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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Room-temperature ferromagnetism in Mn and Fe codoped In2O3

G. Peleckis, X. L. Wang, and S. X. Dou

Appl. Phys. Lett. 88, 132507 (2006); http://dx.doi.org/10.1063/1.2191093 (3 pages) | Cited 44 times

Online Publication Date: 28 March 2006

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The synthesis and characterization of polycrystalline room-temperature ferromagnetic semiconductor (In0.9Fe0.1−xMnx)2O3 (x = 0–0.1) oxide are reported. All of the samples with intermediate x values are ferromagnetic at room temperature. The highest saturation magnetization moment at 300 K per total amount of magnetic ion is reached in the (In0.9Fe0.04Mn0.06)2O3 sample. The lattice constant a increases linearly with increasing Mn content. Fe-only doped samples were paramagnetic, while a Mn-only doped sample was found to be ferromagnetic below TC = 46 K.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.20.Ck Nonmetals

Grain and grain-boundary critical currents in coated conductors with noncorrelating YBa2Cu3O7 and substrate grain-boundary networks

A. Palau, T. Puig, X. Obradors, R. Feenstra, A. A. Gapud, E. D. Specht, D. M. Feldmann, and T. G. Holesinger

Appl. Phys. Lett. 88, 132508 (2006); http://dx.doi.org/10.1063/1.2172737 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2006

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The superconducting grain-boundary (GB) network of coated conductors (CCs) is usually assumed to be a replica of the substrate network. In this letter, we analyze IBAD and RABITS CCs, where such replica either do or do not exist. We have analyzed the effect of GB overgrowth on the critical currents by quantifying the average superconducting grain size and determining the intragrain and grain-boundary critical current densities, JcG and JcGB. We have employed a recently developed inductive methodology enabling the simultaneous determination of these three parameters. We show that the percolative JcGB may be reduced by 50% if the GB networks do not correlate, while JcG and the grain pinning properties appear unaffected.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
61.72.Mm Grain and twin boundaries

Influence of Co addition on the magnetocaloric effect of FeCoSiAlGaPCB amorphous alloys

V. Franco, J. M. Borrego, A. Conde, and S. Roth

Appl. Phys. Lett. 88, 132509 (2006); http://dx.doi.org/10.1063/1.2188385 (3 pages) | Cited 31 times

Online Publication Date: 28 March 2006

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The FeCoSiAlGaPCB alloys can be prepared as bulk amorphous materials, with outstanding mechanical properties and increased electrical resistivity. These features can be beneficial for their application as a magnetic refrigerant. The influence of Co addition on the magnetic entropy change of the alloy has been studied. This compositional modification displaces the temperature of the peak entropy change closer to room temperature, but reduces the refrigerant capacity of the material. For the Co-free alloy, the peak entropy change is increased with respect to a Finemet alloy containing Mo, but its refrigerant capacity is not enhanced.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
81.05.Bx Metals, semimetals, and alloys

Transport properties of low angle grain boundaries in Y1−xCaxBa2Cu3O7−δ films at high magnetic fields

A. Weber, C. W. Schneider, S. Hembacher, Ch. Schiller, S. Thiel, and J. Mannhart

Appl. Phys. Lett. 88, 132510 (2006); http://dx.doi.org/10.1063/1.2190460 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2006

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The critical current density of grain boundaries and grains in Y1−xCaxBa2Cu3O7−δ films has been measured in magnetic fields up to 10 T. As a function of temperature the critical current densities across 8° [001]-tilt boundaries display a maximum at ≈ 15–20 K for 0.04 ⩽ x ⩽ 0.2 and fields of several teslas. Opposite to the behavior of large angle grain boundaries, calcium doping is found not to enhance the critical current densities of low angle grain boundaries (θ ⩽ 8°).
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Enhanced and oscillatory magnetoresistance of thin Fe(001) films

C. Martinez-Boubeta, Ll. Balcells, and A. Cebollada

Appl. Phys. Lett. 88, 132511 (2006); http://dx.doi.org/10.1063/1.2191092 (3 pages) | Cited 4 times

Online Publication Date: 29 March 2006

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We have studied the magnetoresistance of single-crystalline (001) Fe films prepared by sputtering techniques and covered by epitaxial MgO or Pt protective layers. The influence of the thickness of the magnetic layer as well as of the nature of the capping layer on the Fe anisotropic magnetoresistance was investigated by four-terminal probe, measurements performed with the current J in the [110] magnetically hard direction. We found an enhancement in the magnetoresistance value with respect to bulk and oscillations in the high field regime in MgO covered Fe/MgO(001) ultrathin films. A plausible explanation is that the enhanced magnetoresistance is due to electronic confinement effects, not present in similar Pt/Fe/MgO(001) samples.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

First-principles calculations on magnetic properties of interface-rippled Co/α-Al2O3/Co

Chiho Kim and Yong-Chae Chung

Appl. Phys. Lett. 88, 132512 (2006); http://dx.doi.org/10.1063/1.2191408 (3 pages) | Cited 3 times

Online Publication Date: 31 March 2006

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The effects of the interface fluctuations on the magnetic properties of a Co/α-Al2O3/Co magnetic tunnel junction were intensively investigated using first-principles calculations. Hybridization of Co-3d and O-2p orbitals resulted in the covalent bonds between Co and three O atoms at the interface of Co(111)/α-Al2O3(0001) and, subsequently, interfacial Co atoms became undulated as much as 34.6% of the interlayer distance measured in the z direction. The magnetic moment of Co atoms at the rippled interface was enhanced to 1.95μB, while the value of the other ferromagnetic Co atoms remained unchanged. Significantly induced minority-spin density of states at the Fermi energy of the Co-interface atoms led to a highly negative spin polarization, −52.0%, at the junction interface. Interestingly, the spin polarization value for the barrier layer was in the range of −6.3%–59.2%.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Finite-temperature magnetism of tetragonal iron

Jian-Tao Wang, Ding-Sheng Wang, and Y. Kawazoe

Appl. Phys. Lett. 88, 132513 (2006); http://dx.doi.org/10.1063/1.2191469 (3 pages) | Cited 2 times

Online Publication Date: 31 March 2006

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Based on ab initio Monte Carlo approach, finite-temperature magnetism of tetragonal Fe is studied. It is shown that the ground state magnetic structure changes from ferromagnetic to antiferromagnetic as the structure transforms from bcc to fcc. The Curie temperature (TC) or Néel temperatures (TN) are very sensitive to the lattice distortion, which decreases from bcc to fcc and then increases over the fcc range. There are a maximum of TC at the bcc and a minimum of TN around the fcc limit due to the change of the coupling distance and symmetry consideration.
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75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
64.70.K- Solid-solid transitions
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Enhanced ferroelectric properties of Cr-doped BiFeO3 thin films grown by chemical solution deposition

Jong Kuk Kim, Sang Su Kim, Won-Jeong Kim, Amar S. Bhalla, and Ruyan Guo

Appl. Phys. Lett. 88, 132901 (2006); http://dx.doi.org/10.1063/1.2189453 (3 pages) | Cited 97 times

Online Publication Date: 27 March 2006

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Multiferroic Cr-doped BiFeO3 (BFO) thin films were prepared on Pt/TiO2/SiO2/Si(100) substrates by a chemical solution deposition method. From the x-ray photoelectron spectroscopy measurements, it was observed that the valence number of Fe ion in undoped and Cr-doped BFO thin films was found to be almost 3+. It was found that Cr-doped BFO thin films exhibited good ferroelectric properties, such as improved leakage-current density and P-E hysteresis characteristics. The 3 mol % Cr-doped BFO thin film showed a leakage-current density of 9.2×10−7 A/cm2 at 100 kV/cm and a large remanent polarization (Pr) of 61 μC/cm2 at room temperature.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.Dj Domain structure; hysteresis
75.50.Ee Antiferromagnetics
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Ej Polarization and depolarization

Effect of misfit strains on fourth and sixth order permittivity in (Ba0.60,Sr0.40)TiO3 films on orthorhombic substrates

W. K. Simon, E. K. Akdogan, A. Safari, and J. Bellotti

Appl. Phys. Lett. 88, 132902 (2006); http://dx.doi.org/10.1063/1.2189667 (3 pages) | Cited 17 times

Online Publication Date: 27 March 2006

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The in-plane dielectric response of [110] oriented Ba0.60Sr0.40TiO3 epitaxial films grown on [100] NdGaO3 is used to determine the field induced polarization at 10 GHz. The nonlinear polarization curve is used to determine the linear and nonlinear permittivity terms for the in-plane principal directions, [001] and [math10]. Studied films are in the thickness range of 75–1200 nm, and clearly show the influences that drive tunability down with increasing residual strain. The variation of the tunability, along the [001] direction, proves to be less sensitive to residual strain then the [math10] direction, although [math10] is capable of greater tunability at low residual strains.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.60.Bs Mechanical and acoustical properties
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
81.40.Jj Elasticity and anelasticity, stress-strain relations

Molecular beam epitaxy of YMnO3 on c-plane GaN

Y. Chye, T. Liu, D. Li, K. Lee, D. Lederman, and T. H. Myers

Appl. Phys. Lett. 88, 132903 (2006); http://dx.doi.org/10.1063/1.2189832 (3 pages) | Cited 21 times

Online Publication Date: 27 March 2006

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Epitaxial YMnO3 films were grown on (0001) GaN-on-sapphire templates using molecular beam epitaxy. The YMnO3 maintained the (0001) orientation with an in-plane YMnO3/GaN epitaxial relationship of (0001)‖(0001); [1math00]‖[11math0]. The YMnO3 was ferroelectric at room temperature with a remanent polarization of ∼ 3.2 μC/cm2 and a saturation polarization of ∼ 12 μC/cm2. This heterostructure is a promising candidate for multifunctional structures that integrate ferroelectrics with GaN-based high-power and short-wavelength light-emitting devices.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
77.22.Ej Polarization and depolarization

High dielectric tunability in ferroelectric-paraelectric bilayers and multilayer superlattices

S. Zhong, S. P. Alpay, and J. V. Mantese

Appl. Phys. Lett. 88, 132904 (2006); http://dx.doi.org/10.1063/1.2189909 (3 pages) | Cited 31 times

Online Publication Date: 27 March 2006

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The dielectric tunability of ferroelectric/paraelectric bilayers and multilayer superlattices are examined theoretically. A numerical analysis is carried out for a pseudomorphic (001) BaTiO3/SrTiO3 heteroepitaxial bilayer on (001) SrTiO3 and a stress-free BaTiO3/SrTiO3 bilayer. We show that these structures are capable of tunabilities greater than 90% due to electrostatic and electromechanical coupling between layers. Moreover, we develop the methodology for incorporation conventional integrated circuit silicon dielectrics into heteroepitaxial structures that can reduce current leakage while maintaining high tunability, thereby enabling the device designer flexibility toward the optimization of microwave and millimeter wave elements.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Growth of ultrathin ZrO2 films on Si(100): Film-thickness-dependent band alignment

A. Sandell, P. G. Karlsson, J. H. Richter, J. Blomquist, P. Uvdal, and T. M. Grehk

Appl. Phys. Lett. 88, 132905 (2006); http://dx.doi.org/10.1063/1.2190073 (3 pages) | Cited 18 times

Online Publication Date: 27 March 2006

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The band alignment of ultrathin ZrO2 films of different thickness formed on Si(100) have been monitored with synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy. The films were deposited sequentially by way of metal-organic chemical-vapor deposition in ultrahigh vacuum. A significant decrease in the conduction band offset is found for increasing film thickness. It is accompanied by a corresponding increase of the valence band offset. The variations originate in the formation of an interfacial layer characterized by a lower degree of Zr-O interaction than in bulk ZrO2 but with no clear evidence for partially occupied Zr 4d dangling bonds.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
77.55.-g Dielectric thin films
71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces

New phase transition associated with configuration of oxygen vacancies in VO1.965 nanometer ceramics

X. M. Xiong, L. Chen, L. L. Zhang, X. Y. Wu, C. M. Zheng, and J. X. Zhang

Appl. Phys. Lett. 88, 132906 (2006); http://dx.doi.org/10.1063/1.2190447 (3 pages) | Cited 1 time

Online Publication Date: 27 March 2006

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Little attention was paid to the effect of oxygen vacancy configuration, although it is well known that oxygen vacancy plays a key role in determining the electrical and optical properties of VO2. By means of different heat treatments, the oxygen vacancy configuration in VO1.965 nanometer ceramic is controlled and its behavior is investigated in detail. It is found that VO1.965 ceramic aged at 60 °C for a day displays a new first order phase transformation at about 30 °C, which is associated with the oxygen vacancy distribution. An explanation based on the symmetry conforming principle is tentatively presented.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.07.Bc Nanocrystalline materials
64.70.K- Solid-solid transitions
61.72.J- Point defects and defect clusters
81.40.Gh Other heat and thermomechanical treatments
61.46.Hk Nanocrystals

Influence of annealing temperature on the band structure of sol-gel Ba0.65Sr0.35TiO3 thin films on n-type Si(100)

H. Lu, J. S. Pan, X. F. Chen, W. G. Zhu, and O. K. Tan

Appl. Phys. Lett. 88, 132907 (2006); http://dx.doi.org/10.1063/1.2189828 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2006

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The annealing temperature effect on the band structure of Ba0.65Sr0.35TiO3 (BST) thin films coated on n-type Si(100) substrate was investigated by ellipsometry and x-ray photoelectron spectroscopy. The band energy shifts of sol-gel BST films annealed at different temperatures are dependent on their developed microstructure. Related to the amorphous BST films annealed at 600 °C, the polycrystalline BST film annealed at 700 °C exhibits narrow band gap, upwards-moved Fermi level, and downwards-moved conduction band minimum, which are believed to contribute the enhanced field emission of BST-coated Si field emitter arrays.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
71.20.Ps Other inorganic compounds
77.80.-e Ferroelectricity and antiferroelectricity
81.40.Gh Other heat and thermomechanical treatments
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Phase transformation and electric field tunable pyroelectric behavior of Pb(Nb,Zr,Sn,Ti)O3 and (Pb,La)(Zr,Sn,Ti)O3 antiferroelectric thin films

Zhengkui Xu, Jiwei Zhai, Wai-Hung Chan, and Haydn Chen

Appl. Phys. Lett. 88, 132908 (2006); http://dx.doi.org/10.1063/1.2191413 (3 pages) | Cited 14 times

Online Publication Date: 31 March 2006

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Phase transformation and pyroelectric behavior of Pb(Nb,Zr,Sn,Ti)O3 (PNZST) and (Pb,La)(Zr,Sn,Ti)O3 (PLZST) antiferroelectric (AFE) thin films were investigated as a function of temperature and dc bias field. A large pyroelectric coefficient of the order of ∼ 3×10−7 C cm−2 K−1 was realized at the ferroelectric (FE) to AFE and the AFE to FE phase transformations in the PLZST and PNZST films, respectively. The phase transformation temperature could be readily adjusted by dc bias for both films. The large pyroelectric coefficient combined with excellent dc tunability at the phase transformation temperature makes these two systems promising candidates for uncooled tunable pyroelectric thermal sensing applications.
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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.B- Phase transitions and Curie point
77.70.+a Pyroelectric and electrocaloric effects

Enhanced electrical polarization and ferromagnetic moment in a multiferroic BiFeO3/Bi3.25Sm0.75Ti2.98V0.02O12 double-layered thin film

Zhenxiang Cheng, Xiaolin Wang, Chinna Venkatasamy Kannan, Kyoshi Ozawa, Hideo Kimura, Takashi Nishida, Shujun Zhang, and Thomas R. Shrout

Appl. Phys. Lett. 88, 132909 (2006); http://dx.doi.org/10.1063/1.2191732 (3 pages) | Cited 30 times

Online Publication Date: 31 March 2006

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Multiferroic BiFeO3/Bi3.25Sm0.75Ti2.98V0.02O12 double-layered thin films on Pt/Ti/SiO2/Si were fabricated using the pulsed-laser deposition technique. The films showed greatly enhanced ferroelectric and ferromagnetic properties. The values of the remanent polarization (2Pr) and coercive field (Ec) were 71.8 μC/cm2 and 148 kV/cm at a maximum applied voltage of 13 V, respectively. The value of the magnetic moment was found to be 17.5 emu/cm3. The enhancement of the polarization originated from the BiFeO3 with Bi3.25Sm0.75Ti2.98V0.02O12 working as a barrier layer. The enhancement of the magnetization is from the structural distortion of BiFeO3, due to partial epitaxial growth on the bismuth titanate surface.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Microphotoluminescence of exciton and biexciton around 1.5 μm from a single InAs/InP(001) quantum dot

G. Saint-Girons, N. Chauvin, A. Michon, G. Patriarche, G. Beaudoin, G. Brémond, C. Bru-Chevallier, and I. Sagnes

Appl. Phys. Lett. 88, 133101 (2006); http://dx.doi.org/10.1063/1.2185008 (3 pages) | Cited 10 times

Online Publication Date: 27 March 2006

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We report on the fabrication by low-pressure metalorganic vapor phase epitaxy of InAs/InP(001) quantum dots (QDs) emitting around 1.5 μm, and on the observation of microphotoluminescence (μPL) from a single QD in this wavelength range. The QDs are diamond shaped, with a density of 6.3∙109 cm−2. μPL experiments were carried out on a QD sample covered with a gold mask containing apertures (diameter of 200 nm). Well defined peaks corresponding to the emission of single QDs were recorded between 1.24 and 1.6 μm. The analysis of the pump power dependence of their intensity allows us to discriminate between exciton and biexciton emission lines.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Invasive growth of Co on (math×2math)R45° reconstructed O/Cu(001)

Xiangdong Liu, Takushi Iimori, Kan Nakatsuji, and Fumio Komori

Appl. Phys. Lett. 88, 133102 (2006); http://dx.doi.org/10.1063/1.2189190 (3 pages) | Cited 10 times

Online Publication Date: 27 March 2006

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Submonolayer growth of Co on the reconstructed Cu(001)(math×2math)R45°–O surface has been investigated by scanning tunneling microscopy. Cu atoms are displaced from the Cu(001)(math×2math)R45°–O structure by incoming Co atoms and subsequently aggregate into elongated islands. The deposited Co atoms are randomly distributed in the oxygen adsorbed surface as individual atoms and clusters at low coverages [ ⩽ 0.4 monolayers (ML)]. For larger coverages ( ≥ 0.5 ML), compact fcc Co patches are formed. The adsorbed oxygen acts as a surfactant. Interfacial intermixing is reduced when Co is deposited on the Cu(001)(math×2math)R45°–O surface.
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68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.43.Fg Adsorbate structure (binding sites, geometry)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.35.Fx Diffusion; interface formation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Mn Adsorption kinetics

Atomically resolved dynamic force microscopy operating at 4.7 MHz

Shigeki Kawai and Hideki Kawakatsu

Appl. Phys. Lett. 88, 133103 (2006); http://dx.doi.org/10.1063/1.2189193 (3 pages) | Cited 17 times

Online Publication Date: 27 March 2006

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We demonstrate atomically resolved frequency modulation dynamic force microscopy operating at 4.7 MHz using the third flexural mode of a silicon cantilever. A high spring constant due to the higher mode realized stable imaging with an amplitude of 2 Å, which was calculated to be a favorable value for high-resolution imaging. Although excessive stiffness decreases the sensitivity of the detection, a stable imaging was realized with a low noise heterodyne laser Doppler interferometer and a narrow bandwidth feedback circuit. An atomically resolved constant frequency shift images of the Si(111)-7×7 were obtained with the exposed and terminated dangling bonds at the tip apex.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
07.60.Ly Interferometers
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces

Comparison of structural and optical properties of InAs quantum dots grown by migration-enhanced molecular-beam epitaxy and conventional molecular-beam epitaxy

N. K. Cho, S. P. Ryu, J. D. Song, W. J. Choi, J. I. Lee, and Heonsu Jeon

Appl. Phys. Lett. 88, 133104 (2006); http://dx.doi.org/10.1063/1.2189195 (3 pages) | Cited 23 times

Online Publication Date: 27 March 2006

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We strongly support Guryanov’s speculation—that a thinner wetting layer is expected with quantum dots (QDs) grown by migration-enhanced epitaxy—with structural and optical measurements. InAs QDs grown by migration-enhanced molecular-beam epitaxy showed a larger size, lower density, ∼ 40% enhanced uniformity, ∼ 2 times larger aspect ratio, and a measurement temperature insensitivity of the photoluminescence linewidth compared to QDs grown by conventional molecular-beam epitaxy. The thickness of the wetting layer for the migration-enhanced epitaxial InAs QD (2.1 nm) was thinner than that of the counterpart (4.0 nm).
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.08.Bc Wetting

Fabrication of InP/InAs/InP core-multishell heterostructure nanowires by selective area metalorganic vapor phase epitaxy

Premila Mohan, Junichi Motohisa, and Takashi Fukui

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages) | Cited 54 times

Online Publication Date: 27 March 2006

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We report the growth of InP/InAs/InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4 K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values.
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81.07.Vb Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.67.Lt Quantum wires
78.55.Cr III-V semiconductors

Thermoelectric effect in very thin film Pt/Au thermocouples

M. C. Salvadori, A. R. Vaz, F. S. Teixeira, M. Cattani, and I. G. Brown

Appl. Phys. Lett. 88, 133106 (2006); http://dx.doi.org/10.1063/1.2189192 (3 pages) | Cited 11 times

Online Publication Date: 28 March 2006

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The thickness dependence of the thermoelectric power of Pt films of variable thicknesses on a reference Au film has been determined for the case when the Pt film thickness, t, is not large compared to the charge-carrier mean free path. Pt film thicknesses down to 2.2 nm were investigated. We find that ΔSF = SB−SF (where SB and SF are the thermopowers of the Pt bulk and film, respectively) does not vary linearly as 1/t is the case for thin film thermocouples when the film thickness is large compared to the charge-carrier mean free path.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.At Metal and metallic alloys
07.20.-n Thermal instruments and apparatus

Geometrical enhancement of field emission of individual nanotubes studied by in situ transmission electron microscopy

Zhi Xu, X. D. Bai, and E. G. Wang

Appl. Phys. Lett. 88, 133107 (2006); http://dx.doi.org/10.1063/1.2188389 (3 pages) | Cited 35 times

Online Publication Date: 28 March 2006

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Field emission of an individual multiwalled carbon nanotube, driven by a customer-built piezomanipulator, was measured in a transmission electron microscope. The measurement geometry and the nanotube structure were imaged in situ. A linear dependence of field enhancement factor β on the distance d between the nanotube tip and its counteranode is found. The enhanced field emission mechanism is studied by a tip-flat emission model. The results indicate that the radius of emission apex r is an important factor in field emission with a relationship of β∝r−1/2, while the tube length has little influence on β.
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79.70.+q Field emission, ionization, evaporation, and desorption
61.46.Fg Nanotubes
68.37.Lp Transmission electron microscopy (TEM)

Implementation of submicrometric periodic surface structures toward improvement of organic-solar-cell performances

C. Cocoyer, L. Rocha, L. Sicot, B. Geffroy, R. de Bettignies, C. Sentein, C. Fiorini-Debuisschert, and P. Raimond

Appl. Phys. Lett. 88, 133108 (2006); http://dx.doi.org/10.1063/1.2188600 (3 pages) | Cited 29 times

Online Publication Date: 28 March 2006

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Submicrometric periodic patterning of an organic solar cell surface is investigated in order to optimize the photovoltaic conversion efficiency of the device. Patterning is achieved using a single-step all-optical technique based on photoinduced mass transport in azopolymer films. The polymer film with a structured surface is used as a substrate for an organic solar cell based on a copper phthalocyanine/C60 heterojunction. The effect of periodic patterning is investigated through the solar-cell optical-absorption properties and external quantum efficiency measurements. The possibility to increase the short circuit current density and the corresponding photovoltaic conversion efficiency is evidenced with one-dimensional periodic structures.
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84.60.Jt Photoelectric conversion
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Mn Polymer surfaces
85.60.-q Optoelectronic devices
61.41.+e Polymers, elastomers, and plastics

Synthesis and electronic properties of ZnO/CoZnO core-shell nanowires

Song Han, Daihua Zhang, and Chongwu Zhou

Appl. Phys. Lett. 88, 133109 (2006); http://dx.doi.org/10.1063/1.2187435 (3 pages) | Cited 12 times

Online Publication Date: 29 March 2006

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ZnO/CoZnO core-shell nanowires have been synthesized by depositing an epitaxial layer of CoxZn1−xO (x = 0.05−0.25) onto single-crystalline ZnO nanowires via pulsed-laser deposition. Detailed material analysis confirmed the core-shell structure and revealed a homogeneous distribution of Co atoms in the ZnO lattice. Field-effect transistors have been fabricated based on individual ZnO/CoZnO nanowires. These devices exhibited n-type transistor characteristics and intriguing magnetoresistance below 30 K.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
81.07.Vb Quantum wires
81.05.Dz II-VI semiconductors
85.30.Tv Field effect devices
75.50.Pp Magnetic semiconductors
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