Francisco Javier Ramirez Fernandez

Photoluminescence quenching effect on porous silicon films for gas sensors application.

Porous silicon (PS) films were investigated by Raman, and photoluminescence (PL) spectroscopies using different laser excitations: 488.0, 514.5, 632.8, and 782.0 nm. The analysis of the first-order and second-order Raman spectra have shown that the band gaps of the PS films are indirect as in the bulk c-Si. The Raman phonon and the PL spectra as well as the spectral distribution of the linear polarisation degree (LPD) of PS layers have shown to be dependent on the laser excitation energy. This dependence cannot be explained within the quantum confinement model. A mechanism for the PL emission in PS layers is presented in which the radiative recombination of electron-hole pairs occurs in localised centres (the Si-O-SiR moieties) at the pore/crystallite interface. These quasi-molecular centres are Jahn-Teller active, i.e. the radiative recombination is a phonon-assisted phenomena. The adsorption of gas molecules on the porous silicon surface was studied throughout photoluminescence quenching effect. The adsorption experiments were performed at 10(-6) bar of pressure using gas molecules of organic solvents. In all these cases, the PL intensity was recovered after gas desorption. The PL quenching effect was explained in the sense of electron transfer mechanism (ET).

Influence of laser excitation on raman and photoluminescence spectra and FTIR study of porous silicon layers

A porous silicon lm (PS) was investigated by FTIR, Raman and photoluminescence (PL) spectroscopies. The Raman and PL spectra were obtained using four different laser excitations: 488, 514, 633 and 782 nm. The analysis of the first order and second order Raman scattering lines permits to identify the band energy structure of the crystallites inside the PS film. The analysis of PL spectra shows that the intensity and full width at half-maximum values of PL emission depends on intensity and energy of laser excitation. The linear polarization degree (LPD) of the PL spectra also presents a dependence of laser excitation. The observed dependence of Raman and PL spectra due to laser excitation energy cannot be explained within the quantum confinement alone. We propose a mechanism for PL emission in PS layers, in which the radiative recombination occurs in localized centers at pore/crystallite interface. These quasi-molecular centers are Jahn-Teller active.

Self-assembled systems obtained by chemical and electrochemical techniques for photonic crystal fabrication

Abstract The present work reports the formation of self-assembled systems by chemical and electrochemical techniques for photonic crystal structures fabrication. The chemical technique was used to the fabrication of self-assembled polystyrene micro-spheres structures. The influence of temperature setup and monodispersion concentration in the chemical self-assemble mechanism was studied. The electrochemical technique also was used to fabricate the self-assembled porous alumina structures. The influence of electrolyte type and anodic voltage in the electrochemical self-assemble process was studied. The self-assembled structures were analyzed to the possibility of application as photonic crystal structures

A new paradigm on fingerprint classification using directional image

This work presents a simple method to obtain fingerprint classification via directional map smoothing. The program was developed in C++ language, using statistical techniques. The strategy allows to extract attributes of an image and to increase the quality of the process due to the reduction of noise, compared with results obtained by other methods. The experimental results obtained by this technique demonstrate that a better directional map is arranged.

Recognition of mental task with the analysis of long-range temporal correlations on EEG brain oscillation

The aim of this work is to explore the presence of LongRange Temporal Correlation (LRTC) and scaling the behavior in the brain signal EEG and its brain bands, while the subjects were developing different mental tasks. The statistic differences between the mental tasks will be studied and analyzed. The LRTC was calculated on the EEG signal and its brain bands with a Detrended Fluctuation Analysis (DFA) and the Wilcoxon signed-rank test that were applied for analyzing the statistical difference for each mental task. The EEG signals and the Theta Band reported the presence of long-range power-law correlations and scaling behavior. The Delta Band reported the presence of long-range correlations; however, this one approached the smoothness of the Brownian noise. Our results reported significant differences (p<; 0.05) in 7 out of 10 pair of mental tasks. The presence of (LRTC) and scaling behavior in the Delta and Theta band are reported. DFA has also shown to be a useful tool for discriminating mental tasks.

Emotion recognition system using Open Web Platform

This paper proposes a model for recognizing emotions through movement of facial muscles inspired by FACS (Facial Action Coding System) and FACSAID (Facial Action Coding System Affect Interpretation Dictionary). The computational implementation of the proposed model, here called WeBSER (Web-Based System for Emotion Recognition), was produced in Open Web Platform and is able to infer the users emotional state in real time. The images of the users face are captured using a webcam and emotions are classified using a Computer Vision system that uses the Web as a platform. Given the sequences of images acquired in real time via webcam, the WeBSER performs the following steps: Face detection and segmentation (eyes with eyebrows, nose and mouth); Entering reading points; Classification of emotions based on the movement of the reading points. For face detection and segmentation of face regions such as eyes, nose and mouth, the Viola-Jones method was used. Given the face image and the location of the segmented regions, 20 reading points were identified in image. The movement of each reading point is analyzed relatively to the other points. The direction of the movement of reading points is classified in bands of 45 degrees; Thus, each point can assume one of eight directions or remain stationary. Finally, the classification of emotions is made based on the movement of the reading points. This proposed model has a mean accuracy of 76,6% for determining exact emotions, and 84.4% to indicate uncomfortable states of persons suggesting suspicious behaviors.

Phase synchrony analysis of gamma band as tools to discriminate cognitive tasks

Recent studies report an increase of synchrony between different brain areas and bands during the development of mental tasks. Furthermore, there is a high interest in the study of gamma band because the literature reports considerable evidence that neural oscillations and synchronization in high frequency and large-scale integration [1]. The analysis of synchrony (Phase Locking Value) for the analysis of gamma band was applied for the discrimination of cognitive tasks and their performances were compared with the implementation of Wavelet transform. The results showed that PLV analysis reported a difference of 9 pairs of mental tasks in comparison with the Wavelets analysis that reported a difference of 5 mental tasks. Moreover, the approach with PLV reported a smaller processing time; the analysis of synchronous brain thus shows encouraging results as a tool for discriminating cognitive tasks.

Micromechanical structure development for chemical analysis: study of porous silicon as an adsorbent

The aim of this work is to investigate the use of microchannels to concentrate pollutants present in the air. Devices with a length of 30 cm, a width of 100 micrometers and a depth of 30 micrometers , sealed by anodically bonded glass, were manufactured. Tests of adsorption characteristics were made using n-hexane. To reliably insert N2 contaminated with 1000 ppm of n-hexane in the microstructure, a simple setup was manufactured. This setup allows to insert the reactant, remove the amount of reactant adsorbed and to detect it. An amount of 20 mg was inserted in the microstructure. In order to improve the adsorption characteristics, PS layers were manufactured in the microchannels using silicon nitride as mask. The sealing of the microstructure with anodic bonded glass showed to be feasible either if the surface present PS or silicon nitride. Samples of PS layers covered by a plasma polymerized film, produced using HMDS, were analyzed by Raman microscopy. It was noticed that the nanocrystals are completely fulfilled by the deposited material, indicating the high reactivity of the PS layer.

Methodology and platform for fault co-emulation

A platform and a technique to improve stuck-at fault grading efficiency through the use of hardware co-emulation is presented. IC manufacturers are always seeking for new ways to test their devices in order to deliver parts with zero defects to their customers. Scan is a well known technique that attains high fault coverage results with efficiency. Demands for new features motivate the creation of high complex systems with a mixture of analog and digital blocks with a communication interface that is difficult to cover with scan patterns. In addition, the logic that configures the chip for each of the different test modes, some BIST memory interfaces, asynchronous clock dividers or generators, among others, are examples of circuits that are blocked or have few observation/control points during scan. A FPGA based-platform that uses heterogeneous models to emulate digital, analog and memory blocks for fault grading patterns on complex systems is described. Also introduced in our proposal are four types of models that can be used with FPGAs, and the results of applying our fault co-emulation technique to some benchmark circuits including ISCAS89, ADC, iopads and memory controllers.

Fractal Brownian motion for feature extraction in noisy signals from gas sensors

The present work reports on a new pattern recognition method applied to the electrical response of a gas sensor. The sensor is a tin oxide device used as an electronic nose. It yields noisy responses when submitted to organic solvents. Signals were analyzed by the epsilon-blanket fractal dimension associated with the fractal Brownian motion. The classification of features shows close to 100% recognition rate for five different gases.