Showing papers on "Hydrofluoric acid published in 1997"

Improvement of 13C and 15N CPMAS NMR spectra of bulk soils, particle size fractions and organic material by treatment with 10% hydrofluoric acid

Abstract: Summary The small organic matter content of mineral soils makes it difficult to obtain I3C and 15N nuclear magnetic resonance (NMR) spectra with acceptable signal-to-noise ratios. Subjecting such samples to hydrofluoric acid removes mineral matter and leads to a relative increase in organic material. The effect of treatment with 10% hydrofluoric acid on bulk chemical composition and resolution of solid-state 13C NMR spectra was investigated with six soils, some associated particle size fractions, plant litter and compost. The treatment enhanced the signal-to-noise ratio of the solid-state I3C NMR spectra. The improvement in spectrum quality was greatest in the clay fraction of soil contaminated with coal ash. The removal of paramagnetic compounds associated with the ash may be the main reason for the improvement. Based on total C, total N, C/N ratio and intensity distribution of the solid-state I3C NMR spectra, no changes in organic matter composition could be detected, except for a possible loss of carbohydrates. After treatment with HF, solid-state I5N NMR spectra of particle size fractions were obtained and indicated that the observable nitrogen is present mostly as peptides and free amino groups. Extraction with hydrofluoric acid is recommended as a routine treatment prior to solid-state I3C and "N NMR on soil containing little C or N and soil samples containing paramagnetic compounds from natural or anthropogenic sources.

Discovery of Interstellar Hydrogen Fluoride

Abstract: We report the first detection of interstellar hydrogen fluoride. Using the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO), we have detected the 121.6973 micron J = 2-1 line of HF in absorption toward the far-infrared continuum source Sagittarius B2. The detection is statistically significant at the 13 sigma level. On the basis of our model for the excitation of HF in Sgr B2, the observed line equivalent width of 1.0 nm implies a hydrogen fluoride abundance of approximately 3 x 10(exp -10) relative to H2. If the elemental abundance of fluorine in Sgr B2 is the same as that in the solar system, then HF accounts for approximately 2% of the total number of fluorine nuclei. We expect hydrogen fluoride to be the dominant reservoir of gas-phase fluorine in Sgr B2, because it is formed rapidly in exothermic reactions of atomic fluorine with either water or molecular hydrogen; thus, the measured HF abundance suggests a substantial depletion of fluorine onto dust grains. Similar conclusions regarding depletion have previously been reached for the case of chlorine in dense interstellar clouds. We also find evidence at a lower level of statistical significance (approximately 5 sigma) for an emission feature at the expected position of the 4(sub 32)-4(sub 23) 121.7219 micron line of water. The emission-line equivalent width of 0.5 nm for the water feature is consistent with the water abundance of 5 x 10(exp -6) relative to H2 that has been inferred previously from observations of the hot core of Sgr B2.

Pore Creation in Silicon Oxycarbides by Rinsing in Dilute Hydrofluoric Acid

Abstract: We have prepared silicon oxycarbides by the pyrolysis of siloxane polymers at a maximum temperature of 1000 °C. The resulting silicon oxycarbides are networked glasses which we believe also contain some graphene sheets. After washing in a dilute solution of hydrofluoric acid for times between 2 min and 24 h, these materials lost, at most, 40% of their mass. Powder X-ray diffraction (XRD), small-angle scattering (SAX), BET surface area measurements, elemental analysis, and silicon K-edge X-ray absorption spectroscopy (XAS) were used to determine the physical structure of the bulk material and the local chemical environments of the Si atoms. It was found that a microscopic pore network was created in the material upon HF washing. The number of pores, but not their size, increased with HF washing time. The HF etching revealed a passivating layer, which we believe consists mainly of silicon and carbon, that prevented further etching of the material. The electrochemical behavior of these materials in Li batter...

Development of a boron buffered solution culture system for controlled studies of plant boron nutrition

Abstract: Chelated-buffered nutrient solutions are used for studies on micronutrient metals but so far no equivalent system exists for boron nutrition studies: the present investigation was initiated with that intention From a literature review, it was noted that a range of substances form chelates with boron including polyhydric alcohols, sugars and phenolic compounds However, none apart from hydrofluoric acid formed chelates with formation constants comparable to those of micronutrient metal chelates like diethylenetriaminepentaacetic acid (DTPA) Moreover, most chelating substances had deleterious side effects which reduced their possible use in water culture: many of the compounds are substrates for bacterial growth, some are harmful to handle, and others are toxic to plants or humans Borosilicate glass; was tested in a laboratory experiment but found to release boron too slowly into solution to maintain constant boron concentration in solution even when very finely ground Current investigations centre around the use of a boron-specific resin, which strongly complexes H3BO3 on its N-methyl glucamine functional groups The boron sorption capacity of the resin varied from 22 to 50 mg B g-1 resin Boron saturated resin maintained an equilibrium solution boron concentration of 46 ut M when added at the rate of 2 g of resin to 1 L of boron free triple deionised water Plants grown in complete nutrient solution with boron saturated resin added at 1 g per litre of nutrient solution grew as well as plants grown in conventional nutrient solution containing 92 ut M boron and their shoots contained adequate boron concentrations for growth There was no evidence that the resin had effects on plant growth other than in releasing and equilibrating boron concentration in the nutrient solution

Cleaning method for peeling and removing photoresist

Abstract: A cleaning method for peeling and removing photoresists from a semiconductor by applying ultrasound to a cleaning solution comprising a mixture of an organic solvent diluted with pure water and halogenated alkali metal salts, hydrofluoric acid, or ammonium fluoride. The cleaning method removes organic film such as a photoresist or the like at room temperature, not by dissolving, but rather by peeling. The cleaning liquid does not degrade over a long period of time and, moreover, has a strong cleaning effect yet chemical vapors and water vapors are essentially not generated.

Method of treating spent potliner material from aluminum reduction cells

Abstract: A process for treating spent potliner material from aluminum reduction cells and recovering useful products. In the process, spent potliner material is introduced into an acid digester (24) containing, for example, sulfuric acid. A gas component is produced which includes hydrogen fluoride and hydrogen cyanide. A slurry component is produced which includes carbon, silica, alumina, sodium compounds such as sodium sulfate, aluminum compounds such as aluminum sulfate, iron compounds such as iron sulfate, magnesium and calcium compounds such as magnesium and calcium sulfate. The slurry component remains in the digester after the gas component is removed. The gas component is recovered and heated an effective amount to convert or decompose the hydrogen cyanide to a remaining gas component including carbon dioxide, water, and nitrogen oxides as well as HF gas. The remaining gas component is directed through a water scrubber (44) in which the HF gas is converted to liiquid hydrofluoric acid. The hydrofluoric acid is then admixed with alumina trihydrate to form aluminum fluoride and water.

Spectroscopic Observation of the Formyl Cation in a Condensed Phase

Abstract: The formyl cation, HCO+, has long been believed to be an important intermediate in the chemistry of carbon monoxide (CO) in acidic environments, but its spectroscopic observation in solution has been elusive. This species was generated by the reaction of CO with the liquid superacid hydrofluoric acid-antimony pentafluoride (HF-SbF5) under pressure and was observed by nuclear magnetic resonance and infrared spectroscopy. Equilibria between CO in the gas phase, CO dissolved in HF-SbF5, the SbF5 adduct of formyl fluoride, and HCO+ associated with several equilibrating anions of the type [SbxF5x+1]- are proposed to describe the system.

Mechanism of Copper Deposition on Silicon from Dilute Hydrofluoric Acid Solution

Abstract: Metal deposition on silicon from HF-based solutions is initiated by electrochemical reduction of metal ions, a process which is driven by the difference between the electron quasi Fermi energy in the silicon, E{sub Fn}, and the redox energy level of the ions in solution, eE{sub M{sup z+}/M{sup o}}. Mechanisms for metal ion reduction are elucidated by aligning the silicon bands with the redox levels of ions in solution. For copper, the reduction reaction occurs by capture of conduction band electrons, a process which requires nucleation of nanometer-sized precipitates on the silicon surface. As the concentration of electrons at the surface is increased (e.g., by n-type doping, illumination, or cathodic biasing), the nucleation rate of precipitates, N, increases steeply. N is further dependent on the activity of the metal ion in solution and the amount of surface charge at the Si/HF interface. The growth rate, v, of copper nuclei is determined by the surface concentration of holes and is increased by illumination and p-type doping. The predicted effects on N and v of illumination level, doping level, and substrate bias were verified by immersion tests on Czochralski wafers in 1:100 HF. Total reflection x-ray fluorescence was used to measure copper coverage;more » atomic force microscopy and surface-sensitive minority carrier lifetime measurements were used to determine the areal density of copper precipitates. Application of these findings to reduce copper deposition from HF in industrial wafer cleaning practice are discussed.« less

Etching composition and use thereof.

Abstract: An aqueous etchant composition containing about 0.01 to about 15 percent by weight of sulfuric acid and about 0.01 to about 20 percent by weight of hydrogen peroxide or about 1 to 30 ppm of ozone, and about 0.01 to 100 ppm of hydrofluoric acid is effective in removing polymer and via residue from a substrate or conductive material, and especially from an integrated circuit chip having aluminum lines thereon.

Surface treatment of indirect resin composite surfaces before cementation.

Abstract: Statement of problem. Controversy surrounds the use of hydrofluoric acid to prepare precementation surfaces of indirect composites. Purpose. This study was conducted to compare effects of combining hydrofluoric or orthophosphoric acid with microetching as precementation treatments. Material and methods. Nine specimens of three composite materials were prepared to simulate heat-cured indirect restorations. The specimen surfaces were prepared with one of three treatments. Adhesive Bond II and Twinlook cements were used to bond a phosphoric acid-etched disk of P50 to the treated surface. Analysis of variance and Scheffe tests were used to assess the bond strength data. Scanning electron microscopy and microscopic analysis of the fractured and treated surfaces were also performed. Results. Bond strengths for all surface treatments did not significantly differ. Hybrids had a higher bond strength with etching than microfills, and mechanical roughening produced the greatest bond strengths with microfills. Microetching with orthophosphoric acid produced higher bond strengths than microetching with hydrofluoric acid on hybrids. Conclusions. Acid etching alone is not sufficient to produce effective bond strengths, and hydrofluoric acid treatments are detrimental to the resin composite. (J Prosthet Dent 1997;77:568-72.)

Deposition of Copper Films on Silicon from Cupric Sulfate and Hydrofluoric Acid

Abstract: A novel method of galvanic deposition of copper is described. The solution is composed of cupric sulfate and hydrofluoric acid. The main principle of deposition is the reduction copper ion by electrons released from silicon. This electrochemical reaction includes the silicon dissolution and copper deposition simultaneously. The copper film thickness increases with the hydrofluoric acid concentration and the deposition time. The growth properties are investigated, and the possibility of using such a technology for copper deposition on silicon is demonstrated. The resistivity of deposited Cu on silicon is 2.16 μΩ cm.

A Cu seed layer for Cu deposition on silicon

Abstract: A novel copper deposition method has been developed in which the solution is composed of hydrofluoric acid and cupric sulfate. Here, we investigate the growth mechanism of Cu film on silicon. The copper film thickness is dominated by copper ion diffusion in the solution and, hence, follows a parabolic relation with deposition time and a linear relation with copper ion concentration. In addition, we study the Cu deposited on a silicon strip, which shows an isotropic etching property with an undercut against the mask. Furthermore, the deposited Cu on silicon shows a Schottky diode behavior. Its Schottky barrier height, leakage current and ideality factor are all studied in this paper.

Quantification of hydrofluoric acid species by chemical-modeling regression of near-infrared spectra

Abstract: Near-infrared spectroscopy in the wavelength region 800−1100 nm has been applied to the measurement of aqueous solutions of hydrofluoric acid over the concentration range 0.01−2.65 M and the pH range 2−13. The analysis is based on the detection of subtle perturbations of the water spectrum which result from the presence of the acid and other species in solution. Spectral characterization of the hydrofluoric acid system was performed using a spectrophotometric titration and multivariate model-based regression. Excellent agreement was observed between the spectra and a simple equilibrium model describing the acid's dissociation. Five species, including hydrofluoric acid, fluoride, bifluoride, hydronium, and hydroxide ions, were quantitated with estimation errors below 10 mM using this procedure. In addition, the species' spectral profiles were recovered, and optimum estimates of the system's equilibrium constants were determined.

Erratum: Calculation of nuclear magnetic shieldings. X. Relativistic effects [J. Chem. Phys. 105, 3175 (1996)]

Abstract: Due to errors in our computer code, the numbers in Table II are incorrect. Corrected version of Table II is given and it shows that the conventionally used theory approximates the matrix method nucleation rates very well in the am water system. The conclusions considering the ammonia–water system are changed, respectively. In Fig. 6 the axes representing number of ammonia molecules and number of water molecules should be interc We thank Gerald Wilemski and Barbara Wyslouzil for informing us of their test calculations indicating an error results.

Activation bath for electroless nickel plating

Abstract: In a process for the electroless plating of nickel onto a substrate made of aluminum or an aluminum alloy, an aqueous acidic solution containing as an essential component a palladium salt is used as an activator of the substrate prior to the nickel plating of the substrate The activating solution contains a palladium salt, an alkali metal fluoride or hydrofluoric acid, a carboxylic acid complexing agent, an alkali metal salt of gluconic acid, an iron salt, a nickel salt, and deionized water

In situ infrared characterization of the silicon surface in hydrofluoric acid

Abstract: The surface of silicon in hydroflouric acid (HF) is coated with covalently attached hydrogen (SiHx groups, with x=1,2,3), with probably a very small concentration of SiF bonds. In contrast with a recent claim by Niwano et al. [J. Appl. Phys. 79, 3708 (1996)], we show that the concentration of SiF bonds is as yet beyond infrared detection limits. Our analysis indicates that the band at 2230 cm−1 observed by these authors actually arises from electrolyte absorption.

Method and apparatus for cleaning of semiconductor substrates using hydrofluoric acid (HF)

Abstract: A cleaning method and apparatus using very dilute hydrofluoric acid (HF) for cleaning silicon wafers and semiconductor substrates. The HF is delivered to the core of a brush where the solution is absorbed by the brush and then applied by the brush onto the substrate. This delivery system applies the chemical solutions uniformly to the semiconductor substrate and reduces the volumes of chemical solutions used in a scrubbing process. The process of the present invention uses very dilute HF and allows a thin oxide to be etched but not completely removed so as to maintain a hydrophilic surface state. Thus, this invention presents a chemical mechanical cleaning process with in-situ etching with the use of PVA brushes on a brush scrubber. Very accurate control of etch rate is obtained and, therefore, makes this process suitable to multiple cleaning applications of silicon wafers and semiconductor substrates.

On-site generation of ultra-high-purity buffered-hf and ammonium fluoride

Abstract: Provided is a novel method and system for preparing ultra-high-purity buffered-hydrofluoric acid or ammonium fluoride controlled concentration. The method comprises bubbling purified ammonia vapor into ultra-pure hydrofluoric acid. The inventive method and system can be used as an on-site subsystem in a semiconductor device fabrication facility for supplying the buffered-hydrofluoric acid and ammonium fluoride to points of use in the semiconductor device fabrication facility.

The Prevention of Si Pitting in Hydrofluoric Acid Cleaning by Additions of Hydrochloric Acid

Abstract: Bare Si surfaces, when immersed in hydrofluoric acid (HF), are susceptible to oxidizing metallic impurities such as Cu -2 and undergo a galvanic reaction. The Si is oxidized and dissolves in the HF solution, while the Cu +3 , for example, is reduced to metallic Cu. The manifestation of the Si oxidation is the generation of pits or roughened surfaces, depending on the level of metallic contaminants present in the HF. We investigated the pitting effects of several metallic contaminants (Cu +2 , Hg +2 , Ag', Fe +3 , Ti +4 , V +5 , and Cr +6 ) intentionally added to a concentrated HF (1:1 HF/H 2 O) mixture. All except Fe +3 and Ti +4 created pits on bare Si. However, adding hydrochloric acid (HCl) to the HF suppressed the pitting or surface roughening phenomena of Cu +2 , Hg -2 , and Ag' contaminants, making the process immune to metallic impurities in the HF. Gate oxide test structure results indicate no adverse effect of adding HCl to HF.

Effects of hydrogenation of hydrogen termination of p+-silicon (100) surfaces by hydrofluoric acid

Abstract: We have investigated the hydrogen termination of p+-Si(100) surfaces treated with a dilute hydrofluoric acid solution after hydrogen plasma is used to deactivate the dopant. The carrier concentration of hydrogenated p+-Si is reduced by an order of magnitude by this hydrogen passivation but it can be largely restored simply by thermal annealing at moderate temperatures. Contact angle measurement and thermal desorption spectroscopy revealed that the hydrogenated p+-Si surface is efficiently terminated by hydrogen in HF solutions and that the H-terminated surface is more stable in water than the original p+-Si surface is. The hydrogenated p+-Si surface reacts with HF solutions in ways quite similar to these in which a p−-Si surface does. On the other hand, the hydrogenation does not affect the HF treatment properties of n+-Si. This hydrogen–plasma passivation enables us to obtain a clean H-terminated p+-Si surface by using the conventional dilute HF treatments.

Microwave digestion for determination of aluminum, boron, and 13 other elements in plants by inductively coupled plasma atomic emission spectrometry

Abstract: A microwave digestion procedure was developed for determining aluminum and boron and 13 other elements in plant tissues by inductively coupled plasma atomic emission spectrometry (ICP-AES). The sample (0.5 g) was digested in a closed Teflon vessel with 10 mL concentrated nitric acid and 3 mL hydrofluoric acid, and further digested in an open Teflon vessel with 5 mL hydrogen peroxide. Excess hydrofluoric acid was eliminated by adding 0.2 g silicon (lV) oxide. Four National Institute of Standards and Technology standard reference materials (apple leaves, peach leaves, tomato leaves, and pine needles) were analyzed to test the reliability of the method. The excellent recoveries indicate that the proposed procedure is simple and effective for determination of Al, B, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, P, S, Sr, and Zn in plants.

Hydrofluoric acid solution calorimetric investigation of the effects of anorthite component on enthalpies of K-Na mixing in feldspars

Abstract: Enthalpies of solution have been measured at 50°C in 20.1 wt% hydrofluoric acid under isoperibolic conditions for a nine-member K-Na ion-exchange series based on a disordered oligoclase specimen containing 23.1 mol% anorthite (An) component. The series displays positive enthalpies of K-Na mixing, but magnitudes are substantially reduced relative to An-free analogs. Volumes of K-Na mixing for the series are similarly reduced; the asymmetry of these with respect to composition is the opposite of that for alkali feldspars. Lower magnitudes of the mixing properties are probably related to the shortened compositional range of this series, relative to normal alkali-feldspar series, and to a 23% An structural background against which the energetic effects of K-for-Na substitution are dampened.

The Structure Change of Liquid Phase Deposited Silicon Oxide by Water Dilution

Abstract: The silicon oxyhydrogen (Si-OH) bonds were found in large amounts in conventional liquid-phase-deposited silicon dioxide using silica powder or gel as a saturation reagent in hydrofluorosilicic acid (H 2 SiF 6 ). However, a more dense structure of LPD-SiO 2 devoid of Si-OH bonds was found if the reagent is changed to silicic acid (SiO 2 :xH 2 O) and the concentration of H 2 SiF 6 is kept above 2 M. At 30°C, the water dilution of H 2 SiF 6 from 2.5 to 1 M tends to enhance the deposition rate of silicon oxide and to introduce substantial amount of Si-OH bonds into the film when H 2 SiF 6 concentration drops to below 1.5 M. This is attributed to the fact that water dilution tends to dilute the concentration of all components, but the decay of etching rate of SiO 2 by HF is much faster than the growth rate of SiO 2 , because the removal of one silicon needs more HF molecules (from one to four HF) and the growth of one silicon needs onlv one intermediate species. The growth rate of silicon oxide decreases when H 2 SiF 6 concentration is further lowered to 0.5 M. The delay time during initial oxide growth follows the SiO 2 growth rate, it is concluded that the delay time is the time that the solution needs to modify part of the Si-OH or Si-H bonds on the growth surface of SiO 2 to Si-F bonds by hydrofluoric acid (HF).

Effect of Chemical Fluorination of Carbon Anodes on Their Electrochemical Properties in KF‐2HF

Abstract: Two kinds of carbon-fluorine surface layers on carbon electrodes were prepared and the electrochemical properties of these electrodes were studied in the KF-2HF melt. The first film was prepared in situ by electrochemical oxidation of carbon in KF-2HF during the fluorine evolution reaction. The surface layer is mainly composed of conducting graphite intercalation compounds, C x' (HF) y F, usually denoted C x ,F. The second film was prepared ex situ by chemical fluorination of carbon with fluorine gas at 275 C, leading to a mixture of C x' F and graphite fluorides, CF x . The fluorine evolution reaction is thus completely inhibited in KF-2HF XPS investigations have shown that ionic and covalent carbon-fluorine bonds are present in the C x' F and CF x compounds, respectively. When doping aluminum particles were inserted into carbon before chemical fluorination, the fluorine evolution reaction occurred due to the presence of C x' F-AlF 3 phases randomly scattered on the electrode surface and within the film. It is supposed that the electron transfer occurs either directly from the electrolyte to the substrate or by tunnel effect via intermediate states. These particles also facilitate fluorine bubble detachment from the surface of the electrode.

Method for pickling products in a metal alloy containing iron and in titanium and alloys thereof

Abstract: A method for pickling products made of metal alloys containing iron, and products made of titanium and alloys thereof, in the absence of nitric acid as an oxidising agent, characterised by the fact that the product to be pickled is submerged in the anolyte (as the pickling solution) of an electrolytic cell in which the anolyte is made up of an aqueous solution of sulphuric acid, of hydrofluoric acid and optionally of phosphoric acid and hydrochloric acid, and with the catholyte made up of an aqueous solution of sulphuric acid and the oxidising agent in the pickling solution being the ferric ion, or the ions titanium(III) and titanium(IV).

Cleaner for semiconductor device

Abstract: PROBLEM TO BE SOLVED: To extremely easily exfoliate a resist residue remained after dry etching and ashing with use of a reaction gas without corroding a wiring materials and the like, by using a cleaner for semiconductor device comprising a mix of each predetermined volume of water, fluorine compound, and water-soluble organic solvent. SOLUTION: The cleaner for semiconductor device is prepared by mixing by 0.1-10 wt.% fluorine compound, 50-80 wt.% water-soluble organic solvent, and total remnant of water. The actual example of the fluorine compound is expressed by a general formula R4 NF (R stands for hydrogen atom or 1-4C alkyl) and ammonium fluoride, hydrofluoric acid, ammonium acid fluoride, and the like are its typical example. The typical examples of the soluble organic solvent are formamide, monomethylformamide, dimethylfolmamide, and the like. A surface-active agent of cation, anion, nonion, and the like can be added to the cleaner for semiconductor device.

Binder solution for battery and manufacture thereof

Abstract: PROBLEM TO BE SOLVED: To make it stable to nonaqueous electrolyte, and improve adhesive strength to a current collecting base body by containing a hydrofluoric acid by a specific quantity to weight of a vinylidene fluoride polymer dissolved in an organic solvent, and also adding an acid except for the hydrofluoric acid. SOLUTION: A vinylidene fluoride polymer is dissolved in an organic solvent, and a nonaqueous battery forming binder solution is adjusted. A hydrofluoric acid of 400 to 20000ppm is contained to weight of a vinylidene fluoride polymer in this binder solution. An acid except for the hydrofluoric acid is also added. The formation of the hydrofluoric acid is promoted by heating a vinylidene fluoride solution or addition of alkali. An organic acid is used as the acid except for the hydrofluoric acid. Electrode mix slurry for a nonaqueous battery is obtained by dispersing a powdery electrode material in this vinylidene fluoride polymer binder solution. This slurry is applied on a current collecting base body, and is dried, and is formed as an electrode structure body having an electrode mix layer.