Electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride

The electrical behavior of multi-walled carbon nanotube network embedded in amorphous silicon nitride is studied by measuring the voltage and temperature dependences of the current. The microstructure of the network is investigated by cross-sectional transmission electron microscopy. The multi-walled carbon nanotube network has an uniform spatial extension in the silicon nitride matrix. The current-voltage and resistance-temperature characteristics are both linear, proving the metallic behavior of the network. The I-V curves present oscillations that are further analyzed by computing the conductance-voltage characteristics. The conductance presents minima and maxima that appear at the same voltage for both bias polarities, at both 20 and 298 K, and that are not periodic. These oscillations are interpreted as due to percolation processes. The voltage percolation thresholds are identified with the conductance minima

Stress-induced traps in multilayered structures

The trap parameters of defects in Si/CaF2 multilayered structures were determined from the analysis of optical charging spectroscopy measurements. Two kinds of maxima were observed. Some of them were rather broad, corresponding to "normal" traps, while the others, very sharp, were attributed to stress-induced traps. A procedure of optimal linear smoothing the noisy experimental data has been developed and applied. This procedure is based on finding the minimal value of the relative error with respect to the value of the smoothing window. In order to obtain a better accuracy for the description of the trapping-detrapping process, a Gaussian temperature dependence of the capture crosssections characterizing the stress-induced traps was introduced. Both the normal and the stress-induced traps have been characterized, including some previously considered as only noise features.Comment: 37 pages, 9 figure

Recycling of EPDM Rubber Waste Particles by Chemical Activation with Liquid Polymers

The steady growth of the rubber industry requires attention regarding the waste management and the methods applied in recycling and in the reclaiming processes. The ok in this thesis responds to the demand for an efficient recycle method for EPDM rubber waste. A solvent free chemical activation method to recycle EPDM rubber waste which provides high-quality recycled products, despite of the high amount of recycled particles used as a substitute of the raw material, was developed. The process needed to be both environmentally sustainable and applicable on an industrial scale without requiring special equipment. The final aim of this project was to use the activated particles in the production of seals and sealing systems on an industrial scale. In order to achieve this, the recycling of EPDM rubber waste particles by means of chemical activation using low molecular weight polymers (liquid polymers) was investigated. These liquid polymers are highly compatible with the waste rubber particles from the EPDM rubber and also suitable for sulphur vulcanisation. In comparison with other methods used for recycling of rubber and when considering environmental and economic aspects, chemical activation at the surface particle using low molecular weight polymers offers great recycling potential. In order to demonstrate the potential of the activated particles as a substitute for the raw material, aspects were investigated including: (1) characterization of the EPDM rubber waste particles; (2) optimization of the ratio between the waste rubber particles and the low molecular weight polymers; (3) investigation of the influence of various amounts of curing system; (4) study of the effect of the diene and ethylene percentage contained by the low molecular weight polymer used for activation of the particles; (5) investigation of the influence of the amount of activated particles used as substitute of the raw material; (6) study of the type of curing system used and (7) application of the process on an industrial scale

Quantum Well Solar Cells

Several structures with different absorbers from 3-5 and 4 groups are described and discussed. Various technological and design solutions, such as multiple quantum well solar cells with graded band gap, with tandem configurations, with strain-balanced structure, and strain-balanced structure improved with nanoparticles deposited atop are analyzed. The cell parameters are discussed and related to the materials and technology.</jats:p

Quantum Well Solar Cells

Quantum well solar cells with p-i-n structure are presented. The physical processes in multiple quantum well solar cells, the materials commonly used for photovoltaic applications, and technological aspects are analyzed. The quantum confinement effect produces resonant energy levels located in the valence and conduction bands of well layers. In addition, it produces energy quantum confinement levels located in the energy band gap of both well and barrier layers. The absorption on both resonant and quantum confinement levels leads to an extension of the internal quantum efficiency in near infrared domain. Several structures with different absorbers from 3-5 and 4 groups are described and discussed. Various technological and design solutions, such as multiple quantum well solar cells with graded band gap, with tandem configurations, with strain-balanced structure, and strain-balanced structure improved with nanoparticles deposited atop are analyzed. The cell parameters are discussed and related to the materials and technology. </jats:p