The kinetics of photodissolution of Ag in amorphous As2S3 films

A new technique, measurement of the electrical resistance change of the Ag layer, is developed to study the kinetics of photodissolution of Ag in amorphous As₂S₃. It is shown that the photodissolution rate is proportional to the light intensity absorbed in the As₂S₃ at the As₂S₃Ag interface, but photoelectrons ejected from the Ag into the As₂S₃ also contribute. The process is shown to be two-stage. Firstly a critical “radiation damage” dose must be accumulated in the As₂S₃. Secondly, the Ag atom is photon-assisted across the As₂S₃Ag interface activation barrier.     

Thermal dissolution of Ag(Cu) in amorphous Ge(Sx Se1 − x)2 system

Thermally induced solid state reaction of Ag(Cu) into thin Ge(S_x Se_1 − x)₂ films with x = 0, 0.1, 0.4 and 1.0 was investigated using a step by step technique in order to design films with exact Ag(Cu) concentrations for applications in integrated IR optical devices. A thin film of Ag(Cu) was deposited on top of the host Ge(S_x Se_1 − x)₂ films followed by annealing in vacuum at constant temperature, which resulted in homogeneous films of good optical quality. The variation in Ag(Cu) concentration in the films ranged between 5 and 35 at.%. The kinetics of the diffusion and dissolution of metal in the host films was measured by optically monitoring the change in thickness of doped chalcogenide during consecutive thermal annealing steps. The kinetics studies revealed that the thermal dissolution rate of the Cu is greater than that of Ag. Optical UV-VIS transmission spectra of chalcogenide glass layers, undoped and thermal doped by Ag(Cu), were measured to establish the optical properties of the films. The spectra were analyzed using the technique proposed by Swanepoel and the results show that the addition of metal increases the absorption coefficient in the power-law regime and consequently the optical gap decreases and the refractive index increases. The amorphous character of the films was checked by X-ray diffraction which confirmed the amorphous structure of all Ag(Cu)GeSSe thin films.     

Raman spectrum of vitreous As2S3

The spontaneous Stokes and anti-Stokes Raman spectrum of vitreous As₂S₃ is reported. The spectrum was recorded with both HeNe and Ar ion laser excitation lines in the transmission and reflection modes respectively. Spectra were recorded at various temperatures between 20°K and 465°K, the softening temperature of As₂S₃ glass. It is shown conclusively that the quasicontinous scattering observed at low wave number shifts (< 100 cm⁻¹) is real in agreement with the theory of Shuker and Gammon and not an arbitrary background as previously reported. An approximate density of vibrational states is deduced from the polarized Raman spectra.     

One-step fabrication of Fe2O3/Ag core-shell composite nanoparticles at low temperature

The Fe₂O₃/Ag core-shell composite nanoparticles were successfully prepared via a simple method at low temperature. X-ray diffraction data revealed the formation of core-shell composite nanoparticles, with Fe₂O₃ as the core and silver as the shell. The results from the transmission electron microscopy and scan electron microscopy further indicated that the composite nanoparticles were spherical with a core diameter and shell thickness of 26.0 nm and 13.5 nm, respectively. Magnetic measurements showed that the composite nanoparticles exhibited a typical ferromagnetic behavior, a specific saturation magnetization of 0.95 emu/g and an intrinsic coercivity of 104.0 Oe at room temperature. For a standard two-probe analysis at room temperature, the composite nanoparticles showed a typical conductive behavior and its conductivity was about 3.41 S/m. Moreover, this present synthesis method of Fe₂O₃/Ag core-shell composite nanoparticles shows an easy processing and does not need high-temperature calcining to attain the final product, which can be applied in a variety of areas, including catalysis, medicine, photonics, and new functional device assemblies.     

Ag diffusion in amorphous As50Se50 films studied by XPS

X-ray photoelectron spectroscopy and depth profile analysis were used to investigate the X-ray-induced silver photodiffusion into an amorphous As₅₀Se₅₀ thin film. At the initial stages of irradiation an induction period was observed while core level spectra analysis revealed the existence of a mixed As–Se–Ag interlayer between the metal and the chalcogenide matrix. It was found that during the induction period this interlayer is enriched in silver and the existing As–Se–Ag intermediate species are transformed to Ag–Se–Ag that form the metal source for the effective silver photodiffusion. With further irradiation photodiffusion proceeds by the disruption of Ag–Se bonds and the recombination of As atoms with Se to stable As–Se units. Ultimately, silver concentration reaches a plateau when the diffusion stops. A separated Ag₂Se phase on the film’s surface is identified at this stage. Depth profile analysis shows that silver has been homogenously diffused into the chalcogenide matrix and the Ag₂Se phase exists only at the top surface layers probably in the form of quasi-crystalline clusters that prohibit further Ag diffusion.     

Thermally modulated differential scanning calorimetry of a glass of composition 45Na2O-40B2O3-10Al2O3-5In2O3

The kinetics of structural relaxation and of glass transition of the 45Na₂O-40B₂O₃-10Al₂O₃-5In₂O₃ glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems).     

Orthophosphate nanostructures in SiO2-P2O5-CaO-Na2O-MgO bioactive glasses

Vibrational spectroscopy, ²⁹Si and ³¹P magic-angle spinning nuclear magnetic resonance spectroscopy and high resolution transmission electron microscopy were used to investigate structural aspects of SiO₂-P₂O₅-CaO-Na₂O-MgO glasses. The experimental results show that for the two compositions, 25.3SiO₂-10.9P₂O₅-32.6CaO-31.2MgO and 33.6SiO₂-6.40P₂O₅-19.0CaO-41.0MgO, phosphorous is present in a nano-crystalline form with interplanar distances in the 0.21-0.26 nm range. The two glasses develop a surface CaP-rich layer and the presence of any intermediate silica-rich layer was not detected. It was suggested that the phosphate nano-regions may play a key role in the initial stages of the bioactive process, acting as nucleation sites for the calcium phosphate-rich layer.     

Synthesis and characterization of single-crystalline PrCO3OH dodecahedral microrods and its thermal conversion to Pr6O11

Single-crystalline PrCO₃OH dodecahedral microrods with an orthorhombic structure have been successfully synthesized by the hydrothermal method used urea as the precipitator. Pr₆O₁₁ dodecahedral microrods have been obtained by thermal conversion of PrCO₃OH dodecahedral microrods at 600 °C in air for 6 h. The as-synthesized products were characterized by X-ray powder diffraction, field-emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectra, fourier transform infrared spectroscopy and thermogravimetry–differential thermal analysis. The effect of the reaction parameters on the morphology of the product has been investigated. The dodecahedral microrods with larger size and better crystallinity can be obtained under the higher reaction temperature. The possible formation mechanism of PrCO₃OH microrods was discussed.     

Crystal growth of boron monophosphide using a B2H6-PH3-H2 system

Boron monosphide (BP) with (100) orientation can be epitaxially grown on Si substrates with (100) orientation by thermal decomposition of B₂H₆ and PH₃ in hydrogen. In a horizontal CVD system, the growth rate was studied as a function of gas phase composition and temperature. The growth rate is independent of the PH₃ partial pressure in the region where the PH₃ is in excess. For low values of the B₂H₆ partial pressure the growth rate is proportional to the B₂H₆ partial pressure (a linear region) with an activation energy of 1.8 eV, and for high values of the B₂H₆ partial pressure the growth rate becomes constant (a saturation region) with an acivation energy of 3.0 eV. A simple adsorption-reaction model can be proposed to explain the experimental growth kinetics. The conductivity of the as-grown layer is determined by the PH₃ partial pressure. n-type BP can be obtained for high values of the PH₃ partial pressure and p-type BP for low values. Si doping during the growth and phosphorus anti-site donors are two possibilities to explain the results.     

Characterisation of ALCVD Al2O3-ZrO2 nanolaminates, link between electrical and structural properties

Al₂O₃ and ZrO₂ mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al₂O₃ and ZrO₂ films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO₂ on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al₂O₃. Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high-k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al₂O₃ and ZrO₂ films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1-1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation.     

Morphology and structural studies of Ag photo-diffused GeySe1−y thin films prepared by RF-sputtering

Thin films of Ag photo-doped-Ge_ySe_1−y films were prepared by RF co-sputtering technique. A systematic study of the relation existing between the host layer composition and the saturation rate in silver was carried out. Morphology and composition studies before and after chemical etchings were performed by scanning electron microscopy and electron probe micro-analyses, respectively. Raman spectroscopy studies showed the presence of corner-sharing and edge-sharing Ge(Se_1/2)₄ tetrahedra in all thin films. The vibration mode corresponding to Se_n-chains is observed for the Ge-poor host layer and on the contrary, Ge-rich thin films exhibited some tendency to form homopolar Ge–Ge bonds as a part of ethane-like Ge₂Se₆ units. These investigations revealed the amount of Ag that could be incorporated in the host layer. Such an amount strongly depends on the relative ratio Ge/Se in the Ge_ySe_1−y thin film. For the Ge-poor host layer, an incorporation of Ag (54 at.%) was observed but also a drastic increase in the film heterogeneity. On the other hand, the host layers with higher Ge content showed homogeneous surfaces and a saturation level of 32–41 at.% Ag.     

Growth and scintillation properties of the Na2W2O7 crystal

The growth and scintillation properties of the Na₂W₂O₇ crystal are reported. The solid reaction between Na₂CO₃ and WO₃ is used to synthesise the Na₂W₂O₇ material. The Na₂W₂O₇ single crystal has been grown by the Bridgman method. And the Na₂W₂O₇ single crystal with sizes 14×7×6 mm³ has been achieved. The transmission spectra, the Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra of the Na₂W₂O₇ crystal are measured. The measurement results show that the Na₂W₂O₇ crystal is a promising intrinsic scintillator.     

Structure and thermal stability of (Zr0.6Al0.4)O1.8 thin film on strained SiGe layer

Zr_0.6Al_0.4O_1.8 dielectric films were deposited directly on strained SiGe substrates at room temperature by ultra-high vacuum electron-beam evaporation (UHV-EBE) and then annealed in N₂ under various temperatures. X-ray diffraction (XRD) reveals that the onset crystallization temperature of the Zr_0.6Al_0.4O_1.8 film is about 900 °C, 400 °C higher than that of pure ZrO₂. The amorphous Zr_0.6Al_0.4O_1.8 film with a physical thickness of ∼12 nm and an amorphous interfacial layer (IL) with a physical thickness of ∼3 nm have been observed by high-resolution transmission electron microscopy (HRTEM). In addition, it is demonstrated there is no undesirable amorphous phase separation during annealing at temperatures below and equal to 800 °C in the Zr_0.6Al_0.4O_1.8 film. The chemical composition of the Zr_0.6Al_0.4O_1.8 film has been studied using secondary ion mass spectroscopy (SIMS).     

Crystallization behavior of (GeS2)0.1(Sb2S3)0.9 glass

The crystal growth kinetics of antimony trisulfide in (GeS₂)_0.1(Sb₂S₃)_0.9 glass has been studied by microscopy and DSC. The linear crystal growth kinetics has been confirmed in the temperature range 492 ? T ? 515 K (E_G = 405 ± 7 kJ mol⁻¹). The applicability of standard growth models has been assessed. From the crystal growth rate corrected for viscosity plotted as a function of undercooling it has been found that the most probable mechanism is interface controlled 2D nucleated growth. The non-isothermal DSC data, corresponding to the bulk sample, can be described by the Johnson-Mehl-Avrami equation.     

The crystallization kinetics of glassy Pd0.775Cu0.06Si0.165

The crystallization kinetics of a Pd_0.775Cu_0.06Si_0.165 metallic glass have been determined by calorimetry over the temperature interval 665–680 K. We observe a change in the time dependence from t⁴ at 665 K to t³ at 680 K. In this temperature interval the activation enthalpy for crystallization was observed to be (95 ± 5) kcal/mol, in good agreement with the activation enthalpy for viscous flow as determined previously by Chen.     

Study of microstructure in Agx(As0.33Se0.67)100−x chalcogenide glasses

Glasses with general formula Ag_x(As_0.33Se_0.67)_100−x were studied by means of modulated differential scanning calorimetry (MDSC), conductivity and permittivity measurements and atomic force acoustic microscopy (AFAM). In the whole range of doping (x = 2–12 at.% Ag) a phase separation was supposed. The proportional amount of the ion-conductive Ag rich phase increased with the Ag content. A rapid increase (almost four orders of magnitude) in the conductivity was observed in the Ag concentration range 4–8 at.%, which could be associated with the interconnection of this ion-conductive phase. The transition from a hole conductivity (at low Ag concentration) to a mixed ionic-hole conductivity at higher Ag concentration was studied by permittivity measurements.     

Solubility of Ag2O into the Na2O–B2O3–Al2O3 system

The solubility of Ag₂O was measured for the Na₂O–B₂O₃ and Na₂O–B₂O₃–Al₂O₃ system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag₂O for the Na₂O–B₂O₃ system above the melting point of Ag for the first time. It was found that the addition of Na₂O decreases the solubility of Ag₂O while the addition of Al₂O₃ had little effect on the solubility. The effect of Na₂O and Al₂O₃ on the solubility of Ag₂O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag₂O in Na₂O–B₂O₃–Al₂O₃ melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver.     

Crystallization of amorphous Ni35Zr65 and Fe40Ni40P14B6 under proton irradiation

Two amorphous alloys, Ni₃₅Zr₆₅ and Fe₄₀Ni₄₀P₁₄B₆, were irradiated using 400 keV protons at several temperatures below the crystallization temperature, T_x, to peak doses in the neighborhood of 3.5 to 4.5 dpa. Irradiation at 250°C resulted in the crystallization of both alloys, which were examined by transmission electron microscopy of samples electrolytically polished to various distances from the irradiated surface to study the effect of dose. Samples masked from the proton beam remained amorphous during irradiation. In the Ni₃₅Zr₆₅ alloy crystallization of the equilibrium phases propagated throughout the entire sample, while the in the Fe₄₀Ni₄₀P₁₄B₆ alloy crystallization was observed only in those parts of the samples lying within the proton range. Neither alloy crystallized during irradiation at 100°C. In both these alloys the amorphous phase is therefore evidently stable at irradiation temperatures below approximately 0.6 T_x. An examination of the literature on irradiation damage of binary alloys and intermetallic compounds suggests that there is a tendency for initially amorphous alloys to remain amorphous at irradiation temperatures, T_irr < 0.3 T_L, where T_L (≈T_x) is the “melting” temperature (either a eutectic, peritectic or congruent melting temperature). Also, these same alloys, even when they are initially crystalline, transform to the amorphous state during irradiation at T < 0.3 T_L. Some other crystalline alloys have also been shown to transform to the amorphous state at T_irr < 0.3 T_L even though they have never been prepared in this condition by rapid quenching techniques. The temperature 0.3 T_L appears to be a lower limit, however, since the crystalline to amorphous transformation occurs in many of these alloys at temperatures greater than 0.3 T_L. It is suggested, by analogy with results on void formation in irradiated metals, that this low temperature limit is related to the low mobility of vacancies in these materials, although the mechanism of crystallization, or conversely amorphization, is not fully understood.     

Bond character and properties of the mixed alkali system Na2OK2OAl2O3SiO2

The mixed alkali glass system Na₂OK₂OAl₂O₃SiO₂ was investigated. Density, transformation temperature, refractive index, and chemical durability were studied. Optical absorption and ESR spectra of the CuO-doped glasses were determined.Calculations of the polarizability of O^2?, bonding parameters of the Cu²⁺ complex, and the packing density are presented. It was found that for the mixed alkali glasses, the oxygen- alkali bond has a more ionic character than expected from additivity. This fact enables the non-linear changes of the refractive index, of the shift of the Cu²⁺ absorption band, and of the covalency to be interpreted as the Na mole fraction is varied. It is also possible to explain qualitatively the density, T_g and chemical durability non-linear variations with change of the Na content by the ionicity deviations of the bond character and the postulated pairs of Na⁺ and K⁺ ions in the mixed alkali glasses.     

Growth kinetics and micromorphology of NH4Cl:Mn2+ crystals formed in the NH4Cl-MnCl2-H2O-CONH3 system

The growth kinetics and elementary growth processes on the surface of NH₄Cl:Mn²⁺ heterogeneous crystals formed in the NH₄Cl-MnCl₂-H₂O-CONH₃ system are experimentally studied. It is found that a change in the composition of complexes in an NH₄Cl crystal from Mn(NH₄)₂Cl₄ · 2H₂O to MnCl₂ · 2CONH₃ leads to the occurrence of a local maximum in the kinetic curve and a change in the shape of dislocation growth centers from flat to conical. The growth kinetics of {100} faces of heterogeneous NH₄Cl:Mn²⁺ crystals is described within the Bliznakov model using the Fowler-Guggenheim adsorption isotherm, which takes into account the lateral interaction of adsorbed particles.