E. Jimenez

SiO2∕PbTe quantum-dot multilayer production and characterization

We report the fabrication of multilayer structures containing layers of PbTe quantum dots (QDs) spaced by 15–20 nm thick SiO2 layers. The QDs were grown by the laser ablation of a PbTe target using the second harmonic of Nd:YAG laser in an argon atmosphere. The SiO2 layers were fabricated by plasma chemical vapor deposition using tetramethoxysilane as a precursor. The influence of the ablation time on the size and size distribution of the QDs is studied by high-resolution transmission electron microscopy. Optical absorption measurements show clearly the QDs confinement effects.

Structure of PbTe(SiO(2))/SiO(2) multilayers deposited on Si(111)

The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO2, named as PbTe(SiO2), between homogeneous layers of amorphous SiO2 deposited on a single-crystal Si(111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO2)/SiO2 multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers.

Structure of PbTe(SiO2)/SiO2 multilayers deposited on Si(111)

The structure of thin films composed of a multilayer of PbTe nanocrystals embedded in SiO2, named as PbTe(SiO2), between homogeneous layers of amorphous SiO2 deposited on a single-crystal Si(111) substrate was studied by grazing-incidence small-angle X-ray scattering (GISAXS) as a function of PbTe content. PbTe(SiO2)/SiO2 multilayers were produced by alternately applying plasma-enhanced chemical vapour deposition and pulsed laser deposition techniques. From the analysis of the experimental GISAXS patterns, the average radius and radius dispersion of PbTe nanocrystals were determined. With increasing deposition dose the size of the PbTe nanocrystals progressively increases while their number density decreases. Analysis of the GISAXS intensity profiles along the normal to the sample surface allowed the determination of the period parameter of the layers and a structure parameter that characterizes the disorder in the distances between PbTe layers.

PbTe quantum dots multilayer for optical switching device

In this work we report the fabrication of PbTe quantum dots multilayers embedded in SiO2 by alternatively use of Laser Ablation and Plasma Enhanced Chemical Vapor Deposition techniques. The quantum dots were grown by pulsed laser deposition (PLD) of a PbTe target using the second harmonic of a Q-Switched Quantel Nd:YAG laser in high purity argon atmosphere. The glass matrix was fabricated by PECVD using tetramethoxysilane (TMOS) as precursor. The RF power was supplied by a RF-150 TOKYO HI-Power operating at 13.56 MHz and coupled to the RF electrodes through a matching box. The deposition rates as well as the best growth parameters for both the nanoparticles and the glass matrix were obtained from a previous work. The morphological properties of the nanostructured material were studied by means of igh Resolution Transmission Electron Microscopy(HRTEM), grazing-incidence small-angle X-ray scattering (GISAXS) and X-ray reflectometry . Unlike HRTEM, which extracts information of a submicron region of the sample and only a few thousand particles are observed, GISAXS signal is obtained through an average over orders of magnitude larger number of particles (perhaps 1012 particles) distributed over an area of tens of square millimeters. This fact means that GISAXS sampling is much more representative of the sample as whole. Finally, multilayers were grown inside a Fabry-Perot cavity. The complete system operates as an optical switching device for the infrared region. The device was characterized by Scanning Electron Microscopy and optical absorption.

Multilayers of PbTe quantum dots embedded in SiO/sub 2/

In the present work, PbTe quantum dots embedded in a dielectric host (SiO/sub 2/) were fabricated. The structural and optical properties of the multilayers were studied.

PbTe quantum dots: SiO2 multilayers for optical devices

Thin films of glass doped with PbTe quantum dots were successfully fabricated. The semiconducting quantum dots were grown by laser ablation of a PbTe target (99.99%) using the second harmonic of a Q-Switched Quantel Nd:YAG laser under high purity argon atmosphere. The glass matrix was fabricated by a plasma chemical vapor deposition method using vapor of tetramethoxysilane (TMOS) as precursor. The QDs and the glass matrix were alternately deposited onto a Si (100) wafer for 60 cycles. Cross-section TEM image clearly showed QDs layer well separated from each other with glass matrix layers. The influence of the ablation time on the size distribution of the quantum dots is studied. HRTEM revealed anisotropy in the size of the QDs: they were about 9nm in the high and 3-5 in diameter. Furthermore HRTEM studies revealed that the QDs basically growth in the (200) and (220) directions. The thickness of the glass matrix layer was about 20 nm. Absorption, photo luminescence and relaxation time of the multilayer were also measured.

Laser equipment development and laser-matter interaction investigations at Havana University

The research projects at the Laser Technology Laboratory of Havana University are devoted to Nd:YAG lasers development and to the implementation of new laser applications in different fields. Relative to the lasers research the objective is the development of compact, light and relative low-cost lasers. This development is based on a vertical integration strategy that establishes the own elements production as pumping cavities, multilayer mirrors and filters, power supplies control units and others. Several investigations are carried out using these lasers: thin film deposition of semiconductor, ferroelectric and magnetic materials by laser ablation, subsurface laser marking of transparent materials, pulse laser surface silicon texturing and laser cleaning of art works.

PZT thin films grown by laser ablation

PZT thin films were deposited by laser ablation at high vacuum and at room temperature. After that, some of the samples were annealed at air in the temperature range 450 degree(s)C - 550 degree(s)C. The samples were characterized by XPS and X-ray diffraction. A decrease in the oxygen composition of the as-deposited sample was observed. In the as-deposited film metallic lead (Pb) appeared. The as-deposited analyzed film showed a weak crystallization. A posterior annealing of the as-grown films improved their crystalline structure. This annealing treatment provoked the disappearance of the metallic Pb bonds in the films.