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11 Jun 2012

Volume 100, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 241101 (2012); http://dx.doi.org/10.1063/1.4724309 (3 pages)

Miriam S. Vitiello, Leonardo Viti, Lorenzo Romeo, Daniele Ercolani, G. Scalari, J. Faist, F. Beltram, L. Sorba, and A. Tredicucci
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Electronic and quantum phase coherence properties of bismuth thin films

M. Rudolph and J. J. Heremans

Appl. Phys. Lett. 100, 241601 (2012); http://dx.doi.org/10.1063/1.4729035 (4 pages)

Online Publication Date: 11 June 2012

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We present a method to deposit bulk-like Bi films by thermal evaporation and study the electrical, quantum coherence, and physical properties. A two stage growth procedure was found to optimize the film properties, with an initial wetting layer deposited at lower temperature followed by an active layer at higher temperature. Transport measurements indicate carrier properties comparable to molecular beam epitaxial films and display weak-antilocalization, from which the quantum phase coherence lengths are deduced. A 76 nm film is found to optimally exhibit both bulk-like Bi characteristics and the 2-dimensional quantum coherence properties desired for Bi-based quantum devices.
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71.20.Gj Other metals and alloys
72.15.Rn Localization effects (Anderson or weak localization)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.aj Insulators
68.08.Bc Wetting

Graphene monolayer rotation on Ni(111) facilitates bilayer graphene growth

Arjun Dahal, Rafik Addou, Peter Sutter, and Matthias Batzill

Appl. Phys. Lett. 100, 241602 (2012); http://dx.doi.org/10.1063/1.4729150 (4 pages) | Cited 3 times

Online Publication Date: 11 June 2012

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Synthesis of bilayer graphene by chemical vapor deposition is of importance for graphene-based field effect devices. Here, we demonstrate that bilayer graphene preferentially grows by carbon-segregation under graphene sheets that are rotated relative to a Ni(111) substrate. Rotated graphene monolayer films can be synthesized at growth temperatures above 650 °C on a Ni(111) thin-film. The segregated second graphene layer is in registry with the Ni(111) substrate and this suppresses further C-segregation, effectively self-limiting graphene formation to two layers.
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81.05.ue Graphene
68.35.Dv Composition, segregation; defects and impurities
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Pq Graphene films

Structured surfaces for enhanced pool boiling heat transfer

Kuang-Han Chu, Ryan Enright, and Evelyn N. Wang

Appl. Phys. Lett. 100, 241603 (2012); http://dx.doi.org/10.1063/1.4724190 (4 pages) | Cited 2 times

Online Publication Date: 11 June 2012

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We experimentally investigated surface roughness-augmented wettability on critical heat flux (CHF) during pool boiling with horizontally oriented surfaces. Microstructured surfaces with a wide range of well-defined surface roughness were fabricated, and a maximum CHF of ∼208 W/cm2 was achieved with a surface roughness of ∼6. An analytical force-balance model was extended to explain the CHF enhancement. The excellent agreement found between the model and experimental data supports the idea that roughness-amplified capillary forces are responsible for the CHF enhancement on structured surfaces. The insights gained from this work suggest design guidelines for new surface technologies with high heat removal capability.
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47.55.dd Bubble dynamics
47.55.dp Cavitation and boiling
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena

Atomic intermixing in short-period InAs/GaSb superlattices

Y. Ashuach, Y. Kauffmann, D. Isheim, Y. Amouyal, D. N. Seidman, and E. Zolotoyabko

Appl. Phys. Lett. 100, 241604 (2012); http://dx.doi.org/10.1063/1.4729058 (4 pages) | Cited 3 times

Online Publication Date: 12 June 2012

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High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and laser-assisted local-electrode atom-probe (LEAP) tomography are utilizing for characterizing short-period InAs/GaSb superlattices with an emphasis on obtaining the atomic concentration profiles with sub-nm resolution. HAADF-STEM permits direct visualization and counting of atomic columns in individual sub-layers. The spatial resolution of HAADF-STEM is sufficient to resolve the anion-cation dumbbells and, on this basis, to follow the atomic distributions across a superlattice. Both methods confirm that InAs-on-GaSb interfaces are wider than GaSb-on-InAs interfaces. The interfacial widths deduced from LEAP tomographic measurements are slightly larger than those extracted from HAADF-STEM micrographs, with the maximum total width not exceeding 4.5 monolayers. LEAP tomographic analysis shows the presence of about 7 at. % of Sb atoms in the middle of the InAs sub-layers, as a result of As/Sb substitutions during growth.
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68.65.Cd Superlattices
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.35.Ct Interface structure and roughness

Electrical growth of metallic nanoparticles in mesoporous silica films using atomic force microscopy

Christophe Hubert, Hamza Amrani, Murtaza Ali Khan, Francis Vocanson, and Nathalie Destouches

Appl. Phys. Lett. 100, 241605 (2012); http://dx.doi.org/10.1063/1.4729039 (3 pages) | Cited 1 time

Online Publication Date: 13 June 2012

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We report the formation of silver nanoparticles in mesoporous silica films under a polarized micro-tip. By applying a bias voltage between an atomic force microscope conductive tip and an indium tin oxide substrate, reduction of silver ions initially impregnated in a mesoporous silica film occurs and leads to the creation of silver nanoparticles. This technique allows both the precise positioning of the nanoparticles via the control of the tip position and the control of the nanoparticles size by varying the bias voltage applied to the tip or the contact time.
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81.16.-c Methods of micro- and nanofabrication and processing
61.43.Gt Powders, porous materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.37.Ps Atomic force microscopy (AFM)

Graphene on Rh(111): Scanning tunneling and atomic force microscopies studies

E. N. Voloshina, Yu. S. Dedkov, S. Torbrügge, A. Thissen, and M. Fonin

Appl. Phys. Lett. 100, 241606 (2012); http://dx.doi.org/10.1063/1.4729549 (4 pages) | Cited 8 times

Online Publication Date: 14 June 2012

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The electronic and crystallographic structure of the graphene/Rh(111) moiré lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy (STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.
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73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
71.20.-b Electron density of states and band structure of crystalline solids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)

The influence of substrate morphology on thickness uniformity and unintentional doping of epitaxial graphene on SiC

Jens Eriksson, Ruth Pearce, Tihomir Iakimov, Chariya Virojanadara, Daniela Gogova, Mike Andersson, Mikael Syväjärvi, Anita Lloyd Spetz, and Rositza Yakimova

Appl. Phys. Lett. 100, 241607 (2012); http://dx.doi.org/10.1063/1.4729556 (5 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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A pivotal issue for the fabrication of electronic devices on epitaxial graphene on SiC is controlling the number of layers and reducing localized thickness inhomogeneities. Of equal importance is to understand what governs the unintentional doping of the graphene from the substrate. The influence of substrate surface topography on these two issues was studied by work function measurements and local surface potential mapping. The carrier concentration and the uniformity of epitaxial graphene samples grown under identical conditions and on substrates of nominally identical orientation were both found to depend strongly on the terrace width of the SiC substrate after growth.
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68.35.bt Other materials
73.30.+y Surface double layers, Schottky barriers, and work functions
65.40.gh Work functions
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