Aqua Regia Etching Research Articles

Recovery of Au and Pd from the etching solution of printed circuit boards by cementation, solvent extraction, reduction, and precipitation

Printed circuit boards (PCBs) contain precious metals like Au and Pd. Therefore, it is important to recover these metals from waste PCBs. A process was developed in this work to recover pure Au powders and Pd compounds from the aqua regia etching solution of waste PCBs. Au(III) and Pd(II) were separated by cementation with Cu powder from the etching solutions containing Al(III), Cu(II), Fe(III), Na(I), Ni(II), Sn(II) and Zn(II). The Au and Pd metals present in the cemented Cu were dissolved together with Cu by the mixture of HCl and NaClO. Au(III) was separated from the leaching solution of the cemented Cu by solvent extraction with Cyanex 272. Then pure Au powders were recovered from the thiourea stripping solution by chemical reduction with hydrazine. In order to recover Pd(II) from the raffinate after extraction of Au(III), Pd(II) was oxidized to Pd(IV) by adding NaClO3 and then pure Pd compound ((NH4)2PdCl6) was recovered by precipitation with NH4Cl. Optimum conditions of these steps were obtained at room temperature. The purity of the recovered Au and Pd compound was higher than 99%.

Surface modification of single-walled carbon nanotubes by functional nitrogen-containing groups and study of their properties

Treatment of single-walled carbon nanotubes (SWCNT) in a gaseous 40%NH3–1%С2Н2–C2H4 mixture at 600 and 700°С led to “nitrogen-containing carbon coating–single-wall carbon nanotubes” composites. Single-walled carbon nanotubes after etching in aqua regia (SWCNTetch) and doped with nitrogen (N-SWCNT) were studied by XPS, electron microscopy, and IR spectroscopy. It was found that the initial SWCNTetch surface contains various oxygen-containing functional groups. Treatment of SWCNTetch in a 40%NH3–1%С2Н2–C2H4 mixture led to the formation of a thin carbon coating on the carbon nanotube surface due to polymerization and condensation of hydrocarbons. After treatment at 600°C, the formation of nitrogen-containing functional groups is insignificant; however, when the treatment temperature is increased to 700°C, the nitrogen content reaches 0.5 at % of the weight of the N-SWCNT sample.

Impact of Heterointerfaces in Solar Cells Using ZnSnP2 Bulk Crystals.

We report on the optimization of interface structure in ZnSnP2 solar cells. The effects of back electrode materials and related interface on photovoltaic performance were investigated. It was clarified that a conventional structure Mo/ZnSnP2 showed a Schottky-behavior, while an ohmic-behavior was observed in the Cu/ZnSnP2 structure annealed at 300 °C. STEM-EDX analysis suggested that Cu-Sn-P ternary compound was formed at the interface. This compound is considered to play an important role to obtain the ohmic contact between ZnSnP2 and Cu. In addition, it was clarified that the aqua regia etching of ZnSnP2 bulk crystals before chemical bath deposition process for the preparation of buffer layer was effective to remove the layer including lattice defects introduced by mechanical-polishing, which was supported by TEM observations and photoluminescence measurements. This means that the carrier transport across the interface was improved because of the reduced defect at the interface. Consequently, the conversion efficiency of approximately 2% was achieved with the structure of Al/ZnO;Al/ZnO/CdS/ZnSnP2/Cu, where the values of short circuit current density, JSC, open circuit voltage, VOC, and fill factor, FF, were 8.2 mA cm-2, 0.452 V, and 0.533, respectively. However, the value of VOC was largely low considering the bandgap value of ZnSnP2. To improve the conversion efficiency, the optimization of buffer layer material is considered to be essential in the viewpoint of band alignment.

Convenient and Efficient Surface Reforming of LaTiO2 N Photocatalyst: Poly(4-styrenesulfonic acid) Treatment and Microwave Assisted CoO x Deposition

The overall water splitting by solar-energy-driven photocatalysts is a crucial issue as a solution for today’s mass scale energy and environmental problems. The activity of those photocatalysts is to be improved by their surfaces where the water splitting reactions take place. This time we report two useful tips to enhance the efficiency of LaTiO2N, an important candidate oxynitride for photocatalysis. One is to clean off the debris and defects on the particle surface. Domen et al.1 reported a brief, effective aqua regia treatment was in removing surface defects of LaTiO2N. However, aqua regia accompanies drawbacks of its severe reactivity. We need quick, elaborate washing to stop etching of the oxynitride in a contolled manner, and we need to isolate the aqua regia’s corrosive fume from the environment. More convenient and effective altanative surface treatment reagents are wanted in this sense. Two is to modify the surface of LaTiO2N with CoO x nanoparticles as so-called co-catalysts. The co-catalysts are supposed to assist the separation of photogenerated charges as well as promotion of surface reactions to evolve O2. CoO x nanoparticles, composed of earth abundant elements, are conventionally loaded by the liquid impregnation/calcination method.2 However the process of calcination on LaTiO2N brings about a complexity of heating in NH3 flow to avoid surface oxidation, simultaneously introducing chances of CoO x particle sintering and metallization. Our solutions for there problems are by rinsing in aqueous poly(4-styrenesulfonic acid) (PSS) solution followed by loading CoO x with a microwave assisted deposition. Static treatment of the LaTiO2N powder in PSS solution for 17 hours and microwave assisted one-pot loading of CoOx with Co(NH3)3Cl3 in Eyleneglycol solution, prior to fabrication into an electrode, increased the photoanodic current up to 8.9 mA cm-2 at 1.23 VRHE, which is 3 times larger than that without these reforming. We also confirmed that LaTiO2N was treated with PSS solution conveniently and care-freely in comparison with etching in aqua regia, and cocatalyst was coated throughout the surface of LaTiO2N particle by using microwave quick heating. M. Matsukawa, R. Ishikawa, T. Hisatomi, Y. Moriya, N. Shibata, J. Kubota, Y. Ikuhara and K. Domen, Nano Lett. 2014, 14, 1038−1041. F. Zhang, A. Yamakata, K. Maeda, Y. Moriya, T. Takata, J. Kubota, K. Teshima, S. Oishi and K. Domen, J. Am. Chem. Soc., 2012, 134, 8348−8351. Figure 1

Properties of the Master Alloys for White Gold Products with Silicon Contents

Abstract We prepared 8 samples of non-silver and silver-added master alloys containing silicon to confirm the existence ofnickel-silicides. We then prepared products made of 14K and 18K white gold by using the prepared master alloys containing0.25, 0.35, and 0.50 wt% silicon to check for nickel release. We then employed the EN 1811 testing standard to investigatethe nickel release of the white gold products, and we also confirmed the color of the white gold products with an UV-VIS-NIR-color meter. We observed NiSi x residue in all master alloys containing more than 0.50 wt% Si with EDS-nitric acid etching.For the white gold products, we could not confirm the existence of NiSi x through XRD after aqua-regia etching. In the EN1811 test, only the white gold products with 0.25 wt% silicon master alloys successfully passed the nickel release regulations.Moreover, we confirmed that our white gold products showed excellent Lab indices as compared to those of commercial whitegold ones, and the silver-added master alloys offered a larger L index. Our results indicate that employing 0.25 wt% siliconmaster alloys might be suitable for white gold products without nickel-silicide defects and nickel release problems. Key wordsmaster alloy, white gold, silicon content, nickel release, energy dispersive spectroscopy.

Electrical and luminescent properties and deep traps spectra in GaN nanopillar layers prepared by dry etching

Electrical properties, microcathodoluminescence spectra, and spectra of deep traps were studied for nanopillar structures prepared by dry etching of undoped GaN films using natural masks formed by Ni nanoparticles. It is shown that as-prepared nanopillar structures have low bandedge intensity, very high leakage current of Schottky diodes, their electrical properties are determined by 0.2 eV electron traps or, after etching in aqua regia, 0.14 eV electron traps that are commonly associated with radiation defects. Deep levels transient spectroscopy spectra measured after aqua regia etching are dominated by 1 eV electron traps, other common radiation defects. Annealing at 600 °C is instrumental in eliminating the 0.2 eV and 0.14 eV electron traps, but not the 1 eV traps. A higher temperature annealing at 900 °C is required for strongly suppressing the latter and increasing the bandedge luminescence peak magnitude by 2 times compared to control sample. The best results in terms of luminescence efficiency increase are produced by additional etching in aqueous solution of KOH, but subsequent etching in aqua regia is necessary to suppress excessive surface leakage due to surface contamination by the KOH treatment.

Patterning of platinum (Pt) thin films by chemical wet etching in Aqua Regia

The chemical and physical properties of platinum (Pt) make it a useful material for microelectromechanical systems and microfluidic applications such as lab-on-a-chip devices. Platinum thin-films are frequently employed in applications where electrodes with high chemical stability, low electrical resistance or a high melting point are needed. Due to its chemical inertness it is however also one of the most difficult metals to pattern. The gold standard for patterning is chlorine RIE etching, a capital-intensive process not available in all labs. Here we present simple fabrication protocols for wet etching Pt thin-films in hot Aqua Regia based on sputtered Ti/Pt/Cr and Cr/Pt/Cr metal multilayers. Chromium (Cr) or titanium (Ti) is used as an adhesion layer for the Pt. Cr is used as a hard masking layer during the Pt etch as it can be easily and accurately patterned with photoresist and withstands the Aqua Regia. The Cr pattern is transferred into the Pt and the Cr mask later removed. Only standard chemicals and cleanroom equipment/tools are required. Prior to the Aqua Regia etch any surface passivation on the Pt is needs to be removed. This is usually achieved by a quick dip in dilute hydrofluoric acid (HF). HF is usually also used for wet-etching the Ti adhesion layer. We avoid the use of HF for both steps by replacing the HF-dip with an argon (Ar) plasma treatment and etching the Ti layer with a hydrogen peroxide (H2O2) based etchant.

Fluorescence signals of core–shell quantum dots enhanced by single crystalline gold caps onsilicon nanowires

We use nanoscale (20–300 nm in diameter) single crystalline gold (Au)-capson silicon nanowires (NWs) grown by the vapor–liquid–solid (VLS) growthmechanism to enhance the fluorescence photoluminescence (PL) signals ofhighly dilute core/shell CdSeTe/ZnS quantum dots (QDs) in aqueous solution (10−5 M).For NWs without Au-caps, as they appear, for example, after Au etching in aqua regia or bufferedKI/I2-solution, essentially no fluorescence signal of the same diluted QDs could beobserved. Fluorescence PL signals were measured using excitation with a laserwavelength of 633 nm. The signal enhancement by single crystalline, nanoscaleAu-caps is discussed and interpreted based on finite element modeling (FEM).

PFabrication of gold tips by chemical etching in aqua regia

We present a method to produce sharp gold tips for applications in apertureless near-field optical microscopy and spectroscopy. Thin gold wires are tapered by chemical etching in aqua regia, covered by an isooctane protective layer. Tips with apical radii of curvature of <50 nm are obtained with a 40% yield. The tip performances have been checked by shear-force imaging of amyloid fibrils samples and compared to optical fiber probes. The analysis of the tip morphology, carried out by scanning electron microscopy, shows the existence of two different etching processes occurring in bulk and at the liquid-liquid interface. A simple analytical model is presented to describe the dynamics of the tip formation at the liquid-liquid meniscus interface that fits remarkably well the experimental results in terms of tip shape and length.

The etching behavior of n-GaP in aqua regia solutions

The etching of GaP, whether in strong HNO3 or in strong HCl is severely inhibited, whereas mixtures of HNO3/HCl are commonly employed as etchants for chemical polishing. The etching mechanism of n-GaP in aqua regia (3HCl/1HNO3) has been investigated. Aqua regia etching may occur by accomplishing both the following two processes :(1) oxidation and (2) dissolution. First, the nascent chlorine and nitrate ions obtained from the vigorous interaction between HCl and HNO3, may easily oxidize the surface atoms of GaP, then nucleophilic attacked by Cl− on the electron-poor trivalent gallium ions of the oxide lattice generally takes place over the passive surface. Moreover, the remaining phosphate or phosphorus oxide is very soluble. Ga and P atoms are thus carried away from the surface by the etchant system. In HNO3-etch, the nitrate ion formed is a weak nucleophile and the amount of its production is very small. In the HCl-etch, Cl− causes a direct attack on GaP substrate via an Ga(I) chloro intermediate whose thermodynamics is very unfavorable. Thus, the experimental observations are in good agreement with the mechanistic concepts presented.

Experimental Study of Electrochemical Deuterium Loading of Pd Cathodes in the LiOD/D 2O System

The electrochemical loading behaviour of Pd cathodes in the LiOD/D 2O system has been studied experimentally. The preparation conditions of Pd cathodes significantly affect the D/Pd loading ratios. In addition, the D/Pd ratio is affected by the current density profile, current increasing pattern and anodic treatments. The major treatments were (1) a vacuum annealing to release the stress, to recrystallise and to clean the surface by thermal etching, and (2) a surface treatment to remove surface defects and to clean the surface. It was concluded that higher annealing temperatures (∼1000 °C) result in a higher D/Pd ratio. In addition, etching in aqua regia proved to be a better surface treatment than polishing. It was confirmed that using the pre-electrolysis treatments resulted in higher D/Pd ratios. The electrolysis current pattern and anodic treatment cycles likewise affected the D/Pd ratio. The effects are also discussed in detail below.

TEM observations of surface-step and hole-edge faceting in acid-etched and annealed MgO thin foils

Surface-steps formed during the cleavage of MgO on {100} planes, the smaller steps of which may be of atomic height, have been observed in Reflection-Electron Microscopy investigations to be accurately aligned along &lt;001&gt; directions. Steps of atomic height also have been identified on MgO smoke-particle platelets; these steps may be curved or straight, with the straight steps showing evidence for faceting along &lt;001&gt;. Reference also is made to faceting along &lt;011&gt; and &lt;012&gt; directions. Straight steps ∼2 unit cells high, with edges along &lt;100&gt; also have been imaged by High-Resolution Profile-Imaging at the peripheries of MgO smoke microcubes. After etching in aqua-regia and annealing in air, however, high densities of “large” steps several unit cells high, as well as numerous holes, are formed. It is faceting in these foils that is reported here.As can be seen in fig 1, obvious faceting of the surface-step traces is extremely rare in these foils, in marked contrast to substrates such as LaAlO3 and SrTiO3, on which surface-step traces facet readily after a similar preparation treatment.

PtSi contact metallurgy formed by three-temperature annealing sequences and short annealing time

PtSi contact metallurgy has been formed using a wide series of annealing sequences, employing the three-temperature scheme developed earlier but with much shorter annealing durations. Using either 200-300-550 °C or 200-300-450 °C schemes and a total annealing time between 20 and 40 min in forming gas (N2-H2 9:1), all the films show complete reaction between Pt and Si, a necessary condition for high-quality PtSi contact used in devices as determined from earlier studies. The films also show surface passivating oxide layers of good resistance against etching in aqua regia. The results obtained make the three-temperature process a promising one for the fabrication of devices containing PtSi contact metallurgy.

PtSi Contact Metallurgy Using Sputtered Pt and Different Annealing Processes

contacts have been formed by different annealing processes using sputtered Pt. Two annealing sequences are compared: a single‐temperature one at 550°C and a three‐temperature one at 200°–300°–550°C. Three annealing ambients are compared for each sequence: forming gas, nitrogen, and oxygen. The process using the three‐temperature sequence in forming gas differs from all the others in that it allows a complete reaction between Pt and Si, leaving a thin passivating oxide layer with excellent protection against etching in aqua regia, a desirable step in device fabrication. films formed by all the other processes, on the other hand, show incomplete reactions between Pt and Si, with a thicker but very poor surface oxide layer which is completely etched off by aqua regia. Film structures and composition are analyzed, Schottky diodes fabricated from different processes are measured, and the results are discussed.

Effect of the sintering process on the formation and passivation of PtSi

PtSi films have been formed using different annealing sequences and ambients. Using sputtered Pt, the passivating oxide layer formed on the PtSi films shows a clear dependence on the annealing sequence and ambient used. Using a one-temperature sequence at 550 °C in forming gas (N2–H2 9 : 1), nitrogen or oxygen, the passivating oxide layers all show very poor resistance against etching in aqua regia, an undesirable condition for device fabrication. This is attributed to the incomplete reaction between Pt and Si using such a process. Using a three-temperature sequence at 200–300–550 °C in forming gas, a much improved oxide is obtained with excellent resistance against etching in aqua regia. The process is shown to allow a complete reaction between Pt and Si, a necessary step for the subsequent formation of high quality surface oxide. The three-temperature process using nitrogen or oxygen, however, shows incomplete reaction between Pt and Si, and surface oxide of poor quality, similar to those obtained by the single-temperature process in various gases.

PtSi contact metallurgy using electron-beam evaporated Pt films and different annealing processes

Pt films deposited by electron-beam evaporation onto both heated and unheated Si substrates have been used to form PtSi by different annealing sequences and ambients. Pt films deposited on substrates at 350 °C show complete formation of PtSi. Subsequent annealing at 550 °C is needed to form the protective oxide desired for device processing, with little dependence on the annealing ambients used. Pt films deposited on unheated substrates, on the other hand, show a partial formation of Pt2Si. The formation of PtSi by further annealing of such films is clearly dependent on the annealing sequence and ambient used. A three-temperature sequence at 200/300/550 °C in forming gas is shown to allow a complete reaction between Pt and Si, and to develop a surface protective oxide of excellent resistance against etching in aqua regia. PtSi films formed by single-temperature annealing at 550 °C in various ambients, however, show incomplete reactions between Pt and Si, leaving unreacted Pt and traces of Pt2Si, and a surface passivating oxide of poor resistance against aqua regia. The results on such evaporated Pt films are therefore similar to those reported earlier for the sputtered Pt. Film structures and compositions, phases formed, and Schottky diodes using different processes are analyzed and compared with those using sputtered Pt.

PtSi contact metallurgy: Effect of silicide formation process

PtSi films have been formed by different formation processes using sputtered Pt. Two annealing sequences are compared: a single-temperature annealing at 550 °C and a three-temperature annealing at 200–300–550 °C; and three annealing gases are compared: forming gas, nitrogen, and oxygen. Silicide films formed using the single-temperature process all show incomplete reaction between Pt and Si, leaving a protective surface oxide layer of poor quality, which extends rather deeply into the PtSi film and is completely etched off by aqua regia. The silicide films formed by the three-temperature process in forming gas, however, show a complete reaction between Pt and Si, and a thin surface oxide layer with excellent protection of the PtSi layer from the subsequent aqua regia etching often needed for device fabrication.

PtSi Contact Metallurgy by Different Formation Processes

ABSTRACTPtSi films have been formed using sputtered Pt and different annealing sequences and ambients. A clear dependence on the annealing sequence and ambient is observed for both the PtSi films and the passivating oxide layers formed. The single-temperature process at 550°C using forming gas (N2-H2 9:1), nitrogen and oxygen shows incomplete reactions between Pt and Si, with a surface oxide layer of poor resistance against etching in aqua regia. A three-temperature process using forming gas is shown to provide complete reactions between Pt and Si, with a surface oxide layer of excellent resistance against aqua regia. The three-temperature process using nitrogen or oxygen, however, fails to provide films of high quality, and the results are similar to those obtained by the single-temperature process in various gases.

Margins of complete crowns—Literature review

The margin is one of the components of the cast restoration most susceptible to failure, both biologically and mechanically. Most of the investigative proof shows that supragingival margins are kinder to the gingiva than are subgingival margins. However, practicality dictates that supragingival margins are not always usable. There is some indication that quality of the margin may be of as much importance to gingival health as location. Research on the configuration of margins seems to agree with the majority of authors writing technical articles. Most agree that feather edge or knife edge margins are not always the most acceptable. Apparently bulky margins with subtle internal line angles are best. Bevels are recommended where esthetics allows due to their slip-joint effect affording closer adaptation. Most cemented castings do not fit nearly as well as theoretical tests of cement film thicknesses would lead us to believe. Venting or providing space for cement through electromilling, aqua regia etching, or die spacing markedly improves the seating and, therefore, the marginal fit of castings. This seems to be a more useful approach to close fitting margins than burnishing and finishing margins, particularly for subgingival margins. Most of the commonly used fixed partial denture alloys, both precious and non-precious, are too hard to be burnished effectively. As long as fixed prosthodontics must rely on the cemented casting, the search for more knowledge about an innocuous, esthetic, indestructible margin must continue.

Etching procedures for Gap surfaces

Chemical treatments of the (111) GaP surface were investigated. The investigations were carried out using scanning electron microscopy, ellipsometry and Schottky barrier characterization. A 1HCl: 1HNO 3: 1CH 3COOH etchant was developed as the most suitable for polishing etching. It provided damage-free GaP surfaces with minimum residual oxide (18 Å) and nearly ideal Schottky barrier characteristics. A complex chemical treatment was required for the removal of a thick surface layer from the GaP crystals. It consisted of aqua regia etching followed by etching with 1HCl:1HNO 3:1CH 3COOH, 1HCl:3HNO 3:2CH 3COOH:3HClO 4 or 1K 3Fe(CN) 6:3KOH:60H 2O.