Applied Surface Science (v.258, #12)
Effect of annealing on photoluminescence and optical properties of porous anodic alumina films formed in sulfuric acid for solar energy applications by Mondher Ghrib; Rachid Ouertani; Monir Gaidi; Najoua Khedher; Mohamed Ben Salem; Hatem Ezzaouia (4995-5000).
► Porous alumina tends to amorphous structure as the annealing temperature reaches 650 °C. ► Raman spectroscopy and XRD spectra has confirmed the amorphisation of porous alumina films. ► Refractive index increases while optical losses decrease with annealing temperature. ► Reflectivity increases to reach 97% when porous alumina films become amorphous. ► Photoluminescence spectra of porous alumina films in sulfuric acid displays α and β band peaks.Photoluminescence and optical properties of porous oxide films formed by two-step aluminum anodization at a fixed current 200 mA have been investigated. It was found that the crystallographic structure depend strongly on the annealing temperature. X-ray diffraction (XRD) reveals an amorphisation of the porous oxide films after annealing. This evolution has been confirmed by Raman spectroscopy measurement. Spectroscopic ellipsometry (SE) in the UV–vis and near infra red (IR) spectra shows that refraction index n increases and the extinction coefficient k decreases with annealing temperature. This observation has been confirmed with reflectivity measurements. As a consequence the reflectivity reaches 97% when porous alumina films were annealed at 650 °C. Photoluminescence (PL) measurements show two PL peaks in the emission and excitation spectra. The first emission peak is centered at 460 nm (α-band) and the second (β-band) shifts from 500 to 525 nm, depending on excitation wavelength. For excitation spectra, one spectral peak is located at 271 nm and the second shifts to longer wavelengths with increasing emission wavelength. The results indicate the existence of two PL centers. One is associated with oxygen adsorption at the pore wall and oxygen vacancies inside the alumina. The other is related to the adsorption of water and/or OH groups at the surface of the pore wall and to structure defects and sulfur inclusion inside the films.
Keywords: Porous oxide films; Annealing; Photoluminescence; Ellipsometry; Reflectivity;
Thermal reliability of thin SiGe epilayers by Ming-Jhang Wu; Hua-Chiang Wen; Tun-Yuan Chiang; Chien-Huang Tsai; Wen-Kuang Hsu; Chang-Pin Chou (5001-5004).
► We evaluated the thermal reliability of thin SiGe epilayers. ► The significant observe cracking dominating on both sides of the scratches on the films. ► The annealing treatment induces lower coefficients of friction and higher shear resistances.The SiGe heterostructures can play a role that drastically enhances the carrier mobility of SiGe heterodevices, such as strained Si metal oxide semiconductor field effect transistors. However, it is difficult to access the both issues, that is, the propagation of the dislocation and thermal reliability of annealed SiGe films. In this study, we used ultrahigh-vacuum chemical vapor deposition to grow Si0.8Ge0.2 films (ca. 200 nm thick for heteroepitaxy) epitaxially on bulk Si. The samples were subsequently furnace-crystallized at temperatures of 800, 900, and 1000 °C. We used nanoscratch techniques to determine the frictional characteristics of the SiGe epilayers under various ramping loads and employed atomic force microscopy to examine their morphologies after scratching. From our investigation of the pile-up phenomena, we observed significant cracking dominating on both sides of the scratches on the films. The SiGe epilayers films that had undergone annealing treatment possessed lower coefficients of friction, suggesting higher shear resistances.
Keywords: SiGe; Ultrahigh-vacuum chemical vapor deposition; AFM; Nanoscratch;
Nanoporous copper incorporated platinum composites for electrocatalytic reduction of CO2 in ionic liquid BMIMBF4 by Qiuju Feng; Suqin Liu; Xuanyun Wang; Ganhua Jin (5005-5009).
► Nanoporous electrode consisting of copper skeletons and platinum shells was prepared. ► NPC–Pt electrode displayed higher electrocatalytic activity for CO2 reduction. ► Current efficiency for CO2 reduction at NPC–Pt electrode was higher (83%).A three-dimensional porous nanostructure electrode composed of copper skeletons and platinum shells (NPC–Pt) was prepared by electroless plating for the first time. The electrochemical behavior of this electrode for electrocatalytic reduction CO2 in ionic liquid, 1-butyl-3-methylimidazoliumtetrafluoborate (BMIMBF4), had been studied by cyclic voltammogram and electrochemical impedance spectroscopy with a reduction peak at −2.24 V (vs. Ag) which was more positive 180 mV than that obtained on a pure platinum electrode. The electrolyses experiments were carried out in an undivided cell under mild conditions without any toxic solvents, catalysts and supporting electrolytes, affording the dimethyl carbonate in a good yield (81%). In addition, the current for the CO2 reduction at NPC–Pt electrode was stable, with a higher current density and current efficiency (83%). Moreover, current efficiency remained after reusing it for five times.
Keywords: Electrocatalytic; Nanoporous; Carbon dioxide; Dimethyl carbonate; Ionic liquid;
Synthesis, characterization and UV-A light photocatalytic activity of 20 wt%SrO–CuBi2O4 composite by Elaziouti Abdelkader; Laouedj Nadjia; Bekka Ahmed (5010-5024).
► 20 wt%SrO–CuBi2O4 heterogeneous nanoparticles have been successively synthesized via the milling–annealing technique. ► 20 wt%SrO–CuBi2O4 nanocomposites were characterized by various characterization technologies. ► 20 wt%SrO–CuBi2O4 exhibited excellent photocatalytic performance in UV–visible light. ► The mechanism of enhanced UV–visible photocatalytic activity of 20 wt%SrO–CuBi2O4 was investigated by the p–n heterojunction principle and the valance band theory.A novel nanoscale powder 20 wt%SrO–CuBi2O4 has been successfully synthesized for the first time by ion exchange through doping Sr(NO3)2 into CuBi2O4 matrix and characterized using TG/DTA, XRD, EDX, SEM and electrical measurements. The as-prepared 20 wt%SrO–CuBi2O4 composite exhibit much higher photocatalytic activity than 20 wt%SrO–CuBi2O4 synthesized via physical process and pure phase CuBi2O4 under UV-A light irradiation (λ = 365 nm) in the course of the photocatalytic redox activity of Congo red (CR). Maximum degradation was achieved within 220 min of irradiation time under UV-A light as a result of 97.22% of photocatalytic efficiency of CR. The mechanisms of the enhancement of photocatalytic activity of the nanocomposite photocatalyst will be discussed by the p–n heterojunction principle (charge separation and photochemical diode models) and the valance band theory. The pure nanocomposite systems have been also reported for a comparative purpose.
Keywords: 20 wt%SrO–CuBi2O4 composite; TG/TDA; XRD, EDX; SEM; Electrical measurements; Congo red; Photocatalytic activity; p–n heterojunction;
Mechanical and tribological properties of Ti-DLC films with different Ti content by magnetron sputtering technique by Jinfeng Cui; Li Qiang; Bin Zhang; Xiao Ling; Tao Yang; Junyan Zhang (5025-5030).
► High target poisoning methods can be employed to grow low Ti concentration carbon films. ► Introduction of low content of Ti will obtain low stress carbon films with hardness retaining. ► Introduction of low content of Ti will endow carbon films low friction coefficient (0.05) as well as extremely low wear rate (∼10−10 mm3/Nm).Ti-doped diamond-like carbon (DLC) films were deposited on Si substrates at room temperature by magnetron sputtering Ti twin-target in methane and argon mixture atmosphere. The DLC films with different Ti concentrations were fabricated by varying the gas flow ratio of Ar/CH4. X-ray photoelectron spectroscopy (XPS), Raman spectra were used to analyze the composition and the microstructure of the films. The internal stress was calculated by using the Stoney equation, where the curvature of the film/substrate was measured by BGS 6341 type film stress tester. The mechanical and tribological properties of the films were systematically studied by the nano-indentor and reciprocating ball-on-disc tester, respectively. The Ti atomic concentration in the films increased from 0.41% to 8.2% as the Ar/CH4 flow ratio increased from 60/190 to 140/110. The Ti atoms exist mainly in the form of metallic-like Ti rather than TiC when Ti concentration is 0.41%, confirmed by XPS analysis. As the Ti concentration rose to 6.7%, the Ti-DLC films transformed to composite DLC films with carbide phase embedded in the DLC matrix because of the formation of TiC. As a result, the hardness is decreased, while the stress is dramatically increased. The Ti-DLC films with 0.41% Ti doping showed a relatively high hardness (13.75 GPa), low stress (0.56 GPa), extremely low wear rate (∼10−10 mm3/Nm) and low friction coefficient (0.05).
Keywords: Diamond-like carbon film; Different concentration Ti doping; Low concentration Ti doping; Mechanical properties; Tribological performance;
Photocatalytic degradation of gaseous toluene on Fe-TiO2 under visible light irradiation: A study on the structure, activity and deactivation mechanism by Song Sun; Jianjun Ding; Jun Bao; Chen Gao; Zeming Qi; Xiaoyan Yang; Bo He; Chengxiang Li (5031-5037).
Display Omitted► The 0.7% Fe-TiO2 shows the best photocatalytic activity for gaseous toluene degradation under visible light irradiation. ► Different Fe3+ doping concentrations lead the differences in the electron–hole separation efficiency. ► Photocatalyst deactivation can be attributed to the occupancy of the active sites by the stable intermediates, benzaldehyde and benzoic acid.The Fe-TiO2 photocatalysts synthesized by a sol–gel method have the mesoporous structure with a narrow pore size distribution, large pore volume and high surface area. The incorporated Fe3+ substitutes the octahedrally coordinated Ti4+ in the TiO2 lattice to extend the absorption of TiO2 to visible light region and promote the formation of electron–hole pair. Additionally, the separation and transportation efficiency increase with the doping of Fe3+ increasing from 0.1% to 0.7%, while decreases remarkably with the doping concentration increasing from 0.7% to 1.5%. The Fe-TiO2 shows excellent photocatalytic performance for toluene degradation under visible light irradiation. The optimal Fe/Ti ratio is 0.7%. Partial deactivation of the photocatalytic activity was observed after 20 consecutive reaction runs. From the in situ DRIFTS experiment, the deactivation reason can be attributed to the formation of stable intermediates, such as benzaldehyde and benzoic acid, which occupied the active sites on the surface of the photocatalyst. The adsorbed benzaldehyde and benzoic acid can be removed with heat treatment at 653 K for 3 h and the deactivated photocatalyst can be regenerated completely.
Keywords: Photocatalysis; Fe-TiO2; DRIFTS; Gaseous toluene; Visible light;
Photoelectrochemical properties and photocatalytic activity of nitrogen-doped nanoporous WO3 photoelectrodes under visible light by Yuyang Liu; Ya Li; Wenzhang Li; Song Han; Canjun Liu (5038-5045).
► Nitrogen doping of self-organized anodic nanoporous WO3 photoelectrodes obtained by one step annealing in a NH3/N2 gas mixture. ► Nitrogen-doped nanoporous WO3 photoelectrodes show a significant enhancement in conversion efficiency in the visible light. ► Nitrogen-doped nanoporous WO3 photoelectrodes were used for photocatalytic and photoelectrocatalytic degradation of methyl orange. ► Nitrogen-doped samples exhibited higher levels of activity under visible light irradiation.In the present work, nitrogen-doped tungsten oxide (WO3) nanoporous photoelectrode was studied by photoelectrochemical and photocatalytic methods in order to evaluate the photoactivity and the possibility of its application in solar photocatalysis. WO3 nanoporous photoelectrodes were prepared by anodization of tungsten foil in NH4F/(NH4)2SO4 electrolytes, followed by annealing in NH3/N2 to incorporate N as a dopant. The crystal structure, composition and morphology of pure and nitrogen doped WO3 were compared using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). The results indicate that nitrogen can be doped successfully into WO3 nanoporous photoelectrodes by controlling annealing temperature. Incident photon to current efficiency measurements carried out on PEC cell with N-doped WO3 nanoporous photoelectrodes as anodes demonstrate a significant increase of photoresponse in the visible region compared to undoped WO3 nanoporous photoelectrodes prepared at similar conditions. In particular, the photocatalytic and photoelectrocatalytic activity under visible light irradiation for newly synthesized N-doped WO3 nanoporous photoelectrodes were investigated by degradation of methyl orange. The photoelectrocatalytic activity of N-doped WO3 nanoporous photoelectrodes was 1.8-fold enhancement compared with pure WO3 nanoporous photoelectrodes.
Keywords: Tungsten oxide; Nanoporous photoelectrode; Nitrogen-doped; Photocatalytic activity;
Effect of film thickness on properties of electrodeposited Ni–Co films by Ali Karpuz; Hakan Kockar; Mursel Alper (5046-5051).
► The aim of this study is to investigate the effects caused by change of film thickness on the properties of Ni–Co films. ► The Ni–Co films with different thicknesses were produced by using the electrodeposition technique. ► Their microstructural, magnetic and magnetotransport properties were investigated. ► According to results, the H c of the Ni–Co films has dependence on their preferential growth orientations.A series of Ni–Co films with different thicknesses was produced by using the electrodeposition technique and their microstructural, magnetic and magnetotransport properties were investigated. The X-ray (XRD) diffraction measurements showed that the films have the face centered cubic structure and the preferential orientations of the films were in the order of (1 1 1), (2 2 0) and (2 2 0) for the films with 1, 2 and 4 μm thicknesses, respectively. The magnetic measurements revealed that the coercivity decreased from 52 Oe to 37 Oe due to the regular transition of preferential orientation from (1 1 1) to (2 2 0) with increasing film thickness. The study demonstrated that magnetic properties of the films changed according to the microstructural properties. Magnetoresistance investigations exhibited that all films have anisotropic magnetoresistance (AMR).
Keywords: Electrochemical synthesis; Metals and alloys; Magnetic properties of monolayers and thin films; Texture;
Fabrication of micro-structures on a PVDF/TiO2 nano-composite film using photocatalytic lithography by Ningli An; Hongzhong Liu; Yucheng Ding; Bingheng Lu; Min Zhang (5052-5055).
As a photocatalyst, TiO2 can induce degradation of PVDF via UV irradiation. To further promote the degradation of PVDF and form the three-dimensional micro-structure, deionised water was continuously cycling in the gap between the mask and film.Display Omitted► Micro-structures were replicated on a PVDF/TiO2 film with photocatalytic lithography. ► Micro-structure patterns were obtained via water phase process with UV irradiation. ► PVDF defluorination occurs in the micro-structure grooves.In the present study, a poly(vinylidene fluoride) (PVDF)/TiO2 nano-composite film was prepared by coating a substrate with an acetone/DMF solution, which was then evaporated at a temperature of 110 °C. Micro-structure patterns were fabricated on a PVDF/TiO2 nano-composite film with photocatalytic lithography. The morphological and chemical compositions of the micro-structure were investigated by optical microscope, SEM and XPS. Experimental results show that the micro-structure patterns can be directly replicated on the PVDF/TiO2 nano-composite film with photocatalytic lithography. The micro-structure is approximately 4 μm in depth which is obtained during the water phase of the process with UV-LED irradiation in 5 h. The results indicate that the fabrication methodology can be potentially applied towards the large-scale fabrication of actuators and sensor devices.
Keywords: PVDF; TiO2; Micro-structure; Photocatalytic; Degradation;
Synthesis, characterization and optical property of graphene oxide films by Juan Yang; Yazhou Zhou; Lei Sun; Nan Zhao; Chuanliang Zang; Xiaonong Cheng (5056-5060).
► Graphene film with controllable thickness and optical property was fabricated. ► Electrically conductive Ag particles were decorated onto the films. ► Transmittance of the film was improved by the decoration of Ag particles.Graphene oxide (GO) sheets were used to build up films via layer-by-layer electrostatic self-assembly technique. GO sheets and poly(diallyldimethylammonium chloride) (PDDA) alternately deposited on the quartz substrate during the self-assembly process. To make the films electrically active, reduction treatment involving the thermal annealing in Ar/H2 atmosphere at 600 °C was conducted. The microstructure and morphology of the obtained films were investigated by FT-IR, TEM, XPS and SEM. The optical property was examined by UV–vis instrument at room temperature. Results show that the surfaces of the obtained films are uniform. Films with 5 and 10 assembly cycles have transmittances of 74 and 49%, respectively, at a wavelength of 500 nm. To improve the optical and electrical property, Ag particles was decorated into the film and the transmittance at 500 nm was increased to 82% with 5 assembly cycles, while the surface resistance was about 95 kΩ □−1, much lower than that of pure film, 430 kΩ □−1.
Keywords: Graphene oxide films; Self-assembly technique; Electrical property; Optical property; Ag decoration;
Effect of processing methods on drug release profiles of anti-restenotic self-assembled monolayers by Susan E. Stoebner; Gopinath Mani (5061-5072).
► Anti-restenotic self-assembled monolayers (ARSAMs – paclitaxel attached SAMs) on Co–Cr alloy were processed by room temperature treatment, heat treatment, cold treatment, and quenching. ► Processing methods have significant influence on the polymorphism, morphology, and distribution of paclitaxel on SAMs coated Co–Cr alloy. ► Processing methods influence the percentage of drug release from ARSAMs at certain time points. ► Potential applications in drug-eluting stents and other medical devices.The use of anti-restenotic self-assembled monolayers (ARSAMs) has been previously demonstrated for delivering drugs from stents without polymeric carriers. ARSAMs have been prepared by coating an anti-restenotic drug (paclitaxel – PAT) on –COOH terminated phosphonic acid self-assembled monolayers (SAMs) coated Co–Cr alloy specimens. This study investigates the effect of different processing methods on the percentage of drug release from ARSAMs. The different methods that were used in this study to process ARSAMs include room temperature (RT) treatment, heat treatment (HT), cold treatment (CT) and quenching. The changes in polymorphism, chemical structure, morphology, and distribution of PAT on SAMs coated specimens were investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. DSC showed dihydrate, dehydrated dihydrate, semi-crystalline, and mixed (amorphous and dihydrate) forms of PAT for RT, HT, CT, and quenched specimens, respectively. FTIR showed that the chemical structure of PAT was unaltered in all the specimens processed by various methods employed in this study. SEM showed a mixture of spherical, ovoid, and bean-shaped morphologies of PAT on RT, HT, and CT while particle-like and needle-shaped morphologies of PAT were observed on quenched specimens. AFM showed PAT was uniformly distributed on RT, HT and CT specimens while particle-like PAT was well distributed and needle-shaped PAT was sparsely distributed on quenched specimens. CT specimens showed greater density of PAT crystals when compared to other methods. Thus, this study demonstrated that processing methods have significant influence on the polymorphism, morphology, and distribution of PAT on SAMs coated Co–Cr alloy specimens. The in vitro drug elution studies for up to 56 days showed sustained release for all the different groups of specimens. CT showed lesser percentage of drug release when compared to that of other methods on the first day. The treatment at high temperatures (HT-100 °C or HT-140 °C) improved the stability of PAT on alloy surfaces and showed lesser percentage of drug release when compared to that of RT or HT-70 °C at different time points. Large data scatter was observed for the release profiles of quenched specimens. No other major differences in the percentage of drug release were observed for the specimens prepared by different processing methods. These factors should be taken into consideration when drug delivery platforms are developed for stents or other medical devices.
Keywords: Biomaterials surfaces; Cobalt–chromium alloy; Self-assembled monolayers; Drug-eluting stents;
Low temperature epitaxial growth and characterization of Ga-doped ZnO thin films on Al2O3 (0 0 0 1) substrates prepared with different buffer layers by Seung Wook Shin; G.L. Agawane; In Young Kim; Ye Bin Kwon; In Ok Jung; Myeng Gil Gang; A.V. Moholkar; Jong-Ha Moon; Jin Hyeok Kim; Jeong Yong Lee (5073-5079).
► Growth and characterization of high quality GZO thin films deposited at low growth temperature of 250 °C by introducing different buffer layer. ► ZnO and GaN buffer layer enables the epitaxial growth of GZO thin films. ► Growth mechanism of GZO thin films are strongly related to the different lattice constant between buffer layer and GZO. ► ZnO buffer layer does not improve the electrical properties of GZO thin film.This article reports the epitaxial growth and characterization of 1 wt% Ga-doped ZnO (GZO) thin films prepared without buffer layer and with three different buffer layers of ZnO, GaN and MgO on Al2O3 (0 0 0 1) substrates by RF magnetron sputtering at a growth temperature of 250 °C. X-ray diffraction and transmission electron microscopy studies showed that the GZO thin films deposited on the GaN- and ZnO-buffered substrates were grown epitaxially. However, the GZO thin films deposited on the non- and MgO-buffered substrates had a polycrystalline hexagonal wurtzite phase with a highly c-axis preferred out-of-plane and a random in-plane orientation. Electrical studies of the GZO thin film deposited on the non-buffered substrate showed the lowest resistivity of 6.8 × 10−3 Ω cm as compared to these deposited on three buffered substrates. The crystallinity, microstructure, morphological, optical and electrical properties of the GZO thin films were influenced by the nature of the three investigated buffered layers.
Keywords: Ga doped ZnO (GZO); Buffer layer; Low growth temperature; Epitaxial growth;
Superhydrophobicity of superparamagnetic nanocomposite modified with polystyrene by Jingjing Zhang; Zhongli Lei (5080-5085).
► Magnetic superhydrophobic nanocomposite was synthesized. ► The obtained samples have superparamagnetic property. ► The obtained samples have superparamagnetic property.In this work, we report the fabrication of magnetic superhydrophobic nanocomposite by combining of the organic and inorganic materials. The resulting products were characterized by means of Fourier transformation infrared spectroscopy (FI-IR), scanning electron microscopy (SEM) and UV–vis absorption spectroscopy. The results indicated that polystyrene can be grafted onto Fe3O4@SiO2 nanoparticles via covalent bond. Surface wetting properties of the magnetic PS-g-Fe3O4@SiO2 nanoparticles film were evaluated by measuring water contact angle which were measured to be 160° and a water droplet roll-off angle of less than 5°. Moreover, based on the magnetism analysis of the PS-g-Fe3O4@SiO2, it has superparamagnetic property. The excellent superhydrophobic and superparamagnetic property enlarges potential applications of the superhydrophobic surfaces.
Keywords: Superhydrophobic surface; Contact angle; Polystyrene; Magnetic nanoparticle;
Carrier recombination in Cu doped CdS thin films: Photocurrent and optical studies by Richa Panda; Vandana Rathore; Manoj Rathore; Vilas Shelke; Nitu Badera; L.S. Sharath Chandra; Deepti Jain; Mohan Gangrade; T. Shripati; V. Ganesan (5086-5093).
► Photoconductivity in Cu doped CdS films is reported. ► 2% Cu enhances the aspect ratio of nanorods and photosensitivity. ► Anomalous changes are also seen in structural, transport and optical properties. ► Quenching of photocurrent is described by carrier recombination. ► Quick photo response upon illumination can be tuned for applications.Quenching of photocurrent in Cu doped CdS prepared by Spray pyrolysis technique is reported. Anomalous changes in surface morphology are seen at 2% of Cu in CdS. Surface morphology of pure CdS film shows rod like structure. Aspect ratio of such rods has a maximum around 2% Cu substitution. This in turn produces anomalous changes in photoconductivity, which is further supported by marked changes seen in mean crystallite size, strain and grain size, roughness, transmittance, optical band gap, activation energy and finally in the photocurrent. Pronounced effects are seen in transmittance as a broad profile centered on 590 nm. The observed effects are explained in terms of carrier recombination mechanisms.
Keywords: Thin film; Photocurrent; Quenching; Recombination; Solar materials;
Oxidation control in plasma spraying NiCrCoAlY coating by Qi Wei; Zhiyong Yin; Hui Li (5094-5099).
Display Omitted► The oxidation of NiCrCoAlY particles was studied during the spray process. ► Two different oxidation mechanisms involved in the in-flight oxidation. ► In-flight oxidation is the dominant mechanism for NiCrCoAlY particles in spray. ► Adding shrouding inert gas is an effective method to decrease the oxide content.Atmospheric plasma spraying is usually accompanied by oxidation reactions, which result in the formation of oxides in the coatings. The presence of oxides in metallic coatings is usually undesirable because they cause the coating properties to deteriorate. This study highlights how the high temperature oxidation resistance of plasma sprayed NiCrCoAlY coating is influenced by both the oxidation behavior of NiCrCoAlY particles and by the shrouding gas during the spray process. It is shown that two different oxidation mechanisms are involved in the in-flight oxidation. One is diffusion oxidation, and the other is convective oxidation. The convective oxidation of NiCrCoAlY particles is the dominating oxidation mechanism when the plasma jet is at a distance of 55 mm from the torch nozzle exit; while diffusion oxidation was found to be the dominant mechanism when the spray distance is greater than 55 mm. Oxidation mainly occurs during in-flight and after impact on the substrate. In-flight oxidation is the dominant mechanism for NiCrCoAlY particles in plasma spray. Adding inert-gas shrouding is an effective method for decreasing the oxide content of the NiCrCoAlY coating, which significantly increases the coating's oxidation resistance.
Keywords: Plasma spray; Convective oxidation; Diffusible oxidation; Oxidation resistance;
Substrate temperature influence on W/WCN x bilayers grown by pulsed vacuum arc discharge by R. Ospina; D. Escobar; E. Restrepo-Parra; P.J. Arango; J.F. Jurado (5100-5104).
► WCN coatings present C and N concentration competition depending on the process production parameters as the substrate temperature. ► WCN coatings studied by means of Raman spectroscopy showed D and G bands corresponding to an amorphous component. ► The increase in the carbon inclusion in the WCN lattice produces an increment in the amorphous component.W/WCN x coatings were produced by using a repetitive pulsed vacuum arc discharge on stainless-steel 304 substrates, varying the substrate temperature from room temperature to 200 °C. Energy dispersive spectroscopy (EDS) was used for determining W, C and N concentrations dependence on the substrate temperature. A competition between C and N can be observed. Atomic force microscopy was employed for obtaining the thickness and grain size that present similar tendencies as a function of the temperature. X-ray diffraction characterization showed phases of W and α-WCN (hexagonal). Raman spectra for all substrate temperatures were obtained, presenting two peaks corresponding to D (disorder) and G (graphite) bands in the region of 1100–1700 cm−1 due to the amorphous carbon. As an important conclusion, it was stated that substrate temperature has strong influence on the structure, chemical composition and morphology of W/WCN x bilayers, caused by the competition between carbon and nitrogen.
Keywords: Tungsten; EDS; XRD; Structure; Raman; Morphology;
Investigation of thin layers deposited by two PVD techniques on high speed steel produced by powder metallurgy by D. Jakubéczyová; P. Hvizdoš; M. Selecká (5105-5110).
► Techniques ARC and LARC were used for deposition of thin coatings onto PM cutting tools. ► The layers AlTiCrN and nACo (nanocomposite) were analyzed by standard techniques for surface status. ► The layer nACo achieved lower roughness, higher hardness and better quality than AlTiCrN layer. ► Durability testing of the cutting tools was carried out according to the standard ISO 3685-1999. ► The tested coated tools had ∼3-times higher durability than equivalent uncoated materials.This study was intended to investigate the properties and cutting performance with thin layers applied by two PVD techniques. PVD techniques ARC and LARC were used for the deposition of thin coatings onto cutting tools prepared by powder metallurgy. Advanced types of layers – monolayer AlTiCrN and nanocomposite type of nc-AlTiN/Si3N4 layer – were analyzed by standard techniques for surface status and quality assessment – roughness, hardness, layer thickness, chemical composition by GDOES, tribological properties at room and elevated temperature. Durability testing of the cutting tools was carried out according to the standard ISO 3685-1999. The nanocomposite nc-AlTiN/Si3N4 layer achieved lower roughness when compared to monolayer AlTiCrN which leads to the achievement of higher hardness and better layer quality. The HV0.5 hardness values were ∼26 GPa. The results showed a 2–3-times longer durability of the cutting tools in comparison with equivalent uncoated PM and traditional materials. The deposited coatings contributed to the improvement of their durability.
Keywords: Cutting tool; PVD layer; Roughness; Hardness; GDOES; Pin-on-disc; Durability;
Controlling silicate meso-structures using sucupira oil as a new swelling agent by J.N.M. Batista; E.H. de Faria; P.S. Calefi; K.J. Ciuffi; E.J. Nassar; W.R. Cunha; J.M.A. Caiut; L.A. Rocha (5111-5116).
Small angle X-ray scattering (SAXS) patterns of samples synthesized in different oil concentrations.Display Omitted► Expanded mesoporous silica have been synthesized by incorporation of sucupira oil. ► The oil demonstrated great potentials in the pore size engineering fields. ► The materials presented an increase of pores sizes up to 26 Å. ► We tailor the final pore morphology from hexagonal to cubic or lamellar structures.Ordered mesoporous SiO2 particles have been synthesized by incorporation of natural oil as swelling agent from solutions containing deionized water, ammonium hydroxide, tetraethylorthosilicate, cetyltrimethylammonium bromide as structure-directing agent. The present work shows that the “sucupira oil” is an effective expander agent to enlarge the pore size and even allows obtaining different structural rearrangements of mesoporous materials. The obtained materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and nitrogen adsorption–desorption analysis. The results obtained show a highly ordered hexagonal, cubic and lamellar mesostructure depending of oil concentration. Furthermore, the increase of pore diameter in function of oil concentration was clearly observed by nitrogen adsorption–desorption analysis.
Keywords: Mesoporous silica; Structures; Swelling agent; Sucupira oil;
Strong-bonding calcium phosphate coatings on carbon/carbon composites by ultrasound-assisted anodic oxidation treatment and electrochemical deposition by Xueni Zhao; Hejun Li; Mengdi Chen; Kezhi Li; Bin Wang; Zhanwei Xu; Sheng Cao; Leilei Zhang; Hailiang Deng; Jinhua Lu (5117-5125).
Display Omitted► USAT of C/C is a simple and effective technique to improve bonding strength between CaP and C/C. ► Surface energy of USAT–C/C-50 was much higher than that of UT–C/C. ► High content of O-containing and some P-containing groups were grafted onto C/C by USAT. ► P-containing species were bonded with C/C by C―P―O or C―O―P bonding. ► Shear bond strength of CaP coatings on USAT–C/C-50 was about twice that of coatings on UT–C/C.The current work describes the ultrasound-assisted anodic oxidation treatment of carbon fiber-reinforced carbon (C/C) composites with H3PO4. The aim was to create chemical bonds between the surface-treated C/C composites and subsequently deposited calcium phosphate (CaP) coatings. The surface energy of C/C obviously increased after undergoing ultrasound-assisted anodic oxidation treatment at a current density of 50 mA/cm2 in aqueous 0.5 M H3PO4 solution (USAT–C/C-50). A large number of O-containing groups and some P-containing groups were found on the treated C/C substrate. The formation of O-containing groups may have been promoted by the energy input of the ultrasound and electric field. P-containing species could be bonded to C/C by C―P―O or C―O―P bonding. Among the species formed, the formation of (H2PO4)− on C/C was promoted by ultrasound. When USAT–C/C-50 was used as the substrate for CaP coatings deposited by ultrasound-assisted electrochemical deposition (USECD), the surface of USAT–C/C-50 acquired strong CaP induction ability, and large amounts of CaP were deposited on it during the initial deposition process. After USECD, very strong-bonding CaP coatings formed on USAT–C/C-50. The average shear bond strength of the coatings obtained on the USAT–C/C-50 substrate [(12.14 ± 1.30) MPa] was about twice that of the coatings obtained on untreated C/C [(6.78 ± 1.06) MPa].
Keywords: Ultrasound-assisted anodic oxidation treatment; Carbon/carbon composites; Ultrasound-assisted electrochemical deposition; Calcium phosphate; Bond strength;
Light field intensification induced by nanoinclusions in optical thin-films by Zhiwu Zhu; Xiangai Cheng; Liangjin Huang; Zejin Liu (5126-5130).
► Particulates of tens of nanometers can cause laser intensification in optical coatings. ► Electric field and energy deposition was modeled by finite element analysis. ► Light intensification as large as 4× can occur owing to a metallic nanoinclusion. ► Power deposition tends to have a highest value at a certain extinction coefficient. ► Over the range of dielectric extinction coefficient the power deposition increases linearly.Inclusions even in tens of nanometers scale (nanoinclusion) can cause electric field intensifications locally in an optical thin-film when irradiated by laser. It was modeled by using finite element analysis, and the dependences of local light field on complex refractive index, diameter and embedded depth of the nanoinclusion were simulated. In addition, the average light intensity inside the nanodefect was calculated as well as the energy deposition rate. The modeling results show that extinction coefficient of a nanoinclusion has more significant effects on local light field than real part of the refractive index. A light intensification as large as 4× can occur owing to a metallic nanoinclusion and the peaks of electric field distribution locating on the boundary of the particulate. Energy deposition rate, reflecting the behavior of laser induced damage to the thin-film, is found to have the highest value at a certain extinction coefficient, instead of the state that, for a defect, a higher extinction coefficient causes a higher speed of laser absorption. And when this coefficient is relatively small, the energy deposition rate grows linearly with it. Finally, regarding high absorptive nanoinclusions, the larger can induce stronger laser intensification and higher average of energy deposition rate, whereas no significant difference is made by low absorptive nanoinclusions of different sizes.
Keywords: Optical thin-film; Laser damage; Light intensification; Nanoinclusion; Temperature field;
A coating of silane modified silica nanoparticles on PET substrate film for inkjet printing by J. Wu; L. Liu; B. Jiang; Z. Hu; X.Q. Wang; Y.D. Huang; D.R. Lin; Q.H. Zhang (5131-5134).
► The nanoporous coating used this method was fabricated first. ► The microstructure of the inkjet material was analyzed and discussed in detail. ► The ink absorption was examined and analyzed from microstructure.The paper aims to design nanoporous coatings for inkjet printing and study its microstructure influence on the ink absorption. In the present work, two inkjet materials were prepared: one with unmodified nano-SiO2 (S_1), the other with silica coupling agent modified nano-SiO2 (S_2). The surface characteristic changing after modification was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM). Wetting with contact angles was determined by the dynamic contact angle analysis test (DCAT). Through measurements, the dispersion of modified nano-SiO2 particles in the coating was superior to the dispersion of unmodified nano-SiO2 particles, surface roughness value (Ra) of S_1 was significantly higher than that of S_2, dynamic contact angle of S_2 is smaller than that of S_1 and ink droplet absorption in S_2 was much faster than in S_1. These results also reveal that the modification method is effective and offers a potential way to fabricate inkjet material with the advantages of microstructure and ink absorption over traditional methods.
Keywords: Silica nanoparticles; Coating; Microstructure; Silane coupling agent; Polymer film; Inkjet printing;
A novel Ir–Zr gradient coating prepared on Mo substrate by double glow plasma by Xiangna Cong; Zhaofeng Chen; Wangping Wu; Jiang Xu; Fred Edmond Boafo (5135-5140).
► Dense and uniform Ir–Zr coating was obtained by double glow plasma on Mo. ► The Ir–Zr coating was obviously comprised of two parts. ► A model has been made to explain the formation process of the gradient layer.Ir–Zr gradient coating was obtained on the Mo substrate by double glow plasma. The structure and composition of the coatings were confirmed by SEM, AFM, XRD and EDS, respectively. The adhesion strength between the coating and the substrate was evaluated by a scratch tester. Compared with preferential growth orientation of (2 2 0) crystal plane of Ir coating, the Ir–Zr coating had a random orientation structure. The RMS roughness value of the Ir–Zr coating is 19.3 nm, which was lower than the roughness value of 45 nm for Ir coating. The Ir–Zr coating with the thickness of 5.0 μm was composed of two distinct layers. The proportion of Ir decreased gradually from the surface of the coating to the coating/substrate interface. The Zr distribution decreased slightly in the coating. The adhesive force of the Ir–Zr coating was 15 N.
Keywords: Iridium; Zirconium; Structure; Gradient coating;
Effects of drying time on the surface morphology evolution of urushiol–formaldehyde diethylenetriamine polymer microporous films by Yanlian Xu; Weibin Bai; Zhen Luo; Yao Jin; Bichen Peng; Lixia Feng; Binghuan Hu; Jinhuo Lin (5141-5145).
No pores films formed when the TF drying time of UFDP was 90 min; whereas ordered patterns were observed in the films, when the TF drying time of UFDP was decreased to 2.5 min.Display Omitted► Honeycomb-patterned UFDP films were prepared by breath figures approach. ► The drying time plays decisive role in the microporous UFDP films morphology. ► The shorter the drying time was, the more ordered porous films were obtained.Raw lacquer, a renewable and eco-friendly biopolymer material with excellent physico-mechanical properties, has been principally used to coat objects of high artistic and pleasing beauty for centuries. In previous reports, we studied microporous urushiol-based polymer (UBP) films by the water-assisted assembly method. The effect of drying time on the formation of breath figures with honeycomb patterns in the microporous films of urushiol–formaldehyde diethylenetriamine polymer (UFDP) was investigated in this paper. The pattern structure was studied with optical microscopy (OM) and scanning electron microscopy (SEM). The drying time, which is influenced by the reflux time, plays a decisive role in the morphology, such as pore size and distribution periodicity, of the microporous UFDP films.
Keywords: Breath figures; Drying time; Surface morphology; Urushiol;
Diode laser heat treatment of lithium manganese oxide films by J. Pröll; R. Kohler; A. Mangang; S. Ulrich; M. Bruns; H.J. Seifert; W. Pfleging (5146-5152).
► Laser annealing for adjustment of grain size and formation of spinel-like Li–Mn–O phase. ► Reversible CV scans indicating appropriate crystalline phases were obtained. ► Mechanical degradation due to cycling were identified as relevant. ► Chemical degradation due to cycling was assigned to formation of surface reaction layer.The crystallization of lithium manganese oxide thin films prepared by radio frequency magnetron sputtering on stainless steel substrates under 10 Pa argon pressure is demonstrated by a laser annealing technique. Laser annealing processes were developed as a function of annealing time and temperature with the objective to form an electrochemically active lithium manganese oxide cathode. It is demonstrated, that laser annealing with 940 nm diode laser radiation and an annealing time of 2000 s at 600 °C delivers appropriate parameters for formation of a crystalline spinel-like phase. Characteristic features of this phase could be detected via Raman spectroscopy, showing the characteristic main Raman band at 627 cm−1. Within cyclic voltammetric measurements, the two characteristic redox pairs for spinel lithium manganese oxide in the 4 V region could be detected, indicating that the film was well-crystallized and de-/intercalation processes were reversible. Raman post-analysis of a cycled cathode showed that the spinel-like structure was preserved within the cycling process but mechanical degradation effects such as film cracking were observed via scanning electron microscopy. Typical features for the formation of an additional surface reaction layer could be detected using X-ray photoelectron spectroscopy.
Keywords: Laser annealing; Thin film crystallization; Lithium-ion battery; Lithium manganese oxide; Surface reaction layer;
Photochemical reactions of thiol-terminated self-assembled monolayers (SAMs) for micropatterning of gold nanoparticles and controlled surface functionality by Xuemingyue Han; Chong Wu; Shuqing Sun (5153-5156).
► Thiol-functionalization of SiO2/Si surfaces were achieved through the formation of SAMs of MTS. ► Photopatterned SAMs were used as template to direct the site-specific assembly of AuNPs. ► Fluorinated surface was obtained using thiol-ene “click” chemistry.This paper reported a facile method for the patterning of gold nanoparticles (AuNPs) on SiO2/Si by combining photochemical reaction and self-assembly techniques, and the conversion of surface functionality through thiol-ene click chemistry. The oxidation of terminal thiols in self-assembled monolayer of (3-mercaptopropyl)trimethoxysilane upon exposure to 254 nm UV light under ambient atmosphere was investigated. Chemically well-defined microstructures were obtained by UV irradiation through a mask, and subsequent immersion of the substrate into a dispersion of AuNPs resulted in site-specific assembly of AuNPs via Au–S covalent bond in the unexposed area. Thiol-ene “click” reaction between surface thiol-group and alkene-containing molecules under illumination of 365 nm UV light was also demonstrated. X-ray photoelectron spectroscopy study indicated the successful conversion of surface functionality.
Keywords: Thin films; Nanomaterials; Surfaces; Patterning;
Phase evolution in zirconia thin films prepared by pulsed laser deposition by Maneesha Mishra; P. Kuppusami; Akash Singh; S. Ramya; V. Sivasubramanian; E. Mohandas (5157-5165).
► Deposition of zirconia thin films by pulsed laser deposition technique. ► Study of evolution of phases as a function of temperature and pressure. ► Measurements of optical properties at different substrate temperature and oxygen partial pressure. ► Determination of band gap as a function of process parameters.Zirconia thin films were deposited on silicon (1 0 0) and quartz substrates using pulsed laser deposition. Phase formation in zirconia films was monitored as a function of substrate temperature (473–973 K) and oxygen partial pressure (0.001–1 Pa). Volume fraction of tetragonal zirconia is determined from X-ray diffraction and Raman analysis. Tetragonal volume fraction of zirconia films varies from 10 to 76% for different substrate temperature and oxygen partial pressure. Zirconia films show a good transparency in the visible region, except for the films deposited at 473 K and at 0.002 Pa. The band gap values and refractive index of the films are discussed in relation with the microstructure and phase composition of the zirconia films as well as with 8 mol% yttria stabilised zirconia films.
Keywords: Zirconia; Pulsed laser deposition; Phase transformation; Crystallite size; Optical properties;
Effect of surface structure and wettability of DLC and N-DLC thin films on adsorption of glycine by Mukhtar H. Ahmed; John A. Byrne (5166-5174).
► Diamond Like Carbon (DLC) Synthesised and characterised, DLC surface modified with Nitrogen (N-DLC) Adsorption study using amino acid glycine. ► Investigation of glycine configuration using surface energy measurement, spectroscopic ellipsometry, FTIR and Raman spectroscopes Nitrogen content DLC decreases the hydrophobicity. ► Mechanism of adsorption investigated change due to esterification of carboxyl species Small amount of nitrogen content DLC enhance the glycine adsorption.Diamond-like carbon (DLC) is known to have excellent biocompatibility. Various samples of DLC and nitrogen-doped DLC thin films (N-DLC) were deposited onto silicon substrates using plasma-enhanced chemical vapour deposition (PECVD). Subsequently, the adsorption of amino acid glycine onto the surfaces of the thin films was investigated to elucidate the mechanisms involved in protein adhesion. The physicochemical characteristics of the surfaces, before and after adsorption of glycine, were investigated using Fourier transfer infrared (FTIR), Raman spectroscopy, spectroscopic ellipsometry (SE) and contact angle (θ). The Raman study highlighted decrease slightly in the ID/IG ratio at low levels of N (5.4 at.%), whilst increasing the nitrogen dopant level (>5.4 at.%) resulted in a increase of the ID/IG ratio, and the FTIR band at related to C＝N. Following exposure to glycine solutions, the presence of Raman bands at 1727 cm−1 and 1200 cm−1, and FTIR bands at 1735 cm−1 indicates that the adsorption of glycine onto the surfaces has taken place. These results which obtained from SE and surface free energy, show that low levels of nitrogen doping in DLC enhances the adsorption of the amino acid, while, increased doping led to a reduced adsorption, as compared to undoped DLC. Glycine is bound to the surface of the DLC films via both de-protonated carboxyl and protonated amino groups while, in the case of N-DLC gylcine was bound to the surface via anionic carboxyl groups and the amino group did not interact strongly with the surface. Doping of DLC may allow control of protein adsorption to the surface.
Keywords: Diamond-like carbon (DLC); Wettability; Surface free energy; Glycine adsorption; Raman spectroscopy; Fourier transform infrared spectroscopy (FTIR);
Formation of hard surface layer on austenitic stainless steels via simultaneous chromising and nitriding by pack cementation process by D. Zeng; S. Yang; Z.D. Xiang (5175-5178).
► It is feasible to simultaneously chromise and nitride the surface of austenitic stainless steels by pack cementation process. ► Cr2N powders can be used as a source of both N and Cr for the simultaneous process. ► A top Cr2N layer with a Cr enriched alloy layer underneath is formed on the steel surface. ► Hardness values higher than 1800 HV can be achieved in the outermost surface. ► Hardness profile at cross-section of treated surface depends on the chemistry of pack powders.This study aims to increase surface hardness of austenitic stainless steels via simultaneous chromising and nitriding by the pack cementation process. The pack powder mixtures used for the process consisted of Cr2N as a source of both N and Cr for the simultaneous process, NH4Cl as activator and Al2O3 as inert filler; in some cases, Cr powder was added as an additional source for depositing Cr. The AISI204 austenitic stainless steel is studied as a substrate. It is demonstrated that a top Cr2N layer with a Cr enriched layer underneath can be formed on the steel surface at 1100 °C. Hardness values of more than 1800 HV are obtained at the outermost surface of the treated specimen. It has been shown that the hardness profile at the cross-section of the surface depends on the pack chemistry.
Keywords: Nitriding; Chromising; Surface hardness; Austenitic stainless steels; Pack cementation;
Polysaccharide films as templates in the synthesis of hematite nanostructures with special properties by Marimuthu Nidhin; Kalarical Janardhanan Sreeram; Balachandran Unni Nair (5179-5184).
► Chitosan forms self-assembled films with pectin and blends with starch. ► Compared to chitosan–pectin solutions, films offer better size tuning. ► Films carrying adsorbed Fe2+ on calcination generate hematite nanoparticles. ► Template governs magnetic properties of synthesized hematite nanoparticles. ► Films provide for weak-ferromagnetism.Cationic chitosan can form polyionic complexes with anionic polysaccharides such as pectin, which can be cast into films in a similar manner to that of chitosan–starch blends. We report the use of such films as templates in the synthesis of hematite nanoparticles. Mechanistically, the interaction of the iron(II) centers with the carboxyl, amino and other functional groups in the film, after their adsorption into the pores of the template is the key to subsequent synthesis of nanoparticles through calcination. The spatial separation that the specificity of interaction provides is amply made use of through controlled calcination resulting in monodisperse nanoparticles of hematite nanoparticles. This paper also highlights the specific advantages such as rhombohedral shape, ∼40 nm intensity average diameter, narrow size distribution and weak ferromagnetic properties of using the polyion films at pH 2 as templates over polysaccharides either alone or in combination in solution or as blends.
Keywords: Chitosan; Polysaccharides; Hematite; Nanosynthesis; Template; VSM;
Mechanism of Ge2Sb2Te5 chemical mechanical polishing by Liangyong Wang; Zhitang Song; Min Zhong; Weili Liu; Weixia Yan; Fei Qin; Aodong He; Bo Liu (5185-5190).
► GST CMP mechanism at pH 2 and pH 11. ► GST has four zero charge points, larger solubility at pH 11. ► Alkaline slurry shows faster RR, higher selectivity but lower RR/SER ratio. ► GST CMP includes oxidation, hydration, molecule removal, electrochemical process.We report the exploration of Ge2Sb2Te5 (GST) chemical mechanical polishing (CMP) mechanism. Static etching experiments of GST film were first conducted in two typical silica-based slurries (pH 2 and pH 11). To investigate the chemical nature of GST in different chemical environments, solubility of GST in slurries and also the zeta potentials of GST powders vs pH were measured. We further compared the polishing performance to the removal rate (RR), surface roughness, polishing selectivity of GST over oxide, and influence on the phase change property by using the two typical slurries. Then measurements were done for the hardness of GST films before and after polishing, particle size of the slurry during polishing, and also the open circuit potential (OCP) of GST in the two slurries. On the basis of the aforementioned results, we proposed a possible mechanism for GST CMP including reaction formulas, removal of GST as molecules instead of as a lump, surface hydration in alkaline region and electrochemical process, which was partially supported by residue analysis for 8″ patterned wafers using energy dispersive spectroscopy (EDS) under transmission electron microscope (TEM).
Keywords: CMP; GST; Mechanism;