Amorphous Silica Substrates Research Articles

Sol-gel processed barium titanate waveguides

Monolayer monomode and multilayer multimode BaTiO3 waveguides have been prepared on amorphous silica substrates by using the dip-coating technique and the sol-gel process. After heat treatment, these waveguides were hard and of good optical quality (losses as low as 2.6 dB/cm were measured) but, their structure was found to depend strongly on the number of layers. Monolayer waveguides were totally amorphous even when heated at 1000°C, while multilayer ones exhibited the tetragonal BaTiO3 structure at an annealing temperature of 600°C.

AES characterization and depth profiles measurements of AIN thin films on SiO2 substrates

Depth profiles measurements of the elements Al, Si, N and O were determined using Auger electron spectrometry during ion etching of an AIN C.V.D. thin film deposited on an amorphous silica substrate. The Auger spectra collected at various time intervals showed the presence of Al-O, Si-O and Si-N chemical bondings in the interphase AlN/SiO 2 . This result indicates that the growth of an AlN thin film on a silica substrate begins by a strong oxidation of aluminium which involves a partial nitridation of silicon

In-Plane Magnetic and Structural Anisotropies in NI and FE Films Produced by Ion-Assisted Deposition

ABSTRACTWe report the results of our microstructural investigations into the origin of in-plane uniaxial magnetic anisotropies induced in Ni and Fe thin films by low energy ion beam assisted deposition. 1000 Å films were prepared by ion beam sputtering onto amorphous silica substrates under simultaneous bombardment by 100 eV Xe+ ions under an oblique angle of incidence. The induced anisotropy is studied as a function of ion-to-adsorbate atom arrival ratio, R, from values of 0 to 0.35. The maximum anisotropy field is 150 Oe for Ni and 80 Oe for Fe, but their hard axes are oriented orthogonal to each other. Asymmetric x-ray diffraction is employed to study both in-plane and out-of-plane lattice spacings and crystallographic orientation. In agreement with previous work, we find evidence of a anisotropic in-plane strain of magnitude 0.2-0.5%. In all films, the direction perpendicular to the ion bombardment is compressed relative to parallel. The uniaxial magnetic anisotropy is correlated with this in-plane anisotropic strain using a simple magnetoelastic model.

Biaxially-Textured YBa2Cu3O7–x Thin Film Growth on Polycrystalline and Amorphous Substrates Using Ion Assisted Laser Deposition of Yttria-Stabilized Zirconia Intermediate Layers

ABSTRACTThe growth of (001)-textured, biaxially-aligned yttria-stabilized zirconia (YSZ) intermediate layers on amorphous or randomly-oriented polycrystalline substrates is desirable for subsequent YBa2Cu3O7–x (YBCO) c-axis thin film growth. Laser deposition of YSZ on polycrystalline metal substrates (Haynes Alloy #230) in 1.0 millitorr oxygen at 70°C produces partial (001) texture but no alignment of in-plane axes. Highly-textured biaxially-aligned layers are obtained by using an ion beam to assist growth. Similar layers are obtained on amorphous silica and polycrystalline alumina substrates. The effects of ion-beam parameters including incident angle, source gas, and beam voltage and current are presented. Highly c-axis-oriented, biaxiallyaligned YBCO thin films have been deposited in situ on these YSZ layers, with Tc(R=0) ∼ 92K and Jc(77K) = 6 × 105 A/cm2. Angular magnetoresistance data shows a dip in resistance with magnetic field normal to the film, in contrast to films grown epitaxially on single crystal substrates, which have maximum resistance with field normal.

LiF films: absorption and luminescence of colour centres

LiF films 1 μm thick have been produced by thermal evaporation on amorphous silica substrates. X-ray diffraction has shown the existence of a polycrystalline structure. The films were subjected at room temperature to electron beam irradiation of energy 3 keV and current 120 μA on anea of about 0.5 cm 2. This irradiation produced F 2 and F 3 + centres stable at room temperature that were observed by light absorption measurements. Although the concentration of the centres was much higher than that obtained usually in bulk crystals, luminescence was also observed.

Preparation and characterization of thin films of TiO 2PbO and TiO 2Bi 2O 3 compositions

Single and multilayer thin films of PbTiO 3, PbTi 4O 9 and TiO 2Bi 2O 3 compositions have been prepared on glass and amorphous silica substrates by using the dip-coating technique. After drying and densification, these films have a high optical quality. They have been characterized by the optical transmission technique and XPS. For certain values of their thickness they present almost flat transmission characteristics in the visible range and can be used as achromatic beam splitter or neutral-colored solar-energy-reflecting windows. Their use as a passive optical waveguide with a propagation of up to 4 modes at γ = 632.8 nm is also reported.

Formation by ion mixing of almn thin films in amorphous and quasi-crystalline phases: Comparison of their electronic structure as determined by optical measurements

Alternate layers of aluminium and manganese were deposited by sputtering on amorphous silica substrates. The ratio of aluminium to manganese layer thicknesses was adjusted in order to vary the total manganese concentration. The layers were ion beam mixed with a 500 keV Xe + beam to a fluence of 10 16 Xe cm −2. The mixing efficiency was checked using Rutherford backscattering spectrometry analysis. Amorphous or quasi-crystalline phases are obtained, depending on the substrate temperature during the mixing. The atomic structure was controlled by transmission electron microscopy. For manganese concentrations from 15% to 20%, ion beam mixing at 150 °C results in the icosahedral phase; mixing at 77 K provides samples in the amorphous state. It is emphasized that all samples in this concentration range are single phase. The optical conductivity was determined from reflectance and/or ellipsometric measurements in the energy range from 0.5 to 6 eV. All spectra are strongly dominated by the manganese d states. No drastic differences are observed between the amorphous and the icosahedral states for manganese concentrations between 15% and 20%.

Structure sensitivity: Hydrogenolysis of n-butane and hydrogenation of ethylene on nickel clusters condensed onto amorphous silica

The crystallite size dependence of n-butane hydrogenolysis and ethylene hydrogenation has been studied over silica supported nickel catalysts. The samples were prepared by vapour condensation of nickel atoms onto a flat amorphous silica substrate. The support was grown by thermal oxidation of the silicon (111) surface. The growth mechanism and the crystalline and electronic structures of the nickel particles were followed by in-situ RHEED and AES techniques, while the absolute coverage, ranging from 10 13 to 10 16 atoms cm −2, and the size distribution of the metal particles, have been measured independently by RBS and TEM techniques respectively. The dependence of turnover frequency on crystallite size has been studied for n-butane hydrogenolysis and ethylene hydrogenation. Maximum turnover frequency for n-butane hydrogenolysis and ethylene hydrogenation is observed for nickel crystallite sizes in the range of 15–20 and 5–7 Å respectively. It has been found that the hydrogenolysis of n-butane requires a minimum number of atoms.

Mineralogy and Diagenesis of Miocene and Pleistocene Sediments, Northeastern Gulf of Mexico: ABSTRACT

Cored Miocene and Pleistocene sediments from the northeastern Gulf of Mexico (ranging in depth from 1,400 to 2,000 m) consist of interbedded sands, silts, and muds with varying degrees of consolidation. Samples selected from these sediments were studied for their mineralogy and diagenesis. The Miocene sediments represent various subenvironments of the ancestral Mississippi River delta complex; Pleistocene sediments are marine shelf deposits. Sands from both Miocene and Pleistocene cores are fine to very fine-grained feldspathic litharenites with abundant (approx. = 25%) matrix fines and minor (<7%) carbonate clasts and shell fragments. Carbonate diagenesis is a continuing process in these sediments. Clayey sands contain disseminated siderite crystallites formed during organic matter fermentation. In clean sands, scattered thin (<15 cm) bands of poikilotopic carbonate-cemented sand are present in the middle of thicker unconsolidated intervals. Cemented bands are thicker in the Miocene section, having grown during burial through dissolution of shell fragments and reprecipitation at the margin of cemented zones. Diagenetic events evident in the Miocene core illustrate processes that could occur in the Pleistocene sediments with continued burial. These are: (1) dolomitization of some calcite cements, (2) precipitation of Fe-carbonate as crystallites, rims on dolomite cements, and overgrowths on siderite crystallites, andmore » (3) zeolite formation on amorphous silica substrates. Amorphous silica is associated with limited dissolution of feldspars or lithic fragments.« less

Measurement of preferred orientations in the silver-silica interface

The crystal orientation of thin silver films evaporated onto amorphous silica substrates was studied by X-ray pole figure measurements before and after annealing. Orientation relationships resulting in interfaces of low energy were measured by observing the rotation of single-crystal silver spheres on silica. The orientation distribution of these spheres revealed two cusps in the interfacial energy vs. misorientation curve. The cusps correspond to orientations for which close-packed planes in silver lie parallel to the substrate surface.

Control of thin film orientation by glancing angle ion bombardment during growth

Glancing angle ion bombardment during thin film deposition is shown to have a pronounced alignment effect on crystallographic orientation. Restricted fiber texture is achieved in Nb films deposited at room temperature onto amorphous silica substrates by Ar ion beam sputtering, with simultaneous bombardment by 200 eV Ar+ ions at 20° from glancing angle. The alignment direction corresponds to a channeling direction for the incident ions between (110) planes, for which a low sputtering yield is expected. The degree of alignment is measured as a function of ion/atom arrival rate ratio up to 1.3 Ar+ ions per Nb film atom, and is shown to increase monotonically with the fraction resputtered. Also, the fiber axis tilts slightly towards the incident ion beam direction, favoring the channeling direction.

Alignment of thin films by glancing angle ion bombardment during deposition

Glancing angle ion bombardment during thin-film deposition is shown to have a pronounced alignment effect on crystallographic orientation. Restricted fiber texture is achieved in Nb films deposited at room temperature onto amorphous silica substrates by Ar ion beam sputtering, with simultaneous bombardment by 200 eV Ar+ ions at 20° from glancing angle. The alignment direction corresponds to a channeling direction for the incident ions between (110) planes, for which a low sputtering yield is expected. The degree of alignment is measured as a function of ion/atom arrival rate ratio up to 1.3 Ar+ ions per Nb film atom, and is shown to increase monotonically with the fraction resputtered.

Microstructure of Niobium Films Oriented By Non-Normal Incidence Ion Bombardment During Growth

ABSTRACTWe demonstrate that non-normal incidence ion bombardment applied during thin film growth has a pronounced alignment effect on crystallographic orientation. Restricted fiber texture is achieved in Nb films deposited at room temperature onto amorphous silica substrates with simultaneous 200 eV Ar+ ion bombardment at 20 degrees from glancing angle. Xray pole figure measurements and transmission electron diffraction show that the alignment direction is a channeling direction for the incident ions between (110) planes. The degree of alignment increases linearly with the fraction resputtered by the ion beam. Recommendations are given for optimizing this ion beam orientation effect.

Growth Characteristics of Rutile Film by Chemical Vapor Deposition

Thin film rutile has been grown by the chemical vapor deposition reaction of and O2 on silicon and a variety of oxide substrates over a range of temperatures (673°–1320°K) and reactant partial pressures . At high oxygen partial pressures between 990° to 1100°K, the films have been found to contain the rutile modification of almost exclusively. Polycrystalline deposits on silicon, fused quartz, and amorphous silica (thermally grown or chemically vapor deposited) substrates displayed some preferred growth orientation (fiber texture). Epitaxial films were obtained on (001)‐, (110)‐ and (111)‐rutile, , and (0001)‐sapphire substrates at elevated temperatures.