Titanium nitride thin films by the electron shower process

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Includes bibliographical references (leaves 54-56).by Patrick R. LeClair.B.S

Spin-dependent tunneling in magnetic tunnel junctions

The phenomenon of electron tunneling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent tunneling in magnetic tunnel junctions (MTJs) has recently aroused enormous interest and has developed in a vigorous field of research. The large tunneling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible applications in non-volatile random access memories and next-generation magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of spindependent tunneling. In this review article we present an overview of this field of research. We discuss various factors that control the spin polarization and magnetoresistance in magnetic tunnel junctions. Starting from early experiments on spin-dependent tunneling and their interpretation, we consider thereafter recent experiments and models, which highlight the role of the electronic structure of the ferromagnets, the insulating layer and the ferromagnet/insulator interfaces. We also discuss the role of disorder in the barrier and in the ferromagnetic electrodes and their influence on TMR

Spin-dependent tunneling in magnetic tunnel junctions

The phenomenon of electron tunneling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent tunneling in magnetic tunnel junctions (MTJs) has recently aroused enormous interest and has developed in a vigorous field of research. The large tunneling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible applications in non-volatile random access memories and next-generation magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of spindependent tunneling. In this review article we present an overview of this field of research. We discuss various factors that control the spin polarization and magnetoresistance in magnetic tunnel junctions. Starting from early experiments on spin-dependent tunneling and their interpretation, we consider thereafter recent experiments and models, which highlight the role of the electronic structure of the ferromagnets, the insulating layer and the ferromagnet/insulator interfaces. We also discuss the role of disorder in the barrier and in the ferromagnetic electrodes and their influence on TMR

Impact of Antimalarial Treatment and Chemoprevention on the Drug Sensitivity of Malaria Parasites Isolated from Ugandan Children

Changing treatment practices may be selecting for changes in the drug sensitivity of malaria parasites. We characterized ex vivo drug sensitivity and parasite polymorphisms associated with sensitivity in 459 Plasmodium falciparum samples obtained from subjects enrolled in two clinical trials in Tororo, Uganda, from 2010 to 2013. Sensitivities to chloroquine and monodesethylamodiaquine varied widely; sensitivities to quinine, dihydroartemisinin, lumefantrine, and piperaquine were generally good. Associations between ex vivo drug sensitivity and parasite polymorphisms included decreased chloroquine and monodesethylamodiaquine sensitivity and increased lumefantrine and piperaquine sensitivity with pfcrt 76T, as well as increased lumefantrine sensitivity with pfmdr1 86Y, Y184, and 1246Y. Over time, ex vivo sensitivity decreased for lumefantrine and piperaquine and increased for chloroquine, the prevalences of pfcrt K76 and pfmdr1 N86 and D1246 increased, and the prevalences of pfdhfr and pfdhps polymorphisms associated with antifolate resistance were unchanged. In recurrent infections, recent prior treatment with artemether-lumefantrine was associated with decreased ex vivo lumefantrine sensitivity and increased prevalence of pfcrt K76 and pfmdr1 N86, 184F, and D1246. In children assigned chemoprevention with monthly dihydroartemisinin-piperaquine with documented circulating piperaquine, breakthrough infections had increased the prevalence of pfmdr1 86Y and 1246Y compared to untreated controls. The noted impacts of therapy and chemoprevention on parasite polymorphisms remained significant in multivariate analysis correcting for calendar time. Overall, changes in parasite sensitivity were consistent with altered selective pressures due to changing treatment practices in Uganda. These changes may threaten the antimalarial treatment and preventive efficacies of artemether-lumefantrine and dihydroartemisinin-piperaquine, respectively

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Spin polarized electron tunneling

no abstrac

Half-metallic CrO_2 thin films for spintronic applications

CrO_2 is a well-established half-metallic oxide with near perfect spin polarization - known to have the highest spin polarization among all known materials theoretically as well as experimentally. This means that the conduction electrons in CrO_2 have only one kind of spin i.e. conduction is due only to the majority spin electrons. Because of its high spin polarization, CrO_2 stands as an ideal and one of the most attractive candidates for spin-electronic applications as well as of fundamental interests. The enormous potential of CrO_2 is still untapped since thin film growth modes, interface/surface properties and various factors affecting them are not very well understood or, relatively unknown. Reported works confirm strained growth of (100) CrO_2 films and strain free growth of (110) CrO_2 films on iso-structural TiO_2 substrates investigated using X$-$ray diffraction. Superconducting quantum interference device (SQUID) and element specific X-ray magnetic circular dichroism (XMCD) techniques were employed to investigate the effect of this substrate-induced strain on the magnetic properties of the films. Magnetic tunnel junctions (MTJ) were fabricated with CrO_2 , Cr_2 O_3 [natural oxide of Cr] as the thin insulating barrier and Co as the other ferromagnetic electrode using photolithography. I-V characteristics of this spin-electronic device are reported. Also, results on the low pressure chemical vapor deposition (CVD) growth of CrO_2 and its comparison with standard growth technique under atmospheric pressure are reported. (Published By University of Alabama Libraries

Growth of epitaxial bcc Co(001) electrodes for magnetoresistive devices

The applicability of the strain-induced bcc phase of Co in magnetoresistive devices was studied. Ultrathin bcc Co(001) films and the influence of the additional layers needed for magnetoresistive devices were examined by means of /sup 59/Co nuclear magnetic resonance (NMR). NMR is shown to be a discriminating technique for determining the presence of structurally and magnetically pure bcc Co. The maximum stability for uncovered and Fe-covered layers grown on Fe(001)/GaAs(001) and Fe(001)/Ge(001) seed layers is found to be about 2 nm. Growth of an Al/sub 2/O/sub 3/ top layer preserves the bcc phase, in contrast to a Cu film which causes a transformation of the bcc structure to the fcc or the hcp phase. The bcc-preserving effects of Al/sub 2/O/sub 3/ imply the possibility to fabricate magnetic tunnel junctions with bcc Co(001) bottom electrodes. Although bcc Co is a force-induced structure, thin layers are shown to be stable over a few years when Al/sub 2/O/sub 3/ has been grown on top. Junction structures using bcc Co(001) bottom electrodes were grown and characterize