Thermally stimulated currents in layered Ga4SeS3 semiconductor

Cataloged from PDF version of article.Thermally stimulated current (TSC) measurements are carried out on nominally undoped Ga4SeS3 layered semiconductor samples with the cur-rent flowing along the c-axis in the temperature range of 10 to 150 K. The results are analyzed according to various methods, such as curve fitting, initial rise and Chen's methods, which seem to be in good agreement with each other. Experimental evidence is found for the presence of three trapping centers in Ga4SeS3 with activation energies of 70, 210 and 357 meV. The calculation yielded 7.9 x 10(-21), 7.0 x 10(-19) and 1.5 x 10(-13) cm(2) for the capture cross section, and 1.6 x 10(10), 6.5 x 10(10) and 1.2 x 10(11) cm(-3) for the concentration of the traps studied. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Study of dielectric relaxations in cellulose by combined DDS and TSC

In this work, thermally stimulated currents (TSC) analyses combined with dynamic dielectric spectroscopy (DDS) have been applied to the investigation of molecular mobility of cellulose. The correlation between results obtained by both methods allows us to attribute the low temperature DDS relaxation mode to the c-mode resolved in TSC. The values of its activation parameters point out that the chain mobility remains localized. At high temperature, the various dielectric relaxation phenomena are separated by applying a recent analytical protocol. The comparison between the activation enthalpy values obtained by DDS and TSC leads to the assignment of the socalled a-mode to cooperative movements of polymeric sequences. The Arrhenius behavior of a-relaxation time is explained using the strong/fragile pattern. The influence of water content on secondary and primary relaxation modes was examined as well

Thermally stimulated currents of Zn-Bi-O thin film arresters

Ceramic varistors based on zinc oxide have excellent properties as protection devices used in power industry. However, their breakdown voltage, dependent on number of grain boundaries, is too high for use in electronic applications. In this work, performance of micro-devices having varistor-type current-voltage characteristics with low breakdown voltage is reported. The thermally stimulated depolarisation current (TSDC) technique was used to study the dielectric relaxation of the Zn-Bi-0 thin-film arresters. The surface varistor layers were prepared by r.f. magnetron sputtering on nickel support. The TSDC measuring system and cryostat apparatus used in experiment have been described

Thermally stimulated currents on oxide based TFTs

Dissretação de Mestrado, Engenharia Eletrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2016Óxidos amorfos semiconductores têm assumido um papel de liderança para aplicações em Transístores de Filme Fino (TFTs). Este tipo de transístores tem aplicações em ecrãs planos que usam Díodos Emissores de Luz (LEDs). Os TFTs controlam a activação de cada pixel luminoso. Em teoria os óxidos semiconductores podem ser fabricados em substratos de grandes dimensões, e eventualmente num futuro próximo, em substratos flexíveis de baixo custo, como o plástico e o papel. Esta possibilidade torna esta tecnologia um competidor direto com a electrónica orgânica, em particular onde o desempenho e o custo são um requisito essencial. Esta dissertação apresenta a caracterização eléctrica de um conjunto de Transístores de Efeito de Campo (FET) com base em filme finos de óxidos amorfos. Apresenta os métodos de fabrico, os materiais usados, estrutura física, modo de funcionamento e as características eléctricas. TFTs com base em óxidos semiconductores sofrem de um conjunto de problemas que afectam o seu desempenho. Uma das instabilidades é a alteração das propriedades eléctricas quando expostos à luz. Este problema é tanto mais grave já que umas das aplicações dos TFTs é justamente em ecrãs. O objectivo principal desta dissertação é identificar a origem física da instabilidade à luz. Com este objectivo usou-se um conjunto de técnicas eléctricas desenhadas para obter informação sobre os estados electrónicos que são induzidos quando o TFT é exposto à luz. Um das técnicas usadas foi o método das Correntes Termo Estimuladas (TSC). O óxido semiconductor em estudo foi o Zinc Tin Oxide (ZTO). Os resultados obtidos permitiram concluir que a luz induz um estado electrónico no semiconductor. Este estado electrónico comporta-se como um dopante e aumenta a condutividade eléctrica do material. As TSCs permitiram ainda identificar que este dopante esta energeticamente localizado a 0.14 eV da banda de condução do semicondutor. O estado induzido pela luz é muito mais raso que o estado responsável pela condução eléctrica normal, quando o TFT não é exposto à luz. TFTs não expostos à luz mostram um processo de condução termicamente ativado mas com uma energia de activação de 0.22 eV. Os estados electrónicos induzidos pela luz tem um tempo de vida de algumas horas. Este tempo de vida é suficientemente longo para considerar a possibilidade de usar este efeito em foto-sensores do tipo Charge-Coupled Devices (CCD) ou em memórias ópticas. Desta forma um efeito que é prejudicial pode ser convertido numa aplicação prática

Influence of homocysteine on the physical structure and molecular mobility of elastin network in cultured arteries

The thermal and dielectric properties of the elastin network were investigated in arteries cultured with physiological and pathological concentrations of homocysteine, an aminoacid responsible of histological impairments in human arteries. The glass transition of this amorphous protein was investigated by Differential Scanning Calorimetry (DSC). To explore the molecular dynamics of the elastin network in the nanometer range, we used Thermally Stimulated Currents (TSC), a dielectric technique running at low frequency and measuring the dipolar reorientations in proteins subjected to a static electrical field. Combining TSC and DSC experiments with determination of the activation parameters of relaxation times reveals the molecular mobility of the proteins. The major differences in the relaxation behavior of elastin between arteries cultured with physiological and pathological concentrations of homocysteine are discussed

Changes in the physical structure and chain dynamics of elastin network in homocysteine-cultured arteries

The thermal and dielectric properties of the elastin network were investigated in arteries cultured with physiological and pathological concentrations of homocysteine, an aminoacid responsible of histological impairments in human arteries. The physical structure of this amorphous protein was investigated by differential scanning calorimetry (DSC). To explore the molecular dynamics of the elastin network in the nanometer range, we used thermally stimulated currents (TSC), a dielectric technique running at low frequency, and measuring the dipolar reorientations in proteins subjected to a static electrical field. Combining DSC and TSC experiments reveals the molecular mobility of the proteins, both in the glassy state and in the liquid state. Significant differences are evidenced in the physical structure and relaxation behavior of elastin network in cultured arteries (physiological and pathological concentrations of homocysteine) and discussed

Molecular mobility of poplar cell wall polymers studied by dielectric techniques

In this work, thermally stimulated currents (TSC) analyzes combined with dynamic dielectric spectroscopy (DDS) have been applied to the investigation of polymers’ molecular mobility involves in poplar cell wall. The molecular origin of the various dielectric relaxations has been determined. Cellulose and lignin effects in wood dielectric response were distinguished. The correlation between results obtained by both dielectric methods allows us to follow molecular mobility involved in delocalized movement as primary relaxation mode. For these two major components of wood, the evolution of relaxation times involve in a-relaxation mode is explained using the strong/fragile pattern. We compared the cellulose and lignin in situ and ex situ responses to interpret wood compound behavior. The importance of structural wood interactions which modified the molecular mobility of polymer components will be underlined

New electrochemical and physical measurements on sensitive glasses in thin-film technology

All-solid-state sensors have several advantages compared to conventional ones. These include, e.g., miniaturization, planar design, location independence and an uncomplicated realization of sensors for high pressure and high temperature. Therefore, a number of physical sensors, such as temperature sensors, pressure sensors, rotation angle sensors and force sensors are available in thin-film techniques. The presented paper shows the advantages to combination of thin and thick film techniques to manufacture electrochemical sensors, especially using pulsed laser ablation to create amorphous layers of glass. Furthermore, it investigates the range of possibilities for characterization of bulk and surface properties with electrochemical methods and specialized techniques with thermally stimulated currents (TSC)

Influence of the architecture on the molecular mobility of synthetic fragments inspired from human tropoelastin

This work deals with the vibrational, thermal and dielectric characterization of a synthetic peptide (S4) released during the proteolysis of human tropoelastin. This peptide was shown to form amyloid-like fibers implied in neurodegenerative pathologies. The comparison between the linear peptides and the associated amyloidlike fibers evidences the strong influence of the secondary structures on the physical structure and chain dynamics of these polypeptides

A method for pet mechanical properties enhancement

A method for PET mechanical properties enhancement by reactive blending with HBA/HNA Liquid Crystalline Polymers for in situ highly fibrillar composites preparation is presented. LCP/PET blends were reactively extruded in presence of Pyromellitic Di-Anhydride (PMDA) and then characterized by Differential Scanning Calorimetry, Thermally Stimulated Currents and tensile mechanical properties. Moderate amounts of LCP in the PET (0.5 and 5%) and small amounts of thermo-active and reactive compatibilizer in the blend (0.3%) were found to significantly improve LCP melt dispersion, melts shear transfer and LCP fibril formation and adhesion. An unexpected improvement was probably due to the presence of two distinct phases’ supra-molecular structures involving PET-LCP and PMDA