J. Martínez-Juárez

Raman scattering and photoluminescence studies on Cu 2 O

Cuprous oxide (Cu2O) crystals were grown by the two step crystallization method in air atmosphere conditions from polycrystalline copper plates. The method comprises two stages; in the first one the copper plates are oxidized at 1020degC by some hours in line with its initial thickness. In the second stage the growth of large crystalline areas is promoted by annealing the Cu2O samples at 1100degC for long periods. The effects on the crystalline structure and photoluminescence (PL) response were studied as a function of the conditions used in the second stage of the synthesis method. Raman scattering and X-ray measurements demonstrates the existence of the single phase Cu2O. PL spectra were taken from 10 to 180 K to define the main radiative recombination paths. Besides of the near band excitonic transitions, two strong emission bands at 720 and 920 nm associated with relaxed excitons at oxygen and copper vacancies were detected. Both excitonic-vacancy bond transitions presented similar intensities which can be associated with the preparation method. The PL and the Raman scattering measurements were used to assess the evolution of the crystalline quality.

Evaluation of optical and electronic properties of silicon nano-agglomerates embedded in SRO: applying density functional theory

In systems in atomic scale and nanoscale such as clusters or agglomerates constituted by particles from a few to less than 100 atoms, quantum confinement effects are very important. Their optical and electronic properties are often dependent on the size of the systems and the way in which the atoms in these clusters are bonded. Generally, these nanostructures display optical and electronic properties significantly different to those found in corresponding bulk materials. Silicon agglomerates embedded in silicon rich oxide (SRO) films have optical properties, which have been reported to be directly dependent on silicon nanocrystal size. Furthermore, the room temperature photoluminescence (PL) of SRO has repeatedly generated a huge interest due to its possible applications in optoelectronic devices. However, a plausible emission mechanism has not been widely accepted in the scientific community. In this work, we present a short review about the experimental results on silicon nanoclusters in SRO considering different techniques of growth. We focus mainly on their size, Raman spectra, and photoluminescence spectra. With this as background, we employed the density functional theory with a functional B3LYP and a basis set 6-31G* to calculate the optical and electronic properties of clusters of silicon (constituted by 15 to 20 silicon atoms). With the theoretical calculation of the structural and optical properties of silicon clusters, it is possible to evaluate the contribution of silicon agglomerates in the luminescent emission mechanism, experimentally found in thin SRO films.

Growth and characterization of ZnO films deposited by chemical bath and annealed by microwaves (CBD-AμW)

A study of the growth and the physical properties of ZnO films deposited by chemical bath technique and annealed by microwave are presented. For the deposition solution the molar ratio between zinc nitrate and urea is varied in a range of 1:1... 1:10. By X-ray obtains that layers have hexagonal polycrystalline wurtzite type unitary cell. The Raman spectra show the first order experimental Raman spectra of ZnO. The first order Raman modes are identified in the ZnO Raman spectra. The 300K photoluminescence shows radiative bands labelled by red, yellow, green and violet bands, which are associated to defects of oxygen and zinc vacancies. By EDS measurements determined their stoichiometry, which allows relating it with the intensity of radiative bands associated to oxygen and zinc vacancies.

Análisis del Grabado Dental Utilizando el Microscopio Metalográfico y el Software AnalySIS

Resumen Se muestra que el microscopio metalografico y el software AnalySIS representan tecnicas adecuadas para el analisis del grabado dental acido. Se grabo la superficie vestibular de 25 dientes humanos permanentes, de reciente extraccion y libres de caries, se observaron al microscopio (100X) y se procesaron con el software AnalySIS. Se determino el diametro de poros seleccionados aleatoriamente y se evaluaron diferentes concentraciones de acido fosforico variando el tiempo de exposicion. Los resultados demuestran que a concentraciones de acido fosforico al 50% se presentan los mayores poros con diferencias estadisticamente significativas (ρ≤0.05). Los tratamientos de 30 y 60 segundos presentaron mayores poros sin diferencias estadisticas. Se concluye que el microscopio metalografico y el software AnalySIS representan una herramienta importante para analisis de grabado dental. Palabras clave: grabado dental, acido fosforico, microscopio metalografico, programa AnalySIS Analysis of Dental Etching Using the Metallographic Microscope and AnalySIS Software

The Luminescent Properties and Atomic Structures of As-Grown and Annealed Nanostructured Silicon Rich Oxide Thin Films

Not long ago, we developed a theoretical model to describe a set of chemical reactions that can potentially occur during the process of obtaining Silicon Rich Oxide SRO films, an off stoichiometry material, notwithstanding the technique used to grow such films. In order to elucidate the physical chemistry properties of such material, we suggested the chemical reactions that occur during the process of growing of SRO films in particular for the case of the Low Pressure Chemical Vapor Deposition LPCVD technique in the aforementioned model. The present paper represents a step further with respect to the previous published work, since it is dedicated to the calculation by Density Functional Theory DFT of the optical and electronic properties of the as-grown and annealed SRO structures theoretically predicted on the basis of the previous work. In this work, we suggest and evaluate either some types of molecules or resulting nanostructures and we predict theoretically, by applying the DFT, the contribution that they may have to the phenomenon of luminescence PL, which is experimentally measured in SRO films. We evaluated the optical and electronic properties of both the as-grown and the annealed structures.

Characterization of Wurtzite Type ZnS Grown by RF Magnetron Sputtering

ZnS was grown on (001) GaAs substrates at different temperatures by RF magnetron sputtering. ZnS chemical stoichiometry was determined by energy-dispersive X-ray spectroscopy (EDS). The XRD analysis and Raman scattering reveal that ZnS deposited thin films showed hexagonal crystalline phase wurtzite type. The average crystallite size range of the film was from 8.15 to 31.95 nm, which was determined using the Scherrer–Debye equation on diffractograms. Besides, an experimental study on first- and second-order Raman scattering of ZnS films is made. The observed emission peaks in the room temperature photoluminescence spectra are associated at oxygen traps and interstitial sulphur.

Optical and structural characterization of antimony doped zinc oxide single crystal

The optical and structural study of the antimony doping in zinc oxide (ZnO) single crystal (001) performed by atomic diffusion is presented. Diffusion was carried out with a temperature of 1000 ° C for periods of 1 and 2 hrs from a solid source prepared by partial oxidation of antimony, characterization of each step process was performed by photoluminescence (PL), x-ray diffraction (XRD) and high resolution x-ray diffraction (HRXRD). The characterization by PL shows the effect of antimony doping on the emission band intensity attributed to reduction of oxygen vacancies by antimony introduction. The results of XRD showed that antimony source has a Sb2O3 crystalline phase. Reciprocal space maps of doped samples revealed the low dimensional structural modification of single crystal produced by the introduction of antimony. Results indicate that antimony is introduced fully into surface of ZnO and produce low dimensional changes on structure.

Optical and Structural Characterization of ZnO Films Deposited by Chemical Bath and Activated by means of Microwaves

Zinc oxide (ZnO) is a direct, wide band gap semiconductor material having many promising properties for UV/blue optoelectronics, transparent electronics, spintronic devices and sensor applications. The ZnO is synthesized by the technique of Chemical Bath Deposition by microwaves heating (MW-CBD). The urea concentration in the solution is varied, maintaining constant the zinc nitrate in ratio 1:1 … 1:10. The physical properties of ZnO thin films were examined by X-ray diffraction (XRD), SEM-EDS, and Raman scattering, which are convenient tools that can provide us with plenty of information about crystal structure and elementary excitons. By X-rays one obtains that it has hexagonal polycrystalline wurtzite type structure. The IR absorption line at 3577 cm-1 detected at 300 K in bath chemical ZnO is assigned an O–H bond primarily aligned with the c-axis of the crystal and bonding between Zn-O (473cm-1, 532 cm-1). The Raman spectra show the first order experimental Raman spectra of ZnO excited by 514.5 nm laser line. The first order Raman modes A1T, E1T, E2(H), A1Land E1L are identified as the peaks sited at 385, 426, 437, 572 and 584 cm-1