Visible luminescence from hydrogenated amorphous silicon modified by femtosecond laser radiation

Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells

Effect of hydrogen concentration on structure and photoelectric properties of a-Si:H films modified by femtosecond laser pulses

The crystallization of hydrogenated amorphous silicon films with femtosecond laser pulses is one of the promising ways to produce nanocrystalline silicon for photovoltaics. The structure of laser treated films and their hydrogen content are the most important factors for determining the photoelectric properties of materials. In this work we investigated the effect of femtosecond laser irradiation of a-Si:H films with different fluences on crystalline volume fraction, hydrogen concentration, and photoelectric properties of this material. Our results point out that hydrogen out-diffusion accompanies the crystallization process. The increase of hydrogen concentration in the initial a-Si:H films structure affects the kinetics of the crystallization process, but does not lead to a substantial increase of hydrogen concentration remaining in the film after the treatment. The deficiency of hydrogen in the films’ structure results in degradation of their photoconductivity, thus other strategies of a-Si:H laser crystallization or postprocessing should be found to obtain device-quality films using ultrafast laser processing

Co3O4 as p-Type Material for CO Sensing in Humid Air

International audienceNanocrystalline cobalt oxide Co3O4 has been prepared by precipitation and subsequent thermal decomposition of a carbonate precursor, and has been characterized in detail using XRD, transmission electron microscopy, and FTIR spectroscopy. The sensory characteristics of the material towards carbon monoxide in the concentration range 6.7-20 ppm have been examined in both dry and humid air. A sensor signal is achieved in dry air at sufficiently low temperatures T = 80-120 degrees C, but the increase in relative humidity results in the disappearance of sensor signal in this temperature range. At temperatures above 200 degrees C the inversion of the sensor signal in dry air was observed. In the temperature interval 180-200 degrees C the sensor signal toward CO is nearly the same at 0, 20 and 60% r.h. The obtained results are discussed in relation with the specific features of the adsorption of CO, oxygen, and water molecules on the surface of Co3O4. The independence of the sensor signal from the air humidity combined with a sufficiently short response time at a moderate operating temperature makes Co3O4 a very promising material for CO detection in conditions of variable humidity

Femtosecond laser induced crystallization of hydrogenated amorphous silicon for photovoltaic applications

Femtosecond laser assisted crystallization is used to produce nanocrystalline silicon from hydrogenated amorphous silicon. Changes in structural, optical, electrical and photoelectric properties of laser modified amorphous silicon were investigated. Laser treated films were characterized using atomic force microscopy, Raman spectroscopy, constant photocurrent method and current measurements. Crystalline volume fraction as well as conductivity of laser irradiated films increased with the applied laser fluence, while hydrogen concentration in the films was found to decrease with the fluence. Spectral dependences of absorption coefficient, measured by constant photocurrent method, are discussed in terms of hydrogen out-effusion and additional defect state formation in silicon films during the laser treatment

Assuring access to quality antiretroviral medicines: the WHO Prequalification of Medicines Program and access to HIV treatment

International audienceNanocrystalline cobalt oxide Co3O4 has been prepared by precipitation and subsequent thermal decomposition of a carbonate precursor, and has been characterized in detail using XRD, transmission electron microscopy, and FTIR spectroscopy. The sensory characteristics of the material towards carbon monoxide in the concentration range 6.7-20 ppm have been examined in both dry and humid air. A sensor signal is achieved in dry air at sufficiently low temperatures T = 80-120 degrees C, but the increase in relative humidity results in the disappearance of sensor signal in this temperature range. At temperatures above 200 degrees C the inversion of the sensor signal in dry air was observed. In the temperature interval 180-200 degrees C the sensor signal toward CO is nearly the same at 0, 20 and 60% r.h. The obtained results are discussed in relation with the specific features of the adsorption of CO, oxygen, and water molecules on the surface of Co3O4. The independence of the sensor signal from the air humidity combined with a sufficiently short response time at a moderate operating temperature makes Co3O4 a very promising material for CO detection in conditions of variable humidity

Visible luminescence from hydrogenated amorphous silicon modified by femtosecond laser radiation

Visible luminescence is observed from the composite of SiO2 with embedded silicon nanocrystallites produced by femtosecond laser irradiation of hydrogenated amorphous silicon (a-Si:H) film in air. The photoluminescence originates from the defect states at the interface between silicon crystallites and SiO2 matrix. The method could be used for fabrication of luminescent layers to increase energy conversion of a-Si:H solar cells

Co3O4 as p-Type Material for CO Sensing in Humid Air

Nanocrystalline cobalt oxide Co3O4 has been prepared by precipitation and subsequent thermal decomposition of a carbonate precursor, and has been characterized in detail using XRD, transmission electron microscopy, and FTIR spectroscopy. The sensory characteristics of the material towards carbon monoxide in the concentration range 6.7–20 ppm have been examined in both dry and humid air. A sensor signal is achieved in dry air at sufficiently low temperatures T = 80–120 °C, but the increase in relative humidity results in the disappearance of sensor signal in this temperature range. At temperatures above 200 °C the inversion of the sensor signal in dry air was observed. In the temperature interval 180–200 °C the sensor signal toward CO is nearly the same at 0, 20 and 60% r.h. The obtained results are discussed in relation with the specific features of the adsorption of CO, oxygen, and water molecules on the surface of Co3O4. The independence of the sensor signal from the air humidity combined with a sufficiently short response time at a moderate operating temperature makes Co3O4 a very promising material for CO detection in conditions of variable humidity

Structural and electrophysical properties of femtosecond laser exposed hydrogenated amorphous silicon films

This paper studies the effect of femtosecond laser treatment in air of hydrogenated amorphous silicon thin films (a-Si:H) on their structural, electrical and photoelectric properties. The possibility of laser-induced crystallization of a-Si:H films with controlled crystalline volume fraction was shown. A sufficient increase of dark conductivity was observed for laser treated a-Si:H films which crystallinity exceeds 7%. Such increase was attributed to change in conductivity mechanism. However, spectral dependences of absorption coefficient did not show any qualitative changes with the laser fluence increase. It was found that spallation and oxidation of the film took place when laser fluence became reasonably high