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11 Aug 2008

Volume 93, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 93, 062101 (2008); http://dx.doi.org/10.1063/1.2968206 (3 pages)

K. Shibata and K. Hirakawa
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Origin of enhanced field emission characteristics postplasma treatment of multiwalled carbon nanotube array

Kyu Lee, Seong Chu Lim, Young Chul Choi, and Young Hee Lee

Appl. Phys. Lett. 93, 063101 (2008); http://dx.doi.org/10.1063/1.2969783 (3 pages) | Cited 8 times

Online Publication Date: 11 August 2008

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Field emission properties of chemical-vapor-deposition-grown multiwalled carbon nanotubes (MWCNTs) with plasma treatment have been investigated. Origin of the enhanced field emission current was interpreted in terms of surface morphology of MWCNTs, work function, field enhancement factor, and emission area. Contrary to the general belief, the change in the work function increased slightly with the plasma treatment time, whereas the field enhancement factor decreased. We found that the number of emittable MWCNTs played a dominant role in the current enhancement.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.bp Fullerenes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
52.77.-j Plasma applications

Ion-beam induced fcc-bcc transition in ultrathin Fe films for ferromagnetic patterning

W. Rupp, A. Biedermann, B. Kamenik, R. Ritter, Ch. Klein, E. Platzgummer, M. Schmid, and P. Varga

Appl. Phys. Lett. 93, 063102 (2008); http://dx.doi.org/10.1063/1.2969795 (3 pages) | Cited 4 times

Online Publication Date: 12 August 2008

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Ar+ ion irradiation is used to induce a structural change from fcc to bcc in a 1.5 nm thick Fe film epitaxially grown on a Cu(100) crystal. Scanning tunneling microscopy and low-energy electron diffraction show the nucleation of bcc nanocrystals, which grow with increasing ion dose. As a consequence of the structural change, the irradiated iron film becomes strongly ferromagnetic at room temperature. We present a model for the process of the transformation and demonstrate writing a magnetic pattern at the 100 nm scale by ion-beam projection lithography.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
61.80.Jh Ion radiation effects
81.16.Rf Micro- and nanoscale pattern formation
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys

Gallium phosphide photonic crystal nanocavities in the visible

Kelley Rivoire, Andrei Faraon, and Jelena Vuckovic

Appl. Phys. Lett. 93, 063103 (2008); http://dx.doi.org/10.1063/1.2971200 (3 pages) | Cited 25 times

Online Publication Date: 14 August 2008

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Photonic crystal nanocavities at visible wavelengths are fabricated in a high refractive index (n>3.2) gallium phosphide membrane. The cavities are probed via a cross-polarized reflectivity measurement and show resonances at wavelengths as low as 645 nm at room temperature, with quality factors between 500 and 1700 for modes with volumes 0.7(λ/n)3. These structures could be employed for submicron scale optoelectronic devices in the visible, and for coupling to emitters with resonances in the visible such as nitrogen vacancy centers, and biomolecules and organic molecules.
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42.70.Qs Photonic bandgap materials
81.07.Bc Nanocrystalline materials
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Unusual catalyst-free epitaxial growth of silicon nanowires by thermal evaporation

Y. Qin, X. N. Zhang, K. Zheng, H. Li, X. D. Han, and Z. Zhang

Appl. Phys. Lett. 93, 063104 (2008); http://dx.doi.org/10.1063/1.2967875 (3 pages) | Cited 3 times

Online Publication Date: 14 August 2008

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We report a catalyst-free epitaxial growth of silicon nanowires on polyhedral facets of mother Si nanoparticles by thermal evaporation process. Single silicon nanowires and octopuslike silicon nanowires (OSNWs) were synthesized under different temperatures. The OSNWs have several directions including ⟨112⟩, ⟨110⟩, and the unusual directions of ⟨100⟩ and ⟨111⟩. A catalyst-free temperature-dependent epitaxial growth model was suggested. Using the Wulff theory and first principle calculations, these growth directions can be explained by the preferential selection of temperature-dependent surface energies. It thus revealed an important but simple growth model in which the growth directions could be delicately controlled through only determining temperature and substrate orientation.
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81.16.-c Methods of micro- and nanofabrication and processing
68.55.ag Semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.03.Cd Surface tension and related phenomena
68.35.Md Surface thermodynamics, surface energies
71.15.-m Methods of electronic structure calculations

Controllable resistance and temperature dependency of carbon nanotube bundles

P. Mahanandia and K. K. Nanda

Appl. Phys. Lett. 93, 063105 (2008); http://dx.doi.org/10.1063/1.2970033 (3 pages) | Cited 9 times

Online Publication Date: 14 August 2008

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We report the controllable resistance of multiwalled carbon nanotube bundles for the possible application in nanoscale electronics. The resistance as well as the variation of resistance with temperature depends on the bundle diameter. The larger the diameter, smaller is the resistance and weaker is the variation of resistance with temperature that make the bundles advantageous in nanoscale electronics and in some other applications. As the resistance and the variation can be controlled by monitoring the bundle diameter, the temperature dependency of resistance can be employed in temperature thermometry.
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73.61.Wp Fullerenes and related materials
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems

Self-organized metallic nanoparticle and nanowire arrays from ion-sputtered silicon templates

T. W. H. Oates, A. Keller, S. Noda, and S. Facsko

Appl. Phys. Lett. 93, 063106 (2008); http://dx.doi.org/10.1063/1.2959080 (3 pages) | Cited 19 times

Online Publication Date: 15 August 2008

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We demonstrate a production method for self-organized arrays of metal nanoparticles and aligned nanowires. Ion beam-sputtered Si/SiO2 substrates are used as templates for metallic vapor deposition, forming aligned arrays of 5–20 nm silver and cobalt nanoparticles with a period of 35 nm. The 20 nm diameter cobalt nanowires with lengths in excess of a micrometer are produced under appropriate conditions. All processing steps can be integrated into a single vacuum chamber and performed in a matter of minutes at mild temperatures. This inherently scalable technique can be extended to a range of substrate materials, array patterns, and nanoparticle materials.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Bx Metals, semimetals, and alloys
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.Dn Self-assembly

Hydrogen storage in alkali-metal-decorated organic molecules

Bing Huang, Hoonkyung Lee, Wenhui Duan, and Jisoon Ihm

Appl. Phys. Lett. 93, 063107 (2008); http://dx.doi.org/10.1063/1.2971201 (3 pages) | Cited 13 times

Online Publication Date: 15 August 2008

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We investigate the feasibility of alkali-metal (AM)-decorated organic molecules for hydrogen storage using first-principles density functional calculations. The present studies indicate that AMs bind strongly to some organic molecules, and Li-doped organic molecules exhibit a higher storage capacity (>10 wt %) than Na or K. The adsorption energies of dihydrogen on Li-decorated organic molecules are in the range of 10–30 kJ/mol, acceptable for reversible H2 adsorption/desorption near room temperature. Regarding the H2 adsorption mechanism, it is demonstrated that the dipole originating from the charge transfer within the AM-organic molecule complex induces a dipole in the H2 molecule.
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84.60.-h Direct energy conversion and storage
68.43.Mn Adsorption kinetics
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