Renxiong Li

Gas-dependent photoresponse of SnS nanoparticles-based photodetectors

SnS nanoparticles were synthesized with a facile hydrothermal method and characterized by X-ray diffraction (XRD), Raman, transmission electron microscope (TEM) and scanning electron microscope (SEM). The red light photoresponse of the SnS-based devices in different gas environments were also systematically investigated, and revealed that the adsorbed gas molecules play important roles in the photosensitive properties. Compared with that in vacuum, the photosensitivity was enhanced in O2 (or air) and reduced in NH3. The dynamic response time was much longer in a gas environment. These influences were ascribed to the charge transfer between the adsorbed gas molecules and SnS.

Edge-states ferromagnetism of WS2 nanosheets

The multilayer WS2 nanosheets prepared from WO3 nanowires exhibit strong ferromagnetic behavior with saturation magnetization (MS) of 0.0058 emu/g and coercive field (HC) of 92 Oe at room temperature. By decreasing the temperature down to 3 K the Hc is increased up to 1115 Oe, revealing the existence of long-range magnetic ordering. Density functional theory spin-polarized calculations predict that strong ferromagnetic moments in WS2 nanosheets are attributed to the zigzag edge sulphur S and tungsten W atoms. Our findings also suggest that the WS2 nanosheets with a high density of edge spins could be used to fabricate spintronics devices, which are circuits utilizing the spin of the electron to process and store information.

Low temperature electrical transport and photoresponsive properties of H-doped MoO3 nanosheets

α-MoO3 nanosheets were synthesized by a water bath method using ammonium heptamolybdenum tetrahydrate and concentrated nitric acid as precursors. Hydrogen was doped by a chemical reduction in aqueous acidic media, with hydrazine hydrate used as the reducing agent. Temperature dependent resistance showed that the low temperature Peierls transition of H-doped MoO3 nanosheets breaks below 50 K, and its resistance is satisfied at temperatures lower than 37 K (37–10 K). This phenomenon was induced by thermal disturbance and the dominance of defects in low temperature transport, which was confirmed by photoresponse measurements taken before and after the break of the new phase.

Improving the field-effect performance of Bi2S3 single nanowires by an asymmetric device fabrication.

High-quality Bi2 S3 nanowires are synthesized by chemical vapor deposition and their intrinsic photoresponsive and field-effect characteristics are explored in detail. Among the studied Au-Au, Ag-Ag, and Au-Ag electrode pairs, the device with stepwise band alignment of asymmetric Au-Ag electrodes has the highest mobility. Furthermore, it is shown that light can cause a sevenfold decrease of the on/off ratio. This can be explained by the photoexcited charge carriers that are more beneficial to the increase of Ioff than Ion . The photoresponsive properties of the asymmetric Au-Ag electrode devices were also explored, and the results show a photoconductive gain of seven with a rise time of 2.9 s and a decay time of 1.6 s.

Effect of Electrical Contact on the Performance of Bi2S3 Single Nanowire Photodetectors

Bi2S3 single-crystalline nanowires are synthesized through a hydrothermal method and then fabricated into single nanowire photodetectors. Due to the different contact barrier between the gold electrode and Bi2S3 nanowires, two kinds of devices with different electrical contacts are obtained and their photoresponsive properties are investigated. The non-ohmic contact devices show larger photocurrent gains and shorter response times than those of ohmic contact devices. Furthermore, the influence of a focused laser on the barrier height between gold and Bi2S3 is explored in both kinds of devices and shows that laser illumination on the Au-Bi2S3 interface can greatly affect the barrier height in non-ohmic contact devices, while keeping it intact in ohmic contact devices. A model based on the surface photovoltage effect is used to explain this phenomenon.

Synthesis of Bi2S3–Bi2O3 composites and their enhanced photosensitive properties

Bi2S3–Bi2O3 composites were synthesized by a facile hydrothermal method with surfactant as template. The structure and morphology of the as-synthesized products were characterized in detail. The photosensitive behavior of the Bi2S3–Bi2O3 composites was investigated carefully. Under the illumination of a 650 nm laser in air or vacuum, the device displayed enhanced photosensitive performance compared to the pure Bi2S3, pure Bi2O3 and mechanical mixture of Bi2S3 and Bi2O3 based devices. The photoswitch ratio (Iphoto/Idark) was as high as 30 in a vacuum with fast photoresponse speed, which indicated their potential applications in manufacturing photodetectors and optoelectronic devices. The possible mechanism of enhanced photosensitivity was also proposed.

Oxygen-induced abnormal photoelectric behavior of a MoO3/graphene heterocomposite

A MoO3 nanoflakes/graphene heterocomposite synthesized by a water bath method showed unusual photoelectric behavior. Its resistance increased under visible light irradiation in air. The behavior arises from the physical contact between the two materials, which leads to hole doping in graphene. Thus, the increase of electrons in the MoO3 nanoflakes induced by desorption of oxygen molecules from its surface under visible light was probably the main reason for the change in resistance. This was confirmed by the resistance of the heterocomposite in a vacuum being 102 times larger than that in air, and by the photoelectric measurements under Ar. The MoO3 nanoflakes/graphene heterocomposite exhibits great potential for use in oxygen gas sensing.

High uniformity of self-organized InAs quantum wires on InAlAs buffers grown on misoriented InP(001)

Highly uniform InAs quantum wires (QWRs) have been obtained on the In0.5Al0.5As buffer layer grown on the InP substrate 8 degrees off (001) towards (111) by molecular-beam epitaxy. The quasi-periodic composition modulation was spontaneously formed in the In0.5Al0.5As buffer layer on this misoriented InP (001). The width and period of the In-rich bands are about 10 and 40 nm, respectively. The periodic In-rich bands play a major role in the sequent InAs QWRs growth and the InAs QWRs are well positioned atop In-rich bands. The photoluminescence (PL) measurements showed a significant reduction in full width at half maximum and enhanced PL efficiency for InAs QWRs on misoriented InP(001) as compared to that on normal InP(001). (c) 2006 American Institute of Physics.