碱性水溶液中甲醛在硅电极表面的电化学行为及其对硅化学刻蚀的影响

研究了KOH水溶液中氧化剂甲醛在p-Si和n-Si(100)单晶半导体电极表面的电化学行为及其对硅化学刻蚀表面形貌的影响．实验结果表明,甲醛不仅影响p-和n-型半导体电极在碱性溶液中的阳极氧化峰电流,而且在负电位区能在Si(100)电极上发生还原．在光照条件下,p-Si(100)电极上也观测到了HCHO的电化学还原及光电流倍增效应．甲醛在硅电极表面的电化学还原反应分两步进行,反应终产物为甲醇．此外,HCHO能有效抑制碱性溶液中Si表面“金字塔”型表面粗糙颗粒的形成。     

Specific features of etching of the (001) surface of single-crystalline silicon in KOH-based solutions

Specific features of the micro-and nanorelief of the (001) surface of single-crystalline silicon upon etching in aqueous KOH solutions of various concentrations and at various temperatures, in the presence of new modifying additives (KMnO₄, KNO₃) and without them, were studied. The formation of the main Si(001) defects was attributed to temporary local adsorption of silicates (products of silicon etching) on the silicon surface.     

A study of the differential capacitance of zinc in aqueous solution with potassium silicate additions

The differential capacitance of the polycrystalline zinc electrode has been studied in aqueous solutions of KCl, KNO₃ and KOH both with and without the addition of potassium silicate. Double layer capacitance measurements can be made in KCl and KNO₃ without the interaction of OH^? at low pH values < 3.0. The reduction of the nitrate ion takes place at the zinc electrode in aqueous potassium nitrate.The silicate ion is adsorbed on the zinc electrode in aqueous KOH solutions at a potential close to the dissolution potential. This results in inhibition of metal dissolution, due to limited interaction of OH^? with the metal surface. The electrode resistance is increased by this adsorbed layer of silicate ion. In alkaline solution the h.e.r. is stimulated by the addition of potassium silicate.     

A novel convenient synthesis of benzoquinazolines

[reaction: see text] A novel synthetic pathway to benzoquinazolines from naphthylamines is reported. Benzoquinazoline nucleus was cyclized in good yield from N-protected naphthylamines using hexamethylenetetramine in TFA and potassium ferricyanide in aqueous ethanolic KOH. This method is efficient and convenient with respect to previously reported synthetic pathways.     

A new access to quinazolines from simple anilines

A new synthetic pathway to quinazolines is described. This new method uses hexamethylenetetramine in TFA and potassium ferricyanide in aqueous ethanolic KOH, starting from simple N-protected anilines. The method affords substituted quinazolines with high selectivities and good yields, reducing reaction-time and work-up operations.     

Synthesis of 2 -methylthieno [2, 3-b] thieno [ 2, 3-d] thiazole

The synthesis of a new heterocyclic base, 2-methylthieno[2, 3-b]thieno[2, 3-d]thiazole, is described. It is obtained by oxidizing 2-thioacetylamino[2, 3-b]thiophene in alkaline medium with 10% aqueous potassium ferricyanide.     

Ion-transfer voltammetry at silicon membrane-based arrays of micro-liquid-liquid interfaces

Microporous silicon membranes, fabricated by lithographic patterning and wet and dry silicon etching processes, were used to create arrays of micro-scale interfaces between two immiscible electrolyte solutions (muITIES) for ion-transfer voltammetry. These membranes served the dual functions of interface stabilization and enhancement of the rate of mass-transport to the interface. The pore radii were 6.5 microm, 12.8 microm and 26.6 microm; the pore-pore separations were ca. 20- to 40-times the pore radii and the membrane thickness was 100 microm. Deep reactive ion etching (DRIE) was used for pore drilling through the silicon, which had been previously selectively thinned by potassium hydroxide etching. DRIE produces hydrophobic fluorocarbon-coated internal pore walls. The small pore sizes and large pore-pore separations used resulted in steady-state voltammograms for the transfer of tetramethylammonium cation (TMA(+)) from the aqueous to the organic phase, whereas the reverse voltammetric sweeps were peak-shaped. These asymmetric voltammograms are consistent with the location of the ITIES at the aqueous side of the silicon membrane such that the organic phase fills the micropores. Comparison of the experimental currents to calculated currents for an inlaid disc micro-interface revealed that the interfaces were slightly recessed, up to 10 microm (or 10% of the pore length) in one case. Facilitated ion transfer, with an organic-phase ionophore, confirmed the location of the organic phase within the pores. These microporous silicon membranes offer opportunities for various analytical operations, including enhancing the rate of mass transport to ITIES-based sensing devices and stabilization of the ITIES for hydrodynamic applications.     

A computer controlled continuous dilution dilatometer for the determination of solute molar volumes and direct measurement of reaction volumes in solution

The design and operation of a computer controlled continuous dilution dilatometer utilizing a diode array detection system is presented. To test the accuracy and reproducibility of the technique, apparent molar volumes of dilute aqueous solutions of potassium ferricyanide and potassium ferrocyanide have been measured. To provide supporting data for high pressure studies of reaction volumes and molar volume change in solutions of high ionic strength, study of these electrolytes was extended by dilution into 0.1M and 1.0M potassium nitrate solutions rather than extrapolation to zero ionic strength as is normal. In addition, the system has been used to determine reaction volumes of some acid-base reactions by direct measurement, using the equipment as an automatic titration dilatometer.     

Coupled diffusion produced by hydrolysis of aqueous potassium phosphate

Conductimetric and diaphragm cell techniques have been used to measure diffusion of aqueous potassium phosphate solutions at 25°C from 0.01 to 0.10 mol-dm^–3 (M). A significant portion of the aqueous K₃PO₄ component diffuses as equimolar amounts of potassium hydrogen phosphate and potassium hydroxide produced by hydrolysis: K₃PO₄+H₂O=K₂HPO₄+KOH. Because OH^– diffuses more rapidly than HPO ₄ ^2– , the total flow of KOH exceeds the flow of K₂HPO₄. The extra flow of KOH constitutes coupled transport of a second solute component. Ternary diffusion coefficients that describe interacting flows of K₃PO₄ and KOH components are reported. At low concentrations where phosphate is strongly hydrolyzed, the molar flux of the KOH component produced by diffusion of K₃PO₄ is six times larger than the flux of the K₃PO₄ component. Binary diffusion coefficients for aqueous K₂HPO₄ solutions are also reported. It is shown that ternary transport coefficients for K₃PO₄ solutions can be estimated from the properties of binary solutions of K₂HPO₄ and KOH.     

亚硫酸根离子在硅和二氧化硅的湿法腐蚀中的作用

运用光刻技术和原子力显微技术(AFM)研究了亚硫酸根离子对硅和二氧化硅在40％(w)氟化铵水溶液中腐蚀速率的影响.结果表明硅和二氧化硅的腐蚀速率和亚硫酸根离子浓度有关.高分辨X射线光电子能谱(XPS)分析在有/没有亚硫酸根的溶液中腐蚀后的硅和二氧化硅表面氟元素的结果表明在这两种溶液中腐蚀得到的表面化学成分是有差别的.实验结果证明亚硫酸根离子在硅和二氧化硅的湿腐蚀中不只是表现为一种除氧剂，还干预了表面腐蚀反应过程.     

A light detection cell to be used in a micro analysis system for ammonia

This paper describes the design, realization and characterization of a micromachined light detection cell. This light detection cell is designed to meet the specifications needed for a micro total analysis system in which ammonia is converted to indophenol blue. The concentration of indophenol blue is measured in a light detection cell. The light detection cell was created using KOH/IPA etching of silicon. The KOH/IPA etchant was a 31 wt.% potassium hydroxide (KOH) solution with 250 ml isopropyl alcohol (IPA) per 1000 ml H(2)O added to it. The temperature of the solution was 50 degrees C. Etching with KOH/IPA results in 45 degrees sidewalls ({110} planes) which can be used for the in- and outcoupling of the light. The internal volume of the realized light detection cell is smaller than 1 mul, enabling measurements on samples in the order of only 1 mul. Measurements were performed on indophenol blue samples in the range of 0.02 to 50 muM. In this range the measurements showed good reproducibility.     

Fabrication of highly antireflective silicon surfaces with superhydrophobicity

Highly antireflective porous silicon surfaces with superhydrophobicity were obtained by means of chemical etching and fluoroalkylsilane self-assembly. The results show that wettability and reflectivity of these surfaces strongly depend on the etching method and the resultant surface morphology. All of the four resultant porous silicon surfaces by alkaline etching, acidic etching, thick Pt-assisted acidic etching, and thin Pt-assisted acidic etching can reduce reflectance, but the efficiency differs greatly. Except for the alkaline etching, the porous silicon surfaces produced by the other three etching methods can reach superhydrophobicity after fluoroalkylsilane modification. These differences are due to the different surface morphology and roughness. Moreover, the porous silicon surface produced by thin Pt-assisted acidic etching presents abundant holes and particles with diameters ranging from nanometers to submicrometers. This morphology enables the porous silicon surface to own a very low reflectance value that is averaged to be about 3% over the whole experimental photon wavelength spanning 300-800 nm.     

ChemInform Abstract: Potassium Salts of Hypodiphosphoric Acid.

Six different potassium salts are obtained from aqueous solutions of H₄P₂O₆ and KOH with different ratios.     

硅(100)晶面上硅和二氧化硅的横向与纵向腐蚀速率

The method established previously for studying the etching rates of micro-scale silicon and silica was used to study the etching process of silicon and silica on the Si（100）surface. Photolithography was used to pattern a positive photoresist mask to confine the etching area,and the atomic force microscopy was used to probe the etched surface. The lateral etching rate of silicon or silica on the silicon surface was defined,and the lateral and longitudinal etching rates of silicon and silica on the Si（100）surface in 40% ammonium fluoride aqueous solution were measured. The effect of the dissolved oxygen on the etching rates was studied by bubbling the solution with high purity nitrogen. The lateral and longitudinal etching rates of silicon and silica on the（100）surface increase with temperatures except for the lateral etching rate of silica in a N2 -bubbled solution which probably reaches the limit of diffusion controlled reaction. The etching rates of silicon and thermal silica on the Si（100）surface show remarkable difference with that on the Si（111）surface in both air-saturated and N2 -bubbled solutions. The apparent activation energies for the silicon and silica etching processing in ammonium fluoride solution were obtained from the etching rates at different temperatures in the range 20. 6-34. 1℃. The similarity of the apparent activation energies for the etching processing of silicon and silica on the（100）surface to that on the（111）surface probably suggests that the rate-determined-step is the same in both cases. A lot of gas bubbles are seen to aggregate on the surface in silicon dissolution process at 38. 2℃,and it is found that the gas bubbles have great influence on the silicon etching rate. The formation of bubbles accelerates the silicon dissolution at the beginning but blocks the etching as the bubbles gradually aggregate on the surface.     

Dissolution of chitin in aqueous KOH

Our NMR experiments show that chitin can dissolve well in aqueous KOH through a freeze-thawing process, and the dissolution power of the alkali solvent systems is in the order of KOH > NaOH > LiOH aqueous solution, which is totally contrary to that of cellulose in the alkali aqueous solution (i.e., LiOH > NaOH ? KOH). In this work, we systematically study the dissolution process in KOH and KOH/urea aqueous solutions. Chitin has good solubility (solubility ~80 %) in 8.4–25 wt% KOH aqueous solution at ?30 °C. The role of urea also has been investigated: unlike aqueous chitin-NaOH solutions, urea indeed enhances the solubility of chitin in KOH aqueous solutions, but the increased degree becomes unobtrusive with decreasing temperature and increasing dissolution time; the DA decline curves of chitin-KOH and chitin-KOH/urea aqueous solutions are nearly overlapping, indicating that the effect of the urea on the degree of acetylation of chitin in KOH aqueous solutions is small, similar to the NaOH/urea solvent.     

Isotope effect of potassium in an aqueous/amalgam system

The isotope fractionation of potassium in an aqueous (KOH)/amalgam system has been studied. Two types of isotope effects with opposite isotope enrichment directions were observed in the electrolysis of potassium from the aqueous into the amalgam phase under constant electrolytic potentials. It was found that the first isotope effect causing the light isotope enriched in the amalgam is related to the kinetic process of the mass transfer through the aqueous/amalgam interface, while the second one leading to the enrichment of the heavy isotope in the amalgam phase is produced by the isotope-exchange equilibrium. The temperature dependence of the equilibrium isotope effect was also investigated using single-stage and multi-stage techniques. It was observed that the equilibrium isotope effect increases as the temperature increases in the range of 293-371 K. An empirical equation was used to fit the variations of the isotope effects with temperature for potassium together with the other alkaline and alkaline earth metals studied in the same system. The origin of the equilibrium isotope fractionation in the electron-exchange system was discussed. Furthermore, the mass dependence of the separation coefficients of the alkaline and alkaline earth metals observed in aqueous/amalgam and ion-exchange systems were compared. At 293 K the equilibrium isotope separation coefficient for the ³⁹K/⁴¹K isotopes in the amalgam system was determined as (5.6±0.6).10^-3.     

Bulk electrochemical etching of semiconductor single-crystal silicon in HF-containing solutions

Effect of the component composition of an HF-containing electrolytic aqueous solution on the polishing electrochemical etching of semiconductor single-crystal silicon was studied. Propanol-2, SV-1017, and NH₄F served as additional components of solutions used for this purpose. The conditions in which this process can be employed to form elements with 3D structure in microsystems devices were determined. An analysis of the results obtained led to an assumption that the hydrogen passivation of the surface of semiconductor single-crystal silicon is the rate-determining factor affecting the development of a bulk polishing electrochemical etching of this material. Because the process of polishing electrochemical etching of silicon wafers is preserved during approximately 20 min, the method is acceptable for formation of shallow grooves in microsystems devices.     

Oxidation of hydroxylamine by ferricyanide in presence of zinc sulfate: A rapid method for estimating hydroxylamine and hydrazine in a mixture

The direct titration of alkaline ferricyanide in presence of zinc sulfate with hydroxylamine sulfate has been studied. A clear white precipitate of zinc potassium ferrocyanide indicates the end-point. Hydroxylamine is oxidized to nitric acid and water, and millingram-quaantities of hydroxylamine; can be determinred. In the absence of zinc sulfate and in weakly alkaline medium, hydrazine and hydroxylamine are converted to nitrogen, while in presence of zine sulfate hydrazine is oxidized to nitrogen By ferricyanide oxidation of a mixed sample uinler different conditions, hydrarine and hydroxylamine when present together can be determined rapidly.     

The morphology modulation of graphene to produce wrinkles and folds for effective electrochemical determination of Hg(II)

A highly efficient electrode material, three-dimensional reduced graphene oxide with varying wrinkles and folds (WRGO), applicable for electrochemical determination of Hg(II) was obtained by treating graphene oxide (GO) with KOH aqueous solution. After alkaline etching, the relatively flat graphene was altered and its self-aggregation was significantly alleviated, producing more wrinkles and folds, which provided more active adsorption sites for heavy metal ions. WRGO-5 modified electrode system herein offers a highest sensitivity of (31.83 μAμM⁻¹) and a lowest LOD of (16.28 nM). Moreover, the electrode sensor possesses good stability and reproducibility.     

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.