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)     

Determination of refractive indexes of dielectric films by the use of immersion liquids

Examples of using immersion liquids in ellilipsometry and multiple-beam interferometry are given. The refractive index of very thin (∼ 5.0 nm) silica films on silicon and on films of silicon nitride are determined by the ellipsometry method. The method of precise determination of refractive index of monolayer dielectric films is described when a precision equal to ± 3 · 10⁻⁴ was reached. A method of determination film thicknesses near the substrate surface in a twolayer system is suggested. The construction of different prisms is given by means of which the immersion liquids are inserted. The selection of the equations for the determination of refractive index in the multiple-beam interferometry is discussed. Two versions of the use of immersion liquids for the determination of refractive indexes of dielectric films by interferometry method are given.     

Characteristics of poly(alkyl silsesquioxane) thin films prepared from chemically linked alkyl units

Poly(alkyl silsesquioxane), PASSQ, copolymers containing the different alkyl components were synthesized by sol–gel polymerization with a bridged alkoxysilane as a matrix component, and the potential applications of low-k films were verified using TGA, FT-IR, ¹³C and ²⁹Si solid state NMR after pore forming process by the thermal decomposition. As the higher alkyl groups in PASSQ were decomposed, the lower refractive indices were achieved from 1.45 to 1.27 due to the formation of nanoporous in the film. In particular, the modulus for the three different PASSQ films were significantly higher than 3.8 GPa of the typical thin film of poly(methyl silsesquioxane). The enhanced moduli for the films are ascribed to the formation of rigid film structure by the introduction of bridged ethylene of BTMSE in spite of the porous structure. In addition, the partial decomposition of bridge ethylene groups was accompanied with the dominant occurrence of methyl silicon groups, which reduced the mechanical properties with microporous structure.     

Spray deposition and characterization of undoped and In‐doped tin disulphide thin films

Undoped and Indium doped tin disulphide (SnS₂) thin films had been deposited onto glass substrates at T_s = 300 °C using spray pyrolysis technique under atmospheric pressure with stannous chloride, indium chloride and thiourea as precursors. The structural, optical and electrical properties of the deposited films were characterized. The XRD pattern revealed that the undoped and doped films had preferred orientation along (002) plane with hexagonal structure. FESEM micrographs had shown that morphologies of the films changed with indium doping. Optical constant such as refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constants were evaluated from transmittance and reflectance spectra in UV‐Visible spectroscopy. The optical absorption data were used to determine the band gap energy and it was found to be 2.75 eV for undoped and 2.50 eV for indium doped films respectively. The room temperature dark resistivity was found to be 4.545 × 10³ Ω‐cm and 5.406 × 10³ Ω‐cm for undoped and In‐doped films respectively.     

Investigation of optical parameters of Ag-In-Se thin films deposited by e-beam technique

The optical properties of the Ag-In-Se (AIS) thin films deposited by e-beam technique were investigated by means of the optical transmittance measurements. The optical absorption coefficients of the films were found to vary from 10³ to 10⁵ cm⁻¹ over the wavelength range of 300-1100 nm. The real and imaginary parts of the refractive index and dielectric constant for the as-grown and annealed films in between 100 and 400 °C were evaluated by means of both envelope method (EM) and continuous wavelet transform (CWT) method and the results were in quite good agreement with each other. The refractive index, n, dispersion over the measured wavelength range was explained by applying single-oscillator model (SOM) and the related parameters were calculated. The optical absorption process for the AIS thin films was characterized by three direct transitions from three closely spaced valence bands to a single conduction band due to the splitting of the valence band under the influence of the tetragonal crystalline field and spin-orbit interaction. The direct optical band gap energy decreases as the annealing temperature increases because of the increase in the width of band tail states near valence-band edge caused by the Se segregation. The two distinct parameters of the quasicubic model; crystal-field splitting, Δ_CF, and spin-orbit splitting, Δ_SO, were calculated for as-grown and annealed AIS thin films.     

Optical constants of DC magnetron sputtered titanium dioxide thin films measured by spectroscopic ellipsometry

Optical constants of DC magnetron sputtered TiO₂ thin film have been determined by Spectroscopic Ellipsometry in the photon energy range 1.2 to 5.5 eV at room temperature. The measured dielectric‐function spectra reveal distinct structures at energies of the E1, E1 + Δ1 and E2 critical points are due to interband transitions. The root mean square roughness of the magnetron sputtered TiO₂ thin films evaluated by ex‐situ atomic force microscopy is 5.8 nm. The Dielectric constant values were found to be substantially lower than those for the bulk TiO₂. The dielectric related Optical constants, such as the refractive index, extinction coefficient, absorption coefficient and normal incidence of reflectivity determined from the spectroscopic ellipsometry data are presented and analyzed. The optical constants of the films were also determined using the optical transmittance measurements and the results were discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties and chemical bonding characteristics of amorphous SiNX:H thin films grown by the plasma enhanced chemical vapor deposition method

Amorphous silicon nitride (SiN_X:H) thin films grown by the plasma enhanced chemical vapor deposition (PECVD) method are presently the most important antireflection coatings for crystalline silicon solar cells. In this work, we investigated the optical properties and chemical bonding characteristics of the amorphous SiN_X:H thin films deposited by PECVD. Silane (SiH₄) and ammonia (NH₃) were used as the reactive precursors. The dependence of the growth rate and refractive index of the SiN_X:H thin films on the SiH₄/NH₃ gas flow ratio was studied. The chemical bonding characteristics and the surface morphologies of the SiN_X:H thin films were studied using the Fourier transform infrared spectroscopy and atomic force microscopy, respectively. We also investigated the effect of rapid thermal processing on the optical properties and surface morphologies of the SiN_X:H thin films. It was found that the rapid thermal processing resulted in a decrease in the thickness, increase in the refractive index, and coarser surfaces for the SiN_X:H thin films.     

Analysis of proton-conducting organic-inorganic hybrid materials based on sulphonated poly(ether ether ketone) and phosphotungstic acid via ASAXS and WAXS

In the present paper the distribution of phosphotungstic acid (PTA, H₃PW₁₂O₄₀) dispersed in sulfonated poly(ether ether ketone), SPEEK, was investigated by Anomalous Small Angle X-ray scattering (ASAXS) and Wide-Angle X-Ray Scattering WAXS techniques. The hydrolysis and condensation of 3-aminopropyltrimethoxysilane or zirconium tetrapropylate in this polymeric matrix were used to produce poly(3-aminopropyl silsesquioxane) or ZrO₂, as nanofillers. Contrary to previous results reported for membranes containing phosphomolybdic acid, the PTA could be completely dissolved in the SPEEK matrix. The applicability of the Guinier approximation for the SPEEK/PTA membrane confirmed that the PTA was dispersed as isolated nanoparticles. The incorporation of poly(3-aminopropyl silsesquioxane) in the SPEEK/PTA system caused the agglomeration of the heteropolyacid as 30 nm large particles. The ZrO₂ had little effect on the distribution of PTA in the SPEEK matrix. On the other hand, no crystallization of the heteropolyacid was observed in the membranes.     

Preparation and characterization of ZrO2-SiO2 binary films for planar optical waveguides

ZrO₂-SiO₂ binary films for active optical waveguides were prepared by the sol-gel method with zirconium oxychloride and tetraethoxysilane as precursors. The main factors that influence the film thickness and refractive index have been found. The relationship between the film refractive index composition and heat treatment temperature has been determined. The continuous tuning of the thickness and refractive index of the thin films has also been achieved, which will open up new possibilities in the development of active optical waveguides.     

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.     

Epitaxial growth of ferroelectric PLZT [(Pb,La)(Zr,Ti)O3] thin films

Thin films of PLZT were epitaxially grown at around 700°C on sapphire and SrTiO₃ substrates: (111) PLZT  (0001) sapphire and (100) PLZT  (100) SrTiO₃. PLZT films on semiconductor substrates were also grown at around 620°C. The crystal quality of these PLZT films was investigated by X-ray diffraction, reflection electron diffraction, scanning electron microscopy (SEM), and Auger electron spectroscopy (AES). The epitaxy of PLZT films grown on different single crystal substrates is discussed. The refractive index of the film on the sapphire substrate was determined as 2.49₇ by an optical waveguide technique.     

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.     

Glass formation, physico-chemical properties, and structure of glasses based on Ga2S3-GeS2-Sb2S3 system

We prepared sulfide glasses based on a Ga₂S₃-GeS₂-Sb₂S₃ system and investigated the compositional dependences of their physico-chemical properties and structure. Additivities were observed for density and refractive index; i.e., these properties were presented by the summation of the contribution from each component. With the increase of Sb₂S₃ content, the density, refractive index, and thermal expansion coefficient increased while the glass transition and softening temperatures decreased, and the short-wavelength absorption edge shifted to the longer wavelength side. These variations are expected from the incorporation of a heavy element (Sb) into the glasses. On the other hand, the replacement of GeS₂ by Ga₂S₃ increased the density and refractive index, and shifted the short-wavelength absorption edge to the longer wavelength side. These variations were explained by the increase of the number densities of the cations with the replacement and the formation of metal-metal bonds. The latter was confirmed from the Raman spectra. We also investigated the effects of Ag₂S incorporation on the optical properties. The incorporation of Ag₂S increased the density and refractive index whereas the position of the short-wavelength absorption edge varied little. These results show the possibility of fabricating an optical waveguide by Ag incorporation into the glasses.     

Refractive index,band gap and oscillator parameters of amorphous GaSe thin films

GaSe thin films are obtained by evaporating GaSe crystals onto ultrasonically cleaned glass substrates kept at room temperature under a pressure of ∼10^–5 Torr. The X‐ray analysis revealed that these films are of amorphous nature. The reflectance and transmittance of the films are measured in the incident photon energy range of 1.1–3.0 eV. The absorption coefficient spectral analysis revealed the existence of long and wide band tails of the localized states in the low absorption region. The band tails width is calculated to be 0.42 eV. The analysis of the absorption coefficient in the high absorption region revealed an indirect forbidden band gap of 1.93 eV. The transmittance analysis in the incidence photon wavelength range of 500–1100 nm allowed the determination of refractive index as function of wave length. The refractive index–wavelength variation leads to the determination of dispersion and oscillator energies as 31.23 and 3.90 eV, respectively. The static refractive index and static dielectric constant were also calculated as a result of the later data and found to be 9.0 and 3.0, respectively. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polystyrene Derivative Films for Liquid Crystal Alignment

We studied the alignment of liquid crystal molecules on rubbed, thin polymer films of polystrene and its derivatives. Liquid crystal molecules were aligned perpendicular to the rubbing direction, although the polymer main chains of rubbed films were oriented along the rubbing direction. The alignment of the liquid crystal depended on the choice of side phenyl groups of polystyrene derivatives, and the pretilt angle varied with the type and the position of the substituents that were introduced into the side phenyl groups. Homogeneous alignment for ferroelectric liquid crystal was obtained by using poly(NO₂ styrene), poly(p-OH styrene) and poly(4-vinylpyridine) films, which have relatively high β-dispersion and glass transition temperatures.     

Optical and structural properties of Ge–Se bulk glasses and Ag–Ge–Se thin films

The optical and structural properties of Ge₂₀Se₈₀, Ge₂₅Se₇₅ and Ge₃₀Se₇₀ bulk glasses and Ag_x(Ge_0.20Se_0.80)_100−x thin films, where x = 0, 6, 11, 16, 20 and 23 at.% were studied. All samples were confirmed as amorphous according to XRD. The Raman spectra showed increase in 260 cm⁻¹ and 237 cm⁻¹ and decrease in 198 cm⁻¹ and 216 cm⁻¹ bands with different Se content in the bulk samples. The optical bandgap energy of bulk samples decreased (2.17–2.08 eV) and refractive index increased (2.389–2.426 at 1550 nm) with increasing Se content in bulk glasses. The Ge₂₀Se₈₀ thin films were prepared by vacuum thermal evaporation from Ge₃₀Se₇₀ bulk glasses. The Raman spectra of the films showed that peaks at 260 cm⁻¹ and 216 cm⁻¹ decreased their intensities with increasing Ag content in the thin films. The significant red shift of bandgap energy occurred upon different Ag content. The optically induced dissolution and diffusion resulted in graded refractive index profile along the film thickness caused by different Ag concentration. The refractive index increased from the substrate side to the top of thin films. The graded profile was getting more uniform with increasing content of silver in the thin film.     

Effect of substrate temperature on the optical constants of zincphthalocyanine thin films

The influence of the film thickness and substrate temperature on optical constants of the vacuum evaporated ZincPhthalocyanine (ZnPc) thin films have been reported in this paper. The direct and allowed optical band gap energy has been evaluated from the (αhυ)² vs. (hυ) plots. The optical constants such as extinction coefficient (k_f) and refractive index (n) have been evaluated from the transmittance values and the observed results strongly dependent on substrate temperature and film thickness. The low values of the refractive index have been observed for the films prepared at T_s=200°C. The change in crystallanity and phase transformation affect the optical constants and the lower values of the optical constants will leads to the good quality of the ZnPc thin films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Compositional dependence of optical parameters in Se–Bi–Te–Ag thin films

Compositional dependence of optical parameters in thermally evaporated amorphous Se_80.5Bi_1.5Te_18 ? yAg_y (for y = 0, 1.0, 1.5 and 2.0 at.%) quaternary thin films has been studied using well established Swanepoel method. The optical properties like, refractive index (n), extinction coefficient (k), absorption coefficient (α) and optical band gap (E_g) have been determined from the transmission spectra in the spectral range from 500 to 2500 nm. The optical band gap (E_g) has been estimated by using Tauc's extrapolation method and is found to increase with an increase in the Ag concentration. Present study shows that the refractive index, extinction coefficient and optical band gap increase with the increasing Ag content which is in agreement with the earlier studies. While the increase in the refractive index with Ag content over the entire spectral range can be attributed to the increased polarizability of larger Ag atomic radius (153 pm) compared to the Te atomic radius (135 pm), the increase in the optical band gap with increasing Ag concentration is correlated to an increase in the cohesive energy and decrease in the electronegativity of the films under study. The dielectric constant and optical conductivity (σ) of the thin films under study are also found to increase with the Ag concentration.     

Ion-implanted treatment of (Ba,Sr)TiO3 films for DRAM applications

The effects of ion implantation on the properties of spin-on sol–gel Ba_0.7Sr_0.3TiO₃ (BST) thin films were studied by implanted Ar⁺, N⁺, and F⁺ doses. The F⁺-implanted BST samples present leakage current density <10⁻⁶ A/cm² at 2.5 V and dielectric constant 450. The leakage current of F⁺-implanted BST samples was reduced about one order of magnitude as compared with that of samples with implanted Ar⁺, N⁺ or without implantation. The thickness shrinkage from 135 to 115 nm was observed in F⁺-implanted BST films (before annealing treatment) and a respective increase in the refractive index from 1.84 to 2.05 was measured. After annealing the implanted samples, the changes of thickness and refractive index depend on the concentration of implanted dose. Based on an infrared transmission study of the samples we suggest that the ion-implanted samples with smaller dose (5×10¹⁴ cm⁻²) have fewer −OH contaminants than the non-implanted or implanted samples with the larger doses (1×10¹⁵ cm⁻²). Based on the results presented, we conclude that suitable ion implantation densifies the spin-on sol–gel BST films and reduces the −OH contaminants in the films.     

Fabrication of inorganic–organic hybrid films for optical waveguide

Inorganic–organic hybrid guiding and buffer layers for optical waveguides were synthesized by the sol–gel process. An acid-catalyzed solution of 3-(trimethoxysilyl)propylmethacrylate and tetraethylorthosilicate was used as a precursor to produce thick films by spin-coating. Incorporation of a UV-sensitive functional group leads to the fabrication of the photo-patternable guiding layer. High-resolution patterned films with 8 μm linewidth were obtained using a conventional photo-lithography. Furthermore, the amount of phenyltrimethoxysilane added as a refractive index modifier varied in order to control the refractive index of the underlying buffer layer. The refractive index variations and structural changes of these inorganic–organic hybrid films as a function of the processing conditions were analyzed using the prism coupling technique and a Fourier transform infrared spectrometer. We have produced optically transparent films at above 500 nm with a propagation loss of 0.84 and 1.49 dB/cm at 1310 and 1550 nm, respectively.