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30 Jan 2006

Volume 88, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 051101 (2006); http://dx.doi.org/10.1063/1.2168491 (3 pages)

H. Lohmeyer, K. Sebald, C. Kruse, R. Kröger, J. Gutowski, D. Hommel, J. Wiersig, N. Baer, and F. Jahnke
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Capacitance-voltage investigation of high-purity InAs/GaSb superlattice photodiodes

Andrew Hood, Darin Hoffman, Yajun Wei, Frank Fuchs, and Manijeh Razeghi

Appl. Phys. Lett. 88, 052112 (2006); http://dx.doi.org/10.1063/1.2172399 (3 pages) | Cited 28 times

Online Publication Date: 3 February 2006

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The residual carrier backgrounds of binary type-II InAs/GaSb superlattice photodiodes with cutoff wavelengths around 5 μm have been studied in the temperature range between 20 and 200 K. By applying a capacitance-voltage measurement technique, a residual background concentration below 1015 cm−3 has been found. At temperatures below 100 K carrier freeze-out is observed with a thermal activation energy of 4.5 meV, leading to net carrier concentrations at 77 K in the mid 1014 cm−3.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Observation of the subgap optical absorption in polymer-fullerene blend solar cells

L. Goris, A. Poruba, L. Hod’ákova, M. Vaněček, K. Haenen, M. Nesládek, P. Wagner, D. Vanderzande, L. De Schepper, and J. V. Manca

Appl. Phys. Lett. 88, 052113 (2006); http://dx.doi.org/10.1063/1.2171492 (3 pages) | Cited 52 times

Online Publication Date: 3 February 2006

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This letter reports on highly sensitive optical absorption measurements on organic donor-acceptor solar cells, using Fourier-transform photocurrent spectroscopy (FTPS). The spectra cover an unprecedented dynamic range of eight to nine orders of magnitude making it possible to detect defect and disorder related sub-band gap transitions. Direct measurements on fully encapsulated solar cells with an active layer of poly[2-methoxy-5-(3′,7′-dimethyl-octyloxy)]-p-phenylene-vinylene:(6,6)-phenyl-C61-butyric-acid (1:4 weight ratio) enabled a study of the intrinsic defect generation due to UV illumination. Solar cell temperature annealing effects in poly(3-hexylthiophene):PCBM (1:2 weight ratio) cells and the induced morphological changes are related to the changes in the absorption spectrum, as determined with FTPS.
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84.60.Jt Photoelectric conversion
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments

Negative refraction of spintronics and spin beam splitter

Xiangdong Zhang

Appl. Phys. Lett. 88, 052114 (2006); http://dx.doi.org/10.1063/1.2167792 (3 pages) | Cited 12 times

Online Publication Date: 3 February 2006

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The spin-polarized injections through the lateral interface between two regions with different strengths of spin-orbit interactions have been investigated. In the presence of the spin-orbit coupling of both Rashba and Dresselhaus types, the phenomena of negative refraction of spintronics have been found. An electron beam with some angles of incidence after passing through such an interface splits into two beams with different spin polarizations propagating in negative and positive directions, respectively. Thus, a spin beam splitter has been proposed based on such an interface.
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72.25.Mk Spin transport through interfaces
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
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Cycle-by-cycle observation of single-domain-to-vortex transitions in magnetic nanodisks

Ana-Vanessa Jausovec, Gang Xiong, and Russell P. Cowburn

Appl. Phys. Lett. 88, 052501 (2006); http://dx.doi.org/10.1063/1.2170403 (3 pages) | Cited 10 times

Online Publication Date: 30 January 2006

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The switching behavior of permalloy (Ni81Fe19) disks with dimensions close to the experimentally determined phase boundary separating the single domain and vortex ground states was investigated. The disks fabricated with electron beam lithography and thermal evaporation were 97 nm wide and 26 nm thick. The remanence curve, measured with a magneto-optical Kerr magnetometer, shows the presence of three different remanence states in different magnetic field regimes; vortex state at fields below 110 Oe, metastable state at fields 110 Oe<H<520 Oe, and single domain state at fields above 520 Oe. High sensitivity magneto-optical measurements combined with an advanced applied field sequence allowed a cycle-by-cycle observation of the collapse of the single domain state into the vortex ground state via a partially remanent metastable state.
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75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Tt Fine-particle systems; nanocrystalline materials

Superconductor-semiconductor magnetic microswitch

C. Castellana, F. Giazotto, M. Governale, F. Taddei, and F. Beltram

Appl. Phys. Lett. 88, 052502 (2006); http://dx.doi.org/10.1063/1.2172018 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2006

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A hybrid superconductor-two-dimensional electron gas microdevice is presented. Its working principle is based on the suppression of Andreev reflection at the superconductor-semiconductor interface caused by a magnetic barrier generated by a ferromagnetic strip placed on top of the structure. Device switching is predicted with fields up to some mT and working frequencies of several GHz, making it promising for applications ranging from microswitches and storage cells to magnetic field discriminators.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
73.20.−r
73.23.−b
73.40.−c

Fabrication and microstructure of high coercivity FePt thin films at 400 °C

Z. L. Zhao, J. S. Chen, J. Ding, J. B. Yi, B. H. Liu, and J. P. Wang

Appl. Phys. Lett. 88, 052503 (2006); http://dx.doi.org/10.1063/1.2168256 (3 pages) | Cited 21 times

Online Publication Date: 1 February 2006

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L10 phase FePt thin films deposited on MgO (100) single-crystal substrate with good (001) texture were investigated. Epitaxial growth of the FePt (001) films was observed with a deposition temperature of 400 °C. With ultrathin Ag intermediate layers deposited between FePt layers, the film structures changed from an interconnection network to an isolated-island character. The perpendicular coercivity of the FePt film dramatically increased from 6.5 to 32.5 kOe. The improvement of the magnetic properties may be attributed to the formation of island structures by the additive Ag in the FePt films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology

Nonbolometric photoresponse in (La,Pr)0.67Ca0.33MnO3 thin films

Rajeswari M. Kolagani, M. A. Overby, V. N. Smolyaninova, A. Davidson, and D. E. Cox

Appl. Phys. Lett. 88, 052504 (2006); http://dx.doi.org/10.1063/1.2168687 (3 pages) | Cited 1 time

Online Publication Date: 1 February 2006

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We have studied light-induced resistance changes (photoresponse) in the colossal magnetoresistive manganite material (La,Pr)0.67Ca0.33MnO3. The metal-insulator transition in this material is understood to be driven by the percolation of the metallic channel in an inhomogeneous matrix of insulating and metallic components. Our experiments reveal a nonthermal (nonbolometric) component of the light-induced resistance change, in addition to the expected resistance change related to heating (bolometric effect). This nonthermal component is seen only in the metal-insulator transition region. Our results suggest that this component may be associated with the light-induced resistance decrease in the insulating regions through an electronic mechanism.
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75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
71.30.+h Metal-insulator transitions and other electronic transitions
72.60.+g Mixed conductivity and conductivity transitions
64.60.A- Specific approaches applied to studies of phase transitions

Micromagnetic properties of MnAs(0001)/GaAs(111) epitaxial films

R. Engel-Herbert, T. Hesjedal, D. M. Schaadt, L. Däweritz, and K. H. Ploog

Appl. Phys. Lett. 88, 052505 (2006); http://dx.doi.org/10.1063/1.2171790 (3 pages) | Cited 6 times

Online Publication Date: 2 February 2006

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The micromagnetic properties of MnAs thin films grown on the (111)B-oriented GaAs surface have been investigated. Compared to films grown on (001) surfaces, these films exhibit completely different domain patterns, as the c axis of the hexagonal unit cell is oriented normal to the surface. In the course of the first order phase transition, ferromagnetic α-MnAs forms a network of quasihexagonal areas separated by β-MnAs. We present an analysis of the micromagnetic properties based on imaging and simulations. We observe closure domains that either appear as a vortex-like state or a stripe structure.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.50.Dd Nonmetallic ferromagnetic materials

Magnetic field dependence of voltage-current characteristics of Fe3O4 thin films at room temperature

Kun Zhao, Jiafeng Feng, Yanhong Huang, Jian-gao Zhao, Huibin Lu, Xiufeng Han, and Wenshan Zhan

Appl. Phys. Lett. 88, 052506 (2006); http://dx.doi.org/10.1063/1.2171791 (3 pages) | Cited 3 times

Online Publication Date: 2 February 2006

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Fe3O4 thin films have been fabricated on glass substrate by the facing-target sputtering technique and their field-modulated voltage-current behavior was investigated. The nonlinear dependence of voltage on current density displays a switching from high-resistivity to low-resistivity states above a threshold current density. The low-resistivity state is very sensitive to the applied magnetic field, and a large negative magnetoresistance of ∼ −27% is observed at 300 Oe under a high current density of 100 A cm−2 at room temperature. Furthermore, the dependence of the magnetoresistance on the magnetic field reveals a good linear relationship. The observed results seem to favor a picture of spin-polarized intergrain tunneling through the grain boundaries.
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75.70.Ak Magnetic properties of monolayers and thin films
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport

Observation of thermally activated domain wall transformations

M. Laufenberg, D. Backes, W. Bührer, D. Bedau, M. Kläui, U. Rüdiger, C. A. F. Vaz, J. A. C. Bland, L. J. Heyderman, F. Nolting, S. Cherifi, A. Locatelli, R. Belkhou, S. Heun, and E. Bauer

Appl. Phys. Lett. 88, 052507 (2006); http://dx.doi.org/10.1063/1.2168677 (3 pages) | Cited 54 times

Online Publication Date: 2 February 2006

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The spin structure of head-to-head domain walls in Ni80Fe20 structures is studied using high-resolution photoemission electron microscopy. The quantitative phase diagram is extracted from these measurements and found to exhibit two phase boundaries between vortex and transverse domain walls. The results are compared with available theoretical predictions and micromagnetic simulations and differences to the experiment are explained, taking into account thermal excitations. Temperature-dependent measurements show a thermally activated transformation of transverse to vortex domain walls in 7 nm thick and 730 nm wide structures at a transition temperature between 260 °C and 310 °C, which corresponds to a nucleation barrier height for a vortex wall between 6.7×10−21 J and 8.0×10−21 J.
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75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Fe implanted ferromagnetic ZnO

K. Potzger, Shengqiang Zhou, H. Reuther, A. Mücklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdörfer, and T. P. Papageorgiou

Appl. Phys. Lett. 88, 052508 (2006); http://dx.doi.org/10.1063/1.2169912 (3 pages) | Cited 61 times

Online Publication Date: 2 February 2006

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Room-temperature ferromagnetism has been induced within ZnO single crystals by implant doping with Fe ions. For an implantation temperature of 623 K and an ion fluence of 4×1016 cm−2, very tiny Fe particles, formed inside the host matrix, are responsible for the ferromagnetic properties. They were identified using synchrotron x-ray diffraction and Mössbauer spectroscopy. On the other hand, Fe ions implanted at a temperature of 253 K and an ion fluence of 4×1015 cm−2 are incorporated into the host matrix and develop a room temperature diluted magnetic semiconductor.
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75.50.Pp Magnetic semiconductors
61.72.uj III-V and II-VI semiconductors
75.50.Bb Fe and its alloys
61.72.S- Impurities in crystals
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Enhanced spin injection polarization in Co/Cu/Co nonlocal lateral spin valves

Y. Ji, A. Hoffmann, J. E. Pearson, and S. D. Bader

Appl. Phys. Lett. 88, 052509 (2006); http://dx.doi.org/10.1063/1.2170138 (3 pages) | Cited 30 times

Online Publication Date: 2 February 2006

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Nonlocal spin injection is demonstrated in Co/Cu/Co lateral spin valves. Measurement of a series of structures with varying Cu length between the Co electrodes permits a direct determination of both the Cu spin diffusion length λs and the spin injection polarization P at the Co/Cu interface. The value of λs is 200±20 nm at 10 K and ≥ 110 nm at 300 K, which is shorter than previously reported, due to the possible presence of impurities in the Cu. However, the value of P is >7%, which is improved compared with previous reports of 2%, which is attributed to a higher interfacial quality.
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72.25.Ba Spin polarized transport in metals
75.47.Np Metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Hx Magnetic impurity interactions
75.50.Cc Other ferromagnetic metals and alloys
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Observation of [110] surface band within {101} a-domain of heteroepitaxial PbTiO3 thin film fabricated by hydrothermal epitaxy

S. K. Choi, S. H. Ahn, W. W. Jung, J. C. Park, S. A. Song, C. B. Lim, and Yasuo Cho

Appl. Phys. Lett. 88, 052901 (2006); http://dx.doi.org/10.1063/1.2171489 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2006

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Heteroepitaxial PbTiO3 film on an Nb-doped (001) cubic SrTiO3 substrate was fabricated by hydrothermal epitaxy at 200 °C. Piezoresponse force microscopy and x-ray Θ rocking curves confirmed that the film showed a c/a/c/a multi-domain structure even though it did not undergo a cubic paraelectric (PE) to tetragonal ferroelectric (FE) phase transition. After heat treatment of this film at 600 °C, we observed the [110] surface band within the a-domain, which was formed through the PE to FE phase transition. We also found that a [110] surface band existed along the (1math1) plane within the a-domain. We predicted that the [110] surface band would be monoclinic phase due to the interaction of two different variants of a-domains in the presence of a c-domain in the heteroepitaxial PbTiO3 film.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments

Microscopic model for dielectric constant in metal-insulator-metal capacitors with high-permittivity metallic oxides

Stéphane Bécu, Sébastien Crémer, and Jean-Luc Autran

Appl. Phys. Lett. 88, 052902 (2006); http://dx.doi.org/10.1063/1.2170137 (3 pages) | Cited 13 times

Online Publication Date: 31 January 2006

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A microscopic model for metal-insulator-metal (MIM) capacitors with high permittivity metallic oxides is developed to determine the electric field dependence of dielectric constant. The model indicates that the metallic cation displacement in the tetrahedral cell is at the origin of the dielectric constant variations. The temperature dependence has also been included to compare the model with experiment and to give an indication of the reliability of the model. The experimental data that are compared to our model have been obtained from capacitance versus voltage (C-V) characterization on MIM capacitors with alumina as dielectric and TiN electrodes. The C-V curves have been performed at a frequency of 100 kHz for different temperatures ranging from 200 to 400 K.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
77.22.Ch Permittivity (dielectric function)

Electrical and dielectric behaviors of Ti3SiC2/hydroxyapatite composites

Sui-Lin Shi, Wei Pan, Ruo-Bing Han, and Chun-Lei Wan

Appl. Phys. Lett. 88, 052903 (2006); http://dx.doi.org/10.1063/1.2168684 (2 pages) | Cited 4 times

Online Publication Date: 1 February 2006

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Ti3SiC2/Hydroxyapatite composites were prepared by spark plasma sintering. The effective dc conductivity and dielectric behavior of the composites were studied. The percolation theory was applied to demonstrate the dielectric behavior of the composites. The experimental results showed that the dielectric constant increased greatly with the Ti3SiC2 concentration, and can reach as high as 700 when the Ti3SiC2 concentration was close to the percolation threshold.
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77.84.Lf Composite materials
72.80.Tm Composite materials
77.22.Ch Permittivity (dielectric function)

Preparation of perovskite Pb(Zn1/3Nb2/3)O3-based thin films from polymer-modified solution precursors

Kui Yao, Shuhui Yu, and Francis Eng Hock Tay

Appl. Phys. Lett. 88, 052904 (2006); http://dx.doi.org/10.1063/1.2171801 (3 pages) | Cited 13 times

Online Publication Date: 3 February 2006

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Epitaxial perovskite Pb(Zn1/3Nb2/3)O3 (PZN)-based ferroelectric thin films were prepared through a chemical solution approach, in which the solution precursors were appropriately modified with polyethylene glycol (PEG). The addition of PEG in the solution dramatically promoted the perovskite phase while suppressed the pyrochlore phase, although PEG was pyrolyzed before the crystallization. The interactions between PEG and metal ions were identified through examining the chemical states of the ions using x-ray photoelectron spectroscopy. The ferroelectric and piezoelectric properties of an obtained thin film sample with a composition of 0.462PZN–0.308PMN–0.23PT [PT:PbTiO3;PMN:Pb(Mg1/3Nb2/3)O3] were characterized, showing a very low coercive field, high dielectric constant, and strong piezoelectric effect.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
79.60.Bm Clean metal, semiconductor, and insulator surfaces
77.65.-j Piezoelectricity and electromechanical effects
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Effects of substrate curvature on the adsorption of poly(3-hexylthiophene) on single-walled carbon nanotubes

Roland G. S. Goh, Nunzio Motta, John M. Bell, and Eric R. Waclawik

Appl. Phys. Lett. 88, 053101 (2006); http://dx.doi.org/10.1063/1.2168514 (3 pages) | Cited 13 times

Online Publication Date: 30 January 2006

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A detailed study of poly(alkylthiophene) self-assembly and organization on single-walled carbon nanotubes (SWNTs) is presented. Monolayers of regioregular poly(3-hexyl thiophene) (rrP3HT) adsorbed on SWNTs have been imaged by using scanning tunneling microscopy. Our results show that the rrP3HT interchain distance is greater for rrP3HT monolayers adsorbed onto the curved surfaces of SWNTs than on the flat surfaces of highly ordered pyrolytic graphite samples. Comparisons between the native polymer deposited on graphite and the composite structure confirmed that the presence of carbon nanotubes in rrP3HT produces a new material with a high degree of order at the molecular level.
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81.05.Qk Reinforced polymers and polymer-based composites
81.05.ub Fullerenes and related materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.43.Mn Adsorption kinetics
81.16.Dn Self-assembly

GaN quantum dots doped with Tb

Y. Hori, T. Andreev, D. Jalabert, E. Monroy, Le Si Dang, B. Daudin, M. Tanaka, and O. Oda

Appl. Phys. Lett. 88, 053102 (2006); http://dx.doi.org/10.1063/1.2168504 (3 pages) | Cited 10 times

Online Publication Date: 30 January 2006

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Tb-doped GaN quantum dots grown by molecular beam epitaxy have been studied. These nanostructures present intense photoluminescence from intra-4f transitions of Tb3+ ions. It has been found that Tb atoms enhance the desorption process of Ga adatoms from the growing surface, leading to a reduction of the growth rate and, eventually, to an inhibition of the GaN quantum dot formation for a Tb content of about 2% at the growth temperature of 760 °C. The presence of Tb inside quantum dots is suggested by intense photoluminescence in the green spectral range at room temperature from intra-4f transitions of Tb3+ ions, by contrast to the Tb-doped GaN thick layers.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
68.43.Mn Adsorption kinetics

Pore size dependence of field emission from nanoscale porous carbon

M. Ojima, S. Hiwatashi, H. Araki, A. Fujii, M. Ozaki, and K. Yoshino

Appl. Phys. Lett. 88, 053103 (2006); http://dx.doi.org/10.1063/1.2170436 (3 pages) | Cited 2 times

Online Publication Date: 30 January 2006

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Carbon inverse opals with three-dimensional nanoporous structures are fabricated by a template method using synthetic opals formed by the sedimentation of SiO2 spheres. The pore size of the carbon inverse opals ranges widely from about 74 nm to 550 nm depending on the diameter of the SiO2 spheres. These nanoporous structures of carbon exhibit excellent characteristics as electron emitters. As the pore size of porous carbon decreases, the effective emission area of field emission increases. The main emitter sites of porous carbon are interpreted to be the edges formed in the boundary of the neighboring pores. The emission characteristics have drastically improved upon heat treatment at high temperatures (about 2760 °C).
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79.70.+q Field emission, ionization, evaporation, and desorption
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials

In situ synthesis and nonlinear optical properties of Au:Ag nanocomposite polymer films

B. Karthikeyan, M. Anija, and Reji Philip

Appl. Phys. Lett. 88, 053104 (2006); http://dx.doi.org/10.1063/1.2168667 (3 pages) | Cited 38 times

Online Publication Date: 30 January 2006

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We report a simple in situ synthesis procedure for Au:Ag nanocomposite polymer (NCP) films using polyvinyl alcohol as the reducing agent. Optical measurements show absorption bands of varying strengths around 530 and 410 nm. The presence of nanoparticles is confirmed from Transmission Electron Microscopy (TEM). Nonlinear optical response is studied using 7 ns laser pulses, for near-resonant and off-resonant excitation wavelengths (532 and 1064 nm, respectively). Samples exhibit saturable as well as induced absorption. These materials have the potential to be used as saturable absorbers and optical limiters.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.-w Optical properties of specific thin films
81.16.-c Methods of micro- and nanofabrication and processing
78.40.-q Absorption and reflection spectra: visible and ultraviolet
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Two-dimensional nanotriangle and nanoring arrays on silicon wafer

Dongdong Jia and Anura Goonewardene

Appl. Phys. Lett. 88, 053105 (2006); http://dx.doi.org/10.1063/1.2168938 (3 pages) | Cited 9 times

Online Publication Date: 30 January 2006

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Gold and tungsten were deposited on silicon wafer and/or glass substrates by using random incidence sputtering deposition and thermal vapor deposition techniques. Two-dimensional tungsten nanotriangle and gold nanoring arrays were obtained on the silicon wafer substrate and examined using scanning electron microscope and atomic force microscope analysis. The size of the equal tungsten nanotriangles is within 100 nm per side and 210 nm apart from each other. The size of gold nanorings is 220 nm diameter, 40 nm wide, 10 nm thick, and 560 nm apart from each other. No nanorings were found on the glass substrate. Mechanisms for the formation of nanoring arrays are discussed.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Cd Deposition by sputtering
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)

Specific contact resistivity of nanowire devices

E. Stern, G. Cheng, M. P. Young, and M. A. Reed

Appl. Phys. Lett. 88, 053106 (2006); http://dx.doi.org/10.1063/1.2163454 (3 pages) | Cited 20 times

Online Publication Date: 30 January 2006

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We present a study of specific contact resistivity from multiterminal Kelvin measurements for GaN nanowire (NW) devices. Nanowire specific contact resistivity is found to be process-independent and in good agreement to that of epitaxially grown GaN. A strong dependence of NW specific contact resistivity on carrier density is observed to be in good agreement with theory.
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85.35.-p Nanoelectronic devices
85.30.-z Semiconductor devices
73.40.Cg Contact resistance, contact potential

Nonlinear characteristics of the Fowler–Nordheim plot for field emission from In2O3 nanowires grown on InAs substrate

S. Q. Li, Y. X. Liang, and T. H. Wang

Appl. Phys. Lett. 88, 053107 (2006); http://dx.doi.org/10.1063/1.2159092 (3 pages) | Cited 21 times

Online Publication Date: 31 January 2006

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Nonlinear characteristics of the Fowler–Nordheim (F–N) plot for field emission from In2O3 nanowires (NWs) is investigated. The field emission from the aligned and nonaligned In2O3 NWs are measured and a stable emission with fluctuations less than 10% was obtained for the aligned In2O3 NWs. It is found that the nonaligned In2O3 NWs with a longer length have higher turn-on and threshold electric fields. Their F–N plots, showing pronounced nonlinear characteristics, are divided into several regions based on physical origins. Field penetration competes with surface states in influencing the field emission of the In2O3 NWs with increasing the electric field, which is responsible for the nonlinear characteristics of the F–N plots.
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81.07.Bc Nanocrystalline materials
73.22.-f Electronic structure of nanoscale materials and related systems
79.70.+q Field emission, ionization, evaporation, and desorption

Membrane folding to achieve three-dimensional nanostructures: Nanopatterned silicon nitride folded with stressed chromium hinges

William J. Arora, Anthony J. Nichol, Henry I. Smith, and George Barbastathis

Appl. Phys. Lett. 88, 053108 (2006); http://dx.doi.org/10.1063/1.2168516 (3 pages) | Cited 27 times

Online Publication Date: 31 January 2006

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Silicon nitride membranes were nanopatterned and then folded into three-dimensional (3D) configurations. The out-of-plane folding was achieved using stressed metal hinges. The concept of folding nanopatterned membranes into 3D shapes is referred to as nanostructured origami because of the similarity to the Japanese paper-art of origami, in which two-dimensional surfaces are folded into volumetric shapes. The stressed metal hinges were modeled analytically and compared to experiment. Experimental results demonstrated controllable folding of nanopatterned silicon nitride membranes.
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81.07.Bc Nanocrystalline materials
81.16.Rf Micro- and nanoscale pattern formation
61.46.-w Structure of nanoscale materials

Moments-based tight-binding calculations of local electronic structure in InAs/GaAs quantum dots for comparison to experimental measurements

Jun-Qiang Lu, H. T. Johnson, V. D. Dasika, and R. S. Goldman

Appl. Phys. Lett. 88, 053109 (2006); http://dx.doi.org/10.1063/1.2171473 (3 pages) | Cited 6 times

Online Publication Date: 31 January 2006

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Local electronic properties of InAs/GaAs nanostructures are studied using a real-space moments method sp3d5s* tight-binding approach. The order (N) method is unique because it allows for accurate and highly resolved determination of local density of states that accounts for local strain, disorder, and defects, without diagonalization of the full tight-binding Hamiltonian. The effects of free surfaces and strain are first investigated by considering pure, cuboidal GaAs nanostructures. The quantum confinement in an embedded InAs quantum dot is then shown directly through the local densities of states projected on different atoms in the structure. The relationship between effective energy band gap and quantum dot size is mapped onto a simple equation. Finally, the real-space study is applied to quantum dot structures observed experimentally using scanning tunneling microscopy. Atomic positions are obtained from the images and used as input into the tight-binding calculations in order to study interfacial effects on the local electronic structure of real embedded quantum dots.
Show PACS
71.20.Nr Semiconductor compounds
73.21.La Quantum dots
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
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