173 research outputs found
Low-Energy Electron Microscopy Studies of Interlayer Mass Transport Kinetics on TiN(111)
In situ low-energy electron microscopy was used to study interlayer mass
transport kinetics during annealing of three-dimensional (3D) TiN(111) mounds,
consisting of stacked 2D islands, at temperatures T between 1550 and 1700 K. At
each T, the islands decay at a constant rate, irrespective of their initial
position in the mounds, indicating that mass is not conserved locally. From
temperature-dependent island decay rates, we obtain an activation energy of
2.8+/-0.3 eV. This is consistent with the detachment-limited decay of 2D TiN
islands on atomically-flat TiN(111) terraces [Phys. Rev. Lett. 89 (2002)
176102], but significantly smaller than the value, 4.5+/-0.2 eV, obtained for
bulk-diffusion-limited spiral step growth [Nature 429, 49 (2004)]. We model the
process based upon step flow, while accounting for step-step interactions, step
permeability, and bulk mass transport. The results show that TiN(111) steps are
highly permeable and exhibit strong repulsive temperature-dependent step-step
interactions that vary between 0.003 and 0.076 eV-nm. The rate-limiting process
controlling TiN(111) mound decay is surface, rather than bulk, diffusion in the
detachment-limited regime.Comment: 26 pages, 5 figure
Orientation-dependent binding energy of graphene on palladium
Using density functional theory calculations, we show that the binding
strength of a graphene monolayer on Pd(111) can vary between physisorption and
chemisorption depending on its orientation. By studying the interfacial charge
transfer, we have identified a specific four-atom carbon cluster that is
responsible for the local bonding of graphene to Pd(111). The areal density of
such clusters varies with the in-plane orientation of graphene, causing the
binding energy to change accordingly. Similar investigations can also apply to
other metal substrates, and suggests that physical, chemical, and mechanical
properties of graphene may be controlled by changing its orientation.Comment: 5 pages, 6 figure
Geometrical Frustration in Nanowire Growth
Idealized nanowire geometries assume stable sidewalls at right angles to the growth front. Here we report growth simulations that include a mix of nonorthogonal facet orientations, as for Au-catalyzed Si. We compare these with in situ microscopy observations, finding striking correspondences. In both experiments and simulations, there are distinct growth modes that accommodate the lack of right angles in different ways-one through sawtooth-textured sidewalls, the other through a growth front at an angle to the growth axis. Small changes in conditions can reversibly switch the growth between modes. The fundamental differences between these modes have important implications for control of nanowire growth
GaAs:Mn nanowires grown by molecular beam epitaxy of (Ga,Mn)As at MnAs segregation conditions
GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by
molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs
phase separation. Their density is proportional to the density of catalyzing
MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate
temperature. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the
nanowires combine one-dimensional properties with the magnetic properties of
(Ga,Mn)As and provide natural, self assembled structures for nanospintronics.Comment: 13 pages, 6 figure
Influence of the crystal orientation of substrate on low temperature synthesis of silicon nanowires from Si2H6
Selective Growth of Vertical-aligned ZnO Nanorod Arrays on Si Substrate by Catalyst-free Thermal Evaporation
By thermal evaporation of pure ZnO powders, high-density vertical-aligned ZnO nanorod arrays with diameter ranged in 80–250 nm were successfully synthesized on Si substrates covered with ZnO seed layers. It was revealed that the morphology, orientation, crystal, and optical quality of the ZnO nanorod arrays highly depend on the crystal quality of ZnO seed layers, which was confirmed by the characterizations of field-emission scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and photoluminescence measurements. For ZnO seed layer with wurtzite structure, the ZnO nanorods grew exactly normal to the substrate with perfect wurtzite structure, strong near-band-edge emission, and neglectable deep-level emission. The nanorods synthesized on the polycrystalline ZnO seed layer presented random orientation, wide diameter, and weak deep-level emission. This article provides a C-free and Au-free method for large-scale synthesis of vertical-aligned ZnO nanorod arrays by controlling the crystal quality of the seed layer
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