Xiangyang Ma

Synthesis of flower-like ZnO nanostructures by an organic-free hydrothermal process

Flower-like ZnO nanostructures, which consisted of sword-like ZnO nanorods, have been prepared by an organic-free hydrothermal process. The XRD pattern indicated that the flower-like ZnO nanostructures were hexagonal. The SAED and HRTEM experiments implied that the sword-like ZnO nanorods were single crystal in nature and preferentially grew up along the [001] direction. The effects of temperature, pH value and mineralizer on the morphology have been also investigated. It is considered that pH value is the main factor to influence the morphology because of its effect on the initial nuclei and growth environment of ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the flower-like ZnO nanostructure is discussed.

ULTRAVIOLET ELECTROLUMINESCENCE FROM ZNO/P-SI HETEROJUNCTIONS

Nominally undoped ZnO films were deposited by reactive sputtering on the lightly boron-doped (p−) and heavily boron-doped (p+) silicon substrates. The sputtered ZnO films were identified to be highly ⟨002⟩ oriented in crystallinity and n type in electrical conductivity. The current-voltage (I‐V) characteristics revealed that the ZnO∕p−‐Si heterojunction exhibited well-defined rectifying behavior while the ZnO∕p+‐Si heterojunction did not possess rectifying function. As for the ZnO∕p+‐Si heterojunction, it was electroluminescent to a certain extent in the visible region under sufficient forward bias with the positive voltage on the silicon substrate, while it emitted ultraviolet light characteristics of near-band-edge emission of ZnO under the reverse bias, which significantly dominated the visible emission. In contrast to the ZnO∕p+‐Si heterojunction, the ZnO∕p−‐Si heterojunction did not exhibit detectable electroluminescence (EL) under either forward or reverse bias. The I‐V characteristics and EL mechan...

Electrically pumped ZnO film ultraviolet random lasers on silicon substrate

The electrically pumped ultraviolet (UV) random lasing in c-axis oriented ZnO polycrystalline films has been demonstrated. For this demonstration, a metal-oxide-semiconductor structure of Au∕SiOx(x<2)∕ZnO film was fabricated on a silicon substrate. With ever-higher forward bias where the negative voltage was connected to the silicon substrate, the UV electroluminescence from such a ZnO-based device transformed from the spontaneous emission to the random lasing in the ZnO film. It is believed that the recurrent scattering and interference of the enough strong electroluminescent UV light in the in-plane random cavities formed in the ZnO film leads to electrically pumped UV random lasing.The electrically pumped ultraviolet (UV) random lasing in c-axis oriented ZnO polycrystalline films has been demonstrated. For this demonstration, a metal-oxide-semiconductor structure of Au∕SiOx(x<2)∕ZnO film was fabricated on a silicon substrate. With ever-higher forward bias where the negative voltage was connected to the silicon substrate, the UV electroluminescence from such a ZnO-based device transformed from the spontaneous emission to the random lasing in the ZnO film. It is believed that the recurrent scattering and interference of the enough strong electroluminescent UV light in the in-plane random cavities formed in the ZnO film leads to electrically pumped UV random lasing.

Arrays of ZnO nanowires fabricated by a simple chemical solution route

A sol–gel process and a nanochannel aluminium template were employed to fabricate an orderly array of ZnO nanowires. The ZnO nanowires, with a hexagonal structure, were identified by means of x-ray diffraction and selected-area electron diffraction. The arrays of ZnO nanowires were characterized by scanning electron microscopy. Transmission electron microscopy (TEM) shows that the diameters of the ZnO nanowires are very uniform, at about 60 nm. Furthermore, high-resolution TEM provides lattice images of {100}, {002} and {101} planes in the nanowires, indicating that the nanowires are well crystallized.

Single crystalline CdS nanorods fabricated by a novel hydrothermal method

Abstract Cadmium sulphide (CdS) nanorods have been prepared by a novel thioglycolic acid assisted hydrothermal method. X-ray diffraction shows that the nanorods are of hexagonal structure, and high-resolution transmission electron microscopy further identifies that the CdS nanorods are single crystalline in nature. The optical properties of CdS nanorods were characterized by ultraviolet–vis and photoluminescence spectra. Furthermore, the mechanism for the TGA assisted hydrothermal synthesis of CdS nanorods has been preliminary presented.

Fairly pure ultraviolet electroluminescence from ZnO-based light-emitting devices

Fairly pure ultraviolet (UV) electroluminescence (EL) was realized on a ZnO-based metal-insulator (SiOx,x⩽2)-semiconductor structure on a silicon substrate, which was easily fabricated by the reactive direct current sputtering and electron beam evaporation. The UV EL originated from the near-band-edge (NBE) emission of ZnO was achieved at room temperature when the device was under sufficient forward bias with the negative voltage applied on the silicon substrate. Moreover, the intermediate SiOx layer should be thick enough to confine the electrons in the conduction band of ZnO beneath the ZnO∕SiOx interface, which is critical for generation of NBE emission from ZnO.

Directional CdS nanowires fabricated by chemical bath deposition

Directional CdS nanowires have been fabricated by using chemical bath deposition (CBD) and porous anodic aluminum oxide (AAO) template. X-ray diffraction and selected area electron diffraction show that the nanowires are hexagonal polycrystalline in nature. Transmission electron microscopy (TEM) reveals that the diameters of nanowires are about 60 nm. Furthermore, the high-resolution TEM illustrates the lattice images of {0 0 2}, {1 0 1} and {1 0 0} planes in the nanowires. The directional growth of nanowires is verified by scanning electron microscopy. It is believed that the ion-by-ion mechanism dictates the CBD of CdS nanowires within the pores of AAO template.

From ZnO nanorods to 3D hollow microhemispheres: solvothermal synthesis, photoluminescence and gas sensor properties

A novel solvothermal process using ethylene glycol (EG) as solvent has been employed to synthesize 3D ZnO hollow microhemispheres consisting of numerous orderly and radical nanorods with diameter of about 50 nm and length of several hundred nanometers. The glycol such as EG and the solvothermal process play the critical role in the synthesis of the 3D ZnO hollow microhemispheres by the primary formation of glycolate precursors and subsequent transformation into ZnO. The morphology, structure and optical property of the 3D ZnO hollow microhemispheres have been characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), x-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). Furthermore, the 3D ZnO hollow microhemisphere based gas sensor exhibits high sensitivity for ethanol and ammonia as well as quick response and recovery time at room temperature due to the high surface-to-volume ratio.

Long Bi2S3 nanowires prepared by a simple hydrothermal method

Long Bi2S3 nanowires have been prepared via the thioglyolic acid (HSCH2COOH, TGA) assisted hydrothermal method. The x-ray diffraction pattern shows that the Bi2S3 nanowires obtained are of orthorhombic phase. High resolution transmission electron microscopy identifies that the Bi2S3 nanowires are single crystalline in nature. Furthermore, we give a preliminary presentation of the mechanism for the TGA-assisted hydrothermal synthesis of Bi2S3 nanowires.

Grown-in defects in nitrogen-doped Czochralski silicon

Grown-in defects including oxygen precipitates and voids in nitrogen-doped Czochralski (NCZ) silicon have been investigated. It was found that the formation of grown-in oxygen precipitates in NCZ silicon can be divided into two stages. The large precipitates supposed to be enhanced by N2–V2–Ox complexes are generated around 1150 °C, while the small precipitates supposed to be enhanced by NmOn complexes are formed at 750 °C and below. Moreover, it was revealed that the oxygen precipitation behavior in the mixed-type NCZ silicon, which contains vacancy-type and interstitial-type defects distinguished by an OSF-ring in the oxidized wafer, is in sharp contrast to that in the mixed-type Czochralski (CZ) silicon, when subjected to one-step high temperature annealing (1050 °C/32 h) and two-step annealing (800 °C/4 h+1050 °C/16 h). On the other hand, it was found that, compared with CZ silicon, NCZ silicon has much denser crystal originated particles in smaller sizes, which were verified to have been annihilated ...