110 research outputs found
Geometrical control of the magnetization direction in high aspect-ratio PdNi ferromagnetic nano-electrodes
We present a study of electron-beam evaporated Pd0.4Ni0.6 alloy thin films by
means of ferromagnetic resonance measurements on extended films of varying
thickness and anisotropic magnetoresistance measurements of lithographically
patterned high aspect-ratio ferromagnetic electrodes, respectively. The results
reveal that the direction of the magnetization strongly depends on the
electrode lateral dimensions, transitioning from in-plane magnetization for
extended films to out-of-the-plane magnetization for electrode widths below 2-3
microns, reaching 58 degrees off-plane for 100 nm-wide nanoelectrodes.Comment: Preprint submitted to PRB (14 pages, 4 figures
Colloquium: Spintronics in graphene and other two-dimensional materials
After the first unequivocal demonstration of spin transport in graphene
(Tombros et al., 2007), surprisingly at room temperature, it was quickly
realized that this novel material was relevant for both fundamental spintronics
and future applications. Over the decade since, exciting results have made the
field of graphene spintronics blossom, and a second generation of studies has
extended to new two-dimensional (2D) compounds. This Colloquium reviews recent
theoretical and experimental advances on electronic spin transport in graphene
and related 2D materials, focusing on emergent phenomena in van der Waals
heterostructures and the new perspectives provided by them. These phenomena
include proximity-enabled spin-orbit effects, the coupling of electronic spin
to light, electrical tunability, and 2D magnetism.Comment: 30 pages, 12 figure
Screening and interlayer coupling in multilayer graphene field-effect transistors
With the motivation of improving the performance and reliability of
aggressively scaled nano-patterned graphene field-effect transistors, we
present the first systematic experimental study on charge and current
distribution in multilayer graphene field-effect transistors. We find a very
particular thickness dependence for Ion, Ioff, and the Ion/Ioff ratio, and
propose a resistor network model including screening and interlayer coupling to
explain the experimental findings. In particular, our model does not invoke
modification of the linear energy-band structure of graphene for the multilayer
case. Noise reduction in nano-scale few-layer graphene transistors is
experimentally demonstrated and can be understood within this model as well.Comment: 13 pages, 4 figures, 20 reference
Observation of the Fractional Quantum Hall Effect in Graphene
When electrons are confined in two dimensions and subjected to strong
magnetic fields, the Coulomb interactions between them become dominant and can
lead to novel states of matter such as fractional quantum Hall liquids. In
these liquids electrons linked to magnetic flux quanta form complex composite
quasipartices, which are manifested in the quantization of the Hall
conductivity as rational fractions of the conductance quantum. The recent
experimental discovery of an anomalous integer quantum Hall effect in graphene
has opened up a new avenue in the study of correlated 2D electronic systems, in
which the interacting electron wavefunctions are those of massless chiral
fermions. However, due to the prevailing disorder, graphene has thus far
exhibited only weak signatures of correlated electron phenomena, despite
concerted experimental efforts and intense theoretical interest. Here, we
report the observation of the fractional quantum Hall effect in ultraclean
suspended graphene, supporting the existence of strongly correlated electron
states in the presence of a magnetic field. In addition, at low carrier density
graphene becomes an insulator with an energy gap tunable by magnetic field.
These newly discovered quantum states offer the opportunity to study a new
state of matter of strongly correlated Dirac fermions in the presence of large
magnetic fields
Tunable stress and controlled thickness modification in graphene by annealing
Graphene has many unique properties which make it an attractive material for
fundamental study as well as for potential applications. In this paper, we
report the first experimental study of process-induced defects and stress in
graphene using Raman spectroscopy and imaging. While defects lead to the
observation of defect-related Raman bands, stress causes shift in phonon
frequency. A compressive stress (as high as 2.1 GPa) was induced in graphene by
depositing a 5 nm SiO2 followed by annealing, whereas a tensile stress (~ 0.7
GPa) was obtained by depositing a thin silicon capping layer. In the former
case, both the magnitude of the compressive stress and number of graphene
layers can be controlled or modified by the annealing temperature. As both the
stress and thickness affect the physical properties of graphene, this study may
open up the possibility of utilizing thickness and stress engineering to
improve the performance of graphene-based devices. Local heating techniques may
be used to either induce the stress or reduce the thickness selectively.Comment: 19 pages, 7 figures, accepted by ACS nan
Chemically-induced Mobility Gaps in Graphene Nanoribbons: A Route for Upscaling Device Performances
We report a first-principles based study of mesoscopic quantum transport in
chemically doped graphene nanoribbons with a width up to 10 nm. The occurrence
of quasibound states related to boron impurities results in mobility gaps as
large as 1 eV, driven by strong electron-hole asymmetrical backscattering
phenomena. This phenomenon opens new ways to overcome current limitations of
graphene-based devices through the fabrication of chemically-doped graphene
nanoribbons with sizes within the reach of conventional lithography.Comment: Nano Letters (in press
Vitamin C Depletion and All-Cause Mortality in Renal Transplant Recipients
Vitamin C may reduce inflammation and is inversely associated with mortality in the general population. We investigated the association of plasma vitamin C with all-cause mortality in renal transplant recipients (RTR); and whether this association would be mediated by inflammatory biomarkers. Vitamin C, high sensitive C-reactive protein (hs-CRP), soluble intercellular cell adhesion molecule 1 (sICAM-1), and soluble vascular cell adhesion molecule 1 (sVCAM-1) were measured in a cohort of 598 RTR. Cox regression analyses were used to analyze the association between vitamin C depletion (≤28 µmol/L; 22% of RTR) and mortality. Mediation analyses were performed according to Preacher and Hayes’s procedure. At a median follow-up of 7.0 (6.2–7.5) years, 131 (21%) patients died. Vitamin C depletion was univariately associated with almost two-fold higher risk of mortality (Hazard ratio (HR) 1.95; 95% confidence interval (95%CI) 1.35–2.81, p < 0.001). This association remained independent of potential confounders (HR 1.74; 95%CI 1.18–2.57, p = 0.005). Hs-CRP, sICAM-1, sVCAM-1 and a composite score of inflammatory biomarkers mediated 16%, 17%, 15%, and 32% of the association, respectively. Vitamin C depletion is frequent and independently associated with almost two-fold higher risk of mortality in RTR. It may be hypothesized that the beneficial effect of vitamin C at least partly occurs through decreasing inflammation
How Servant Leadership Influences Organizational Citizenship Behavior: The Roles of LMX, Empowerment and Proactive Personality
While the link between servant leadership and organizational citizenship behavior (OCB) has been established, the individual-level mechanisms underlying this relationship and its boundary conditions remain poorly understood. In this study, we investigate the salience of the mediating mechanisms of leader-member exchange (LMX) and psychological empowerment in explaining the process by which servant leaders elicit discretionary OCB among followers. We also examine the role of followers’ proactive personality in moderating the indirect effects of servant leadership on OCB through LMX and psychological empowerment. Analysis of survey data collected from 446 supervisor-subordinate dyads in a large Chinese multinational firm suggests that while servant leadership is positively related to subordinate OCB through LMX, psychological empowerment does not explain any additional variance in OCB above that accounted for by LMX. Moderated mediation tests confirm the moderating effect of proactive personality through LMX. By providing a nuanced understanding of how and when servant leadership leads followers to go above and beyond their job role, our study assists organizations in deciding how to develop and utilize servant leaders in their organizations
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