Made available in DSpace on 2014-06-11T19:35:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-08-09Bitstream added on 2014-06-13T20:07:27Z : No. of bitstreams: 1 pereira_alj_dr_bauru.pdf: 5282854 bytes, checksum: ce33659a03b871de70411c643f913412 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A busca por um melhor entendimento da inter-relação entre os parâmetros envolvidos no processo de crescimento de filmes de dióxido de titânio (Tio2) e as propriedades estruturais, eletrônicas e magnéticas resultantes foi a principal motivação deste trabalho. Para isso, filmes Ti)2 foram crescidos usando a técnica de RF magnetron sputtering em diferentes condições. Um primeiro conjunto de filmes de Ti)2 não dopados foi depositado com fluxo contínuo de O2. Em outro conjunto, utilizou-se sistemáticas interrupções no fluxo de O2 durante a deposição. O último grupo de amostras foi depositado usando fluxo contínuo O2 e dopagem com Mn. Os filmes do primeiro grupo apresentaram morfologia colunar com estrutura majoritariamente anatase e com gap óptico de ~3,3 eV, independente da temperatura dos substratos (450ºC e 600ºC) e da razão Ar/O2 utilizada. A diminuição do fluxo de O2 provocou um aumento da absorção sub-gap que foi associada a um aumento dos defeitos eletrônicos no material. Um tratamento térmico em vácuo a 800ºC, realizado sobre filmes de TiO2 puros, revelou um aumento da fração rutila e da absorção óptica, o que também foi associado a um aumento da concentração de defeitos eletrônicos. A análise dos filmes onde o fluxo de oxigênio foi sistematicamente interrompido durante a deposição mostrou que o aumento no número de interrupções não interferiu significativamente na morfologia colunar dos filmes, mas produziu um considerável aumento na fração rutila dos filmes, bem como um aumento na absorção óptica sub-gap. O aumento na absorção na região do visível e infravermelho próximo foi atribuído a um aumento na concentração de defeitos que, de acordo com cálculos baseados na teoria do funcional da densidade, estão relacionados a estados de energia provenientes de vacâncias de oxigênio. Os filmes de TiO2 dopados com diferentes concentrações de Mn pertencentes ao terceiro grupo também / The search for a better understanding of the interrelation between the parameters involved in the process of film growth and the resulting structural, electronic and magnetic properties was the main motivation of this work. To the purpose, TiO2 films were grown by RF magnetron sputtering technique in different conditions. In a first set, TiO2 films were deposited with continuous O2 flow. In another set, systematic interruptions in the O2 flow were performed during the deposition. The last group of samples was deposited using a continuous O2 flow and Mn doping. A detailed analysis of the first group showed that these films exhibit columnar morphology with mainly anatase structure and optical gap of ~3.3eV, independent of the substrate temperature (450ºC and 600ºC) and the ratio used. THe decrease in O2 flux caused an increase in the sug gap absorption which associated with the increase in electronic defects of the material. Anneling in vacuum at 800ºC performed on pure TiO2 films showed an increase in the rutilo fraction, a red shift of the optical absorption edge, and an increase of the sub gap absorption associated with the increase of the electronic defects. The analysis of the films were the O2 flow was systematically interrupted during the deposition showed that the increase in the number of interruptions did not interfere significantly in the columnar morphology, but produced a significant increase in the fraction of rutile and brookite as well as an increase in sub-gap absorption. The increase in absorption in the visible and near infrared was attributable to an increase in the concentration of defects that, according to calculations based on the density functional theory, should be related to energy states provides by O vacancies. The Mn doped films also present a compact columnar morphology and a strong and systematic favoring of the rutile... (Complete abstract click electronic access below)

Growing demand for clean source of energy in the recent years has increased the manufacture of solar cells for converting sun energy directly into electricity. Research has been carried out around the world to make a cheaper and more efficient solar cell technology by employing new architectural designs and developing new materials to serve as light absorbers and charge carriers. Aluminum doped Zinc Oxide thin film, a Transparent conductive Oxides (TCO) is used as a window material in the solar cell these days. Its increased stability in the reduced ambient, less expensive and more abundance make it popular among the other TCO’s. It is the aim of this work to obtain a significantly low resistive ZnO:Al thin film with good transparency. Detailed electrical and materials studies is carried out on the film in order to expand knowledge and understanding. RF magnetron sputtering has been carried out at various substrate temperatures using argon, oxygen and hydrogen gases with various ratios to deposit this polycrystalline films on thermally grown SiO2 and glass wafer. The composition of the films has been determined by Xray Photoelectron Spectroscopy and the identification of phases present have been made using X-ray diffraction experiment. Surface imaging of the film and roughness calculations are carried out using Scanning Electron Microscopy and Atomic Force Microscopy respectively. Determination of resistivity using 4-Probe technique and transparency using UV spectrophotometer were carried out as a part of electrical and optical characterization on the obtained thin film.The deposited thin films were later annealed in vacuum at various high temperatures and the change in material and electrical properties were analyzed.

Molybdenum (Mo) thin film back contact layers for thin film CuIn(1-x)GaxSe2 (CIGS) solar cells were deposited onto soda lime glass substrates using a direct current (DC) planar magnetron sputtering deposition technique. Requirements for the Mo thin film as a back contact layer for CIGS solar cells are various. Sheet resistance, contact resistance to the CIGS absorber, optical reflectance, surface morphology, and adhesion to the glass substrate are the most important properties that the Mo thin film back contact layer must satisfy. Experiments were carried out under various combinations of sputtering power and working gas pressure, for it is well known that mechanical, morphological, optical, and electrical property of a sputter-deposited Mo thin film are dependent on these process parameters. Various properties of each Mo film were measured and discussed. Sheet resistances were measured using a four-point probe equipment and minimum value of 0.25 Ω/sq was obtained for the 0.6 µm-thick Mo film. Average surface roughnesses of each Mo film ranged from 15 to 26 Å were measured by Dektak profilometer which was also employed to measure film thicknesses. Resistivities were calculated from the sheet resistance and film thickness of each film. Minimum resistivity of 11.9 µΩ∙cm was obtained with the Mo thin film deposited at 0.1 mTorr and 250 W. A residual stress analysis was conducted with a bending beam technique with very thin glass strips, and maximum tensile stress of 358 MPa was obtained; however, films did not exhibit a compressive stress. Adhesive strengths were examined for all films with a "Scotch-tape" test, and all films showed a good adhesion to the glass substrate. iv Sputter-deposited Mo thin films are commonly employed as a back contact layer for CIGS and CuInSe2 (CIS)-based solar cells; however, there are several difficulties in fabricating a qualified back contact layer. Generally, Mo thin films deposited at higher sputtering power and lower working gas pressure tend to exhibit lower resistivity; however, such films have a poor adhesion to the glass substrate. On the other hand, films deposited at lower power and higher gas pressure tend to have a higher resistivity, whereas the films exhibit an excellent adhesion to the glass substrate. Therefore, it has been a practice to employ multi-layered Mo thin film back contact layers to achieve the properties of good adhesion to the glass substrate and low resistivity simultaneously. However, multi layer processes have a lower throughput and higher fabricating cost, and requires more elaborated equipment compared to single layer processes, which are not desirable from the industrial point of view. As can be seen, above mentioned process parameters and the corresponding Mo thin film properties are at the two extreme ends of the spectrum. Hence experiments were conducted to find out the mechanisms which influence the properties of Mo thin films by changing the two process parameters of working gas pressure and sputtering power individually. The relationships between process parameters and above mentioned properties were studied and explained. It was found that by selecting the process parameters properly, less resistive, appropriatesurfaced, and highly adhesive single layer Mo thin films for CIGS solar cells can be achieved.

With the advent of the 21st century, one of the serious problems facing mankind is harmful effects of global warming. Add to that the ever increasing cost of fuel and the importance of development of clean energy resources as alternative to fossil fuel has becomes one of the prime and pressing challenges for modern science and technology in the 21st century. Recent studies have shown that energy related sources account for 50% of the total emission of carbon dioxide in the atmosphere. All research activities are focused on developing various technologies that are capable of converting sunlight into electricity with high efficiency and can be produced using a cost-effective process. One of such technologies is the CuIn1-xGaxSe2 (CIGS) and its alloys that can be produced using cost-effective techniques and also exhibit high photo-conversion efficiency. The work presented here discusses some of the fundamental issues related to high volume production of CIGS thin film solar cells. Three principal issues that have been addressed in this work are effect of reduction in absorber thickness on device performance, micrononuniformity involved with amount of sodium and its effect on device performance and lastly the effect of working distance on the properties of molybdenum back contact. An effort has been made to understand the effect of absorber thickness on PV parameters and optimize the process parameters accordingly. Very thin (

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography : leaves 72-73. / M.S.

No description available.

Heterojunctions of n-ZnO/p-Si solar cells were fabricated by RF sputtering ZnO:Al onto boron-doped (100) silicon (Si) substrates. Zinc Oxide (ZnO) films were also deposited onto soda lime glass for electrical measurements. Sheet resistance measurements were performed with a four-point-probe on the glass samples. Values for samples evacuated for 14 hours prior to deposition increased from 7.9 to 10.17 and 11.5 O/□ for 40 W, 120 and 160 W in RF power respectively. In contrast, those evacuated for 2 hours started with a higher value of 22.5 O/□, and decreased down to 7.6 and 5.8 O/□. Vacuum annealing was performed for both the glass and the Si samples. Current-voltage measurements were performed on the ZnO/Si junctions in the dark and under illumination. Parameters such as open-circuit voltage, Voc; short-circuit current, Isc; fill factor, FF; and efficiency, eta were determined. A maximum efficiency of 0.25% among all samples was produced, with an I sc of 2.16 mA, Voc of 0.31V and a FF of 0.37. This was a sample fabricated at an RF power of 80 W. Efficiency was found to decline with vacuum annealing. Furthermore, interfacial state density calculated based on capacitance-voltage measurements showed an increase in the value with vacuum annealing. The results found suggest that the interface states may be due to an interdiffusion of atoms, possibly those of Zn into the Si surface. The Electron Beam Induced Current (EBIC) method was used to determine diffusion length to be at a value ∼40--80 mum and therefore a minority carrier lifetime calculated of 3 musec. It was also used to determine the surface recombination velocity (SRV) of the fractured surface of the Si bulk from the fabricated solar cells. An SRV of ∼500 cm/sec was determined from the fractured Si surface, at a point located at 30 and 20 mum away from the junction interface.

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Solid lubricant coatings with controlled microstructures are good candidates in providing lubricity in moving mechanical assembly applications, such as orthopedics and bearing steels. Nanocrystalline ZnO coatings with a layered wurtzite crystal structure have the potential to function as a lubricious material by its defective structure which is controlled by sputter deposition. The interrelationships between sputtered ZnO, its nanocrystalline structure and its lubricity will be discussed in this thesis. The nanocrystalline ZnO coatings were deposited on silicon substrates and Ti alloys by RF magnetron sputtering with different substrate adhesion layers, direct current biases, and temperatures. X-ray diffraction identified that the ZnO (0002) preferred orientation was necessary to achieve low sliding friction and wear along with substrate biasing. In addition, other analyses such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were utilized to study the solid lubrication mechanisms responsible for low friction and wear.

No description available.