242 research outputs found
Enhanced Ferromagnetic Stability in Cu Doped Passivated GaN Nanowires
Density functional calculations are performed to investigate the room
temperature ferromagnetism in GaN:Cu nanowires (NWs). Our results indicate that
two Cu dopants are most stable when they are near each other. Compared to bulk
GaN:Cu, we find that magnetization and ferromagnetism in Cu doped NWs is
strongly enhanced because the band width of the Cu td band is reduced due to
the 1D nature of the NW. The surface passivation is shown to be crucial to
sustain the ferromagnetism in GaN:Cu NWs. These findings are in good agreement
with experimental observations and indicate that ferromagnetism in this type of
systems can be tuned by controlling the size or shape of the host materials.Comment: Nano Lett., ASAP Article, 10.1021/nl080261
Transition from Ferromagnetism to Antiferromagnetism in GaMnN
Using density functional theory, we study the magnetic stability of the
GaMnN alloy system. We show that unlike GaMnAs, which
shows only ferromagnetic (FM) phase, GaMnN can be stable in either
FM or antiferromagnetic phases depending on the alloy concentration. The
magnetic order can also be altered by applying pressure or with charge
compensation. A unified model is used to explain these behaviors.Comment: 4 pages, 4 figure
Theoretical Study of Corundum as an Ideal Gate Dielectric Material for Graphene Transistors
Using physical insights and advanced first-principles calculations, we
suggest that corundum is an ideal gate dielectric material for graphene
transistors. Clean interface exists between graphene and Al-terminated (or
hydroxylated) Al2O3 and the valence band offsets for these systems are large
enough to create injection barrier. Remarkably, a band gap of {\guillemotright}
180 meV can be induced in graphene layer adsorbed on Al-terminated surface,
which could realize large ON/OFF ratio and high carrier mobility in graphene
transistors without additional band gap engineering and significant reduction
of transport properties. Moreover, the band gaps of graphene/Al2O3 system could
be tuned by an external electric field for practical applications
Controlling doping in graphene through a SiC substrate: A first-principles study
Controlling the type and density of charge carriers by doping is the key step
for developing graphene electronics. However, direct doping of graphene is
rather a challenge. Based on first-principles calculations, a concept of
overcoming doping difficulty in graphene via substrate is reported.We find that
doping could be strongly enhanced in epitaxial graphene grown on silicon
carbide substrate. Compared to free-standing graphene, the formation energies
of the dopants can decrease by as much as 8 eV. The type and density of the
charge carriers of epitaxial graphene layer can be effectively manipulated by
suitable dopants and surface passivation. More importantly, contrasting to the
direct doping of graphene, the charge carriers in epitaxial graphene layer are
weakly scattered by dopants due to the spatial separation between dopants and
the conducting channel. Finally, we show that a similar idea can also be used
to control magnetic properties, for example, induce a half-metallic state in
the epitaxial graphene without magnetic impurity doping
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