No description available.

Summary in English. / Bibliography: pages 102-118. / Synthetic diamonds are successfully substituting for natural diamonds in the area of industrial application. Synthetic diamonds increased their market share from 10% in 1960 to 50% in 1968 and to 90% in 1994. The success of synthetic diamonds may be ascribed largely to technological advance in the area of diamond manufacture. Two technologies in particular contributed to this advance: (i) High pressure and high temperature (HPHT) processes for crystallising carbon material and (ii) chemical vapour deposition (CVD) of these materials. The substitution of synthetic for natural diamond occurred in a systematic and predictable manner. Further technological advance could threaten the concept of diamond as a unique and desirable substance in the minds of the consumers and may require the repositioning of its image.

Abstract A range of di®erent high-quality single crystal diamonds synthesized under high pressure and high temperature (HPHT) conditions have been studied in view of their potential as candidates for specialized electronic devices with emphasis on particle detectors. The studies incorporated a long range of spectroscopic and electronic characterization techniques. Special attention was given to electronic properties and device performance re- lated to the electrical contacts applied, the type and the concentration of impur- ities and the crystallographic defects present. The electronic response of a dia- mond detector as far as impurities are concerned is predominantly determined by the single substitutional nitrogen (SSN) and boron acceptors. Di®erent tech- niques were used to assess the role of such impurities in the diamond crystals stud- ied, as well as to study the dynamics due to the interaction of such impurities with each other (compensation). Hence, the electron spin resonance (ESR) and the current-deep level transient spectroscopy (I-DLTS) techniques were used in this re- spect to extract the information concerning activation energies, nitrogen-boron dy- namics, and the nitrogen and boron concentrations. ii iii It was found that the SSN content was below 1013 cm¡3 with this result giving the approximate concentration of boron acceptors, being the same value as of that of the SSN, or slightly above. Maximum activation energies of boron acceptors were extracted from three di®erent regions in the bulk of the diamond. The values were approximately 0.311 eV § 0.0027 eV in the center region, 0.308 eV § 0.007 eV in the intermediate region and 0.29 eV § 0.007 eV at the edge region, respectively. The maximum activation energy when boron is fully compensated is about 0.37 eV. Properties of ohmic and Schottky contacts as a function of concentration of SSN and boron acceptors were investigated using Current-Voltage characteristic and photo- current measurements. Di®erent surface treatment conditions and di®erent types of diamonds (IIa, IIb and Ib) were used. Electronic properties as a function of contacts were assessed for high purity synthetic type IIa diamond detector, incorporating a time of °ight (TOF) UV laser set-up. The maximum hole collection distance at room temperature was found to be 91.00 cm, the maximum transient time for holes was about 1.00 ms and the e±ciency was approximately 41%, with contacts made of Ti/Pt/Au-Ru. When Ru-Ru contacts are applied, the maximum hole mobility and the velocity were extracted at room temperature to be about 17963.44 cm2V¡1s¡1 and 5.02 £107 cms¡1, respectively, and the e±ciency of the device is about 30%. The maximum applied external electric ¯elds with Ru-Ru contacts were increased to about 1.32 times that at low temperature and to about 1.84 times that at room temperature. iv Large signals generated by ®-particles from 228Th were obtained without using amp- li¯cation. However, a full analysis of the pulse was not possible due to the narrow bandwidth of the electronic probes used. In a detector made of type Ib diamond, with SSN concentrations of about 50 ppm, it was found that regions in the bulk exhibiting better charge collection properties contained small concentrations of uncompensated boron impurity. On the other hand, the di®erence in the concentrations of SSN between the two type Ib diamonds, with about 50 ppm and about 200 ppm of SSN concentrations, respectively, resulted in approximately 70 ps di®erence in the transit time between two detectors made of these diamonds. Keywords: Synthetic diamond, detector, HPHT, type Ib, type IIa, single substitutional ni- trogen, SSN, ESR, ARP, I-DLTS, metallization, uncompensated boron impurity, crystallographic defects, rise and decay times, charge carrier life time, charge carrier mobility, carrier mean free path , charge collection distance, carrier Schubweg.

No processo de retificação a dressagem desempenha um papel fundamental, uma vez que ela é responsável pela topografia da superfície de trabalho do rebolo, podendo afetar os resultados da retificação em termos da integridade superficial e precisão dimensional da peça, bem como a confiabilidade do processo. Portanto, como parte integrante da operação de retificação, a dressagem pode melhorar significativamente a qualidade das peças retificadas caso melhores dressadores sejam produzidos. Este trabalho tem o objetivo de estudar as principais características necessárias ao projeto de dressadores sinterizados que utilizam diamantes sintéticos de perfil constante e verificar experimentalmente a distribuição de temperaturas no dressador, obtidas através de ensaios práticos e simulação computacional pelo método dos elementos finitos. O modelo utilizado contém algumas limitações, porém os resultados obtidos mostraram que os níveis de temperaturas no dressador foram afetados pelos parâmetros de dressagem considerados no trabalho, a saber, a profundidade de dressagem (\'a IND. d\'), o grau de recobrimento de dressagem (\'U IND. d\') e a vazão do fluido refrigerante (Q). O desgaste do dressador foi afetado apenas pelos parâmetros de dressagem. / In grinding operations, dressing tools are of major importance, since they are responsible for the topography of the wheel working surface and, consequently, can affect the grinding results in terms of surface integrity, dimensional accuracy and process reliability. Therefore, as an important part of the grinding operation, dressing can significantly improve the quality of ground parts if better dressing tools are produced. This work studies the main needs for designing sintered dressing tools made with constant cross sectional synthetic diamonds. It also analyses the temperature distribution over a novel dressing tool design using experimental measurements to feed computacional simulation by the finite element method (FEM). The temperature model employed showed some limitations but the obtained results indicated that temperature levels over the dressing tool were affected by the dressing parameters considered in this work, namely the dressing depth of cut (\'a IND. d\'), the dressing overlapping parameter (\'U IND. d\') and the flow rate (Q). Additionally, one can say that the dressing tool wear was affected only by the dressing parameters

No processo de retificação a dressagem desempenha um papel fundamental, uma vez que ela é responsável pela topografia da superfície de trabalho do rebolo, podendo afetar os resultados da retificação em termos da integridade superficial e precisão dimensional da peça, bem como a confiabilidade do processo. Portanto, como parte integrante da operação de retificação, a dressagem pode melhorar significativamente a qualidade das peças retificadas caso melhores dressadores sejam produzidos. Este trabalho tem o objetivo de estudar as principais características necessárias ao projeto de dressadores sinterizados que utilizam diamantes sintéticos de perfil constante e verificar experimentalmente a distribuição de temperaturas no dressador, obtidas através de ensaios práticos e simulação computacional pelo método dos elementos finitos. O modelo utilizado contém algumas limitações, porém os resultados obtidos mostraram que os níveis de temperaturas no dressador foram afetados pelos parâmetros de dressagem considerados no trabalho, a saber, a profundidade de dressagem (\'a IND. d\'), o grau de recobrimento de dressagem (\'U IND. d\') e a vazão do fluido refrigerante (Q). O desgaste do dressador foi afetado apenas pelos parâmetros de dressagem. / In grinding operations, dressing tools are of major importance, since they are responsible for the topography of the wheel working surface and, consequently, can affect the grinding results in terms of surface integrity, dimensional accuracy and process reliability. Therefore, as an important part of the grinding operation, dressing can significantly improve the quality of ground parts if better dressing tools are produced. This work studies the main needs for designing sintered dressing tools made with constant cross sectional synthetic diamonds. It also analyses the temperature distribution over a novel dressing tool design using experimental measurements to feed computacional simulation by the finite element method (FEM). The temperature model employed showed some limitations but the obtained results indicated that temperature levels over the dressing tool were affected by the dressing parameters considered in this work, namely the dressing depth of cut (\'a IND. d\'), the dressing overlapping parameter (\'U IND. d\') and the flow rate (Q). Additionally, one can say that the dressing tool wear was affected only by the dressing parameters