Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se₈₀Te₂₀)_100 ? xAg_x (0 ≤ x ≤ 4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328 K) and in between glass transition temperature and crystallization temperature (343 K). Thin films annealed at 343 K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100 nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10^? 5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358 K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.     

Thermal stability of thin InGaN films on GaN

The thermal stability of ∼200-nm-thick InGaN thin films on GaN was investigated using isothermal and isochronal post-growth anneals. The In_xGa_1−xN films (x=0.08–0.18) were annealed in N₂ at 600–1000 °C for 15–60 min, and the resulting film degradation was monitored using X-ray diffraction (XRD) and photoluminescence (PL) measurements. As expected, films with higher indium concentration showed more evidence for decomposition than the samples with lower indium concentration. Also for each alloy composition, decreases in the PL intensity were observed starting at much lower temperatures compared to decreases in the XRD intensity. This difference in sensitivity of the PL and XRD techniques to the InGaN decomposition suggest that defects that quench luminescence are generated prior to the onset of structural decomposition. For the higher indium concentration films, the bulk decomposition proceeds by forming metallic indium and gallium regions as observed by XRD. For the 18% indium concentration film, measurement of the temperature-dependent InGaN decomposition yields an activation energy, E_A, of 0.87±0.07 eV, which is similar to the E_A for bulk InN decomposition. The InGaN integrated XRD signal of the 18% film displays an exponential decrease vs. time, implying InGaN decomposition proceeds via a first-order reaction mechanism.     

Temperature-assisted electrical poling of TeO2-Bi2O3-ZnO glasses for non-linear optical applications

The suitability for effective thermal poling of the ternary tellurite glasses with the compositions (100 − 2x)TeO₂-xBi₂O₃-xZnO (x = 5, 10 and 15, in molar percentage) for the second harmonic generation (SHG) was analyzed. The glass transitions and crystallization temperatures were studied via differential thermal analysis. The structural properties of the annealed glasses and furtherly heat-treated samples were probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. Thermal poling of the glasses was undertaken conventionally at various temperatures close to the glass transition temperature under high vacuum and the second harmonic generated signals were compared. A new technique of two stage poling was tested for comparison. The non-linear second harmonic signal of the poled glasses was analyzed using the Maker-fringe technique and it was found that the two stage poling enhanced the non-linear efficiency when compared to the conventionally poled samples.     

Effect of annealing temperature on the structural and optical properties of amorphous Sb2Te2Se thin films

Thin films of Sb₂Te₂Se were prepared by conventional thermal evaporation of the presynthesized material on Corning glass substrates. The chemical composition of the samples was determined by means of energy‐dispersive X‐ray spectrometry. X‐ray diffraction studies on the as‐deposited and annealed films revealed an amorphous‐to‐crystalline phase transition. The as‐deposited and annealed films at T _a = 323 and 373 K are amorphous, while those annealed at T _a= 423 and 473 K are crystalline with a single‐phase of a rhombohedral crystalline structure as that of the source material. The unit‐cell lattice parameters were determined and compared with the reported data. The optical constants (n , k ) of the investigated films were determined from the transmittance and reflectance data at normal incidence in the spectral range 400–2500 nm. The analysis of the absorption spectra revealed non‐direct energy gaps, characterizing the amorphous films, while the crystalline films exhibited direct energy gaps. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characteristics and biocompatibility of Na2O–K2O–CaO–MgO–SrO–B2O3–P2O5 borophosphate glass fibers

A novel Na₂O–K₂O–CaO–MgO–SrO–B₂O₃–P₂O₅ borophosphate glass fiber is prepared. The thermal properties including differential thermal analysis (DTA) and viscosity measurement of the glass were presented. The tensile strength of the glass fiber is measured. The reaction of the glass fibers in the SBF solution is characterized by XRD, FTIR and SEM. XRD and FTIR indicate that the carbonate hydroxyapatite has formed rapidly on the glass. Cell attachment, spreading and proliferation on the glass are determined by MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide] assay method using Human osteosarcoma MG-63 cells. The bioactivity and biocompatibility of the glass fiber make it a good potential prospect in the field of tissue engineering.     

Nanophase separation and effects on properties of Ge–As–Se chalcogenide glasses

Nanophase separation in the bulk Ge–As–Se chalcogenide glasses was observed by SEM and supported by XRD and IR measurements. Effects of nanophase separation on glass transition temperature (T_g), microhardness (H_v), optical band gap (E_opt) and thermal expansion coefficient (α) were investigated in terms of glass rigidity transitions. According to the correlations between the properties and average coordination number Z, it is established that nanophase separation becomes more intensive when Z is larger than 2.64.     

Effect of liquid state on the crystallization of Zr65Al7.5Ni10Cu17.5 metallic glass

The correlation between the quenching temperature and the crystallization of the Zr₆₅Al_7.5Ni₁₀Cu_17.5 metallic glass was examined. The electrical resistivity and the thermal property were measured to monitor the structural change of the samples quenched at the temperature of 1473 K, 1573 K, 1673 K and 1773 K, respectively. The consistent results of DSC and d(ρ_(T)/ρ₀)/dT‐T curves indicated different crystallization behaviors of the samples. For the samples quenched from 1773 K, the increase in ΔT_x, T_rg and γ imply higher glass forming ability. Moreover, according to the XRD patterns of samples annealed at different temperatures, the melt temperature influences the formation of crystallized phases of amorphous Zr₆₅Al_7.5Ni₁₀Cu_17.5 alloy.     

The influence of CaF2 content on the physical properties and apatite formation of bioactive glass coatings for dental implants

This report details the physical properties, bioactivity and biocompatibility of manufactured glasses containing a range of calcium fluoride (CaF₂) concentrations. Compositions were based on the following system: SiO₂, CaO, Na₂O, K₂O, P₂O₅, ZnO and MgO, and in total seven glasses were synthesized using a melt–quench route. The ratio of the base compounds was kept constant, but had increasing CaF₂ concentrations (0.00, 2.44, 4.77, 9.11, 10.33, 11.53 and 13.00 mol%). Glasses were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dilatometery. Density was quantified according to Archimedes method and apatite formation tested following immersion in simulated body fluid (SBF) and Tris-buffer solution. Glass coatings were prepared by enamelling technique using 10 mm in diameter pure titanium disks. XRD demonstrates that all glasses are amorphous and that the sintering window, glass transition and softening temperatures decrease with increasing CaF₂ content. In contrast, thermal expansion coefficient and glass density increase with CaF₂ content. After 1 week immersion in SBF and Tris, XRD and Fourier transform infrared (FTIR) spectroscopy showed that the surfaces of all glasses underwent structural changes with evidence of surface apatite formation. Fluoride-electrode analysis indicates that the amount of fluoride released was proportional to the original CaF₂ content. The survival and growth of osteoblasts on the surface of these glasses is consistent with biocompatible characteristics.     

Structural investigation and electronic band transitions of nanostructured TiO2 thin films

Titanium dioxide (TiO₂) thin film was deposited on n‐Si (100) substrate by reactive DC magnetron sputtering system at 250 °C temperature. The deposited film was thermally treated for 3 h in the range of 400‐1000 °C by conventional thermal annealing (CTA) in air atmosphere. The effects of the annealing temperature on the structural and morphological properties of the films were investigated by X‐ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD measurements show that the rutile phase is the dominant crystalline phase for the film annealed at 800 °C. According to AFM results, the increased grain sizes indicate that the annealing improves the crystalline quality of the TiO₂ film. In addition, the formation of the interfacial SiO₂ layer between TiO₂ film and Si substrate was evaluated by the transmittance spectra obtained with FTIR spectrometer. The electronic band transitions of as‐deposited and annealed films were also studied by using photoluminescence (PL) spectroscopy at room temperature. The results show that the dislocation density and microstrain in the film were decreased by increasing annealing temperature for both anatase and rutile phases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical resistivity evolution in the annealed amorphous Fe78Si9B13 ribbons

The electrical resistivity was measured at room temperature for the amorphous Fe₇₈Si₉B₁₃ ribbons annealed at various temperatures for different holding time. Although the annealed Fe₇₈Si₉B₁₃ ribbons are in full amorphous state, their electrical resistivity obviously varies with the annealing time. At every annealed temperature, the electrical resistivity evolution can be divided into regions I, II, and III, respectively. Using X-ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we investigated the ribbons overlapping regions I and II (called the focused ribbons, FRs). The results show that the change of electrical resistivity, fracture morphology, thermal effect in DSC analysis of the focused ribbons (FRs) can be ascribed to the evolution of the short range order (SRO) in the amorphous alloy.     

Thermal properties of chalcogenide glasses in the GeSe2–As2Se3–CdSe system

In the present work, thermal properties of GeSe₂–As₂Se₃–CdSe glasses were investigated via DSC measurements. The dependences of glass transition temperature and thermal stability on glass composition were discussed. XRD measurement was also performed to validate the effect of cadmium on the thermal properties of glasses. The calculated Avrami exponent was used to demonstrate the three-dimensional growth of crystals in the glass matrices. The crystallization kinetics for the glasses was studied by using the modified Kissinger and Ozawa equations.     

Birefringence simulation of annealed ingot of magnesium fluoride single crystal

We developed a method for simulating birefringence of an annealed ingot of MgF₂ single crystal for lithography optics. This method provides the optical path difference caused by crystal symmetry and residual stress existing in the crystal. The method consists of the heat conduction analysis, the residual stress analysis and the birefringence analysis. Because there exists no experimental data on the inelastic behavior of MgF₂ single crystal, the residual stress was estimated with the elastic thermal stress analysis using the finite element method by assuming a stress-free temperature. In this analysis, the temperature dependence of material properties and crystal anisotropy were taken into account. In the birefringence analysis, the distributions of optical path difference were calculated by an approximate method using the result of the residual stress analysis. This approximate method uses the average stress along the wave normal and is equivalent to the exact method in case of low stress dealt with the present study. In this analysis, it is possible to consider both the intrinsic birefringence and the stress birefringence in any crystal orientation. The distribution of the optical path difference in the annealed ingot obtained from the present calculation agrees qualitatively with that of the experiment. Its calculated value also agrees reasonably well with that of the experiment, when a stress-free temperature is adequately selected.     

Characterization of the free volume in a Zr45.0Cu39.3Al7.0Ag8.7 bulk metallic glass by reverse Monte Carlo simulation and density measurements

The absolute contents of free volume in the as-cast and annealed Zr_45.0Cu_39.3Al_7.0Ag_8.7 bulk metallic glass (BMG) samples were quantified by density measurements and reverse Monte Carlo (RMC) simulation using the total structural factors F(Q) determined by X-ray diffraction (XRD) experiments as fitting constraints. The densities of the as-cast, annealed and crystallized samples measured by Archimedes method are 7.319, 7.327 and 7.342 g/cm³ (precision ± 0.003 g/cm³), respectively. A new approach was used in the RMC simulation to define the free volume as the difference between the volume of the Voronoi polyhedron and the volume of the Wigner-Seitz cell of the constituent atoms. Two types of initial configurations were constructed: (1) in configuration A, all types of potential atomic pairs are allowed; (2) in configuration B, Al-Al and Ag-Ag atomic pairs are excluded. The contents of free volume in the as-cast and annealed samples were found to be 0.59% and 0.39% (configuration A), 0.55% and 0.34% (configuration B), respectively (precision ± 0.03%). The probability distribution of the as-calculated free volume can be well-fitted by the equation proposed by Turnbull and Cohen. Finally, it is shown that the contents of free volume determined by density measurements and RMC are comparable, while the discrepancy of the results is discussed.     

Co nanoclusters as origin of ferromagnetism in sol‐gel synthesized Zn1‐xCoxO (x = 0.05, 0.10 and 0.15) samples

We report on the structural and magnetic properties of the polycrystalline samples of Zn_1‐xCo_xO (x = 0.05, 0.10 and 0.15) synthesized via sol‐gel route. The air sintered samples of all compositions exhibit paramagnetic behaviour at room temperature, on the other hand the same samples on annealing in Ar/H₂ atmosphere show room temperature ferromagnetism (RTFM) with enhanced magnetization. The value of magnetization increases with the Co concentration (x) in both the air sintered and Ar/H₂ annealed samples. The observed ferromagnetism in the Ar/H₂ annealed Zn_1‐xCo_xO (x = 0.05, 0.10 and 0.15) samples is attributed to the presence of Co nanoclusters as detected by XRD and FESEM‐EDAX. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal Expansion of Bismuth Triborate

Thermal expansion of the monoclinic nonlinear optical crystal BiB₃O₆ (bismuth triborate) was measured by dilatometry within the temperature range from 173 K to 573 K using single crystal samples of dimensions ∼7 x 7 x 8 mm³. The four independent tensor coefficients are given and the calculated loci of zero thermal expansion of BiB₃O₆ are related to the loci of phase matching for second harmonic generation. Characteristic features of the crystal structure are taken to discuss the marked anisotropy of thermal expansion of BiB₃O₆.     

Preparation and optical properties of AgGaS2 nanofilms

In this paper, AgGaS₂ nanofilms have been prepared by a two‐step process involving the successive ionic layer absorption and reaction (SILAR) and annealing method. Using AgNO₃, GaCl₃ and Na₂S₂O₃ as reaction sources, the mixture films were firstly deposited on quartz glass substrates at room temperature, and then annealed in Ar environment at 200–500 °C for 4 h, respectively. The effects of annealing temperature on structural and optical properties were investigated by XRD, UV‐Vis, EDS and photoluminescence (PL) spectra. It was revealed in XRD results that α‐Ag₉GaS₆ was contained in the samples annealed at 200 °C, and this phase was decreased with increase of the annealing temperatures. When the sample was annealed at above 400 °C, the chalcopyrite AgGaS₂ nanofilm was obtained. The preferred orientation was exhibited along the (112) plane. It was shown in atomic force microscopy (AFM) results that the grain sizes in AgGaS₂ nanofilms were 18‐24 nm and the thin films were smooth and strongly adherent to the substrates. When the annealing temperature was higher than 400 °C, it is an optimum condition to improve the structural and optical properties of the AgGaS₂ thin films. The room temperature PL spectra of AgGaS₂ nanofilms showed prominent band edge emission at 2.72 eV. Based on all results mentioned above, it can be concluded that the SILAR‐annealing method is preferable to preparing high‐quality AgGaS₂ nanofilms. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray diffraction study of the effects of boron on occurrence of deformation faults in Ni3Al alloy

Ni₃Al and Ni₃Al alloys containing varying amounts of boron in L1₂ phase were prepared. All the samples were suitably annealed and then cold-worked by hand filing. X-ray diffraction data are collected on annealed and cold-worked samples. The deformation fault probabilities have been evaluated by two methods, viz. peak shift analysis of powder pattern X-ray reflections of annealed and cold-worked samples, and lattice parameter change between annealed and corresponding cold-worked samples. The values obtained by both the methods are in reasonable agreement. It has been found that the deformation fault probability of Ni₃Al and Ni₃Al containing boron alloys are very high compared to Ag and Cu base alloys. Further the deformation fault probability of Ni₃Al is more sensitive to boron addition. It has been found that at least 1.22 at. % of boron goes into the Ni₃Al lattice.     

Preparation and thermal properties of fire resistant metakaolin-based geopolymer-type coatings

Geopolymer-type coatings prepared by using an industrially available sodium silicate solution (SiO₂:Na₂O = 3.1) and metakaolin were applied to steel substrates. The coatings exhibited excellent adhesion to steel substrates achieving greater than 3.5 MPa tensile stress. Dissolution of the coating in water after 72 h of static testing varied between 12.8 and 34.5 wt.% depending on the water content of initial formulations. Coating formulations showed up to 3% thermal expansion after heating to 800 °C. Coatings maintained high structural integrity with steel substrates when subjected to a heat treatment by a gas torch and formulations calcined at 1000 °C for 1 h showed an X-ray amorphous structure.     

The effect of thermal annealing on the structural and mechanical properties of a-C:H thin films prepared by the CFUBM magnetron sputtering method

a-C:H films were prepared by closed-field unbalanced magnetron (CFUBM) sputtering on silicon substrates using argon (Ar) and acetylene (C₂H₂) gases, and the effects of post-annealing temperature on structural and mechanical properties were investigated. Films were annealed at temperatures ranging from 300 °C to 700 °C in increments of 200 °C using rapid thermal annealing equipment in vacuum ambient. Variations in microstructure were examined using Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface and mechanical properties were investigated by atomic force microscopy (AFM), nano-indentation, residual stress tester, and nano-scratch tester. We found that the mechanical properties of a-C:H films deteriorated with increased annealing temperature.