Concentrated HCl Solutions Research Articles

MAX Phase Thin Films As Electrical-Conductive Corrosion-Protective Coatings with Self-Healing Abilities

Nanolaminate Mn+1AXnphases (short MAX) are materials, that show interesting properties [1]. They exhibit high hardness as well as good thermal and chemical stability, which is commonly a ceramic like behavior. On the other hand, they are good conducting materials in the range of metals. MAX phases are a class of ternary carbides and nitrides, where M is an early transition metal, A is an element belonging to the groups IIIA to VA and X is either carbon or nitrogen. One of their properties which is similar to a ceramic material is their good chemical stability and therefore, they are very well suitable as corrosion protective coating. Up till now the corrosion behavior was investigated for bulk materials in different corrosive media [2] or at elevated temperatures [3,4]. Nevertheless, there is still an ongoing discussion about the mechanisms behind the corrosion protective properties. In most of the cases it is attributed to the crystalline structure of these materials. MAX phases show a hexagonal structures build of MX-octahedrons with intermediate A-element layers between them. Some attribute the corrosion protection properties to the passivation of the A element others to the passivation of the M element. In the presented work, the focus lies on the investigation of the corrosion protective properties of MAX phase thin films. Therefore, multilayer thin films of the three elements were deposited onto the substrates using PVD magnetron sputtering. The formation of the MAX phase was achieved using a subsequent rapid thermal annealing [5,6]. Afterwards the anodic behavior of the deposits was investigated electrochemically in 1M HCl and H2SO4 electrolytes. A good stability of the films in this media could be shown. To prove the self-healing behavior of this thin films, the deposits where mechanically scratched and afterwards annealed at 1000°C in air. A healing of the films could be shown attributed to the formation of oxides during the annealing. All obtained properties show that MAX phases are very well suitable as corrosion protective coatings in aggressive medias and damage can be repaired taking advantage of the self-healing properties of the films. [1] M.W. Barsoum, The MN+1AXN phases: A new class of solids, Prog. Solid State Chem. 28 (2000) 201–281. [2] V.D. Jovic, B.M. Jovic, S. Gupta, T. El-Raghy, M.W. Barsoum, Corrosion behavior of select MAX phases in NaOH, HCl and H2SO4, Corros. Sci. 48 (2006) 4274–4282. [3] Z.J. Lin, M.S. Li, J.Y. Wang, Y.C. Zhou, High-temperature oxidation and hot corrosion of Cr2AlC, Acta Mater. 55 (2007) 6182–6191. [4] J. Xie, X. Wang, A. Li, F. Li, Y. Zhou, Corrosion behavior of selected Mn+1AXn phases in hot concentrated HCl solution: Effect of A element and MX layer, Corros. Sci. 60 (2012) 129–135. [5] M. Hopfeld, R. Grieseler, T. Kups, M. Wilke, P. Schaaf, Thin Film Synthesis of Ti3SiC2 by Rapid Thermal Processing of Magnetron-Sputtered Ti-C-Si Multilayer Systems, Adv. Eng. Mater. 15 (2013) 269–275. [6] R. Grieseler, T. Kups, M. Wilke, M. Hopfeld, P. Schaaf, Formation of Ti2AlN nanolaminate films by multilayer-deposition and subsequent rapid thermal annealing, Mater. Lett. 82 (2012) 74–77.

Highly Efficient Visible-Light Driven Carbon Particles/g-C3N4 Photocatalysts with Enhanced Photocatalytic H2 Production

As a typical metal free inorganic semiconductor, graphitic C3N4 (g-C3N4) has attracted intensive attention for H2 generation, pollutant degradation and CO2 reduction. It is well-known that the band gap of g-C3N4 is about 2.7 eV, which can absorb visible light up to 460 nm. Furthermore, the conduction band minimum of g-C3N4 is extremely negative, so photogenerated electrons should have high reduction ability. However, the photocatalytic efficiency of the pure g-C3N4 is limited by the high recombination rate of its photo-generated electron–hole pairs. One of the techniques for increasing the separation efficiency of photo-generated electron–hole pairs is to load a nonmetal element into a photocatalyst. For the increase of the photocatalytic activity, an extensively studied carbonaceous candidate is carbon particles with tunable size and band gap, abundant hydrophilic surface groups, and long term stability. Particularly, carbon particles can act as spectral converters to overcome the contradiction between optical absorption and chemical reaction dynamics of various semiconductors with UV and visible light activity because of its large cross-section of upconversion absorption and a wide range of emission spectra that boost the energy band-gap matching. In this study, novel carbon particles and g-C3N4 composite photocatalysts were prepared through a facile two-step calcination using carbon particles and melamine as a starting material. The synthesized samples were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nitrogen-sorption, UV-Vis diffuse reflectance spectra (DRS), photoluminescence spectra (PL), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Photocatalytic activity of carbon particles modified g-C3N4 (C/g-CN) was evaluated by photocatalytic hydrogen production under visible irradiation (λ ≧ 420 nm). Firstly, 3.6 g of glucose was dissolved in distilled water (40 mL) to form a clear solution, then 40 mL of concentrated HCl solution was dropped into the solution of glucose. Afterward, the mixture solution was transferred into a 100 mL Teflon liner followed by hydrothermal treatment at 180 ℃ for 6 h. After hydrothermal reaction, the black precipitates were centrifuged and get brown carbon particles solution. Carbon particles and g-CN composite photocatalysts were prepared by two step calcination of the mixture of carbon particles and melamine. Before calcination, 5 mL of carbon particles suspension in ethanol was added into 3g of melamine, then ethanol was evaporated. This obtained ingredient was applied two times calcination, first heating at 550 ℃ for 3h, second heating at 500 ℃ for 10h. Physicochemical measurement of the samples were characterized by XRD, FT-IR, XPS, nitrogen-sorption, DRS, PL, SEM, and TEM. The pyrex column vessel reactor (inner volume: 123 mL) was used for the photocatalytic H2 production from aqueous solution (40 mL) containing 10 vol% triethanolamine (TEA) as a sacrificial donor. 2 wt% Pt loaded on the surface of the photocatalyst by the in situ photodeposition method using H2PtCl6. Before irradiation, N2 gas was bubbled into the reaction solution for 30 min to remove a dissolved O2. Typically, 40 mg of the photocatalyst were added into the reaction solution. A 300 W Xe lamp with a UV cut filter (λ<420 nm) was applied as a light source. The concentration of H2 production from the aqueous TEA solution was analyzed by GC with TCD. The rate of hydrogen production for pure g-CN was approximately 7.9 μmol/g・h. After modified carbon particles, photocatalytic performance was higher. The highest photocatalytic hydrogen evolution rate for 0.5 wt% C/g-CN was approximately 340 μmol/g・h, which was about 43 times faster than that of pure g-CN. DRS spectra showed that the absorbing wavelength region expanded after loading carbon particles. Especially, 5.0 wt% C/g-CN could be absorbed over NIR. However, the photocatalysts which is the highest photocatalytic performance is 0.5 wt% C/g-CN. This result was attributed to the light shading effect. PL spectra represented the peak intensity of C/g-CN were weaker than that of pure g-CN. In this case, this result was implied to preventing recombination of electron-hole pairs which derived from carbon particles loaded. In conclusion, the highest photocatalytic hydrogen evolution rate for 0.5 wt% C/g-CN was approximately 340 μmol /g・h, which was about 43 times higher than that of pure g-CN. The improved photocatalytic activity was attributed to the fact that carbon particles acted electron reservoirs to trap the electrons for promoting charge separation and light harvesters to enhance the visible light absorption.

Synthesis and single crystal structure analysis of 3,3',5,5'-tetramethyl-4,4'-bipyrazolium tetrachlorocobaltate(ii) monohydrate [H&lt;sub&gt;2&lt;/sub&gt;ME&lt;sub&gt;4&lt;/sub&gt;BPZ][CoCl&lt;sub&gt;4&lt;/sub&gt;]·H&lt;sub&gt;2&lt;/sub&gt;O

Slow evaporation of a solution of 3,3',5,5'-tetramethyl-4,4'-bipyrazolium chloride ([H2Me4bpz]Cl2) with the cobalt chloride in concentrated aqueous HCl solution yielded block blue crystals and X-ray single crystal structure determination at 100K revealed that the molecule crystallized in the monoclinic system with a P21/n space group. The asymmetric units consist of tetrahedral [CoCl4]2- anions and tetramethyl bipyrazolium [H2Me4bpz]2+ dications and one water molecule which are connected through N—H····Cl and N—H····O hydrogen bond networks in the crystal lattice.Keywords: Crystal structure, Hydrogen bond and crystal engineering

Robust carbon nanotube membranes directly grown on Hastelloy substrates and their potential application for membrane distillation

A new class of robust carbon nanotube (CNT) membranes is developed using a scalable chemical vapor deposition method by direct growth of the CNT on a nickel alloy (Hastelloy) mesh with micrometer-sized openings. The developed membranes have a dense, entangled network of CNT with 50–500 nm pore openings and are superhydrophobic. These CNT membranes are resistant to air oxidation up to ∼500 °C and chemical corrosion in concentrated HCl or NaCl solutions. Adhesion and ultrasonication tests suggest that the developed CNT membranes are resistant to delamination and demonstrate a high interfacial bonding of the grown CNT with the alloy substrate. Potential application of the developed CNT-Hastelloy membranes for separation is explored by conducting membrane distillation tests using a 10,000 mg/L NaCl solution. The developed membranes show similar salt rejection performance compared with a carbon bucky paper membrane. These robust carbon nanotube membranes are reusable and expected to be less susceptible to fouling because of their superhydrophobic properties. Furthermore, if fouled, they can be regenerated by heating in air or using an acid wash.

Assessing the selectivity of composite ion-exchange membranes within the framework of the extended three-wire model of conduction

The possibility of assessing the selectivity of composite perfluorated membranes MF-4SK modified with polyaniline (PANI), based on the concentration dependence of their specific conductivity in terms of the extended three-wire model of conduction of ion-exchange materials is investigated. To check the reliability of results obtained, the transport numbers of ions are calculated based on the electrodiffusion coefficients of counter ions and coions determined from concentration dependences of conductivity and diffusion permeability of ion-exchange membranes. The transport numbers of hydrogen ions found by these two methods are shown to coincide with high accuracy throughout the whole range of concentrations of HCl solutions for the original MF-4SK membrane and membranes with the fixed thickness of the modified polyaniline layer on their one side. For the MF-4SK sample the with gradient distribution of polyaniline, which exhibits asymmetrical transport characteristics, the deviation between the transport numbers of ions calculated with the use of electrodiffusion coefficients of counter ions and coions and those determined in terms of the extended three-wire model of conduction is shown to increase with the increase in solution concentration but not exceed 4%.

Characterization of acid functional groups of carbon dots by nonlinear regression data fitting of potentiometric titration curves

The oxygenated functional groups present on the surface of carbon dots with an average size of 2.7±0.5nm were characterized by a variety of techniques. In particular, we discussed the fit data of potentiometric titration curves using a nonlinear regression method based on the Levenberg–Marquardt algorithm. The results obtained by statistical treatment of the titration curve data showed that the best fit was obtained considering the presence of five Brønsted–Lowry acids on the surface of the carbon dots with constant ionization characteristics of carboxylic acids, cyclic ester, phenolic and pyrone-like groups. The total number of oxygenated acid groups obtained was 5mmolg−1, with approximately 65% (∼2.9mmolg−1) originating from groups with pKa<6. The methodology showed good reproducibility and stability with standard deviations below 5%. The nature of the groups was independent of small variations in experimental conditions, i.e. the mass of carbon dots titrated and initial concentration of HCl solution. Finally, we believe that the methodology used here, together with other characterization techniques, is a simple, fast and powerful tool to characterize the complex acid–base properties of these so interesting and intriguing nanoparticles.

Melon ( Cucumismelo ) and Groundnut ( Arachishypogaea ) peel extracts as corrosion inhibitors for mild steel in hydrochloric acid solution

The corrosion inhibition of mild steel in 2M hydrochloric acid solution by Melon ( Cucumismelo )(MPE) and Groundnut ( Arachishypohaea ) peel extracts (GPE) at room temperature has been investigated using weight loss method. Inhibition efficiencies of 94.40% and 92.64% for2M HCl concentration was observed for GPE and MPE respectively. Generally, the weight loss of the coupons decreases at different concentrations of HCl solutions while the inhibition efficiencies of the inhibitors (MPE and GPE) increased with increasing inhibitor concentrations. Keywords: Cucumismelo, Arachishypogaea , corrosion, inhibitors

Response surface methodology for optimizing adsorption performance of gel-type weak acid resin for Eu(III)

The conditions relating to enhanced adsorption procedure of earth element europium (Eu) onto gel-type weak acid resin (110-H) in aqueous solution were optimized by means of the response surface methodology (RSM), which proved that 110-H owned satisfactory adsorption capacity (346.85 mg/g) in optimum conditions, belonging to one of the high adsorption capacity materials. Then, the adsorption and desorption behaviors were investigated by batch studies. The adsorption performance showed high agreement with the Lagergren-first-order model and Langmuir isotherm with thermodynamic adsorption parameters of ΔH= 36.1 kJ/mol and ΔS=200 J/(mol-K). Desorption study revealed that 110-H could be effectively eluted by a low concentration of HCl solution (0.1 mol/L) to regenerate and reuse. Finally, the 110-H and Eu(III) loaded 110-H were characterized by IR spectroscopy and scanning electron microscope (SEM) to analyze the mechanism of adsorption, which proved to be chemisorbed.

Fe(III) recovery from HCl solutions using amberlite XAD‐7 resin impregnated with a tetraalkyl phosphonium ionic liquid

AbstractFe(III) is efficiently extracted from concentrated HCl solutions using Amberlite XAD‐7 impregnated with tetraalkyl phosphonium chloride ionic liquid (IL) (synthesis of extractant‐impregnated resin, EIR). The sorption efficiency is controlled by metal speciation and IL loading in the EIR. Sorption isotherms in mono‐component solutions are described by the Langmuir equation, while the extended Langmuir equation perfectly fits sorption isotherms from binary Fe(III)/Zn(II) solutions. The thermodynamic study confirms the endothermic nature of the sorption. Uptake kinetics are fitted by the pseudo‐second order rate equation. While temperature and metal concentration have a relatively limited effect on kinetics, the IL content more significantly affects the mass transfer of Fe(III). Water, sodium sulphate, nitric acid, and sulphuric acid almost completely desorb Fe(III) from loaded EIRs. Resin recycling was tested for eight cycles without significant decrease of the sorption and desorption efficiencies.

Synthesis of a bimodal porous Cu with nanopores on the inner surface of Gasar pores: Influences of preparation conditions

A bimodal porous Cu with regular Gasar micrometer or millimeter pores and random dealloying nanometer pores was fabricated by chemical corrosion of Cu–Zn alloy layers on the inner surface of Gasar Cu pores. In order to accomplish this object, a two-step corrosion method was conducted, including the selective corrosion of Zn element from Cu–Zn alloy layers by NaOH solution, and the removal of the surface oxide obtained in the first step to expose the bottom nanoporous Cu films by HCl solution. Influences of preparation conditions, such as HCl solution concentration and processing time, NaOH solution dealloying time, Gasar pore diameter, and the distance from Gasar pore openings on the microstructure of the resulting nanoporous Cu films were discussed.

Fabricating and Tailoring Polyaniline (PANI) Nanofibers with High Aspect Ratio in a Low-Acid Environment in a Magnetic Field.

In a 0.010 m HCl solution, we successfully transformed irregular polyaniline (PANI) agglomerates into uniform PANI nanofibers with a diameter of 46-145 nm and a characteristic length on the order of several microns by the addition of superparamagnetic Fe3 O4 microspheres in a magnetic field. The PANI morphological evolution showed that the PANI nanofibers stemmed from the PANI coating shell synthesized on the surface of the Fe3 O4 microsphere chains. It was found that the magnetic field could optimize the PANI nanofibers with a narrow diameter size distribution, and effectively suppressed secondary growth. When compared with other microspheres (like silica and polystyrene), only the use of superparamagnetic Fe3 O4 microspheres resulted in the appearance of PANI nanofibers. Attempts to form these high-quality PANI nanofibers in other concentrations of HCl solution were unsuccessful. This deficiency was largely attributed to the inappropriate quantity of aniline cations.

Innovative methodology for comprehensive utilization of saprolite laterite ore: Recovery of metal-doped nickel ferrite and magnesium hydroxide

A new hydrometallurgical process was developed to synthesize metal-doped nickel ferrite (NiFe2O4) and magnesium hydroxide (Mg(OH)2) from saprolite laterite ore. Selective extraction of Ni and Fe with a controlled Fe-to-Ni mole ratio (RFe/Ni) from saprolite laterite ore was investigated. It is shown that the leaching efficiencies of Ni and Fe were approximately 85.0% and 17.0% with an RFe/Ni of 2.6 after hydrothermal leaching at 200°C with a liquid-to-solid ratio of 6:1mL·g−1 and HCl solution concentration of 2mol·L−1. After the leaching process, the hydrothermal coprecipitation method (200°C, 2h) was adopted to separate Ni, Co, Fe, Mn and Al from Mg ions in the leaching solution by controlling the initial pH value of 7.0. Under optimal conditions, metal-doped NiFe2O4 magnetic material with a cubic spinel structure was successfully synthesized directly from the precipitate; meanwhile, Mg(OH)2 (96.8wt.%) was obtained from the filtrate. Moreover, it is estimated that 96.95g of metal-doped NiFe2O4 and 278.6g of Mg(OH)2 could be produced from 1000g of processed saprolite laterite ore.

Cleaning of InGaAs and InP Layers for Nanoelectronics and Photonics Contact Technology Applications

InGaAs and InP layers were treated by using Ar and He direct plasmas coupled with wet chemical treatments. InP surfaces are more sensitive to the various treatments than the InGaAs ones. Suitable and efficient treatments have been proposed to offer a good compromise between impact on surface and native oxide removal. We have demonstrated that concentrated HCl solution cleanings followed by He direct plasma treatment are efficient for the removal of InGaAs native oxides whereas He plasma exposure combined to a diluted HCl solution cleaning is more suitable for InP surfaces.

Separation of platinum(IV) and palladium(II) from concentrated hydrochloric acid solutions by mixtures of amines with neutral extractants

Separation of platinum and palladium from concentrated HCl solutions by extraction with mixture of amines (Aliquat 336/Alamine 336/TOA) and neutral extractants (TBP/TOP/MIBK) have been investigated. The mixture of Aliquat 336 and TBP led to higher Pt(IV) separation factor at 6M HCl solution. McCabe–Thiele diagram for the extraction of Pt by this mixture was constructed. Low concentration of thiourea in the HCl solution resulted in selective stripping of Pd from the loaded organic. Pt solution with 99.9% purity was obtained by extraction and stripping from the solution containing Pd. A process was proposed to separate the two metals.

Improved surface and electrical properties of passivated GaSb with less alkaline sulfide solution

The surface quality of HCl-etched and ammonium sulfide [(NH4)2S]-based treated bulk n-GaSb(100) were compared using x-ray photoelectron spectroscopy (XPS) and TOF-SIMS. It has been found that native oxides present on the GaSb surface are more effectively removed when etched with concentrated HCl solution. With additional [(NH4)2SO4+S] substances or hydrogen ions in the passivation solution, the treated samples displayed significant reduction of native oxides and formation of the sulfides compared with pure (NH4)2S solution. The treated samples also result in a noteworthy improvement in the current–voltage (I–V) characteristics of Au/n-GaSb Schottky contacts, as evidenced by the lower ideality factor (n), higher barrier height (Φb) and higher rectification ratio at ±0.2V. The I–V measurement provided definitive confirmation of XPS and TOF-SIMS results, establishing the need for less alkaline solution for greater passivation stability.

Investigation of trace element contents in edible oils sold in Turkey using microemulsion and emulsion procedures by graphite furnace atomic absorption spectrophotometry

In this study, Pb, Cu, Cr, Ni and Cd in edible oils (sun flower, corn, olive, hazel nut) sold in Turkey were determined by graphite furnace atomic absorption spectrophotometry (GFAAS) after formation of emulsions and microemulsions. In order to prepare the emulsions, 1.0 g of edible oil sample, 1.0 mL of toluene and 0.1 g Triton X-114 were mixed. The mixture was then completed to 10.0 mL with 0.2% HNO3. To prepare microemulsion of edible oil samples, 0.1 mL of concentrated HCl solution and 0.5 g of oil sample were mixed. The total volume of mixture was completed to 10 mL with propan-2-ol. The both emulsions were homogenized in ultrasonic bath for 5 min. The phase separation was not observed at least 1 week at room temperature. Aqueous standards were used for calibration. The limits of detection (LOD) obtained from emulsion and microemulsion were 10.9, 15.3, 24.9, 6.2, 4.2 ng g−1 and 13.4, 16.2, 25.6, 9.1, 6.2 ng g−1 for Pb, Cu, Cr, Ni, Cd, respectively. The analytical parameters such as LOD, sensitivity for emulsion are were better compared to those for microemulsion.

Characterization of two low charge vermiculites after hydrochloric acid treatment

Two natural vermiculites (Ver) with very similar chemical composition but slightly different low charge on the layers were investigated to find an answer the question, how to change their structural and chemical properties after exposure to different concentrations of HCl solutions. Vermiculite from Bulgaria (Ver-B) with the layer charge 0.47 eq/O10(OH)2 and from Brazil (VerSL) with the layer charge 0.36 eq/O10(OH)2 were studied on their particle size fraction less than 40 μm after treatment at different HCl concentrations (0.5 M HCl and 1 M HCl). Both samples represent a mixed-layer structure after incomplete transformation of mica (biotite) to vermiculite. Based on the XRD patterns, Ver-B may be considered as the mixed-layer vermiculite interstratified with small proportion of mica layers and Ver-SL as the mixed-layer micavermiculite. The leaching with 0.5 M HCl increased SA of Ver-B from 29.5 m 2 .g -1 to 261 m 2 .g -1

Pitting and Hydrogen Evolution on Aluminum in Concentrated HCl Solutions

According to the Pourbaix diagram, Al is amphoteric, exhibiting passivity in the mid-pH region and dissolving to form aluminate and Al3+ ions at high and low pH, respectively. This prediction, which is based on thermodynamics, would indicate that pitting corrosion should occur only in neutral solutions because a passive film is required for the establishment of pitting. Furthermore, the pH of pit environments in Al is considered to be on the order of 3. This study investigates the behavior of Al in concentrated HCl solutions, not because it is a material of construction for such environments, but because of the insight it might shed on Al pit stability. Some retained passivity and pit formation can be observed on surfaces of pure Al samples polarized to high potentials in solutions with as much as 4 M HCl. In very concentrated HCl solutions, the surface is roughened, with more attack at grain boundaries, but no evidence of pitting. The rate of hydrogen evolution (HE), which has previously been observed to occur to about 20% of the total anodic current density in pits formed in neutral solutions, was measured during anodic polarization. Similar to the situation found on anodically polarized Mg, the rate of HE increases with increasing applied anodic current density. However, unlike Mg, a prepolarized Al surface does not exhibit enhanced cathodic reactivity during a subsequent cathodic polarization measurement. The implications of these observations on the Al pitting mechanism will be addressed.

Cleaning of InGaAs and InP Layers for Nanoelectronics and Photonics Contact Technology Applications

In the context of III-V contact technology for nanoelectronic and photonic applications and for a sake of reducing parasitic resistances between metal and source / drain regions, very cleaned and native oxide free surfaces must be provided prior to metal deposition. In order to meet the requirements set out in the ITRS roadmap and to propose a contact technology on III-V compounds compatible with the Si CMOS technology, we assume that the cleaning of S/D regions should involve a two-step procedure where a wet cleaning treatment is coupled with an in situ plasma exposure (e.g. a plasma treatment realised, without air break, in the same equipment as the metal deposition). If wet chemical cleanings of InGaAs and InP surfaces have already been reported in literature, in situ treatments have not been extensively considered. In this work, we studied the pretreatment of InGaAs and InP layers by employing Ar- and He-based direct plasmas and NH3, H2, NF3/NH3 remote plasmas carried out in a 300 mm platform usually dedicated to silicide process and fully compatible with the Si CMOS technology. Moreover, the combination of wet chemical treatments followed by in situ plasma treatments have been investigated. The characterisation of cleaning efficiency has been performed on the CEA Minatec Nanocharacterisation Platform (PFNC) using several surface analyses like X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy in attenuated total reflection mode (FTIR-ATR). FTIR-ATR results coupled with XPS analyses highlighted that Ar- and He-based direct plasmas were efficient for the removal of InGaAs native oxides whereas all the remote plasmas involved were inadequate to remove the III-V oxides. Moreover, for NF3/NH3 exposed samples, we noticed the addition of undesirable In-F and Ga-F bonds. Regarding Ar and He direct plasmas, investigations exhibited that both seem to be efficient for removing arsenic oxides whereas the elimination of indium and gallium oxides is more effective with Ar plasma. We also studied the addition of hydrogen into He direct plasma and, unexpectedly, we demonstrated that increasing the H2 content leads to a decrease in the removal of arsenic oxides. This trend could be correlated with the increase of pressure induced by hydrogen addition. On the other hand, the impact on indium and gallium oxides is not notable (i.e. the removal of group III oxides is nor enhanced, nor reduced) but we observed a reducing effect of hydrogen on indium and the emergence of In-In type bonds. Then, the combination of wet chemical treatment with in situ plasma was studied. We highlighted that the wet chemical treatment of InGaAs layers in concentrated HCl solutions is beneficial for reducing the oxide component of indium and gallium. Moreover, using a wet cleaning appears to modify the InGaAs layers behaviour towards plasma treatment. Indeed, He direct plasmas provide the best results for reducing As and In oxides whereas Ar plasmas are more convenient for eliminating Ga oxides. Finally, whatever the plasma pretreatment, no degradation of surface morphology and roughness was observed by AFM. The RMS values obtained after surface treatments are similar with the ones acquired for the reference samples. InP surfaces appear to be more sensitive to air re-oxidation than InGaAs layers. For indium phosphide material, we showed that the surface was very sensitive to the direct plasma treatments. Indeed, AFM studies highlighted that the use of Ar-based plasma drastically impacts the surface morphology and its roughness. This impact on surface morphology is correlated with the increase of In-In bonds at the surface of InP layers (e.g. a phosphorus depletion occurred at the InP surface). On the other hand, He plasmas appear to be less invasive for the surface. We also noticed that, if concentrated HCl solutions (e.g. > 4 M) were efficient for reducing InP oxides, they lead to a significant modification of the surface morphology and the appearance of boat-like shape of the etch pits. Reducing the HCl concentration allows removing the P and In oxides without damaging the surface. Finally, wet chemical cleaning followed by in situ treatments showed that He direct plasma exhibits the best compromise in terms of surface impact and oxide removal. We have investigated the impact of various plasma treatments on InGaAs and InP layers. Wet chemical cleaning in concentrated HCl solutions followed by argon or helium direct plasmas is efficient to remove InGaAs native oxides. InP surfaces are more sensitive to plasma treatment than the InGaAs ones but He direct plasma preceding by diluted HCl solution cleaning appears to offer a good compromise between surface deterioration and oxide removal.

Synthesis and Characterization of Nanoporous SnO2 Thin Film

SnO2 is a kind of typical n-type semiconductor material. Due to its excellent performance in conductivity, optics, thermal stability and corrosion resisting, it has been widely applied in fields of gas sensor, solar cell, chemical electrode materials. A novel synthesis route, originated from dealloying of Sn-Zn alloys films in hydrochloric acid (HCl) solution and then thermal treating, has been developed for the preparation of SnO2 films with three-demensional (3D) nanoporous. The influences of the HCl solution concentration and immersion time on crystal structure and morphology have been investigated. Porous structure and fracture surface morphology of the samples were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results indicated that the corrosion weight loss of Zn increased with the increasing of immersion time in HCl solution。An average pore diameter of the porous SnO2 films is 50~200nm after heat treatment at 500°C for 2 hours. XRD patterns show that the films are SnO2 with rutile structure.