semiconducting two-dimensional (2D) materials, particularly extremely thin molybdenum disulfide (MoS) films, are attracting considerable attention from academia and industry owing to their distinctive optical and electrical properties. Here, we present the direct growth of a MoS monolayer with unprecedented spatial and structural uniformity across an entire 8 inch SiO/Si wafer. The influences of growth pressure, ambient gases (Ar, H), and S/Mo molar flow ratio on the MoS layered growth were explored by considering the domain size, nucleation sites, morphology, and impurity incorporation. Monolayer MoS-based field effect transistors achieve an electron mobility of 0.47 cm V s and on/off current ratio of 5.4 × 10. This work demonstrates the potential for reliable wafer-scale production of 2D MoS for practical applications in next-generation electronic and optical devices.
We describe here a new principle for ion detection in time-of-flight (TOF) mass spectrometry in which an impinging ion packet excites mechanical vibrations in a silicon nitride (Si(3)N(4)) nanomembrane. The nanomembrane oscillations are detected by means of time-varying field emission of electrons from the mechanically oscillating nanomembrane. Ion detection is demonstrated in the MALDI-TOF analysis of proteins varying in mass from 5729 (insulin) to 150,000 (Immunoglobulin G) daltons. The detector response agrees well with the predictions of a thermomechanical model in which the impinging ion packet causes a nonuniform temperature distribution in the nanomembrane, exciting both fundamental and higher order oscillations.
Batch growth of high-mobility (μFE > 10 cm2V–1s–1) molybdenum disulfide (MoS2) films can be achieved by means of the chemical vapor deposition (CVD) method at high temperatures (>500 °C) on rigid substrates. Although high-temperature growth guarantees film quality, time- and cost-consuming transfer processes are required to fabricate flexible devices. In contrast, low-temperature approaches (<250 °C) for direct growth on polymer substrates have thus far achieved film growth with limited spatial homogeneity and electrical performance (μFE is unreported). The growth of a high-mobility MoS2 film directly on a polymer substrate remains challenging. In this study, a novel low-temperature (250 °C) process to successfully overcome this challenge by kinetics-controlled metal–organic CVD (MOCVD) is proposed. Low-temperature MOCVD was achieved by maintaining the flux of an alkali-metal catalyst constant during the process; furthermore, MoS2 was directly synthesized on a polyimide (PI) substrate. The as-grown film exhibits a 4 in. wafer-scale uniformity, field-effect mobility of 10 cm2V–1s–1, and on/off ratio of 105, which are comparable with those of high-temperature-grown MoS2. The directly fabricated flexible MoS2 field-effect transistors demonstrate excellent stability of electrical properties following a 1000 cycle bending test with a 1 mm radius.
We present spontaneous symmetry breaking in a nanoscale version of a setup prolific in classical mechanics: two coupled nanomechanical pendula. The two pendula are electron shuttles fabricated as nanopillars [D. V. Scheible and R. H. Blick, Appl. Phys. Lett. 84, 4632 (2004).10.1063/1.1759371] and placed between two capacitor plates in a homogeneous electric field. Instead of being mechanically coupled through a spring they exchange electrons, i.e., they shuttle electrons from the source to the drain "capacitor plate." The nonzero dc current through this system by external ac excitation is caused via dynamical symmetry breaking. This symmetry-broken current appears at sub- and superharmonics of the fundamental mode of the coupled system.
Phase transition and coexistence of 2H (trigonal prismatic structure) and 1T′ (distorted octahedral structure) phases occur easily in molybdenum ditelluride (MoTe 2 ) when compared with other 2D MX 2 type (M = Mo, W and X = S, Se) transition metal dichalcogenides (TMDs) because of small discrepancies in the cohesive energy. [1][2][3][4] Phase-engineered 2D TMDs, particularly MoTe 2 films including 2H, 1T′, and 1T phases, are very attractive candidates for numerous electronic applications, such as ambipolar field-effect transistors (FETs), environmental sensors, superconductors, spintronics, and valley optoelectronics. [5][6][7][8] Atomically thin-layer 2H MoTe 2 possesses a narrow bandgap energy of 1 eV in comparison to the bandgap energy (1.89 eV) of monolayer MoS 2 and is a potential candidate for various optoelectronic device applications, such as solar cells and photodetectors. [3,8,9] From the electronic device application point of view, the 2H and the 1T phases, i.e., semiconducting and semimetal MoTe 2 are applicable as a 2D materials beyond molybdenum disulfide such as molybdenum ditelluride (MoTe 2 ) have attracted increasing attention because of their distinctive properties, such as phase-engineered, relatively narrow direct bandgap of 1.0-1.1 eV and superior carrier transport. However, a wafer-scale synthesis process is required for achieving practical applications in next-generation electronic devices using MoTe 2 thin films. Herein, the direct growth of atomically thin 1T′, 1T′-2H mixed, and 2H phases MoTe 2 films on a 4 in. SiO 2 /Si wafer with high spatial uniformity (≈96%) via metal-organic vapor phase deposition is reported. Furthermore, the wafer-scale phase engineering of few-layer MoTe 2 film is investigated by controlling the H 2 molar flow rate. While the use of a low H 2 molar flow rate results in 1T′ and 1T′-2H mixed phase MoTe 2 films, 2H phase MoTe 2 films are obtained at a high H 2 molar flow rate. Field-effect transistors fabricated with the prepared 2H and 1T′ phases MoTe 2 channels reveal p-type semiconductor and semimetal properties, respectively. This
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