Structural, chemical and optical features of nanocrystalline Si films prepared by PECVD techniques

The nanostructural and chemical features of nanocrystalline Si (nc-Si) films, which were prepared by plasma-enhanced chemical vapor deposition (PECVD), were investigated in terms of various deposition conditions such as reaction gas fractions and substrate temperature. Such features were related with the photoluminescence (PL) phenomena of the nc-Si films. The phase of the nc-Si films prepared at room temperature is somewhere between amorphous and crystalline states, containing about 2 nm size nanocrystallites, which are well passivated by hydrogen. These films exhibit significant PL intensities near blue light region; the PL peaks shift to lower wavelength with decreasing nanocrystallite size.     

SnO2纳米晶的水热合成及其气敏特性

SnO2 nanocrystal with different crystalline sizes were prepared with SnCl2 2H2O and H2O2 raw materials by a hydrothermal process. The synthesized powders at different reaction temperatures were characterized by means of powder X-ray diffraction, transmission electron microscope, specific surface area and gas sensitivity measurements. The results revealed that the pure SnO2 nanocrystallites synthesized at 120 ℃ have high specific surface area （210.3 m2/g）, and show a high sensitivity to C2H5OH gas. Both traits are beneficial in gas-sensitive detection application.     

Comparison study on structure of Si and Cu doping CrN films by reactive sputtering

CrN, CrSiN and CrCuN films were deposited by DC magnetron reactive sputtering with hot pressed pure Cr, CrSi, and CrCu targets, respectively. As substrate bias increased from −50 V to −200 V, the preferred orientation of CrN films changed from (1 1 1) to (2 0 0). And the Si doping did not change this condition. However, the Cu doping films kept (2 0 0) orientation all along. CrN films presented typical columnar structure, and the alloying of Si and Cu could restrain columnar growth leading to dense structure. The CrSiN film was composed of nanocrystallites distributed in amorphous Si₃N₄, while no amorphous phase existed in CrCuN films.     

铁酸锌纳米晶的机械化学合成

以αFe₂O₃和ZnO粉体为原料,在高能球磨的作用下,室温(约25℃)合成了铁酸锌(ZnFe₂O₄)纳米晶.用XRD、TEM、M?sbauer谱及IR光谱等方法对纳米晶进行了表征.结果表明:所得纳米晶具有非正型分布的尖晶石结构,为超顺磁性;纳米晶内存在着较多的缺陷.     

Synthesis and characterizations of hierarchical biomorphic titania oxide by a bio-inspired bottom-up assembly solution technique

As a representative semiconductor metal oxide, hierarchical biomorphic mesoporous TiO₂ with interwoven meshwork conformation was successfully prepared using eggshell membrane (ESM) as a biotemplate by an aqueous soakage technique followed by calcination treatment. The synthesis conditions were systematically investigated by controlling the concentration, the pH value of the precursor impregnant, and so on. The nucleation, growth, and assembly into ESM-biomorphic TiO₂ in our work depended more on the functions of ESM biomacromolecules as well as the processing conditions. As-prepared TiO₂ meshwork exhibiting hierarchical porous structure with the pore size from 2 nm up to 4 μm, was composed of intersectant fibers assembled by nanocrystallites at three dimensions. Based on the researches into the N₂ adsorption-desorption isothermal and corresponding BJH pore-size distribution, the biomorphic TiO₂ would arose interesting applications in some fields such as photocatalysis, gas sensors, antistatic coating, dye-sensitized solar cells, etc. This mild method and the relevant ideas offer a feasible path to synthesize a new family of functional materials by integrating material science, chemistry, and biotechnology.     

Structural studies on the yttrium-doped cobalt ferrite powders synthesized by sol–gel combustion method

Y_0.2CoFe_1.8O₄ nanopowders were prepared using a sol–gel combustion method. Metal nitrates, such as yttrium nitrate, cobalt nitrate and ferric nitrate, were used as the source materials. Citric acid and polyvinyl alcohol were used as the burning agent and agglomeration reducing agent, respectively. The pH of the precursor was maintained at 7. The mean crystallite size of the prepared ferrite was in the range of ∼20–70 nm. The inverse spinel structure, cubic morphology, and the identification of functional groups of the yttrium-doped cobalt ferrite were analyzed systematically using several analytical tools.     

SnO2纳米晶的水热合成及其气敏特性

以SnCl2·2H2O和H2O2为主要原料,在无水乙醇和水的混合溶剂中,不同温度下,水热法制备了不同粒径的SnO2纳米晶.利用X射线粉末衍射、透射电子显微镜和比表面积测定等手段对产物进行了表征,并对产物的气敏性进行了测定和分析.结果表明,120、150和180℃时制备的产物均为单相SnO2,其对应的比表面积分别为210.3、125.6和69.2m2/g.产物SnO2对还原性气体CO和C2H5OH均有一定的气敏性,其中对C2H5OH气体的气敏性远大于CO气体.产物气敏性的大小与其比表面积的大小有关,比表面积越大,气敏性越高.     

草酸钙结石患者尿液中纳米级和微米级晶体研究

尿液中存在的微晶与尿石症的形成密切相关。采用X射线粉末衍射(XRD)、傅里叶变换红外光谱(FTIR)、纳米粒度仪、扫描电子显微镜(SEM)和透射电子显微镜(TEM)研究了20位草酸钙结石患者尿液中纳米级和微米级晶体的组分、形貌和Zeta电位,并与结石组分进行了比较。结果表明,草酸钙结石中常常含有少量共生的尿酸、磷酸钙和磷酸铵镁;而草酸钙结石患者的尿微晶组分主要为尿酸、磷酸盐和草酸钙等,晶体棱角尖锐,尺寸不一,从几十纳米到几十微米不等,并且有明显的团聚现象。20位草酸钙结石患者的尿纳米晶体的Zeta电位平均值为-5.92 mV,明显高于20位健康对照者尿纳米晶体的Zeta电位(平均值-12.9 mV);相比之下,结石患者尿液pH值(平均值为6.03)则与健康对照者(平均值5.92)没有明显差异。利用现代仪器分析方法分析尿液微晶与尿石组分的关系,可为临床上对症下药,制定预防与治疗措施提供重要的依据。     

Rotary target method to prepare thin films of CdS/SiO2 by pulsed laser deposition

Thin films of CdS-doped SiO₂ glass were prepared by using the conventional pulsed laser deposition (PLD) technique. The laser target consisted of a specially constructed rotary wheel which provided easy control of the exposure-area ratio to expose alternately the two materials to the laser beam. The physical target assembly avoided the potential complications inherent in chemically mixed targets such as in the sol–gel method. Time-of-flight (TOF) spectra confirmed the existence of the SiO₂ and CdS components in the thin-film samples so produced. X-ray diffraction (XRD) and atomic force microscopy(AFM) results showed the different sizes and structures of the as-deposited and annealed films. The wurtzite phase of CdS was found in the 600^oC-annealed sample, while the as-deposited film showed a cubic–hexagonal mixed structure. In the corresponding PL (photoluminescence) spectra, a red shift of the CdS band edge emission was found, which may be a result of the interaction between the CdS nanocrystallite and SiO₂ at their interface.