Applied Surface Science (v.297, #C)
Editorial Board (ii).
Synthesis of biomedical composite scaffolds by laser sintering: Mechanical properties and in vitro bioactivity evaluation by Fwu-Hsing Liu (1-8).
Synthesis of biomedical composite scaffold obtained by selective laser sintering.In this study, biomedical composite materials were employed to fabricate bone scaffolds using a self-developed rapid prototyping (RP) apparatus. The slurry formed by combining hydroxyapatite (HA), silica sol, and sodium tripolyphosphate (STPP) was heated by a CO2 laser. Under appropriate processing parameters, a biocomposite green body was subsequently fabricated. Its mechanical properties, including surface roughness, bending and compression strengths, volume shrinkage rate, and surface microstructure, were analyzed after heat treatment to 1200 °C, 1300 °C, and 1400 °C. The results showed that after heating the specimen to 1200 °C, its compression and bending strengths increased significantly to 43.26 MPa and 1.28 MPa, respectively; the surface roughness was 12 μm; and surface pores were of size 5–25 μm. Furthermore, the results of WST-1 and LDH assay indicate that the biocomposites showed no cytotoxicity on 3T3 fibroblast. An optical density (OD) of 1.1 was also achieved, and the specimen was suitable for the adhesion and growth of osteoblast-like cells (MG63). Therefore, the biocomposite bone scaffolds fabricated in this study have potential to be bone implants for developing hard tissue.
Keywords: Layered structures; Ceramic-matrix composites (CMCs); Selective laser sintering; 3D printing;
X-ray nanotomography of a nanofiber: Quantitative measurement of diameter fluctuations by Masoud Allahkarami; Sudheer Bandla; Robert P. Winarski; Jay C. Hanan (9-15).
Imaging nanostructures in three-dimension is beneficial for understanding their formation and interactions. This paper presents application of X-ray imaging as a tool for visualizing the shape fluctuation in polymer nanofibers. Synchrotron X-ray nanotomography is a non-destructive technique that can reveal material internal and surface features at the nanoscale. Diameter fluctuations as a result of processing the polymer nanofiber obtained through forcespinning were imaged using monochromatic synchrotron hard X-rays of 8 keV energy. Reconstructed binary images containing geometric information of the fiber surface were visualized and meshed in 3D. A new approach for processing of the reconstructed data to achieve a quantitative interpretation of 3D results was developed. A local 3D regression approach was developed for tracing the fiber center line, and to determine the minimum distance between triangular surface elements from the center line (radius). Fiber diameter fluctuations measured were presented qualitatively by applying surface coloring to the local fiber diameter information. Nanotomography revealed that the fiber has upto 19% (±43 nm) deviation in fiber radius over the average radius of 221 nm.
Keywords: X-ray nanotomography; Computed tomography; Nanofiber; Fiber diameter;
Atomic layer deposition of Y2O3 and yttrium-doped HfO2 using a newly synthesized Y(iPrCp)2(N-iPr-amd) precursor for a high permittivity gate dielectric by Jae-Seung Lee; Woo-Hee Kim; Il-Kwon Oh; Min-Kyu Kim; Gyeongho Lee; Chang-Wan Lee; Jusang Park; Clement Lansalot-Matras; Wontae Noh; Hyungjun Kim (16-21).
We systematically investigated the effects of Y doping in HfO2 dielectric layer, focusing on structural phase transformation and the dielectric properties of the resultant films. Y doping was carried out using atomic layer deposition (ALD) with a novel Y(iPrCp)2(N-iPr-amd) precursor, which exhibits good thermal stability without any decomposition and clean evaporation. As a result, the ALD process of the Y2O3 films showed well-saturated and linear growth characteristics of ∼0.45 Å/cycle without significant incubation delays and produced pure Y2O3 films. Then, yttrium-doped HfO2 films with various Y/(Y + Hf) compositions (yttrium content: 0.6– 4.8 mol%) were prepared by alternating Y2O3 and HfO2 growth cycles. Structural and electrical characterization revealed that the addition of yttrium to HfO2 induced phase transformations from the monoclinic to the cubic or tetragonal phases, even at low post-annealing temperatures of 600 °C, and improved leakage current densities by inducing oxygen vacancy-related complex defects. A maximum relative dielectric constant of ∼33.4 was obtained for films with a yttrium content of ∼1.2 mol%. Excellent EOT scalability was observed down to ∼1 nm without dielectric constant degradation.
Keywords: High-k; Rare earth; HfO2; Y2O3; Dielectric constant; Yttrium; Leakage current; Gate oxide; ALD; Atomic layer deposition; Precursor;
Evolution of self-organization in nano-structured PVD coatings under extreme tribological conditions by G. Fox-Rabinovich; A. Kovalev; M.H. Aguirre; K. Yamamoto; S. Veldhuis; I. Gershman; A. Rashkovskiy; J.L. Endrino; B. Beake; G. Dosbaeva; D. Wainstein; Junifeng Yuan; J.W. Bunting (22-32).
The evolution of the self-organization process where dissipative structures are formed under the extreme frictional conditions associated with high performance dry machining of hardened steels has been studied in detail. The emphasis was on the progressive studies of surface transformations within multilayer and monolayer TiAlCrSiYN-based PVD coatings during the running-in stage of wear when self-organization process occurs. The coating layer was characterized by high resolution electron energy-loss spectroscopy (HREELS). It is shown that the nano-multilayer coating possesses higher non-equilibrium structure in comparison to the monolayer. Comprehensive studies of the tribo-films (dissipative structures) formed on the friction surface were made using a number of advanced surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). The data obtained for the tribo-films was combined with the detailed TEM studies of the structural and phase transformations within the underlying coating layer. This data was related to the micro-mechanical characteristics of the coating layer and its wear resistance. It was demonstrated that the evolution of the self-organization process is strongly controlled by the characteristics of the tribo-films formed at different stages of the wear process. Within running-in stage (after length of cut of 15 m) fully protective mullite tribo-films predominantly form on the surface of nano-multilayer coating, establishing a functional hierarchy within the layer of tribo-films. This reduces entropy production during friction and leads to significant surface damage reduction and wear rate stabilization. In contrast, in a monolayer coating with a lower structural complexity, a variety of protective and non-protective tribo-films form during the running-in stage, which cannot fully protect the surface. Therefore the wear rate on the monolayer is not stabilized and its wear resistance is lower. The results obtained show that it is possible to control tribo-films evolution during self-organization by means of increase in structural complexity and the non-equilibrium state of the surface engineered layer with simultaneous tuning of its integrative behaviour.
Keywords: Self-organization; Tribo-films; Evolution; Nano-structured hard PVD coatings; Extreme tribological conditions;
Fabrication of a superhydrophobic surface from porous polymer using phase separation by Jianfeng Liu; Xinyan Xiao; Yinlong Shi; Caixia Wan (33-39).
A superhydrophobic porous polymeric surface was fabricated by a simple phase separation process. The as-prepared surface shows a high superhydrophobicity, which mainly arises from its porous structure.The present work reports a simple method to fabricate superhydrophobic porous polymeric surfaces by a phase separation process. The method involves the in situ polymerization of butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) in the presence of co-porogens of 1,4-butanediol (BDO) and N-methyl-2-pyrrolidone (NMP) to afford superhydrophobic surfaces with the micro/nano roughness structure. The influences of the polymerization mixture on the morphology and hydrophobicity were investigated by adjusting the composition of the co-porogens and the mass ratio of monomers to co-porogens, respectively. And a precise description of the underlying mechanism of the microstructure formation was presented. The as-prepared surface shows a superhydrophobicity with water contact angle (WCA) of 159.5° and low sliding angle (SA) of 3.1°. Moreover, the superhydrophobic surface shows good chemical stability with better resistance to acid, alkali or salt aqueous solutions and excellent thermal stability. The method is simple and low-cost and can be used for the preparation of the self-cleaning superhydrophobic surfaces.
Keywords: Superhydrophobic; Porous polymer; Porogen; Phase separation; Water contact angle;
Laser induced forward transfer of Ag nanoparticles ink deposition and characterization by M. Makrygianni; I. Kalpyris; C. Boutopoulos; I. Zergioti (40-44).
In this work, we report on the printing of silver nanoparticles (Ag NPs) ink by means of laser-induced forward transfer (LIFT) process. The optimum conditions for printing circular shaped features using a Nd:YAG laser at 266 nm have been examined. A study of the influence of the laser fluence and the use of a pre-coated intermediate layer (sacrificial layer) on the donor substrate was performed in order to understand how these parameters affect the printed droplets morphology. We also provide a detailed discussion of the influence of the annealing temperature on the printed features morphology and on their resistivity. Based on these results, the conditions have been determined for printing uniform circular shaped droplets with a diameter as small as 25 μm and an average thickness of 150 nm. Atomic force microscopy on the cured printed droplets revealed a uniform surface morphology with no coffee ring effect. Finally, conductive features with reasonably low resistivity (approximately eleven times that of bulk silver) and at sufficiently low sintering temperatures (100–150 °C) were produced on silicon oxide on silicon and flexible polyimide substrates.
Keywords: Laser-induced forward transfer; Sintering; Silver nanoparticles ink;
Dependence of secondary electron emission on surface charging in sapphire and polycrystalline alumina: Evaluation of the effective cross sections for recombination and trapping by K. Said; G. Damamme; A. Si Ahmed; G. Moya; A. Kallel (45-51).
The evolution of the secondary electron emission from sapphire and polycrystalline alumina during electron irradiation, achieved in a scanning electron microscope at room temperature, is derived from the measurement of the induced and the secondary electron currents. The semi-logarithmic plot of the secondary electron emission yield versus the surface density of trapped charges displays a plateau followed by a linear variation. For positive charging, the slope of the linear part, whose value is of about 10−9 cm2, is independent of the primary electron energy, the microstructure and the impurities. It is interpreted as an effective microscopic cross section for electron–hole recombination. For negative charging of sapphire, the slope is associated with an effective electron trapping cross section close to 10−11 cm2, which can be assigned to the dominant impurity trap. These effective values reflect the multiple interactions leading to the accumulation of charges. The yield corresponding to the plateau is controlled by the initial density of impurity traps. A charge transport and trapping >model, based on simplifying assumptions, confirms qualitatively these inferences.
Keywords: Secondary electron emission; Surface trapped charges; Recombination and trapping cross; Section; Alumina insulator, Electron irradiation;
Ultra-small platinum and gold nanoparticles by arc plasma deposition by Sang Hoon Kim; Young Eun Jeong; Heonphil Ha; Ji Young Byun; Young Dok Kim (52-58).
Ultra-small (<2 nm) nanoparticles of platinum and gold were produced by arc plasma deposition (APD) in a systematic way and the deposition behavior was studied. Nanoparticles were deposited on two dimensional amorphous carbon and amorphous titania thin films and characterized by transmission electron microscopy (TEM). Deposition behavior of nanoparticles by APD was studied with discharge voltage (V), discharge condenser capacitance (C), and the number of plasma pulse shots (n) as controllable parameters. The average size of intrinsic nanoparticles generated by APD process was as small as 0.9 nm and deposited nanoparticles began to have crystal structures from the particle size of about 2 nm. V was the most sensitive parameter to control the size and coverage of generated nanoparticles compared to C and n. Size of APD deposited nanoparticles was also influenced by the nature of evaporating materials and substrates.
Keywords: Nanoparticles; Interfaces; Pt; Au; Arc plasma deposition;
Catalytic behavior and synergistic effect of nanostructured mesoporous CuO-MnO x -CeO2 catalysts for chlorobenzene destruction by Chi He; Yanke Yu; Qun Shen; Jinsheng Chen; Nanli Qiao (59-69).
Mesoporous CuO-MnO x -CeO2 composite metal oxides with different copper and manganese loadings were prepared by a urea-assistant hydrothermal method, and were further adopted for the complete catalytic combustion of chlorobenzene. The effects of reaction conditions such as inlet reagent concentration and water feed concentration on chlorobenzene combustion were also studied. The structure and textural properties of the synthesized catalysts were characterized via the XRD, N2 adsorption/desorption, FE-SEM, TEM, H2-TPR, O2-TPD, and XPS techniques. The characterization results reveal that the presence of a small amount of Mn species can facilitate the incorporation of Cu and Mn ions into ceria lattice to form Cu-Mn-Ce-O solid solution. The synergistic effect of Cu and Mn species can reduce the redox potential of the composite catalysts, and produce large amounts of oxygen vacancies in the interface of CuO x , MnO x , and CeO2 oxides. The catalyst with Cu/Mn atomic ratio of 1/1 exhibits the best chlorobenzene elimination capability, oxidizing about 95% of the inlet chlorobenzene at 264 °C with CO2 selectivity higher than 99.5%. The concentration and mobility of the chemically adsorbed oxygen are vital for the effective removal of surface Cl species, which inhibits the dissociation of oxygen molecules and decreases the reducibility of the copper and manganese species. It can be rationally concluded that the superior catalytic performance and durability of the mesoporous CuO-MnO x -CeO2 composite oxides are primarily attributed to the higher surface oxygen concentration and better active oxygen mobility.
Keywords: Mesoporous CuMnCeO x ; Chlorobenzene; Catalytic combustion; Reaction conditions; Synergistic effect; Catalyst deactivation;
Relative contributions of surface and grain boundary scattering to the spin-polarized electrons transport in the AlN/NiFe/AlN heterostructures by Chong-Jun Zhao; Zhi-Duo Zhao; Zheng-Long Wu; Guang Yang; Fen Liu; Lei Ding; Jing-Yan Zhang; Guang-Hua Yu (70-74).
When the film thickness approaches the electron mean free path (MFP), the relative contributions of surface/grain boundary scattering to the resistivity remain indefinitive. In this work, series of NiFe films sandwiched by AlN barriers were employed to study the transport properties. Surface scattering is found to provide the strongest contribution to the resistivity increase for very thin films (d NiFe ≤ 10 nm). With the increase of the film thickness, the effect of the grain boundary scattering gradually increases while the surface scattering decreases. When the thickness of the film is over 30 nm, the former becomes predominant.
Keywords: Spin electrons transport; NiFe/AlN interface; Grain boundary scattering; Surface scattering;
Oxidation of Ag nanoparticles in aqueous media: Effect of particle size and capping by Yuri L. Mikhlin; Elena A. Vishnyakova; Alexander S. Romanchenko; Svetlana V. Saikova; Maxim N. Likhatski; Yurii V. Larichev; Fedor V. Tuzikov; Vladimir I. Zaikovskii; Sergey M. Zharkov (75-83).
Many applications and environmental impact of silver-bearing nanomaterials critically depend upon their specific reactivity, which is still poorly understood. Here, silver nanoparticles (Ag NPs) of about 3–5 nm and 10–12 nm in diameter, uncapped and capped with l-glucose or citrate, were prepared, characterized using UV–vis absorption spectroscopy, SAXS, TEM, and their (electro)chemical oxidation was examined in comparison with each other and bulk metal applying scanning tunneling microscopy and spectroscopy, cyclic voltammetry, and XPS. A resistive switching effect was found in the tunneling spectra measured in air at the smaller uncapped Ag NPs deposited on HOPG and was interpreted in terms of Ag transfer between the particle and the probe. The anodic oxidation of these Ag NPs in 1 M NaOH yielded 3D Ag2O, while only a layer of “primary” Ag(I) oxide emerged on larger uncapped nanoparticles during the potential sweep. The formation of AgO at higher potentials proceeded readily at the “primary” oxide but was retarded at the smaller NPs. The citrate- and glucose-capping substantially impeded the formation both of Ag2O and AgO. The findings highlighted, particularly, a non-trivial effect of particle size and transient mobilization of Ag species on the reactions of silver nanoparticles.
Keywords: Silver nanoparticles; Oxidation; Resistive switching effect; X-ray photoelectron spectroscopy;
Fabrication of nanoporous Au films with ultra-high surface area for sensitive electrochemical detection of glucose in the presence of Cl− by Hwakyeung Jeong; Jongwon Kim (84-88).
Nanoporous Au films with ultra-high surface area (roughness factor greater than 1000) were prepared via one-step anodization of Au in citric acid solution. The as-prepared surface of nanoporous Au films was covered with carbonaceous materials, which could be removed by electrochemical methods to produce electrochemically active surfaces. The cleaned nanoporous Au films exhibited high electrochemical activities for glucose oxidation; however, the expansion of the surface area did not necessarily contribute to the sensitivity enhancement in the absence of Cl−. The ultra-high surface area of the nanoporous Au significantly enhanced the sensitivity of the electrochemical detection of glucose in the presence of 100 mM of Cl−, enabling sensitivity as high as 120 μA mM−1 cm−2. Nafion-coated nanoporous Au exhibited a linear amperometric response to glucose with high sensitivity without interference from ascorbic acid. The preparation of nanoporous Au with ultra-high surface area will offer new opportunity for electroanalytical applications based on nanoporous Au structures.
Keywords: Nanoporous Au; Anodization; Citric acid; Glucose; Electrochemical detection;
Thermal stability of barrierless Cu–Ni–Sn films by X.N. Li; M. Wang; L.R. Zhao; C.M. Bao; J.P. Chu; C. Dong (89-94).
To increase the thermal stability against interface reaction, barrierless Cu–Ni–Sn seed layers, with compositions formulated according to the cluster-plus-glue-atom model for stable solid solutions, was investigated in this paper. In this model, Sn is dissolved in Cu via Ni which is soluble both with Cu and with Sn, and the stable solid solution is formulated as [Sn–Ni12]Cu x , where the Sn-centered [Sn–Ni12] octahedral clusters are embedded in an FCC Cu matrix of x atoms. Cu–Ni–Sn films with various Ni/Sn ratios were deposited onto the Si(1 0 0) substrate by magnetron sputtering and were characterized for microstructure and for electrical resistivity. The (Sn1.1/13.1Ni12/13.1)0.3Cu99.7 (at.%) film, with its Ni/Sn composition ratio being close to the ideal 12/1 value of the model, showed the minimum electrical resistivity of 2.7 μΩ cm on 500 °C/1 h annealing among all the samples. The resistivity maintained as low as 2.8 μΩ cm even after 400 °C/40 h annealing. No Cu silicide was observed by XRD and TEM in this sample, though a minute amount of fine Cu–Sn compound precipitates was present. The superior diffusion inhibiting effect was attributed to Sn in solid solution via intermediate of Ni.
Keywords: Cu alloys; Thin film; Electrical resistivity; Silicide; Cluster-plus-glue-atom model;
Cell adhesion and growth on ultrananocrystalline diamond and diamond-like carbon films after different surface modifications by J. Miksovsky; A. Voss; R. Kozarova; T. Kocourek; P. Pisarik; G. Ceccone; W. Kulisch; M. Jelinek; M.D. Apostolova; J.P. Reithmaier; C. Popov (95-102).
Diamond and diamond-like carbon (DLC) films possess a set of excellent physical and chemical properties which together with a high biocompatibility make them attractive candidates for a number of medical and biotechnological applications. In the current work thin ultrananocrystalline diamond (UNCD) and DLC films were comparatively investigated with respect to cell attachment and proliferation after different surface modifications. The UNCD films were prepared by microwave plasma enhanced chemical vapor deposition, the DLC films by pulsed laser deposition (PLD). The films were comprehensively characterized with respect to their basic properties, e.g. crystallinity, morphology, chemical bonding nature, etc. Afterwards the UNCD and DLC films were modified applying O2 or NH3/N2 plasmas and UV/O3 treatments to alter their surface termination. The surface composition of as-grown and modified samples was studied by X-ray photoelectron spectroscopy (XPS). Furthermore the films were characterized by contact angle measurements with water, formamide, 1-decanol and diiodomethane; from the results obtained the surface energy with its dispersive and polar components was calculated. The adhesion and proliferation of MG63 osteosarcoma cells on the different UNCD and DLC samples were assessed by measurement of the cell attachment efficiency and MTT assays. The determined cell densities were compared and correlated with the surface properties of as-deposited and modified UNCD and DLC films.
Keywords: Ultrananocrystalline diamond films; Diamond-like carbon films; Surface modification; Direct contact cell tests;
Controllable preparation, growth mechanism and the properties research of TiO2 nanotube arrays by Yinchang Li; Qun Ma; Jun Han; Lili Ji; Junxia Wang; Jieyu Chen; Yongqian Wang (103-108).
FESEM images of top view (a), fracture surface (b) and bottom view (c) of TiO2 nanotubes. The FESEM of titanium dioxide prepared in the glycol electrolyte which contains 0.5 wt% NH4F and 10 vol% H2O at room temperature and calcined 2 h at 450 °C, the oxidation voltage is 30 V and the oxidation time is 1 h. In the figure, (a) is the surface of titanium dioxide, from which we can see that the titanium dioxide nanotubes generated on titanium substrate is neatly, highly ordered, the tubular structure is uniform and clear, the inner diameter is about 60–100 nm. (b) is a lateral view of nanotubes, the length of nanotubes we measured is about 2.12 μm. (c) is the bottom figure of nanotube arrays, we can see that the bottom of the nanotubes is closed, well-organized. So we prepared the titanium dioxide nanotube arrays successfully.In this paper we prepared titanium nanotube arrays in ethylene glycol organic electrolyte which contains ammonium fluoride through anodic oxidation method. We found that the preparation of the structure and morphology of TiO2 nanotube arrays can be controlled by changing the preparation parameters. While the oxidation voltage is the main factor that controls the diameter of nanotubes, the length of nanotubes is mainly depending on the oxidation time, and the crystal type is closely related to the annealing temperature. Its photo-degradation rate of methylene blue can reach to 92% which is almost two times than the titania(P25).
Keywords: TiO2; Nanotube arrays; Controllable preparation; Growth mechanism;
Enhanced corrosion resistance and hemocompatibility of biomedical NiTi alloy by atmospheric-pressure plasma polymerized fluorine-rich coating by Penghui Li; Limin Li; Wenhao Wang; Weihong Jin; Xiangmei Liu; Kelvin W.K. Yeung; Paul K. Chu (109-115).
To improve the corrosion resistance and hemocompatibility of biomedical NiTi alloy, hydrophobic polymer coatings are deposited by plasma polymerization in the presence of a fluorine-containing precursor using an atmospheric-pressure plasma jet. This process takes place at a low temperature in air and can be used to deposit fluoropolymer films using organic compounds that cannot be achieved by conventional polymerization techniques. The composition and chemical states of the polymer coatings are characterized by fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the coated and bare NiTi samples is assessed and compared by polarization tests and electrochemical impedance spectroscopy (EIS) in physiological solutions including simulated body fluids (SBF) and Dulbecco's Modified Eagle's medium (DMEM). The corrosion resistance of the coated NiTi alloy is evidently improved. Protein adsorption and platelet adhesion tests reveal that the adsorption ratio of albumin to fibrinogen is increased and the number of adherent platelets on the coating is greatly reduced. The plasma polymerized coating renders NiTi better in vitro hemocompatibility and is promising as a protective and hemocompatible coating on cardiovascular implants.
Keywords: Corrosion resistance; Hemocompatibility; Plasma polymerization; Fluorine; Coatings;
A comparative study of microstructures on the photoelectric properties of tungsten trioxide films with plate-like arrays by Chaoqun Yang; Qiang Zhu; Shunping Zhang; Zhijun Zou; Kuan Tian; Changsheng Xie (116-124).
WO3 plate-like array film was grown on the FTO electrodes by a simple hydrothermal method. In order to change the microstructures of the WO3 films, the as-grown films were further post-heat treated in air and in H2, respectively. The photoresponse characteristics of the as-prepared WO3 films are investigated in the gas phase, and to explain the slow decay of the photocurrent of WO3, the electron trapping effect is proposed. We found that both of the phase structures and oxygen vacancies had great influences on the photoresponse characteristics of WO3 films. For the three WO3 films, the photocurrent decreased significantly with the distortion of the octahedra which were the building blocks of the various crystal structures and with the decreasing of oxygen vacancy concentration. The untreated-WO3 shows 2.5 times higher photocurrent intensity than hydrogen-treated WO3 and the hydrogen-treated WO3 shows 17 times higher photocurrent intensity than air-treated WO3. The experimental results revealed the influence of phase structure on the photoelectric performance of WO3 was far greater than that of oxygen vacancy. We also found that the hydrogen-treated WO3 exhibited excellent infrared photoresponse property, which was 20 times higher than that of the pristine WO3. This was attributed to the existing large number of oxygen vacancies yielding extended energy states which often formed a continuum extending to and overlapping with the conduction band (CB) edge.
Keywords: WO3; Photoconductivity; Electron trapping; Infrared light response;
The electrical properties of low pressure chemical vapor deposition Ga doped ZnO thin films depending on chemical bonding configuration by Hanearl Jung; Doyoung Kim; Hyungjun Kim (125-129).
The electrical and chemical properties of low pressure chemical vapor deposition (LP-CVD) Ga doped ZnO (ZnO:Ga) films were systematically investigated using Hall measurement and X-ray photoemission spectroscopy (XPS). Diethylzinc (DEZ) and O2 gas were used as precursor and reactant gas, respectively, and trimethyl gallium (TMGa) was used as a Ga doping source. Initially, the electrical properties of undoped LP-CVD ZnO films depending on the partial pressure of DEZ and O2 ratio were investigated using X-ray diffraction (XRD) by changing partial pressure of DEZ from 40 to 140 mTorr and that of O2 from 40 to 80 mTorr. The resistivity was reduced by Ga doping from 7.24 × 10−3 Ω cm for undoped ZnO to 2.05 × 10−3 Ω cm for Ga doped ZnO at the TMG pressure of 8 mTorr. The change of electric properties of Ga doped ZnO with varying the amount of Ga dopants was systematically discussed based on the structural crystallinity and chemical bonding configuration, analyzed by XRD and XPS, respectively.
Keywords: Ga doped ZnO; Electrical properties; Chemical bonding configuration;
Local equilibrium in the dissolution and segregation kinetics of Ag on Cu(1 1 1) surface by Min Lin; Xu Chen; XinYi Li; Chi Huang; YanXiu Li; JiangYong Wang (130-133).
The local equilibrium in the kinetic processes of dissolution and segregation of Ag on Cu(1 1 1) surface is addressed. The measured dissolution and segregation kinetic data of Ag on Cu(1 1 1) surface at temperature of 450 °C are well fitted by the modified Darken model. The segregation parameters, i.e. segregation energy, interaction and diffusion parameters, in the Cu(1 1 1)(Ag) binary system are obtained upon fitting. Using the obtained segregation parameters, the discontinuous transition of Ag surface concentration against the bulk concentration of the surface neighboring layers deduced from the local equilibrium model is quantitatively interpreted.
Keywords: Local equilibrium; Surface segregation; Dissolution; Kinetics; Modified Darken model;
Femtosecond laser fabrication of large-area periodic surface ripple structure on Si substrate by L. Hong; Rusli; X.C. Wang; H.Y. Zheng; H. Wang; H.Y. Yu (134-138).
In this paper, we report the fabrication of a large area uniformly distributed periodic nano-ripple structure on silicon substrate through the proper scanning of a line-shaped femtosecond laser beam. The fabricated nano-ripple structure has a periodicity of ∼600 nm and a ripple depth of ∼300 nm. The modulation depth is much deeper than the one previously reported. The developed structure is demonstrated to be able to substantially reduce light reflection due to the effective optical coupling between the incident sunlight with the nano-ripple structure and exhibit an absorption enhancement of ∼41% compared with planar silicon wafer. The physics underlying the formation of the nano-ripple structure is also discussed.
Keywords: Femtosecond pulsed laser; Ripple formation; Si; Laser fluence; Optical reflection;
Controlled synthesis of transition metal dichalcogenide thin films for electronic applications by Riley Gatensby; Niall McEvoy; Kangho Lee; Toby Hallam; Nina C. Berner; Ehsan Rezvani; Sinéad Winters; Maria O’Brien; Georg S. Duesberg (139-146).
Two dimensional transition metal dichalcogenides (TMDs) are exciting materials for future applications in nanoelectronics, nanophotonics and sensing. In particular, sulfides and selenides of molybdenum (Mo) and tungsten (W) have attracted interest as they possess a band gap, which is important for integration into electronic device structures. However, the low throughput synthesis of high quality TMD thin films has thus far hindered the development of devices, and so a scalable method is required to fully exploit their exceptional properties. Within this work a facile route to the manufacture of devices from MoS2 and WS2, grown by vapour phase sulfurisation of pre-deposited metal layers, is presented. Highly homogenous TMD films are produced over large areas. Fine control over TMD film thickness, down to a few layers, is achieved by modifying the thickness of the pre-deposited metal layer. The films are characterised by Raman spectroscopy, electron microscopy and X-ray photoelectron spectroscopy. The thinnest films exhibit photoluminescence, as predicted for monolayer MoS2 films, due to confinement in two dimensions. By using shadow mask lithography, films with well-defined geometries were produced and subsequently integrated with standard microprocessing process flows and electrically characterised. In this way, MoS2 based sensors were produced, displaying sensitivity to NH3 down to 400 ppb. Our device manufacture is versatile, and is adaptable for future nanoscale (opto-) electronic devices as it is reproducible, cost effective and scalable up to wafer scale.
Keywords: 2D materials; Transition metal dichalcogenides; Nanoelectronics; Sensors; Spectroscopy; Thin films;
Superhydrophilic surface modification of fabric via coating with nano-TiO2 by UV and alkaline treatment by Mingyu Li; Tingting Deng; Shuxian Liu; Fengxiu Zhang; Guangxian Zhang (147-152).
Increasing the hydrophilicity of poly(ethylene terephthalate) (PET) fabric has been an ongoing research goal. In this study, a rapid, environmentally friendly, and highly efficient method for modifying the surface of PET fabric is presented. In a solution of 30 g/L nano-TiO2, 50 g/L H2O2, and 30 g/L NaOH, PET fabric was modified to become superhydrophilic by ultraviolet (UV) irradiation (1000 W) for only 30–40 min. The water contact angle of the modified PET fabric was decreased to 0°, and the water absorption rate of the modified PET fabric was increased from 85% to 104%. The capillary rise height increased from 0.2 cm to 6.2 cm, and the spraying rating decreased from 4 to 1. The crease recovery angles of modified PET fabrics were reduced by only 1.2–8.8%. The mechanical and physical properties of the modified PET fabric remained good. Compared to the surface of unmodified PET fabric, scanning electron microscopy showed that the surface of the modified PET fiber was rough and covered by a layer of other materials. Fourier transform infrared spectroscopy showed the materials on the surface of modified PET fibers likely included ―COOH and ―OH groups. X-ray diffraction demonstrated the formation of crystalline material. Finally, differential scanning calorimetry thermograms showed that the modification process slightly improved the thermostability of PET fibers.
Keywords: PET fabric; Surface modification; Ultraviolet radiation; TiO2 nanoparticle; Superhydrophilicity;
Room temperature deposited transparent p-channel CuO thin film transistors by K.C. Sanal; L.S. Vikas; M.K. Jayaraj (153-157).
Copper oxide thin films were grown by rf magnetron sputtering on glass substrates at room temperature varying the oxygen partial pressure. Using the XRD and XPS analytical measurements, the deposition condition for the formation of Cu2O and CuO phases were optimised. The optical band gap of the Cu2O and CuO was 2.31 and 1.41 eV, respectively. The bottom gate structured transparent TFTs fabricated using p-type CuO active layers operated in enhancement mode with an on/off ratio of 104 and field-effect mobility of 0.01 cm2/V s.
Keywords: rf-Sputtering; CuO; GXRD; XPS; TFT;
Electrical transport in layer-by-layer solution deposited Cu2SnS3 films: Effect of thickness and annealing temperature by Devendra Tiwari; Tapas K. Chaudhuri; T. Shripathi (158-166).
Thermoelectric and photothermoelectric analysis have been employed to determine the carrier transport in solution deposited Cu2SnS3 films in temperature range 120–273 K. The effect of varying thickness and annealing temperatures on the electrical conduction are studied. The variation in conductivity is found to be thermally activated. The change in conductivity with thickness and annealing temperature is resolved into individual contributions of carrier concentration and mobility. Both carrier concentration and mobility change have been found to affect the conductivity under different variations. The changes observed have been qualitatively correlated with incorporation of defects during layer by layer deposition of films. The change in concentration and distribution of these defects are suggested to alter observed electrical transport of Cu2SnS3 films of different thickness and after annealing at different temperatures.
Keywords: Cu2SnS3 films; Solution deposition; Electrical conductivity; Thermoelectric power; Carrier transport;
In-situ reflection-XANES study of ZDDP and MoDTC lubricant films formed on steel and diamond like carbon (DLC) surfaces by Ardian Morina; Hongyuan Zhao; J. Fred W. Mosselmans (167-175).
Chemical characterisation of boundary lubricated interfaces is essential for developing mechanistic models that describe lubricant additive interactions with the surface and their effect on tribological performance. In this study the potential for using the synchrotron-based reflection mode X-ray absorption spectroscopy (XAS) technique for in-situ chemical characterisation of lubricant films has been studied. Thermal films formed from zinc dialkyl dithio phosphate (ZDDP) and molybdenum dialkyl dithio carbamate (MoDTC) lubricant additives have been formed and analysed in-situ using the X-ray absorption near edge structure (XANES) spectroscopy technique. The surface sensitivity of this approach was improved by doing the analysis in reflection mode, enabling analysis of only top layer (up to around 10 nm) of the solid surface. In addition, in-lubro analysis of pre-formed tribofilms from the same additives was done using non-vacuum conditions. The results are discussed in conjunction with XANES and X-ray photoelectron spectroscopy (XPS) analysis of similar additives published in the literature. The results obtained are consistent with the existing ZDDP and MoDTC literature and provide some new insight into intermediate species not reported before. The advantages and disadvantages of the developed XANES methodology for in-situ surface chemical analysis of lubricated conditions are discussed.
Keywords: Lubricant additives; Tribofilm; XANES; MoDTC; ZDDP;
Effects of cathodic voltages on structure and wear resistance of plasma electrolytic oxidation coatings formed on aluminium alloy by Qingbiao Li; Jun Liang; Baixing Liu; Zhenjun Peng; Qing Wang (176-181).
Plasma electrolytic oxidation (PEO) coatings were prepared on aluminium alloy using pulsed bipolar power supply at constant anodic voltage and different cathodic voltages. The samples were prepared to attain the same coating thickness by adjusting the processing time. The scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and tribometer were employed to investigate the microstructure, element content, phase composition and wear resistance of the coatings respectively. It was found that the coating growth rate enhanced obviously and the coatings exhibited a more compact structure with thicker inner layer and lower surface roughness when the cathodic voltage increased. The coatings were mainly composed of crystalline γ-Al2O3 and amorphous silicate oxides and their relative content changed with the cathodic voltage. The wear resistance of the coatings improved significantly with the increase of cathodic voltage.
Keywords: Plasma electrolytic oxidation; Aluminium alloy; Cathodic voltages; Wear resistance;
A modified co-precipitation process to coat LiNi1/3Co1/3Mn1/3O2 onto LiNi0.8Co0.1Mn0.1O2 for improving the electrochemical performance by Xibin Lu; Xinhai Li; Zhixing Wang; Huajun Guo; Guochun Yan; Xing Yin (182-187).
A modified LiNi1/3Co1/3Mn1/3O2-coating process is introduced to improve the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 (LNCM811). The coating process is carried on a precursor, Ni0.8Co0.1Mn0.1(OH)2 (NCM811), rather than on LNCM811. Unlike the electro-inert metal oxide coatings, the LiNi1/3Co1/3Mn1/3O2 (LNCM111) layer is electrochemically active and able to relieve reactions between the highly delithiated Li1−μ Ni0.8Co0.1Mn0.1O2 and the electrolyte on account of the decrease of nickel content in outer layer. The LNCM111-coated LNCM811 material shows superior electrochemical performance, with an initial discharge capacity of 153 mAh g−1 and capacity retention of 90% after 100 cycles at 2C rate between 2.8 and 4.3 V at 60 °C.
Keywords: Li-ion battery; Coating; LiNi0.8Co0.1Mn0.1O2; LiNi1/3Co1/3Mn1/3O2;
Studies on structure and Raman spectroscopy of Ni-doped copper phthalocyanine thin films by XueYan Wang; JianBang Zheng; Kai Qiao; JunRong Qu; ChongDe Cao (188-194).
Ni-doped copper phthalocyanine (CuPc) organic films with different mixing ratios were prepared in high vacuum (HV) chamber. The results of AFM, XRD, UV–vis and Raman spectroscopy indicated that the surface morphologies of the films were found to be flater and the structures of the CuPc films still kept their original α-phase crystal, with only the crystallinity or crystallite sizes being changed and the versatile structure or charge transport being modified with the increase of Ni-doping ratios. Moreover, 514 nm-visible-light-excited normal Raman spectra (NRS), 325 nm-ultraviolet-excited and 633 nm-excited resonance Raman spectra (RRS) were analyzed by comparison and by density functional theory (DFT) calculations of the amorphous nickel atoms clusters, confirming that there were no chemical changes between CuPc molecules and nickel atoms; and the amorphous nickel atoms clusters had a noticeable light absorption loss, offering us an insightful structural understanding of the Raman effect of the different concentrations of Ni-doped CuPc films.
Keywords: Organic thin film; The amorphous nickel atoms clusters; Raman polarization; Resonance Raman spectra; Ni-Doped.;
Thermally induced evolution of sol–gel grown WO3 films on ITO/glass substrates by T. Caruso; M. Castriota; A. Policicchio; A. Fasanella; M.P. De Santo; F. Ciuchi; G. Desiderio; S. La Rosa; P. Rudolf; R.G. Agostino; E. Cazzanelli (195-204).
The electronic, morphological and structural properties of WO3 thin films, synthesized via a sol–gel route and deposited on ITO/glass substrates by spin-coating, were analyzed as a function of annealing temperature (100–700 °C range) by Scanning Electron Microscopy, Atomic Force Microscopy, micro-Raman spectroscopy, X-ray Diffraction and Photoelectron Spectroscopy. We have found evidence of two competing processes when the film is annealed at high temperatures (600–700 °C): a structural phase transition from amorphous to crystalline WO3 and a temperature-activated diffusion of sodium ions, from the substrate into the WO3 film, which induces the formation of sodium tungstate. The surface of the films was found to be oxygen deficient after deposition but reverted to fully oxidized WO3 after high temperature annealing in air. The annealing also induced a restructuring of the films with formation of nano-crystalline aggregates. The influence of film thickness on these processes was also investigated.
Keywords: Tungsten trioxide; Thin film annealing; Sol–gel; Raman spectroscopy; Photoelectron spectroscopy; Sodium diffusion;
Effect of microstructure on corrosion behavior of Ag-30Cu-27Sn alloy in vitro media by Mehdi Salehisaki; Maryam Aryana (205-212).
In the present work, three simple heat treatment cycles were used to study the effects of microstructure on electrochemical corrosion behavior of Ag-30Cu-27Sn dental alloy.The electrochemical impedance spectroscopy (EIS) measurements and potentiodynamic polarization tests were carried out to investigate the corrosion behavior of as-cast and heat treated samples in synthetic saliva solution. The presence of intermetallic compounds were studied by X-ray diffraction method (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray detector (EDAX). The microstructural observations and electrochemical corrosion results revealed that, increasing the cooling rate improves the corrosion behavior of under investigation samples. Improvement of the corrosion behavior is attributed to reducing the area of fine distributed Ag3Sn islands in the Cu-rich matrix which decrease the cathode/anode ratio of microgalvanic cells.
Keywords: Restorative tooth material; Heat treatment; Microstructure; Electrochemical corrosion; Synthetic saliva;