Bare Glass Substrate Research Articles

Conformation and luminescence of isolated molecular semiconductor molecules.

In this article, we describe, for the first time, direct comparisons of the detailed structures of two small molecule organic semiconductors, oligo(phenylenvinylene) (OPV) molecules with chains of five and six phenyl rings (5R-OC(8)H(17) and 6R-OC(8)H(17)), respectively, and their luminescence properties on a single molecule level. Our data originate from a combination of two powerful diagnostic tools in physical chemistry: ion mobility and single molecule fluorescence spectroscopy. These techniques enable us to precisely determine the shapes of isolated molecules in the gas phase and to correlate these structures to the emission from single molecules supported on bare glass substrates. The principal structural uncertainty in OPVs is the (possible) presence and location of cis-vinylene linkages (cis-defects) in the oligomer. The results show that the structures observed in the gas phase are strongly correlated to the categories of molecules observed in the single molecule polarization anisotropy measurements with nearly identical distributions for the two OPV molecules studied. Each category is also characterized by the luminescence efficiency of the molecules in each class, providing a direct correlation between the luminescence efficiency and the shape of the molecule. This combination of techniques provides a level of information far beyond that obtained via any other analytical technique.

Effect of metal underlayers on low temperature silicon growth

Silicon films were deposited on bare glass, copper- and gold-coated glass substrates at 200 °C. X-ray diffraction (XRD) showed that the films deposited on substrates with gold underlayer were polycrystalline while those deposited on bare glass and copper-coated glass had no identifiable crystalline silicon XRD peak. Raman spectroscopy was used to confirm the film’s crystalline properties. The Raman spectra indicated that films deposited on gold-coated glass substrates were composed of predominantly crystalline silicon with small amounts of amorphous silicon. Atomic force microscopy (AFM) was used to study the topography and adatom diffusion on the surface. AFM micrographs showed that the polycrystalline silicon films had grain size up to 95 nm.

Linear Electro-Optics Effect in ZnO-F Film-Glass Interface

We have discovered large linear electro-optics (Pockels) effect in ZnO crystalline films doped with fluorine and deposited on bare glass. A complex approach including self-consistent band structure calculations together with a Car-Parinello molecular dynamics simulation of the film–glass interface structure was used. The non-centrosymmetric charge density distribution between the ZnO–F wurtzite-like crystalline films and the bare glass substrate causes the observed Pockels effect.

Multiwavelength imaging of defects in ultraviolet optical materials.

Laser-induced damage in bare glass substrates and thin films has long been widely acknowledged as a localized phenomenon associated with the presence of micrometer and submicrometer scale defects. The scanning of both optical absorption and scattering allows us to discriminate between absorbing and nonabsorbing defects and can give specific information about the origin of the defects. We investigate the spectral properties of defects in thin films and fused-silica surfaces. Absorbing and scattering defects are studied at different wavelengths in the ultraviolet, visible, and infrared ranges. Absorbing defects are shown to be highly wavelength dependent, whereas we have observed significant correlation between scattering defects.

Giant Pockels effect in ZnO-F films depositedon bare glasses

A giant linear electro-optics (Pockels) effect (up to17 pm V-1) (for wavelength about 435 nm) in ZnOcrystalline films doped with fluorine and deposited on bareglass has been found. For description of the observedphenomenon, a complex approach including self-consistent band structure calculations together with an appropriate moleculardynamics simulation of the interface structure was applied.Experimental ellipsometric and refractive index measurementsconfirm an efficiency of the mentioned approach for descriptionof the observed interface (between the film and glass)processes. The origin of the observed effect is caused by substantial non-centrosymmetric charge density distributionbetween the ZnO wurtzite-like crystalline films and the bareglass substrate, as well as by additional charge densitypolarization caused by fluorine atoms.

Anomalously Large Pockels Effect in ZnO-F Single Crystalline Films Deposited on Bare Glass

Large linear electrooptics (the Pockels effect) of up to 17 pm/V for the wavelength 435 nm has been observed in ZnO films doped by fluorine and deposited on bare glass. In order to describe the phenomenon observed, a complex approach, including self-consistent band structure calculations together with the appropriate molecular dynamics simulations of the interfaces, was applied. The origin of the effect observed is linked to substantial charge density non-centrosymmetry between the wurtzitelike crystalline films and the bare glass substrate, as well as to additional charge density polarisation caused by the fluorine.

Scattering measurements on optical disks and their relation to media noise

We have conducted measurements of scattered light from bare polycarbonate and glass substrates and from complete optical disks using a He-Ne laser beam in different polarization states and at different angles of incidence. The results are compared with the measured media noise obtained from the same disks on a dynamic tester. Both the scattered light and the media noise originate from the jaggedness and other imperfections of the groove structure, the roughness of the substrate's surface, and the inhomogeneities of the bulk of the substrate. Although some sources of media noise manifest themselves in the scattered light distribution, others cannot be easily detected by this type of measurement.

Comparison of titanium oxide films grown on bare glass and boiled glass in 50% H2SO4 by metal-organic chemical vapor deposition

Titanium oxide films were deposited on bare glass and boiled glass in 50% H2SO4 for 30 min at various substrate temperatures by metal-organic chemical vapor deposition. We investigated the effects of a substrate temperature between 300 and 550 °C on such properties as thermal stability, deposition rate, and chemical states of the films. The thickness of the films is independent of the substrate treatments. The deposition rate of the films is linearly decreased with increasing substrate temperature. Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy results indicate that the H2SO4 treated glass substrate is superior to the bare glass substrate in the suppression of out-diffusion of sodium and calcium through the TiO2 film till a substrate temperature of 500 °C. There exist only Ti3+ and Ti4+ oxidation states in the film regardless of a substrate temperature and substrate treatment. Ti3+ fractional composition are changed slightly between 0.11 and 0.17 and Ti4+ fractional composition are changed between 0.82 and 0.90 with varying substrate temperature.

Investigation of β-In 2S 3 growth on different transparent conductive oxides

Thin films of β-In 2S 3, obtained by physical vapor deposition process followed by a post-annealing, are studied on bare glass substrates and those coated with SnO 2, In 2O 3 and ZnO transparent conductive oxides (TCOs). These films have an optical band gap of about 2.8 eV, good covering efficiency, and n-type conductivity, making them good candidates for buffer layer in CuInSe 2 solar cells. The structural, optical and morphological properties of these bilayers have been studied with X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy depth profiling, and optical transmission. All results show that our method of synthesis allows us to grow β-In 2S 3 films on glass and TCO-coated glass coated substrates. Moreover, these films are exempt from pinholes, cracks, or other morphological defaults even for very small thickness.

Properties of photoconductive In 2Se 3 thin films, crystallized by post-deposition heat treatment in nitrogen atmosphere

Textured thin films of γ-In 2Se 3 were grown on glass substrates by sequential thermal evaporation of In and Se. The crystallization was achieved by annealing the as-deposited films in flowing nitrogen. It is shown by X-ray diffraction (XRD) measurements that single phase γ-In 2Se 3 films are obtained by annealing half an hour at 673 K. The films obtained on bare glass substrates and on SnO 2 coated glass substrates are textured along the (001) direction while those obtained on mica sheet and gold coated glass are not. The films are stoichiometric. Films deposited on glass substrates have been optically characterized. At room temperature, the measured band gap is 1.8 eV. In the case of thick films (1 μm), the surface of the films becomes rough, which can explain the higher photoconductivity of the films when the light beam is incident upon the substrate. Effectively, at the interface glass/film there is not any rugosity and the trap density is smaller than at the interface film surface/air. Photoluminescence spectra are obtained in the temperature range 78–200 K. Two peaks are observed. The width and the energy position of the main peak are temperature dependent. It is situated in the gap energy range and can be attributed to exciton recombination, while the other small one can be attributed to some intrinsic defects.

Crystallization of a‐Si:H on Glass for Active Layers in Thin Film Transistors: Effects of Glass Coating

One hundred nanometer thick a‐Si:H films deposited by plasma‐enhanced chemical vapor deposition from hydrogen diluted silane at temperatures in the range 150–320°C were used as precursor materials for solid‐phase crystallization (SPC) of polycrystalline silicon (poly‐Si) on which n‐channel thin film transistors (TFTs) were fabricated. Furnace annealing at 600°C was used in order to study the SPC kinetics as a function of deposition temperature and substrate coating. The substrates were either bare or silicon nitride coated Corning 7059 glass. The poly‐Si films were characterized by using ultraviolet reflectance spectrophotometry to determine the annealing time for crystallization and by using transmission electron microscopy for grain size measurement and nuclei density analysis. It was found that there is a strong relation between grain size and deposition temperature for films deposited on bare glass substrates. For films deposited on silicon nitride coated glass substrates this correlation is not as strong; however, upon full crystallization, a‐Si:H deposited on nitride coated glass yielded grains that were larger than those in a‐Si:H deposited on bare glass. The presence or absence of a barrier layer between an a‐Si precursor film and substrate glass is observed to greatly affect the SPC process. TFT parameter measurements, on the other hand, have shown that the ‐coating of glass has a significant impact on TFT performance: transistor leakage current is observed to be markedly reduced by coating. This is attributed to the increase in grain size and the decrease in the impurity content of active poly‐Si caused by ‐coating of glass. © 1999 The Electrochemical Society. All rights reserved.

Ellipsometry on sputter-deposited tin oxide films: optical constants versus stoichiometry, hydrogen content, and amount of electrochemically intercalated lithium

Tin oxide thin films were deposited by reactive radio-frequency magnetron sputtering onto In(2)O(3):Sn-coated and bare glass substrates. Optical constants in the 3002500-nm wavelength range were determined by a combination of variable-angle spectroscopic ellipsometry and spectrophotometric transmittance measurements. Surface roughness was modeled from optical measurements and compared with atomic-force microscopy. The two techniques gave consistent results. The fit between experimental optical data and model results could be significantly improved when it was assumed that the refractive index of the Sn oxide varied across the film thickness. Varying the oxygen partial pressure during deposition made it possible to obtain films whose complex refractive index changed at the transition from SnO to SnO(2). An addition of hydrogen gas during sputtering led to lower optical constants in the full spectral range in connection with a blueshift of the bandgap. Electrochemical intercalation of lithium ions into the Sn oxide films raised their refractive index and enhanced their refractive-index gradient.

Dynamic force microscopy by means of the phase-controlled oscillator method

Dynamic force microscopy, a technique also known as non-contact force microscopy, has proved to be a powerful tool for atomic resolution imaging. A number of schemes have been developed, but recently the oscillator method has become the preferred operating mode. Here, the force sensor acts as resonator in an active feedback circuit. A practical implementation of the method is described and the underlying key concepts are discussed. It is shown that a tracking oscillator excitation scheme is superior to the more standard direct feedback method for cases in which the force sensor exhibits only a weak resonance enhancement. Furthermore, the simultaneous measurement of dissipative interaction channels is an important extension of dynamic force microscopy. It allows one to differentiate between sample materials via their plasto-mechanical response. As an example, a Cr test grating has been imaged in the constant force gradient mode. The dissipation measured on Cr-covered areas is significantly lower than that on the bare quartz glass substrate, which enables one to distinguish between the two materials with a lateral resolution comparable to that of the topographic image.

Optical surface analysis of graded index coatings on glass

A method for the determination of the refractive index close to an interface, valid for inhomogeneous films, is presented as an extension of the Abelès—Hacskaylo technique used for homogeneous films. Consistent refractive index values, with precision in the third decimal place, are determined for Ag + (1.550 ± 0.001) and K + (1.522 ± 0.002) ion-exchange films on glass, as well as for bare glass substrates (1.509 ± 0.002), in the neighborhood of their interface with air. The validity of the method is discussed in simple fundamental terms, which, along with the experimental evidences, indicates applicability to any graded index film, provided an index discontinuity is present at one of its extremes.

Estimation of Stress in Polycrystalline CuInSe2 Films Deposited on Mo-Coated Glass Substrates

Stress and strain in polycrystalline thin films of CuInSe 2 deposited on soda-lime glass and Mo-coated glass substrates were determined from the optical reflectance spectra by utilizing the broadening of the optical absorption band tail. The contributions of both intrinsic (due to grain boundary and lattice vibrations) and extrinsic stresses (due to thermal mismatch of film and substrate) were considered. It was observed that the films deposited on Mo-coated glass substrates had lower grain size and higher stress (3 x 10 7 Pa) compared to those of the bare glass substrates (1.1 x 10 7 Pa). This process of estimation of mechanical properties of thin films from optical measurements on both absorbing (Mo/glass) and non-absorbing (glass) substrates appears to be very attractive due to its non-destructive nature. The defect state density (Q t ) at the grain boundary region along with the internal built-in average electric field (F av ) were determined with the variation of the Cu/In ratio in the films, deposited on glass and Mo-coated glass substrates. It was observed that both Q t and F av were higher for Cu/In < 1.0 and decreased as the stoichiometric composition was approached.

Oriented Tin-Doped Indium Oxide Films on Preferred Oriented Polycrystalline ZnO Films

<111>-oriented tin-doped indium oxide (ITO) films were deposited by rf magnetron sputtering on ZnO-coated glass substrates (ZnO/glass). The ZnO underlayers were also deposited by rf magnetron sputtering and have been known to exhibit <001> preferred orientation in a wide range of deposition conditions. The X-ray diffraction profiles of the ITO films deposited on the ZnO/glass showed predominant <111> orientation without any differently oriented crystallites, whereas the ITO films deposited on bare glass substrates (ITO/glass) under the same deposition conditions showed <100>-preferred orientation with small areas of several other orientations. A mechanism of the heteroepitaxial growth of In2O3(111)|| ZnO(001) was explained by comparing the atomic configurations of oxygen between the oxygen mostly dense-packed planes of In2O3 and ZnO parallel to In2O3(111) and ZnO(001) planes, respectively. Sn concentrations and lattice constants of the <111>-oriented films (ITO/ZnO/glass) were found to be greater than those of <100> preferred oriented films (ITO/glass) in spite of the fact that the target and deposition conditions were the same, which could be associated with the electrical properties of the films.

The Effect of Source Microstructure on the Close-Space Sublimation of CdTe Thin Films for Solar Cell Applications

ABSTRACTThe microstructure of CdTe sources grown on bare 7059 and SnO2-coated 7059 glass substrates used in the close-space sublimation (CSS) growth of CdTe films, is affected by nucleation conditions during their fabrication. For CdTe sources grown on bare glass substrates, denser source microstructures with smaller grains are promoted by low-temperature nucleation conditions. Growth rates of CdTe films deposited using these source plates are inversely proportional to the packing density of the grains. CdTe sources grown on glass undergo significant texture changes during their use in subsequent CSS deposition. CdTe sources grown on SnO2-coated glass substrates exhibit dense structures both with and without low-temperature nucleation and increased grain size with low-temperature nucleation. These source plates show less texture change associated with thermal annealing than their bare-glass counterparts, however, they are much more susceptible to CdO formation during subsequent CSS deposition processes in which oxygen is present. Source oxidation results in a decrease of the (111)/(220) x-ray diffraction intensity. Analysis of the (111)/(220) intensity ratio with and without source oxidation suggests the preferential formation of CdO on the (111) planes. In general, source oxidation appears to be a inversely proportional to the grain size of the source material.

Influences of Indium Tin Oxide Layer on the Properties of RF Magnetron-Sputtered (BaSr)TiO3 Thin Films on Indium Tin Oxide-Coated Glass Substrate

Nearly stoichiometric ((Ba+Sr)/Ti=1.08-1.09) and optically transparent (BaSr)TiO3 thin films were deposited on an indium tin oxide (ITO)-coated glass substrate by means of rf magnetron sputtering for their application to the insulating layer of an electroluminescent flat panel display. The influence of the ITO layer on the properties of (BaSr)TiO3 thin films deposited on the ITO-coated substrate was investigated. The ITO layer did not affect the crystallographic orientation of (BaSr)TiO3 thin film, but enhanced the grain growth. Another effect of the ITO layer on (BaSr)TiO3 thin films was the interdiffusion phenomenon, which was studied by means of secondary ion mass spectrometry (SIMS). As the substrate temperature increased, interdiffusion intensified at the interface not only between the grown film and ITO layer but also between the ITO layer and base glass substrate. The refractive index (nf) of (BaSr)TiO3 thin film deposited on a bare glass substrate was 2.138-2.286, as a function of substrate temperature.

Surface induced liquid-crystal alignment studied by optical second-harmonic generation

The orientational order induced in a liquid crystal (LC) monolayer of adsorbed 4-n-octyl-4′-cyanobiphenyl molecules on rubbed substrates is studied by measuring the second-harmonic response. By systematically varying the rubbing conditions and measuring the induced LC bulk and monolayer alignment, we can conclude that the homogeneity of the LC bulk alignment and the surface in-plane order parameter of the LC monolayer are closely related. The polar and azimuthal ordering of the LC monolayer, however, are found to be decoupled. By rubbing polyimide films twice and studying other rubbed surfaces, we show that two mechanisms are responsible for the LC alignment, depending on the kind of substrate that is used. For rubbed bare glass substrates long-range elastic interactions, which do not affect the monolayer alignment, are dominant. In the case of rubbed polyimide films molecular short-range interactions are responsible for the alignment of both the LC bulk and the LC monolayer.

Ionized Cluster Beam Deposition of Polycrystalline Thin Films of CuInSe2

Thin films of CuInSe2 were prepared by three-source ionized cluster beam (ICB) deposition on bare and Mo-coated glass substrates. Of the three elements composing CuInSe2, only In was ionized and accelerated. Single-phase chalcopyrite films were obtained in films prepared at acceleration voltages higher than 1 kV. The Cu/In ratio, as well as the electrical resistivity, was found to be controlled by changing the acceleration voltage. X-ray diffraction patterns, optical micrographs and scanning electron micrographs revealed that the crystallinity and the homogeneity of CuInSe2 grains were improved by application of acceleration voltages. The improvement was more obvious in the films grown on Mo-coated substrates.