Electrical and magnetic investigations on transition metal implanted GaAs

In dieser Arbeit wurde ein Halbleiter-Ferromagnet-Hybrid-Materialsystem aus (Ga,Mn)As hergestellt, wobei ferromagnetische Cluster in ein Halbleiter eingebettet sind. Die eingesetzte $\textit {Molekularstrahl-Epitaxie-fokusierte Ionenstrahlen}$ (MBE-FIB)-Technik bietet dabei eine nützliche Methode an, um Materialien dieser Art herzustellen. Die Dotierung von Halbleitern mit magnetischen Atomen stellt einerseits die Konzentration und Typ der Ladungsträger ein, andererseits ermöglicht sie den Einbau von magnetischen Momenten. Zu diesem Zweck wurden Mn-Ionen in GaAs implantiert. Nach der thermischen Ausheilung wurden $Mn:Ga_{n}As_{m}$ Cluster mittels Rasterkraft-Mikroskopie und EDX-Spektroskopie an der Probenoberfläche beobachtet. Für die elektrische und magnetische Charakterisierung wurden SQUID, Hall- und Magnetotransportmessungen durchgeführt und Curie-Temperaturen bestimmt. Mit der MBE-FIB-Technik kann 57% der deponierten Mn-Ionen auf gewünschte Position in GaAs eingebaut werden.In this thesis, a semiconductor-ferromagnetic hybrid material system was synthesized composed of (Ga,Mn)As, where ferromagnetic clusters are embedded in a semiconducting lattice. The applied molecular beam epitaxy-focused ion beam (MBE-FIB)-technique offers a useful method for manufacturing such kind of material systems. The doping of semiconductors with magnetic atoms sets on the one hand the concentration and the type of the charge carriers, on the other hand it creates the incorporation of magnetic moments. For this purpose, Mn ions are implanted into GaAs. After thermal treatment, $Mn:Ga_{n}As_{m}$ clusters are observed by means of atomic force microscopy and energy dispersive X-ray spectroscopy at the sample surface. For the electrical and magnetic characterisation SQUID, Hall- and magnetotransport measurements are performed and Curie temperatures are determined. With the MBE-FIB technique, 57% of the deposited Mn atoms can be incorporated on substitutional positions in GaAs

High temperature ferromagnetism in Co-implanted TiO2TiO_2 rutile

We report on structural, magnetic and electronic properties of Co-implanted TiO2 rutile single crystals for different implantation doses. Strong ferromagnetism at room temperature and above is observed in TiO2 rutile plates after cobalt ion implantation, with magnetic parameters depending on the cobalt implantation dose. While the structural data indicate the presence of metallic cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra gives clear evidence for a substitutional Co 2+ state. The detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the rutile phase, and the second one is a superparamagnetic phase originates from the formation of metallic cobalt clusters in the implanted region. Using x-ray resonant magnetic scattering, the element specific magnetization of cobalt, oxygen and titanium in Co-implanted TiO2 single crystals are investigated. Magnetic dichroism was observed at the Co L edges as well as at the O K edge. The interaction mechanism, which leads to ferromagnetic ordering of substituted cobalt ions in the host matrix, is also discussed.Comment: 19 pages, 16 figure

Mortality analysis of COVID-19 infection in chronic kidney disease, haemodialysis and renal transplant patients compared with patients without kidney disease: a nationwide analysis from Turkey

Background. Chronic kidney disease (CKD) and immunosuppression, such as in renal transplantation (RT), stand as one of the established potential risk factors for severe coronavirus disease 2019 (COVID-19). Case morbidity and mortality rates for any type of infection have always been much higher in CKD, haemodialysis (HD) and RT patients than in the general population. A large study comparing COVID-19 outcome in moderate to advanced CKD (Stages 3-5), HD and RT patients with a control group of patients is still lacking. Methods. We conducted a multicentre, retrospective, observational study, involving hospitalized adult patients with COVID-19 from 47 centres in Turkey. Patients with CKD Stages 3-5, chronic HD and RT were compared with patients who had COVID-19 but no kidney disease. Demographics, comorbidities, medications, laboratory tests, COVID-19 treatments and outcome [in-hospital mortality and combined in-hospital outcome mortality or admission to the intensive care unit (ICU)] were compared. Results. A total of 1210 patients were included [median age, 61 (quartile 1-quartile 3 48-71) years, female 551 (45.5%)] composed of four groups: Control (n = 450), HD (n = 390), RT (n = 81) and CKD (n = 289). The ICU admission rate was 266/ 1210 (22.0%). A total of 172/1210 (14.2%) patients died. The ICU admission and in-hospital mortality rates in the CKD group [114/289 (39.4%); 95% confidence interval (CI) 33.9-45.2; and 82/289 (28.4%); 95% CI 23.9-34.5)] were significantly higher than the other groups: HD = 99/390 (25.4%; 95% CI 21.3-29.9; P<0.001) and 63/390 (16.2%; 95% CI 13.0-20.4; P<0.001); RT = 17/81 (21.0%; 95% CI 13.2-30.8; P = 0.002) and 9/81 (11.1%; 95% CI 5.7-19.5; P = 0.001); and control = 36/450 (8.0%; 95% CI 5.8-10.8; P<0.001) and 18/450 (4%; 95% CI 2.5-6.2; P<0.001). Adjusted mortality and adjusted combined outcomes in CKD group and HD groups were significantly higher than the control group [hazard ratio (HR) (95% CI) CKD: 2.88 (1.52- 5.44); P = 0.001; 2.44 (1.35-4.40); P = 0.003; HD: 2.32 (1.21- 4.46); P = 0.011; 2.25 (1.23-4.12); P = 0.008), respectively], but these were not significantly different in the RT from in the control group [HR (95% CI) 1.89 (0.76-4.72); P = 0.169; 1.87 (0.81-4.28); P = 0.138, respectively]. Conclusions. Hospitalized COVID-19 patients with CKDs, including Stages 3-5 CKD, HD and RT, have significantly higher mortality than patients without kidney disease. Stages 3-5 CKD patients have an in-hospital mortality rate as much as HD patients, which may be in part because of similar age and comorbidity burden. We were unable to assess if RT patients were or were not at increased risk for in-hospital mortality because of the relatively small sample size of the RT patients in this study