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15 Jan 2005

Volume 97, Issue 2, Articles (02xxxx)

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Optical properties of a nanoporous array in silicon

L. Tian, K. Bhargava Ram, I. Ahmad, L. Menon, and M. Holtz

J. Appl. Phys. 97, 026101 (2005); http://dx.doi.org/10.1063/1.1831541 (3 pages) | Cited 6 times

Online Publication Date: 22 December 2004

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We demonstrate an approach for producing an array of nanopores on a silicon surface. The methods used combine nonlithographic pattern transfer and chlorine plasma etching to produce ∼ 60 nm diam holes up to 1 μm in depth. The near-normal specular optical reflectance of these systematically modified surfaces is found to decrease dramatically with pore depth across the entire 2.0–6.0 eV photon energy range studied. We adapt an effective medium approximation to model specular reflectance taking into account diffuse scattering by the nanopatterned surface. Micro-Raman measurements show a systematic intensity increase with pore depth. The observed dependence suggests that both insertion and extraction are enhanced by the nanopatterning.
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81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
81.07.Bc Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
78.30.Am Elemental semiconductors and insulators

Magnetic metal-base transistor with organic emitter

M. S. Meruvia, M. L. Munford, I. A. Hümmelgen, A. S. da Rocha, M. L. Sartorelli, A. A. Pasa, W. Schwarzacher, and M. Bonfim

J. Appl. Phys. 97, 026102 (2005); http://dx.doi.org/10.1063/1.1836880 (3 pages) | Cited 16 times

Online Publication Date: 22 December 2004

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We have fabricated a magnetic metal-base transistor using particularly simple processes. The emitter is organic, consisting of evaporated C60 or tris(8-hydroxiquinoline) aluminum, the base is an electrochemically deposited Co/Cu/Co multilayer, and the collector is the n-Si substrate. The collector current measured in the common-base configuration increases significantly in the presence of an applied field.
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85.30.Pq Bipolar transistors
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
81.15.Pq Electrodeposition, electroplating
73.40.Vz Semiconductor-metal-semiconductor structures

Morphological change of multiwalled carbon nanotubes through high-energy (MeV) ion irradiation

H. M. Kim, H. S. Kim, S. K. Park, J. Joo, T. J. Lee, and C. J. Lee

J. Appl. Phys. 97, 026103 (2005); http://dx.doi.org/10.1063/1.1834721 (3 pages) | Cited 12 times

Online Publication Date: 23 December 2004

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Multiwalled carbon nanotubes (MWCNTs) were expanded by 2.5 times in diameter through high-energy (MeV) ion irradiation. Pristine MWCNTs were synthesized onto SiO2 substrate by chemical vapor deposition. The 4 MeV Cl2+ ions with a dose of 3×1016 ions/cm2 were irradiated on MWCNTs. From high-resolution transmission electron microscopy (HR-TEM) images, the average diameter of the high-energy-ion-irradiated MWCNTs was ∼ 180 nm, while that of the pristine MWCNTs was ∼ 70 nm. The wall thickness of the pristine and the high-energy-ion-irradiated MWCNT samples was ∼ 20 nm and 40–50 nm, respectively. We observed the clear formation of nanocompartments with bamboolike structure inside the tubes after ion irradiation. The amorphous carbon structure in the ion-irradiated MWCNT shells was observed from Raman spectra. Based on the results of HR-TEM and Raman spectra, the expansion of the systems represents morphological transition from crystalline graphite structure to amorphous carbon or finite sized graphite structure due to the ion impact. We suggest that high-energy ion irradiation can be useful for the modification of MWCNT structures.
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81.07.De Nanotubes
64.70.K- Solid-solid transitions
61.80.Jh Ion radiation effects
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.43.Er Other amorphous solids
61.82.Rx Nanocrystalline materials
78.67.Ch Nanotubes
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.30.Na Fullerenes and related materials

Bending optical solitons in nonlinear photonic crystal waveguides

Xiong-Wen Chen, Xu-Sheng Lin, and Sheng Lan

J. Appl. Phys. 97, 026104 (2005); http://dx.doi.org/10.1063/1.1839650 (3 pages)

Online Publication Date: 23 December 2004

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We investigate the propagation of optical solitons through nonlinear photonic crystal (PC) waveguide bends. Our studies focus on the waveguide bends in two-dimensional PC slabs which are widely used for the manipulation of photons. It is found that optical solitons are completely destroyed when trying to pass through the conventional waveguide bend. With appropriate modifications to the bend structure, however, perfect transmission of optical solitons can be realized. The criteria for the design of waveguide bends with low reflection loss are also generalized.
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42.65.Wi Nonlinear waveguides
42.65.Tg Optical solitons; nonlinear guided waves
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Origin of pinning enhancement in a ferromagnet-superconductor bilayer

Marta Z. Cieplak, X. M. Cheng, C. L. Chien, and Hai Sang

J. Appl. Phys. 97, 026105 (2005); http://dx.doi.org/10.1063/1.1839631 (3 pages) | Cited 11 times

Online Publication Date: 27 December 2004

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Vortex pinning has been studied for the superconducting Nb film covering ferromagnetic Co/Pt multilayer with perpendicular magnetic anisotropy, in which the magnetization reversal proceeds via domain-wall motion. Large enhancement of pinning in the Nb film has been observed in the final stages of the reversal process, and we demonstrate that it is caused by residual uninverted dendrite-shaped magnetic domains.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
68.65.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Organic thin-film transistors with improved characteristics using lutetium bisphthalocyanine as a buffer layer

Jun Wang, Haibo Wang, Jian Zhang, Xuanjun Yan, and Donghang Yan

J. Appl. Phys. 97, 026106 (2005); http://dx.doi.org/10.1063/1.1840093 (3 pages) | Cited 18 times

Online Publication Date: 27 December 2004

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Organic thin-film transistors (OTFTs) with a buffer layer sandwiched between source/drain electrodes and organic semiconductor are demonstrated. An intrinsic molecular semiconductor, Lutetium bisphthalocyanine (LuPc2), is used as the buffer layer due to its high carrier density (1016 cm3). Compared with conventional OTFTs, the introduction of the buffer layer leads to on-state current increases from 700 nA to 2.5 μA, field-effect mobility increases from 0.7×10−2 to 1.58×10−2 cm2/V s, and threshold voltage downshifts from −21 to −11 V for the linear region. The on/off current ratio is improved to a level of 104. Mechanisms of performance improvement are attributed to include the difference of the Fermi level and interface dipolar between LuPc2 and Au. Our results demonstrate that it is an effective method to improve linear region characteristics by using a molecular semiconductor as the buffer layer.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Dn Low-field transport and mobility; piezoresistance
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