Combined AFM and Brewster-angle analysis of gradually etched ultrathin SiO2 - Comparison with SRPES results

Two surface sensitive techniques are employed to assess both structural and optical properties of an inhomogeneous Si(1 1 1)/silicon oxide multilayer system. Upon gradual etch-back of the native silicon oxide layer, structural changes of the respective interfaces were determined by contact-mode atomic force microscopy (CM-AFM); optical data were obtained by Brewster-angle analysis (BAA) at a single wavelength. It is shown, that the sensitivity of BAA leads to the identification of an additional strained sub-surface layer that was investigated by subsequent etching experiments and following optical analysis. Inclusion of this layer and its interfaces into a multilayer model allowed precise numerical evaluation of the respective oxide thicknesses in the range between 12 Å and 2 Å. These values, obtained by combination of BAA and AFM, are in excellent agreement with results obtained by synchrotron radiation photoelectron spectroscopy (SRPES). It is furthermore shown, that the thickness resolution limit of BAA (at constant nanotopographic roughness) is well below 1 Å. A limitation of BAA single-wavelength analysis is reached when the roughness variation, in terms of an effective layer and its thickness, exceeds the oxide thickness variation.     

Wavelet analysis of the surface morphologic of nanocrystalline TiO2 thin films

Surface morphologies of nanocrystalline TiO₂ thin films were studied by analyzing the surface profile of AFM images using wavelet transform method. Based on characterizing the fractal feature and computing the image details at different orientations and resolutions, the surface textures of nanocrystalline TiO₂ thin films before and after chemical treatment were examined. The results reveal that titanium isopropoxide treatment leads to an increase of surface roughness. The related mechanism of modification of the microstructure by chemical treatment associated with the improvement of the photocurrent response is discussed.     

单片机在用电集中抄表中的应用

为了解决用电抄表问题，研究了一种以单片机为核心的８路脉冲集中采集电路。这种独特的硬件设计方法实现了低造价的集中抄表，在实际应用中得到了用户的好评。该方法对其它行业集中抄表也有借鉴作用。     

The adsorption of NO on an oxygen pre-covered Pt(1 1 1) surface: in situ high-resolution XPS combined with molecular beam studies

Adsorption of NO on a Pt(1 1 1) surface pre-covered with a p(2 × 2) atomic oxygen layer has been studied in situ by high-resolution X-ray photoelectron spectroscopy and temperature-programmed XPS using third-generation synchrotron radiation at BESSY II, Berlin, combined with molecular beam techniques and ex situ by low energy electron diffraction and temperature-programmed desorption. O 1s XP spectra reveal that an ordered p(2 × 2)-O layer dramatically changes the adsorption behavior of NO as compared to the clean surface. The atomic oxygen occupies fcc hollow sites, and therefore blocks NO adsorption on these sites, which are energetically preferred on clean Pt(1 1 1). As a consequence, NO populates on-top sites at low coverage. At 110 K for higher coverages, NO can additionally adsorb on hcp hollow sites, thereby inducing a shift of the O 1s binding energy of atomic oxygen towards lower energies by about 0.25 eV. The bond strength of the hcp hollow NO species to the substrate is weakened by the presence of atomic oxygen. A sharp p(2 × 2) LEED pattern is observed for NO adsorption on the oxygen pre-covered surface, up to saturation coverage. The total saturation coverage of NO on Pt(1 1 1) pre-covered with varying amounts of oxygen (below 0.25 ML) decreases linearly with the coverage of oxygen. The initial sticking coefficient of NO is reduced from 0.96 on clean Pt(1 1 1) to 0.88 on a p(2 × 2) oxygen pre-covered surface.     

自燃煤耗氧速度分析及其实验研究

在分析煤炭自燃机理时着重讨论了自燃氧化放热量与表面反应热的关系，由此在自行研制的ＤＫＨ—１型动态控温耗氧测定仪上对大同忻州窑矿１１＃煤８９２０面混煤进行了分粒度级耗氧速度测定，取得初步成果。     

Synthesis of ultrathin semiconducting iron silicide epilayers on Si(1 1 1) by high-temperature flash

In this work ultrathin iron silicide epilayers were obtained by the reaction of iron contaminants with the Si(1 1 1) substrate atoms during high-temperature flash. After repeated flashing at about 1125 °C, reflection high-energy electron diffraction indicated silicide formation. Scanning tunneling microscopy revealed highly ordered surface superstructure interrupted, however, by a number of extended defects. Atomic-resolution bias-dependent imaging demonstrated a complex nature of this superstructure with double-hexagonal symmetry and (2√3×2√3)-R30° periodicity. Among the possible candidate phases, including metastable FeSi₂ with a CaF₂ structure and FeSi_1+x with a CsCl structure, the best match of the interatomic distances to the measured 14.4 Å × 14.4 Å unit cell dimensions pointed to the hexagonal Fe₂Si (Fe₂Si prototype) high-temperature phase. The fact that this phase was obtained by an unusually high-temperature flash, and that neither its reconstruction nor its semiconducting band-gap of about 1.0 ± 0.2 eV (as deduced form the I-V curves obtained by scanning tunneling spectroscopy) has ever been reported, supports such identification. Due to its semiconducting properties, this phase may attract interest, perhaps as an alternative to β-FeSi₂.     

Scanning tunneling and atomic force microscopy study of the misfit layer compounds (LaS)1.14(NbS2)n (n=1, 2) and [(Pb,Sb)S)]1.14NbS2

The misfit layer compounds (LaS)_1.14(NbS₂)_n (n=1, 2) and [(Pb,Sb)S]_1.14NbS₂ were examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). In these compounds the NaCl-type double MS (M=La, Pb, Sb) layers (Q layers) alternate with the NbS₂ layers (H layers) made up of NbS₆ trigonal prisms. It was possible to record AFM and STM images for only the H layers for (LaS)_1.14(NbS₂)_n, but for both the H- and Q-layers for [(Pb,Sb)S]_1.14NbS₂. Partial and total electron density plots of the H and Q layers were calculated to interpret the observed STM and AFM images. The bright spots in the STM and AFM images of the H layer correspond to S atoms, and those of the Q layer to Pb and Sb atoms. The STM images for the Q layers of [(Pb,Sb)S]_1.14NbS₂ suggest that a short-range ordering of the Pb and Sb atoms occurs in the (Pb,Sb)S sheets of the Q layer.     

Hydrogen adsorption on Gd(0001)

The electronic structure of hydrogen adsorbate-induced states on Gd(0001) was investigated by means of photoelectron spectroscopy with linearly polarized radiation. The E vector of the incoming photon beam is rotatable. Clean and well-ordered rare-earth (0001) surfaces exhibit a highly localized surface state near the Fermi edge. After the adsorption of hydrogen, the surface state disappears and an additional sharp feature at about 4 eV binding energy is observed. For this latter state, the ratio of the radial matrix elements as well as the relative phase shifts were determined to be R=R_p/R_f=2.4±0.3 and δ_f−δ_p=310±10°, respectively. The removal of the Gd surface state by hydrogen adsorption was investigated by means of scanning tunneling microscopy (STM) and spectroscopy (STS). The removal of the surface state exhibits domain-like behavior, with surface steps acting as domain boundaries. The tunneling spectra reveal that hydrogen adsorption causes a dramatic reduction in the differential conductivity near the Fermi level.     

双圈同轴式光纤涡轮流量计的智能化设计

为了克服现有电磁式涡轮流量计的量程小,易受电磁干扰的缺点,本文设计了一种双圈同轴式光纤的涡轮流量智能检测系统。该测试系统由三大模块组成,双圈同轴式的光纤传感器作为信号拾取工具,硬件电路对信号进行预处理,TMS320F2812 DSP对信号进一步软件处理。经过实验验证,该测试系统在5-300Hz的测量范围内,测量误差小于0.5%。因此,该测试系统具有较高的测量精度和可靠性,这为光纤涡轮流量计的样机制作提供了重要依据。     

GPRS技术在农村用水远程自动抄表系统中的应用

目前许多偏远农村地区用水长期以来一直采用的是包月制方式,这种模式的特点是不论用户的月用水量是多少,只要每月交付一定的水费即可。用水量与用水费的严重不一致,不仅不利于供水部门对用户用水的实时监管,更不利于环保节水的实现。农村地区地理位置比较分散,考虑目前移动网络覆盖范围之广,利用中国移动或中国联通的GPRS网络在实验室搭建无线自动抄表系统。实验结果表明,GPRS技术在农村用水监管系统中的应用,一方面可以降低传统人工抄表员的工作强度;另一方面抄读回的计量数据精确无误,完全克服了人工抄表的缺点。