Characterization of deposits produced by TEA CO2 pulsed laser ablation of silicon mono- and dioxide

Silicon based deposits were prepared by TEA CO₂ pulsed laser ablation (PLA) of SiO and SiO₂ targets in the atmosphere of selected gases (N₂, He, Ne, Ar, Kr). These deposits possess high specific area of several hundreds m² per gram. Owing to the high specific area, some chemical groups and hydrogen related radical were detected by means of FTIR and EPR analyses and theoretical calculations: silyl (E′ center) Si, silylen Si:, silanon SiO, POL (peroxy linkage) SiOOSi and/or NBOHC (non-bridging oxygen hole center) SiO, POR (peroxy radical) SiOO and dioxysilirane Si(O)₂. In SiO₂ deposits the concentration of silyl Si resp. POR SiOO was determined to be 5.8 × 10¹⁸/g resp. 6.2 × 10¹⁹/g. In SiO deposits the ratio [Si:]:[Si] = (3.1-5.7) × 10¹⁹/g: (5.3-9.8) × 10¹⁹/g was measured. Estimated concentration of [Si] in deposits was increased nearly five times in comparison with SiO target. After exposure of the SiO deposits to H₂ EPR doublet with hyperfine splitting of 7.7 mT was observed. The best agreement between calculated theoretical and experimental values was found for the model [(HO)₃SiO]₂HSi. FTIR measurements and calculations of the silanol theoretical model clusters enabled us to discuss the chemical surroundings of the silanol and to determine the defects in the deposits.     

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.     

Local atomic and electronic structures of equiatomic liquid alloy KSb from 923 to 1773 K

The local atomic and electronic structures of equiatomic liquid alloy KSb have been investigated using ab initio molecular dynamics simulations. There is a small peak located at about 62° in the covalent SbSb bond-angle distribution function. The height of 62° peak increases with temperature. The further analysis show that this peak attributes to the triangular structures with each Sb atom covalently bonded to the other two in the liquid KSb and their number increases with temperature. Therefore, there exist isolated Sb atoms, covalently bonded Sb dimers, triangles with three covalent SbSb bonds and short covalently bonded Sb chains in the liquid KSb. Upon temperature increasing the covalent Sb chains tend to break into short pieces so that the isolated Sb atoms, covalently bonded Sb dimers and triangles with three covalent SbSb bonds increase in numbers. The obtained total electronic densities of states at different temperatures give a reasonable explanation of the electronic conductivity increasing with temperature.     

Fourier transform infrared spectroscopy investigation of chemical bonding in low-k a-SiC:H thin films

Fourier Transform Infrared (FTIR) Spectroscopy has long been utilized as an analytical technique for qualitatively determining the presence of various different chemical bonds in gasses, liquids, solids, and on surfaces. Most recently, FTIR has been proven to be extremely useful for understanding the different types of bonding present in low dielectric constant “low-k” organosilicate materials. These low-k materials are predominantly utilized in the nanoelectronics industry as the interlayer dielectric material in advanced Cu interconnect structures. In this article, we utilize FTIR to perform a detailed analysis of the changes in chemical bonding that occur in Plasma Enhanced Chemically Vapor Deposited (PECVD) low-k a-SiC:H thin films. PECVD low-k a-SiC:H materials are equally important in advanced Cu interconnects and are utilized as both etch stop and Cu diffusion barrier layers. We specifically investigate the changes that occur in low-k a-SiC:H films as the dielectric constant and mass density of these films are decreased from > 7 to < 3 and from 2.5 to 1 g/cm³ respectively. We show that decreases in mass density and dielectric constant are accompanied by both an increase in terminal SiH_x and CH_x bonding and a decrease in SiC network bonding. At densities of 1.85 g/cm³, the concentration of terminal SiH_x bonding peaks and subsequent hydrogen incorporation are achieved predominantly via terminal CH₃ groups. Low-k a-SiC:H films with k < 3.5 and density < 1.3 g/cm³ can be achieved via incorporating larger organic phenyl groups but result in non-stoichiometric carbon rich films. Electron beam curing of these lower density a-SiC:H films results in volatilization of the phenyl groups leaving behind nanoporous regions and production of some CCC chain linkages in the network.     

Influence of the deposition parameters on the microstructure and opto-electrical properties of hydrogenated nanocrystalline silicon films by HW-CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared at high deposition rates (> 13 Å/s) from pure silane without hydrogen dilution by hot wire deposition method by varying filament-to-substrate distance (d_s-f). In this study we have systematically and carefully investigated the effect of filament-to-substrate distance on structural, optical and electrical properties of the Si:H films. A variety of characterization techniques, including Raman spectroscopy, low angle X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FE-SEM), UV-Visible-NIR spectroscopy and electrical dark and photoconductivity measurement were used to characterize these films. Films deposited at d_s-f > 5 cm are amorphous while those deposited at d_s-f < 5 cm are biphasic; a crystalline phase and an amorphous phase with nano-sized crystallites embedded in it. Low angle X-ray diffraction analysis showed that the crystallites in the films have preferential orientation along (111) directions. Decrease in d_s-f, the crystallinity and crystalline size increases whereas hydrogen bonding shifts from mono-hydride (SiH) to di-hydride (SiH₂) and poly-hydride (SiH₂)_n complexes. The band gaps of nc-Si:H films (~ 1.9-2.0 eV) are high compared to the a-Si:H films, while hydrogen content remains < 10 at.%. We attribute the high band gap to the quantum size effect. A correlation between electrical and structural properties has been established. Finally, from the present study it has been concluded that the filament-to-substrate distance is a key process parameter to induce the crystallinity in the films by hot wire method. The ease of depositing films with variable crystallite size and its volume fraction, and tunable band gap is useful for fabrication of tandem/micro-morph solar cells.     

Properties and structure of copper ultraphosphate glasses

The structures of xCuO · (1 − x)P₂O₅ glasses (0 ? x ? 0.50) prepared in vacuum sealed silica ampoules were investigated using vibrational spectroscopies. With the addition of CuO, both infrared and Raman spectra indicate a systematic transformation from a three-dimensional ultraphosphate network dominated by Q³ tetrahedra into a chain-like metaphosphate structure dominated by Q² tetrahedra. IR spectra clearly show two distinct Q³ sites with bands at 1378 and 1306 cm⁻¹, assigned to PO bonds on isolated Q³ tetrahedra and PO bonds on tetrahedra that participate in the coordination environments of the Cu-octahedra, respectively. As CuO content increases, the intensity of the PO band associated with the tetrahedra increases to a maximum x ∼ 0.33, then decreases with a concomitant increase of the intensity of the band at 1265 cm⁻¹, due to the asymmetric vibration of the PO₂ groups on Q² tetrahedra. When x > 0.33 the isolated Cu-octahedra begin to share common oxygens to form a sub-network in the phosphate matrix. The effects of glass structure on the glass properties, including density, refractive index, and glass transition temperature, are discussed.     

Consolidation mechanism of materials obtained from sodium silicate solution and silica-based aggregates

A study based on the use of sodium silicate gels as binder for cold consolidation of silica-based aggregates has been investigated. The gels used as precursor of binder were synthesized by adding hydrochloric acid to a concentrated sodium silicate solution. Consolidated materials were obtained by mixing the previous solution before gelation with granular materials (fine silica powder and sand). The study of the gel-silica-sand ternary system shows that the existence domain of materials depends on the sand size distribution. The microstructure of gel-silica-sand ternary samples reveals the presence of the three components with a partial attack of grain surface. This was confirmed by FTIR experiments during the monitoring of the synthesis. Actually, the ν_asSiOSi broad band resulting from the average of the contribution of the set of Q⁴, Q³ and Q² units with a sharp peak located around 1078 cm^− 1, firstly shifts to lower wavenumber until 21 days and then to higher wavenumber characteristic of dissolution/precipitation reactions. On the other hand, the consolidation of the material is strong when the amount of fine silica in the material is high leading to efficient mechanical properties. Therefore, consolidation could be explained by the dissolution of small particles of silica and their precipitation into the grain boundary of sand.     

Point defect formation and annihilation in silica glass by heat-treatment: Role of water and stress

It was discovered that E′ centers were created by heat-treatment when silica glass contains water and has residual stress. Silica glass samples were heat-treated at 1000 °C for various lengths of time in 355 torr (47 000 Pa) water vapor pressure and dry nitrogen gas atmospheres. The electron paramagnetic resonance (EPR) signal of E′ centers increased initially with heat-treatment time in both atmospheres but then decreased afterwards in the wet atmosphere. It is known that water molecules eliminate paramagnetic defects, such as E′ centers and non-bridging oxygen hole centers (NBOHCs) by reacting with these defects in the glass, transforming them to non-paramagnetic species such as Si-OH or Si-H. The present study indicates that water molecules are also capable of initially creating paramagnetic defects in the glass structure by breaking the silica network structure in the presence of stress. The present observation may be relevant to mechanical strength reduction of silica glasses, which is commonly observed in the presence of water and stress.     

Surface smoothing of sputter deposited amorphous CNx films by silicon addition

Amorphous carbon nitride (CN_x) films with silicon addition up to 16 at.% are sputter deposited on Si(1 0 0) substrate, and the surface morphology is studied with scaling method based on atomic force microscopy. The surface roughness σ, the roughness exponent α, and the lateral correlation length ξ decrease with silicon content of the films, reaching 0.33 nm, 0.80 and 50 nm, respectively, for the film with [Si] = 16 at.%. The addition of silicon in the films leads to additional Si-N, Si-C-N and CN bonds revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The films undergo a structural transition from columnar to smooth morphology in cross-section with silicon addition demonstrated by field emission scanning electron microscopy. Nano-sized clusters sparsely dispersed in amorphous matrix of the film with [Si] = 16 at.% are observed by high-resolution transmission microscopy. According to the surface growth mechanism in which surface diffusion and geometrical shadowing drive structural and morphological evolution of the sputter deposited films, surface smoothing of the amorphous CN_x films by silicon addition is explained by the formation of Si-N and Si-C-N bonds that impede surface diffusion of the adsorbed species during film growth, which leads to the reduced size of the columnar structures.     

Bioactive glasses in the system CaO-B2O3-P2O5: Preparation, structural study and in vitro evaluation

Glasses in the system x B₂O₃(1 − x) [y CaO P₂O₅], (x = 0, 0.1, 0.2, 0.3, y = 2, 2.6, 3, 4, 5) have been prepared by fast quenching of high temperature melts. The presence of B₂O₃ affected the glass forming ability, allowing the preparation of calcium phosphate glasses with y ? 2.6. The structure of glasses was analyzed by μ-Raman and infrared spectroscopy. The analysis indicated that the glass network is dominated by highly charged species from phosphate tetrahedra with 3 (pyro) or 4 (ortho) NBOs, while the boron atoms are incorporated mainly in 3 coordinated sites in the form of B∅₃ or B∅₂O⁻ units. A small fraction of units was also evident from the spectra analysis of glasses with high CaO content. All calcium borophosphate glasses exhibited bioactivity after soaking in SBF solution within a few days. This was observed by μ-Raman and SEM microscopy, while XRD patterns clearly revealed growth of hydroxyapatite phase. The presence of boron in the glass network has a catalytic effect at favoring bioactivity of the otherwise bioinert calcium phosphate glasses.     

Chemical bonding and optical properties of germanium–carbon alloy films prepared by magnetron co-sputtering as a function of substrate temperature

Amorphous non-hydrogenated germanium carbide (a-Ge_{1 − x}C_x) films have been prepared by magnetron co-sputtering system designed by ourselves. The chemical bonding and microstructure have been analyzed using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The optical properties of the films have been investigated by means of spectroscopic ellipsometry. The relationship between the chemical bonding and the optical properties has been explored. It has been found that all films with the constant carbon content are amorphous. The sp² CC and sp³ GeC bonds increase with T_s, and some sp² CC bonds gain infrared activity. The fraction of sp³ GeC bonds rises with T_s, but the fraction of sp³ GeGe bonds gradually drops down. In addition, the refractive index and extinction coefficient increase with T_s. The film optical gap is seen to reach 1.15 eV when T_s is 200 °C. However, the optical properties of a-Ge_{1 − x}C_x films almost remain stable with the substrate temperature.     

Transparent K2OTiO2P2O5SiO2 monolithic gels and inorganic amorphous solids through incomplete hydrolysis

Sol–gel derived transparent glasses are of technological interest because of its precisely controlled composition for multicomponent glasses at low temperature processing. The present work demonstrates a new and simple methodology for preparing transparent multicomponent oxide gels by incomplete hydrolysis of alkoxides. Through this processing, a small quantity of organic agencies resulted from incomplete hydrolysis of alkoxides self-disperses in inorganic oxide network, and thus control the formation of the monolith gel free of cracks. Specially, K₂OTiO₂P₂O₅SiO₂ gel monoliths have been synthesized through this route. The gels transformed into transparent K₂OTiO₂P₂O₅SiO₂ inorganic amorphous solids after heat treatment above 450 °C. This approach could be applied to many other multicomponent oxides.     

Metalorganic chemical vapor deposition of mesoporous SiTiOC nanostructured thin films

SiTiOC mesoporous thin films have been obtained by metalorganic chemical vapor deposition (MOCVD) using titanium iso-propoxide (TIP) and tetraethylorthosilicate (TEOS) as starting precursors. The influences of both carrier gas and deposition temperature on the properties of the produced films were extensively studied. The low-angle XRD analysis confirms that, all produced films under different conditions (gas type and temperature) have the mesoporous structure. However, the deposition temperature was found to be much effective in controlling both morphology and composition of the final films than the type of carrier gas. The morphology of the produced films was totally converted from spherical shape-like nanoparticles at 700 °C to lengthy at higher temperature of 1000 °C. The SEM-EDX investigations proved that the composition of the produced films was composed of SiTiOC structure system. The PL analysis has demonstrated along with FT-IR data that all the deposited films at various deposition parameters were composed mainly of SiO₂, SiOC, SiC, TiO₂ and TiOC bond structures and most probably nanocomposite SiTiOC system thin films.     

Electron paramagnetic resonance and thermal behavior of vanadyl-doped mixed alkali bismuth borate glasses

Glasses with composition 15 Li₂O15K₂O10Bi₂O₃(60 ? x) B₂O₃: xV₂O₅ where x = 1, 3, 5, 7, and 9 mol% are prepared by normal melt-quench technique. Characterization of the prepared samples is done using X-ray diffraction, density and differential scanning calorimetry. The density and molar volume are found to increase with increasing x whereas the glass transition temperature decreases. Electron paramagnetic resonance spectra of the prepared samples are recorded using EPR-spectrometer operating in the X-band frequency. The resonance spectra are well resolved for x ≥ 5 mol% and the intensity of the resonance peak is found to increase with increasing x. The values of spin-Hamiltonian parameters (SHP) and molecular orbital coefficients are evaluated. From the values of SHPs it is concluded that V⁴⁺ ions in the present glass system exist as vanadyl ions in octahedral co-ordination with tetragonal compression. It is observed that the SPHs depend slightly on the relative concentration of V₂O₅. Further, the theoretical optical basicity of the glasses has also been evaluated and it is observed that the changes in optical basicity values are in accordance with the changes in SHPs.     

Glasses in the SiOCN system produced by pyrolysis of polycyclic silazane/siloxane networks

In this work, polycyclic silazane/siloxane networks bearing SiO and SiN bonds were synthesized, via hydrosilylation reaction, from cyclotrisilazane, [CH₂CH(CH₃)SiNH]₃, and cyclotetrasiloxane, [CH₃(H)SiO]₄, with different SiH:Sivinyl molar ratios. The resulting polymers were pyrolyzed up to 1000 °C, in N₂ atmosphere, producing SiOCN glasses. The polymer-to-ceramic transformation was studied by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), and chemical analysis. The 1000–1500 °C, high temperature structural evolution was also studied using X-ray diffraction (XRD) and FTIR. The hydrosilylation reaction produced ethylenic bridge crosslinked polymeric precursors with good thermal stability. The SiOCN glasses obtained with ceramic yields higher than 80 wt% showed spectra absorptions of SiN, SiO, and SiC bonds in FTIR. The XRD patterns of the products obtained at 1500 °C displayed diffraction peaks characteristic of β-SiC and a broad halo centered at 22° (2θ), due to the amorphous silica phase. β-SiC diffraction peaks in the XRD patterns were more intense for the precursor richer in polysiloxane units, although absorptions of SiN, SiC, and SiO bonds were also observed in the FTIR spectra. Thus, the final materials were characterized as SiC/SiOCN composites in nano/amorphous phases.     

Preparation,crystallization behavior and magnetic properties of nanoparticles magnetic glass–ceramics in the systems Fe2O3 CoO MnO2, Fe2O3 NiO MoO3 and Fe2O3 CoO V2O5

Ferrimagnetic glass–ceramics were prepared in the systems Fe₂O₃ CoO MnO₂ (S1), Fe₂O₃ NiO MoO₃ (S2) and Fe₂O₃ CoO V₂O₅ (S3). Small amount of H₃BO₄ was added to make the melting process easier. The samples were characterized using DTA, XRD, TEM and EDX. Sequence of crystallization was studied by applying heat-treatment at 800 and 1000 °C for 4 h. CoFe₂O₄ with crystallite sizes of ≈ 14–20 nm was successfully prepared beside FeCoOBO₃ and Co₃BO₅ in S1. NiMoO₄, (FeNi₂)O₂(BO₃) and NiO with crystallite size ≈ 56–79 nm were crystallized in S2. CoFe₂O₄, FeCoOBO₃ and Co₃BO₅ with crystallite size ≈ 6–8 nm were crystallized in S3. Magnetic hysteresis cycles were analyzed with a maximum applied field of 20 kOe at room temperature. From the obtained hysteresis loops Ms records higher values for S1 and S3 and lower value for S2, while coercivity reach maximum for S2. The variable, magnetic, data range gives a wide range for different applications.     

IR and ESR investigations on V2O5–P2O5–BaO glass system with opto-electronic potential

The changes observed in the IR and ESR spectra of the xV₂O₅(1 ? x)[0.8P₂O₅ ? 0.2BaO] glass system with 0 ≤ x ≤ 50 mol% show that vanadium oxide acts as a network modifier at low concentration (x ≤ 5 mol%) and as a network former for high content (x ≥ 10 mol%). Thus the IR bands belonging to the phosphate groups are strongly reduced except the specific bands of the short chain phosphate units due to the phosphate network depolymerization and the spectra are dominated by the vibrations characteristic for POP, POV and VOV linkages. At the same time the changes observed in the ESR spectra of these glasses are explained supposing the superposition of two signals, one with a well-resolved hyperfine structure typical for isolated V⁴⁺ ions and a broad line characteristic for clustered ions. The line width dependence versus V₂O₅ content shows that dipole–dipole interactions exist between vanadium ions until x = 5 mol% and the superexchange interactions prevail at high content (x > 10 mol%).     

Structural characterization of lanthanum aluminosilicate glasses by 29Si solid-state NMR

We investigate the network structures of LaSiAlO glasses by ²⁹Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR). Their compositions span most of the glass-forming region of the ternary La₂O₃Al₂O₃SiO₂ system at 1600 °C. The ²⁹Si NMR resonances narrow and become progressively deshielded when Al substitutes for Si in the network, as well as for increasing La-content of the glass, which leads to network depolymerization. We compare experimental and calculated center of gravities of the ²⁹Si NMR peaks, the latter generated from different simplified models for the distributions of Al and Si as well as bridging oxygen (BO) and non-bridging oxygen (NBO) atoms over the networks. The data do not permit accurate quantifications and may only be interpreted in limiting scenarios. However, they indicate that both distributions are essentially randomized, implying a clear deviation of the Al/Si ordering from that according to a Loewenstein Al-avoidance, coupled with a nearly uniform partitioning of the NBO atoms between Al and Si tetrahedra.