HF HNO3 Research Articles

Simple Smoothing of the Bottom Silicon Surface Using Wet Chemical Etching Methods for Epitaxial III‐V/Silicon Tandem Manufacturing

The implementation of diverse technologies has recently facilitated the production of cost‐effective and highly efficient solar cells. High‐efficiency solar cells with III‐V compounds tandem crystalline silicon cells have achieved photovoltaic efficiency of higher than 39%. Etching silicon wafers plays a vital role in the deposition of epitaxial layers, neutralizing dangling bonds, and surface passivation for tandem solar cells. The wafers are polished using a solution of HF–HNO3–CH3COOH (HNA) and 20% KOH to smoothen the wafer surface. When HNA wet etching is performed for 3.5 min and the 20% KOH etching lasts for 6 min, the microroughness of the wafer is 1.9 nm with a measurement area of 10 × 10 μm2 and 0.816 nm within an area of 1 × 1 μm2. Compared with the as‐cut wafer, the reflectance increases from 31.7% to 34.7%, and the effective minority carrier lifetime, with 30 nm Al2O3 passivation after 450 °C activated, increases from 1.4 to 1.8 ms in a carrier density of 1.0 × 1015 cm−3.

Development of Chemical Procedures for Isotope Harvesting: Separation of Trace Hafnium from Tungsten

ABSTRACT The separation of trace hafnium from bulk tungsten alloys is of interest for isotope harvesting at the National Superconducting Cyclotron Laboratory and the Facility for Rare Ion Beams because 172Hf, the parent of 172Lu, accumulates in tungsten alloy beam blockers at these facilities. In this work, a procedure for the separation of trace hafnium from a bulk tungsten alloy (454 g) was established using tracer isotopes (175Hf, 88Zr, 173Lu, and 88Y). The procedure employed dissolution in an HF–HNO3 solution followed by a calcium fluoride precipitation, and then extraction chromatography was used for more selective separation steps. Two stages of column separations using LN resin (HDEHP based) and TRU resin (CMPO based) were performed. Gamma-ray spectroscopy and mass spectrometry were used to analyze the final hafnium sample and follow the steps in the chemical processing. The final recovery of hafnium was high (90 ± 8)%, and the mass of tungsten and other transition metals was reduced to near background levels (as determined by ICP-MS of the blank acid solutions). Zirconium follows hafnium quantitatively in this procedure; there was no detectable 173Lu in the final hafnium sample.

Study on the mechanism of the influence of HNO3 and HF acid treatment on the CO2 adsorption and desorption characteristics of coal

In order to cooperate with the application of acid fracturing enhanced permeability technology, this paper proposes using CO2 adsorption and desorption system and low-temperature nitrogen adsorption method to conduct experimental research on the changes in the CO2 adsorption and desorption characteristics of coal after treatment with HF solution and HNO3 solution. In addition, Combined with X-ray diffraction experiments, the indirect relationship between mineral dissolution and adsorption and desorption characteristics is analyzed. The research results show that: The acid solution transforms the pore structure of coal through the dissolution of mineral impurities. In the microporous stage, hydrofluoric acid is mainly used for pore formation and nitric acid for pore expansion. Acid treatment changed the adsorption characteristics of the coal sample, reduced the saturated adsorption capacity a, and increased the adsorption constant b. And a and b were linearly related to the specific surface area and pore volume, respectively. This paper has determined that adsorption equilibrium pressure 1.91 MPa and 2.57 MPa are the enhanced adsorption thresholds of hydrofluoric acid and nitric acid, respectively. After exceeding the threshold, acid treatment will no longer play a role in increasing CO2 adsorption. In addition, the acid treatment also changed the desorption characteristics of the coal sample, increased the initial desorption amount and the final desorption amount, shortened the desorption time. The effect of hydrofluoric acid was more evident than that of nitric acid.

Validation and setting up quality control for characterization of aluminum alloys in non-ferrous fraction of auto-shredders

The improvement of recycling rates of metal waste, namely those of end-of life vehicles, is nowadays becoming imperative. Aluminum and its alloys are the main metal components in non-ferrous fraction of auto-shredders separated out after sampling. Silicon, Mg, Cu, Zn, Mn, Ti, Fe and Cr are alloying elements, which allowed the identification and differentiation of Al alloys. Flame Atomic Absorption Spectrometry was used for quantification after HCl-HNO3 digestion, with the exception of Si, where HCl–HNO3–HF–H3BO3 digestion was used. Performance characteristics of measurement procedures, namely analytical dynamic ranges, limits of detection and quantification, precision and trueness were evaluated and measurement uncertainty estimated by applying an approach based on precision and trueness validation studies and quality control data. Target values, for repeatability, intermediate precision, trueness (recovery) and measurement uncertainty, were specified to differentiate Al alloys based on their own fit-for-purpose. Metrological traceability of the measurements results of the alloying elements was established by using certified values of British Chemical Standard (BCS) of Al alloys, BCS no 181/1, BCS No 268. BCS No 300 and Standard Reference Material of Al-base alloy, SRM 87. The quantification of Si, Mg, Cu, Zn, Mn, Ti, Fe and Cr in aluminum alloys from the non-ferrous fraction of automatic crushers was determined successfully through the validated procedures.

Texturization of diamond wire sawn multi-crystalline silicon wafers by micro-droplet etching

Diamond wire sawn multicrystalline silicon (DWS mc-Si) solar cell wafers have been known to be difficult to texturize by conventional acidic wet etching texturization process. A novel texturization method based on localized micro-droplet etching (MDE) has been developed, in which the micro-droplet is generated by controlled condensation of thermal vapor from a HF–HNO3–H2O bath. Uniformly distributed micron scale etch-pit type surface textures on DWS mc-Si wafers are made by the MDE process. Their light reflectivity is reduced to 18–21%, and their sawmarks are removed. Full size DWS mc-Si wafer samples were MDE textured, and send to a solar cell fabrication line along with the conventionally wet textured DWS mc-Si wafers as reference, without any adjustment of processing parameters for the MDE textured wafers. The average short circuit current of the MDE textured cells has been found to increase as compared to the reference cells, in a relative ratio approximately matching the final light reflection reduction ratio induced by the MDE textures. The average open circuit voltage and fill factor of the MDE textured cells are found to increase slightly, indicating that the MDE texture has not induced any significant increase in surface recombination of carriers, neither poorer contact of printed grid contact on cell surfaces. In average, 0.52% absolute increase of energy conversion efficiency is obtained.

Etching Shapes the Topography of Silicon Wafers: Lattice-Strain Enhanced Chemical Reactivity of Silicon for Efficient Solar Cells

Multiwire sawing of silicon (Si) bricks is the state-of-the-art technology to produce multicrystalline Si solar wafers. The massive indentation of the abrasive Si carbide or diamond particles used leads to a heavily mechanically damaged layer on the wafer surface. Etching the surface layer using typical HF–HNO3–H2SiF6 acid mixtures reveals an unevenly distributed etch attack with etch rates several times higher than known for bulk Si etching. The present study follows the hypothesis that lattice strain, introduced by the sawing process, leads to an increase of the etch rate and determines the topography of the etched wafer, the so-called texture. Scratches were introduced into single crystalline Si surfaces in model experiments, and the magnitude and local distribution of lattice strain were extracted from confocal Raman microscopy measurements. The essential parameter used to describe the local reactivity of Si is the local etch rate, which was derived by confocal microscopy from the local height before ...

Photoluminescence, morphological and electrical properties of porous silicon formulated with different HNO3 concentrations

Abstract In this study, porous silicon (PS) with observable luminescence was fabricated on p-type Si (1 0 0) substrate by wet chemical etching with the mixture of HF and different HNO3 concentrations in the ratio of 1:100. The porosity of PS shows dependent on HNO3 concentration. SEM images exhibit the average pore size increases with the increasing of HNO3 concentration. The emission of PS was characterized by photoluminescence (PL) spectroscopy. The PS is able to emit orange-red visible PL under UV illumination with the peak falls within the wavelength region of (620–660) nm. Brighter emission is observed on PS etched at higher HNO3 concentration, and the emission peak shifts to shorter wavelength when the energy gap and surface roughness increase. The calculated band gaps are lied in the range of (1.90–2.00) eV, which is higher than Si. Moreover, the surface conductivity decreases as the PS energy gap increases.

Mehaničke i strukturne karakteristike slojeva prevlake Nb deponovane u vakuumu

In this paper analyzed was the influence of implementation of inert Ar gas and a mixture of inert plasma Ar / He gases in a vacuum chamber on the deposition of reactive niobium (Nb) powder. The aim of this paper was to deposit coating layers of high density, without oxide content, that will find application in the field of biomedicine. Detailed examination was performed of mechanical properties of microhardness using the HV0.3 method, of tensile bond strength by tensile testing and of the microstructure of the coating layers in the deposited state and after etching. For etching a solution of nitric acid HNO3 and hydrofluoric acid HF in a ratio of 1:1was used. It was found that inert gases, at low pressure prevent the reaction of gases with the metal droplets of molten Nb powder particles during the plasma spray deposition process. The density of the deposited coating in vacuum chamber is higher than that of coatings which are deposited at atmospheric pressure with reactive plasma gases N2 and H2. This is attributed to the elimination of thin oxide and nitride films at the interlamellar Nb contact, substantially increasing the ductility of the coating, eliminating the micro cracks through the deposited layers, which was confirmed by metallographic examination of samples. Tests have shown that VPS - Nb coating layers have mechanical properties and microstructure which completely enable the use of the coating on implants.

Corrosion of sintered SiC ceramics in mixed acid solution: temperature and time dependences

The corrosion behaviour and mechanism of solid-state sintered silicon carbide ceramics in the mixed HF–HNO3 acid solution were investigated in this paper. The corrosion results of SiC in different corrosion medium demonstrated that the corrosion of ceramic was affected by the coefficient of HF and HNO3. In addition, the results of different corrosion time showed that the corrosion process can be divided into three stages: 0–6, 6–24, 24–96 h, which was also proved by the strength degradation of SiC after being corroded for different time. Because the relationship between mass loss and corrosion time was linear, the corrosion of first two stages was controlled by chemical reaction. Owing to the scattered data of mass loss in the third stage, the apparent activation is introduced to investigate the control mechanism. The corrosion results at different corrosion temperatures demonstrated that the corrosion mechanism was diffusion control in the third stage, and the apparent activation energy was 198.47 ± 13.97 kJ mol−1.

Removal of Surface Scale from Titanium Metal by Etching with HF–HNO<sub>3</sub> Mixed Acid

Removal of Surface Scale from Titanium Metal by Etching with HF–HNO<sub>3</sub> Mixed Acid

Mineralization of TiO2 nanoparticles for the determination of titanium in rat tissues

In order to draw appropriate conclusions about the possible adverse biological effects of titanium dioxide nanoparticles (TiO2—NPs), the so-called “dose?effect” relationship must be explored. This requires proper quantification of titanium in complex matrices such as animal organs for future toxicological studies. This study presents the method development for mineralizing TiO2—NPs for analysis of biological tissues. We compared the recovery and quantification limits of the four most commonly used mineralization methods for metal oxides. Microwave-assisted dissolution in an HNO3–HF mixture followed by H2O2 treatment produced the best results for a TiO2—NPs suspension, with 96 ± 8% recovery and a limit of quantification as low as 0.9 µg/L. This method was then used for the determination of titanium levels in tissue samples taken from rats. However, our tests revealed that even this method is not sensitive enough for quantifying titanium levels in single olfactory bulbs or hippocampus in control animals.

Characterization of the products obtained from the reactions of Zircaloy-4 with an acid mixture of concentrated HNO3and dilute HF with the aim of understanding pickle salts of zirconium alloys

Pickling of zirconium alloys in nitric-hydrofluoric acid has been widely used in the nuclear materials industry. However, the pickle salts still remain a curiosity and a thorough knowledge of the products of the system Zr–(HNO3–HF) still needs to be well established. The present study investigated the products obtained from the reactions of Zircaloy-4 with an acid mixture of HNO3 (65 wt%) and HF (40 wt%) in a volume ratio of 94 : 6, similar to the one used under nuclear industry conditions. It shows that after the reactions, a gel-like solution was present. When drying it at a high relative humidity (at 25 °C and 70 ± 5% RH), an amorphous solid product formed, while in the case of at a low relative humidity (at 15/25 °C and 25 ± 5% RH), besides the amorphous solid, crystalline zirconium hydroxide nitrates Zr(OH)2(NO3)2·4.71H2O and Zr(OH)2(NO3)2·1.65H2O (possible) with low degree of crystallinity formed. These compounds were identified with the help of successfully synthesizing completely crystalline Zr(OH)2(NO3)2·4.71H2O from the gel-like solution by ultrasonication, which in itself was a breakthrough. Such a study can be expected to provide a deep understanding of pickle salts of zirconium alloys in practical use.

Corrosion behavior of NdFeB sintered magnets in HNO3–HF acid mixture solution

Corrosion behavior of NdFeB magnet in HNO3–HF solutions was investigated using open circuit potential and polarization measurements and impedance technique. Results showed that the additions of HF increased open circuit potential, corrosion potential and film/inductive/charge transfer resistance, but decreased corrosion current density of magnet. The HF effects on the corrosion performance were closely related to the formation of NdF3 corrosion products on magnet surface, in turn which depended on its content. Also the corrosion mechanism of magnet was discussed on the basis of structural observation, composition and EIS analyses.

One-step hydrothermal method to prepare nitrogen and lanthanum co-doped TiO2 nanocrystals with exposed {0 0 1} facets and study on their photocatalytic activities in visible light

The photocatalytic activity of TiO2 can be mainly improved from three approaches: (1) enhancing the separation efficiency of photoelectrons and holes, (2) enhancing surface energy, and (3) increasing availability of visible light. Here, we report a one-step method to obtain nitrogen and lanthanum co-doped TiO2 nanosheets with dominant {001} facets through a hydrothermal process, using TBOT, triethylamine and LaCl3·nH2O as precursor and sources of N, La respectively in HF–HNO3 mixed aqueous solution, and the samples were characterized by XRD, SEM, TEM, XPS, UV-DRS and BET analyses. The XRD and XPS results confirmed that N was doped into the lattice of anatase TiO2, while La was not. N acts as an O–Ti–N structure or interstitial N and La exists as LaF3 in TiO2 nanosheets. The SEM and TEM results show that the percentage of {001} facets in the as-synthesized N,La–TiO2 nanosheets is estimated to be about 75% on average at RF=1.0. N,La–TiO2 nanosheets can absorb visible light due to the red shift in the absorption edges, and compared with N–TiO2 nanosheets, N and La co-doping can further strengthen the absorption of visible light. N,La–TiO2 nanosheets exhibited higher photocatalytic activity for photodegradation of Rh B under visible light than pure TiO2, N–TiO2, La–TiO2 nanosheets and N,La–TiO2 nanoparticles. N and La co-doping could produce a synergistic effect. The N doping narrowed the band gap of TiO2, while the La doping could improve the separation efficiency of photoelectrons and holes. In addition, the La doping could enhance the adsorption property of photocatalyst for organic pollutants.

One-Pot Fabrication of C–Fe-Codoped TiO2 Sheets with Dominant {001} Facets for Enhanced Visible Light Photocatalytic Activity

C–Fe-codoped TiO2 sheets (CFTS) with dominant {001} facets have been synthesized by a one-pot hydrothermal approach using TiC and Fe2O3 as the reactants in a HNO3–HF mixed solution. The obtained CFTS samples appear as the aggregates of highly truncated bipyramidal microsheets with the length of 1–2 μm and the thickness of 100–200 nm. The doped C atoms exist as the O–Ti–C structure or interstitial C in TiO2 lattice, while the doped Fe atoms replace some of Ti4+ to form the Ti–O–Fe structure. In comparison with the C-doped TiO2 sheets, all CFTS samples exhibit a narrower band gap, stronger visible light absorption, and higher separation efficiency of photogenerated carriers. Moreover, when the atomic ratio of Fe to Ti is 1%, the CFTS sample shows the highest photocatalytic activity by measuring the decomposition rate of RhB under visible light. These CFTS materials may become promising visible light photocatalysts for organic pollutant degradation and efficient H2 evolution.

Application of the Zr/Hf ratio in the determination of hafnium in geochemical samples by high-resolution inductively coupled plasma mass spectrometry.

Hafnium content and its change are of significance in geochemistry and cosmochemistry; however, the determination of hafnium has always been problematic in analytical chemistry. In this paper, a new idea is proposed for the determination of hafnium in geochemical samples, including rocks, soils, and stream sediments. Through the comparison of two conventional open-type acid digestion methods (HF-HNO3-HClO4 and HF-HNO3-H2SO4), it was found that although neither of these methods could fully digest the zirconium and hafnium in a sample, the zirconium and hafnium digestion behaviors in one sample were consistent in the 60 experimental geochemical reference materials with different properties, so the experimentally determined Zr/Hf ratio in solution could be used to calculate the hafnium content in a sample. In addition, possible mass spectral interferences during the determination of zirconium and hafnium by high resolution inductively coupled plasma mass spectrometry (HR-ICPMS) were studied, and it was found that the mass spectral interferences of the selected isotopes (90)Zr and (178)Hf could be neglected. The mass spectral behaviors of (90)Zr and (178)Hf were also very consistent during the determination by HR-ICPMS. Since the hafnium content was calculated using the ratio value, all of the errors (including the errors in weighing process, the accidental errors during operation and the instrument fluctuation in the determination) of the Zr/Hf ratio could be effectively reduced or even eliminated. The relative standard deviation of the actual samples was lower than 3.2%, and the detection limit of the method (considering the dilution effect and matrix effect during measurement of the Zr/Hf ratio and zirconium content) was 0.04 μg/g. The proposed method could satisfy the requirement for the determination of hafnium in geochemical samples.

Studies of the products from the reactions of co-acids containing concentrated HF and dilute HNO3 with Zircaloy-4

The pickling of Zircaloy with HF–HNO3 solution as an important surface treatment has been widely used in the nuclear materials industry. However, a thorough knowledge of the products from the reactions of HF–HNO3 system with Zircaloy still needs to be well established. In the present study, the acid solution containing HF (40wt.%) and HNO3 (65wt.%) with four volume ratios, 100:0, 94:6, 89:11 and 80:20, was employed and it reacted with Zircaloy-4 violently with gas releasing at an air pressure of 1bar, a relative humidity of 30±5% and a temperature of 25°C. Meanwhile, white products formed within minutes. These products were identified by using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The usage of the concentrated HF solution leads to the formation of crystalline ZrF4(H2O), while the usage of co-acids containing concentrated HF and dilute HNO3 results in the formation of crystalline ZrF4(H2O) and NH4ZrF5. In addition, with decreasing the volume fraction of HF and increasing that of HNO3 in the co-acid used, the weight fraction of crystalline ZrF4(H2O) decreases while that of crystalline NH4ZrF5 increases in the products obtained.

A study of mottling phenomenon on textured multicrystalline silicon wafers and its potential effects on solar cell performance

The mottling phenomenon refers to the appearance of irregular dark patterns on HF–HNO3 acid etching textured multicrystalline silicon (mc-Si) wafers. The mottles have been identified as clusters of dislocation etch pits. In the acidic texturization, conditions favoring light reflectivity reduction usually lead to enhanced mottling. In a belief of adverse effect of the mottles to cell performance, light reflectivity reduction is more or less compromised in industry to avoid the mottling. The present study aims to identify whether appearance of the mottles alone really adversely affects the wafers minority carrier lifetime. Both serial examinations of an acid etched mc-Si wafer sample and parallel examinations of neighboring pairs of mc-Si wafer samples etched in acids of different HF/HNO3 ratios were carried out. The results show that development of the mottling, i.e., growth of dislocation etch pits, does not deteriorate mc-Si wafers in their minority carriers lifetime; rather it even slightly increases the lifetimes. Light reflectivity measurement and modeling show that the mottles can contribute to reduction of light reflectivity, and ~3% relative reduction of reflectivity is expected for multicrystalline silicon wafers of ordinary level of dislocation density. Removal of the defected zone surrounding a dislocation by the etching is postulated as a reason for the observed mottling-enhancement of the lifetime. It is further postulated that, in texturization of mc-Si wafers for cell production, instead of compromising light reflectivity reduction to avoid the mottling, it may be better to pursue lower light reflectivity, allowing some extent of the mottling. Meanwhile, more attention should be paid to compatibility of the cone-shaped dislocation etch-pit with grid printing of solar cells.

Texturing of SiC-slurry and diamond wire sawn silicon wafers by HF–HNO3–H2SO4 mixtures

The reactivity of HF(40wt%)–HNO3(100wt%)–H2SO4(97wt%) etching mixtures towards conventional SiC-slurry and diamond-wire sawn silicon wafers has been studied. Sulfuric acid-rich mixtures exhibit adequate etching rates (r<5µmmin−1) and generate homogenously distributed, small etching pits on both types of silicon wafers. Textured wafer surfaces were characterized by means of scanning electron microscopy (SEM), laser scanning microscopy (LSM), surface roughness analyses and reflectivity studies. The surface roughness is influenced by the etch depth and the type of saw damage. Etching in sulfuric acid-rich mixtures significantly reduces the reflection of SiC-slurry sawn wafers and, in particular, of diamond-wire sawn wafers. The reflection of etched silicon surfaces is discussed in terms of etch depth and surface roughness. Compared to the conventional HF–HNO3–H2O etching process, multicrystalline silicon (SiC-slurry and diamond-wire sawn) based solar cells texturized by sulfuric acid-rich mixtures exhibit increased efficiencies.

Sequential Extraction of Vanadium in Different Soil Samples Using Conventional and Ultrasonic Devices

Abstract A rapid ultrasound accelerated sequential extraction (USE) procedure was used to develop chemical partitioning of vanadium (V), proposed by the Community Bureau of Reference/European Union Measurement and Testing Programme (BCR). The effects of ultrasonic treatment on the extraction of V in different soil samples collected from the vicinity of a thermal power plant and agricultural areas of Sindh, Pakistan, were evaluated. In the conventional BCR-sequential extraction method, each extraction step takes 16 h. With the use of ultrasound energy, Steps 1–3 of the USE procedure (excluding the hydrogen peroxide digestion in Step 3, which was performed conventionally) could be completed in 45, 40, and 45 min, respectively. Analysis of the extracts was performed by electrothermal atomic absorption spectrometry. The total contents of V were obtained by digestion with two acid mixtures: H2O2–HF–HNO3–H2SO4 and HClO4–HF–HNO3–H2SO4. Validation was performed by the standard addition technique. Results obtained for each fraction by both methods were statistically compared; no significant differences were found (P &amp;lt; 0.05). The accuracy of the USE procedure was checked by comparing the sum of the V contents in the three fractions and residue with the total content of V. The results of this work provide information on the chemical composition, distribution, and potential mobility of the V in different soils.