arXiv subjects

Mu-Tung Chang

Publications and source records attributed to Mu-Tung Chang.

3 recordsLinked to original sources

arXiv2015

Low-voltage coherent electron imaging based on a single-atom electron

It has been a general trend to develop low-voltage electron microscopes due to their high imaging contrast of the sample and low radiation damage. Atom-resolved transmission electron microscopes with voltages as low as 15-40 kV have been demonstrated. However, achieving atomic resolution at voltages lower than 10 kV is extremely difficult. An alternative approach is coherent imaging or phase retrieval imaging, which requires a sufficiently coherent source and an adequately small detection area on the sample as well as the detection of high-angle diffracted patterns with a sufficient resolution. In this work, we propose several transmission-type schemes to achieve coherent imaging of thin materials (less than 5 nm thick) with atomic resolution at voltages lower than 10 kV. Experimental schemes of both lens-less and lens-containing designs are presented and the advantages and challenges of these schemes are discussed. Preliminary results based on a highly coherent single-atom electron source are presented. The image plate is designed to be retractable to record the transmission patterns at different positions along the beam propagation direction. In addition, reflection-type coherent electron imaging schemes are also proposed as novel methods for characterizing surface atomic and electronic structures of materials.

physics.ins-det↗

arXiv2012

Synthesis of Large-Area MoS2 Atomic Layers with Chemical Vapor Deposition

Large-area MoS2 atomic layers are synthesized on SiO2 substrates by chemical vapor deposition using MoO3 and S powders as the reactants. Optical, microscopic and electrical measurements suggest that the synthetic process leads to the growth of MoS2 monolayer. The TEM images verify that the synthesized MoS2 sheets are highly crystalline.

cond-mat.mtrl-sci↗

arXiv2012

Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates

The two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high quality and large-area MoS2 atomic thin layers is still rare. Here we report that the high temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS2 thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS2 sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS2 layer is comparable with those of the micromechanically exfoliated thin sheets from MoS2 crystals. This synthetic approach is simple, scalable and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.

cond-mat.mtrl-sci↗