Aqueous HF Solution Research Articles

Effect of Pickling Process on Adhesion Strength of Ti Oxide Layer on Titanium Alloy Substrate

Titanium alloys are commonly used in biomedical application in hard tissues replacement especially for knee and hip implants. Surface modifications are required prior to diamond coating process for improving the tribological and wear properties of the titanium alloy. In this study, experiments were carried out to investigate the effects of different pickling times as well as temperature on the adhesion strength of oxide layer formed on the Titanium alloy after oxidation process. The aqueous acid solution of HF and HNO3 was used as a pickling solution. The chemical pretreatment was carried out at 4 levels by varying the pickling time as well as temperature. All treated samples were thermally oxidized in a fixed parameters at 900 °C for 25 hours. Surface morphology, oxide layer thickness and adhesion strength were measured after each step using FESEM and Blast Wear Tester (BWT). It was revealed that the thickness of oxide layer increases with pickling time but the adhesion strengths become weaker. It was also found that the adhesion strength of oxide layer formed on Ti substrate surface increases with the increase of temperature while the thickness of the oxide layer decreased within 40oC pickling temperature.

Oxidation of Aryl Alcohols by Morpholinium Fluorochromate(VI) on Silica Gel, a Selective and Efficient Heterogeneous Reagent

Morpholinium fluorochromate(VI), MFC, is easily synthesized by reacting morpholine to an aqueous solution of CrO3 and HF. This reagent selectively oxidizes aryl alcohols to their corresponding aldehydes and ketones under mild conditions. Moreover, it is inert towards aldehydes, ketons, oximes, thiols, sulfids, phenols, pyrans, trimethylsilanes, malonates and thioacetamides. The durability, reaction rate, ease of filtration and efficiency of MFC are considerably increased upon its absorption on silica gel.

Properties of Si Nanowires Synthesized by Galvanic Cell Reaction

A galvanic cell reaction is used to synthesize Si nanowires (SiNWs) in AgNO3/HF solution at 30 °C for 60 min. The AgNO3 concentration ise varied from M=0.0001 to 0.6 mol/L in aqueous HF solution (5 mol/L). Vertically well-aligned SiNW arrays are found to be formed in the limited AgNO3 concentration range of M∼0.02–0.08 mol/L. The maximum nanowire length is ∼35 µm (M∼0.05 mol/L). The photoluminescence (PL) spectra of the SiNWs exhibit a broad peak centered at ∼1.8 eV. Below M∼0.02 or above ∼0.08 mol/L, the solutions produce only roughened surfaces. No PL emission is observed from such surfaces. Passive HF etching of the SiNWs leads to the removal of the surface oxide overlayer and changes the wettability from highly hydrophilic (∼5°) to superhydrophobic (∼135°). Optical absorption and Fourier-transform infrared spectroscopy show that the SiNWs have an extremely large optical absorbability not only in the interband-transition region but also in the far-infrared spectral region.

Fabrication of Encoded Rugate Porous Silicon Interferometer for Biosensor

Multi-encoded rugate porous silicon (PSi)-based optical biosensor was developed to specify the biomolecules. Multi-encoded rugate PSi was generated by an electrochemical etching of silicon wafer using an electrode configuration in aqueous ethanolic HF solution. Multi-encoded rugate PSi displayed three very sharp reflection bands whose reflection maxima varied spatially across the PSi. The sensor system studied consisted of a multilayer of PSi modified with biotin. The system was probed with various fragments of an aqueous protein analyte. The sensor operates by measurement of the reflection peaks in the white light reflection spectrum from the PSi layer. When the biotin-derivatized rugate PSi was exposed to protein in phosphate buffer solution (PBS), the molecular binding caused a change of its refractive index is detected as a shift in wavelength of these reflection peaks. A red-shift of reflective spectra were observed, when the biotin-modified rugate PSi was exposed to a flow of protein.

Comparing the IR spectra of H‐terminated inner and outer silicon surfaces

AbstractAn array of nanocavities in silicon offers an inner surface defined by nearly flat, highly ordered, planes which can be passivated by hydrogen injection from aqueous solution of HF. The infrared spectrum shows that the inner surface is mainly constituted by monohydrides in different morphologies. The corresponding signals are very narrow (full width at half maximum at room temperature below 5 cm−1, depending on the line), this being evidence for high local order. Such an inner surface can be used as a benchmark for the assignment of infrared signals observed on outer surfaces, where the sources of errors—and the consequent uncertainty in the spectral attribution—may be large. The comparison between the spectra from a well‐characterized external Si(1 0 0) surface and from an internal one (in both cases hydrogen‐terminated) has allowed a better qualification of the external surface. Copyright © 2010 John Wiley & Sons, Ltd.

Assigning chemical configurations to the XPS features observed at pristine (1 0 0) Si surface resulting after etching in HF aqueous solution

While the analysis of the spectra resulting from energy- or angle-resolved X-ray photoelectron spectroscopy allows the in-depth atomic composition in the probed region to be determined even for complex samples, the determination of the bonding configuration is less trivial. In this paper it is shown that a description of the chemical shift in terms of partial charge and Madelung potential (as results from local modelling of the atom) can provide information even in complicate situations, like that characterizing the hydrogen-terminated (1 0 0) Si prepared by HF aq etching of the native oxide.

Design of a Novel Wet-Etch Reactor and Etch Chemistries: Simulations and Experimental Verification

Dilute aqueous solutions of hydrofluoric acid (HF) have been used to etch or remove SiO¬¬2-based layers. Due to the various chemical equilibria established between ionic species in aqueous HF solutions, control of etchant species concentrations and thus etch selectivity is difficult. A short contact time prototype reactor for wet etching studies of silicon-based dielectric films has been designed to investigate the effects of various process parameters during the etch process . For comparison, simulations using Computational Fluid Dynamics (CFD) have been used to predict the effect of process parameters such as flow rates and HF concentrations, thermodynamic equilibria, species transport, intrinsic etch kinetics and geometric parameters of the reactor. Results from CFD and etch experiments are in good agreement. Non-aqueous solutions utilizing fluorine-containing tetrabutylammonium salts have been investigated to control desirable equilibria and tailor etch rates and selectivity.

Growth and characterization of PdO films obtained by thermal oxidation of nanometric Pd films by electroless deposition technique

Structural and electrical characterization of palladium oxide (PdO) films grown by thermal oxidation of nanometric Pd films is reported. Pd films were deposited on n-type silicon (1 1 1) substrates by the electroless deposition technique (EDT) in a PdCl2–HF aqueous solution. The growth rate and the structural properties of PdO films were characterized using X-ray diffraction and Raman spectroscopy techniques. The electrical properties of the PdO films were measured by the van der Pauw method. The PdO films resulted p-type with a hole concentration of 1020 cm−3 and mobility in the range of 2–32 cm2/V s.

Alkanethiol Self-Assembled Monolayers Formed on Silicon Substrates

We have prepared alkanethiol monolayers, directly attached to a silicon substrate, by immersing hydrogen-terminated silicon in 1-hexadecanethiol solution at 150 °C. The evidence for the 1-hexadecanethiol monolayer formation was obtained and the resulting monolayers were compared with the monolayers formed from 1-hexadecanol using water contact angle measurements, X-ray photoelectron spectroscopy, ellipsometry, and atomic force microscopy. The densities of the alkyl chains in the 1-hexadecanethiol monolayers were lower than those of the 1-hexadecanol monolayer. The durability of these monolayers to 5% HF aqueous solution was also examined. The 1-hexadecanethiol monolayer is found to be less durable than the 1-hexadecanol monolayer.

Removal of spatter by chemical etching after microdrilling with high productivity fiber laser

In this work, improved productivity in titanium microdrilling is proposed with a solution that comprises of use of a fiber laser system with nanosecond pulses and the removal of generated spatter by means of chemical etching. In particular the paper is aimed at pointing out the action exerted by the chemical solution on both the melted and heat affected zones surrounding the laser drilled hole. In the experimentation, microholes with spatter are laser microdrilled on titanium making use of a nanosecond pulsed fiber laser in the condition which minimizes the drilling time. Then spatter is chemically etched with a H2SO4+HF aqueous solution. The decrease in the spatter area and the change in entrance and exit hole diameters are evaluated as a function of etching time.

Room temperature growth of wafer-scale silicon nanowire arrays and their Raman characteristics

We report a simple, inexpensive, and rapid process for large area growth of vertically aligned crystalline silicon nanowires (SiNWs) of diameter 40–200 nm and variable length directly on p-type (100) silicon substrate. The process is based on Ag-induced selective etching of silicon wafers wherein the growth of SiNWs was carried out using the aqueous HF solution containing Ag+ ions at room temperature in a Teflon vessel. Effect of etching time has been investigated to understand the evolution of SiNW arrays. It has been found that the length of SiNWs has a linear dependence on the etching time for small to moderate periods (0–2 h). However, etching rate decreases slowly for long etching times (>2 h). Scanning electron microscopy was used to study the morphology of the SiNW arrays. Structural and compositional analysis was carried out using Raman spectroscopy and high-resolution transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. Orders of magnitude intensity enhancement along with a small downshift and broadening in the first-order Raman peak of SiNW arrays was observed in comparison to the bulk crystalline silicon.

Electroless deposition of bismuth on Si(111) wafer from hydrogen fluoride solutions

Thin Bi layers were deposited by simple immersion of silicon chip into diluted HF aqueous solution, containing bismuth(III) ions. Bi nanoparticles or continuous up to 300 nm thick Bi film can be grown on silicon by the variation of the temperature and deposition time. Prepared surfaces have been characterized by atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering, photoluminescence and resistivity measurement methods. It was found that thinner Bi layers have a yellowish colour.

Formation of Straight 10 nm Diameter Silicon Nanopores in Gold Decorated Silicon

We observe pore formation with diameters in the 10 nm range in silicon when it is covered with gold particles. This pore etching occurs when the sample is put in 5 wt % hydrofluoric acid (HF) solution for a few minutes. The pores form along the 100 direction, which is also the preferred direction of macro- and mesopores electrochemically etched into silicon. No etching occurs if the dissolved oxygen is removed from the aqueous HF solution or the gold is removed from the silicon surface. This leads to the assumption that the dissolved oxygen acts as an oxidant as in the case of stain etching with gold as cathodic material. A tentative model is suggested to explain why all of the observed nanopores have roughly the same diameter of about 10 nm. These pores can occur for inhomogeneously gold-covered planar silicon surfaces but also in MBE (molecular beam epitaxy) grown silicon nanowires since these nanowires are covered unintentionally with gold nanoclusters at their cylindrical surface.

Simply Modified Biosensor for the Detection of Human IgG Based on Protein AModified Porous Silicon Interferometer

A biosensor has been developed based on induced wavelength shifts in the Fabry-Perot fringes in the visible reflection spectrum of appropriately derivatized thin films of porous silicon semiconductors. Porous silicon (PSi) was generated by an electrochemical etching of silicon wafer using two electrode configurations in aqueous ethanolic HF solution. Porous silicon displayed Fabry-Perot fringe patterns whose reflection maxima varied spatially across the porous silicon. The sensor system studied consisted of a mono layer of porous silicon modified with Protein A. The system was probed with various fragments of an aqueous Human Immunoglobin G (Ig G) analyte. The sensor operated by measurement of the Fabry-Perot fringes in the white light reflection spectrum from the porous silicon layer. Molecular binding was detected as a shift in wavelength of these fringes.

Enhanced Efficiency of Dye-Sensitized Solar Cells Using Anodic Titanium Oxide Nanotube Arrays

This paper concerns the microstructure of the anodic titanium oxide (ATO, ) nanotube (NT) and its use for the dye-sensitized solar cell (DSSC) device. The ATO length was controlled by various electrolytes and anodic time at various constant applied voltages. The lengths of the NTs at 0.3–0.5 and were controlled by HF and KF aqueous solutions for varied periods of anodization . The electrolyte in ethylene glycol can produce for varied periods of anodization . ATO made of 0.3 ( HF), 12 ( KF), and ( ) was used for the DSSC anode; the best cell performance attained 0.13, 3.76, and 6.18%. The DSSC made of ATO has a short-circuit current density of , a fill factor of 0.64, an open voltage of , and a photocurrent efficiency of 6.18% under an air mass 1.5 illumination test.

Room Temperature Synthesis of the Larger Power, High Silver Density Cathode Material Ag4V2O6F2 for Implantable Cardioverter Defibrillators

New cathode materials will lead to technological advances for implantable cardioverter defibrillators, ICDs, such as reduced size and increased performance of the device. While the industry standard silver vanadium oxide Ag2V4O11 exhibits great chemical/electrochemical stability, dense silver oxide fluoride materials are advantageous because of high crystal density that can result in an increased capacity above 3 V. This report highlights the reactivity at room temperature between Ag2O and V2O5 in an aqueous HF solution which affords a rapid precipitation of sub-micrometer sized Ag4V2O6F2 (SVOF), a high capacity Li-battery cathode material. This system opens new and novel synthetic strategies in the design of new oxide fluoride materials.

Light energy storage and photoelectrochemical behavior of the titanate nanotube array/Ni(OH) 2 electrode

A new kind of TiO 2 nanotube array/Ni(OH) 2 (TiO 2/Ni(OH) 2) composite electrode with the storage ability of light energy was prepared by the deposition of Ni(OH) 2 on the TiO 2 nanotube array, which was synthesized by anodizing Ti foils in an HF aqueous solution. SEM and XRD results showed that Ni(OH) 2 particles were well distributed on high density, well-ordered and uniform TiO 2 nanotube arrays. The photoelectrochemical properties of the TiO 2/Ni(OH) 2 electrode were investigated in NaHCO 3/NaOH buffer solution (pH 10) by means of UV–vis absorption spectra, cyclic voltammogram (CV) and photocurrent measurements. It was found that the TiO 2/Ni(OH) 2 electrode was highly sensitive to light and exhibited excellent photoelectrochromic properties. Upon UV irradiation, the photogenerated holes by TiO 2 nanotube arrays can oxidize Ni(OH) 2 to NiOOH, and thus the TiO 2/Ni(OH) 2 electrode can be photo-charged by light.

Magnetite nanoparticles embedded in biodegradable porous silicon

Magnetite nanoparticles, which are coated with oleic acid in a hexane solution and exhibit an average diameter of 7.7 nm, were embedded in a porous silicon (PS) matrix by immersion under defined parameters (e.g. concentration, temperature, time). The porous silicon matrix is prepared by anodization of a highly n-doped silicon wafer in an aqueous HF-solution. Magnetic characterization of the samples has been performed by SQUID-magnetometry. The superparamagnetic behaviour of the magnetite nanoparticles is represented by temperature-dependent magnetization measurements. Zero field (ZFC)/field cooled (FC) experiments indicate magnetic interactions between the particles. For the infiltration into the PS-templates different concentrations of the magnetite nanoparticles are used and magnetization measurements are performed in respect with magnetic interactions between the particles. The achieved porous silicon/magnetite specimens are not only interesting due to their transition between superparamagnetic and ferromagnetic behaviour, and thus for magnetic applications but also because of the non-toxicity of both materials giving the opportunity to employ the system in medical applications as drug delivery or in medical diagnostics.

Novel surface treatment for hydrogen storage alloy in Ni/MH battery

A novel surface treatment for the MlNi3.8Co0.75Mn0.4Al0.2 (La-rich mischmetal) hydrogen storage alloy has been carried out by using an aqueous solution of HF and KF with a little addition of KBH4. The results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that rough surface was formed and Al was partly dissolved into the solution after the treatment. The result of XPS indicated the formation of Ni3B and LaF3 compounds on the alloy surface by the treatment. The probable chemical reaction mechanism for the surface treatment was introduced. The treatment resulted in significant improvements in the activation property, discharge capacity and cycle life of the alloy, especially the high rate dischargeability (HRD). The HRD of the treated alloy still remained 54.9% while that of the untreated one was only 15.1% at a discharge current density of 1200 mA/g.

Electrochemical Polishing of p-Type 4H SiC

This article discusses the electrochemical polishing of silicon-face p-type 4H SiC using diluted aqueous HF solution. Etchings on the silicon and carbon faces of SiC samples are performed and compared. The experimental results show that the RMS surface roughness of the electrochemically polished Si-face could be as low as about 2 nm. Carbon-face electrochemical polishing gives a rougher surface. Therefore, silicon-face 4H SiC is a better candidate for MEMS processing. The underlying mechanism is also discussed.