Studies of stoichiometry of electrochemically grown CdSe deposits

The proper deposition bath composition for electrochemical synthesis of the CdSe deposit in the hexagonal structure of the right elemental stoichiometry, and photoreacting as an n-type semiconductor which can be used as a stable photoanode is investigated. The deposits were prepared by a cyclic potentiodynamic technique and the concentration of Cd²⁺ and SeO₃²⁻ in the deposition baths varied from 10⁻⁴ M to 0.1 M, and from 10⁻⁵ M to 10⁻³ M, respectively. The electrochemical, the X-ray diffraction (EDS and XRD), and the photoactivity studies of a number of deposits have shown that application of the solution composition following Cd:Se = 5:1 results in deposition of the stoichiometric CdSe. The detected ratio of reagents is explained on the base of reaction mechanism and necessary excess of cadmium ions preventing CdSe deposit dissolution. The procedure of CdSe electrosynthesis was developed to yield of a direct semiconductor in the hexagonal structure. The necessity for cadmium cations excess is explained on the basis of the mixed electrochemical/chemical deposition mechanism.     

Fabrication of a miniature twin-fuel-cell on silicon wafer

The fabrication and performance evaluation of a miniature twin-fuel-cell on silicon wafers are presented in this paper. The miniature twin-fuel-cell was fabricated in series using two membrane-electrode-assemblies sandwiched between two silicon substrates in which electric current, reactant, and product flow. The novel structure of the miniature twin-fuel-cell is that the electricity interconnect from the cathode of one cell to the anode of another cell is made on the same plane. The interconnect was fabricated by sputtering a layer of copper over a layer of gold on the top of the silicon wafer. Silicon dioxide was deposited on the silicon wafer adjacent to the copper layer to prevent short-circuiting between the twin cells. The feed holes and channels in the silicon wafers were prepared by anisotropic silicon etching from the back and front of the wafer with silicon dioxide acting as intrinsic etch-stop layer. Operating on dry H₂/O₂ at 25 °C and atmospheric pressure, the measured peak power density was 190.4 mW/cm² at 270 mA/cm² for the miniature twin-fuel-cell using a Nafion 112 membrane. Based on the polarization curves of the twin-fuel-cell and the two single cells, the interconnect resistance between the twin cells was calculated to be in the range from 0.0113 Ω (at 10 mA/cm²) to 0.0150 Ω (at 300 mA/cm²), which is relatively low.     

Surface-initiated atom transfer radical polymerization of polyhedral oligomeric silsesquioxane (POSS) methacrylate from flat silicon wafer

A polyhedral oligomeric silsesquioxane (POSS) methacrylate monomer, i.e. 3-(3,5,7,9,11,13,15-heptacyclopentyl-pentacyclo [9.5.1.1.^3,91.^5,151^7,13]-octasiloxane-1-yl) propyl methacrylate (POSS-MA), was directly grafted from flat silicon wafers using surface-initiated atom transfer radical polymerization (ATRP). Two methods were used to improve the system livingness and control of polymer molecular weights. By ‘adding free initiator’ method, a linear relationship between the grafted poly(POSS-MA) layer thickness and monomer conversion was observed. By ‘adding deactivator’ method, the poly(POSS-MA) thickness increased linearly with reaction time. Poly(POSS-MA) layers up to 40 nm were obtained. The chemical compositions measured by X-ray photoelectron spectroscopy (XPS) agreed well with their theoretical values. Water contact angle measurements revealed that the grafted poly(POSS-MA) was extremely hydrophobic. The surface morphologies of the grafted polymer layers were studied by an atom force microscopy (AFM).     

On the dynamic model of promoted molybdenum sulfide catalysts

On the basis of the fundamental concepts of catalysis by transition metal sulfides (TMSs) a new dynamic model of the promoted Mo-sulfide catalysts functioning under HDS conditions has been developed. According to the model under hydrogen atmosphere sulfidation degree of the edges of different layers of the slab can vary and surface sulfur can migrate from one layer to a neighboring layer so that average sulfidation state of the slab remains constant under given reaction conditions. The model describes oscillations by sulfur and promoter atoms between the adjacent layers of the slab on the atomic scale level. The driving force of such processes is the heterolytic dissociation of the gas phase hydrogen and formation of hydride hydrogen linked to a promoter atom. This hydride hydrogen triggers an electron transfer from a promoter to Mo with the formation of the vacancy. This model correlates with radioisotopic data and an earlier suggested “forcing out” mechanism and gives some new interpretations of the important statements of the electron theory of promotion and the “rim-edge” model.     

一种太阳能硅片清洗剂的制备方法

研制一种用于工业生产中太阳能硅片的水基专用清洗剂,适用于硅片的表面清洗处理。该清洗剂以非离子表面活性剂和阴离子表面活性剂为主剂,溶液呈碱性,不含有机溶剂,无刺激性气味、成本低、具有良好的去污、清洗性能。清洗方法操作方便、无毒、对人体无危害、对环境无污染。     

硅片切割技术的现状和发展趋势

随着太阳能技术和半导体技术的飞速发展,对硅片的直径,厚度和精度提出了更高的要求,传统的硅片加工方式已经不能满足需要.文章分析内圆切割、多线切割、电火花钱切割和超声振动切割四种硅片切割方式,指出多线切割是硅片的主要切割方式,电火花线切割硅片技术有很大的发展潜力,超声振动切割优于其它三种硅片切割方式.     

硅钼蓝光度法快速测定SAPO-34分子筛中硅含量

建立一种以分光光度法测定SAPO-34分子筛中硅含量的分析方法。以硅和钼酸铵在盐酸介质中形成硅钼黄杂多酸,再以抗坏血酸将硅钼黄还原成硅钼蓝后,对硅含量进行测定。结果表明,体系中硅钼蓝的最大吸收波长为806 nm,绘制的标准曲线在0.100 0~6.000 mg/L内服从朗伯-比尔定律,所得相关系数为R2=0.999 5。该分析方法用于SAPO-34分子筛中硅含量的测定,精密度及稳定性良好,操作简单、快速。     

水葫芦生物质炭的制备与染料吸附性能研究

以水葫芦为原料,采用限氧升温热解的方法制备了水葫芦生物质炭,研究热解温度对生物质炭理化结构与染料吸附性能的影响。结果表明,通过SEM、XRD、BET表征可以看出,在一定温度范围内,随温度升高生物质炭比表面积越大,孔隙结构越发达。当热解温度为500℃,生物质炭会有更多的含氧官能团以及较好的孔隙结构。随着热解温度的升高,生物质炭对染料吸附量先增加后有所降低,生物质炭对阳离子染料亚甲基蓝能达到更好的吸附效果,刚果红次之,甲基蓝的吸附效果一般。     

Aromatic reduction properties of molybdenum sulfide clusters in HY zeolite

Molybdenum sulfide catalysts supported on an HY zeolite at various Mo contents were studied. Catalysts were prepared by incipient wetness impregnation with ammonium heptamolybdate solution and calcined without drying. Their reactivity has been evaluated in toluene hydrogenation under typical hydrotreating conditions. Compared to alumina supported catalysts, zeolite supported Mo catalysts are extremely active for aromatics hydrogenation. At low molybdenum loading, molybdenum sulfide phases inside the zeolite show a particularly high intrinsic activity. This activity can be attributed to molybdenum sulfide clusters differing from MoS₂ slabs.     

Wettability and adhesion characteristics of photo-crosslinkable adhesives for thin silicon wafer

Acrylic pressure-sensitive adhesives (PSAs) have many applications in the processes of electronic industry. As the silicon wafers become thinner, the acrylic PSAs need to show proper adhesion and better wettability on the thin wafer. The acrylic copolymers were synthesized by solution polymerization of 2-ethylhexyl acrylate, ethyl acrylate, and acrylic acid with AIBN as an initiator. Photo-crosslinkable PSAs were synthesized by reaction of the acrylic copolymers with glycidyl methacrylate (GMA) and lauryl glycidyl ether (LGE). The adhesion performance of acrylic photo-crosslinkable PSAs was investigated based on wettability, probe tack, peel strength, cohesiveness, and viscoelastic properties. The adhesion characteristics varied significantly depending on the ratio of GMA to LGE in the photo-crosslinkable PSAs.     

Characterization of electrochemically formed thin layers of binary alloys by linear sweep voltammetry

It has been demonstrated that linear sweep voltammetry can be used as anin situ technique for characterization of electrodeposited thin layers of binary alloys. The anodic dissolution characteristics of linear sweep voltammograms are very sensitive to the type of electrodeposited alloy. If both metals do not passivate in the investigated solution, eutectic type alloys are characterized by two sharp dissolution peaks, indicating no miscibility between components in the solid phase. From the ideal solid solutions, components of the alloy dissolve simultnaeously, while in the case of intermediate phases and intermetallic compounds each phase, or compound, has its own peak of dissolution.     

Determination of lead and copper content in surface layers of electrochemically colored glass

Translated from Steklo i Keramika, No. 7, pp. 29–30, July, 1991.     

硅片化学机械抛光表面材料去除非均匀性实验

化学机械抛光技术已成为超大规模集成电路制造中实现硅片全局平面化的实用技术和核心技术。CMP的最大问题之一是硅片材料去除的非均匀性,它是集成电路对硅片表面平坦化需求的一个重要指标。文章提出了硅片表面材料去除非均匀性计算公式,在CP-4实验用抛光机上进行了硅片化学机械抛光实验,并用美国ADE公司生产的WaferCheck-7200型非接触式电容厚度测量设备对单晶硅片的厚度进行高精度检测,经过计算,得出了不同抛光速度下硅片表面材料去除非均匀性的数据,为理解硅片CMP材料去除非均匀性形成机理,进一步揭示硅片CMP材料去除机理提供了理论依据。     

Plasma-activated direct bonding of diamond-on-insulator wafers to thermal oxide grown silicon wafers

Diamond-on-insulator (DOI) wafers featuring ultrananocrystalline diamond are studied via atomic force microscopy, profilometer and wafer bow measurements. Plasma-activated direct bonding of DOI wafers to thermal oxide grown silicon wafers is investigated under vacuum. DOI wafer with chemical mechanical polishing (CMP) on the diamond surface makes a poor bonding to silicon wafers with thermal oxide. Our results show that plasma enhanced chemical vapor deposition of silicon dioxide on top of the DOI wafer, CMP of the oxide layer and annealing are essential to achieve very high quality direct bonding to thermal oxide grown on silicon wafers. Plasma activation results in the formation of high quality bonds without exceeding 550 °C in the direct wafer bonding process.     

Distribution and chemistry of phases developed in the brazing of silicon nitride to molybdenum

Silicon nitride was brazed to molybdenum using two different nickel-based brazing alloys. The alloys used were AWS BNi-5 (Ni–18Cr–19Si at%) and an alloy with the same Ni/Cr ratio as BNi-5 but with 10 at% Si. Brazing experiments were carried out at 1220 and 1300°C for times ranging from 1 to 10 min. The quality and microstructure of the S₃N₄/Mo couples were strongly influenced by the composition of the joining alloys, brazing time and temperature. Microchemical analysis revealed an elaborate joint microstructure with the formation of complex reaction products in the interface. Joint strengths of up to 50 MPa were achieved when these materials were brazed with an alloy containing 10% Si.     

Catalytic functionality of unsupported molybdenum sulfide catalysts prepared with different methods

The catalytic functionality and structural properties of three kinds of unsupported molybdenum sulfide catalysts were investigated by model test reactions and BET, TEM, XPS and XRD analyses. The results indicated that highly bent multi-layered MoS₂ structures were more catalytically active, while a well crystallized MoS₂ structure was more favorable for direct S-extrusion during the reactions of dibenzothiophene. It was proposed that the curvature of MoS₂ basal planes was catalytically active, though they were less active for hydrodesulfurization than the edge planes.     

The microstructure of polymer-derived amorphous silicon carbide layers

In order to achieve thin amorphous silicon carbide layers a two-stage process was applied. The deposition of thin layers from liquid chlorovinylsilanes was carried out under argon flow using a spin-coating-system. Afterwards, the samples were pyrolysed in a temperature range between 800 °C and 1200 °C with different hydrogen concentrations in the atmosphere. Additionally, bulk material was pyrolysed in order to characterise structural changes by transition oligomer to a-SiC:H.In this work we present studies on the structure of the layers and of bulk material, which were carried out by XRD, MAS NMR and Raman spectroscopy, depending on pyrolysis conditions. Following results were obtained: Both, silicon carbide layers and bulk material, pyrolysed at 800 °C, were amorphous. Increase of the temperature to 1200 °C leads to a partial amorphous-to-crystalline transition forming β-SiC. Moreover, derivations from stoichiometric SiC were observed: Free silicon was found in thin layers, whereas crystallites of graphite were detected in the bulk material. The amount of excess carbon can be influenced by addition of hydrogen to the pyrolysis atmosphere.     

Mechanical damage to estabragh fibers in the production of thermobonded layers

Estabragh (Asclepias procerais) fibers are natural, hollow fibers, and the mechanical behavior of these fibers plays a major role in mechanical processing. This work explores the mechanical behavior of estabragh fibers in three different areas—tensile failure, carding behavior, and the construction of nonwoven layers—and reports the main barriers in the spinning process of these fibers. In the first step, a typical stress–strain curve of estabragh fibers is plotted. Fractography of the broken ends by scanning electron microscopy shows the granular nature of the fracture. The likely mechanism of tensile failure is discussed and compared with the fracture of cotton fibers under tensile loading. In the second stage, the carding behavior and likely mechanism of fiber damage during the carding process of estabragh fibers are studied. Both qualitative and quantitative studies show that estabragh fibers experience serious damage during the carding process. The effect of the hollowness of the fibers on their mechanical properties is discussed as well. In the final approach, thermobonded layers of two different blends of estabragh fibers and bicomponent poly(ethylene terephthalate) fibers are produced. Some properties of the produced layers, including moisture absorption, ultraviolet absorption, and bending length, are reported. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Correlating chemical and water purity to the surface metal on silicon wafer during wet cleaning process

Trace metals in hydrogen peroxide and high-purity water, used in wet cleaning of wafers, is correlated to the metallic contamination of the wafer surface since metal contamination adversely impacts IC device yield. Hydrogen peroxide with different level of trace metals, ranging from 100 ppt level to 10 ppb level, is used in the experiment to determine the level of selected metal deposition on the silicon surface. Significant amounts of these trace metallic impurities can be removed by subsequent treatment of the silicon wafer by an acidified solution of water. Contamination of a wafer surface by sodium is also correlated to the level of sodium present in deionized water used in the final rinsing of the wafer. The threshold and mechanism for metal deposition for various metals on wafer surfaces are different. This information is useful in determining purity requirements for process chemicals and improving the wet cleaning process for the next generation of semiconductor devices.