Transmittance Of Thin Films Research Articles

Hydrogen-induced changes of mechanical stress and optical transmission in thin Pd films

Loading of palladium with hydrogen not only leads to pronounced changes of its optical and electrical properties, but is also accompanied by significant density changes leading to stress formation. Therefore, the loading has been investigated by in-situ mechanical stress and optical transmittance measurements. The exposure of palladium films to hydrogen results in a significant transmittance increase and mechanical stresses of several thousand MPa upon loading with hydrogen. The phase transition from the α-phase to the β-phase was observed in both stress and transmittance data. The influence of a thin oxide layer, which is formed in air and can be removed in a hydrogen gas, was observed. Hence, the stress and transmittance data are governed by a superposition of irreversible oxide removal and reversible loading with hydrogen.

Thin-film transmission IR spectroscopy as an in situ probe of the gas–solid interface in photocatalytic processes

A thin-film transmission infrared spectroscopy system was designed as an in situ probe for heterogeneous interfacial photocatalytic reactions. A photocatalyst, TiO 2, supported on a silicon wafer substrate was located in an airtight cell containing BaF 2 windows. This supported photocatalyst was simultaneously illuminated with both UV light and the infrared beam. The performance of the cell was tested using the photocatalytic decomposition of ethanol. The quality of the spectra for a porous TiO 2 film of approximately 0.5 microns of thickness proved to be good for detecting bands of reactant and product species (ethanol, ethoxide, acetaldehyde, and acetate). This transmission cell was coupled to a gas phase infrared cell for the simultaneous analysis of reactants and products of this photodegradation of ethanol which appear in the gas phase. The affinity of the surface of TiO 2 for water was investigated under air and argon environments in both the presence and the absence of UV illumination. In an air environment, UV illumination enhanced the adsorption of water on TiO 2. A similar enhanced adsorption occurred in the argon environment without UV illumination. During UV illumination, bands of peroxide (O 2 2−) species could be detected on the surface of TiO 2 under the conditions of a dry air flow. Both peroxide (O 2 2−) as well as superoxide (O 2 −) species could be detected after several hours in post-irradiated systems.

Novel materials based on organic–tungsten oxide hybrid systems II: electronic properties of the W–O framework

Abstract In this paper we report experimental and theoretical results concerning the band structure of tungsten trioxide and how this system relates to a new class of layered organic–inorganic hybrid materials based on a tungsten oxide framework. UV–visible spectroscopy was performed on various tungsten trioxide samples. Diffuse reflectance on powder samples indicates a single absorption edge centred at 2.8 eV, while transmission and reflectance of thin films show a strong feature at 4.0 eV. This is supported by ab initio calculations, in which a strong peak is seen at 4.0 eV in the density of states. For the hybrid system, 1, n -diaminoalkane tungsten oxide, a change in the calculated band structure is seen compared with the tungsten oxide system; a peak appears just above 3.0 eV in the density of states with a low intensity `tail' below this. UV–visible spectra of powder reflectance of hybrid samples indicate a dominant absorption edge centred at 4.0 eV.

In vitro bioactivity of laser ablation pseudowollastonite coating

Pseudowollastonite (psW) coatings on titanium alloys substrates were prepared by laser ablation and immersed in simulated body fluid (SBF) for different periods in order to investigate the nucleation and growth of hydroxyapatite (HA)-like formation on their surface. The structure of the coatings before soaking was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The interfacial reactions product was examined by thin-film XRD, SEM and transmission electron microscopy at low and high resolution level, both fitted with energy-dispersive X-ray spectroscopy. Additional changes in ionic concentration, using inductively couple plasma atomic emission spectroscopy, were determined as well as pH right at the psW-coatings/SBF interface using an ion-sensitive field effect transistor. The solution composition changes, increasing the Ca 2+ and Si 4+ concentration and pH as a function of the soaking time while HPO 4 2− decreased. The results obtained showed that the coating surfaces were covered by HA-like, which indicated that the psW-coating possesses good bioactivity and also suggested that the mechanism of HA-like layer formation in SBF was similar to that showed in in vitro test by other silica-based materials.

Optical properties ofMgH2measuredin situby ellipsometry and spectrophotometry

The dielectric properties of alpha-MgH2 are investigated in the photon energy range between 1 and 6.5 eV. For this purpose, a novel sample configuration and experimental setup are developed that allow both optical transmission and ellipsometric measurements of a transparent thin film in equilibrium with hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about 80% over the whole visible spectrum. The dielectric function found in this work confirms very recent band structure calculations using the GW approximation by Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a cap layer we report also the optical properties of PdHx thin films.

Controlling the transmission at the surface plasmon resonance of nanocomposite films using photonic structures

The transmission of nanocomposite thin films formed by Cu nanocrystals embedded in an amorphous aluminum oxide (Al2O3) matrix has been enhanced in the vicinity of the surface plasmon resonance wavelength, by the design of one-dimensional photonic structures. The nanocrystals are distributed in layers, whose separation and periodicity are used to control the optical response of the films. It is found that at the SPR a transmission enhancement up to 36% can be achieved with respect to a film with an homogeneous distribution of the nanocrystals. These photonic structures have been successfully produced by pulsed laser deposition.

Far-infrared thermal spectroscopy of low-Tc and high-Tc superconductor films

Temperature dependence of far-infrared transmission of NbN thin films deposited on MgO and Si substrates was measured at several frequencies from 0.4 to 4.3 THz. Activated exponential increase of relative penetration depth at low temperatures and a peak in transmission near Tc were observed for frequencies below the optical gap. On the other hand, the transmission measured at frequencies above the gap exhibits only flat, almost linear temperature dependence. This behaviour is consistent with the BCS theory of superconductivity. Similar measurements were performed also on YBa2Cu3O7−δ thin films deposited on MgO and sapphire substrates. Low-temperature variation of transmission indicates the d-wave symmetry. The peak below Tc predicted by the BCS theory is not observed. Flat temperature dependence of transmission at higher frequencies shows that the photon energy was sufficient for excitation over the optical gap. The s-wave BCS theory is adequate for NbN films but not for the YBa2Cu3O7−δ materials. Using the theoretical BCS model we show that the transmission peak is not correlated to the coherence peak in real conductivity at given frequency and other parameters relevant to experiment.

Quantum confinement in CdSe-nanocrystallites synthesized by ion implantation

Nanocrystalline semiconductors offer a wide variety of possible applications in optical and optoelectronic devices. Embedding nanocrystals in compatible and stable host materials is of fundamental technical and scientific interest. In this work, buried nanocrystals of the direct band gap II–VI compound semiconductor CdSe were synthesized by sequential high dose ion beam implantation into thin thermally grown silicon dioxide layers and subsequent rapid thermal processing. Bulk CdSe has a bandgap energy of 1.75 eV that can be shifted to larger values by reducing the crystal size to dimensions smaller than the Bohr radius of the exciton. The size of the CdSe precipitates was controlled by the implantation and annealing parameters. The photoluminescence (PL) emission was exited by an Ar ion laser and measured in a temperature range between 80 and 295 K. The energy shift of the PL emission of the embedded CdSe nanocrystals is in quantitative agreement with the shift due to quantum confinement calculated from the mean size of the nanocrystals determined from thin film X-ray diffraction spectra (XRD) and transmission electron microscopy (TEM) images.

Light extinction in bulk and thin film opal photonic crystals

Transmission, scattering and reflectance of bulk opals and thin opal films have been studied using a micro-optical set-up. Spectra of transmitted and scattered light are similar and complementary to reflectance spectrum. Long- and short-range attenuation mechanisms have been identified and related to the scattering on lattice defects.

Magneto-optic effects in spin-injection devices

The magneto-optic properties of semi-transparent ferromagnetic films are presented in the context of ferromagnet/GaAs spin-injection devices. We have measured the polarization-dependent photoresponse and magneto-optic properties of Co/n-GaAs, Co/p-GaAs and NiFe/n-GaAs Schottky diodes and NiFe/SiO2 and Co/SiO2 structures as a function of ferromagnetic film thickness, ranging from 8 to 100 nm. Our results show that magneto-optic effects intrinsic to the ferromagnetic films (2%–3%) are sufficient to account for the majority of the polarization-dependent photoresponse of the ferromagnet/GaAs systems studied. These effects are well described by a simple thin-film transmission model, which gives an upper limit of 0.4% for spin-transmission effects.

The Nitric Acid Hydrates: Ab Initio Molecular Study, and RAIR Spectra of the Solids

The molecular complexes formed by nitric acid with one, two, and three water molecules have been investigated by high level ab initio calculations. The B3LYP/aug-cc-pVTZ method and basis set have been used to derive equilibrium geometries and binding energies and to predict the infrared spectra of these complexes. It has been found that the complexes become stable through the formation of several hydrogen bonds. The main one is established between the acid, which acts as a donor, and the first water molecule, but further bonds are created between successive water molecules, with a weaker bond making a closed structure between the last water unit and the acid. Films of nitric acid mono-, di-, and trihydrates (NAM, NAD, and NAT) have been prepared by deposition on a cold surface and annealing to induce crystallization. RAIR spectra have been taken of these films. The spectra are compared to previous investigations, and the assignments of the spectra and the structure of the crystals are discussed. A global good agreement is obtained with previous transmission and RAIR spectra of thin films and extinction spectra of aerosols.

Extreme-ultraviolet calibration of thin-film Zr filters for the cosmic hot interstellar plasma spectrometer.

The design and calibration of thin-film Zr transmission filters for the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) spaceborne astronomical telescope is presented. The transmission of a 1,000-A-thick Zr filter is measured for wavelengths from 45 to 1,304 A as well as its variability with respect to expected space-flight enviromental extremes of temperature, vibration, and atomic O bombardment. For the CHIPS spectral band of 90-260 A, the transmission of the Zr fiter is deemed useful between 90 and 200 A and is stable with respect to expected temperature and vibrational changes. The maximum atomic O bombardment decreases the filter transmission between 90 and 130 A by approximately 20% and does not appreciably affect the rest of the CHIPS bandpass. These results make Zr an acceptable filter candidate for CHIPS.

Microwave frequency tuning and harmonic generation in ferroelectric thin film transmission lines

We evaluate dielectric tuning on nanosecond time scales in ferroelectric Ba0.3Sr0.7TiO3 thin films by measuring nonlinear harmonic generation at a fundamental frequency of 3 GHz. We compare the form of the distributed nonlinear capacitance per unit length C(Vrf) extracted from a simple model of harmonic generation in coplanar waveguide transmission line structures with the nonlinear capacitance C(Vdc) measured using a dc bias voltage, and obtain excellent agreement for temperatures in the range 235–295 K. This demonstrated agreement implies that full dielectric tuning can be expected in these ferroelectric thin films on nanosecond time scales, and also demonstrates that detrimental high-frequency nonlinear effects in device structures can be accurately predicted based on dc biased measurements.

Infrared dispersion of liquid tripropylamine

The spectra of the real and imaginary components of the complex refractive index were determined from thin-film transmission studies of liquid tri- n-propylamine (TPA) using a new method, which takes into account the dispersion of the refractive index in the visible range and integration over the entire NIR, IR and FIR absorption regions. From these data, the spectra of both components of the complex electric permittivity and complex polarizability of liquid TPA were determined in broad optical range (25,000–150 cm −1). Related high-frequency dielectric properties, especially the molar vibrational polarization of the liquid related to various spectral ranges has been determined and discussed. It has been found to be extremely small for overtones. The main contribution stems from deformation modes of the molecule.

Infrared dispersion of liquid triethylamine

The spectra of the real and imaginary components of the complex refractive index were determined from thin film transmission studies of liquid triethylamine (TEA) using a new method, which takes into account the dispersion of the refractive index in the visible range and integration over the entire NIR, IR and FIR absorption range. From these data the spectra of both components of the complex electric permittivity and complex polarizability of liquid TEA were determined in a broad optical range (25 000–150 cm −1). Related high-frequency dielectric properties, especially the molar vibrational polarization of the liquid related to various spectral ranges has been determined and discussed. It has been found to be extremely small for overtone bands. The main contribution stems from the region of deformation modes of the molecule.

Calculation of thermodynamic, electronic, and optical properties of monoclinic Mg2NiH4

Ab initio total-energy density functional theory is used to investigate the low temperature (LT) monoclinic form of Mg2NiH4. The calculated minimum energy geometry of LT Mg2NiH4 is close to that determined from neutron diffraction data, and the NiH4 complex is close to a regular tetrahedron. The enthalpies of the phase change to high temperature (HT) pseudo-cubic Mg2NiH4 and of hydrogen absorption by Mg2Ni are calculated and compared with experimental values. LT Mg2NiH4 is found to be a semiconductor with an indirect band gap of 1.4 eV. The optical dielectric function of LT Mg2NiH4 differs somewhat from that of the HT phase. A calculated thin film transmittance spectrum is consistent with an experimental spectrum.

Optical transmission of magnesium hydride thin film with characteristic nanostructure

Optical and structural properties of rare-earth free and pure Mg thin film coated with Pd have been investigated. Optical examination indicates that the fully hydrogenated films are in a color-neutral transparent state. With increasing temperature up to 453 K in air, nontransparent scratch-like parts that correspond to dehydrogenated Mg precipitate in macroscopic scale, and their number gradually increases and grows sharply along specific orientations. The structural characterization indicates that the Mg layer is composed of epitaxial columnar grains whose widths are less than 100 nm with a c-axis preferred orientation for the Mg layer. The columnar grains are restructured to grains with 50–100 nm diameter during hydrogenation–dehydrogenation (optical switching) cycles.

Nanosecond pulsed field magnetization reversal in thin-filmNiFe studied by Kerr effect magnetometry

Magnetization reversal has been studied in a 5 nm thickNi80Fe20 film under the action of a pulsed magnetic field,for pulse durations between 2-102 ns. Fast pulses were applied tothe sample from a thin-film microstrip transmission line andmagnetization changes were measured using a continuous wave lasermagneto-optic Kerr effect magnetometer. The switching field was foundto increase as the pulse duration decreased, in qualitative agreementwith simple models. More unusually, the switching field was alsofound to increase as a function of a quasi-static bias field inexcess of the value of that bias. This effect is stronger for theshorter pulses. Evidence is presented which suggests that this is dueto rapid relaxation of the magnetization after the termination of thepulsed field.

Light transmission and haze of polyethylene blown thin films

AbstractThe surface and bulk morphologies of polyethylene blown films are obtained using non‐contact Atomic Force Microscopy (AFM). Based on these experimental observations, a model using the Mie Scattering theory is proposed to describe the forward transmission and scattering of a plane wave through the film. The light transmission properties are computed from the proposed model and the results are validated by experimental measurements.

Preparation of tellurite thin films from tellurium isopropoxide precursor by sol–gel processing

An investigation into the use of sol–gel processing for the fabrication of tellurite (TeO 2) thin films from tellurium isopropoxide (Te(OPr i ) 4) is described. Commercial tellurium isopropoxide was characterised structurally and its hydrolysis was studied. The work also involved the identification of suitable strategies to control the hydrolysis reaction of tellurium isopropoxide to allow thin films to be successfully produced and characterised. The transmittance of thin films was investigated, together with their phase composition. The success in producing these thin films by sol–gel processing provides new opportunities for making tellurite thin film devices for practical applications, such as optical data storage and non-linear optical switching.