一种基于MEMS工艺的新型THz喇叭天线的设计与仿真

提出了一种太赫兹(THz)天线结构:基于MEMS 工工艺的THz角锥喇叭天线.采用电磁场仿真软件Ansoft HFSS 11对所设计的天线进行仿真,结果表明该天线在2.5 THz ～3.5 THz范围以内具有回波损耗优于-25 dB,增益大于15 dB的良好特性.天线可以通过MEMS工艺(硅基KOH刻蚀)制造,具有加工...     

Modulated Cr(III) oxidation in KOH solutions at a gold electrode: Competition between disproportionation and stepwise electron transfer

The electrochemical oxidation of aqueous Cr(III) was examined using cyclic voltammetry with a polycrystalline Au electrode in KOH solutions of varying pH and Cr(III) concentration. The mechanism and kinetics for the oxidation of Cr(III) is a quasi-reversible diffusion-controlled reaction and is largely dependent on the solution pH. The reaction mechanism is initiated by an irreversible electrochemical electron transfer to form Cr(IV) which is the rate-determining step (RDS). Following the RDS, subsequent oxidation of Cr to its hexavalent state occurs by the disproportionation of Cr(IV) at low KOH concentrations and electron transfer at high KOH concentrations due to the involvement of OH⁻ in the disproportionation reaction. As the solution pH increases, the Cr(III) oxidation peak potential shifts negatively owing to the involvement of OH⁻ in the RDS. The competitive adsorption of OH⁻ and CrO₂⁻ on the electrode surface also plays an important role in the oxidation behavior.     

Convex corners undercutting and rhombus compensation in KOH with and without IPA solution on (1 1 0) silicon

The present investigation introduces convex corners undercutting and results of rhombus compensation patterns in 40% aqueous KOH solution and in KOH saturated with isopropanol (IPA) solution. All experiments are carried out on (1 1 0) silicon at 70 °C. Undercuts take place on convex corners in both solutions. Moreover, the front etch planes governing undercut vary with solutions. Rhombus compensations are used to correct the undercut. Perfect acute corner without residue is obtained, and there are only some residue structures on both sides of obtuse convex corners in KOH with IPA solution, which are better results than those in pure aqueous KOH solution.     

Dedolomitization in different alkaline media: Application to Portland cement paste

The dedolomitization reaction kinetics is studied through several long-term experiments consisting of an aqueous dispersion of fine powders of dolomite and portlandite with alkalinity between 0.1 and 1 M KOH, at 25 and 75 °C. The experimental results are numerically simulated to calculate the apparent dissolution constant rates for dolomite, k_dol. At low temperature, two dissolution stages were observed. In an early stage, part of dolomite powder dissolves quickly until an apparent steady is reached. After several days, the reaction continues at a lower rate. The calculated dissolution rate for dolomite in the first stage is one order of magnitude higher than that of the second stage. At 75 °C, the k_dol is two orders of magnitude higher than at 25 °C. The addition of alkali increases the k_dol at high temperature, but reduces it at room temperature.     

Potassium Hydroxide/Dimethyl Sulfoxide Superbase‐Promoted Transition Metal‐Free Synthesis of 2‐Substituted Benzothiophenes under Visible Light

A potassium hydroxide/dimethyl sulfoxide (KOH/DMSO) superbase‐promoted method for the synthesis of 2‐substituted benzothiophenes has been developed via photoinduced intermolecular annulation of 2‐halothioanisoles with terminal alkynes at ambient temperature. The present protocol uses commercially available 2‐halothioanisoles as substrates and visible light as energy force, which offers a wide range of benzothiophenes regioselectively in moderate to good yields. Such a facile and effective transformation will provide an environment‐friendly approach to the synthesis of benzothiophene derivatives.

     

Preparation of Activated Carbons from Tobacco Stems by Potassium Hydroxide Activation and Phosphine Adsorption

Activated carbon preparation from tobacco stems by KOH activation at different activation temperatures and KOH/char mass ratios were investigated in this study. The effects of preparation parameters on activated carbon pore structure, morphometrics, microcrystallinities, and surface functional groups were characterized by N₂ adsorption, SEM, XRD, and FTIR technologies, respectively. The optimum preparation condition of activated carbon was activation temperature of 850°C, and KOH/char mass ratio of 2. Under this condition, the BET surface area of 2215 m²/g, and the pore volume of 1.343 cm³/g can be obtained. Prepared activated carbon showed clearly honeycomb holes, and a predominated amorphous structure. With increase of activation temperature and KOH/char mass ratio, decrease of surface oxygen functional group, and aromatization of the carbon structure was found. The activated carbon was subject to PH₃ purification, and the maximum PH₃ adsorption capacity of 253 mg/g can be realized based on well prepared KOH-AC with modification of 2.5% Cu. It seems that the activated carbon produced from chemical activation of tobacco stem would be an effective and alternative adsorbent for PH₃ adsorption because of its high surface area, adsorption capacity, and low cost.     

微薄膜结构的湿法腐蚀技术研究

通过对流量传感器制造工艺中微薄膜结构的研究,分别介绍了采用氢氧化钾和四甲基氢氧化铵(TMAH)交替腐蚀实现感应薄膜释放的基本原理、工艺方法、工艺参数,及在制作流量芯片中的具体应用实例,实现了微米级厚度薄膜释放,为流量传感器和其它需要超薄薄膜微结构的制作奠定了基础。     

Surface modification of textured silicon and its wetting behaviour

Textured silicon (Si) substrate were prepared using various texturing methods both chemical and physical and their water contact angle, surface topography and Raman spectra were studied and investigated. The effect of plasma and chemical treatment on micro/nanostructure and roughness of the surface with and without deposition of Octadecyltrichlorosilane (ODTS, Cl₃Si (CH₃)₁₇), self-assembled monolayer (SAM) is investigated for achieving higher water contact angle (θ_c). The importance of synergism of texturing with deposition of ODTS SAM in preparing superhydrophobic silicon surfaces has been discussed. It is shown that superhydrophobic silicon surfaces can be achieved on silicon surfaces by coating with ODTS, irrespective of whether it is textured or not, polished or unpolished, provided a chemical treatment is given to the surface prior to the ODTS coating.     

三维多级孔石墨烯/聚苯胺复合材料的制备及电化学性能

采用水热法合成聚糠醇（PFA）,探究了表面活性剂聚乙烯吡咯烷酮（PVP）添加量和反应时间对PFA微观形貌的影响。将改进Hummers法制备的氧化石墨烯（GO）对PFA、泡沫Ni进行包覆,探讨了PFA模板与GO不同质量比的包覆效果。去模板后成功构筑三维大孔石墨烯（3D rGO）,3D rGO再经KOH活化获得三维多级孔石墨烯（3D PrGO）,3D PrGO经与聚苯胺（PANI）原位复合获得3D PrGO/PANI复合材料。采用XRD、SEM、TEM、FTIR、XPS和比表面（BET）分析法对材料的物相组成、微观结构、形貌、比表面和孔径进行表征,采用循环伏安、恒流充放电、电化学阻抗谱分析了3D PrGO/PANI复合材料的电化学性能。结果表明:通过控制糠醇、PVP及水的比例,在180℃水热反应24 h成功制备了球径在500 nm左右的PFA微球。在PFA与GO质量比为1∶1时包覆效果最佳。450℃热处理6 h成功去除PFA模板并形成400~600 nm左右的大孔,经KOH活化后,在3D PrGO上形成介孔结构。3D PrGO/PANI复合材料在0.5 A/g电流密度下比电容为433 F/g,在1 A/g下1 000次循环充放电之后,3D PrGO/PANI复合材料的比电容保留率为75%,高于纯PANI的69%。