Structural characterization of silicon-substituted hydroxyapatite synthesized by a hydrothermal method

Silicon-substituted hydroxyapatite (Si-HA) was prepared successfully by hydrothermal method. The crystalline phase, microstructure, chemical composition, morphology and thermal stability of Si-HA were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results show that the substitution of the silicate groups for the phosphate groups causes some OH^- loss to maintain the charge balance and changes the lattice parameters of HA. Furthermore, the substitution of the silicate groups restrains the growth of Si-HA crystal. DSC analysis shows that the small amount of silicon incorporates into HA lattice does not influence the thermal stability of HA.     

Surface microstructure and cell biocompatibility of silicon-substituted hydroxyapatite coating on titanium substrate prepared by a biomimetic process

Silicon-substituted hydroxyapatite (Si-HA) coatings with 0.14 to 1.14 at.% Si on pure titanium were prepared by a biomimetic process. The microstructure characterization and the cell compatibility of the Si-HA coatings were studied in comparison with that of hydroxyapatite (HA) coating prepared in the same way. The prepared Si-HA coatings and HA coating were only partially crystallized or in nano-scaled crystals. The introduction of Si element in HA significantly reduced P and Ca content, but densified the coating. The atom ratio of Ca to (P + Si) in the Si-HA coatings was in a range of 1.61–1.73, increasing slightly with an increase in the Si content. FTIR results displayed that Si entered HA in a form of SiO₄ unit by substituting for PO₄ unit. The cell attachment test showed that the HA and Si-HA coatings exhibited better cell response than the uncoated titanium, but no difference was observed in the cell response between the HA coating and the Si-HA coatings. Both the HA coating and the Si-HA coatings demonstrated a significantly higher cell growth rate than the uncoated pure titanium (p < 0.05) in all incubation periods while the Si-HA coating exhibited a significantly higher cell growth rate than the HA coating (p < 0.05). Si-HA with 0.42 at.% Si presented the best cell biocompatibility in all of the incubation periods. It was suggested that the synthesis mode of HA and Si-HA coatings in a simulated body environment in the biomimetic process contribute significantly to good cell biocompatibility.     

Aerosol deposition of silicon-substituted hydroxyapatite coatings for biomedical applications

Silicon-substituted hydroxyapatite (Si-HA) coatings on commercially pure titanium (Ti) were prepared by aerosol deposition using Si-HA powders. Si-HA powders with the chemical formula Ca₁₀(PO₄)_6 − x(SiO₄)_x(OH)_2 − x, having silicon contents up to x = 0.5 (1.4 wt.%), were synthesized by solid-state reaction of Ca₂P₂O₇, CaCO₃, and SiO₂. The Si-HA powders were characterized by X-ray diffraction (XRD), X-ray fluorescence spectrometry, and Fourier transform infrared spectroscopy. The corresponding coatings were also analyzed by XRD, scanning electron microscopy, and electron probe microanalyzer. The results revealed that a single-phase Si-HA was obtained without any secondary phases such as α- or β-tricalcium phosphate for both the powders and the coatings. The Si-HA coating was about 5 µm thick, had a dense microstructure with no cracks or pores, and showed a high adhesion strength ranging from 28.4 to 32.1 MPa. In addition, the proliferation and alkaline phosphatase activity of MC3T3-E1 preosteoblast cells grown on the Si-HA coatings were significantly higher than those on the bare Ti and pure HA coating. These results revealed the stimulatory effects induced by silicon substitution on the cellular response to the HA coating.     

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10^–2–10^–1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca₂P₂O₇, Ca₂P₂O₉ and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.     

X-ray absorption spectroscopy, simulation and modeling of Si-DLC films

Amorphous silicon-containing diamond-like carbon (Si-DLC) films were deposited on silicon wafers by Ar⁺ Ion Beam Assisted Deposition (IBAD) at various energy conditions. The films were examined with X-ray Absorption Near Edge Structure (XANES) spectroscopy and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. The Si K-edge X-ray Absorption Spectroscopy (XAS) results indicate that Si-DLC films have an amorphous structure, where each Si atom is coordinated to four carbon atoms or CH_n groups. This short-range order, where a Si atom is surrounded by four C atoms, was found in all Si-DLC films. The XANES spectra do not indicate Si coordination to oxygen atoms or phenyl rings, which are present in the precursor material. A structural model of Si-DLC is proposed based on XAS findings. Simulated X-ray absorption spectra of the model produced by FEFF8 show a good resemblance to the experimental data.     

Synthesized silicon-substituted hydroxyapatite coating on titanium substrate by electrochemical deposition

Silicon-substituted hydroxyapaptite (Si-HA) coatings were prepared on titanium substrates by electrolytic deposition technique in electrolytes containing Ca²⁺, PO₄ ³⁻ and SiO₃ ²⁻ ions with various SiO₃ ²⁻/(PO₄ ³⁻ + SiO₃ ²⁻) molar ratios(η_si). The deposition was all conducted at a constant voltage of 3.0 V, with titanium substrate as cathode and platinum as anode, for 1 h at 85°C. The coatings thus prepared were characterized with inductively coupled plasma (ICP), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field-emission-type scanning electron microscope (FSEM). The results show that the silicon amount in the coatings increases linearly to about 0.48 wt% at first with increasing η_si between 0 and 0.03, then increases slowly to about 0.55 wt% between 0.03 and 0.10 and finally maintains almost at a level around 0.55 wt% between 0.10 and 0.30. The tree-like Si-HA crystals are observed in the coatings prepared in the electrolyte of η_si = 0.20. And the presence of silicon in electrolytes decreases the thickness of the coatings, with effect being more significant as η_si increased. Additionally, the substitution of Si causes some OH⁻ loss and changes the lattice parameters of hydroxyapatite (HA).     

A new way of incorporating silicon in hydroxyapatite (Si-HA) as thin films

Bioactive silicon-containing hydroxyapatite (Si-HA) thin films that can be used as coatings for bone tissue replacement have been developed. A magnetron co-sputtering technique was used to deposit Si-HA films up to 700 nm thick on titanium substrates, with a silicon level up to 1.2 wt%. X-ray diffraction demonstrated that annealing transformed the as-deposited Si-HA films which were amorphous, into a crystalline HA structure. A human osteoblast-like (HOB) cell model was used to determine the biocompatibility of these films. HOB cells were seen to attach and grow well on the Si-HA films, and the metabolic activity of HOB cells on these films was observed to increase with culture time. Furthermore, mineralisation of the cell layers was observed after 8 weeks of culture. Based on the present findings, Si-HA of different film compositions demonstrate bioactive properties in-vitro, and indicate the potential as biocoatings for a wide variety of medical implants including load-bearing applications such as the femoral stem of hip replacement implants.     

Pulsed laser deposition of crystalline ZrC thin films

ZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique under various conditions. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction and reflectivity, spectroscopic ellipsometry, and four point probe measurements were used to characterize the properties of the deposited films. It has been found that crystalline films could be grown only by using laser fluences higher than 5 J/cm² and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm² and a substrate temperature of 700 °C, cubic ZrC films (a = 0.469 nm) exhibiting a (200)-texture were deposited under vacuum or low pressure C₂H₂ atmosphere. These films were smooth, with surface roughness values below 1.0 nm and mass densities around the tabulated value of 6.7 g/cm³. AES depth profiling investigations showed oxygen contamination around 7% in the bulk region. Despite the relatively high levels of oxygen contamination, the deposited ZrC films were very conductive. The use of a low C₂H₂ pressure atmosphere during deposition had a small beneficial effect on crystallinity and stoichiometry of the films.     

Effect of electron beam irradiation on structure and properties of SiCN thin films prepared by plasma assisted radio frequency magnetron sputtering

Silicon carbon nitride thin films were deposited on Si (100) substrate at room temperature by plasma assisted radio frequency magnetron sputtering. The bonding structure and properties of SiCN films irradiated by pulsed electron beams were studied by means of X-ray photoelectron spectroscopy and nano-indentation. The results showed that electron beam irradiation had a great effect on the structure and property of the films. Under sputtering gas pressure of 3.7 Pa, a transition from the (Si,C)N_x bonded structure to the (Si,C)₃N₄ bonded structure was found in the SiCN thin film with electron beam irradiation. At sputtering gas pressure of 6.5 Pa, the enhancement of hardness in the SiCN film after treatment with electron beam irradiation resulted from the promotion of the sp³-hybridization of carbons bonds.     

Effect of electron beam irradiation on structure and properties of SiCN thin films prepared by plasma assisted radio frequency magnetron sputtering

Silicon carbon nitride thin films were deposited on Si (100) substrate at room temperature by plasma assisted radio frequency magnetron sputtering. The bonding structure and properties of SiCN films irradiated by pulsed electron beams were studied by means of X-ray photoelectron spectroscopy and nano-indentation. The results showed that electron beam irradiation had a great effect on the structure and property of the films. Under sputtering gas pressure of 3.7 Pa, a transition from the (Si,C)N_x bonded structure to the (Si,C)₃N₄ bonded structure was found in the SiCN thin film with electron beam irradiation. At sputtering gas pressure of 6.5 Pa, the enhancement of hardness in the SiCN film after treatment with electron beam irradiation resulted from the promotion of the sp³-hybridization of carbons bonds.     

Inspection of intermediate stress-induced electronic traps in Si/Al2O3 system

The physical characteristics of device-grade thin silicon film at (1 0 0) grown on α-Al₂O₃ substrate using the chemical vapour deposition (CVD) technique has been studied in this paper. Its thickness, crystalline structure, elemental inter-diffusion in the interface region and the quality were characterized by X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), core level X-ray photoelectron spectroscopy (XPS) and nuclear resonance reaction ²⁷Al(p,γ)²⁸Si, respectively. The results of stoichiometric defect profile and individual silicon suboxide (such as SiO, and Si₂O₃ components with respect to the metallic Si element) formation in the intermediate region were observed. The deep traps located around E_c=0.26eV, in ∼500 nm thick n-type Si films, were attributed to the defects caused by the strain of the silicon lattice. Raman spectroscopy was used to evaluate the compressive stress in the Si film.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Gold catalysts for the abatement of environmentally harmful materials: Modeling the structure dependency

FeO_x, TiO₂ and CeO_x layers were deposited by pulsed laser deposition (PLD) technique onto Au films or Au nanoparticles supported on SiO₂/Si(100). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and their reactivity was studied in catalytic CO oxidation. Comparison was made with reference samples of FeO_x/SiO₂/Si(100), TiO₂/SiO₂/Si(100), CeO_x/SiO₂/Si(100) and Au/SiO₂/Si(100) layers. The catalytic activity of the metal-oxide/Au/SiO₂/Si(100) samples must be attributed to active sites located on the metal-oxides overlayer modified by gold underneath, since no Au was exposed to the surface according to the XPS and SIMS. We found a promoting effect of gold on the catalytic activity of the FeO_x overlayer and an inhibiting effect of gold on the TiO₂ and CeO_x overlayers. These findings are discussed in terms of electronic interactions at the Au/metal oxide interface.     

Fabrication of LSS bottom electrode by PLD

Polycrystalline LaNiO₃/SrTiO₃/Si(100) (LSS) conducting substrates were fabricated by pulsed laser deposition (PLD) technique. LSS substrate is a potential candidate for the multiferroic materials for use as bottom electrode. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with EDX system, atomic force microscopy (AFM) and electrical resistivity were employed to characterize the films. Buffer layer SrTiO₃ (STO) deposited at 700 °C resulted in dense, smooth and with crack free features. XRD studies confirmed bi-crystalline [(100), (110)] growth of STO on Si(100) substrate. Deposition of bottom electrode LaNiO₃ (LNO) epitaxially followed the buffer layer. EDX analyses determined the chemical composition of the films. The role of oxygen partial pressure during deposition affecting the crystallinity and resistivity of the films was explored in detail. Atomic force microscopy revealed the atomic scale features of the films desirable for functional devices. Resistivity of the conducting film (LNO) was ∼10⁻⁴ Ω cm at room temperature. Thus it is demonstrated that LNO/STO/Si(100) is a suitable conducting substrate for growth of the multiferroic functional materials.     

Ion beam synthesis of aluminium nitride: characterisation of thin AIN layers formed in microelectronics aluminium

Abstract

Buried AlN thin layers have been formed by high dose N⁺ ion implantation into microelectronics grade Al films (containing 1 at.-%Si), which were deposited on Si wafers. The structures obtained have been characterised by spreading resistance measurements, transmission electron microscopy, secondary ion mass spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show the formation of buried dielectric precipitates of crystalline AlN at implantation doses below the threshold and a continuous polycrystalline AlN layer at doses above the threshold. The AlN grains have the wurtzite structure, sizes of about 10–15 nm, and a preferred orientation in relation to the Al matrix, namely, <110>_AIN parallel to <110>_Al. The data also show that, under certain conditions, the main impurities (Si and O) are gettered in the buried layer. Moreover, for thin Al films, the formation of a Si rich surface layer is observed. This surface layer is formed by Si diffusion from the substrate, probably due to the penetration of N⁺ ions into the Si substrate. The distribution and evolution of these impurities and the different phases formed are studied as a function of the thickness and grain size of the Al film, as well as of the annealing processes.

MST/3304     

Structural and chemical stability of Ta–Si–N thin film between Si and Cu

Thermal stability and barrier performance of reactively sputter deposited Ta–Si–N thin films between Si and Cu were investigated. RF powers of Ta and Si targets were fixed and various N₂/Ar flow ratios were adopted to change the amount of nitrogen in Ta–Si–N thin films. The structure of the films are amorphous and the resistivity increases with nitrogen content. After annealing of Si/Ta–Si–N(300 Å)/Cu(1000 Å) structures in Ar–H₂ (10%) ambient, sheet resistance measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) were employed to characterize barrier performance. Cu₃Si and tantalum silicide phase are formed at the same temperature, and the interdiffusion of Si and Cu occurs through the local defect sites. In all characterization techniques, nitrogen in the film appears to play an important role in thermal stability and resistance against Cu diffusion. A 300 Å thick Ta₄₃Si₄N₅₃ barrier shows the excellent barrier property to suppress the formation of Cu₃Si phase up to 800°C.     

Silicon-substituted hydroxyapatite composite coating by using vacuum-plasma spraying and its interaction with human serum albumin

The incorporation of silicon can improve the bioactivity of hydroxyapatite (HA). Silicon-substituted HA (Ca₁₀(PO₄)_6−x (SiO₄) _x (OH)_2−x , Si-HA) composite coatings on a bioactive titanium substrate were prepared by using a vacuum-plasma spraying method. The surface structure was characterized by using XRD, SEM, XRF, EDS and FTIR. The bond strength of the coating was investigated and XRD patterns showed that Ti/Si-HA coatings were similar to patterns seen for HA. The only different XRD pattern was a slight trend toward a smaller angle direction with an increase in the molar ratio of silicon. FTIR spectra showed that the most notable effect of silicon substitution was that –OH group decreased as the silicon content increased. XRD and EDS elemental analysis indicated that the content of silicon in the coating was consistent with the silicon-substituted hydroxyapatite used in spraying. A bioactive TiO₂ coating was formed on an etched surface of Ti, and the etching might improve the bond strength of the coatings. The interaction of the Ti/Si-HA coating with human serum albumin (HSA) was much greater than that of the Ti/HA coating. This might suggest that the incorporation of silicon in HA can lead to significant improvements in the bioactive performance of HA.     

Dielectric properties of YSZ high-k thin films fabricated at low temperature by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) films were deposited on Pt-coated silicon substrates and directly on n-type Si substrates, respectively, by pulsed laser deposition (PLD) technique using a YSZ (5 mol% Y₂O₃-stabilized ZrO₂) ceramic target. The YSZ films were deposited in 1.5×10⁻² Pa O₂ ambient at 300 °C and in situ post-annealed at 400 °C. X-ray diffraction (XRD) and differential thermal analysis measurements demonstrated that YSZ remained amorphous. The dielectric constant of amorphous YSZ was determined to be about 26.4 by measuring Pt/YSZ/Pt capacitor structure. The 6-nm-thick amorphous YSZ films with an equivalent oxide thickness (EOT) of 1.46 nm and a low leakage current of 7.58×10⁻⁵ A/cm² at 1 V gate voltage exhibit good electrical properties. YSZ thin films fabricated at low temperature 300 °C have satisfactory dielectric properties and could be a candidate of high-k gate dielectrics.     

Surface nano-structured silicon carbide thin film produced using hot filament decomposition of ethylene at low temperature on silicon wafer

The structure and spectroscopic properties of nano-structured silicon carbide (SiC) thin films were studied for films obtained through deposition of decomposed ethylene (C₂H₄) on silicon wafers via hot filament chemical vapor deposition method at low temperature followed by annealing at various temperatures in the range 300-700 °C. The prepared films were analyzed with focus on the early deposition stage and the initial growth layers. The analysis of the film's physics and structural characteristics was performed with Fourier transform infrared spectroscopy and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. The conditions for forming thin layer of cubic SiC phase (3C-SiC) are found. X-ray diffraction and Raman spectroscopy confirmed the presence of 3C-SiC phase in the sample. The formation conditions and structure of intermediate SiC layer, which reduces the crystal lattice mismatch between Si and diamond, are essential for the alignment of diamond growth. This finding provides an easy way of forming SiC intermediate layer using the Si from the substrate.     

Properties of amorphous Si thin film anodes prepared by pulsed laser deposition

Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100 μA/cm² in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5 V at various scan rates from 0.1 to 2 mV/s. The apparent diffusion coefficient (D_Li) calculated from the CV measurements was about ∼10⁻¹³ cm²/s. The Si thin film anode was also successfully coupled with LiCoO₂ thin film cathode. The a-Si/LiCoO₂ full cell showed stable cycle performance between 1 and 4 V.