Misbah Mirza

Van der Waals Epitaxy and Photoresponse of Hexagonal Tellurium Nanoplates on Flexible Mica Sheets

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.

Topological Surface Transport Properties of Single-Crystalline SnTe Nanowire

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.

Novel top-contact monolayer pentacene-based thin-film transistor for ammonia gas detection.

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.

Synthesis of mid-infrared SnSe nanowires and their optoelectronic properties

For the first time, high quality SnSe nanowires were synthesized via chemical vapour deposition (CVD). The synthesized SnSe nanowires are single crystalline. The length of the nanowires is in tens of microns with an average diameter of about 30–40 nm. Further, the optical and electrical properties reveal the potential of SnSe nanowires for photovoltaic and optical devices. These studies will enable significant advancements of the next generation photodetection and solar cell applications.

Telluride-based nanorods and nanosheets: synthesis, evolution and properties

We report for the first time the synthesis of single crystalline In2Te3 nanosheets. Te nanorods were first produced by controlling the reaction kinetics and then In2Te3 nanosheets nucleated at the body of Te nanorods in the presence of organic surfactant. The self-assembly and the certain directional growth process of In2Te3 on the body of Te nanorods resulted in an ordered nanostring-cluster which subsequently gave split In2Te3 nanosheets. The transformation can be attributed to the developed facets and organic surfactants which can greatly enlarge the lateral dimensions and produce nanosheets. The morphology evolution from nanorods to nanosheets is demonstrated with experimental evidence collected via SEM, TEM and XRD studies. The synthesis of nanorods/nanosheets will supply additional opportunities for the exploration of novel fundamental properties of telluride based chalcogenides materials. Initial hydrogen storage results pave the way for utilizing telluride-based nanostructures for gas storage and gas sensing properties. Also, the photoresponse properties of indium telluride offers good knowledge for the fabrication of nanoscale electronic and optoelectronic devices.

Weak Antilocalization Effect of Topological Crystalline Insulator Pb1–xSnxTe Nanowires with Tunable Composition and Distinct {100} Facets

Pb(1-x)Sn(x)Te is a unique topological crystalline insulator (TCI) that undergoes a topological phase transition from topological trivial insulator to TCI with the change of Sn content and temperature. Meanwhile, the surface states properties of Pb(1-x)Sn(x)Te are strongly dependent on crystallographic plane orientation. In this work, we first reported controllable synthesis of rectangular prismatic Pb(x)Sn(1-x)Te nanowires by vapor deposition method. Rectangular prismatic Pb(x)Sn(1-x)Te nanowires exhibits distinct {100} surfaces. Furthermore, The Sn composition of Pb(1-x)Sn(x)Te nanowires can be continuously controlled from 0 to 1. Low temperature magnetotransport shows that PbTe nanowire exhibits weak localization (WL) effect, whereas Pb0.5Sn0.5Te and Pb0.2Sn0.8Te nanowires display pronounced weak antilocalization (WAL) effect. This transition is explained by the topological phase transform of Pb(1-x)Sn(x)Te from trivial to nontrivial insulator with Sn content (x) exceeding 0.38. Pb(x)Sn(1-x)Te nanowires synthesized in this work lay a foundation for probing spin-correlated electron transport and show great potentials for future applications of tunable spintronic devices.

Wide Range Photodetector Based on Catalyst Free Grown Indium Selenide Microwires

We first report the catalyst free growth of indium selenide microwires through a facile approach in a horizontal tube furnace using indium and selenium elemental powders as precursors. The synthesized microwires are γ-phase, high quality, single crystalline and grown along the [112̅0] direction. The wires have a uniform diameter of ∼1 μm and lengths of several micrometers. Photodetectors fabricated from synthesized microwires show reliable and stable photoresponse exhibiting a photoresponsivity of 0.54 A/W, external quantum efficiency of 1.23 at 633 nm with 4 V bias. The photodetector has a reasonable response time of 0.11 s and specific detectivity of 3.94 × 10(10) Jones at 633 nm with a light detection range from 350 to 1050 nm, covering the UV-vis-NIR region. The photoresponse shown by single wire is attributed to direct band gap (Eg = 1.3 eV) and superior single crystalline quality. The photoresponsive studies of single microwires clearly suggest the use of this new and facile growth technique without using catalysts for fabrication of indium selenide microwires in next-generation sensors and detectors for commercial and military applications.

Crystalline indium sesquitelluride nanostructures: synthesis, growth mechanism and properties

In the present work, we report for the first time the growth of uniform single crystalline In2Te3 nanowires via the chemical vapor deposition (CVD) method. The CVD grown In2Te3 nanowires are single crystals along [132] growth direction with a uniform diameter of around 150 nm and an average length of tens of microns. In addition, polycrystalline hierarchical nanostructures of In2Te3 are also fabricated via a solvothermal method under low temperature conditions. The morphology and crystal structures are systematically studied using SEM and TEM. Optical characterization by Raman spectroscopy provides further information of the achieved products, and UV-vis spectroscopy helped to investigate the bandgap of these nanostructures. By surfactant and solvent effects, the morphologies of the nanostructure are controllable. The electrical properties of the two kinds of nanowire are compared. The morphology controllable nanostructure offers the possibility of controlling the properties of In2Te3 and this opens up new means for achieving high performance nanodevices based on these nanostructures.