Transport measurements of single wall carbon nanotube multiterminal devices with normal and ferromagnetic contacts

Spin based electronics or spintronics is a field having the electron's spin degree of freedom as a subject. It is about how to write, transfer and read information using the electron spin. The birth of spintronics is considered to be the discovery of the giant magnetoresistance (GMR) in 1988 [1] and since then a major progress has been achieved in the field [2, 3]. The best example of this progress is the development of so called spin-valves. Modern day spin-valves are based on the GMR and they are used for measuring small magnetic fields. Their most common application is as sensors in hard disk reading heads. Spintronics can conceptually be divided in two parts. The first one is about generating and detecting spin polarized electrons, which is normally done using ferromagnetic materials, but can also be done using optical methods [3]. The latter part is about coherent transfer of spin information. It is of fundamental importance to understand how spin infomation can be transfered coherently over larger distances. In recent years new nanoscale allotropes of carbon have been discovered. In 1985 the first fullerene, the buckyball was discovered [4] and 1991 carbon nanotubes (CNT) were discovered by Sumio Iijima [5]. CNTs behave as onedimensional conductors and the coherence length of the electron in them is very long, especially in individual SWCNT, where the electrons have been found to be coherent over the distance of 3 �m [6]. Moreover, carbon is believed to have long spin coherence length, due to low spin orbit coupling and no nuclear spin of its main isotope 12C . This all makes CNTs an interesting platform for spin transport studies. The first work on CNT spin-valve devices was done on multiwall carbon nanotubes (MWCNTs) contacted by Co electrodes [7]. By applying magnetic field to the device the magnetization of the Co electrodes can be changed between parallel and antiparallel mutual orientation. The resistance for parallel and antiparallel mutual orientation, RP and RA respectively, are measured and the TMR, which is defined as follows TMR = (RA - RP)/ is calculated. The TMR of this first CNT spin-valve was 9% at maximum and it was positive (i.e RA > RP ) [7, 8]. Negative TMR signal was later measured in similar devices, i.e. MWCNTs contacted with Co electrodes. The maximal size of the TMR signal in these devices was 36% for a low current bias, but higher current bias resulted in lower TMR signals [9]. The origin of the di�erent sign of the TMR was not clear by then. The first CNT spin devices fabricated in our lab wereMWCNTs contacted by Pd1-xNix (x ~ 0:7) 1. These ferromagnetic contacts were transparent, having room temperature resistance of 5:6 k[omega]. What was new about these devices was that they were equipped with a back gate and could be tuned between di�erent transport regimes [10]. More importantly it was shown that TMR was dependent on the back gate voltage [11]. Further studies revealed that the TMR signal was either negative or positive dependent on applied gate voltage, but the origin of this behavior was not well understood [12]. When the signal changes in TMR were studied single wall carbon nanotubes (SWCNT) grown in-house by chemical vapor deposition (CVD) using methane as a carbon source became available. The CVD growing process had been optimize to produce individual SWCNT [13]. Individual CVD grown SWCNTs were connected with PdNi contacts. In such device it was shown that the TMR signal was correlated with the coulomb oscillations of the quantum dot which is formed in the SWCNT between the contacts. In SWCNT the quantum dot behavior is much simpler than in MWCNT and the TMR could be tuned smoothly from positive to negative values by the gate voltage [12, 14]. This work demonstrated for the first time the control of spin transport in a three terminal device. There are still many open questions concerning SWCNT spin devices. There are mainly two issues that one should be concerned about when constructing a SWCNT spin valve device. The first one is the switching characteristics of the electrodes. The switching in the devices contacted with PdNi contacts is not always clear indicating that the electrode consists of many magnetic domains. The latter one is due to spurious effects in the SWCNT spin-valves. Such effects could be magneto-coulomb effect [15] or tunnelling anisotropic magnetoresistance (TAMR). Spurious effects could cause a "false TMR signal", i.e. a switching behavior in the signal as a function of applied field that that does not originate from transport of spin. The focus of the this work was mainly to address these issues but some work was also done on how to process of individual SWCNT devices. PdNi electrodes were studied in order to understand their switching behavior better. We worked to optimize the switching characteristics of the spin-valve devices, by trying other contact materials on the SWCNTs. One way of avoiding spurious e�ects is to make multi-terminal devices. It has been shown in metallic nanostructures that by measuring non-local spin signals, artefacts can be avoided. Non-local spin transport measurements have been done on SWCNT contacted by four Co contacts [16]. The multiterminal devices made in this work have two normal contacts and two ferromagnetic contacts. They are gateable with a back-gate enabling it to study the behavior of the three quantum dots that are formed in each segment of the tube between the contacts. Outline of this thesis - Chapter 2 is on the basics of spintronics. It includes a short description on ferromagnetism and on anisotropic magnetoresistance (AMR) and for historical resons giant magnetoresistance (GMR) is briefly discussed. The tunnelling magnetoresistance is explained and Julliére's model. - Chapter 3 is on carbon nanotubes. It is focused on single wall carbon nanotubes (SWCNT), their structure and their electronic properties. - Chapter 4 is on processing of SWCNT devices. The first part of the chapter is on SWCNT production and characterization of the SWCNT material. A lot of time was invested in the lab in finding the best way to obtain individual SWCNT for our nanotube project. Both main approaches tested, i.e spreading tubes from suspension solution and CVD growth are described. In the latter part it is generally described how to make SWCNT devices. - Chapter 5 is on SWCNT based spin valves. The idea behind the SWCNT is discussed (the statement of the problem) and then measurements using different ferromagnetic contact materials are discussed. Temperature dependence on TMR in SWCNT is discussed in the last section of the chapter. - Chapter 6 is on measurements on multiterminal devices. Non-local and semi-nonlocal measurements are shown and discussed. - Chapter 7 is a summary of the thesis. Details on experimental setups and recipes can be found in appendices

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Management of patients with STEMI transported with air-ambulance to Landspitali University Hospital in Reykjavík

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn Skoða/Opna(view/open)INTRODUCTION: A good outcome of patients presenting with STEMI (ST-Segment Elevation Myocardial Infarction) depends on early restoration of coronary blood flow. Pre-hospital fibrinolysis is recommended if primary percutaneous coronary intervention (PPCI) cannot be performed within 90 minutes of first medical contact (FMC). The purpose of this study was to study transport times for patients with STEMI who were transported with air-ambulance from the northern rural areas of Iceland to Landspitali University Hospital in Reykjavík, and to assess if the medical management was in accordance with clinical guidelines. MATERIALS AND METHODS: Retrospective chart review identified 33 patients with STEMI who were transported with air-ambulance to Landspitali University Hospital in Reykjavík during the years 2007 and 2008. RESULTS: The total time from first medical contact to arrival at Landspitali University Hospital emergency room was 3 hours and 7 minutes (median). All patients received aspirin and 26 (78.8%) received clopidogrel and enoxaparin. 16 patients (48.5%) received thrombolytic therapy in median 33 minutes after FMC and 15 patients had PPCI performed in median 4 hours and 15 minutes after FMC. Estimated PCI related delay was 3 hours and 42 minutes (median). One patient died and one was resuscitated within 30 hospital days. Mean hospital stay was 6.0 days. CONCLUSIONS: First medical contact to balloon time of less than 90 minutes is impossible for patients with STEMI transported from the northern rural areas to Landspitali University Hospital in Reykjavík. Medical therapy was in many cases suboptimal and PCI related delay too long.Inngangur:Horfur sjúklinga með brátt ST-hækkunar hjartadrep ráðast af því hversu lengi kransæð er lokuð. Ef kransæðavíkkun verður ekki viðkomið innan 90 mínútna frá komu til læknis er réttast að veita meðferð með segaleysandi lyfi. Tilgangur þessarar rannsóknar var að kanna hversu langan tíma það tók að flytja sjúklinga með STEMI af Norður- og Austurlandi á Landspítala og hvort læknismeðferð var í samræmi við klínískar leiðbeiningar. Efniviður og aðferðir: Rannsóknin er aftursýn og nær til 33 sjúklinga með STEMI frá Norður- og Austurlandi á árunum 2007 og 2008. Niðurstöður:Heildarflutningstími, frá fyrstu samskiptum við lækni í héraði inn á bráðamóttöku Landspítala, var að miðgildi 3 klukkustundir og 7 mínútur. Allir sjúklingar fengu magnýl og 26 sjúklingar (78,8%) fengu clopidogrel og enoxaparin. 16 sjúklingar (48,5%) fengu segaleysandi lyf að miðgildi 33 mínútum eftir fyrstu samskipti við lækni og 15 sjúklingar (45,5%) gengust undir bráða kransæðavíkkun (PPCI) að miðgildi 4 klukkustundum og 15 mínútum eftir fyrstu samskipti við lækni. Áætluð töf í kransæðavíkkun umfram gjöf segaleysandi lyfja var 3 klukkustundir og 42 mínútur. Einn sjúklingur lést og annar var endurlífgaður innan 30 daga eftir hjartadrep. Meðallegutími á Landspítala var 6,0 dagar. Ályktun: Ekki er mögulegt að flytja sjúklinga með ST-hækkunar hjartadrep innan 90 mínútna, frá fyrstu samskiptum við lækni frá Norður- og Austurlandi og þar til æð hefur verið víkkuð á Landspítala í Reykjavík. Lyfjameðferð var í mörgum tilfellum ófullnægjandi og töf í kransæðavíkkun umfram gjöf segaleysandi lyfja of löng

Vitamin-D homeostasis amongst adult Icelandic population

Neðst á síðunni er hægt að nálgast greinina í heild sinni með því að smella á hlekkinn View/OpenBackground: The purpose of this study was to examine the effect of vitamin D intake and production in skin on vitamin D homeostasis in adult Icelanders. Methods: Participants were 30-85 years old, randomly selected from the registry of the Reykjavik area (64 degrees N) and answered a thorough questionnaire on diet and vitamin supplements. Concentrations of 25(OH)-vitamin D [25(OH)D] in peripheral blood were examined based on season during the study period February 2001-January 2003, vitamin D intake and age (age groups 30-45, 50-65, and 70-85 years old). We defined vitamin D deficiency as either [25(OH)D] <25 nmol/l or as [25(OH)D] where the inverse relationship between serum iPTH and [25(OH)D] became statistically significant. Results: Of 2310 invited, 1630 subjects participated (70,6% participation) but 21 individuals were excluded due to primary hyperparathyroidism. Mean [25(OH)D] was 46.5-/+20 nmol/l but varied by season, age and vitamin D intake, highest in June-July, 52.1-/+19.8 and lowest in February-March, 42.0-/+20.5 (p<0.001). [25(OH)D] was highest in the oldest age group, 50.8-/+19.7, but lowest in the youngest, 42.5-/+20 as was the intake 16.6-/+10 microg/day compared to 9.9-/+9 microg/day in the youngest. The correlation between vitamin D intake and [25(OH)D] was highest for the oldest group, r=0.41, p<0.001 but lowest in the youngest, r=0.24, p<0.001. [25(OH)D] was significantly higher among users of vitamin supplements (45.4-/+19.7) or fish oil (53.0-/+18.4) than among non-users (38.0-/+18.9). Vitamin D insufficiency was seen among 14.5% of those participating according to traditional definition, but 50% were below [25(OH)D] of 45 nmol/l where negative correlation between [25(OH)D] and PTH became statistically significant. Conclusions: The serum concentration of 25(OH)D at which vitamin D deficiency becomes biochemically significant is higher than traditionally thought. A daily intake of 15-20 microg/day during wintertime would be required to maintain normal homeostasis in Icelandic adults, which is considerably higher than present recommendations of 7-10 microg/day for adults. Further research is needed to define the limit for vitamin-D sufficiency.Inngangur: Tilgangur þessarar rannsóknar var að kanna D-vítamínbúskap Íslendinga með tilliti til fæðuinntöku og framleiðslu í húð. Rannsóknarhópur og aðferðir: Þátttakendur á aldrinum 30-85 ára voru af höfuðborgarsvæðinu og svöruðu spurningalista um mataræði, bætiefna- og lyfjanotkun. Af 2310 manna úrtaki komu alls 1630 til rannsóknarinnar (70,6% þátttaka) sem stóð frá febrúar 2001 til janúar 2003. Kannaður var styrkur 25(OH)D í sermi eftir D-vítamínneyslu, árstíma og aldursflokkum (30-45 ára, 50-65 ára og 70-85 ára). D-vítamínskortur var skilgreindur á tvo vegu: <25 nmól/l (hefðbundið) og sem sá styrkur 25(OH)D í sermi þar sem neikvætt samband 25(OH)D og kalkvakaóhóf (primary hyperparathyroidism) PTH í sermi varð tölfræðilega marktækt. Niðurstöður: Meðalstyrkur 25(OH)D var 46,5±20 nmól/l án marktæks kynjamunar, mismunandi eftir árstíma, aldri og D-vítamíninntöku með hámarki í júní-júlí, 52,1±19,8 en lágmarki í febrúar-mars, 42,0 ±20,5 (p<0,001). Meðalstyrkur 25(OH)D var mestur í elsta aldurshópnum 50,8±19,7 en minnstur í þeim yngsta 42,5±20 eins og D-vítamíninntakan 16,6±10,4 samanborið við 9,9±9,1 mg/dag. Fylgni milli D-vítamíninntöku og styrks 25(OH)D var mest í elsta aldurshópnum, r=0,41, p<0,001 en minnst í þeim yngsta, r=0,24, p<0,001. Meðalstyrkur 25(OH)D mældist 38,0±18,9 hjá þeim sem tóku ekki bætiefni, 45,4±19,7 hjá þeim sem tóku bætiefni og 53±18,4 hjá þeim sem tóku lýsi (p<0,001). Ályktun: Styrkur 25(OH)D í sermi fullorðinna Íslendinga er breytilegur eftir inntöku D-vítamíns, árstíma og aldri. Tæplega 15% greinast með ónógt D-vítamín samkvæmt hefðbundnum viðmiðunum en rúmlega þrefalt fleiri ef styrkur 25(OH)D í sermi, þar sem neikvæð fylgni við kalkkirtilshormón í sermi verður marktæk (45 nmól/l), er notuð sem viðmið sem samsvarar inntöku 15-20 mg/dag af D-vítamíni yfir vetrartímann. Ráðlagður dagskammtur er nú 7-10 mg/dag. Frekari rannsókna er þörf til að endurmeta skilgreiningu á D-vítamínskorti