Two-dimensional (2D) semiconductors have been proposed for heterogeneous integration with existing silicon technology, however their chemical vapor deposition (CVD) growth temperatures are often too high. Here, we demonstrate direct CVD solid source precursor synthesis of continuous monolayer (1L) MoS2 films at 560°C in 50-minutes, within the 450-to-600°C, 2-hour thermal budget window required for back-end-of-the-line (BEOL) compatibility with modern silicon technology. Transistor measurements reveal on-state current up to ~140 µA/µm at 1 V drain-to-source voltage for 100 nm channel lengths, the highest reported to date for 1L MoS2 grown below 600°C using solid source precursors. The effective mobility from transfer length method (TLM) test structures is 29 ± 5 cm 2 V -1 s -1 at 6.1 × 10 12 cm -2 electron density, which is comparable to mobilities reported from films grown at higher temperatures. The results of this work provide a path towards the realization of high quality, thermal-budget-compatible 2D semiconductors for heterogeneous integration with silicon manufacturing.

Real-time thermal sensing on flexible substrates could enable a plethora of new applications. However, achieving fast, submillisecond response times even in a single sensor is difficult, due to the thermal mass of the sensor and encapsulation. Here, we fabricate flexible monolayer molybdenum disulfide (MoS 2 ) temperature sensors and arrays, which can detect temperature changes within a few microseconds, over 100× faster than flexible thin-film metal sensors. Thermal simulations indicate the sensors' response time is only limited by the MoS 2 interfaces and encapsulation. The sensors also have high temperature coefficient of resistance, ∼1−2%/K and stable operation upon cycling and long-term measurement when they are encapsulated with alumina. These results, together with their biocompatibility, make these devices excellent candidates for biomedical sensor arrays and many other Internet of Things applications.

The quest for a universal quantum computer has renewed interest in the growth of superconducting materials on semiconductor substrates. High-quality superconducting thin films will make it possible to improve the coherence time of superconducting quantum bits (qubits), i.e., to extend the time a qubit can store the amplitude and phase of a quantum state. The electrical losses in superconducting qubits highly depend on the quality of the metal layers the qubits are made from. Here, we report on the epitaxy of single-crystal Al (011) layers on GaAs (001) substrates. Layers with 110 nm thickness were deposited by means of molecular beam epitaxy at low temperature and monitored by in situ reflection high-energy electron diffraction performed simultaneously at four azimuths. The single-crystal nature of the layers was confirmed by ex situ high-resolution x-ray diffraction. Differential interference contrast and atomic force microscopy analysis of the sample’s surface revealed a featureless surface with root mean square roughness of 0.55 nm. A detailed in situ study allowed us to gain insight into the nucleation mechanisms of Al layers on GaAs, highlighting the importance of GaAs surface reconstruction in determining the final Al layer crystallographic orientation and quality. A highly uniform and stable GaAs (001)- reconstruction reproducibly led to a pure Al (011) phase, while an arsenic-rich GaAs (001)- reconstruction yielded polycrystalline films with an Al (111) dominant orientation. The near-atomic smoothness and single-crystal character of Al films on GaAs, in combination with the ability to trench GaAs substrates, could set a new standard for the fabrication of superconducting qubits.

Four-dimensional scanning transmission electron microscopy (4D-STEM) has recently gained widespread attention for its ability to image atomic electric fields with sub-Ångstrom spatial resolution. These electric field maps represent the integrated effect of the nucleus, core electrons and valence electrons, and separating their contributions is non-trivial. In this paper, we utilized simultaneously acquired 4D-STEM center of mass (CoM) images and annular dark field (ADF) images to determine the projected electron charge density in monolayer MoS2. We evaluate the contributions of both the core electrons and the valence electrons to the derived electron charge density; however, due to blurring by the probe shape, the valence electron contribution forms a nearly featureless background while most of the spatial modulation comes from the core electrons. Our findings highlight the importance of probe shape in interpreting charge densities derived from 4D-STEM and the need for smaller electron probes.

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