Applied Surface Science (v.383, #C)
Editorial Board (ii).
Atomic layer deposition of indium oxide thin film from a liquid indium complex containing 1-dimethylamino-2-methyl-2-propoxy ligands by Jeong Hwan Han; Eun Ae Jung; Hyo Yeon Kim; Da Hye Kim; Bo Keun Park; Jin-Seong Park; Seung Uk Son; Taek-Mo Chung (1-8).
Display OmittedIn2O3 thin films were grown from a newly developed, liquid, homoleptic, In-based complex, tris(1-dimethylamino-2-methyl-2-propoxy)indium [In(dmamp)3], and O3 by atomic layer deposition (ALD) at growth temperatures of 150–200 °C. In(dmamp)3 exhibited single-step evaporation with negligible residue and excellent thermal stability between 30 and 250 °C. The self-limiting surface reaction of In2O3 during ALD was demonstrated by varying the In(dmamp)3 and O3 pulse lengths, with a growth rate of 0.027 nm/cycle achieved at 200 °C. The In2O3 films grown at temperatures over 175 °C exhibited negligible concentrations of impurities, whereas that grown below 175 °C had concentrations of residual C of 6–8 at.%. Glancing angle X-ray diffraction revealed that the In2O3 films were polycrystalline in nature when the deposition temperature was greater than 200 °C. The In2O3 films grown at 150–200 °C exhibited carrier concentrations of 1.5 × 1018–6.6 × 1019 cm−3, resistivities of 15.1–2 × 10−3 Ω cm, and Hall mobilities of 0.8–42 cm2/(V s).
Keywords: Novel In precursor; Atomic layer deposition; Indium oxide; Thin film;
Microwave absorption properties of polypyrrole-SrFe12O19-TiO2-epoxy resin nanocomposites: Optimization using response surface methodology by M.S. Seyed Dorraji; M.H. Rasoulifard; A.R. Amani-Ghadim; M.H. Khodabandeloo; M. Felekari; M.R. Khoshrou; I. hajimiri (9-18).
Display OmittedAt a few works are discussed about formation of heterogeneous composites with different distribution of particle shape and size that are used for electromagnetic absorption purposes. In this study a novel heterogeneous nanocpmposites is investigated. The nanocomposite has been successfully prepared based on epoxy resin including various nano-metal oxides (TiO2, SrFe12O19) and polypyrrole (PPy) by sol-gel and the solution chemistry method, respectively. The performance of prepared nanocomposite in absorption of microwave in X-band range was investigated and transmission line method by X-band waveguide straight was used to measure EM parameters of nanocomposites. The Response surface methodology (RSM) with central composite design (CCD) was utilized to study the effects of the wt.% TiO2 in SrFe12O19, wt.% Tio2-SrFe12O19 in PPy and wt.% TiO2-SrFe12O19-PPy in epoxy resin, on the microwave absorption properties with the absorber thickness of only 2 mm. The proposed quadratic model was in accordance with the experimental results with correlation coefficient of 96.5%. The optimum condition for maximum microwave absorption efficiency were wt.% TiO2 in SrFe12O19 of 70, wt.% TiO2-SrFe12O19 in PPy of 10 and wt.% TiO2-SrFe12O19-PPy in epoxy of 25. The sample prepared in optimal conditions indicated reflection loss of −15 dB corresponding to 97% absorption, at the range of 9.2–10.8 GHz.
Keywords: Radar wave absorption; Organic-inorganic composite; Dielectric; Reflection loss;
Native oxides formation and surface wettability of epitaxial III–V materials: The case of InP and GaAs by A. Gocalinska; S. Rubini; E. Pelucchi (19-27).
The time dependent transition from hydrophobic to hydrophilic states of the metalorganic vapour phase epitaxy (MOVPE) grown InP, GaAs and InAs is systematically documented by contact angle measurements. Natural oxides forming on the surfaces of air-exposed materials, as well as the results of some typical wet chemical process to remove those oxides, were studied by X-ray photoemission spectroscopy (XPS), revealing, surprisingly, a fundamental lack of strong correlations between the surface oxide composition and the reported systematic changes in hydrophobicity.
Keywords: Hydrophobic surface; InP; GaAs; XPS; MOVPE;
Growth of graphene on Cu foils by microwave plasma chemical vapor deposition: The effect of in-situ hydrogen plasma post-treatment by Liping Fang; Wen Yuan; Bing Wang; Ying Xiong (28-32).
Display OmittedMicrowave plasma chemical vapor deposition (MPCVD) is a promising method for the large-scale production of high-quality graphene. The aim of this work is to investigate the effect of in-situ hydrogen plasma post-treatment on the MPCVD-grown graphene films. By simply varying the duration time of in-situ hydrogen plasma, surface morphology, number of layers and defect density of as-grown graphene films can be manipulated. The role of hydrogen plasma can be proposed from our observations, promoting to further grow graphene films in the early stage and consequently acting as an etching agent to thin graphene films in the later stage. On the basis of above mechanism, monolayer graphene films with low defect density and smooth surface can be grown by adjusting the times of the growing step and the plasma post-treatment step. This additional in-situ hydrogen plasma post-treatment may be significant for growing well-defined graphene films with controllable defects and number of layers.
Keywords: Graphene; Microwave plasma chemical vapor deposition; Hydrogen plasma; Raman spectrum; Monolayer;
Superhydrophobic perfluoropolymer/polystyrene blend films induced by nonsolvent by Nevin Atalay Gengec; Ugur Cengiz; H.Yildirim Erbil (33-41).
Display OmittedStatistical copolymers of perfluoroalkyl ethyl acrylate (Zonyl-TAN) and methyl methacrylate (MMA) were synthesized in a CO2 polymerization system where a CO2-expanded monomer mixture was formed at 13 MPa, and 80 °C by using AIBN as initiator. Flat and superhydrophobic surfaces were subsequently prepared on glass slides by applying a phase separation process where the synthesized p(TAN-co-MMA) copolymer and polystyrene (PS) were dissolved in THF solvent. Ethanol was added as the non-solvent to introduce superhydrophobicity during film formation. Water contact angle on the flat p(TAN-co-MMA) copolymer was 118° and increased up to 170° with the formation of surface roughness. The ratio of the ethanol non-solvent in the blend solution has an important effect on the magnitude of surface roughness during the phase separation process. Both pits and protrusions of 1–10 μm in size were formed on the surface when non-solvent was used. Surface roughness increased with the increase in the ethanol ratio and the PS content of the blend solution.
Keywords: Superhydrophobic surface; Perfluoroalkyl ethyl acrylate; CO2 polymerization; Polystyrene; Phase-separation; Contact angle;
Storage capacity and oxygen mobility in mixed oxides from transition metals promoted by cerium by Camilo Perdomo; Alejandro Pérez; Rafael Molina; Sonia Moreno (42-48).
Display OmittedThe oxygen mobility and storage capacity of Ce-Co/Cu-MgAl or Ce–MgAl mixed oxides, obtained by hydrotalcite precursors, were evaluated using Toluene-temperature-programmed-reaction, 18O2 isotopic exchange and O2-H2 titration. The presence of oxygen vacancies-related species was evaluated by means of Electron Paramagnetic Resonance. A correlation was found between the studied properties and the catalytic activity of the oxides in total oxidation processes. It was evidenced that catalytic activity depends on two related processes: the facility with which the solid can be reduced and its ability to regenerate itself in the presence of molecular oxygen in the gas phase. These processes are enhanced by Cu-Co cooperative effect in the mixed oxides. Additionally, the incorporation of Ce in the Co-Cu catalysts improved their oxygen transport properties.
Keywords: Mixed oxides; Cooperative effect; Oxygen vacancies; OSC; Isotopic exchange;
Electrochromic properties and performance of NiOx films and their corresponding all-thin-film flexible devices preparedby reactive DC magnetron sputtering by Dongmei Dong; Wenwen Wang; Guobo Dong; Fan Zhang; Yingchun He; Hang Yu; Famin Liu; Mei Wang; Xungang Diao (49-56).
Display OmittedNickel oxide (NiOx) thin films were deposited by direct current magnetron sputtering technique onto flexible substrates with various oxygen (O2) partial pressures. The influence of O2 contents during deposition process on film structure, morphology, composition, optical and electrochromic (EC) characteristics of the films were investigated. The EC response for nonstoichiometric NiOx films shows a strong dependence on grain size variations and surface morphology. Finally, the multiple-layer stacks ITO/NiOx/Ta2O5:H/WO3/ITO were sequentially vacuum deposited over flexible polyethylene terephthalate plates based on the optimization of NiOx single layers. A large optical contrast up to 60% and a good durability are obtained for full device. To perform preliminary research on the mechanical properties within flexible devices, we introduced nontrivial changes to the interfacial properties by replacing the glass with flexible polymers. The effects were studied through static bending and the nano-scratch test.
Keywords: NiOx films; Flexible; Electrochromic device; Magnetron sputtering;
Synthesis of mesoporous niobium nitride nanobelt arrays and their capacitive properties by Biao Gao; Xiang Xiao; Jianjun Su; Xuming Zhang; Xiang Peng; Jijiang Fu; Paul K. Chu (57-63).
Mesoporous niobium nitride nanobelt arrays (Nb4N5 NBAs) are fabricated directly on Nb foils by a hydrothermal reaction in KOH, protonation treatment in HNO3, and calcination in an NH3 ambient. The morphology, composition and pore structure of the Nb4N5 NBAs are characterized in details. In addition, the mesoporous Nb4N5 NBAs electrode has good specific capacitance (37.4 mF cm−2, or 124 F g−1) and delivers excellent rate performance due to the high porosity and good electron conductivity boding well for application to next-generation energy storage systems.
Keywords: Niobium nitride; Nanobelt arrays; Hydrothermal reaction; Mesoporous; Supercapacitor;
New kinetic insight into the spontaneous oxidation process of lithium in air by EPMA by Manuel Otero; German Lener; Jorge Trincavelli; Daniel Barraco; Marcelo Sandro Nazzarro; Octavio Furlong; Ezequiel Pedro Marcos Leiva (64-70).
The exposure of metallic lithium to ambient air produces a fast corrosion reaction of the surface that continues to the bulk of the material. This spontaneous process was explored by means of X-ray Photoelectron Spectroscopy (XPS) and Electron Probe Micro-Analysis (EPMA). The combination of these techniques and Monte Carlo simulations allowed observing the formation of a film of lithium hydroxide (LiOH) and studying the growth within the material during the first 300 s. The corrosion is mainly due to the reaction of lithium with water and the diffusion of water through the growing LiOH film is the rate determining step. On the basis of a kinetic analysis we studied the mechanism of reaction and inferred a diffusion coefficient of D = (5.1 ± 0.4) × 10−12 cm2/s in agreement with results from the literature obtained using different techniques.
Keywords: Lithium corrosion; Electron Probe Micro-Analysis; Oxide growth kinetics;
Organic adlayer on inorganic materials: XPS analysis selectivity to cope with adventitious contamination by Jessem Landoulsi; Michel J. Genet; Sandrine Fleith; Yetioman Touré; Irma Liascukiene; Christophe Méthivier; Paul G. Rouxhet (71-83).
Display OmittedThis work addresses the ubiquitous presence of organic contaminants at inorganic solid surfaces and the improvement of XPS analysis selectivity to cope with it. Water contact angle measurements showed that the adsorption of organic contaminants occurs readily in ambient air, and faster and more extensively under high vacuum. It is stronger on stainless steel (SS) compared to silica and is significantly reduced when SS is sterilized by autoclaving. The reliability of XPS data was evaluated (selectivity, precision, accuracy) by correlations between spectral data incorporating a large amount of results obtained with different XPS spectrometers on SS and glass samples cleaned in different ways and conditioned with several biomacromolecules. The methodology used allows a discrimination to be made between contaminants and deliberately adsorbed biomacromolecules, and offers perspectives for tracking the source of contamination. Furthermore, a discrimination can be made between oxygen from the organic adlayer and oxygen from the substrate, and the O 1s component above 532.0 eV observed for SS is shown to be due to organic contaminants rather than adsorbed water. This approach offers new perspectives to examine the interactions (displacement or not) between contaminants and compounds of interest, e.g. proteins, at the stage of the adsorption process.
Keywords: Organic contamination; XPS; Stainless steel; Passive film; Sterilization; Silica;
Improved field emission from indium decorated multi-walled carbon nanotubes by M. Sreekanth; S. Ghosh; P. Biswas; S. Kumar; P. Srivastava (84-89).
Improved field emission properties have been achieved for Indium (In) decorated MWCNTs and are shown using the schematic of field emission set up with In/CNT cathode, and a plot of J-E characteristics for pristine and In decorated CNTs.Display OmittedMulti-walled carbon nanotube (MWCNT) films were grown using thermal chemical vapor deposition (T-CVD) process and were decorated with indium metal particles by thermal evaporation technique. The In metal particles are found to get oxidized. The In decorated films show 250% enhancement in the FE current density, lower turn-on and threshold fields, and better temporal stability as compared to their undecorated counterpart. This improvement in field emission properties is primarily attributed to increased density of states near the Fermi level. The presence of O 2p states along with a small contribution from In 5s states results in the enhancement of density of states in the vicinity of the Fermi level.
Keywords: Multi-walled carbon nanotubes; Thermal CVD; Field emission; Enhancement factor; Temporal stability; Electron tunneling; Density of states;
Fabrication of Cu2ZnSn(SxSe1 − x)4 solar cells by ethanol-ammonium solution process by Cong Xue; Jianmin Li; Yaguang Wang; Guoshun Jiang; Liu Weifeng; Changfei Zhu (90-97).
Display OmittedIn this paper, Cu2ZnSn(SxSe1 − x)4 precursor films were produced by doctor blade process from SnS-Cu2O-ZnS slurry. To prepare the slurry, SnS, ZnS and Cu2O precipitates, which are outgrowths of stacked layer ZnS/Cu/SnS by CBD (chemical bath deposition)-annealing route, were dissolved in the mixture solvent of ethanol and NH3·H2O. Synthesized precursor films were then annealed at different conditions. The post-annealed films were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman measurements and UV–vis–NIR spectroscopy. SEM studies reveal that the rough and relatively compact absorber thin films are obtained via the sulfidation and sulfidation-selenization processes. X-ray diffraction and Raman spectrum results verify that the obtained films are composed of Cu2ZnSnS4 and Cu2ZnSnSe4 phases, which have high absorbance in visible range and direct band gap energy of 1.01–1.47 eV. The best devices yield total area power conversion efficiency of 1.99% and 2.95% corresponding to Cu2ZnSnS4 and Cu2ZnSn(SxSe1 − x)4 thin film solar cells under AM1.5 illumination without any anti-reflection layer.
Keywords: Cu2ZnSn(SxSe1 − x)4 thin film; Solar cell; Precipitate; Doctor blade;
The adsorption of CO and NO on the MoS2 monolayer doped with Au, Pt, Pd, or Ni: A first-principles study by Dongwei Ma; Weiwei Ju; Tingxian Li; Xiwei Zhang; Chaozheng He; Benyuan Ma; Zhansheng Lu; Zongxian Yang (98-105).
The MoS2 monolayers doped with Au, Pt, Pd, or Ni show enhanced adsorption and sensitivity toward CO or NO molecule.Display OmittedBy performing the first-principles calculation, the adsorption of CO and NO molecules on the Au, Pt, Pd, or Ni doped MoS2 monolayer has been studied. The interaction between CO or NO with the doped MoS2 monolayer is strong and belongs to the chemisorption, as evidenced by the large adsorption energy and the short distance between the adsorbed molecules and the dopants. The charge transfer and the electronic property induced by the molecule adsorption are discussed. It is found that for both CO and NO adsorption, for all the cases charge transfer between the substrates and the adsorbed molecules has been observed. For NO, the adsorption obviously induces new impurity states in the band gap or the redistribution of the original impurity states. These can lead to the change of the transport properties of the doped MoS2 monolayer, by which the adsorbed CO or NO can be detected. The present work shows that introducing appropriate dopants may be a feasible method to improve the performance of MoS2-based gas sensors.
Keywords: First-principles calculation; CO and NO; Adsorption; Doping; MoS2 monolayer;
Resistance to He2+ irradiation damage in metallic glass Ta38Ni62 by Wenjing Hou; Xianxiu Mei; Xiaonan Zhang; Yingmin Wang; Jianbing Qiang; Jianrong Sun; Younian Wang (106-112).
Metallic glass Ta38Ni62 strips, metallic W, and V87.5Cr4.17Ti4.17Nb4.17 alloy were irradiated using a 500 keV He2+ ion beam at different fluence to compare the metallic glass resistance to irradiation. Metallic glass Ta38Ni62 remained amorphous at different He2+ irradiation fluence. Transmission electron microscopy analysis revealed the presence of helium bubbles at the end of the range of helium ions in the metallic glass. No significant damage resulted in the metallic glass surface, and the root mean square roughness increased nonlinearly with the increase in fluence. At 1 × 1018 ions/cm2, metallic W appeared in larger sunken areas on the surface and V87.5Cr4.17Ti4.17Nb4.17 alloy experienced multi-layer flaking. The metallic glass Ta38Ni62 resistance to He2+ ion beam irradiation was better than that of metallic W, and that of the V87.5Cr4.17Ti4.17Nb4.17 alloy was the poorest.
Keywords: He2+ irradiation; Metallic glass Ta38Ni62; Helium bubbles;
Attestation in self-propagating combustion approach of spinel AFe2O4 (A = Co, Mg and Mn) complexes bearing mixed oxidation states: Magnetostructural properties by J. Bennet; R. Tholkappiyan; K. Vishista; N. Victor Jaya; Fathalla Hamed (113-125).
Display OmittedSpinel type nano-sized ferrite compounds AFe2O4 (A = Co, Mg and Mn) have been successfully prepared by self-propagating combustion method using glycine as fuel at 400 °C under air atmosphere for 4 h. The crystal structure, chemical composition, morphology and magnetic properties of the synthesized samples were characterized by X−ray diffraction, Fourier transform infrared spectroscopy, X−ray photoelectron spectroscopy, Energy dispersive X−ray, Scanning and Transmission electron microscopy and vibrating sample magnetometer. The chemical reaction and role of fuel on the nanoparticles formation were discussed. The XRD pattern of the synthesized samples shows the formation of pure phase with average crystallite size of 97, 57 and 98 nm from Scherrer formula and 86, 54 and 87 nm from Williamson and Hall (W–H) formula respectively. FTIR absorption spectra revealed that the presence of strong absorption peaks near 400–600 cm−1 corresponds to tetrahedral and octahedral complex of spinel ferrites. The relative concentrations of electronic states of elements such as cobalt (Co2+ and Co3+), iron (Fe2+ and Fe3+) and manganese (Mn2+ and Mn3+) oxidation states were studied from XPS and it is found that 55% of Fe ions are in Fe2+ state and the remaining is in Fe3+ state and thus the cationic distribution of Fe ions occurred in both tetrahedral and octahedral sites. SEM analysis indicates the presence of pore like morphology which is nearly homogenous because of combustion process. EDS analysis confirms the presence of elements in the ferrite samples. By replacing the active ‘A’ site cations in AFe2O4 (A = Co, Mg and Mn) samples show the different magnetic properties. The parameters like saturation magnetization, coercivity and remnant magnetization obtained from M−H loops are studied in room temperature.
Keywords: Ferrite nanoparticles; Self-propagating combustion method; X−ray photoelectron spectroscopy; X−ray diffraction; Magnetic property;
Preparation, characterization, and activity of α-Ti(HPO4)2 supported metallocene catalysts by Yasai Shi; Yuan Yuan; Qinghong Xu; Jianjun Yi (126-132).
Display OmittedA series of heterogeneous catalysts by loading metallocenes on surface of α-Ti(HPO4)2, a kind of solid acid, has been synthesized. Polymerization of alkenes, including ethylene and propylene, based on participation of the heterogeneous catalysts were studied and the results were compared to metallocenes supported on silica gel, α-Zr(HPO4)2 and clay. Higher catalytic activity, larger polymer molecular weight and narrow distribution of polymer molecular weight were obtained. Acidic strength of the support and its influence to metallocenes were studied to discover intrinsic factors in the polymerizations.
Keywords: Support; Metallocene catalysts; α-Ti(HPO4)2; Acid sites; Alkenes polymerizations;
The applications of populus fiber in removal of Cr(VI) from aqueous solution by Miaomiao Li; Yumei Gong; Aichao Lyu; Yuanfa Liu; Hong Zhang (133-141).
Display OmittedThe surface modification of natural materials to be applied in removal of Cr(VI) from aqueous solutions has attracted much attention. A natural sorbent for Cr(VI) based on natural populus fibers (PF) is prepared by transforming the cyano groups (AN) in polyacrylonitriles (PAN) grafted from PF into amidoxime groups (AO), which has strong ability to attract and chelate heavy metal ions. The prepared sorbent is characterized by Fourier Transform Infrared Spectra (FT-IR), thermogravimetric analysis (TGA), solid-state nuclear magnetic resonance (13C NMR) and scanning electron microscope (SEM). As potassium dichromate solution (K2Cr2O7) is used as a target solution for detecting adsorption capacity of the sorbent, the adsorption kinetics of the sorbent for chromiun is consistent with the pseudo-second-order kinetic model by analyzing the adsorption amount as a function of the sorbent dispersed duration in solution at pH = 2. The expected adsorption mechanism is that the Cr(VI) in anionic ions Cr2O7 2− and HCrO4 − are adsorbed through electrostatic attraction but when Cr(VI) is reduced to Cr(III) by AO, the electronegative nitrogen and oxygen in AO chelate it through coordination bond. The as-prepared PF derivant with high adsorption efficiency of chromium 180.5 mg/g (3.47 mmol/g), low cost, reusability and greenly preparation process suggests that the development of natural PF as a sorbent in removal of Cr(VI) from aqueous solutions is a destined significant approach.
Keywords: Populus fibers; Surface modification; Amidoxime; Chromium sorbent;
Role of surface chemistry in modified ACF (activated carbon fiber)-catalyzed peroxymonosulfate oxidation by Shiying Yang; Lei Li; Tuo Xiao; Di Zheng; Yitao Zhang (142-150).
Display OmittedA commercial activated carbon fiber (ACF-0) was modified by three different methods: nitration treatment (ACF-N), heat treatment (ACF-H) and heat treatment after nitration (ACF-NH), and the effects of textural and chemical properties on the ability of the metal-free ACF-catalyzed peroxymonosulfate (PMS) oxidation of Reactive Black 5 (RB5), an azo dye being difficultly adsorbed onto ACF, in aqueous solution were investigated in this work. Surface density of functional groups, surface area changes, surface morphology and the chemical state inside ACF samples were characterized by Boehm titration, N2 adsorption, scanning electron microscopy in couple with energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS), respectively. XPS spectra deconvolution was applied to figure out the importance of surface nitrogen-containing function groups. We found that π-π, pyridine and amine have promoting effect on the catalytic oxidation while the −NO2 has inhibitory effect on the ACF/PMS systems for RB5 destroy. Sustainability and renewability of the typical ACF-NH for catalytic oxidation of RB5 were also discussed in detail. Information about our conclusions are useful to control and improve the performance of ACF-catalyzed PMS oxidation for organic pollutants in wastewater treatment.
Keywords: Activated carbon fiber; Surface modification; XPS spectra deconvolution; Catalytic peroxymonosulfate oxidation; Nitrogen-containing functional groups;
Electronic and magnetic properties of 1T-HfS2 by doping transition-metal atoms by Xu Zhao; Tianxing Wang; Guangtao Wang; Xianqi Dai; Congxin Xia; Lin Yang (151-158).
Display OmittedWe explored the electronic and magnetic properties of 1T-HfS2 doped by transition metal (TM) atom using the first-principles calculation. We doped the transition metal atoms from the IIIB to VIB groups in nonmagnetic 1T-HfS2. Numerical results show that the pristine 1T-HfS2 is a semiconductor with indirect gaps of 1.250 eV. Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. The polarized charges mainly arise from the localized 3d electrons of the TM atom. The strong p–d hybridization was found between the 3d orbitals of TM and 3p orbitals of S. The substituted 1T-HfS2 can be a metal, semiconductor or half-metal. Analysis of the band structure and magnetic properties indicates that TM-doped HfS2 (TM = V, Fe, Cu) are promising systems to explore two-dimensional diluted magnetic semiconductors. The formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate transition metal atom into the HfS2 under S-rich experimental conditions. In contrast, V-doped HfS2 has relatively wide half-metallic gap and low formation energy. So V-doped 1T-HfS2 is ideal for spin injection, which is important for application in semiconductor spintronics.
Keywords: 2D monolayers; Diluted magnetic semiconductors; Electronic band structure; Half-metallic;
Facile synthesis of Co3O4 hierarchical microspheres with improved lithium storage performances by Xiaojuan Hou; Jian He; Kun An; Jiliang Mu; Xiujian Chou; Chenyang Xue (159-164).
Display OmittedPorous nanosheets-assembled Co3O4 microspheres have been first successfully fabricated by a facile solvothermal method without any surfactant followed by a relatively low annealing temperature (400 °C) with a higher specific surface area compared to the annealing temperature of 600 °C. The nanosheets-assembled microspheres exhibit a high discharge capacity of 1000 mA h g−1 at a current density of 100 mA g−1 after 50 cycles and 850 mA h g−1 at a current density of 500 mA g−1 after 80 cycles, even at a high current density of 1.6 A g−1 the cycling reversible capacity can still keep 750 mA h g−1, the representative capacities are relatively higher than most of reports about pure Co3O4. We attribute the excellent electrochemical performances to the porous nanosheets structure and architectures, which can provide more effective electrode/electrolyte contact area and direct ion transmission path, then lead to faster lithium-ion diffusion, confirmed by EIS measurements. The high specific capacity, excellent cycling and rate performances demonstrate that the porous nanosheets assembled microspheres present promising application in lithium storage.
Keywords: Co3O4; Microspheres; Lithium-ion batteries; Electrochemical performances;
Polyaniline hybridized surface defective ZnO nanorods with long-term stable photoelectrochemical activity by Susanta Bera; Hasmat Khan; Indranil Biswas; Sunirmal Jana (165-176).
Display OmittedWe report surfactant/template free precursor solution based synthesis of polyaniline (PANI) hybridized surface defective ZnO nanorods by a two-step process. Initially, ZnO nanorods have been prepared at 95 °C, followed by hybridization (coating) of PANI onto the ZnO via in situ polymerization of aniline monomer, forming ZnO-PANI nanohybrid (ZP). The structural properties of ZP have been analyzed by X-ray diffraction (XRD) and transmission electron microscopic (TEM) studies. The presence of surface defects especially the oxygen vacancies in ZnO has been characterized by photoluminescence emission, high resolution TEM, X-ray photoelectron spectroscopy (XPS) and micro-Raman spectral measurements. The chemical interaction of PANI with ZnO has been examined by Fourier transform infrared (FTIR) and XPS analyses. A significant enhancement in visible absorption of ZP sample is found as evidenced from UV–vis diffused reflectance spectral study. BET nitrogen adsorption-desorption isotherm shows an improved textural property (pore size, pore volume) of ZP. Moreover, a long-term stable photoelectrochemical activity (PEC) of ZP is found compare to pristine ZnO. The synergic effect of PANI hybridization and the presence of surface defects in ZnO NRs can enhance the PEC by prolonging the recombination rate of photogenerated charge carriers. The effect can also provide large number of active sites to make electrolyte diffusion and mass transportation easier in the nanohybrid. This simple synthesis strategy can be adopted for PANI hybridization with different metal oxide semiconductors towards enhancing PEC activity of the hybrid materials.
Keywords: Low temperature solution method; ZnO nanorods; Polyaniline; Surface defects; Photoelectrochemical activity;
Intelligent saline enabled self-healing of multilayer coatings and its optimization to achieve redox catalytically provoked anti-corrosion ability by Junaid Ali Syed; Shaochun Tang; Xiangkang Meng (177-190).
Display OmittedTo obtain a coating with both self-healing and redox catalytic ability to protect a metal substrate from corrosion under aggressive environment is strongly desired. Herein, we report the design and fabrication of intelligent polyaniline-polyacrylic acid/polyethyleneimine (PANI-PAA/PEI) multilayer composite coatings by spin assembly. The main influencing factors, including solution concentration (c) and disk rotating speed (ω) were studied in order to gain excellent performance. The resulting multilayer coatings with thickness in a range from 0.47 to 2.94 μm can heal severe structural damages and sustain a superior anti-corrosive performance for 120 h in 3.5% NaCl. The PANI-PAA layer enhances the anti-corrosion property and PEI layer contributes to the self-healing ability as well as their multilayer combination strengthens them. The improved self-healing ability is attributed to the rearrangement and reversible non-covalent interactions of the PANI-PAA and PEI layers that facilitates electrostatic repairing.
Keywords: Polyaniline; Composites; Multilayers; Self-healing; Anti-corrosion;
Effect of ZDDP concentration on the thermal film formation on steel, hydrogenated non-doped and Si-doped DLC by S. Akbari; J. Kovač; M. Kalin (191-199).
This work focuses on the ZDDP concentration (1, 5 and 20 wt%) to form a ZDDP film on surfaces during static thermal tests at 150 °C. Silicon-doped and hydrogenated DLC coatings, as well as steel as reference, were studied using Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The results show that, on the three surfaces, the structure of the ZDDP thermal film consists of identical groups of pyrophosphate and zinc oxide, while the sulphuric groups are dissimilar. On the steel surface, the sulphuric part consists of a mixture of organic sulphide and sulphohydryl groups, but on H-DLC and Si-DLC only organic sulphide groups are found; there are no sulphohydryl groups. Moreover, both ATR-FTIR and XPS show that different concentrations of ZDDP do not affect the final chemical structure of the ZDDP thermal film on any of the studied surfaces. In addition, the XPS results show that the thickness of the thermal film is linear with the concentration for the whole range from 1 to 20 wt%, supporting also its uniform chemical structure. These thicknesses further show that the reactivity of the ZDDP film is higher on the steel surface than on the DLC coatings.
Keywords: Zinc dialkyl dithiophosphosphate; Diamond-like carbon coating; Attenuated total reflection-Fourier transform infrared spectroscopy; X-ray photoelectron spectroscopy;
Synthesis of layered double hydroxides containing Mg2+, Zn2+, Ca2+ and Al3+ layer cations by co-precipitation methods—A review by Frederick L. Theiss; Godwin A. Ayoko; Ray L. Frost (200-213).
Display OmittedA flow chart for a simple co-precipitation at variable pH synthesis. Ageing, collection and washing steps have been omitted for clarity.Co-precipitation is a common method for the preparation of layered double hydroxides (LDHs) and related materials. This review article is aimed at providing newcomers to the field with some examples of the types of co-precipitation reactions that have been reported previously and to briefly investigate some of the properties of the products of these reactions. Due to the sheer volume of literature on the subject, the authors have had to limit this article to the synthesis of Mg/Al, Zn/Al and Ca/Al LDHs by co-precipitation and directly related methods. LDHs have been synthesised from various reagents including metal salts, oxides and hydroxides. Co-precipitation is also useful for the direct synthesis of LDHs with a wide range of interlayer anions and various bases have been successfully employed to prepare LDHs. Examples of other synthesis techniques including the urea method, hydrothermal synthesis and various mechanochemical methods that are undoubtedly related to co-precipitation have also been included in this review. The effect of post synthesis hydrothermal has also been summarised.
Keywords: Layered double hydroxide; Hydrotalcite; Synthesis; Co-precipitation; Magnesium; Zinc; Calcium; Aluminium;
Synthesis and visible-light-driven photocatalytic activity of p–n heterojunction Ag2O/NaTaO3 nanocubes by Songbo Yang; Dongbo Xu; Biyi Chen; Bifu Luo; Xu Yan; Lisong Xiao; Weidong Shi (214-221).
Display OmittedThe constructing of p–n heterojunction photocatalytic system has received much attention in environmental purification and hydrogen generation from water. In this study, an efficient visible-light-driven p–n heterojunction Ag2O/NaTaO3 was successfully prepared by chemical precipitation method at room temperature. It showed an enhanced photocatalytic activity for the degradation of rhodamine B (RhB) under visible-light irradiation, much higher than those of either individual Ag2O or NaTaO3. The reactive species scavenger results indicated the superoxide anion radicals (•O2−) played key roles in RhB decoloration. From the experimental results and the relative band gap position of these semiconductors, a detailed possible photocatalytic mechanism of the Ag2O/NaTaO3 heterojunction under visible light was proposed. The enhancement of the photocatalytic activity was attributed to the interfacial electronic interaction between NaTaO3 and Ag2O and the high migration efficiency of photogenerated carriers.
Keywords: Visible-light-driven; Photocatalytic; p–n; Heterojunction; Ag2O; NaTaO3;
Tribological performance of an H-DLC coating prepared by PECVD by J. Solis; H. Zhao; C. Wang; J.A. Verduzco; A.S. Bueno; A. Neville (222-232).
Display OmittedCarbon-based coatings are of wide interest due to their application in machine elements subjected to continuous contact where fluid lubricant films are not permitted. This paper describes the tribological performance under dry conditions of duplex layered H-DLC coating sequentially deposited by microwave excited plasma enhanced chemical vapour deposition on AISI 52100 steel. The architecture of the coating comprised Cr, WC, and DLC (a-C:H) with a total thickness of 2.8 μm and compressive residual stress very close to 1 GPa. Surface hardness was approximately 22 GPa and its reduced elastic modulus around 180 GPa. Scratch tests indicated a well adhered coating achieving a critical load of 80 N. The effect of normal load on the friction and wear behaviours were investigated with steel pins sliding against the actual coating under dry conditions at room temperature (20 ± 2 °C) and 35–50% RH. The results show that coefficient of friction of the coating decreased from 0.21 to 0.13 values with the increase in the applied loads (10–50 N). Specific wear rates of the surface coating also decrease with the increase in the same range of applied loads. Maximum and minimum values were 14 × 10−8 and 5.5 × 10−8 mm−3/N m, respectively. Through Raman spectroscopy and electron microscopy it was confirmed the carbon-carbon contact, due to the tribolayer formation on the wear scars of the coating and pin. In order to further corroborate the experimental observations regarding the graphitisation behaviour, the existing mathematical relationships to determine the graphitisation temperature of the coating/steel contact as well as the flash temperature were used.
Keywords: Hydrogenated diamond-like carbon; Friction; Wear; AISI 52100 steel; Dry sliding;
Adsorption of imidazole on Au(111) surface: Dispersion corrected density functional study by Safia Izzaouihda; Khaled Mahjoubi; Hassna Abou El Makarim; Najia Komiha; David M. Benoit (233-239).
Display OmittedCharge density difference plots for the imidazole molecule on top site of Au(111) surface with 30 Au atoms per layer.We use density functional theory in the generalized gradient approximation to study the adsorption of imidazole on the Au(111) surface and account for dispersion effect using Grimme’s empirical dispersion correction technique. Our results show that the adsorption energy of imidazole depends on the slab size and on the adsorption site. In agreement with other studies, we find the largest adsorption energy for imidazole on a top site of Au(111). However, we also note that the adsorption energy at other sites is substantial.
Keywords: Imidazole; Interaction; Au(111) surface; Adsorbed sites; DFT; DFT-D3; Zeolitic imidazole framework (ZIF);
Iron oxide nanoparticles stabilized with a bilayer of oleic acid for magnetic hyperthermia and MRI applications by Paula I.P. Soares; César A.T. Laia; Alexandra Carvalho; Laura C.J. Pereira; Joana T. Coutinho; Isabel M.M. Ferreira; Carlos M.M. Novo; João Paulo Borges (240-247).
Display OmittedIron oxide nanoparticles (Fe3O4, IONPs) are promising candidates for several biomedical applications such as magnetic hyperthermia and as contrast agents for magnetic resonance imaging (MRI). However, their colloidal stability in physiological conditions hinders their application requiring the use of biocompatible surfactant agents. The present investigation focuses on obtaining highly stable IONPs, stabilized by the presence of an oleic acid bilayer. Critical aspects such as oleic acid concentration and pH were optimized to ensure maximum stability. NPs composed of an iron oxide core with an average diameter of 9 nm measured using transmission electron microscopy (TEM) form agglomerates with an hydrodynamic diameter of around 170 nm when dispersed in water in the presence of an oleic acid bilayer, remaining stable (zeta potential of −120 mV). Magnetic hyperthermia and the relaxivities measurements show high efficiency at neutral pH which enables their use for both magnetic hyperthermia and MRI.
Keywords: Iron oxide nanoparticles; Oleic acid; Magnetic hyperthermia; Magnetic resonance imaging;
Role of surface Ni and Ce species of Ni/CeO2 catalyst in CO2 methanation by Guilin Zhou; Huiran Liu; Kaikai Cui; Aiping Jia; Gengshen Hu; Zhaojie Jiao; Yunqi Liu; Xianming Zhang (248-252).
CeO2, which was used as support to prepare mesoporous Ni/CeO2 catalyst, was prepared by the hard-template method. The prepared NiO/CeO2 precursor and Ni/CeO2 catalyst were studied by H2–TPR, in-situ XPS, and in-situ FT-IR. The catalytic properties of the prepared Ni/CeO2 catalyst were also investigated by CO2 catalytic hydrogenation methanation. H2–TPR and in-situ XPS results showed that metal Ni species and surface oxygen vacancies could be formed by H2 reduction. In-situ FT-IR and in-situ XPS results indicated that CO2 molecules could be reduced by active metal Ni species and surface oxygen vacancies to generate active CO species and promote CO2 methanation. The Ni/CeO2 catalyst presented the high CO2 methanation activity, and CO2 conversion and CH4 selectivity reached 91.1% and 100% at 340 °C and atmospheric pressure.
Keywords: Carbon dioxide; Catalytic hydrogenation; Methanation; Active Ni species; Oxygen vacancies;
One-step electrodeposition for targeted off-stoichiometry Cu2ZnSnS4 thin films by Aiyue Tang; Jingjun Liu; Jing Ji; Meiling Dou; Zhilin Li; Feng Wang (253-260).
Display OmittedCu2ZnSnS4 (CZTS) is a promising quaternary compound suitable for absorber layer of thin film solar cells. The precise control of the atomic ratio of the films are difficult for the electrodeposition of CZTS thin films. Here, we reported targeted off-stoichiometry CZTS thin films synthesized by one-step electrodeposition. We obtained Cu-poor thin films and the chemical composition of the as-deposited thin films were tailored to targeted off-stoichiometry. Based on the different kinetics of the metallic ion reduction, we successfully controlled the chemical composition by varying deposition time. After annealing, pure kesterite structure was obtained and the electronic interactions between Cu and Sn was verified in the films, which contributes to high carrier mobility. The band gap of the thin films were in the range of 1.43–1.52 eV, which is suitable for absorber layers of thin film solar cells. The carrier mobility reached a value of 28.20 cm2/V s with carrier concentration of 2.09 × 1018 cm−3 when Cu/(Zn + Sn) and Zn/Sn ratios were 0.97 and 1.13, respectively. This work paves a way for synthesizing targeted off-stoichiometry compounds by controlling kinetics and reaction time in large scale.
Keywords: Cu2ZnSnS4; Thin film; One-step electrodeposition; Off-stoichiometry; Kesterite; Electronic interaction;
Nonhomogeneous surface properties of parylene-C film etched by an atmospheric pressure He/O2 micro-plasma jet in ambient air by Tao Wang; Bin Yang; Xiang Chen; Xiaolin Wang; Chunsheng Yang; Jingquan Liu (261-267).
Nonhomogeneous surface properties of parylene-C film etched by an atmospheric pressure He/O2 micro-plasma jet in ambient air were systematically investigated.Display OmittedSurface properties of parylene-C film etched by an atmospheric pressure He/O2 micro-plasma jet in ambient air were investigated. The morphologies and chemical compositions of the etched surface were analyzed by optical microscopy, SEM, EDS, XPS and ATR-FTIR. The microscopy and SEM images showed the etched surface was nonhomogeneous with six discernable ring patterns from the center to the outside domain, which were composed of (I) a central region; (II) an effective etching region, where almost all of the parylene-C film was removed by the plasma jet with only a little residual parylene-C being functionalized with carboxyl groups (C＝O, O―C＝O−); (III) an inner etching boundary; (IV) a middle etching region, where the film surface was smooth and partially removed; (V) an outer etching boundary, where the surface was decorated with clusters of debris, and (VI) a pristine parylene-C film region. The analysis of the different morphologies and chemical compositions illustrated the different localized etching process in the distinct regions. Besides, the influence of O2 flow rate on the surface properties of the etched parylene-C film was also investigated. Higher volume of O2 tended to weaken the nonhomogeneous characteristics of the etched surface and improve the etched surface quality.
Keywords: Nonhomogeneous; Surface properties; Parylene-C film; Atmospheric pressure plasma jet; Film etching;
Effect of reaction temperature and time on the electrochemical properties of nickel hydroxide nanosheets by Zijiong Li; Weiyang Zhang; Yuling Su; Haiyan Wang; Baocheng Yang (268-275).
2D (Two-dimensional) Ni(OH)2 nanosheets is synthesized by hydrothermal method with nickel nitrate hexahydrate and hexamethylenetetramine as raw materials. Herein, the effect of reaction temperature and time on the electrochemical performance of Ni(OH)2 nanosheets are studied. The results showed that morphology and performance appeared great changes as the reaction time and temperature changed. The maximum specific capacitance of 1404.6 F g−1 at current density of 1.5 A g−1 by chronopotentiometry is achieved for Ni(OH)2 nanosheets in 6.0 M KOH when reaction temperature and time are 140 °C and 8 h. Moreover, the capacitance only reduced to 88% after 2000 times charge and discharge of constant current. Such results demonstrated that Ni(OH)2 nanosheets is a promising electrode material for the practical application of high-performance supercapacitor and it is worthy of further investigation.
Keywords: Ni(OH)2; Hydrothermal method; Electrochemical performance;
One-pot synthesis of hierarchical Ni2P/MoS2 hybrid electrocatalysts with enhanced activity for hydrogen evolution reaction by Yan-Ru Liu; Wen-Hui Hu; Xiao Li; Bin Dong; Xiao Shang; Guan-Qun Han; Yong-Ming Chai; Yun-Qi Liu; Chen-Guang Liu (276-282).
Display OmittedA simple one-pot synthesis method has been used to fabricate novel Ni2P/MoS2 hybrid electrocatalysts for hydrogen evolution reaction (HER). Owing to the weak conductivity and layered structure of MoS2, Ni2P nanoparticles with excellent conductivity and activity have been doped into MoS2 for improving the electrocatalytic performances for HER. The structure and morphology of the as-prepared Ni2P/MoS2 hybrid nanostructures are characterized. XRD and XPS show the elemental composition and valence of Ni2P/MoS2. SEM and TEM confirm that the close interaction of the hybrid materials and good dispersion of Ni2P nanoparticles. The as-synthesized Ni2P/MoS2 hybrid electrocatalysts exhibit excellent activity with onset overpotential of 75 mV and Tafle slope of 76 mV dec−1, which are much better than that of pure MoS2. The enhanced stability of the as-prepared Ni2P/MoS2 for HER has also been observed. The improved performances for HER may be ascribed to the better conductivity and dispersion of MoS2 nanosheets in Ni2P/MoS2 hybrid electrocatalysts. The small size and good dispersion of Ni2P nanoparticles also contributed to the enhancement of HER activity. Compared with mechanically mixed MoS2 and Ni2P (Ni2P-MoS2), Ni2P/MoS2 hybrid materials demonstrate better electrochemical performances for HER, implying the existence of synergistic effect between Ni2P and MoS2 on HER activity.
Keywords: Ni2P; MoS2; Hybrid; Electrocatalysts; Hydrogen evolution reaction;
Self-assembled monolayers of 1-alkenes on oxidized platinum surfaces as platforms for immobilized enzymes for biosensing by Jose Maria Alonso; Abraham A.M. Bielen; Wouter Olthuis; Servé W.M. Kengen; Han Zuilhof; Maurice C.R. Franssen (283-293).
Display OmittedAlkene-based self-assembled monolayers grafted on oxidized Pt surfaces were used as a scaffold to covalently immobilize oxidase enzymes, with the aim to develop an amperometric biosensor platform. NH2-terminated organic layers were functionalized with either aldehyde (CHO) or N-hydroxysuccinimide (NHS) ester-derived groups, to provide anchoring points for enzyme immobilization. The functionalized Pt surfaces were characterized by X-ray photoelectron spectroscopy (XPS), static water contact angle (CA), infrared reflection absorption spectroscopy (IRRAS) and atomic force microscopy (AFM). Glucose oxidase (GOX) was covalently attached to the functionalized Pt electrodes, either with or without additional glutaraldehyde crosslinking. The responses of the acquired sensors to glucose concentrations ranging from 0.5 to 100 mM were monitored by chronoamperometry. Furthermore, lactate oxidase (LOX) and human hydroxyacid oxidase (HAOX) were successfully immobilized onto the PtOx surface platform. The performance of the resulting lactate sensors was investigated for lactate concentrations ranging from 0.05 to 20 mM. The successful attachment of active enzymes (GOX, LOX and HAOX) on Pt electrodes demonstrates that covalently functionalized PtOx surfaces provide a universal platform for the development of oxidase enzyme-based sensors.
Keywords: Self-assembled monolayers; Platinum; Enzyme immobilization; Lactate biosensor;
On the utility of C24 fullerene framework for Li-ion batteries: Quantum chemical analysis by Zargham Bagheri (294-299).
Display OmittedThe potential application of carbonaceous C24 nanocluster framework as an anode in Li-ion batteries (LIBs) is investigated using density functional theory calculations. We find that this fullerene unexpectedly gives an imaginary cell voltage and cannot be used as an anode in LIBs. Here, we explain the origin of this unusual behavior and introduce a strategy to make it suitable for anode materials. We show that there is no energy barrier for Li+ diffusion through two neighboring hydrogenated C24 fullerenes. The percentage of Hartree Fock (HF) exchange of density functionals reversely affects the adsorption energies of Li and Li+, so that it is decreased and increased by increasing %HF exchange, respectively. Also, a linear relationship between %HF and HOMO or LUMO level of the studied systems is predicted.
Keywords: Nanostructures; Lithium ion battery; Ab initio calculations; Adsorption;
Synthesized TiO2/ZSM-5 composites used for the photocatalytic degradation of azo dye: Intermediates, reaction pathway, mechanism and bio-toxicity by Kefu Zhou; Xin-Yan Hu; Bor-Yann Chen; Chung-Chuan Hsueh; Qian Zhang; Jiajie Wang; Yu-Jung Lin; Chang-Tang Chang (300-309).
Display OmittedIn this study, a one-step solid dispersion method was used to synthesize titanium dioxide (TiO2)/Zeolite Socony Mobil-5 (ZSM-5) composites with substantially reduced time and energy consumption. A degradation efficiency of more than 95% was achieved within 10 min using 50% PTZ (synthesized TiO2/ZSM-5 composites with TiO2 contents of 50 wt% loaded on ZSM-5) at pH 7 and 25 °C. The possible degradation pathway of azo-dye Reactive Black 5 (RB5) was investigated using gas chromatography–mass spectrometry and ion chromatography (IC). The bonds between the N atoms and naphthalene groups are likely attacked first and cleaved by hydroxyl radicals, ultimately resulting in the decolorization and mineralization of the azo dye. A comparative assessment of the characteristics of abiotic and biotic dye decolorization was completed. In addition, the toxicity effects of the degradation intermediates of azo-dye RB5 on cellular respiratory activity were analyzed. The bio-toxicity results showed that the decay rate constants of CO2 production from the azo-dye RB5 samples at different degradation times increased initially and subsequently decreased, indicating that intermediates of higher toxicity could adhere to the catalyst surface and gradually destroyed by further photocatalytic oxidation. Additionally, EDTA (hole scavengers) and t-BuOH (radical scavengers) were used to detect the main active oxidative species in the system. The results showed that the hydroxyl radicals are the main oxidation species in the photocatalytic process.
Keywords: Photocatalyst; Degradation pathway; Biotoxicity; Mechanism;
Charge transfer of edge states in zigzag silicene nanoribbons with Stone–Wales defects from first-principles by Xie Ting; Wang Rui; Wang Shaofeng; Wu Xiaozhi (310-316).
Stone–Wales (SW) defects are favorably existed in graphene-like materials with honeycomb lattice structure and potentially employed to change the electronic properties in band engineering. In this paper, we investigate structural and electronic properties of SW defects in silicene sheet and its nanoribbons as a function of their concentration using the methods of periodic boundary conditions with first-principles calculations. We first calculate the formation energy, structural properties, and electronic band structures of SW defects in silicene sheet, with dependence on the concentration of SW defects. Our results show a good agreement with available values from the previous first-principles calculations. The energetics, structural aspects, and electronic properties of SW defects with dependence on defect concentration and location in edge-hydrogenated zigzag silicene nanoribbons are obtained. For all calculated concentrations, the SW defects prefer to locate at the edge due to the lower formation energy. The SW defects at the center of silicene nanoribbons slightly influence on the electronic properties, whereas the SW defects at the edge of silicene nanoribbons split the degenerate edge states and induce a sizable gap, which depends on the concentration of defects. It is worth to find that the SW defects produce a perturbation repulsive potential, which leads the decomposed charge of edge states at the side with defect to transfer to the other side without defect.
Keywords: Zigzag silicene nanoribbons; Stone–Wales defects; Electronic properties; First-principles;
Quantitative analysis of satellite structures in XPS spectra of gold and silver by N. Pauly; F. Yubero; S. Tougaard (317-323).
Display OmittedIdentification of specific chemical states and local electronic environments at surfaces by X-ray photoelectron spectroscopy (XPS) is often difficult because it is not straightforward to quantitatively interpret the shape and intensity of shake-up structures that originate from the photoexcitation process. Indeed the shape and intensity of measured XPS structures are strongly affected by both extrinsic excitations due to electron transport out of the surface and intrinsic excitations induced by the sudden creation of the static core hole. These processes must be taken into account to quantitatively extract, from experimental XPS, the primary excitation spectrum of the considered transition which includes all effects that are part of the initial photo-excitation process, i.e. lifetime broadening, spin–orbit coupling, and multiplet splitting. It was previously shown [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17] that both extrinsic and intrinsic excitations could be included in an effective energy-differential inelastic electron scattering cross section for XPS which is then convoluted with the primary excitation spectrum to model the full XPS spectrum. This method can thus be applied to determine the primary excitation spectrum from any XPS spectrum. We use this approach in the present paper to determine the Au 4f and Ag 3d photoemission spectra from pure metals. We observe that characteristic energy loss features of the XPS spectra are not only due to photoelectron energy losses. We thus prove the existence of a double shake-up process characterized by a 4d → 5s/5p transition for Ag and a 5d → 6s/6p transition for Au. We finally accurately quantify the energy position and intensity of these shake-up peaks.
Keywords: XPS; Photoelectron spectroscopy; Core hole effect; Surface effect; Gold; Silver;
Ohmic contacts to Gallium Nitride materials by Giuseppe Greco; Ferdinando Iucolano; Fabrizio Roccaforte (324-345).
Display OmittedIn this review article, a comprehensive study of the mechanisms of Ohmic contact formation on GaN-based materials is presented. After a brief introduction on the physics of Ohmic contacts, a resume of the most important results obtained in literature is reported for each of the systems taken in consideration (n-type GaN, p-type GaN and AlGaN/GaN heterostructures). The optimal metallization schemes and processing conditions to obtain low resistance Ohmic contacts are presented, discussing the role of the single metals composing the stack and the modification induced by the thermal annealing, either on the metal layers or at the interface with GaN. Physical insights on the mechanism of Ohmic contact formation have been gained by correlating the temperature dependence of the electrical parameters with a morphological/structural analysis of the interface. In the case of the AlGaN/GaN systems, the influence of the heterostructure parameters on the Ohmic contacts has been taken into account adapting the classical thermionic field emission model to the presence of the two dimensional electron gas (2DEG). Finally, the state of the art of “Au-free” metallization to AlGaN/GaN heterostructures is also presented, being this latter a relevant topic for the integration of GaN technology on large scale Silicon devices fabs.
Keywords: n-GaN; p-GaN; AlGaN/GaN heterostructures; Ohmic contacts;
Iron binary and ternary coatings with molybdenum and tungsten by Gulmira Yar-Mukhamedova; Maryna Ved; Nikolay Sakhnenko; Anna Karakurkchi; Iryna Yermolenko (346-352).
Display OmittedElectrodeposition of Fe-Mo-W and Fe-Mo layers from a citrate solution containing iron(III) on steel and iron substrates is compared. The utilization of iron(III) compounds significantly improved the electrolyte stability eliminating side anodic redox reactions. The influence of concentration ratios and electrodeposition mode on quality, chemical composition, and functional properties of the alloys is determined. It has been found that alloys deposited in pulse mode have more uniform surface morphology and chemical composition and contain less impurities. Improvement in physical and mechanical properties as well as corrosion resistance of Fe-Mo and Fe-Mo-W deposits when compared with main alloy forming metals is driven by alloying components chemical passivity as well as by alloys amorphous structure. Indicated deposits can be considered promising materials in surface hardening technologies and repair of worn out items.
Keywords: Fe-Mo and Fe-Mo-W alloys; Citrate electrolyte; Physical-mechanical properties; Electrodeposition; Corrosion resistance; Pulse electrolysis;
Density functional investigation of CO and NO adsorption on TM-decorated C60 fullerene by A.M. El Mahdy (353-366).
CO and NO adsorption on TM-decorated C60 fullerene are investigated by using the density functional calculations(DFT).Display OmittedWe have analysed the adsorptions of CO and NO molecules on pristine, TM (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) in TM-doped fullerene C60 by using density functional theory (DFT) calculations at B3LYP/6-31g(d) theoretical level. This work revealed that the transition metal doped fullerenes were more highly sensitive to CO and NO adsorption than that of pure fullerene C60. The Fe-doped fullerenes C60 displayed the strongest interaction with C and N atoms of CO and NO molecules respectively. The nature of charge transfer between the d-orbitals of TM, and the π * orbital of the nearby C and N of CO and NO are clarified. Natural bond orbital (NBO) analysis reveals that the electronic configuration of the doped TM metal represents a qualitative change with respect to that of the free-metal. The binding of CO and NO precursor is mostly dominated by the metal E ( i ) ( XO .. TM ) pairwise additive contributions, and the role of the C60 is not restricted to supporting the metal.
Keywords: Adsorption; Fullerenes; Density functional theory; Transition metal doped; Small molecule gasses;
TiO2/SiO2 porous composite thin films: Role of TiO2 areal loading and modification with gold nanospheres on the photocatalytic activity by Irina Levchuk; Mika Sillanpää; Chantal Guillard; Damia Gregori; Denis Chateau; Stephane Parola (367-374).
Display OmittedThe aim of the work was to study photocatalytic activity of composite TiO2/Au/SiO2 thin films. Coatings were prepared using sol-gel technique. Physicochemical parameters of coatings were characterized using UV–vis spectrometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), ellipsometry, tactile measurements, goniometry and diffuse reflectance measurements. The photocatalytic activity of the films was tested in batch mode using aqueous solution of formic acid. Changes of formic acid concentration were determined by means of high pressure liquid chromatography (HPLC). Increase of initial degradation rate of formic acid was detected for TiO2/Au/SiO2 films with gold nanoparticle’s load 0.5 wt.% and 1.25 wt.%. However, deeper insights using more detailed characterization of these coatings demonstrated that the improvement of the photocatalytic activity is more probably attributed to an increase in the areal loading of TiO2.
Keywords: Gold nanoparticles; Coatings; Photocatalysis; Sol-gel; TiO2;
Synthesis in situ of gold nanoparticles by a dialkynyl Fischer carbene complex anchored to glass surfaces by María Candelaria Bertolino; Alejandro Manuel Granados (375-381).
Display OmittedIn this work we present a detailed study of classic reactions such as “click reaction” and nucleophilic substitution reaction but on glass solid surface (slides). We used different reactive center of a dialkynylalcoxy Fischer carbene complex of tungsten(0) to be anchored to modified glass surface with amine, to obtain aminocarbene, and azide terminal groups. These cycloaddition reaction showed regioselectivity to internal triple bond of dialkynyl Fischer carbene complex without Cu(I) as catalyst. Anyway the carbene anchored was able to act as a reducing agent to produce in situ very stable gold nanoparticles fixed on surface. We showed the characterization of modified glasses by contact angle measurements and XPS. Synthesized nanoparticles were characterized by SEM, XPS, EDS and UV–vis. The modified glasses showed an important enhancement Raman-SERS. This simple, fast and robust method to create a polifunctional and hybrid surfaces can be valuable in a wide range of applications such as Raman-SERS substrates and other optical fields.
Keywords: Glass surface; Fischer carbene complexes; Gold nanoparticles;