Mario J. Cazeca

Epoxy matrix for solid-state dye laser applications

The preparation and performance of an epoxy-based matrix impregnated with Pyrromethene 580 for solid-state dye laser applications are discussed. The matrix proved to be stable and efficient as a laser medium when pumped by a frequency-doubled, Q-switched Nd:YAG laser with a 10-ns pulse width. Stability measurements were performed on a 1-mm-thick epoxy sample, doped with Pyrromethene 580 at a concentration of 4 x 10(-3) M. When the sample was pumped at millijoule energy levels, the stability was measured to be ~55,000 pulses from a single spot on the sample before the power dropped by a factor of half.

Enhanced performance of polythiophene derivative based light emitting diodes by addition of europium and ruthenium complexes

Abstract Fabrication of polymer light emitting diodes (PLEDs) from a urethane containing processable polythiophene derivative, poly[2-(3-thienyl) ethanol n -butoxy carbonylmethyl urethane], (PURET) and its composites with luminescent Ruthenium (II) and Europium (III) complexes is discussed. Enhanced electroluminescence (EL) performance was observed, when 1% by weight of europium (III) or ruthenium (II) complexes were added to the PURET polymer. Multi-layered devices with polyaniline as a hole injecting layer and tris-8-hydroxyquinoline-aluminum as an electron injecting layer have also been fabricated. PLEDs from PURET polymer have a threshold voltage of 3.6 V and emit an orange-red light with a brightness of about 500 cd/m 2 under forward bias of 9 V, upon the addition of 1% of europium (III) thenoyl trifluoroacetonate complex to the polymer.

Monte Carlo characterization of a new Yb-169 high dose rate source for brachytherapy application

PURPOSE The objective was to characterize a new Yb-169 high dose rate source for brachytherapy application. METHODS Monte Carlo simulations were performed using the MCNP5 F6 energy deposition tallies placed around the Yb-169 source at different radial distances in both air-vacuum and water environments. The calculations were based on a spherical water phantom with a radius of 50 cm. The output from the simulations was converted into radial dose rate distribution in polar coordinates surrounding the brachytherapy source. RESULTS The results from Monte Carlo simulations were used to calculate the AAPM Task Group 43 dosimetric parameters: Anisotropy function, radial dose function, air kerma strength, and dose rate constant. The results indicate a dose rate constant of 1.12 +/- 0.04 cGy h(-1) U(-1), anisotropy function ranging from 0.44 to 1.00 for radial distances of 0.5-10 cm and polar angles of 0 degrees-180 degrees. CONCLUSIONS The data from the Yb-169 HDR source, Model M42, presented in this study show that this source compares favorably with another source of Yb-169, Model 4140, already approved for brachytherapy treatment.

Mechanism of electroluminescence in dye doped thiophene based conjugated polymer

The optical and electrical properties of polymer light emitting diodes based on poly [2-(3-thienyl) ethanol butoxy carbonyl-methyl urethane] as emitting layer have been studied. The diode structures have been made by utilizing indium tin oxide coated glass as an anode and aluminum as a cathode. Polyaniline and tris(8-hydroxy-quinolino) aluminum have been employed as hole and electron transport layers, respectively. Enhanced electroluminescence (EL) near the turn-on voltage has been observed on addition of 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye. On the basis of current–voltage, luminance–voltage, capacitance–voltage, and impedance measurements, an attempt has been made to understand the mechanism of EL emission in these polymeric light emitting diodes.

Organic polymeric coatings deposited by plasma enhanced chemical vapor deposition

A process of depositing thin organic polymeric coatings on electronic substrates by plasma enhanced chemical vapor deposition (PECVD) has been developed. We have designed halogenated compounds with PECVD reactive functionality attached to optically active moieties. Compounds have been screened selectively to lower the dielectric constant and enhance plasma polymerization efficiency. The chemical, optical, and mechanical properties of the deposited films such as film uniformity, film defectivity, film solubility, resist compatibility, conformality, adhesion to semiconductor substrates, refractive index, optical density, and photolithographic behavior have been studied. Plasma polymerized materials exhibit high sensitivity, excellent resolution, and good process latitude. PECVD provides a completely dry deposition process for wafer coating. The coatings possess high optical density at 193 nm.

Second-order nonlinear optical properties of a photocrosslinkable epoxy-based polymer

The synthesis and characterization of a novel epoxy-based photocrosslinkable nonlinear optical (NLO) polymer exhibiting enhanced thermal stability is reported. The synthesized polymers show spectroscopic properties (NMR, IR, UV) in accordance with the proposed structures. A glass transition temperature (T g ) of 112°C and a thermal degradation temperature (T d ) of 310°C were recorded. The poled polymer film exhibits stable second-order nonlinear optical activity (d 33 = 19.5 pm/V) over a period of 500 h as characterized by the temporal response of the second harmonic signal at room temperature.

A model calculation for surface plasma-enhanced internal photoemission in Schottky-barrier photodiodes

Attenuated total reflection is commonly used to excite the surface plasma wave (SPW) on a metal film. The SPW traveling on the surface of the metal will enhance the emission of photoelectrons from the metal into the semiconducting region of a Schottky barrier photodiode. A model consisting of an aluminum film on n‐type gallium arsenide forming a Schottky barrier photodiode is used to predict the enhanced emission of photoelectrons over the barrier between the aluminum film and the gallium arsenide. The quantum efficiency for this model shows a strong dependence on parameters such as the electron escape depth, film thickness, and the spacer thickness between the prism coupler and the photodiode. The model proved to be effective when used to fit quantum efficiency and reflectivity data resulting from an angle scan experiment.

Stable highly transparent nonlinear optical polymer for laser frequency doubling

Abstract Channel waveguides of a polymer with nonlinear optical properties and transparency down to 400 nm were fabricated to be used for laser frequency doubling. The polymer was corona poled to induce orientation of the nonlinear chromophores, resulting in a stable poled polymer. End-fire coupling was used to couple the fundamental beam into the polymer channel waveguide. Green light was observed in the form of Cerenkov radiation using a Q -switched Nd-YAG laser lasing at 1064 nm as the fundamental beam. The total efficiency of the second harmonic conversion was 1.4 × 10 −3 %/W.

Fabrication of Gold Nano‐Structures with Azopolymer Templates

Fabrication of gold nano‐patterns has been demonstrated employing surface relief structures created on films of an azobenzene‐functionalized polymer as templates. The surface relief templates were photoinscribed on the azopolymer films in one‐step with two laser beams. Thin layers of gold were over‐coated on the polymer templates by thermal evaporation. Gold lines of a few hundred nanometer width were successfully fabricated by pyrolyzing the azobenzene polymer. Sub‐micron gold dots were also created. The resulting gold structures exhibited the same periodicity as the polymer templates.

Intelligent Systems Based on Ordered Arrays of Biological Molecules Using the LB Technique

The Langmuir-Blodgett (LB) technique has been used to incorporate photodynamic proteins into molecular assemblies. One technique of incorporation involves a generalized cassette attachment methodology which employs a biotin-streptavidin complexation with an electroactive polymer matrix. We have focused the efforts described here on phycobiliproteins and bacteriorho dopsin, although antibodies, enzymes, gene probes and other moieties could also be coupled into the system to build in selectivity. Photoconductivity and photobleaching of these protein systems were investigated. These results suggest that coupling these proteins, either in mixed monolayers or in multilayers, with appropriate conductive polymers or other materials will provide the opto electronic signal transduction needed for biosensor, optical display and other applications. Initial studies involving the integration of conductive polymers into the molecular assemblies to enhance optical signal transduction are also discussed.