Van der Waals epitaxy (vdWE) is of great interest due to its extensive applications in the synthesis of ultrathin two-dimensional (2D) layered materials. However, vdWE of nonlayered functional materials is still not very well documented. Here, although tellurium has a strong tendency to grow into one-dimensional nanoarchitecture due to its chain-like structure, we successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. We believe the fundamental understanding of vdWE effect on the growth of 2D tellurium hexagonal nanoplate can pave the way toward leveraging vdWE as a useful channel to realize the 2D geometry of other nonlayered materials.

SnTe has attracted worldwide interest since its theoretical predication as topological crystalline insulator. Because of promising applications of one-dimensional topological insulator in nanoscale electronics and spintronics device, it is very important to realize the observation of topological surface states in one-dimensional SnTe. In this work, for the first time we successfully synthesized high-quality single crystalline SnTe nanowire via gold-catalyst chemical vapor deposition method. Systematical investigation of Aharonov-Bohm and Shubnikov-de Haas oscillations in single SnTe nanowire prove the existence of Dirac electrons. Further analysis of temperature-dependent Shubnikov-de Haas oscillations gives valuable information of cyclotron mass, mean-free path, and mobility of Dirac electrons in SnTe nanowire. Our study provides the experimental groundwork for research in low-dimensional topological crystalline insulator materials and paves the way for the application of SnTe nanowire in nanoelectronics and spintronics device.

2D layered GaTe materials have attracted a great deal of attention for optoelectronic applications due to their direct band structure, whether in bulk or as a single layer. In this paper, for the first time, we have synthesized high quality, single crystalline GaTe nanosheets by employing a facile CVD method. The size of the GaTe nanosheets reached several tens of micrometers, and some of them even exceeded 100 μm. In particular, planar GaTe nanosheets were achieved on a mica substrate following a van der Waals epitaxial growth mechanism. Further, through a systematic comparison of the performances under various conditions, we found that adsorbates on the GaTe surface under ambient conditions strongly deteriorated the GaTe photodetector device performance. After removing the adsorbates in a ∼ 7 × 10(-5) torr vacuum, a flexible, fast response GaTe photodetector with a high photoresponse, high mechanical stability and an excellent linear input-output relationship was obtained. The results presented in this study suggest that the GaTe nanosheets grown by a CVD method are promising candidates for optoelectronic applications in the future.

We report on the fabrication of an organic field-effect transistor (OFET) of a monolayer pentacene thin film with top-contact electrodes for the aim of ammonia (NH3) gas detection by monitoring changes in its drain current. A top-contact configuration, in which source and drain electrodes on a flexible stamp [poly(dimethylsiloxane)] were directly contacted with the monolayer pentacene film, was applied to maintain pentacene arrangement ordering and enhance the monolayer OFET detection performance. After exposure to NH3 gas, the carrier mobility at the monolayer OFET channel decreased down to one-third of its original value, leading to a several orders of magnitude decrease in the drain current, which tremendously enhanced the gas detection sensitivity. This sensitivity enhancement to a limit of the 10 ppm level was attributed to an increase of charge trapping in the carrier channel, and the amount of trapped states was experimentally evaluated by the threshold voltage shift induced by the absorbed NH3 molecular analyte. In contrast, a conventional device with a 50-nm-thick pentacene layer displayed much higher mobility but lower response to NH3 gas, arising from the impediment of analyte penetrating into the conductive channel, owing to the thick pentacene film.

No abstract

No abstract

We report the controlled growth of highly ordered and well aligned one-dimensional tellurium nanostructure arrays via a one-step catalyst-free physical vapor deposition method. The density, size and fine structures of tellurium nanowires are systematically studied and optimized. Field emission measurement was performed to display notable dependence on nanostructure morphologies. The ordered nanowire array based field emitter has a turn-on field as low as 3.27 V μm(-1) and a higher field enhancement factor of 3270. Our finding offers the possibility of controlling the growth of tellurium nanowire arrays and opens up new means for their potential applications in electronic devices and displays.

Since different high-symmetrical crystal planes of topological crystalline insulator possess their own topological electronic structure, manipulating crystal shapes with distinct facets of SnTe nanostructures is crucial for the realization of desired topological surface properties. Here, we developed crystal shapes engineering for the controllable synthesis of SnTe microcrystals and nanowires with specific exposed surfaces by optimizing experimental parameters in the chemical vapor deposition process. Crystal shapes of SnTe microcrystals are tailored from {100} surface-covered cubes, {100} and {111} surface-coated truncated octahedron, to a {111} surface-terminated octahedron. Significantly, with gold nanoparticles as the catalyst, two novel SnTe nanowires, octahedron-attached SnTe nanowires, and truncated octahedron-assisted SnTe nanowires, are achieved. The requirement of minimizing the overall surface energy drives the formation of various crystal shapes of SnTe microcrystals and nanowires. In addition, SnTe nanowires possess a huge thermal activation energy gap (350 ± 17 meV), 14 times larger than the energy scale of room temperature. This huge thermal activation energy gap can protect topological surface states of SnTe nanowires against the disturbance of thermal excitation. Our work provides the building block for the realization of unique topological surface effects on specific facets and novel spintronic devices.