Annealing effect in DC and RF sputtered ITO thin films

The effect of annealing on the physical properties of DC and RF sputtered ITO thin films has been investigated. Two series of samples were deposited onto glass substrates, the first one consists of several In2O3:Sn (ITO) prepared by DC reactive sputtering with different partial pressure of oxygen (ppo); in the second one, the ITO samples were done by RF sputtering with different RF powers. Annealing experiments were done in various conditions: in air, in vacuum and in Ar atmosphere for temperatures in the 100 °C to 500 °C range. Structural properties were studied using Scanning Electron Microscopy (SEM), the usual X-ray diffraction (XRD) and also in-situ X-ray diffraction where X-ray spectra were recorded while the sample was being annealed. The optical properties were inferred by means of a spectrophotometer with wavelength in the 200–900 nm range. It was found that, for DC sputtered films, annealing favours the existing texture either $\langle 111\rangle$ or $\langle 100\rangle$; while, for the RF sputtered ones it always favours the $\langle 111\rangle$ texture. Annealing induced some similar changes in both series of samples such as the increase of grain size, the decrease of the strain and the electrical resistivity. The values of the optical transmission decreases after annealing at temperatures T = 400 °C and T = 500 °C for the DC and the RF sputtered films respectively. The decrease seems to be more important in the DC than in the RF sputtered ITO films

PbTiO3 epitaxial thin films as optical waveguides

Thin films of lead titanate (PbTiO3-PT) have been prepared in-situ on SrTiO3 (100) substrates using radio-frequency sputtering. The epitaxial quality of the films has been investigated as a function of the substrate temperature. Stoichiometric films have been obtained in the temperature range 550°C-600°C. Films have a high degree of c-axis oriented crystalline structure. The optimum conditions for growing epitaxial PbTiO3 layers are reported in this study. Thin films grown at 550°C exhibited a rocking curve full width at a half maximum (FWHM) of 0.26°. The refractive index calculated from optical transmission method has been evaluated to 2.61 @ 632.8nm, which represents 98% of the corresponding bulk material

F.: Robust fingerprint detection for access control

The paper presents a robust novel approach for access control based on the identification of the minutiae present in a fingerprint image based on the analysis of the local properties cards. The classical patterns of minutiae called ridge termination and bifurcation are identified by studying the intensity along squared paths in the image. The presented algorithm works both on grey-level image obtained directly scanning the fingerprint and binarized image and, despite its simplicity, it achieves good accuracy and can be a good candidate to be implemented in hardware or embedded on simple biometric hardware architectures or portable biometric applications such as cellular phones and smart cards

Optical and microstructural properties into nanoporous GaN films grown on sapphire by metal organic chemical vapor deposition

Gallium Nitride (GaN) thin films have been prepared on sapphire by metal organic chemical vapor deposition (MOCVD) technique and a chemical etching method using KOH is used to develop nanoporous structures [1]. We present comparative investigations of porous and nonporous GaN layers. While the pores density is determined, we have investigated the microstructures in GaN films by using transmission electron microscopy (TEM). The refractive index dispersion has been evaluated through different techniques, ellipsometry and guided-wave prism coupling [2]. We have correlated the microstructure with the refractive index of the material. The aim of this research is to demonstrate that optical properties of GaN can be tuned by controlling the pores size and spacing. For a pores density of 20%, we report an index variation ∆n= -12*10-3. The control of the refractive index into GaN is therefore fundamental for the design of active and passive optical devices [1] S-H Gong, A. Stolz,G-H Myeong, E. Dogheche, A. Gokarna, S-W Ryu, D. Decoster, Y-H Cho, Optics letters, vol 36 no.21, pp4272-4274, nov 2011. [2] Y-H Lee, J-H Kang, S-W Ryu, Thin Solid Films, vol.540 150 (2013)