83 research outputs found
Configurations, electronic properties, and diffusion of carbon and nitrogen dopants in rutile TiO2: A density functional theory study
No full text
Defect and impurities in Ge-based electronic devices
No full textFurther advances in the performance and reliability of Ge-based electronic devices require an understanding of the most prominent types of defects and impurities in these systems. In this respect, computational studies can play an important role for the elucidation of the physical mechanisms that control the stability and dynamics of these defects. Here we will review recent results of first-principles calculations within density-functional theory on Ge-related imperfections in the bulk of various dielectrics and at the boundary between a gate oxide and a Ge substrate. We will also discuss results on the stability of hydrogen impurities and dopant-hydrogen complexes in SiGe alloys.</jats:p
Green function studies of the interlayer exchange coupling in magnetic multilayers
No full textThe Interlayer Exchange Coupling (IEC) of magnetic multilayers has been one of the most studied problems in condensed matter physics for the last decade. It is found that for a multilayer structure in which magnetic layers are separated by a spacer, the magnetic moments of each layer orient
themselves parallel, antiparallel or even perpendicular to each other, depending on the thickness of the spacer. This variable interlayer coupling of the magnetizations is oscillatory and usually multiperiodic. Its determination has posed interesting challenges, because often calculated results
differ from the experimental ones. From the application standpoint, multilayer structures are used in the new generation of recording heads. In the first part of the present work, we used the Reflection
Amplitude Approximation (RAA) to calculate the coupling in the prototypical system of an Fe/Cr trilayer. We were able to identify the origin of the long period oscillation in the coupling, and obtain a coupling strength that was among the best theoretical predictions. In the second part, we used a
more accurate method that employed the so called Analytical Green Function (AGF). The results of this approach offered a good checkpoint of RAA, and they were in good agreement with the experimental findings in Fe/Cr and Co/Cu systems. We then calculated the intrinsic biquadratic coupling and compared it to the extrinsic one, obtained from the thickness fluctuation model. We
also studied the effect that the finite thickness of the magnetic layers may have on the coupling, in particular in the appearance of Fano resonances. Finally, we studied how the coupling changes when roughness, alloying of the spacer, or strain are present. In all cases, the results were in very good agreement with experiment, showing that the AGF method is a very accurate, and yet very efficient method, for the determination of the IEC.Submitted by Elizabeth Kent ([email protected]) on 2012-05-25T16:20:47Z
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Reason: thesisItem marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Elizabeth Kent ([email protected]) on 2012-05-25T16:20:47Z
Item is restricted indefinitely.thesisU of I Onl
Magnetic two-dimensional C<sub>3</sub>N<sub>2</sub> carbonitrides: semiconductors, metals and half-metals
No full textUsing density-functional theory (DFT) calculations we probe the spin polarization of functionalized two-dimensional (2D) phthalo-carbonitrides (pc-C3N2), i.e., 2D polymers of tetra-cyanoethylene.</p
Defect-related hysteresis in nanotube-based nano-electromechanical systems
No full textAbstract The electronic properties of multi-walled carbon nanotubes (MWCNTs) depend on the positions of their walls with respect to neighboring shells. This fact can enable several applications of MWCNTs as nano-electromechanical systems (NEMS). In this article, we report the findings of a first-principles study on the stability and dynamics of point defects in double-walled carbon nanotubes (DWCNTs) and their role in the response of the host systems under inter-tube displacement. Key defect-related effects, namely, sudden energy changes and hysteresis, are identified, and their relevance to a host of MWCNT-based NEMS is highlighted. The results also demonstrate the dependence of these effects on defect clustering and chirality of DWCNT shells.</p
Atomic-scale mechanisms of growth and doping of graphene nano-ribbons
No full textControl over structural and electronic properties of graphene samples is necessary for the fabrication of nano-electronic devices. Here we report the results of first-principles quantum-mechanical studies on the growth and doping of graphene nanoribbons (GNR). We find that hydrogenation of open-ended carbon nanotubes (CNT) can lead to successive breaking of tip C-C bonds. If enough hydrogen atoms are supplied then the CNTs unzip to GNRs with specific widths and edge morphologies. We also examine the possibilities that ammonia-related species can inject carriers in graphene. We show that NH3 molecules have a complex dynamics on graphene. Annealing in ammonia can result in the formation of donors on the graphene basal plane, or the de-activation of dopants on graphene and at GNR edges. The results explain available experimental data and suggest new ways to optimize the properties and performance of GNR-based systems.</jats:p
Defect-related hysteresis in nanotube-based nano-electromechanical systems
No full textAbstractThe electronic properties of multi-walled carbon nanotubes (MWCNTs) depend on the positions of their walls with respect to neighboring shells. This fact can enable several applications of MWCNTs as nano-electromechanical systems (NEMS). In this article, we report the findings of a first-principles study on the stability and dynamics of point defects in double-walled carbon nanotubes (DWCNTs) and their role in the response of the host systems under inter-tube displacement. Key defect-related effects, namely, sudden energy changes and hysteresis, are identified, and their relevance to a host of MWCNT-based NEMS is highlighted. The results also demonstrate the dependence of these effects on defect clustering and chirality of DWCNT shells.</jats:p
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