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Applied Surface Science (v.260, #)

Editorial Board (pp. ii).

Preface by Valentin Craciun Guest Editor; Rolly Gaboriaud Guest Editor; Florencio Sánchez Guest Editor; Thomas Schroeder Guest Editor (pp. 1-1).

Very hard TiN thin films grown by pulsed laser deposition by D. Craciun; N. Stefan; G. Socol; G. Dorcioman; E. McCumiskey; M. Hanna; C.R. Taylor; G. Bourne; E. Lambers; K. Siebein; V. Craciun (pp. 2-6).

► TiN films thinner than 400nm were grown at RT and 300°C by PLD technique. ► Simulation of XRR curves acquired showed that TiN films were very dense and smooth. ► XRD spectra found that TiN were crystalline, with crystallites size from 10 to 35nm and micro-strain values of 0.6–1.1%. ► Nanoindentation investigations found hardness values between 35 and 40GPa.TiN films thinner than 400nm were grown on (100) Si substrates at room temperature and 300°C by the pulsed laser deposition (PLD) technique using a KrF excimer laser ( λ=248nm, pulse duration τ=25ns, 6.0J/cm² fluence, and 40Hz repetition rate) under various atmospheres. Simulation of X-ray reflectivity curves acquired from films showed they were very dense and smooth, while X-ray diffraction investigations found they were crystalline, with crystallites size from 10 to 35nm and micro-strain values of 0.6–1.1%. The oxygen content in bulk, measured by Auger electron spectroscopy (AES), was below 3.1at%. Nanoindentation investigations found hardness values between 35 and 40GPa, amongst the highest values reported for TiN films. The high laser fluence used for ablation generated energetic ions and atomic species that bombarded the substrate during growth, resulting in the deposition of very dense films, exhibiting high micro-strain values and small crystallite sizes, which could explain the measured hardness values.

Keywords: TiN; Thin films; Hardness; Micro-strain; Pulsed laser deposition

Structure and strain state of polar and semipolar InGaN quantum dots by T. Koukoula; A. Lotsari; Th. Kehagias; G.P. Dimitrakopulos; I. Häusler; A. Das; E. Monroy; Th. Karakostas; Ph. Komninou (pp. 7-12).

► The properties of ultrathin (0001) and(112¯2) InGaN quantum dots were compared. ► Polar dots grown at high temperatures exhibited defined truncated morphology. ► Indium interdiffusion was reduced under the employed PAMBE growth scheme. ► Lenticular semipolar quantum dots can be deposited at lower temperatures. ► The indium content in the dots was determined taking a plane stress state.The nanoscale structural properties of ultrathin (2nm high) self-assembled (0001) polar and(112¯2) semipolar InGaN/GaN quantum dot (QD) superlattices, grown by plasma-assisted molecular beam epitaxy, were investigated using transmission electron microscopy (TEM) techniques. Samples grown under two sets of temperature ranges were compared. The higher-temperature uncapped polar QDs were well-defined and exhibited a truncated pyramidal morphology. Similar morphology was observed for the embedded QDs, albeit faintly diffused. On the other hand, the polar superlattices grown at lower temperatures were heavily distorted due to a large stacking fault density. Semipolar QDs exhibited lenticular morphology. The QD superlattices were found to be elastically strained using geometrical phase analysis, and their strain state was well-described by a biaxial approximation. The extrapolated indium content was consistent with reduced indium incorporation efficiency for the semipolar case compared with the polar one.

Keywords: Quantum dots; InGaN; III-Nitrides; Transmission electron microscopy; Strain

Assembly and structure of Ni/NiO core–shell nanoparticles by Sergio D’Addato; Vincenzo Grillo; Salvatore Altieri; Stefano Frabboni; Sergio Valeri (pp. 13-16).

► We report an investigation of structure in Ni/NiO core–shell nanoparticles (NP). ► NP have been realized with a gas aggregation source and by controlled oxidation. ► A HR-TEM analysis was performed, also with exit wave reconstruction method. ► Ni NP core has a regular multitwinned Mckay icosahedral structure. ► NiO forms island with direct or opposite (twinned) stacking on Ni (111) surfaces.In this work it is reported a detailed investigation of the structure in Ni/NiO core–shell nanoparticles (NP). An experimental set-up was realized for the preparation and the study of pre-formed NP films. NiO shell was obtained with controlled dosing of O₂ gas in the experimental system. A comparison of HR-TEM experimental images with theoretical simulations shows that the Ni NP core has a regular multitwinned icosahedral structure, composed with single crystal tetrahedra with (111) faces. NiO phase is clearly observed forming islands on the NP surface. In order to better investigate the oxide shell, the exit wave reconstruction method was applied to the images. It was found evidence of oxide island formation with direct or opposite (twinned) stacking on Ni (111) surfaces.

Keywords: Core–shell nanoparticles; Gas-phase synthesis; TEM analysis; Ni, O

Effect of ultraviolet light exposure to boron doped hydrogenated amorphous silicon oxide thin film by Seungsin Baek; S.M. Iftiquar; Juyeon Jang; Sunhwa Lee; Minbum Kim; Junhee Jung; Hyeongsik Park; Jinjoo Park; Youngkuk Kim; Chonghoon Shin; Youn-Jung Lee; Junsin Yi (pp. 17-22).

► We investigated effect of ultraviolet light exposure on p-type a-SiO:H films. ► Change in Urbach energy is lower for films with higher oxygen content. ► Hydrogen diffusion is lower for films with higher oxygen content. ► In higher oxides more OB bonds are converted to SiB bonds due to the UV light. ► Overall degradation of the films are lower for films with higher oxygen content.We have investigated the effect of ultraviolet (UV) light exposure to boron doped (p-type) hydrogenated amorphous silicon oxide (p-a-SiO:H) thin semiconductor films by measuring changes in its structural, electrical and optical properties. After a 50h of UV light soaking (LS) of the films, that have 1.2, 6.9, 15.2, 25.3at.% oxygen content (C(O)) and optical gap (E₀₄) of 1.897, 2.080, 2.146 and 2.033eV, show a relative increase in the C(O) by 28.0%, 9.8%, 2.0%, 3.1%, a relative increase in the Urbach energy ( E_u) by 42%, 24%, 8%, 0%, decrease in the E₀₄ by 66, 2, 12, 19meV and the gap state defect density ( N_d) show an increase by 6.5%, 3.4%, 0.7%, 0.1%. At higher oxygen content the observed UV light induced degradation (LID) is relatively less than that for films with lower oxygen content, indicating that higher oxides face less changes under the UV light.

Keywords: p-Type hydrogenated amorphous silicon oxide; Hydrogen diffusion; Light induced degradation

Atomistic modeling and HRTEM analysis of misfit dislocations in InN/GaN heterostructures by J. Kioseoglou; E. Kalesaki; G.P. Dimitrakopulos; Th. Kehagias; Ph. Komninou; Th. Karakostas (pp. 23-28).

► Identification of misfit dislocations (MD) in-plane configuration in InN/GaN interfaces. ► Energetic mapping designates that MD arrays adopt 〈11−20〉 line directions withb=1/3〈2−1−10〉. ► Local arrangement of the Moiré fringes depends strongly on the thickness of the TEM foil as revealed by HRTEM image simulations. ► Geometric Phase Analysis on simulated images justifies results obtained by energetic mapping.The enhanced structural mismatch of InN and GaN binary alloys leads in almost spontaneous formation of misfit dislocations (MDs) at the corresponding interfaces, thereby accommodating plastic relaxation. The open issue of the MD array in-plane configuration is addressed through a combination of high resolution transmission electron microscopy (HRTEM) observations with energetic mapping and HRTEM image simulation of InN/GaN interfaces extracted by atomistic modeling. Energetic mapping on the interfacial area of InN/GaN supercells relaxed by the Tersoff interatomic potential, designates that the MD arrays adopt〈112¯0〉 line directions and their Burgers vectors areb=1/3〈21¯1¯0〉. HRTEM image simulations further reveal that the local arrangement of Moiré fringes observed in these interfaces depends strongly on the thickness of the TEM foil, thus resolving contradictory experimental reports. Geometric Phase Analysis on the simulated images justifies the results obtained by energetic mapping.

Keywords: Misfit dislocations; InN/GaN; Interfaces; Interatomic potentials

Study of the nitridation process of TiSi₂ powder by L. Maillé; M.A. Dourges; S. Le Ber; P. Weisbecker; F. Teyssandier; Y. Le Petitcorps; R. Pailler (pp. 29-31).

► Nitridation of TiSi₂ creates TiN, Si and Si₃N₃ phases. ► A study of size (micronic and sub micronic) particles is presented. ► Si₃N₄ is created at 1100°C with the nitridation of sub micronic particles.This paper reports on the nitriding process of TiSi₂ micro/submicrometer-sized powders. TiSi₂ powders were treated under nitrogen flow, at 1100°C, during various durations. The composition and morphology of the nitride powders are characterized by X-ray diffraction and observed on cross-section, prepared using ion polishing system by scanning electron microscopy whereas the chemical composition is analyzed by energy dispersive X-ray spectroscopy. All these analyses revealed that under nitrogen flow, TiSi₂ grains are first transformed into a core-shell structure composed of TiN, surrounded by Si. Long nitriding treatments result in the complete transformation of Si₃N₄. These results are discussed in terms of various diffusion limitation phenomena.

Keywords: CMC; Milling; Powder; XRD

Tuning of CeO₂ buffer layers for coated superconductors through doping by Danny E.P. Vanpoucke; Stefaan Cottenier; Veronique Van Speybroeck; Patrick Bultinck; Isabel Van Driessche (pp. 32-35).

► Influence of doping on cerium oxide lattice parameter and bulk modulus. ► Vegard's law analytically derived. ► Doping concentrations of 5% give lattice matching with La₂Zr₂O₇. ► Bulk modulus matching impossible.The appearance of microcracks in cerium oxide (CeO₂) buffer layers, as used in buffer layer architectures for coated superconductors, indicates the presence of stress between this buffer layer and the substrate. This stress can originate from the differences in thermal expansion or differences in lattice parameters between the CeO₂ buffer layer and the substrate. In this article, we study, by means of ab initio density functional theory calculations, the influence of group IV doping elements on the lattice parameter and bulk modulus of CeO₂. Vegard's law behavior is found for the lattice parameter in systems without oxygen vacancies, and the Shannon crystal radii for the doping elements are retrieved from the lattice expansions. We show that the lattice parameter of the doped CeO₂ can be matched to that of the La₂Zr₂O₇ coated NiW substrate substrate for dopant concentrations of about 5%, and that bulk modulus matching is either not possible or would require extreme doping concentrations.

Keywords: CeO; ₂; Doping; Lattice parameter; Bulk modulus; Group IV elements; DFT

Fabrication, characterization, and mechanism of vertically aligned titanium nitride nanowires by Mainul K. Faruque; Kwadwo M-Darkwa; Zhigang Xu; Dhananjay Kumar (pp. 36-41).

► Titanium nitride (TiN) nanowires have been grown on single crystal magnesium oxide substrates using a bottom-up pulsed laser deposition method where Ti–N based gaseous reactants in the laser plume supersaturate the catalytic gold liquid located on the substrate surfaces. ► This bottom-up approach gives rise to a one-dimensional TiN nanowire structure (length: 200–300nm and diameter: 20–30nm) capped with a catalytic Au seed. ► The ascent of Au nanodots to the top of TiN nanowires can be explained based bond-strengths of Ti–O (672kJ/mol), Ti–N (496kJ/mol), Au–N (416kJ/mol), and Au–O (221kJ/mol) bonds. ► The TiN nanowires were provided vertical alignment by selecting a plane of the substrate that provides the least lattice mismatching to the (111) plane of TiN which has lower surface energy than its other planes: (100) or (110).Titanium nitride (TiN) nanowires have been grown on single crystal magnesium oxide (MgO) substrates using a bottom-up pulsed laser deposition method where Ti–N based gaseous reactants in the laser plume supersaturate the catalytic gold (Au) liquid located on the substrate surfaces. Growth of TiN continues as long as the dissolution rate of material into the catalyst matches the extrusion of solid material at the liquid/solid interface. This bottom-up approach gives rise to a one-dimensional TiN nanowire structure (length: 200–300nm and diameter: 20–30nm) capped with a catalytic Au seed. The ascent of Au nanodots to the top of TiN nanowires can be explained based on breaking of weaker bonds and formation of stronger bonds. From strength point of view, these bonds are listed here in order of decreasing strength as follows: Ti–O (672kJ/mol)>Ti–N (496kJ/mol)>Au–N (416kJ/mol)>Au–O (221kJ/mol). The TiN nanowires were provided vertical alignment by selecting a plane of the substrate that provides the least lattice mismatching to the (111) plane of TiN which has lower surface energy than its other planes: (100) or (110).

Keywords: TiN; Nanowires; Pulsed laser deposition; Gold; Catalyst

Pulsed laser deposition of transparent conductive oxide thin films on flexible substrates by G. Socol; M. Socol; N. Stefan; E. Axente; G. Popescu-Pelin; D. Craciun; L. Duta; C.N. Mihailescu; I.N. Mihailescu; A. Stanculescu; D. Visan; V. Sava; A.C. Galca; C.R. Luculescu; V. Craciun (pp. 42-46).

► TCO thin films were grown by PLD on PET substrate at low temperature. ► We found that the quality of TCO on PET substrate depends on the target–substrate distance. ► TCO with high transparency (>95%) and reduced electrical resistivity (∼5×10⁻⁴Ωcm) were obtained. ► Optimized TCO films deposited on PET were free of any cracks.The influence of target–substrate distance during pulsed laser deposition of indium zinc oxide (IZO), indium tin oxide (ITO) and aluminium-doped zinc oxide (AZO) thin films grown on polyethylene terephthalate (PET) substrates was investigated. It was found that the properties of such flexible transparent conductive oxide (TCO)/PET electrodes critically depend on this parameter. The TCO films that were deposited at distances of 6 and 8cm exhibited an optical transmittance higher than 90% in the visible range and electrical resistivities around 5×10⁻⁴Ωcm. In addition to these excellent electrical and optical characteristics the films grown at 8cm distance were homogenous, smooth, adherent, and without cracks or any other extended defects, being suitable for opto-electronic device applications.

Keywords: Flexible TCO; Thin films; PLD; AZO; IZO; ITO; PET

Submicron Raman and photoluminescence topography of InAs/Al(Ga)As quantum dots structures by O.F. Kolomys; V.V. Strelchuk; T.S. Shamirzaev; A.S. Romanyuk; P. Tronc (pp. 47-50).

► Exciton recombination in an ensemble of indirect/direct band-gap (In,Al)As/AlAs QDs with type-I band alignment is studied. ► Resonant Raman scattering was applied for evaluation of composition at various depths InAlAs/AlAs QDs sandwich structures. ► Depth distribution of composition in In(Ga,Al)As alloy layers explained by strain-driven enhanced interdiffusion.Two-period structures with and without vertical coupling between indirect and direct bandgap InAs quantum dots (QDs) both with type I band alignment, grown by molecular-beam epitaxy, were investigated by confocal Raman and photoluminescence (PL) microspectroscopy. The observed blue shift of PL band of the indirect (direct) bandgap QD by 20 (80)meV with decrease of thickness of Ga(Al)As intermediate layer between two InAs QD layers from 30 to 8nm is considered as caused by increase of elastic strains (decrease of QDs sizes) in QD layers and by coupling between QDs electronic states. Scanning confocal resonant Raman microspectroscopy was applied for non-destructive evaluation of composition at various depths along the thickness of vertical coupling of the upper InAs/AlGaAs and lower InAs/AlAs QDs layers of the sandwich structures. Based on the analysis of determined from the in-depth Raman spectra optical phonons frequencies, the depth distribution of composition in InAlAs and GaAlAs alloy layers formed as a result of strain-driven enhanced interdiffusion was determined.

Keywords: Micro-Raman scattering; Photoluminescence; InAs quantum dots; IntermixingPACS; 78.30.Fs; 68.55.Ln; 73.20.Mf

Formation of fivefold axes in the FCC-metal nanoclusters by Vladimir S. Myasnichenko; Mikhail D. Starostenkov (pp. 51-53).

Display Omitted► Formation of fcc-metal nanoclusters having the fivefold symmetry. ► Formation of the cores of icosahedral symmetry in the gold, silver and copper nanoparticles. ► Construction of bimetallic clusters with icosahedral symmetry and increased fractal dimensionality.Formation of atomistic structures of metallic Cu, Au, Ag clusters and bimetallic Cu–Au clusters was studied with the help of molecular dynamics using the many-body tight-binding interatomic potential. The simulation of the crystallization process of clusters with the number of atoms ranging from 300 to 1092 was carried out. The most stable configurations of atoms in the system, corresponding to the minimum of potential energy, was found during super-fast cooling from 1000K. Atoms corresponding to fcc, hcp, and Ih phases were identified by the method of common neighbor analysis. Incomplete icosahedral core can be discovered at the intersection of one of the Ih axes with the surface of monometallic cluster. The decahedron-shaped structure of bimetallic Cu–Au cluster with seven completed icosahedral cores was obtained. The principles of the construction of small bimetallic clusters with icosahedral symmetry and increased fractal dimensionality were offered.

Keywords: Nanocluster; Fivefold symmetry; Icosahedron; Fractal

Out-diffusion of hydrogen from hydrogen plasma-processed oxygen-implanted silicon by A. Misiuk; J. Bak-Misiuk; A. Barcz; P. Romanowski; I. Tyschenko; A. Ulyashin; M. Prujszczyk (pp. 54-58).

► Hydrogen interaction with defects and oxygen is observed for the processed SOI-like structures. ► Vacancy clusters and SiO2−_x clusters are a dominating type of defects in the processed oxygen-implanted silicon. ► Hydrogen-plasma treatment can be used for detection of defects and of depth profile of oxygen in the SOI-like systems.Hydrogen gettering and its out-diffusion from implantation-disturbed buried layers formed in oxygen-implanted silicon, annealed and subsequently treated in hydrogen plasma, have been investigated. Energy and doses of implanted oxygen ions were 200keV and 1×10¹⁷cm⁻², respectively. After implantation Si:O samples were annealed at up to 1573K, also under enhanced hydrostatic pressure, up to 12.3kbar. Depending on processing conditions, disturbed buried layers, containing vacancy-like and other defects, SiO2−_x clusters and/or precipitates, were formed. To produce hydrogen-enriched silicon structures, Si:O,H, with hydrogen accumulated within implantation-disturbed buried layers, Si:O samples were treated in hydrogen plasma. Out-diffusion of hydrogen from Si:O,H samples was investigated after annealing at 723K and 973K under atmospheric pressure. Depth profiles of oxygen and hydrogen were determined using secondary ion mass spectroscopy; X-ray reciprocal space mapping was applied for defect structure determination. Part of hydrogen remains to be present at surface and, especially, within implantation-disturbed areas even after annealing of Si:O,H at 973K.

Keywords: Si:O; Hydrogen gettering; Out-diffusion; High-pressure annealing; SIMS; X-ray diffraction; Defect structure

Finite element modelling of semi and nonpolar GaN/AlN quantum dots by Grzegorz Jurczak; Toby D. Young (pp. 59-64).

►(112¯2) and(112¯0) GaN/AlN quantum dots as a candidate for light emitting devices. ► Elastic relaxation scheme shows similarity regardless the type of growth. ► Spontaneous polarisation follows polar [0001] orientation and localisation phenomena is observed. ► Semipolar-to-nonpolar orientations of a buried QD results in reduction of the electrostatic potential value, peak-to-peak potential drop, and electric field.This paper describes results of a finite element analysis of the elastic and electric field distribution in a semipolar and a nonpolar isolated quantum dot based on previously obtained measurements from transmission electron microscopy. The two quantum dot orientations are each investigated and compared in terms of the resultant piezoelectric fields and their redistribution due to growth orientation and quantum dot geometry/surface effects. Alongside that, a standard polar quantum dot is investigated as a reference-state system. It is found that the geometry of quantum dots grown in alternative orientations affect the elastic strain and, along with orientation dependent spontaneous polarisation, modify the electrostatic potential and the built-in electric fields. A theoretical verification of a reduction in the quantum confined Stark effect by determining the band edge splitting energies for electron and hole states is given.

Keywords: Piezoelectricity; Continuum mechanics; Finite element method; Quantum dots

Stress evolution of Au/Cu/Au tri-layer systems during annealing by Dariusz Chocyk; Adam Proszynski (pp. 65-68).

► We present a experimental observations of the measurements of the average force per width during deposition and annealing of Au/Cu/Au tri-layers attached to silicon substrate. ► We find that one cycle of annealing is sufficient to achieve the thermomechanical stability of the Au/Cu/Au tri-layer systems. ► The beginning of deviation from linear part of stress curve can identify the temperature at which plastic deformation processes occurring in materials of the multilayer.Experimental observations of the measurements of the average force per width (i.e. F/w) during deposition and annealing of Au/Cu/Au tri-layers attached to silicon substrate are reported. Systems with constant thickness of Au films (5nm) and with different thickness of Cu films (5–20nm) are investigated. The total force per width in a system was determined in situ by the substrate curvature measurement method with the laser scanning technique during deposition and annealing. Significant stress evolution during the first cycle of heating was observed for all samples. It was found that during the first annealing cycle, irreversible changes occur in layers. The beginning of deviation from linear part of stress curve can identify the temperature at which plastic deformation processes occurring in materials of the multilayer. Subsequent annealing cycles do not cause major changes in the stress in Au/Cu/Au tri-layer systems.

Keywords: Stress; Annealing; Au/Cu/Au systems; Curvature measurement method

A comparison of the mechanical stability of silicon nitride films deposited with various techniques by Pierre Morin; Gaetan Raymond; Daniel Benoit; Patrick Maury; Remi Beneyton (pp. 69-72).

► LPCVD, RTCVD and ALD as-deposited nitride films present tensile stress dependant on the Si/N ratio and are thermally stable. ► Stress of as-deposited PECVD nitride layers range from compressive to tensile, depending on ion bombardment during growth. ► After high temperature annealing, PECVD nitride films behave similarly to LPCVD layers. ► Young's moduli and density are positively correlated.A comparison of mechanical properties of amorphous silicon nitride thin films deposited with various techniques used for microelectronic applications was conducted. Nitride films with thicknesses less than 80nm were deposited on (001) oriented silicon wafers by using various methods: low pressure chemical vapor deposition (LPCVD), rapid thermal CVD (RTCVD), atomic layer deposition (ALD) and plasma enhanced CVD (PECVD). The wafer curvature method was used to show that the as-deposited LPCVD, RTCVD and ALD films exhibited tensile residual stresses that decreased with silicon richness. In contrast, the stress of the PECVD as-deposited layers ranged from tensile to ultra-compressive, depending on the exposure to high plasma power and ion bombardment during growth. After high temperature annealing, the LPCVD, RTCVD and ALD nitride stresses were almost unchanged, indicating that these films/substrate systems have significant thermal mechanical stability. In contrast, it was observed that, regardless of the initial stress, the annealed PECVD films developed tensile stress after high temperature treatment, with the same dependence of stress on refractive index as was found with the other deposition techniques. The Young's moduli, measured by performing nano-indentation on 200nm thick nitride layers, were found for most samples to be correlated with film density.

Keywords: Silicon nitride; Thin films; Stress; Young's modulus

Identification of nanoscale structure and morphology reconstruction in oxidized a-SiC:H thin films by A.V. Vasin; A.V. Rusavsky; A.N. Nazarov; V.S. Lysenko; P.M. Lytvyn; V.V. Strelchuk; K.I. Kholostov; V.P. Bondarenko; S.P. Starik (pp. 73-76).

► Increase of magnetron discharge power results in densification of a-SiC:H thin films. ► The denser a-SiC:H material the better resistance to oxidation by oxygen. ► Oxidation of soft a-SiC:H films can result in increase of electric conductivity. ► Formation of graphitic clusters was found in a-SiC:H after annealing in oxygen.Oxidation behavior of a-SiC:H layers deposited by radio-frequency magnetron sputtering technique was examined by Kelvin probe force microscopy (KPFM) in combination with scanning electron microscopy, Fourier-transform infra-red spectroscopy and submicron selected area Raman scattering spectroscopy. Partially oxidized a-SiC:H samples (oxidation at 600°C in oxygen) were examined to clarify mechanism of the oxidation process. Nanoscale and microscale morphological defects (pits) with dimension of about 50nm and several microns respectively have appeared after thermal treatment. KPFM measurements exhibited the surface potential of the material in micro pits is significantly smaller in comparison with surrounding material. Submicron RS measurements indicates formation of graphite-like nano-inclusions in the pit defects. We conclude that initial stage of oxidation process in a-SiC:H films takes place not homogeneously throughout the layer but it is initiated in local nanoscale regions followed by spreading over all layer.

Keywords: Amorphous silicon carbide; Oxidation; Kelvin probe force microscopy

Residual stress improvement of platinum thin film in Au/Pt/Ti/p-GaAs ohmic contact by RF sputtering power by M. Parvizian; F. Rahimi-Ashtari; A. Goodarzi; B. Sabrloui; J. Sabaghzade; M.S. Zabihi (pp. 77-79).

► RF sputtering power effect on the residual stress and morphology properties of platinum thin film in Au/Pt/Ti/p-GaAs ohmic contact is investigated. ► Tensile and compressive stresses are minimize at 200W on GaAs surface also stress changes from tensile to compressive on SiO₂ surface when power increases from 200W to 250W. ► Pt roughness and grain size increase by raising deposition power. ► Step coverage deteriorates by power increasing. ► 200W is the optimized RF power for Pt/Ti to achieve a suitable morphology and minimum stress.This work seeks to characterize residual stress and microstructure of platinum thin film in Au/Pt/Ti/p-GaAs ohmic contact. Platinum thin films are deposited on p-GaAs (100) wafer and SiO₂ via patterned area on it by a RF sputtering deposition system while different deposition powers are considered. Evolution of residual stress, roughness and grain size of the films by changing the deposition power are studied. The residual stress is measured by substrate curvature method, and the microstructure of the films is considered by SEM and AFM analysis. AFM analyze shows that Pt layer roughness dramatically increases from 2.2nm to 8.7nm on SiO₂ substrate and from 1.05nm to 5nm on GaAs substrate when power increases from 150W to 300W. Also SEM images show that grain size increases on either GaAs or SiO₂ substrates and step coverage deteriorates by increasing the deposition power. Pt layer stress measurement shows that there is a minimum and suitable point at 200W for GaAs substrate. Also it is observed that the platinum stress changes from tensile to compressive for SiO₂ substrate when RF deposition power increases from 200W to 250W.

Keywords: Residual stress; Platinum; RF sputtering power; Microstructure

Nanostructured nickel-free austenitic stainless steel composites with different content of hydroxyapatite by Maciej Tulinski; Mieczyslaw Jurczyk (pp. 80-83).

► Ni-free austenitic stainless steel/hydroxyapatite composites were produced. ► Nanocrystalline structure was confirmed by three different techniques. ► Nitriding of the surface slightly increases crystallite size. ► The mean grain size of the obtained materials do not exceed 100nm.The aim of this work is to show that Ni-free austenitic stainless steels with nanostructure and their nanocomposites with hydroxyapatite can be synthesized by mechanical alloying, heat treatment and nitriding of elemental microcrystalline powders with addition of hydroxyapatite (HA). Hydroxyapatite was introduced into stainless steel because it is intensively studied for bone repair and replacement applications. Nickel-free austenitic stainless steels seem to have better mechanical properties, corrosion resistance and biocompatibility compared to 316L stainless steels. Therefore it's combination with hydroxyapatite that has high biocompatibility and ability to bond to bone could have improved properties, as well.To confirm nanocrystalline structure of obtained material and reveal topographical features of the surface, small-angle X-ray analysis (SAXS) and atomic force microscopy (AFM) were used. Results are consistent and the mean grain size of the obtained materials do not exceed 100nm.

Keywords: Biomaterials; Nanocrystalline materials; Ni-free austenitic stainless steels

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Applied Surface Science (v.260, #)