Papers by Keyword: Semiconductor

Abstract: Positron annihilation technique is a well known technique to characterize the defects in a material. These defects can be identified by positron annihilation lifetime and coincidence Doppler broadening of positron annihilation radiation measurement. In this chapter we report the room temperature positron annihilation lifetime for single crystalline ZnO. From our study it is confirmed that the present crystal contains V_Zn–hydrogen complexes with low open volumes. Another important nuclear solid technique is the Mossbauer Spectroscopic technique which has been used to probe the local magnetic properties of a solid. Here we have summarized Mossbauer spectroscopic studies on ferrites.

Abstract: Demand for diminishing edge roll off of workpiece has rapidly increased, especially in polishing silicon wafers and glass disks. However, the conventional polishing technologies cannot meet the demand. To address this problem, the influence of carrier film properties and that of polishing pad properties on the stress distribution near the workpiece edge were investigated using finite element methods. Based on the analytical results, double-layered polishing pads having an extra-fine fiber thin layer and a hard polymer layer were developed. Polishing experiments on silicon wafers and glass plates showed that the developed polishing pads achieved high finishing efficiency and extremely flat surface near the edge.

Abstract: This article proposed a liquid phase method to synthesize the small, even sized nano lead sulfide sol in high power (2KW) pulse ultrasonic reactor, which is designed by our research group. The characteristics of this method are the short time, the small granularity, the equal particle size and the mild synthesis condition. The particle size of lead sulfide sol is about 7～8 nanometer and the size distribution is narrow. Ultraviolet and visible spectroscopy shows that the absorption limit of this lead sulfide sol is about 670nm. Compared with the normal sized lead sulfide, the absorption limit is greatly blue shifted because of the quantum size effect.

Abstract: Based on our earlier theoretical investigation, p-type C:Si codoped AlN crystals were grown on SiC substrates by a sublimation method in a improved growth reactor. Hall-effect measurement shows that the AlN crystals have a high hole density of 1.4×10¹⁴ cm^-3 and mobility of 52 cm²V^-1s^-1 in spite of the high resistivity (896 Ω•cm). In the AlN samples, Si dopants act as donors due to substituting Al atoms, and most of C dopants act as acceptors for replacing N atoms. It is also observed that the activation energy of C acceptors in C:Si codoped AlN is reduced by codoping Si donors, which agrees with the computational results.

Abstract: Elemental identification of material is a prime most important in material science field. Electric discharge is used for material elemental identification with optical emission spectroscopy. During electric discharge machining between two electrodes plasma is generated which emits intense radiation in the UV-Visible region. The generated plasma captured by optical emission spectroscopic technique and elements are identified from recorded spectra by matching with standard NIST database. This method is simple, rapid, and inexpensive compared to all other elemental identification method. The elements of the metal, semiconductors, even insulators can be identified without much difficulty. The elemental identification of material has been investigated in macro and micro level.

Abstract: The synthesis of hexagonal phase Mn-doped CdS (Cd_1-xMn_xS) nanorods was achieved by solvothermal treatment of a class of easily obtained, air-stable single-source molecular precursors (cadmium manganese diethyldithiocarbamates, Cd_1-xMn_x-(DDTC)₂) in ethylenediamine at 180 °C for 12 h. The structures and compositions of the as-synthesized products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy.

Abstract: the equilibrium lattice constants, elastic and thermodynamic properties of cubic CdTe are systemically investigated at high temperature using the plane-wave pseudopotential method as well as the quasi-harmonic Debye model. The bulk modulus of CdTe are calculated as a function of temperature up to 1000K, the relationship between bulk modulus B and pressure is also obtained. The results gained from this model will provide overall predictions accurately for the temperature and pressure dependence of various quantities such as the bulk modulus, the heat capacity and the thermal expansion coefficient. More over, the dependences between Debye temperature and temperature are also successfully obtained. Our results are compared with the experimental data and discussed in light of previous works.

Abstract: Paralled flaw precipitation method has been employed to synthesize nanostructured Bi₂O₃. It is found that the bandgap and photocatalytic performance of Bi₂O₃ has a strong dependence on the kind of precipitants. The prepared photocatalysts were characterized by BET, XRD, UV-Vis diffuse reflectance and SEM. The results show that Bi₂O₃ prepared by NH₃·H₂O has the highest BET surface area, pore volume, the smallest pore size and the particle average size. Bi₂O₃ prepared by NH₃·H₂O exhibits the best photocatalytic activity. The results of further experiments show that bandgap and the specific surface area all play an important role in promotion of photocatalytic activity of Bi₂O₃ prepared by NH₃·H₂O.

Abstract: Bismuth selenide (Bi₂Se₃) hexagonal nanosheet crystals with uniform size were successfully prepared via a solvothermal method at 160°C for 22 h using bismuth trichloride(BiCl₃) and selenium powder(Se) as raw materials, sodium bisulfite(NaHSO₃) as a reducing agent, diethylene glycol(DEG) as solvent, and ammonia as pH regulator. Various techniques such as X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), and selected area electron diffraction (SAED) were used to characterize the obtained products. Results show that the as-synthesized samples are pure Bi₂Se₃ hexagonal nanosheet crystals. A possible growth mechanism for Bi₂Se₃ hexagonal nanosheet crystals is also discussed based on the experiment.

Abstract: Size-tunable ZnS nanocrystals were obtained by electron sputtering. Almost sputtered nanocrystals were spherical and well-dispersed. The sizes of deposited ZnS nanocrystals appeared a good gradient distribution according to their distance away from the sputtering target. These nanocrystals had gradual changes in diameter from about 1 to 15 nm. This research may afford a simple and efficient method to prepare well-dispersed semiconductor nanocrystals in a small size range.