Composition and structure of chemically deposited CulnSe2 thin films

The composition, morphology and crystallographic structure of CuInSe₂ films grown at 50°C and 90°C by the chemical method are discussed. Characterization includes EDS, X-ray and transmission electron diffraction and optical absorption spectroscopy. Nearly stoichiometric CuInSe₂ thin films are obtained with chalcopyrite structure and with thickness in the range 1–3 μm and the grain size in the range 0.2–1.5 μm, band gap near 0.9 eV and absorption coefficient α ≅ 10⁵ cm⁻¹.The effect of deposition mixture temperature on film orientation has been studied by X-ray and electron diffraction. Preferred orientation along [112] direction occurs at a deposition-mixture temperature of 90°C.     

Sputter deposition of calcium phosphate/titanium dioxide hybrid thin films

The application of either hydroxyapatite (HA) or titanium dioxide (TiO₂) as coatings onto existing bioinert materials has been explored as the key route for enhancing the surface properties of hard tissue implant devices. However, it has been proposed that composite HA/TiO₂ coatings may provide significant advantages for the application of such surfaces. This work reports on the surface properties of such composite HA/TiO₂ surfaces produced by the sputter deposition of HA onto a titanium surface and their subsequent thermal processing using either post deposition (PDA) or in situ annealing (ISA). For both the PDA and ISA coatings, a hybrid nature was only achieved in the uppermost surface region after annealing at 700 °C. It was observed that the Ca/P ratio decreased with increasing annealing temperature for the PDA coatings and that the coating annealed to 700 °C had a value of 1.82 ± 0.07, which was closest to stoichiometric HA. In comparison, the Ca/P ratio of the ISA samples increased with increasing annealing temperature. It has been shown that the resultant coatings have surface properties that are dependent on the annealing profiles employed, and that a temperature of 700 °C is required in order to create a Ca–P/TiO₂ hybrid surface.     

The crystal structure of epitaxially grown SnO2 thin films

It is shown by computer simulation of the transmission electron diffraction patterns and by structural considerations that the recently reported thin film form β-SnO₂ is equivalent to the high pressure form SnO₂-II. It crystallizes in a columbite-like structure either under the influence of the substrate in the case of epitaxial oxidation of α-SnO to SnO₂ or under the influence of volume contraction conditioned by enhanced pressure and/or temperature during the cassiterite- columbite transformation. The columbite-brookite-cassiterite structural relationship is given and the possibility of the existence of a thin film fluorite-like polymorph is discussed.     

Injectable and fast resorbable calcium phosphate cement for body-setting bone grafts

In this work a calcium phosphate (CPC)/polymer blend was developed with the advantage of being moldable and capable of in situ setting to form calcium deficient hydroxyapatite under physiological conditions in an aqueous environment at body temperature. The CPC paste consists in a mix of R cement, glycerol as a liquid phase carrier and a biodegradable hydrogel such as Polyvinyl alcohol, which acts as a binder. Microstructure and mechanical analysis shows that the CPC blend can be used as an injectable implant for low loaded applications and fast adsorption requirements. The storage for commercial distribution was also evaluated and the properties of the materials obtained do not significantly change during storage at −18°C.     

ITO上磁控溅射ZnO薄膜及其光电性质

在ITO(In2O3:Sn)衬底上射频溅射ZnO薄膜,研究了射频溅射功率对ZnO薄膜的晶体结构,表面形貌及光学透过率的影响.结果表明,随着射频功率的提高,沿(002)方向生长的ZnO薄膜的结晶度显著增强,薄膜的表面颗粒略有减小,表面粗糙度由13.13 nm降低到5.06 nm.在300～400 nm波长范围内薄膜的光学透过率随着射频功率的增加而降低.在双层薄膜中空间内建电场的存在有助于光生电子和空穴有效地分离,使ZnO/ITO双层薄膜具有较强的光电响应能力,光电流达14μA.     

Photoionization coefficient of thin calcium films

The photoionization coefficient of thin calcium films was studied by means of photoemission measurements. The incident photon energies ranged from 2 eV to 5.6 eV. The films were obtained by thermal evaporation and condensation on a silica substrate in ultrahigh vacuum. The mass thicknesses ranged from 2 nm to 50 nm. The photoionization coefficient β exhibited two maxima and reached a constant value for films thicker than 15 nm. The first maximum corresponds to a granular structure (d₁ = 3 nm; β₁ = 62 × 10^?31 per absorbed quantum in a second). The second maximum corresponds to the granular-lacunar structure transition (d₀ ≈ 5.5 nm; β₀ = 36 × 10^?31 per absorbed quantum in a second). An attempt is made to explain the result in terms of an electronic double layer located near the surface.     

Blue-violet phosphate phosphor thin films for EL

Photoluminescence (PL) and electroluminescence (EL) in blue-violet emission were observed in newly developed phosphate phosphor thin films such as Ba₃(PO₄)₂:Eu and Ba₃(PO₄)₂:Ti. These phosphate phosphor thin films were first deposited on thick BaTiO₃ ceramic sheets by r.f. magnetron sputtering using powder targets and then post-annealed in various atmospheres. Blue-violet PL and EL emissions were obtained in Ba₃(PO₄)₂:Eu and Ba₃(PO₄)₂:Ti phosphor thin films that were deposited in an Ar + H₂ (10%) gas atmosphere and then post-annealed above about 900 °C in an Ar + H₂ (10%) gas atmosphere. In particular, the EL observed in Ba₃(PO₄)₂:Eu thin films exhibited two peaks, a red emission peaking at about 615 nm and a blue-violet emission peaking at about 420 nm. A luminance of 2.0 cd/m² in blue-violet emission was obtained in a thin-film EL device using a two step post-annealed Ba₃(PO₄)₂:Eu thin-film emitting layer: step 1, post-annealing at 1000 °C in air for 1 h, and step 2, post-annealing at 1000 °C in an Ar + H₂ atmosphere.     

预置层退火温度对CIGS薄膜晶体结构与光学性质的影响

在众多有关CIGS薄膜的制备实验条件中,温度是影响薄膜生长的重要因素之一。实验利用三步共蒸法在常温下沉积CIGS薄膜,而后对每一步制得的预制膜真空退火处理,系统研究了预置层退火温度对CIGS薄膜的晶体结构、表面形貌及光学性质的影响。研究表明,三步共蒸法中预置层退火温度应严格控制在350℃左右,有利于制备出单一黄铜相结构的CIGS薄膜,近红外波段光学反射率低至2%以下。     

Influence of cathode voltage on electrical property and crystal structure of sputter-deposited Ag thin films

The resistivity and crystal structure of Ag thin films were investigated as a function of the cathode voltage during the Ag sputter deposition. Low emissivity (low-e) coatings with a layered construction of glass/dielectric/Ag/dielectric were deposited by magnetron sputtering. It was found that the Ag layers in the low-e coatings showed lower resistivity when lower cathode voltage was applied. Furthermore, the X-ray diffraction measurement revealed that the crystallite of the Ag layer became larger with the decrease of the cathode voltage. It can be seen from these results that the Ag deposition resulting from low cathode voltage contributes to preferred crystal growth of the Ag layer. This improvement of the Ag crystallinity can be explained by the decrease in the kinetic energy of the Ar atoms backscattered on the Ag sputter target surface.     

Composition control for evaporated CoCr thin films

Composition control was achieved in fabrication of CoCr thin films by evaporation onto tape-shaped polymer substrates. The vapor composition during deposition was determined by an atomic absorption type of detectors and a composition calculator. The gradual change of composition during deposition due to the difference in vapor pressure between Co and Cr was compensated by supplying Cr into the evaporator. As a result, the desirable composition was obtained to within an accuracy of 0.4 wt.%. This composition control system was shown to be suitable for the preparation of CoCr perpendicular magnetic recording media     

Dependence of dendritic morphology on crystal structure in partially crystallized amorphous Ni-P thin films

Electron-beam heating was used to crystallize amorphous electrodeposited thin films of nickel phosphides with a nominal composition of 20 and 22 at % P. High-resolution darkfield microscopy showed that the morphology of the transformed films depends on the rates of electron-beam heating, temperature gradients and variations in the composition of the as-deposited sample. Two distinct types of dendritic morphologies were observed; a low-angle branching dendritic morphology with b c t Ni₁₂P₅ structure and a high-angle branching dendritic morphology with an unknown complex structure. The lowangle branching dendritic morphology is interesting in that the transformation from the as-deposited amorphous Ni-P to the equilibrium Ni₁₂P₅ occurred in one step without going through any intermediary more metastable states, therefore violating the Ostwald rule. The high-angle branching morphology is interesting in that for one branch of dendrite two distinct types of crystals were observed: uniform and twin platelet (heavily striated) crystals. The crystals are layered or overlapped, indicating a two-phase layered structure.     

Composition, structure and optical properties of sputtered thin films of CuInSe2

Thin films of copper indium selenide (CuInSe₂) were produced by radio frequency (RF) sputtering due to the ability of this technique to achieve stoichiometric layers and its scalability to large-area devices. Results of energy dispersive analysis of X-rays (EDAX) revealed that the sputtered films were near to stoichiometry for substrate temperatures T_Sub not exceeding 200 °C. X-ray diffraction (XRD) patterns indicate that the films exhibited some pattern similar to that of bulk crystals of tetragonal chalcopyrite, predominantly [112] oriented. Based on the XRD patterns, the lattice parameters and grain sizes were examined. The band gap E_g, estimated from optical absorption data, was between 0.6-1.08 eV, depending on sputtering conditions such as substrate temperature and bias voltage. High optical absorption coefficients (> 10⁴ cm^− 1) were found.     

Fabrication of thin crystal films of organic compounds

A technique for thin film preparation from non-polar organic molecules based on the Langmuir technique is suggested. By removing the organic crystallites of organic molecules from the water surface to the substrate, high-quality textures were obtained with a simultaneous check of their thicknesses. The films produced were analysed by the transmission high-energy electron diffraction technique.     

Bending of single crystal thin films modeled with micropolar crystal plasticity

The scale-dependent mechanical response of single crystal thin films subjected to pure bending is investigated using a dislocation-based model of micropolar single crystal plasticity via finite element simulations. Due to the presence of couple stresses, the driving force for plastic slip in a micropolar crystal contains an intrinsic back stress component that is related to gradients in lattice torsion-curvature. Strain gradient-dependent back stresses are a common feature of various types of generalized crystal plasticity theories; however, it is often introduced either in a phenomenological manner without additional kinematics or by designating the plastic slips as generalized degrees-of-freedom. The treatment of lattice rotations as fundamental degrees-of-freedom instead of plastic slips greatly reduces the complexity (computational expense) of the single crystal model, and leads to the incorporation of additional elastoplastic kinematics since the lattice torsion-curvature is taken as a work-conjugate continuum deformation measure. A recently proposed single criterion micropolar framework is employed in which the evolution of both the plastic strains and torsion-curvatures are coupled through the use of a unified flow rule. The deformation behavior is characterized by the moment-rotation response and the dislocation substructure evolution for various slip configurations and specimen thicknesses. The results are compared to analogous simulations carried out using a model of discrete dislocation dynamics as well as a statistical-mechanics inspired, flux-based model of nonlocal crystal plasticity. The micropolar model demonstrates good qualitative and quantitative agreement with the previous results up to certain inherent limitations of the current formulation.     

Variation of crystal structure of hydroxyapatite in calcium phosphate cement by the substitution of strontium ions

New routes were used to introduce strontium into calcium phosphate cement in the present article. The study showed that by mixing 50 wt% amorphous calcium phosphate + amorphous strontium phosphate and 50 wt% dicalcium phosphate dihydrate, hydroxyapatite and Sr-hydroxyapatite precipitated separately in the hydrated cement; whereas, by mixing 50 wt% Sr- amorphous calcium phosphate and 50 wt% dicalcium phosphate dihydrate, strontium can be doped into hydroxyapatite lattice and increase the lattice dimensions and lattice volume. The strontium substituted calcium phosphate cement has potential for use in orthopedic surgeries.     

Composition and structure of hafnia films on silicon

Ellipsometry, electron microscopy, and x-ray photoelectron spectroscopy data indicate that, during HfO₂ deposition onto silicon, the native oxide reacts with the HfO₂ deposit to form an amorphous intermediate layer which differs in refractive index (?1.6) from both HfO₂ (1.9–2.0) and SiO₂ (1.46). Thermodynamic analysis of the Si-SiO₂-HfO₂-Hf system shows that Si is in equilibrium with Si/HfO_{2 ? y} only at low oxygen pressures. Starting at a certain oxygen pressure (equivalent to the formation of a native oxide layer), the equilibrium phase assemblage is Si/HfSiO₄/HfO_{2 ? y} .     

Biomimetic calcium phosphate crystal mineralization on electrospun cellulose-based scaffolds

Novel cellulose based-scaffolds were studied for their ability to nucleate bioactive calcium phosphate crystals for future bone healing applications. Cellulose-based scaffolds were produced by electrospinning cellulose acetate (CA) dissolved in a mixture of acetone/dimethylacetamide (DMAc). The resulting nonwoven CA mats containing fibrils with diameters in the range of 200 nm to 1.5 μm were saponified by NaOH/ethanol for varying times to produce regenerated cellulose scaffolds. Biomimetic crystal growth nucleated from the fiber surface was studied as a function of surface chemistry. Regenerated cellulose scaffolds of varying treatments were soaked in simulated body fluid (SBF) solution. Scaffolds that were treated with CaCl(2), a mixture of carboxymethyl cellulose (CMC) and CaCl(2), and NaOH and CaCl(2), were analyzed using X-ray photoelectron spectroscopy, X-ray powder diffraction, and scanning electron microscopy to understand the growth of bioactive calcium phosphate (Ca-P) crystals as a function of surface treatment. The crystal structure of the nucleated Ca-P crystals had a diffraction pattern similar to that of hydroxyapatite, the mineralized component of bone. The study shows that the scaffold surface chemistry can be manipulated, providing numerous routes to engineer cellulosic substrates for the requirements of scaffolding.     

Composition dependence of electrical properties of Al-Sb thin films

Thin films of Al-Sb of varying compositions and thickness have been formed on glass substrates employing three-temperature method. Electrical resistivity (ρ) and activation energy (ΔE) have been studied as a function of composition, thickness (d) and temperature of the film. Films of Al-Sb system with aluminium < 50 at.%, ∼ 50 at.% and > 50 at.% exhibit metallic, semiconducting and metallic to semiconducting behaviours respectively. Activation energy (ΔE) of semiconducting films found to vary inversely with thickness, is attributed to combined effects of change in barrier height due to the size of grains and stoichiometry in the films.