Sol-gel deposition of silica films on silicate glasses: Influence of the presence of lead in the glass or in precursor solutions

Many lead silicate historical glasses suffer degradation phenomena often observed as color changes and iridescence caused by lead ions leaching from the outer layers of the glass. In order to repair and to prevent these phenomena, glasses with large amounts of lead (6.7 and 14.3 at.% of lead) have been coated with silica films at neutral pH by dipping them in a precursor solution of TEOS (tetraethyl orthosilicate), ethyl alcohol and deionized water without any other acid or basic catalyst. Experiments with long dipping times (24 h) and temperatures around 20 °C have been performed to evaluate the role of lead ions of the glass as a catalyst. Silica films of very good quality and optical transparency have been also obtained on lead-free, soda-lime glasses by adding catalytic amounts of Pb(NO₃)₂ instead of HCl to the precursor solution. The films have been characterized by optical microscopy, AFM (Atomic Force Microscopy), XPS (X-ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry).     

Electron energy-loss spectroscopy in irradiation-sensitive rutile-GeO2

This report suggests that an electron energy-loss spectroscopy technique under low beam intensity is useful for beam-sensitive materials. High quality ‘damage-free’ Ge M₄₅ edge near-edge structure can be obtained using this method in rutile-GeO₂, which is susceptible to high-energy electron beam damage. Both experimental and theoretical results indicate that the Ge M₄₅ edge ELNES can be used to distinguish fourfold and sixfold coordinated Ge.     

Vertically aligned N-doped carbon nanotubes by spray pyrolysis of turpentine oil and pyridine derivative with dissolved ferrocene

Vertically aligned nitrogen-doped carbon nanotubes were synthesized from the pyrolysis of a mixture of turpentine oil, 4-tert-butylpyridine (C₉H₁₃N) and ferrocene on silicon and quartz substrate in nitrogen atmosphere at 700 °C by simple spray pyrolysis technique. SEM, TEM, TGA/DTA, Raman spectroscopy, XPS and electron probe micro analysis (EPMA) techniques were used to characterize the structural analysis and composition of the as-grown N-doped carbon nanotubes. Morphology of the films was greatly affected by the nature of the substrate. From the XPS and EPMA data, it was found that nitrogen content of the nanotubes were 1.6 at.% and 2 at.% on silicon and quartz substrate, respectively. Our studies show that two different types of N atoms can be present in these materials. These are ‘pyridinic’ and ‘graphitic’ nitrogen with binding energies of 398.2 eV and 400.4 eV, respectively. Raman spectroscopy reveals that graphitization of carbon nanotubes grown on silicon is better than nanotubes grown on quartz substrate. Thermogravimetric analysis showed that the thermal stability of as-prepared nanotubes grown on silicon substrate is higher than the nanotubes deposited on quartz substrate.     

Xerographic spectroscopy of gap states in Se-rich amorphous semiconductors review

One of the most important parameters which determine the performance of many modern devices based on amorphous semiconductors is the drift mobility-lifetime product, μτ. There has been much interest in determination of charge-carrier ranges in amorphous semiconductors by various measurement techniques. Although the mobility, μ, can be measured by the conventional time-of-flight transient photoconductivity technique, the determination of the lifetime, τ, is often complicated by both experimental and theoretical limitations. The present article provides an overview of xerographic measurements as a tool for studying the electrical properties of amorphous semiconductors. First, details of the experimental set-up are discussed. Thereafter, the analysis and interpretation of dark discharge, the first cycle residual potential, cycled-up saturated residual potential are considered. It is shown that from such measurements the charge-carrier lifetime, τ, the range of the carriers, μτ, and the integrated concentration of deep traps in the mobility gap can be readily and accurately determined. Xerographic measurements on Se-rich amorphous photoconductors have indicated the presence of relatively narrow distribution of deep hole traps with integrated density of about 10¹³ cm^? 3. These states are located at ~ 0.85 eV from the valence band. A good correlation was observed between residual potential and the hole range, in agreement with the simple Warter expression. The capture radius is estimated to be r_c = 2–3 Å. Since r_c for pure a-Se and a-As_xSe_1 ? x is comparable to the Se–Se interatomic bond length in a-Se, it can be suggested that deep hole trapping centers in these chalcogenide semiconductors are neutral-looking defects, possibly of intimate valence-alternation pair (IVAP) in nature. The absence of any electron spin resonance signal (ESR) at room temperature seemed to be a strong argument in favor of this suggestion. Finally, photoinduced effects on xerographic parameters are discussed. It has been shown that photoexcitation of a-As_xSe_1 ? x amorphous films with band-gap light alters deep hole and electron states. During room-temperature annealing photosensitized states relax to equilibrium. Recovery process becomes slower with increasing As content. Qualitative explanation of the observed behavior may be based on associating the deep states with C₃⁺ and C₁^?intimate-valence-alternation–pair (IVAP) centers.     

The structure of GeO2-SiO2 glasses and melts: A Raman spectroscopy study

We have investigated a series of glasses and melts along the GeO₂-SiO₂ join using insitu Raman spectroscopy. The results for both the glasses and melts are consistent with a continuous random network in which there are ‘regions’ that are SiO₂-like, GeO₂-like and mixed GeO₂-SiO₂-like. Incorporation of GeO₂ into the SiO₂ network is initially accommodated via the 3- and 4-membered SiO₄ rings which are lost as they convert to larger mixed Ge/Si rings. The LO-TO mode behavior is also consistent with a network that is composed of different ‘regions’ and is similar to that expected from the Bruggeman effective media model. At the highest temperatures there are indications that the mixed Ge/Si rings convert back to small 3-membered GeO₄ rings and large SiO₄ rings; the small 3- and 4-membered SiO₄ rings are not reformed.     

On the oxidation mechanism of microcrystalline silicon thin films studied by Fourier transform infrared spectroscopy

Insight into the oxidation mechanism of microcrystalline silicon thin films has been obtained by means of Fourier transform infrared spectroscopy. The films were deposited by using the expanding thermal plasma and their oxidation upon air exposure was followed in time. Transmission spectra were recorded directly after deposition and at regular intervals up to 8 months after deposition. The interpretation of the spectra is focused on the Si-H_x stretching (2000-2100 cm⁻¹), Si-O-Si (1000-1200 cm⁻¹), and O_xSi-H_y modes (2130-2250 cm⁻¹). A short time scale (< 3 months) oxidation of the crystalline grain boundaries is observed, while at longer time scales, the oxidation of the amorphous tissue and the formation of O-H groups on the grain boundary surfaces play a role. The implications of this study on the quality of microcrystalline silicon exhibiting no post-deposition oxidation are discussed: it is not sufficient to merely passivate the surface of the crystalline grains and fill the gap between the grains with amorphous silicon. Instead, the quality of the amorphous silicon tissue should also be taken into account, since this oxidation can affect the passivating properties of the amorphous tissue on the surface of the crystalline silicon grains.     

Transition between amorphous and crystalline phases of SiC deposited on Si substrate using H3SiCH3

This paper presents a study of the transition between amorphous and crystalline phases of SiC films deposited on Si(1 0 0) substrate using H₃SiCH₃ as a single precursor by a conventional low-pressure chemical vapor deposition method in a hot-wall reactor. The microstructure of SiC, characterized by X-ray diffraction and high-resolution transmission electron microscopy, is found to vary with substrate temperature and H₃SiCH₃ pressure. The grain size decreases with increasing MS pressure at a given temperature and also decreases with reducing temperature at a given MS pressure. The deposition rates are exponentially dependent on the substrate temperature with the activation energy of around 2.6 eV. The hydrogen compositional concentration in the deposited SiC films, determined by secondary ion mass spectrometry depth profiling, is only 2.9% in the nanocrystalline SiC but more than 10% in the amorphous SiC, decreasing greatly with increasing deposition temperature. No hydride bonds are detected by Fourier transform infrared spectroscopy measurements. The chemical order of the deposited SiC films improves with increasing deposition temperature.     

Anionic structure and elasticity of Na2O-MgO-SiO2 glasses

The structure and elastic properties of a series of xNa₂O · MgO · 4SiO₂ glasses have been studied using both Raman and Brillouin spectroscopy. Relative to Na₂O-SiO₂ glasses, the maximum abundance for phyllosilicate structural units in the present glasses shows a lag of 0.5 units in the number of non-bridging oxygen per silicon atom (NBO/Si). This phenomenon has been attributed to the decrease in the average coordination number of modifying cations due to the presence of Mg²⁺. It has also been found that the decomposition of both metasilicate and disilicate (dimerized SiO₄) anionic structural units in Na₂O-SiO₂ glasses are enhanced by the addition of MgO. However, the presence of Mg²⁺ does not cause a considerable effect on the decomposition of phyllosilicate structural unit. The acoustic data have revealed that both shear and Young’s moduli of the present glasses decrease with increasing NBO/Si (the variation in bulk modulus is reversed, however). The resistance to shear deformation for the anionic structural units in silicate glasses has been found to decrease in the following order: tectosilicate > phyllosilicate > metasilicate > disilicate > orthosilicate. The relative contribution of the various anionic structural units to the bulk modulus of a glass remains to be determined. The ideal mixing model using Makishima-Mackenzie’s relationship for predicting Young’s modulus is not applicable to the present glasses.     

Nanoindentation investigation of amorphous hydrogenated carbon thin films deposited by ECR-MPCVD

Nanomechanical properties of amorphous hydrogenated carbon thin films are performed by nanoindentation technique. The amorphous hydrogenated carbon films are produced on silicon substrate by electron cyclotron resonance microwave plasma chemical vapor deposition (ECR-MPCVD). The effect of negative bias voltage on amorphous hydrogenated carbon films is examined by Raman spectroscopy and the results showed that the intensity ratio of D-peak to G-peak (I_D/I_G) of amorphous hydrogenated carbon films at various bias voltages, increased as the bias voltage increased. The results also showed that Young’s modulus and hardness also increased as the bias voltage increased. In addition, Young’s modulus and hardness both decreased as the indentation depth increased.     

Growth of epitaxial TmFeCuO4 thin films by pulsed laser deposition

Epitaxial thin films of TmFeCuO₄ with a two-dimensional triangular lattice structure were successfully grown on yttria-stabilized-zirconia substrates by pulsed laser deposition and ex situ annealing in air. The films as-deposited below 500 °C showed no TmFeCuO₄ phase and the subsequent annealing resulted in the decomposition of film components. On the other hand, as-grown films deposited at 800 °C showed an amorphous nature. Thermal annealing converted the amorphous films into highly (0 0 1)-oriented epitaxial films. The results of scanning electron microscopic analysis suggest that the crystal growth process during thermal annealing is dominated by the regrowth of non-uniformly shaped islands to the distinct uniform islands of hexagonal base.     

Structure of pulsed-laser deposited arsenic-rich As–S amorphous thin films,and effect of light and temperature

Thin amorphous films from As–S system (∼As₅₀S₅₀) were prepared by the pulsed laser deposition technique. Light- and thermally-induced changes of structure of studied films have been investigated using Raman scattering spectroscopy results and interpreted in terms of chemical reactions and/or phase transitions between individual structural units. The irradiation of as-deposited thin films causes light-induced reactions, in which As₄S₃, α- and β-As₄S₄, and pararealgar/χ-As₄S₄ molecules are formed. Thermal-annealing of exposed thin films leads to the formation of β-As₄S₄ molecules.     

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.     

Investigation of near constant loss contribution to conductivity in lithium bismo-silicate glasses

Glasses having compositions 20Li₂O · (80 − x)Bi₂O₃ · xSiO₂ (x = 55, 60, 65, 70 mol%) were investigated using impedance spectroscopy in the frequency range from 20 Hz to 1 MHz and in the temperature range from 543 to 663 K. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. The increase in conductivity with increase in SiO₂ content is attributed to the change in the structural units of bismuth. Both electric modulus and the conductivity formalism have been employed to study the relaxation dynamics of charge carriers in these glasses. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Similar values of activation energy for dc conduction and for conductivity relaxation time indicates that the ions overcome same energy barrier while conducting and relaxing. The observed conductivity spectra follows power law with exponent ‘s’ which increases regularly with frequency and approaches unity at higher frequencies. Near constant losses (NCL) characterize this linearly dependent region of conductivity spectra. A deviation from ‘super curve’ for various isotherms of conductivity spectra was also observed in high frequency region and at low temperatures, which supports the existence of different dynamic processes like NCL in addition to the ion hopping processes in the investigated glass system.     

Magnetic behaviors of amorphous Fe78Si9B13 thin films prepared by pulsed laser deposition

Amorphous magnetic thin films have been deposited onto BK-7 substrates using the pulsed laser deposition technique. The source material irradiated by the laser was a pack of amorphous ribbons of composition Fe₇₈Si₉B₁₃. The structural properties of thin films were investigated and a large number of droplets were observed in the magnetic layers. Electric current passing through the films causes significant deformation of droplets and consequently changes the magnetic thin films characteristics. Magnetic properties evolution after electrical processing was investigated using magneto-optical Kerr effect.     

The ionic transition and the glass transition in ion-conducting glasses

In an ion-conducting glass, there may be the ionic transition which characterizes ‘melting’ of the modifying ions in a similar way as the glass transition characterizes ‘melting’ of the glass network former. The ionic transition can be observed, electrically, by the thermally stimulated depolarization current technique. It is demonstrated that the relaxation time for the ionic transition is the same (near 100 s) with that for the glass transition in so far as the heating/cooling rate lies within, say, 10⁻¹-10⁻⁵ K/s as adopted in our routine works.     

Different substrate materials effect on structure of ta-C films by Raman spectroscopy for magnetic recording sliders

Raman spectra, using visible (514 nm) and ultraviolet (244 nm) excitation, of tetrahedral amorphous carbon (ta-C) films of thickness of 5 nm have been studied as a function of different substrates materials. These materials are Fe-Co (Fe: 67 at.%, Co: 33 at.%) alloy, Fe-Ni alloy (Fe: 18 at.%, Ni: 82 at.%), Au and Al₂O₃-TiC (Al₂O₃: 64 at.%, TiC: 36 at.%), which are mainly used in magnetic recording sliders. The spectra show that the films deposited on Al₂O₃-TiC contain the highest sp³ content, with a lower sp³ content observed in films deposited to Fe-Co and Fe-Ni alloys. The lowest sp³ content was observed in films on the Au substrate. The results also indicate that the anti-wear performance of ta-C film on different substrates varies as Al₂O₃-TiC (the best) > Fe-Co and Fe-Ni alloy > Au (the worst). Also mechanisms are proposed to explain the effect of substrate material on these thin film properties.     

Compositional dependence of the optical properties of amorphous Sb2Se3−xSx thin films

Thin films of Sb₂Se_3−xS_x solid solutions (x = 0, 1, 2, and 3) were deposited by thermal evaporation of presynthesized materials on glass substrates held at room temperature. The films compositions were confirmed by using energy dispersive analysis of X-rays (EDAX). X-ray diffraction studies revealed that all the as-deposited films as well as those annealed at T_a < 423 K have amorphous phase. The optical constants (n, k) and the thickness (t) of the films were determined from optical transmittance data, in the spectral range 500-2500 nm, using the Swanepoel method. The dispersion parameters were determined from the analysis of the refractive index. An analysis of the optical absorption spectra revealed an Urbach’s tail in the low absorption region, while in the high absorption region an indirect band gap characterizes the films with different compositions. It was found that the optical band gap energy increases quadratically as the S content increases.     

Quantitative measurement of Q species in silicate and borosilicate glasses using Raman spectroscopy

Raman spectroscopy has been used to measure the fraction of tetrahedral silicate units connected at three corners into the network (Q³) in binary lithium silicate glasses and also in the more complex borosilicate glasses used for waste immobilization. Agreement within experimental error was obtained with ²⁹Si MAS NMR measurements of the same samples. Raman provides an alternative method of structural determination for silicon-containing glasses with a high content of paramagnetic species where NMR loses resolution. Analysis was performed on borosilicate glasses containing up to 11.98 mol% Fe₂O₃ and the Q³ values obtained by Raman spectroscopy agree within error with the published ²⁹Si NMR results from borosilicate glasses containing the equivalent quantity of Al₂O₃.