Introduction Liquid targets using top-of-foil loading concept have been succesfully employed for routine high current production of 18F and 13N at Cyclotope (Houston,TX), over the past ten years1,2. These targets are typically filled with 3.5 ml of water, then pressurized with helium gas at 22 bar and bombarded with 18MeV protons (70–100 µA). Average calculated saturation yield for produc-tion of 18F is ~7.8 GBq/µA (210 mCi/µA) using in-house recycled [18O]-water at approximately 93% enrichment. Reduction of beam power per unit of area is one of the advantages of a tilted entrance-foil geo-metry. Implementation of this target geometry on the ACSI TR19 cyclotron 25degrees upwards irradiation port results in an almost horizontal target entrance foil. A 6ml total cavity volume target allows variable liquid fill volumes of 1.2–4.5 ml for beam current operation from 30–120 µA, resulting in a very efficient use of the costly 18O-water. In a near horizontal installation as in the mayority of cyclotrons, the fill volume flexibility is drastically reduced, having a minimum fill volume of 3.3 ml. At the requirement of Laboratorios Bacon, Cyc-lotope modified the target design with a front mounted collimator compatible with the IBA Cyclone 18/9 cyclotron. A second requirement was to reduce the minimum fill volume for horizontally mounted targets to 2.5 ml or less, while maintaining saturation yield performance. To preserve compatibility with existing IBA targets, the target hardware was modified to operate in self-pressurization mode. This paper presents the results obtained with high and low volume Niobium target inserts (6ml and 4 ml) mounted near horizontally on the IBA Cyclone 18/9 cyclotron and operated in self-pressurization mode. We present pressure/current characteristics, target performance (saturation yield, produced activities, maintenance frequency, FDG yields, etc.). Material and Methods The following targets manufactured by Cyclotope were tested and routinely used for production at Laboratorios Bacon: 1-High Volume Target CY2 model (“American Standard”), 6ml Niobium cavity. 2-Low Volume Target, CY3a model (“Traful”), 4ml Niobium cavity. 3- Low volume Target, CY3b model (“Ferrum”), 4.1ml Niobium cavity. Results and Conclusion The advantages of self-pressurization mode (Laboratorios Bacon setup) are: - Using the vapor pressure as a performance parameter - heat removal by boiling/condensation cycle starts at lower temperature (beam cur-rent) . While, the advantages of the pre-pressurized targets (Cyclotope setup) are: - reduced pressure fluctuations - performance is basically unaffected by plumbing dead volume - flexibility to locate instrumentation farther away from radiation fields - less dependence on fill volume - potential target leaks can be detected before starting an irradiation No significant differences were found in target performance when operated in either pressu-rization mode. The self-pressurizing setup seems to require a sligthly lower fill volume (approxi-mately 5%). The maximum beam current was limited by the foil rupture pressure (~ 40 bar). Safe maximum operating pressure was determined as 30 bar. No foil rupture was experienced during nine months of daily irradiation of these targets in self-pressurizing mode at Laboratorios Bacon. The irradiation parameters and target performance for the different targets are shown in Tables 1 and 2 below. The low volume Traful and Ferrum targets have the best saturation activity vs. fill volume, A(sat)/V, relation. Both targets produce 310 ± 31GBq (8.4 ± 0.8 Ci) of high quali-ty fluoride (F-18) in two hours of irradiation at 70 µA. The low volume targets have a low operation pressure (20bar @ 70µA) when compared to the IBA (NIRTA XL) targets. The typical saturation activity for the low volume targets was 592 ± 59 GBq (16 ± 1.6 Ci) of F-18 at 70 µA, 8.5 GBq/µA (228 mCi/µA) using 2.7ml enriched O-18 water (98 % +). The maintenance interval (> 10 mA.h) is very conveniente to reduce personnel radiation dose. No reduction in FDG yields was observed during that operation interval. In contrast, operation of the high volume targets in pre-presurization mode at the Cyclotope facility results in a higher maximum beam current limit (135 µA) for the same operating pressure (25 bar). Nevertheless, more O-18 water will be required to irradiate at this high current (4.5 ml vs. 3.0 ml). In self-pressurizing mode, a higher filling volume will reduce the expansion volume and, in consequence, the maximum beam current.

Few PET isotopes are suitable for antibody labelling since immunoPET requires that the PET isotope can be attached to the mAb with high in-vivo stability and the decay half-life of the isotope should match the pharmacokinetics of the mAb (Phelps 2004). Both 124I (t½ = 4.2 d) and 89Zr (t½ = 3.3 d) have a near ideal half-life for anti-body-based imaging, but there are several ad-vantages of using 89Zr over 124I. For 124I, the high energy of its positrons (2.13 MeV), results in a relatively low PET image resolution and the possible dehalogenation in vivo can lead to significant radioactivity uptake in non-targeted organs. In comparison, for 89Zr the low energy of its positron (395.5 keV), results in a PET images with a higher spatial resolution and furthermore, 89Zr is a residualizing isotope, which is trapped inside the target cell after internalization of the mAb. One disadvantage of 89Zr is its abundant high energy gamma-ray (909 keV), which may limit the radioactive dose that can be administered to the patients. The most popular reaction to produce 89Zr is the 89Y(p,n)89Zr nuclear reaction (Sahar et al., 1966; Link et al., 1986). A proton beam with 14-16MeV energy is used to bombard inexpensive high-purity 89Y metal target (99.9%), avoiding cumbersome recycling of the target material. The yttrium targets could be either a foil (Dejesus and Nickels, 1990), sputtered onto a copper support (Meijs et al., 1994) or Y2O3 pellets (S. A. Kandil, B. Scholten, 2007). Although 89Zr is currently commercially available, its price is prohibitive for routine clinical applications of 89Zr immuno-PET. The motivation of the present work was the fully automated production of small quantities of 89Zr using commercially available automated systems. We also describe a newly designed and tested platinum cradle, capable of holding a metallic foil and being directly transferable/compatible between the IBA NIRTA target and IBA Pinctada Metal dissolution/purification module. Material and Methods The solid target infrastructure used for 89Zr production was identical to the implementation reported earlier for production of 64Cu and 124I (S. Poniger et al. 2012). The commercially avail-able Nirta Solid Target from IBA was coupled to our 18/9 IBA cyclotron using a 2-meter external beam line. A fully automated pneumatic solid target transfer system (STTS) designed by TEMA Sinergie was used to deliver the irradiated tar-gets to a dedicated hotcell. The newly designed platinum cradle holding the yttrium foil (0.127 mm thick, 8 mm d) is shown in FIG. 1. Typical irradiation parameters were 14.9 MeV at 20 μA for 1.5 hours (90o angle of incidence). The irradiated cradle, containing the 89Zr target is then loaded directly into the IBA Pinctada Metal module (see FIG. 2) for dissolution/purification without disassembly. We used the dissolution/purification method described by Holland et al. 2009, without modification (Purification of 89Zr from 89Y, 88Y and other radionuclidic impurities using a hydroxamate column, with 89Zr eluted with 1.0M Oxalic acid). Radionuclidic purities were evaluated by gamma spectroscopy and traces of metallic impurities were determined by ICP-MS. Results and Conclusion FIGURE 3 shows the gamma spectrum of the purified 89Zr solution. Since yttrium has one stable isotope only, relatively pure 89Zr is produced at low energy (14.9 MeV). In these preliminary non-optimized cyclotron productions, average purified 89Zr yield of 0.34 mCi/μAh was achieved, in comparison to values of 1.5 mCi/μAh found in the literature (10° angle of incidence). In these preliminary experiments, no deformation of the foil was observed at 20 μA beam current and higher currents are under investigation.

In recent decades the arbitration has undergone extensive development in the Peru. However, this did not mean the absence of corruption in the arbitral proceedings. in this article the author points out some examples in which corruption manifests itself within them. Also, possible solutions are addressed with particular emphasis on competition, and its necessary condition: information. On this last, the iBA rules acquire special relevance for the resolution of conflicts of interest. / En las últimas décadas el arbitraje ha experimentado un amplio desarrollo en el Perú. Sin embargo, esto no significó la ausencia de corrupción en los procesos arbitrales. e n el presente artículo el autor señala algunos ejemplos en los que la corrupción se manifiesta dentro de ellos. Asimismo, se abordan sus posibles soluciones, con especial énfasis en la competencia y su condición necesaria: la información. s obre esta última adquieren especial relevancia las Reglas IBA para la resolución de conflictos de intereses.

Les auxines sont des composants clés essentiels pour le contrôle du développement des racines et la réponse aux contraintes environnementales en raison de leur rôle central dans la division, l’élongation et la différenciation cellulaires. L’auxine endogène, acide indole-3-butyrique (IBA), bien que moins abondante et moins connue que l'acide indole-3-acétique (IAA), joue un rôle important dans le développement racinaire, en particulier lors de la formation des racines latérales et de l'élongation des poils absorbants. Il est généralement admis que les fonctions de l’IBA dépendent entièrement de la conversion peroxysomale de l’IBA en IAA. Bien que nos connaissances concernant les enzymes impliquées dans cette conversion soient très avancées, nous en savons peu sur les mode de régulation de ces fonctions. Au cours de ma thèse, j'ai démontré que les fonctions de l’IBA lors de l'induction des racines latérales et de l'élongation des poils absorbants dépendent du glutathion, un petit tripeptide rédox qui constitue l'une des molécules les plus importantes impliquées dans les réponses des plantes au stress oxydatif. De plus, j'ai démontré que le lien entre le glutathion et l'auxine IBA est essentiel pour les réponses à l’auxine dans la zone de transition de la racine primaire. Ce contrôle des fonctions de l’IBA par le glutathion pourrait être déterminant dans des conditions de stress abiotiques telles que la carence en phosphore.Une des fonctions du glutathion étant de réduire des réductases de fonctions thiols, les glutaredoxines (GRX), nous avons recherché si certaines GRX sont impliquées dans le développement racinaire. Nous avons constaté que ROXY19 et GRXS17 sont essentiels à la croissance des racines primaires et que ces deux GRX sont également impliqués, mais dans des rôles différents, lors du développement des racines latérales. Un crible suppresseur des phénotypes racinaires du mutant grxs17 avait été mis en place dans le laboratoire. J'ai utilisé des approches bio-informatiques pour isoler les mutations causales après reséquençage du génome de candidats capables de restaurer la croissance des racines primaires et / ou le développement normal des primordia des racines latérales. Malheureusement, cette approche ne nous a pas encore permis d’isoler de nouveaux acteurs. Cependant, elle jette les bases d’un futur grand progrès dans la compréhension de la manière dont GRXS17 contrôle le système racinaire.En conclusion, les résultats de ma thèse soulignent l’importance du glutathion et des glutarédoxines dans le contrôle de la plasticité du système racinaire et lors de conditions de stress abiotiques, notamment via la modulation de la voie auxinique IBA. / Auxins are critical key components for the control of root development and response to environmental constraints by its pivotal roles in cell division, elongation, and cell differentiation. The endogenous auxin Indole-3-butyric acid (IBA), although less abundant than the better-known Indole-3-Acetic Acid (IAA), plays important roles during root development especially during the formation of lateral roots and root hairs elongation. It is generally accepted that IBA functions are fully dependent on peroxisomal IBA-to-IAA conversion. While there is a great advance in our knowledge regarding the enzymes involved in the peroxisomal conversion of IBA-to-IAA, little is known about the mechanisms that modulate its functions. During my thesis, I demonstrated that the IBA functions during the induction of lateral roots and root hairs elongation are dependent on glutathione, which is a small redox tripeptide that constitutes one of the most important molecules involved in plant responses to oxidative stresses. Moreover, I demonstrated that the link between glutathione and the auxin IBA is critical for the auxin distribution that takes place in the transition zone of the primary root. The relevance of the control of IBA functions by glutathione might be determinant during abiotic stress conditions such as phosphorus deprivation.Since glutathione is a reducer of thiol reductases glutaredoxins (GRXs), we investigate if some GRXs are involved in root development. We found that ROXY19 and GRXS17 are critical for the primary root growth, and both GRX proteins play different roles during the formation of lateral roots. Based on this root phenotype, a suppressor screen in grxs17 background had been set up in the lab. I developed bioinformatic pipelines to isolate causal mutations from genome resequencing of candidates that are able to restore the primary root growth and/or the normal development of lateral roots primordia. Unfortunately, this approach did not yet allow us to isolate new actors, however it builds foundations for future big advance in understanding how glutaredoxins control the root system.In conclusion, the results showed in my Ph.D. thesis highlight the importance of glutathione and glutaredoxins in the control of the root system plasticity and during abiotic stress conditions, particularly via the modulation of the auxinic IBA pathway.

Introduction In last decade increasing demand for clinical F-18 Fludeoxyglucose requires a greater F-18 fluoride production. From the other side increasing price of enriched O-18 water compel us to find the most effective way of F-18 activity production. One of the possible way, how to optimize and increase yield of F-18, is to increasing target current with retaining the same or less volume of enriched water. Optimization of F-18 production on IBA Large Volume cylindrical target is presented. Material and Methods Irradiations of [18O]H2O by 18MeV proton beams with intensities 40–55 μA were performed on CYCLON 18/9, IBA cyclotron and on LV cylindrical IBA target. Irradiated enriched water was transported to the hot cell using RDS (Radioactive Delivery System) system and was measured in Curriementor 4 Isotope Calibrator made by PTW. At the beginning it was necessary to satisfy several requirements: i) target and water cooling. Using a simple two dimensional equation we can roughly estimate the equilibrium temperature inside the target [1]: Δt = HT/Ak where: Δt = the temperature rise in the target chamber over cooling water temperature H = is the heat load T = thickness of metal wall A = area of metal in contact with target water k = thermal conductivity In our case with heat load 720 W (40 μA×18 MeV) is Δt = 78 oC. From the curve of boiling point of water as a function of pressure [2], we can observe t = 212 °C at 20 bar or 243 °C at 35 bar, respectively, which corresponds to max. heat load up to 90–95 µA of target current. ii) pressure and filling water volume. Filling water volume was from 2 to 2.15 ml to guarantee stop all beam in water. Also during experiments for safety reasons the operating pressure was limited to 35 bar as the window rupture pressure is > 50 bar for used 0.05 mm Havar foil. In this case increasing target volume with increasing current was provided with longer tube. Results and Conclusion The saturated yields of F-18 for 40 µA to 55 µA target currents are given in TABLE 1. No systematic decrease in yields with increasing target current was observed and yields were in line with the 230 ± 10 mCi/µA measured at acceptance test of target. The [18F]FDG yields from productions using the TRACERlab-Mx module are shown in FIGURE 1. All presented productions of F-18 were prepared with LV target with 55 µA. No decrease in the yield was observed with increasing beam current. It has been demonstrated that it is possible to produce routinely 250 GBq/2hr (6.8 Ci/2hr) of 18F-Fluoride using LV cylindrical target (operating conditions: 55 µA, 18 MeV, 98% enriched water). As the next step we want to test dual beam – 2×55 µA with two LV targets and expected activity about 500 GBq of 18F-Fluoride in 2 hours is expected.

Introduction Liquid targets using top-of-foil loading concept have been succesfully employed for routine high current production of 18F and 13N at Cyclotope (Houston,TX), over the past ten years1,2. These targets are typically filled with 3.5 ml of water, then pressurized with helium gas at 22 bar and bombarded with 18MeV protons (70–100 µA). Average calculated saturation yield for produc-tion of 18F is ~7.8 GBq/µA (210 mCi/µA) using in-house recycled [18O]-water at approximately 93% enrichment. Reduction of beam power per unit of area is one of the advantages of a tilted entrance-foil geo-metry. Implementation of this target geometry on the ACSI TR19 cyclotron 25degrees upwards irradiation port results in an almost horizontal target entrance foil. A 6ml total cavity volume target allows variable liquid fill volumes of 1.2–4.5 ml for beam current operation from 30–120 µA, resulting in a very efficient use of the costly 18O-water. In a near horizontal installation as in the mayority of cyclotrons, the fill volume flexibility is drastically reduced, having a minimum fill volume of 3.3 ml. At the requirement of Laboratorios Bacon, Cyc-lotope modified the target design with a front mounted collimator compatible with the IBA Cyclone 18/9 cyclotron. A second requirement was to reduce the minimum fill volume for horizontally mounted targets to 2.5 ml or less, while maintaining saturation yield performance. To preserve compatibility with existing IBA targets, the target hardware was modified to operate in self-pressurization mode. This paper presents the results obtained with high and low volume Niobium target inserts (6ml and 4 ml) mounted near horizontally on the IBA Cyclone 18/9 cyclotron and operated in self-pressurization mode. We present pressure/current characteristics, target performance (saturation yield, produced activities, maintenance frequency, FDG yields, etc.). Material and Methods The following targets manufactured by Cyclotope were tested and routinely used for production at Laboratorios Bacon: 1-High Volume Target CY2 model (“American Standard”), 6ml Niobium cavity. 2-Low Volume Target, CY3a model (“Traful”), 4ml Niobium cavity. 3- Low volume Target, CY3b model (“Ferrum”), 4.1ml Niobium cavity. Results and Conclusion The advantages of self-pressurization mode (Laboratorios Bacon setup) are: - Using the vapor pressure as a performance parameter - heat removal by boiling/condensation cycle starts at lower temperature (beam cur-rent) . While, the advantages of the pre-pressurized targets (Cyclotope setup) are: - reduced pressure fluctuations - performance is basically unaffected by plumbing dead volume - flexibility to locate instrumentation farther away from radiation fields - less dependence on fill volume - potential target leaks can be detected before starting an irradiation No significant differences were found in target performance when operated in either pressu-rization mode. The self-pressurizing setup seems to require a sligthly lower fill volume (approxi-mately 5%). The maximum beam current was limited by the foil rupture pressure (~ 40 bar). Safe maximum operating pressure was determined as 30 bar. No foil rupture was experienced during nine months of daily irradiation of these targets in self-pressurizing mode at Laboratorios Bacon. The irradiation parameters and target performance for the different targets are shown in Tables 1 and 2 below. The low volume Traful and Ferrum targets have the best saturation activity vs. fill volume, A(sat)/V, relation. Both targets produce 310 ± 31GBq (8.4 ± 0.8 Ci) of high quali-ty fluoride (F-18) in two hours of irradiation at 70 µA. The low volume targets have a low operation pressure (20bar @ 70µA) when compared to the IBA (NIRTA XL) targets. The typical saturation activity for the low volume targets was 592 ± 59 GBq (16 ± 1.6 Ci) of F-18 at 70 µA, 8.5 GBq/µA (228 mCi/µA) using 2.7ml enriched O-18 water (98 % +). The maintenance interval (> 10 mA.h) is very conveniente to reduce personnel radiation dose. No reduction in FDG yields was observed during that operation interval. In contrast, operation of the high volume targets in pre-presurization mode at the Cyclotope facility results in a higher maximum beam current limit (135 µA) for the same operating pressure (25 bar). Nevertheless, more O-18 water will be required to irradiate at this high current (4.5 ml vs. 3.0 ml). In self-pressurizing mode, a higher filling volume will reduce the expansion volume and, in consequence, the maximum beam current.

Few PET isotopes are suitable for antibody labelling since immunoPET requires that the PET isotope can be attached to the mAb with high in-vivo stability and the decay half-life of the isotope should match the pharmacokinetics of the mAb (Phelps 2004). Both 124I (t½ = 4.2 d) and 89Zr (t½ = 3.3 d) have a near ideal half-life for anti-body-based imaging, but there are several ad-vantages of using 89Zr over 124I. For 124I, the high energy of its positrons (2.13 MeV), results in a relatively low PET image resolution and the possible dehalogenation in vivo can lead to significant radioactivity uptake in non-targeted organs. In comparison, for 89Zr the low energy of its positron (395.5 keV), results in a PET images with a higher spatial resolution and furthermore, 89Zr is a residualizing isotope, which is trapped inside the target cell after internalization of the mAb. One disadvantage of 89Zr is its abundant high energy gamma-ray (909 keV), which may limit the radioactive dose that can be administered to the patients. The most popular reaction to produce 89Zr is the 89Y(p,n)89Zr nuclear reaction (Sahar et al., 1966; Link et al., 1986). A proton beam with 14-16MeV energy is used to bombard inexpensive high-purity 89Y metal target (99.9%), avoiding cumbersome recycling of the target material. The yttrium targets could be either a foil (Dejesus and Nickels, 1990), sputtered onto a copper support (Meijs et al., 1994) or Y2O3 pellets (S. A. Kandil, B. Scholten, 2007). Although 89Zr is currently commercially available, its price is prohibitive for routine clinical applications of 89Zr immuno-PET. The motivation of the present work was the fully automated production of small quantities of 89Zr using commercially available automated systems. We also describe a newly designed and tested platinum cradle, capable of holding a metallic foil and being directly transferable/compatible between the IBA NIRTA target and IBA Pinctada Metal dissolution/purification module. Material and Methods The solid target infrastructure used for 89Zr production was identical to the implementation reported earlier for production of 64Cu and 124I (S. Poniger et al. 2012). The commercially avail-able Nirta Solid Target from IBA was coupled to our 18/9 IBA cyclotron using a 2-meter external beam line. A fully automated pneumatic solid target transfer system (STTS) designed by TEMA Sinergie was used to deliver the irradiated tar-gets to a dedicated hotcell. The newly designed platinum cradle holding the yttrium foil (0.127 mm thick, 8 mm d) is shown in FIG. 1. Typical irradiation parameters were 14.9 MeV at 20 μA for 1.5 hours (90o angle of incidence). The irradiated cradle, containing the 89Zr target is then loaded directly into the IBA Pinctada Metal module (see FIG. 2) for dissolution/purification without disassembly. We used the dissolution/purification method described by Holland et al. 2009, without modification (Purification of 89Zr from 89Y, 88Y and other radionuclidic impurities using a hydroxamate column, with 89Zr eluted with 1.0M Oxalic acid). Radionuclidic purities were evaluated by gamma spectroscopy and traces of metallic impurities were determined by ICP-MS. Results and Conclusion FIGURE 3 shows the gamma spectrum of the purified 89Zr solution. Since yttrium has one stable isotope only, relatively pure 89Zr is produced at low energy (14.9 MeV). In these preliminary non-optimized cyclotron productions, average purified 89Zr yield of 0.34 mCi/μAh was achieved, in comparison to values of 1.5 mCi/μAh found in the literature (10° angle of incidence). In these preliminary experiments, no deformation of the foil was observed at 20 μA beam current and higher currents are under investigation.

Introduction In last decade increasing demand for clinical F-18 Fludeoxyglucose requires a greater F-18 fluoride production. From the other side increasing price of enriched O-18 water compel us to find the most effective way of F-18 activity production. One of the possible way, how to optimize and increase yield of F-18, is to increasing target current with retaining the same or less volume of enriched water. Optimization of F-18 production on IBA Large Volume cylindrical target is presented. Material and Methods Irradiations of [18O]H2O by 18MeV proton beams with intensities 40–55 μA were performed on CYCLON 18/9, IBA cyclotron and on LV cylindrical IBA target. Irradiated enriched water was transported to the hot cell using RDS (Radioactive Delivery System) system and was measured in Curriementor 4 Isotope Calibrator made by PTW. At the beginning it was necessary to satisfy several requirements: i) target and water cooling. Using a simple two dimensional equation we can roughly estimate the equilibrium temperature inside the target [1]: Δt = HT/Ak where: Δt = the temperature rise in the target chamber over cooling water temperature H = is the heat load T = thickness of metal wall A = area of metal in contact with target water k = thermal conductivity In our case with heat load 720 W (40 μA×18 MeV) is Δt = 78 oC. From the curve of boiling point of water as a function of pressure [2], we can observe t = 212 °C at 20 bar or 243 °C at 35 bar, respectively, which corresponds to max. heat load up to 90–95 µA of target current. ii) pressure and filling water volume. Filling water volume was from 2 to 2.15 ml to guarantee stop all beam in water. Also during experiments for safety reasons the operating pressure was limited to 35 bar as the window rupture pressure is > 50 bar for used 0.05 mm Havar foil. In this case increasing target volume with increasing current was provided with longer tube. Results and Conclusion The saturated yields of F-18 for 40 µA to 55 µA target currents are given in TABLE 1. No systematic decrease in yields with increasing target current was observed and yields were in line with the 230 ± 10 mCi/µA measured at acceptance test of target. The [18F]FDG yields from productions using the TRACERlab-Mx module are shown in FIGURE 1. All presented productions of F-18 were prepared with LV target with 55 µA. No decrease in the yield was observed with increasing beam current. It has been demonstrated that it is possible to produce routinely 250 GBq/2hr (6.8 Ci/2hr) of 18F-Fluoride using LV cylindrical target (operating conditions: 55 µA, 18 MeV, 98% enriched water). As the next step we want to test dual beam – 2×55 µA with two LV targets and expected activity about 500 GBq of 18F-Fluoride in 2 hours is expected.

Im Mittelpunkt der vorliegenden Arbeit steht die Herstellung ultradünner epitaktischer Galliumnitrid-Schichten auf einem Siliziumkarbid-Substrat mit dem Verfahren der ionenstrahlgestützten Molekularstrahlepitaxie. Für die Analyse der Oberflächentopographie der Galliumnitrid-Schichten direkt nach der Abscheidung – ohne Unterbrechung der Ultrahochvakuum-Bedingungen – wurde ein Rastersondenmikroskop in die Anlage integriert. Als weitere Hauptanalysenmethode wurde die Reflexionsbeugung hochenergetischer Elektronen zur Bestimmung der Oberflächenstrukturen in situ während der Schichtabscheidung eingesetzt. Weiterhin wurden die Galliumnitrid-Schichten hinsichtlich ihrer strukturellen Eigenschaften mittels Röntgenstrahl-Diffraktometrie, Röntgen-Photoelektronenspektroskopie und Transmissionselektronenmikroskopie ex situ charakterisiert. Wesentliches Ziel dieser Arbeit war die Herausstellung des Einflusses maßgeblicher Abscheidungsparameter (vor allem Substrattemperatur und Gallium-Depositionsrate) auf die Schichteigenschaften sowie die Optimierung dieser Wachstumsparameter. Besonderes Augenmerk lag auf der Untersuchung der Auswirkungen des Stickstoffion-zu-Galliumatom-Verhältnisses und des Einflusses der niederenergetischen Ionenbestrahlung auf das Galliumnitrid-Schichtwachstum im Frühstadium. Dies betrifft hauptsächlich den Wachstumsmodus (zwei- oder dreidimensional) und die Bildung der hexagonalen oder der kubischen Phase.

Im Mittelpunkt der vorliegenden Arbeit steht die Herstellung ultradünner epitaktischer Galliumnitrid-Schichten auf einem Siliziumkarbid-Substrat mit dem Verfahren der ionenstrahlgestützten Molekularstrahlepitaxie. Für die Analyse der Oberflächentopographie der Galliumnitrid-Schichten direkt nach der Abscheidung – ohne Unterbrechung der Ultrahochvakuum-Bedingungen – wurde ein Rastersondenmikroskop in die Anlage integriert. Als weitere Hauptanalysenmethode wurde die Reflexionsbeugung hochenergetischer Elektronen zur Bestimmung der Oberflächenstrukturen in situ während der Schichtabscheidung eingesetzt. Weiterhin wurden die Galliumnitrid-Schichten hinsichtlich ihrer strukturellen Eigenschaften mittels Röntgenstrahl-Diffraktometrie, Röntgen-Photoelektronenspektroskopie und Transmissionselektronenmikroskopie ex situ charakterisiert. Wesentliches Ziel dieser Arbeit war die Herausstellung des Einflusses maßgeblicher Abscheidungsparameter (vor allem Substrattemperatur und Gallium-Depositionsrate) auf die Schichteigenschaften sowie die Optimierung dieser Wachstumsparameter. Besonderes Augenmerk lag auf der Untersuchung der Auswirkungen des Stickstoffion-zu-Galliumatom-Verhältnisses und des Einflusses der niederenergetischen Ionenbestrahlung auf das Galliumnitrid-Schichtwachstum im Frühstadium. Dies betrifft hauptsächlich den Wachstumsmodus (zwei- oder dreidimensional) und die Bildung der hexagonalen oder der kubischen Phase.:Kapitel 1 1 Einführung 1 Kapitel 2 5 Grundlagen 5 2.1 Kristallstruktur und Eigenschaften von Galliumnitrid 5 2.2 Wechselwirkung niederenergetischer Ionen mit der Oberfläche 8 2.2.1 Energiefenster für die optimale ionenstrahlgestützte Epitaxie 9 2.3 Einfluss der Teilchenenergie auf die Oberflächenmobilität 11 2.3.1 Strukturzonenmodelle 11 2.3.2 Thermisch induzierte Oberflächenmobilität 13 2.3.3 Ballistisch induzierte Oberflächenmobilität 14 2.4 Herstellungsverfahren 15 2.4.1 Metallorganische Gasphasenepitaxie 15 2.4.2 Molekularstrahlepitaxie 16 2.4.3 Ionenstrahlgestützte Molekularstrahlepitaxie 17 2.5. Schichtwachstum 18 2.5.1 Frühstadium des Wachstums 18 2.5.2 Wachstumsmodi 20 2.5.3 Wachstum an Stufen 21 2.5.4 Ionenstrahlgestütztes GaN-Wachstum 23 2.6 Modellsystem GaN auf 6H-SiC 25 2.6.1 Epitaxiebeziehungen von GaN-Schicht und 6H-SiC(0001)-Substrat 25 2.6.2 Schichtspannungen 28 Kapitel 3 32 Experimentelle Bedingungen 32 3.1 Experimenteller Aufbau 32 3.1.1 UHV-Anlage zur ionenstrahlgestützten Abscheidung 32 3.1.2 Gallium-Effusionszelle 33 3.1.3 Stickstoff-Hohlanoden-Ionenquelle 34 3.1.4 RHEED-System 35 3.1.5 UHV-STM 37 3.2 Probenherstellung 40 3.2.1 Vorbehandlung 40 3.2.2 Abscheide- und Ionenstrahlparameter 41 3.3 Charakterisierung 43 3.3.1 Kristallographische Struktur 44 Reflexionsbeugung hochenergetischer Elektronen 44 Röntgenstrahl-Diffraktometrie 49 Röntgenstrahl-Reflektometrie 52 Transmissionselektronenmikroskopie 53 3.3.2 Oberflächentopographie 54 Rastertunnelmikroskopie 54 Rasterelektronenmikroskopie 56 3.3.3 Chemische Zusammensetzung 57 Röntgen-Photoelektronenspektroskopie 57 Kapitel 4 59 Ergebnisse und Diskussion 59 4.1 GaN-Wachstum auf 6H-SiC(0001) bei Variation des Ion/Atom-Verhältnisses 59 4.1.1 Oberflächenstruktur und Oberflächentopographie 59 4.1.2 Kristallographische Struktur und chemische Zusammensetzung 63 4.1.3 Diskussion: Einfluss des I/A-Verhältnisses 70 4.2 Inselwachstum: Oberflächenstruktur und Oberflächentopographie 74 4.2.1 Einfluss des I/A-Verhältnisses 75 4.2.2 Einfluss der Substrattemperatur 75 4.2.3 Einfluss der Depositionsdauer 78 4.2.4 Diskussion: Einfluss von I/A-Verhältnis, Depositionsdauer und Substrattemperatur auf die Oberflächentopographie der 3D-GaN-Schichten 82 4.3 Inselwachstum: Kristallographische Struktur und Morphologie 84 4.3.1 Morphologie der inselförmigen GaN-Schichten 84 4.3.2 Gitteranpassung und mechanische Spannungen 86 4.3.3 Diskussion: Kubisches GaN und Spannungsaufbau 88 4.4 Zweidimensionales Schichtwachstum: Oberflächenstruktur und Oberflächentopographie 90 4.4.1 Einfluss des I/A-Verhältnisses 90 4.4.2 Oberflächentopographie ultradünner 2D-Schichten 93 4.4.3 Einfluss der Depositionsdauer 96 4.4.4 Einfluss der Substrattemperatur 99 4.4.5 Diskussion: Einfluss von I/A-Verhältnis, Depositionsdauer und Substrattemperatur auf die Oberflächentopographie der 2D-GaN-Schichten 102 4.5 Zweidimensionales Schichtwachstum: Kristallographie und Morphologie 106 4.5.1 Einfluss des I/A-Verhältnisses 106 4.5.2 Einfluss der Depositionsdauer 107 4.5.3 Einfluss der Substrattemperatur 109 4.5.4 Morphologie und Gitterfehlanpassung 112 4.5.5 Koaleszenz von Inseln im Anfangswachstum 116 4.5.6 Diskussion: Einfluss von I/A-Verhältnis, Depositionsdauer und Substrattemperatur auf Struktur und Morphologie der 2D-GaN-Schichten 119 4.6 Moduswechsel von 3D- zu 2D-Wachstum bei sequenzieller Abscheidung unter Verringerung des I/A-Verhältnisses 124 Kapitel 5 128 Zusammenfassung und Ausblick 129 Anhang A 134 Anhang B 136 Literaturverzeichnis 137 Danksagung 145 Veröffentlichungen 146 Lebenslauf des Autors 147 Selbständigkeitserklärung 148