In this dissertation, I present the results of my research on a prototypical interface of the metal oxide ZnO and the organic semiconductor C₆₀. I establish that the physics at such oxide / organic interfaces is complex and very different from the extensively investigated case of organic semiconductor / metal interfaces. The studies presented in this dissertation were designed to address and improve the understanding of the fundamental physics at such hybrid organic / inorganic interfaces. Using photoemission spectroscopies, I show that metal oxide defect states play an important role in determining the interfacial electronic properties, such as energy level alignment and charge carrier dynamics. In particular, I show that for hybrid interfaces, electronic phenomena are sensitive to the surface electronic structure of the inorganic semiconductor. I also demonstrate applications of photoemission spectroscopies which are unique in that they allow for a direct comparison of ultrafast charge carrier dynamics at the interface and the electronic structure of defect levels. The research presented here focuses on a achieving a significant understanding of the realistic and device relevant C₆₀ / ZnO hybrid interface. I show how the complex surface structure of ZnO can be modified by simple experimental protocols, with direct and dramatic consequences on the interfacial energy level alignment, carrier dynamics and carrier collection and injection efficiencies. As a result of this careful study of the electronic structure and dynamics at the C₆₀ / ZnO interface, a greater understanding of the role of gap states in interface hybridization and charge carrier localization is obtained. This dissertation constitutes a first step in achieving a fundamental understanding of hybrid interfacial electronic properties.

No description available.

No description available.

Lietuvoje įrengta 1590 tvenkinių, pastatyta daug kitokių hidrotechnikos statinių ir beveik kiekviename iš jų yra gelžbetoninių elementų ar konstrukcijų. Naudojami statiniai patiria įvairių apkrovų ir agresyvios aplinkos poveikį, dėl to jie ilgainiui nusidėvi, formuojasi pažaidos, statiniai genda ir tampa nebetinkami naudoti. Darbo tikslas – įvertinti defektų ir pažaidų įtaką naudojamų hidrotechnikos statinių gelžbetoninių konstrukcijų techninei būklei. 2006 metais tyrinėtos Marijampolės rajono naudojamų hidrotechnikos statinių gelžbetoninės konstrukcijos. Nustatyta pagrindinė konstrukcijų stiprum���� apibūdinanti charakteristika – gniuždomojo betono stipris. Užfiksuoti konstrukcijų defektai bei pažaidos, aptariamos galimos jų atsiradimo priežastys, konstrukcijų būklė įvertinta balais. Nurodyti dažniausiai pasitaikantys konstrukcijų defektai bei pažaidos, kurie atsirado dėl netinkamų sudėčių bei savybių betono, naudojimo trūkum��. / There are approximately 1590 dams and many other hydraulic structures constructed in Lithuania. Most of them have reinforced concrete elements or constructions. Due to different loads and environmental impact, condition of operational structures gets worse in time. Therefore, some deterioration may occur which leads structures to failure and makes them no longer useful for exploitation. The purpose of this work is to evaluate the influence of defects and deteriorations to the technical state of reinforced concrete hydraulic structures. In 2006, reinforced concrete constructions of hydraulic structures were investigated in Marijampole district. Compression strength is determined as the main characteristic of these constructions. Defects and deteriorations of constructions are noticed; main reasons that influence deterioration are discussed; and condition of constructions is estimated by points. It is established that most common defects and deteriorations are caused because of the use of unfit manufactured concrete and its shortage.

Caffeine, a mild central nervous system stimulant, is a natural component of common hot and cold beverages like coffee, tea, sodas and cocoa. Animal studies have demonstrated caffeine’s teratogenic effects when administered at high concentrations; however, epidemiologic studies have yielded inconsistent results in humans. Because caffeine containing beverages are commonly consumed by pregnant women, we examined the prevalence of use and explored possible associations of maternal caffeine consumption with cardiovascular malformations in 3,274 cases matched with 3,519 controls enrolled in the 1981-89 “Baltimore-Washington Infant Study,” a population-based case-control investigation. We explored several key aspects of the quality of and distribution of measurements of caffeine consumption among mothers in the study population. We concluded with recommendations for refining data collection to reduce potential bias associated with assessing both caffeine content and changes in caffeine consumption during pregnancy in order to inform future research studies and birth defects/adverse birth outcomes surveillance programs.

Investigations made on new materials and their structures for production of particle detectors based on semi-insulating SiC and GaN comprise the technological and applied importance of this study. Innovations in defect control technology, especially, in recognition of extended defects and percolative carrier transport in heavily irradiated detector structures are considered and applied for scientific implementations. These investigations have been performed within a framework of CERN rd50 project. Irradiation by 24 GeV protons varying fluence up to 1016 cm-2 deteriorates rectifying properties of the 4H-SiC particle detectors. Different isotopes produced in 4H-SiC during irradiation by protons have been revealed by gamma spectroscopy. In the non-irradiated GaN material the temperature-dependent variations of leakage current have been unveiled to be caused by the carrier mobility temperature changes. Activation energy values have been extracted for proton radiation induced deep centres in the GaN detectors by thermally stimulated current spectroscopy as well as the isotopes and long-living radio-nuclides have been identified by gamma spectroscopy. In the Si detectors, irradiated by reactor neutrons, the photo-activation energy values have been determined for the deep levels located below the mid-gap by photo-ionisation spectroscopy while isochronal anneals enhance the density of the acceptor-type vacancy-related defects. / Disertacijoje išanalizuoti gilieji centrai didžiavaržiuose Si, SiC ir GaN dariniuose, sietini su didelės energijos protonų bei neutronų spinduliuote sudarytais defektais, atskleistos radiacinių defektų transformacijos po iškaitinimų, didelių energijų spinduliuotės įtaka krūvio pernašai ir pagavai medžiagose, tinkamose jonizuojančiosios spinduliuotės detektoriams, tiriamiems pagal Europos branduolinių tyrimų centro (CERN) projektus. 4H-SiC dariniuose, apšvitintuose 24 GeV/c protonais, išanalizuota elektrinių charakteristikų kaita. Iš šiluma skatinamųjų srovių spektrų nustatytos šiluminės aktyvacijos energijų vertės. Taip pat 4H-SiC dariniuose, apšvitintuose protonų įtėkiais, siekiančiais 1016 cm-2, įvertintas skirtingų spinduliuote sukurtų izotopų kiekis. Neapšvitintose GaN dariniuose nustatyta, kad medžiagos elektrinio laidumo parametrų kaitą nulemia krūvininkų judrio kitimas. Apšvitintuose neutronais GaN dariniuose šiluma skatinamųjų srovių spektroskopijos būdu buvo nustatyti dominuojančių defektų lygmenys. Aptikta, kad po apšvitos 24 GeV/c protonų įtėkiais, siekiančiais 1016 cm-2, GaN susidarė 7Be, 22Na ir kiti ilgaamžiai radionuklidai, kurių atominis skaičius A<70, bei žymiai pakito spinduliuotės detektorių krūvio pernašos savybės. Didžiavaržio silicio detektoriuose po apšvitos reaktoriaus neutronais susidarė visa eilė radiacinių defektų, kuriems priskirtinų giliųjų centrų parametrai buvo įvertinti fotojonizacijos spektroskopijos ir tamsinės srovės temperatūrinių kitimų... [toliau žr. visą tekstą]

Disertacijoje išanalizuoti gilieji centrai didžiavaržiuose Si, SiC ir GaN dariniuose, sietini su didelės energijos protonų bei neutronų spinduliuote sudarytais defektais, atskleistos radiacinių defektų transformacijos po iškaitinimų, didelių energijų spinduliuotės įtaka krūvio pernašai ir pagavai medžiagose, tinkamose jonizuojančiosios spinduliuotės detektoriams, tiriamiems pagal Europos branduolinių tyrimų centro (CERN) projektus. 4H-SiC dariniuose, apšvitintuose 24 GeV/c protonais, išanalizuota elektrinių charakteristikų kaita. Iš šiluma skatinamųjų srovių spektrų nustatytos šiluminės aktyvacijos energijų vertės. Taip pat 4H-SiC dariniuose, apšvitintuose protonų įtėkiais, siekiančiais 1016 cm-2, įvertintas skirtingų spinduliuote sukurtų izotopų kiekis. Neapšvitintose GaN dariniuose nustatyta, kad medžiagos elektrinio laidumo parametrų kaitą nulemia krūvininkų judrio kitimas. Apšvitintuose neutronais GaN dariniuose šiluma skatinamųjų srovių spektroskopijos būdu buvo nustatyti dominuojančių defektų lygmenys. Aptikta, kad po apšvitos 24 GeV/c protonų įtėkiais, siekiančiais 1016 cm-2, GaN susidarė 7Be, 22Na ir kiti ilgaamžiai radionuklidai, kurių atominis skaičius A<70, bei žymiai pakito spinduliuotės detektorių krūvio pernašos savybės. Didžiavaržio silicio detektoriuose po apšvitos reaktoriaus neutronais susidarė visa eilė radiacinių defektų, kuriems priskirtinų giliųjų centrų parametrai buvo įvertinti fotojonizacijos spektroskopijos ir tamsinės srovės temperatūrinių kitimų... [toliau žr. visą tekstą] / Investigations made on new materials and their structures for production of particle detectors based on semi-insulating SiC and GaN comprise the technological and applied importance of this study. Innovations in defect control technology, especially, in recognition of extended defects and percolative carrier transport in heavily irradiated detector structures are considered and applied for scientific implementations. These investigations have been performed within a framework of CERN rd50 project. Irradiation by 24 GeV protons varying fluence up to 1016 cm-2 deteriorates rectifying properties of the 4H-SiC particle detectors. Different isotopes produced in 4H-SiC during irradiation by protons have been revealed by gamma spectroscopy. In the non-irradiated GaN material the temperature-dependent variations of leakage current have been unveiled to be caused by the carrier mobility temperature changes. Activation energy values have been extracted for proton radiation induced deep centres in the GaN detectors by thermally stimulated current spectroscopy as well as the isotopes and long-living radio-nuclides have been identified by gamma spectroscopy. In the Si detectors, irradiated by reactor neutrons, the photo-activation energy values have been determined for the deep levels located below the mid-gap by photo-ionisation spectroscopy while isochronal anneals enhance the density of the acceptor-type vacancy-related defects.

The nonlinear optical response of low-temperature (LT) grown GaAs were studied using four-wave mixing techniques. Through measurements of the four-wave mixing response as a function of pulse delay and photon energy, a strong optical response was identi ed associated with the fundamental band gap exciton. These experiments therefore demonstrated the importance of the exciton in understanding the ultrafast nonlinear optical response of LT-GaAs despite the absence of any evidence of the exciton in past linear absorption studies in this material. Measurement of the fourwave mixing response as a function of pulse delay and the polarization states of the two excitation pulses shows that the dominant contribution to the exciton signal is tied to excitation-induced dephasing. Four-wave mixing experiments in which the sample is exposed to an additional laser pulse indicate that the exciton signal may be strongly diminished due to a combination of screening and a reduction in the total dephasing time. The short temporal duration of the above e ect provides evidence of an ultrashort (< 100 fs) electron trapping time in this system tied to arsenic related defects introduced during low-temperature growth. These ndings are of importance to the understanding of the optical properties of LT-GaAs and will aid in the development of optoelectronic devices using this material system.

No description available.

Several acoustic techniques have been used to determine elastic and damping properties of trees, logs and beams. Time of flight (TOF) measurements in the outerwood of 14-year-old Pinus radiata trees showed that pruning operations increased the outerwood stiffness by up to 25% compared with unpruned trees. However, at the most 5% to 10% of the increased stiffness can be explained by the fact that the outerwood of the pruned trees is free of knots, as TOF measurements are little affected by knots. Thus, it is not known what causes the increase of outerwood stiffness in the pruned trees. One possible explanation could be a smaller microfibril angle (MFA) in the S2 layer of the outerwood cells, which would cause a significant increase in stiffness. Thinning operations decreased the outerwood stiffness by up to 8%. In small Eucalyptus nitens and Pinus radiata logs, which had branch nodes and nodal whorls at specific locations, MOE calculations (using the resonance technique) based on different harmonics gave different results. This indicates that defects do interact with acoustic waves. Acoustic tests on laminated beams with artificial defects (holes filled with dowels) at specific locations also had a significant impact on the MOE. Moreover, it was evident that the damping ratio (evaluated from the Q- factor) of the beams increased with increasing diameter of the holes. However, it was found that holes in laminated beams decreased stiffness while branch nodes and nodal whorls increased stiffness. This shows that relatively small defects, occupying a small volume of the beam, have an impact on acoustic measurements. It is not appropriate to base the MOE calculation on a single harmonic, considering that different harmonics investigate different parts of the specimen