Studies on evaporated titanium oxide thin films for oxygen gas detection

Present work deals with the preparation of TiO₂ thin films of different thicknesses by PVD technique using an electron beam and to characterize the films for oxygen gas detection. The films were characterized using optical transmission measurements, XRD and atomic force microscopy. From the spectral data, the extinction, absorption coefficient and refractive index of the films are evaluated and reported. The optical band gap energy varies between 3 and 3.68 eV. The XRD pattern confirms the formation of polycrystalline anatase structure of Titanium with preferred orientation of (110) plane. The AFM images indicate the presence of coarse and fine grains with uniform as well as smooth surfaces over the entire range of the analyzed surface. Response characteristics of TiO₂ thin films for oxygen gas detection are studied, which indicate a low response time of 120 seconds and high sensitivity of 16 at the operating temperature 450 °C. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Fluorescence detection of exafs: Sensitivity enhancement for dilute species and thin films

The fluorescence intensity is used to measure the X-ray absorption cross-section and is found to yield essentially the same results as a more conventional transmission experiment. However, the fluorescence method is shown to extend the sensitivity of the EXAFS technique by two or more orders of magnitude, and thus nake feasible the study of extremely dilute species.     

Interest for thin scintillating films

This paper reports on the interest for developing thin scintillating films deposited on various substrates for scintillation purposes. The first part will present some advantages of films for fundamental studies. Mainly they are helpful (when deposited on CaF 2 ) for spectroscopic measurements when absorption coefficient is very high (as for CeF 3 ) or when excitation energies are near the fundamental absorption edge. When deposited on silicon substrate, photoelectron spectroscopy may be performed without any charging effects. The second part describes applications using film shaped scintillators, like high resolution X-ray imaging.     

Plasma detection of laser field interaction with optical thin films

Plasmas produced in Q-switched laser irradiation of two types of single-layer optical coatings are detected, and the field effect in this interaction process is analyzed.     

He-Ne散射光检测光学薄膜激光损伤阈值

准确测定光学薄膜的激光损伤阈值可以衡量光学薄膜的抗激光损伤能力,测定损伤阈值的关键是准确地判定损伤的发生与否。建立了He-Ne散射光检测光学薄膜激光损伤阈值系统。通过测量同一样品点的He-Ne散射光能量变化来判断薄膜表面发生的损伤,并对制备的类金刚石薄膜与HfO₂/SiO₂反射膜进行了阈值测试。与等离子体闪光法的阈值测试结果进行比较,具有较好的一致性。分析表明：He-Ne散射光测试系统能有效地判断出激光诱导损伤,易于实现在线检测。     

Radiant-energy detection by?Ba?Cu?O thin films

High T_c superconducting films offer promise as fast sensitive detectors of microwave and infrared. A high T_c superconducting transition-edge bolometer was fabricated from Y–Ba–Cu–O thin film on a (100) SrTiO₃ substrate, and tested at about the T_c midpoint using a 500 K blackbody source. In this initial work only NEP=5×10^–8W/Hz^1/2 was achieved with a large time constant caused by rather thick substrate. The sensitive element was put in the vacuum chamber of a liquid nitrogen metal cryostat for three weeks and through ten cold-hot cycles (80 K-300 K), the sensitivity of the bolometor kept repeatable. Some future work is also discussed.     

Bioglass thin films for biomimetic implants

Pulsed laser deposition (PLD) method was used to obtain bioglass (BG) thin film coatings on titanium substrates. An UV excimer laser KrF* (λ = 248 nm, τ = 25 ns) was used for the multi-pulse irradiation of the BG targets with 57 or 61 wt.% SiO₂ content (and Na₂O-K₂O-CaO-MgO-P₂O₅ oxides). The depositions were performed in oxygen atmosphere at 13 Pa and for substrates temperature of 400 °C. The PLD films displayed typical BG of 2-5 μm particulates nucleated on the film surface or embedded in. The PLD films stoichiometry was found to be the same as the targets. XRD spectra have shown, the glass coatings obtained, had an amorphous structure. One set of samples, deposited in the same conditions, were dipped in simulated body fluids (SBFs) and subsequently extracted one by one after several time intervals 1, 3, 7, 14 and 21 days. After washing in deionized water and drying, the surface morphology of the samples and theirs composition were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), IR spectroscopy (FTIR) and energy dispersive X-ray analysis (EDX). After 3-7 days the Si content substantially decreases in the coatings and PO₄³⁻ maxima start to increase in FTIR spectra. The XRD spectra also confirm this evolution. After 14-21 days the XRD peaks show a crystallized fraction of the carbonated hydroxyapatite (HAP). The SEM micrographs show also significant changes of the films surface morphology. The coalescence of the BG droplets can be seen. The dissolution and growth processes could be assigned to the ionic exchange between BG and SBFs.     

Magnetic equation of state for thin films

The magnetization fluctuations are considered in thin films treated as a set of monoatomic layers parallel to the film surfaces. The correlation functions have been determined and their forms are discussed. The influence of inhomogeneity of magnetization on the equation of state for a magnetic system described by Valenta's model is studied. The behaviour of the spontaneous magnetization as well as the magnetic susceptibility near the Curie point is described.This work is partially supported by the Institute of Physics of the P.A.S.     

Temperature-dependent luminescence dynamics for ZnO thin films

The paper presents the photoluminescence investigation of zinc oxide thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz wafers. The films with different thickness (number of layers) were annealed at different temperatures after the preparation process. It was found that high quality, transparent ZnO thin films could be produced on quartz substrates at relatively low annealing temperature (450–550  $^{\circ }\mathrm{C}$ ). The dependence of the ZnO thin film quality was studied by X-ray diffraction and atomic force microscopy techniques. Optical properties were investigated by classic and time-resolved photoluminescence (TRPL) measurements. Photoluminescence spectra allowed us to estimate energy of the free excitons, bond excitons and their longitudinal optical (LO) phonon replicas as a function of the annealing temperature. An innovative TRPL technique let us precisely measure the decay time of the free- and bond excitons’ in the real time. TRPL measurements as a function of temperature reveal a biexponential decay behavior with typical free/bound exciton decay constants of 970/5310 ps for the as-grown sample and 1380/5980 ps after annealing process. Presented spectra confirm high structural and optical quality of investigated films. We proved that the thermal treatment improve both optical and structural quality and extend the photoluminescence’s lifetimes. The obtained experimental results are important for identification of exciton’s peaks and their LO phonon replicas for the investigated ZnO films.     

A torque magnetometer for thin films applications

We describe the development of an automatic torque magnetometer based on a torsion pendulum. The instrument uses the capacitive arrange developed by Randall D. Peters, Rev. Sci. Instr. 60 (8), 2789 (1989), as sample's angular position sensor. The instrument performance is illustrated by measuring the in plane magnetic anisotropy of Co thin films and systems with exchange-bias. It possesses a sensitivity of 10^?10 Nm and is capable to determine anisotropy constants in magnetic films as thin as 3 nm. The instrument design and the measurement procedures are presented.     

Superheating of thin films for optical recording

Two methods for calculating the temperature in a thin film on a substrate during laser exposure are discussed. A simple algebraic expression gives a satisfactory estimate for the maximum temperature if radial diffusion of heat is negligible. A numerical method is applied to calculate the temperature profile in a tellurium film on a PMMA substrate. The calculations show that for pulse times below about 10 μs, the temperature at which hole opening occurs, is considerably above the melting point of tellurium. This indicates that for small pulses the solid film is locally superheated due to the limiting kinetics of the melting process.     

Hall coefficient for double layer thin films

The conduction electron distribution functions for double layer thin films with the presence of a transverse magnetic field has been derived. A general theoretical solution for the Hall effect of double layer thin films is obtained thereafter.     

Carbon anode thin films for lithium batteries

This paper describes a simple method to create carbon anode films for potential applications to the research field of lithium batteries. Carbon films were prepared using DC magneton sputtering with post-annealing process in the range from room temperature (RT) to 700 °C. Half cells assembled with lithium foils as the counter electrode and 1 M LiPF₆ in EC:DMC (1:1 v/v) electrolytic solution was used to evaluate the discharging capacity of prepared anode thin films. We showed that carbon film deposited at RT can be more suitable for an anode material than that of higher temperature annealed films above 400 °C. A variety of analysis methods including X-ray diffraction spectrometry (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to evaluate the defect density of the films; for example, the more defects on the film were identified when the carbon film was treated at a low temperature such as RT. It is envisioned that DC magnetron-sputtering with optimized process conditions can be useful for fabricating carbon based film anodes.     

Electrons in thin films

The method of evaluation of broken-symmetry Green’s function is presented. This method was applied to electron subsystem of a thin film. It was found that electron concentrations are spatially dependent and their spatial distribution proves the existence of skin effect. The skin effect is most expressed in the films of minimal thickness. The internal energy of electrons lying in the film Fermi volume, decreases with the increase of temperature. It is the consequence of the Pauli principle, which does not allow change of electron velocities. Introduced heat increases electron effective masses and this leads to the decrease of internal energy.     

Segregation in thin films

The longitudinal and transverse components of the image force acting on a moving charge near a metal surface are calculated. In particular, it is found that the transverse force is finite at the surface in contrast to the classical image force. The transverse force leads to deviations in trajectory in grazing incidence reflection inelastic electron scattering experiments, which are estimated. A consequence is the existence of a limiting maximum probability for excitation of surface plasmons.     

Applications of surface polaritons for detection and vibrational spectral analysis of thin films on metals and dielectrics

Phonon-polaritons interactions with molecular vibrations of thin films were used for the detection of film oscillator spectral positions. The gap in the polariton branch was proportional to √ ℓ,ℓ being the thickness of the film on dielectric support. The ATR method in the Otto configuration was used for measurements as well as thermal stimulated emission. The vibrational spectra (infrared absorption) of monomolecular films were detected by surface electromagnetic waves (SEW) - surface plasmon-polaritons propagating along the metallic substrate. A comparison of the reflection-absorption method with the SEW broadband (650-2500cm⁻¹) FT-IR method of thin films detection is made. The better sensitivity of the last one is shown. The prism, grating and edge methods of SEW excitations in IR are discussed.