Quantum dots formed in three-dimensional Dirac semimetal Cd3_3As2_2 nanowires

We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal Cd$_{3}$As$_{2}$ nanowires using two electrostatically tuned p$-$n junctions with a gate and magnetic fields. The linear conductance measured as a function of gate voltage under high magnetic fields is strongly suppressed at the Dirac point close to zero conductance, showing strong conductance oscillations. Remarkably, in this regime, the Cd$_{3}$As$_{2}$ nanowire device exhibits Coulomb diamond features, indicating that a clean single QD forms in the Dirac semimetal nanowire. Our results show that a p$-$type QD can be formed between two n$-$type leads underneath metal contacts in the nanowire by applying gate voltages under strong magnetic fields. Analysis of the quantum confinement in the gapless band structure confirms that p$-$n junctions formed between the p$-$type QD and two neighboring n$-$type leads under high magnetic fields behave as resistive tunnel barriers due to cyclotron motion, resulting in the suppression of Klein tunneling. The p$-$type QD with magnetic field-induced confinement shows a single hole filling. Our results will open up a route to quantum devices such as QDs or quantum point contacts based on Dirac and Weyl semimetals

Solution-processed germanium nanowire-positioned Schottky solar cells

Germanium nanowire (GeNW)-positioned Schottky solar cell was fabricated by a solution process. A GeNW-containing solution was spread out onto asymmetric metal electrodes to produce a rectifying current flow. Under one-sun illumination, the GeNW-positioned Schottky solar cell yields an open-circuit voltage of 177 mV and a short-circuit current of 19.2 nA. Schottky and ohmic contacts between a single GeNW and different metal electrodes were systematically investigated. This solution process may provide a route to the cost-effective nanostructure solar architecture

Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires by Thermal Evaporation Method

Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a Si substrate. Tellurium was evaporated by heating at 300 C at 1 torr and condensed on the Si substrate at 100-150 C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min. The as-synthesized nanowires have diameters between 100-300 nm and lengths up to several micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained nanowires were highly pure as only tellurium metal was used in the vaporization process, and no other reagent, surfactant, or template were used for the growth. This low temperature and high-yield approach to the tellurium nanowires synthesis may facilitate its industrial production for various applications

Experimental and theoretical studies on the structure of N-doped carbon nanotubes: Possibility of intercalated molecular N2

The concentration distribution and electronic structure of N atoms doped in multiwalled banboo-like carbon nanotubes (CNTs) are examined by photon energy-dependent x-ray photoelectron spectroscopy and x-ray absorption near edge structure. The inner part of the nanotube wall has a higher N concentration and contains molecular N-2 presumably intercalated between the graphite layers. These results are supported by the self-consistent charge-density-functional-based tight-binding calculation of double-walled CNTs, showing that the intercalation of N-2 is energetically possible and the graphite-like N structure conformer becomes more stable when the inner wall is more heavily doped. (C) 2004 American Institute of Physicsclose656

Anisotropic 2D SiAs for High-Performance UV–Visible Photodetectors

Recently, extensive efforts have been directed at finding novel 2D-layered structures with anisotropic crystal structures. Herein, the in-plane anisotropic optical and (photo)electrical properties of 2D SiAs nanosheets synthesized using a solid-state reaction and subsequent mechanical exfoliation are reported. The angle-resolved polarized Raman spectrum shows high in-plane anisotropy of the phonon vibration modes, which are consistent with the theoretical prediction. Field-effect transistor devices fabricated using the SiAs nanosheets demonstrate significant anisotropy in the hole mobility with an anisotropic ratio as high as 5.5. Photodetectors fabricated with single SiAs nanosheet exhibit high sensitivity in the UV–visible region, and the anisotropic ratio of the photocurrent reaches 5.3 at 514.5 nm and 2.3 at 325 nm. This work lays the foundation for future research in anisotropic 2D materials

Synthesis of Polytypic Gallium Phosphide and Gallium Arsenide Nanowires and Their Application as Photodetectors

One-dimensional semiconductor nanowires often contain polytypic structures, owing to the co-existence of different crystal phases. Therefore, understanding the properties of polytypic structures is of paramount importance for many promising applications in high-performance nanodevices. Herein, we synthesized nanowires of typical III-V semiconductors, namely, gallium phosphide and gallium arsenide by using the chemical vapor transport method. The growth directions ([111] and [211]) could be switched by changing the experimental conditions, such as H 2 gas flow; thus, various polytypic structures were produced simultaneously in a controlled manner. The nanobeam electron diffraction technique was employed to obtain strain mapping of the nanowires by visualizing the polytypic structures along the [111] direction. Micro-Raman spectra for individual nanowires were collected, confirming the presence of wurtzite phase in the polytypic nanowires. Further, we fabricated the photodetectors using the single nanowires, and the polytypic structures are shown to decrease the photosensitivity. Our systematic analysis provides important insight into the polytypic structures of nanowires