Passivation of pinhole defect microelectrode arrays in ultrathin silica films immobilized on gold substrates

Nanoscopic defects present in ultrathin (~ 6 nm) silica films covalently attached to gold substrates through a gold oxide layer exhibit a voltammetric response consistent with a random array of ultramicroelectrodes. These pinholes can be passivated via electrochemical polymerization of phenol to create insulating poly(phenylene) oxide plugs as documented by atomic force microscopy and infrared reflectance-absorbance spectroscopy. Passivation of pinholes is ~ 99.5% complete after 550 voltammetric cycles of oxidative electropolymerization.     

原料掺杂对多晶ZnS热压工艺及其性能的影响

采用热压法制备多晶ZnS时，由于ZnS是市售原料，杂质含量较多，必须进行提纯处理，即使如此，在热压过程中，晶体内仍然存在空穴、晶格缺陷及少量气孔等，影响材料透过性能，通过原料掺杂，使原料中掺入晶格常数小于ZnS的硫化物，可以起到固溶强化作用，减少空穴及气孔存在，提高晶体致密度,从而提高红外透过度；另外，可以使ZnS晶体结晶压力降低，即降低热压压力，为使用低强度材料作模具创造条件。     

GROSS ALPHA DETERMINATION IN URINE

A short review is given for the determination of gross alpha activity in urine;detailed information is collected including urine mineralization,separation of alpha emitters and source preparation.     

Annealing of ZnS nanocrystals grown by colloidal synthesis

ZnS nanocrystals (NCs) capped with tetramethylammonium (TMAH) were synthesized from ZnCl₂ · 2H₂O and thiourea using a wet chemical process. Further treatments of the nanocrystals such as aging, and annealing have been conducted to examine the stability of the grown samples. The X-ray diffraction spectra show that the crystal has a zinc blende structure with particle size of about 2 nm. The evidence of nanocrystalline character is also clear in the UV–Vis absorption that shows an excitonic peak at about 236 nm (5.2 eV) arising from band edge transitions. A photoluminescence emission peak centered at about 450 nm (2.7 eV) is attributed to transitions between shallow donors and Zn⁺ vacancies. Both absorption and photoluminescence spectra show that sample aging does not affect the characteristics of the sample, possibly due to protection by TMAH capping. Annealing at 700 °C and 900 °C results in the red shift of the photoluminescence.     

硫化锌纳米线的合成和表征

采用化学气相沉积法,以Zn(S2CNEt2)2为单源前驱体,Au为催化剂,在不同的温度下,得到了不同直径的六方相ZnS纳米线.在此基础上,改用Ni为催化剂,得到碳纳米管;改用单质S和Zn为原料,则得到立方相ZnS纳米线.在一定程度上实现了对ZnS纳米线的粒径和物相的控制合成,实现了利用催化剂对ZnS纳米线和碳纳米管的选择性合成.用X-射线粉末衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和能量分散光谱(EDS)对合成产物进行了表征.     

Size dependent optical characteristics of chemically deposited nanostructured ZnS thin films

ZnS thin films of different thicknesses were prepared by chemical bath deposition using thiourea and zinc acetate as S²⁻ and Zn²⁺ source. The effect of film thickness on the optical and structural properties was studied. The optical absorption studies in the wavelength range 250–750 nm show that band gap energy of ZnS increases from 3·68–4·10 eV as thickness varied from 332–76 nm. The structural estimation shows variation in grain size from 6·9–17·8 nm with thickness. The thermoemf measurement indicates that films prepared by this method are of n-type.     

Investigation of the effect of temperature on growth mechanism of nanocrystalline ZnS thin films

In this paper the temperature effect on the growth mechanism of ZnS thin films prepared in a chemical bath containing zinc acetate, ethylenediamine, and thioacetamide aqueous solutions has been studied in the temperature range between 25 and 75 °C. These ZnS thin films possess a nanocrystalline structure, exhibit quantum size effects due to the small crystal size and produce a blue shift in the optical spectra. This blue shift was attributed to a decrease in crystal size by using X-ray diffraction and scanning electron microscopy. The growth mechanism of the thin films is suggested to proceed by two fundamental steps: in the first step, the ZnS nanocrystallites coalesce into small grains through homogeneous nucleation in the solution phase. In the second step, eventually, these small grains or large-sized clusters diffuse and stick to the surface of the substrate to form the ZnS thin film, in a way called a cluster-by-cluster manner, resulting in particulate thin film.     

Study of Interatomic Potentials in ZnS—Crystal-GRID Experiments Versus Ab Initio Calculations

Crystal-GRID measurements have been performed with ZnS single crystals. For the first time, an asymmetric Crystal-GRID line shape could be observed. The preliminary data evaluation indicates that the reported lifetime of the 3221 keV level in ³³S is too short. A value of about 60 fs has been found. Due to this “long” lifetime the line shape is much less structured than calculated with the reported lifetime.     

MBE-Grown Cubic ZnS Nanowires

Ultrathin ZnS nanowires (NWs) were grown on a sapphire (0001) substrate at 430°C by the molecular-beam epitaxy (MBE) technique using self-assembled Au droplets as the catalyst. It was found that these NWs mainly consist of the cubic phase but a small portion was in the hexagonal phase. The analysis of the temperature-dependent band-edge (BE) emission of these NWs and that of a ZnS thin film revealed that the energy shift of the interband transition on temperature in ZnS is mainly attributed to the electron–phonon interactions. The observed blue shift of the BE emission of ZnS NWs could be quantitatively explained by the confinement of the excited excitons in the NW geometry.