HF HNO3 Research Articles

Ultrasonic dissolution for ICP-MS determination of trace elements in lightly loaded airborne PM filters

A simple single-step ultrasonic dissolution procedure for low mass (<1 mg) particulate matter (PM) filter samples using HNO3–HF acid solution is proposed for multi-element determination using ICP-MS. The PM-loaded PTFE filter samples are inserted directly into disposable centrifuge tubes for acid extraction using ultrasonic digestion (UD). Potential interferences owing to contamination and element loss are minimized. Key factors influencing element recoveries are investigated, including digestion solution composition, acid concentration, temperature, and matrix interferences. Optimized conditions for UD include an acid mixture consisting of 4.0 mL HNO3 and 0.1 mL HF with ultrasonication proceeding at 90°C for one hour, followed by 10-fold dilution. Recoveries of 80–120% are achieved for almost all of the 20 elements tested (Be, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Sr, Mo, Ag, Cd, Sb, Ba, Pb and U) in four standard reference materials with contrasting matrices: NIST 1648 (urban PM), NIST 2584 (indoor dust), NIST 2710 (soil), and NIST 1633b (coal fly ash). The exception is Cr in NIST 1648 for which recovery is low (30%) using this method. Element concentrations obtained for PM-loaded filter samples using the proposed UD + ICP-MS method agree with results obtained using energy dispersive X-ray fluorescence (paired t-test p > 0.2; 95% CI).

Trace metals in Daihai Lake sediments, Inner Mongolia, China

A total of 29 surface sediments were collected from the Daihai Lake, China. Concentrations of metals (Cu, Pb, Zn, and Cd) were determined using HR-ICP-MS after digestion with the mixture of HNO3–HF–HCl (aqua regia), and chemically fractionated according to the modified the European Community Bureau of Reference sequential extraction procedure. Total organic carbon contents and grain size were also analyzed. Average concentrations (ppm) for Cu (39.4 ± 10.6), Pb (29.9 ± 6.1), Zn (102.6 ± 23.3), and Cd (0.21 ± 0.07) were found in the sediments. The concentrations of metals are relatively higher in the central area of lake, while lower nearby the area with a shallower water depth. Sequential extraction results show that Cu and Zn are mainly distributed in the residual fraction, while Cd is dominantly in the non-residual fraction. Enrichment factor values and geoaccumulation indexes suggest that there are not obvious enrichments of Cu, Pb, and Zn in the sediments, but Cd pollution can be found in most of the area of Daihai Lake. The sources for Cu, Pb, and Zn are attributed to atmospheric deposition, which might be mainly associated with coal combustion. Agricultural runoff in polluted soils and coal combustion might be main sources of the Cd pollution in the lake.

Robust Process Design towards through-Silicon via Quality Improvement Based on Grey-Taguchi Method

The robust design of chemical etching parameters is dealing with the optimization of the through-silicon via (TSV) roundness error and TSV lateral etching depth in the etching of silicon for laser drilled TSVs. The considered wet chemical etching parameters comprise the HNO3 molarity, HF molarity, and etching time. Grey-Taguchi method is combining the orthogonal array design of experiments with Grey relational analysis (GRA), which enables the determination of the optimal combination of wet chemical etching parameters for multiple process responses. The concept of Grey relational analysis is to find a Grey relational grade, which can be used for the optimization conversion from a multiple objective case to a single objective case. Also, GRG is used to investigate the parameter effects to the overall quality targets.

Etching Silicon with HF–HNO3–H2SO4/H2O Mixtures – Unprecedented Formation of Trifluorosilane, Hexafluorodisiloxane, and Si–F Surface Groups

AbstractThe etching behaviour of sulfuric‐acid‐containing HF–HNO3 solutions towards crystalline silicon surfaces has been studied over a wide range of H2SO4 concentrations. For mixtures with low sulfuric acid concentration, NO2/N2O4, N2O3, NO and N2O have been detected by means of FTIR spectroscopy. Increasing concentrations of nitric acid lead to high etching rates and to an enhanced formation of NO2/N2O4. Different products were observed for the etching of silicon with sulfuric‐acid‐rich mixtures [c(H2SO4) &gt; 13 mol L–1]. Trifluorosilane and hexafluorodisiloxane were identified by FTIR spectroscopy as additional reaction products. In contrast to the commonly accepted wet chemical etching mechanism, the formation of trifluorosilane is not accompanied by the formation of molecular hydrogen (according to Raman spectroscopy). Thermodynamic calculations and direct reactions of F3SiH with the etching solution support an intermediate oxidation of trifluorosilane and the formation of hexafluorodisiloxane. The etched silicon surfaces were investigated by diffuse reflection FTIR and X‐ray photoelectron spectroscopy (XPS). Surprisingly, no SiH terminations were observed after etching in sulfuric‐acid‐rich mixtures. Instead, a fluorine‐terminated surface was found.

Silicon isotropic and anisotropic etching for MEMS applications

In MEMS technology there is an increasing interest in developing high aspect ratio silicon columns having rounded corners, slightly positive tapered shafts, sharp tips, and smooth surfaces. A precise control of the profile can be used for different applications, such as for molds used in polymer hot embossing processes, micro needles used for drug delivery and blood sampling, and neural probes used for controlling motor or sensory prosthetic devices. The mixture of hydrofluoric acid (HF) and nitric acid (HNO3) is an isotropic etchant and is used in MEMS technology to etch silicon. We present a novel way of isotropically and anisotropically etch MEMS structures using the HF–HNO3 etchant. The shape and size of the structure is controlled by the dynamics of acid solution to yield highly repeatable and reproducible needle geometry.

Spectrometric analysis of process etching solutions of the photovoltaic industry—Determination of HNO3, HF, and H2SiF6 using high-resolution continuum source absorption spectrometry of diatomic molecules and atoms

The surface of raw multicrystalline silicon wafers is treated with HF–HNO3 mixtures in order to remove the saw damage and to obtain a well-like structured surface of low reflectivity, the so-called texture. The industrial production of solar cells requires a consistent level of texturization for tens of thousands of wafers. Therefore, knowing the actual composition of the etch bath is a key element in process control in order to maintain a certain etch rate through replenishment of the consumed acids.The present paper describes a novel approach to quantify nitric acid (HNO3), hydrofluoric acid (HF), and hexafluosilicic acid (H2SiF6) using a high-resolution continuum source graphite furnace absorption spectrometer. The concentrations of Si (via Si atom absorption at the wavelength 251.611nm, m0,Si=130pg), of nitrate (via molecular absorption of NO at the wavelength 214.803nm, m0,NO3−=20 ng), and of total fluoride (via molecular absorption of AlF at the wavelength 227.46nm, m0,F=13 pg) were measured against aqueous standard solutions. The concentrations of H2SiF6 and HNO3 are directly obtained from the measurements. The HF concentration is calculated from the difference between the total fluoride content, and the amount of fluoride bound as H2SiF6. H2SiF6 and HNO3 can be determined with a relative uncertainty of less than 5% and recoveries of 97–103% and 96–105%, respectively. With regards to HF, acceptable results in terms of recovery and uncertainty are obtained for HF concentrations that are typical for the photovoltaic industry. The presented procedure has the unique advantage that the concentration of both, acids and metal impurities in etch solutions, can be routinely determined by a single analytical instrument.

Influence of chemical and mineralogical properties of organic amendments on the selection of an adequate analytical procedure for trace elements determination

Six digestion procedures were tested to improve extraction methods for determination of trace elements in various organic amendments with high inorganic fractions. These procedures were tested in terms of pH, CaCO3, organic matter, elemental analysis, BCR sequential extraction and X-ray diffraction analysis. Aqua regia extraction (ISO 11466), total digestion HF–HNO3–HClO4 and four microwave-assisted digestions (i.e., HNO3, HCl–HNO3, HNO3–HF and HCl–HNO3–HF) were used. The effect of acid mixtures on microwave-assisted digestion of mineral fractions was assessed by Si and Al analysis and X-ray diffraction in the solid residues obtained. Microwave HF acid mixtures obtained highest trace element recoveries for all tested metals except Al. CaF2 and CaAlF5 precipitates were also detected using X-ray diffraction in the residues after microwave digestions with HF acid mixtures of amendments with high calcium content. A decision flowchart was suggested to determine the best acid mixture according to the amendment and the metals to be analyzed.

Microwave-assisted acid extraction methodology for trace elements determination in mastic gum of Pistacia lentiscus using inductively coupled plasma atomic emission spectrometry

To ensure food safety, accurate knowledge of the levels of several trace elements is necessary. This is also true for natural products of plants and resins used for human consumption or therapeutic treatment, like the mastic gum of Pistacia lentiscus. The rapid analysis of gum and resin matrices is a challenge because there are problems with the decomposition of such complicated matrices. To develop an efficient multielemental analytical method for the determination of trace elements and to compare different procedures for analyte extraction when microwave-assisted digestion is applied. The inductively coupled plasma atomic emission spectrometric (ICP-AES) technique was applied and the optimum ICP conditions like radiofrequency power, argon flow rate and nebuliser sample uptake flowrate were found. The microwave-assisted procedure was compared with that with conventional heating. Since mastic and resinous materials are difficult for dissolution and extraction of trace element, influential acid mixtures containing hydrofluoric acid proved to be capable of quantitative extraction of the analytes. The digestion of mastic resin or similar matrices is significantly facilitated by using microwave radiation instead of conventional heating since the obtained recovery for several analytes is much higher. It was proved that the acid mixture of HCl-HNO(3)-HF was the most efficient for complete sample digestion and recovery of the analytes. The performance characteristics of the developed method were evaluated against certified reference material and the method was proved reliable and applicable to the analysis of mastic gum and possibly to similar resinous matrices.

A straightforward protocol for Hf purification by single step anion-exchange chromatography and isotopic analysis by MC-ICP-MS applied to geological reference materials and zircon standards

A straightforward one-step Hf purification protocol for geological samples using common anion-exchange chromatography and isotopic measurements by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is described in this paper. The sample is dissolved in concentrated HF–HNO 3 mixtures with round-bottom Savillex™ Teflon screw-top capsules or high-pressure stainless steel jacketed Teflon bombs. After complete dissolution, the chemical separation between Hf and isobarically interfering elements such as Lu, Yb, and matrix elements like Ti, is performed and achieved simultaneously using a common one-step anion exchange resin (AG1-X8). The Hf yields are >90% and total procedural blanks are lower than 20 pg. This protocol not only avoids using multiple-stage ion exchange resins, but also eliminates perchloric acid to break down fluorides after HF treatment of the sample. In addition to whole rock, this protocol is also practical for zircon and baddeleyite Hf purification prior to isotopic measurement. New Hf isotopic data for zircon 91500, Temora, CN92-1 and FM0411, together with Phalaborwa baddeleyite are presented for this method. Multiple analyses of the international geological reference materials and standard zircon and baddeleyite used in U–Pb geochronology demonstrate that this method is simple, economic, efficient and reproducible.

Impact of surface roughness on the electrical parameters of industrial high efficiency NaOH–NaOCl textured multicrystalline silicon solar cell

Sodium hydroxide (NaOH) and sodium hypochlorite (NaOCl) solution (1:1 ratio by volume) based texturization process at 80–82 °C is an easy, low cost and comparatively new and convenient option for fabrication of any multicrystalline silicon (mC-Si) solar cell. In the present study atomic force microscope is used to observe the intragrain surface in a miniscule area (3 μm × 3 μm) of NaOH–NaOCl textured surface by two and three dimensional analysis, roughness analysis and section analysis. The r.m.s value of the surface parameter of 7.0 nm ascertains the smoothness of the textured surface and further the surface reflectivity is minimized to 4–6% in the 500–1000 nm wavelength range by a proper silicon nitride anti-reflection coating. Comparing with the standard HF–HNO 3–CH 3COOH acid textured cell, the NaOH–NaOCl textured cell shows a comparatively lower value of series resistance of 7.17 mΩ, higher value of shunt resistance of 18.4 Ω to yield a fill factor of 0.766 leading to more than 15% cell efficiency in the industrial cell processing line. This AFM study yields different surface roughness parameters for the NaOH–NaOCl textured wafers which can be used as a reference standard for optimized texturing.

A wafer-scale etching technique for high aspect ratio implantable MEMS structures

Microsystem technology is well suited to batch fabricate microelectrode arrays, such as the Utah electrode array (UEA), intended for recording and stimulating neural tissue. Fabrication of the UEA is primarily based on the use of dicing and wet etching to achieve high aspect ratio (15:1) penetrating electrodes. An important step in the array fabrication is the etching of electrodes to produce needle-shape electrodes with sharp tips. Traditional etching processes are performed on a single array, and the etching conditions are not optimized. As a result, the process leads to variable geometries of electrodes within an array. Furthermore, the process is not only time consuming but also labor-intensive. This report presents a wafer-scale etching method for the UEA. The method offers several advantages, such as substantial reduction in the processing time, higher throughput and lower cost. More importantly, the method increases the geometrical uniformity from electrode to electrode within an array (1.5 ± 0.5% non-uniformity), and from array to array within a wafer (2 ± 0.3% non-uniformity). Also, the etching rate of silicon columns, produced by dicing, are studied as a function of temperature, etching time and stirring rate in a nitric acid rich HF–HNO 3 solution. These parameters were found to be related to the etching rates over the ranges studied and more importantly affect the uniformity of the etched silicon columns. An optimum etching condition was established to achieve uniform shape electrode arrays on wafer-scale.

Combined chemical separation of Lu, Hf, Rb, Sr, Sm and Nd from a single rock digest and precise and accurate isotope determinations of Lu–Hf, Rb–Sr and Sm–Nd isotope systems using Multi-Collector ICP-MS and TIMS

A combined procedure for separating Lu, Hf, Rb, Sr, Sm and Nd from a single sample digestion is presented in this paper. The procedure consists of the following four steps: (1) sample dissolution in a mixture of concentrated HF–HNO 3–HClO 4; (2) Lu and Hf separation from the Rb, Sr, LMREE and other matrix elements by HF-free extraction chromatography; (3) Rb, Sr and LMREE separation from other matrix elements using a cation-exchange resin; (4) Sm and Nd separation from others LMREE by extraction chromatography. Analytical feasibility, flexibility and reproducibility of Rb–Sr, Sm–Nd and Lu–Hf isotope systems are demonstrated for international standard solutions and Certified Reference Materials (CRMs). Results show good agreement with previously reported values by isotope dilution methods, indicating the technique has fewer problems in respect to well-known sample inhomogeneity of natural geological materials and demonstrating its potential application to the study of limited and precious terrestrial rocks or minerals (like peridotite, kimberlite and xenoliths) and extra-terrestrial samples (like lunar rock and meteorites).

Surface‐Treated Activated Carbon for Removal of Aromatic Compounds from Water

AbstractModifications of commercial activated carbons by chemical treatment with HNO3 or HCl and HF and the adsorption behavior of simple aromatic compounds (aniline, pyridine, phenol, and benzene) on activated carbon and modified activated carbon were investigated. The results show that the textural properties change a little after these modifications, but the surface acidity (mainly oxygen‐containing groups) of activated carbon modified with HNO3 increases greatly. The effect of ash of activated carbon on adsorption of the organic compounds mentioned above is insignificant. However, addition of surface acidity (mainly surface oxygen‐containing groups) decreases the adsorption capacity of compounds significantly. The adsorption uptake of compounds on activated carbon with oxidation of HNO3 is low possibly due to dispersive interaction, water cluster blocking, or competition between water and compounds adsorbed on activated carbon's surface because of hydrophilic increase of the activated carbon surface. The solubility of aromatic compounds in water has an important effect on the adsorption capacity of activated carbon. qm and KL (Langmuir adsorption parameters) for the aromatic compounds vary similarly.

Texturing of large area multi-crystalline silicon wafers through different chemical approaches for solar cell fabrication

Surface texturing of silicon can reduce the reflectance of incident light and hence increase the conversion efficiency of solar cells. Comparatively lesser concentrated (10%) standard alkaline (NaOH/KOH) solution does not give good textured multi-crystalline silicon (mc-Si) surface, which could give satisfactory open-circuit voltage. This is due to grain-boundary delineation with steps formed between successive grains of different orientations. In this work an attempt has been made to obtain a well-textured mc-Si surface through three different approaches. The first two are with two different types of acid solutions and the third with concentrated alkaline NaOH. Solutions of HF–HNO 3–CH 3COOH/H 2O system with different concentrations of HF and HNO 3 were used for texturing. The results on the effect of texturing of these three solutions on the surface morphology of very large area (125 mm×125 mm) mc-Si wafer as well as on the performance parameters of solar cell are presented in this paper. Attempts have been made to study extensively the surface morphologies of mc-Si wafers in two effective regions of the isoetch curves of the HF:HNO 3:diluent's system. Also we studied the reflectance, uniformity, spectral response, short-circuit current, open-circuit voltage, fill factor and dark current–voltage of the cells fabricated using wafers textured with the three different methods. Short-circuit current of the solar cells fabricated using acid-textured wafers were measured to be in the range of 4.93 A. This value is 0.37 and 0.14 A higher than the short-circuit current values measured in the cells fabricated with isotextured and alkaline-textured wafers, respectively.

Metal-assisted chemical etching of silicon in HF–H 2O 2

Metal-assisted etching of silicon in HF/H 2O 2/H 2O solutions with Ag nanoparticles as catalyst agents was investigated. SEM observations and etch rate measurements were carried out as a function of the etching solution composition. Depending on the relative amount of HF and H 2O 2, different regimes of dissolution take place and a strong similarity with the etching in HF–HNO 3 solution is evidenced, for the first time. Formation of meso- and macroporous Si, etched craters and polished Si are observed as the HF/H 2O 2 ratio decreases. The dissolution mechanisms are discussed on the basis of a localized hole injection from the Ag nanoparticles into Si and in terms of the well known chemistry of Si dissolution in HF-based chemical and electrochemical systems. At high HF/H 2O 2 ratio, there is no formation of oxide at the surface. Hole injection and Si dissolution occur at the level of the Ag nanoparticle only, resulting in the formation of meso and macropores depending on the Ag nanoparticle size. At low HF/H 2O 2 ratio, the Si surface is oxidized, the injected holes are homogeneously distributed and thus polishing occurs. There is an intermediate range of composition in which injected holes diffuse away from the Ag nanoparticles and cone-shaped macropores, several tens of nm in diameter are formed.

Accurate determinations of Ge atom fractions in SiGe semiconductor chips using high performance ICP-OES

The Ge atom fractions in SiGe chips with nominal values in the range 3.5% to 14% were accurately determined using high performance inductively coupled plasma optical emission spectroscopy (HP-ICP-OES). For each chip, Si and Ge were determined in separate HP-ICP-OES experiments, and the Ge atom fraction was calculated from the data. This approach eliminated the need to measure the mass of the chip, thereby avoiding a potentially significant source of uncertainty. Digestion of the chips occurred in the presence of HF–HNO3 at room temperature in closed vessels to prevent the loss of Si as volatile SiF4. Recoveries of both Si and Ge in these digests were observed to be effectively 100%. For the Si determinations, NaOH was introduced to reduce Si background and memory. Expanded uncertainties (95% confidence) associated with the Ge atom fractions determined, accounting for all significant components of uncertainty, were observed to be ∼0.2%.

Rapid multi-reagents exchange TIRFM microfluidic system for single biomolecular imaging

A rapid multi-reagents switching microvalve system integrated with a total internal reflection fluorescence microscopy (TIRFM) was developed for real time imaging of a single protein behavior. The binding and dissociation process between a chaperonin GroEL and cochaperonin GroES was observed in this TIRFM microfluidic system. This TIRFM microfluidic system was constructed by a smooth glass in microchannel surface, that is essential for TIR imaging, and the polydimethylesiloxane (PDMS) microvalves that is operatable with a rapid response of around 100 ms. The smooth glass surface was etched with an optimized hydrofluoric acid and nitric acid (HF–HNO3) solution and had the average surface roughness of 3.2 nm. The microvalves were based on a pneumatic PDMS membrane that is beneficial for a rapid (<100 ms) response. This TIRFM microfluidic system contains three inlet channels and one outlet channel and the flow in every inlet channel were precisely controlled by the PDMS microvalves. These microvalves were operated by air pressure pulses of 100 ms to hold, open or closed for switching. This TIRFM microfluidic system enabled a reagent exchange within 100 ms with TIRFM observation. For single molecular imaging in this system, biotinylated GroEL (D490C) was immobilized to the glass microchannel surface through streptavidin and biotinylated BSA. A solution including 1 nM IC5-GroES was introduced for 100 ms into the observation area and then washed out with 2 mM ATP buffer solution. Fluorescence spots of IC5-GroES appeared after rapid solution switching, and disappeared several seconds later. As a result, we succeeded in detecting fluorescence signal from single molecules in TIRFM microfluidic system. The micro-constructed TIRFM microfluidic system can realize dynamic analysis of the single molecule level protein–protein binding and dissociation under a controlled multi-reagent exchange.

Surface morphology of silicon single crystals treated with acid polishing etchants

The specific features of formation of micro-and nanorelief on the (001) surface of silicon single crystals upon treatment with widely used etchants HF HNO3 H2O and with poorly studied etchants HF KMnO4 H2O were studied. The relief of the etched surface was examined by optical, scanning electron, and atomic-force microscopy. The polishing properties of the etchants and the silicon etching rates were studied in relation to the oxidant content. The polishing properties of the etchants were compared by analyzing statistical distribution of such characteristics of the relief of the etched surface as the height and length of micro- and nanowaves.

Chemical analysis of acidic silicon etch solutions: II. Determination of HNO 3, HF, and H 2SiF 6 by ion chromatography

The processing of silicon in microelectronics and photovoltaics involves the isotropic chemical etching using HF–HNO 3 mixtures to clean the surface from contaminations, to remove the saw damage, as well as to polish or to texture the wafer surface. Key element of an effective etch process control is the knowledge of the actual etch bath composition in order to maintain a certain etch rate by replenishment of the consumed acids. The present paper describes a methods for the total analysis of the etch bath constituents HF, HNO 3, and H 2SiF 6 by ion chromatography. First step is the measurement of the total fluoride and nitrate content in the analyte. In a second step, H 2SiF 6 is precipitated as K 2SiF 6. After careful filtration of the precipitate, the fluoride concentration in the filtrate is measured and the content of free HF is calculated therefrom. The K 2SiF 6 is dissolved again and the fluoride content measured and recalculated as H 2SiF 6. The results obtained with the presented method are discussed with respect to the results from two other, previously published methods, based on a titration using methanolic cyclohexylamine solution as titrant and based on a method using a fluoride ion selective electrode (F-ISE). An evaluation with respect to the needs for an industrial application is given.

Chemical analysis of acidic silicon etch solutions: I. Titrimetric determination of HNO 3, HF, and H 2SiF 6

The chemical etching of silicon using HF–HNO 3 mixtures is a widely used process in the processing of silicon wafers for microelectronic or photovoltaic applications. The control of the etch bath composition is the necessary condition for an effective bath utilization, for the replenishment of the consumed acids, and to maintain a certain etch rate. The present paper describes two methods for the total analysis of the individual etch bath constituents HF, HNO 3, and H 2SiF 6. Both methods start with an aqueous acid–base titration determining the total acid concentration and the concentration of H 2SiF 6. The first method is an acid–base titration using a 0.1 mol L −1 methanolic solution of cyclohexylamine (CHA) as non-aqueous titrant to determine the content of nitric acid. Then, the amount of hydrofluoric acid is calculated from the difference between the total acid and nitric acid content. The second method is based on the determination of the total fluoride concentration using a fluoride ion-selective electrode (F-ISE). The content of hydrofluoric acid is obtained from the difference between the total fluoride content and the amount of fluoride bound as H 2SiF 6. The amount of nitric acid results finally calculated as difference to the total acid content.