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4 Aug 2008

Volume 93, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 051101 (2008); http://dx.doi.org/10.1063/1.2965797 (3 pages)

Mariano A. Zimmler, Jiming Bao, Federico Capasso, Sven Müller, and Carsten Ronning
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Band gap engineering for La aluminate dielectrics on Si (100)

Hua Jin, Young Joon Cho, Suhk Kun Oh, Hee Jae Kang, Ju Chul Park, Sung Heo, and Jae Cheol Lee

Appl. Phys. Lett. 93, 052904 (2008); http://dx.doi.org/10.1063/1.2964181 (3 pages) | Cited 6 times

Online Publication Date: 5 August 2008

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La aluminate (La2O3)x(Al2O3)1−x films were grown by atomic layer deposition method, for which the conduction band offset, valence band offset, and band gap were obtained by using x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy. The valence band offsets were nearly unchanged within the range from 2.23 to 2.37 eV with increasing Al content. The conduction band offsets were changed from 2.40 to 2.86 eV for the above dielectrics. Remarkably, the band gap could be engineered from 5.75 to 6.35 eV by increasing Al content. We also found that La aluminate films have symmetric band profiles.
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71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
77.55.-g Dielectric thin films

Epitaxial growth of aluminum nitride on AlGaN by reactive sputtering at low temperature

C. Duquenne, M. A. Djouadi, P. Y. Tessier, P. Y. Jouan, M. P. Besland, C. Brylinski, R. Aubry, and S. Delage

Appl. Phys. Lett. 93, 052905 (2008); http://dx.doi.org/10.1063/1.2967816 (3 pages) | Cited 7 times

Online Publication Date: 5 August 2008

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We report the synthesis of 1 μm thick single crystalline aluminum nitride films by dc magnetron sputtering on AlGaN/GaN layer grown on sapphire substrate at low temperature (substrate temperature <250 °C). The microstructure of c-axis oriented AlN films deposited on Si (100) and AlGaN ⟨0001⟩ substrates was studied by x-ray diffraction, selected area electron diffraction, and transmission electron microscopy. The optimization of process parameters, involving low energetic ion bombardment on film surface (20–30 eV) during the growth, leads to an increase in the surface mobility and thus promotes AlN epitaxial growth on AlGaN substrate at 250 °C.
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81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors
68.37.Lp Transmission electron microscopy (TEM)

A multiferroic ceramic with perovskite structure: (La0.5Bi0.5)(Mn0.5Fe0.5)O3.09

Asish K. Kundu, R. Ranjith, B. Kundys, N. Nguyen, V Caignaert, V Pralong, W. Prellier, and B. Raveau

Appl. Phys. Lett. 93, 052906 (2008); http://dx.doi.org/10.1063/1.2961022 (3 pages) | Cited 12 times

Online Publication Date: 5 August 2008

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An ABO3 perovskite multiferroic, where the B-site cation is responsible for the magnetic properties and the A-site cation with lone pair electron is responsible for the ferroelectric properties, was synthesized with the composition (La0.5Bi0.5)(Mn0.5Fe0.5)O3.09 at normal conditions. This oxide exhibits a ferromagnetic transition around 240 K with a well defined hysteresis loop, and a significant reversible remnant polarization below 67 K similar to ferroelectric behavior. The magnetic interaction is interpreted by the ferromagnetic Fe3+–O–Mn3+ and antiferromagnetic Fe3+(Mn3+)–O–Fe3+(Mn3+) interactions competed with each other, whereas the ferroelectricity is predominantly due to the polar nature introduced by the 6 s2 lone pair of Bi3+ cations.
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75.80.+q Magnetomechanical effects, magnetostriction
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effects of hydrogen anneals on oxygen deficient SrTiO3−x single crystals

Bharat Jalan, Roman Engel-Herbert, Thomas E. Mates, and Susanne Stemmer

Appl. Phys. Lett. 93, 052907 (2008); http://dx.doi.org/10.1063/1.2969037 (3 pages) | Cited 11 times

Online Publication Date: 6 August 2008

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The influence of hydrogen gas anneals on the electrical properties of nominally undoped, oxygen-deficient SrTiO3−x single crystals was investigated. Titanium getter layers and vacuum anneals were used to obtain oxygen-deficient SrTiO3−x with a low electrical resistivity. These crystals showed an optical absorption peak at 2.92 eV and strong midinfrared absorption. Subsequent anneals at 800 °C in forming gas, which contained 10% hydrogen, returned the crystals into the insulating, transparent state. The mechanisms by which hydrogen anneals can compensate for the effects of oxygen vacancies in SrTiO3−x are discussed. The results show that forming gas anneals of stoichiometric SrTiO3 can lead to complex electrical conduction behavior.
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72.80.Sk Insulators
61.66.Bi Elemental solids
61.66.Dk Alloys
78.30.Hv Other nonmetallic inorganics

Effect of ruthenium oxide electrode on the resistive switching of Nb-doped strontium titanate

Musarrat Hasan, Rui Dong, H. J. Choi, D. S. Lee, D.-J. Seong, M. B. Pyun, and Hyunsang Hwang

Appl. Phys. Lett. 93, 052908 (2008); http://dx.doi.org/10.1063/1.2969052 (3 pages) | Cited 8 times

Online Publication Date: 6 August 2008

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We studied resistance switching characteristics of ruthenium oxide (RuOx)/niobium-doped strontium titanate (Nb:STO) contact. With increasing oxygen content of oxide electrode, the resistance window was improved. The switching speed of RuOx electrode also showed improvement compared to platinum (Pt) electrode. The RuOx film contains amorphous phase and also forms an interface oxide layer at the RuOx/Nb:STO contact, which suggests defect generation near the interface. Additionally, the interface reaction disturbs the crystalline orientation of Nb:STO. These defect sites facilitate switching properties by easy drift of current and oxygen ion and also by modulation of barrier height.
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73.40.-c Electronic transport in interface structures
68.35.Ct Interface structure and roughness

Characterization of laser-transferred bismuth ferrite lead titanate ferroelectric thick films

Tim P. Comyn, Tanusri Chakraborty, Robert E. Miles, and Steven J. Milne

Appl. Phys. Lett. 93, 052909 (2008); http://dx.doi.org/10.1063/1.2969288 (3 pages) | Cited 2 times

Online Publication Date: 7 August 2008

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Thick films of 0.7BiFeO3–0.3PbTiO3 have been deposited on sapphire substrates by tape casting and sintering at 1000 °C. Films 20 μm in thickness were released from the fabrication substrate using KrF pulsed laser radiation, and epoxy bonded to platinized silicon substrates in order to demonstrate the low-temperature integration possibilities of xBiFeO3–(1−x)PbTiO3 films. Despite structural changes at the laser-released film interface, strain-electric field loops are typical of a ferroelectric, showing an ultimate strain of 0.09%. X-ray diffraction and scanning electron microscopy observations suggest that interfacial melting and migration of Bi2O3 is involved in the lift-off process.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.60.Bs Mechanical and acoustical properties

Field-induced soft mode hardening in SrTiO3/DyScO3 multilayers

P. Kužel, C. Kadlec, F. Kadlec, J. Schubert, and G. Panaitov

Appl. Phys. Lett. 93, 052910 (2008); http://dx.doi.org/10.1063/1.2967336 (3 pages) | Cited 6 times

Online Publication Date: 7 August 2008

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We investigate a SrTiO3/DyScO3 epitaxial multilayer with four 50-nm-thick layers of each compound deposited on DyScO3 substrate by pulsed laser deposition. The spectra of SrTiO3 obtained using time-domain terahertz spectroscopy at room temperature with and without electrical bias are explained by the ferroelectric soft mode coupled to a silent central peak, where the bare soft mode frequency is the only field-dependent parameter. We show that terahertz and subterahertz properties of the layers are determined solely by a tremendous hardening of the soft mode with increasing field. We demonstrate that our structure induces more than 40% modulation of the transmitted terahertz power in a broad frequency range of 0.65–1.15 THz at 140 V (93 kV/cm) bias.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.55.-g Dielectric thin films
78.70.Gq Microwave and radio-frequency interactions
81.15.Fg Pulsed laser ablation deposition

Pre-atomic layer deposition surface cleaning and chemical passivation of (100) In0.2Ga0.8As and deposition of ultrathin Al2O3 gate insulators

Byungha Shin, Donghun Choi, James S. Harris, and Paul C. McIntyre

Appl. Phys. Lett. 93, 052911 (2008); http://dx.doi.org/10.1063/1.2966357 (3 pages) | Cited 29 times

Online Publication Date: 8 August 2008

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We have developed and tested the efficacy of a method for pre-atomic layer deposition (ALD) surface preparation that removes native oxides from the (100) In0.2Ga0.8As surface and provides a clean starting surface for ALD of ultrathin Al2O3 layers. Successive wet etching by aqueous HCl and NH4(OH) solutions and in situ pre-ALD thermal desorption of residual elemental As were performed. Photoelectron spectra obtained after ALD of Al2O3 on In0.2Ga0.8As prepared by this method revealed that the interface was free of In, Ga, and As oxides. The resultant metal-oxide-semiconductor capacitors with Pt electrodes exhibited capacitance-derived equivalent oxide thicknesses as small as 1.8 nm.
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81.65.Cf Surface cleaning, etching, patterning
81.65.Rv Passivation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
84.32.Tt Capacitors

Design and simulation of planar electro-optic switches in ferroelectrics

Mahesh Krishnamurthi, Lili Tian, and Venkatraman Gopalan

Appl. Phys. Lett. 93, 052912 (2008); http://dx.doi.org/10.1063/1.2967469 (3 pages) | Cited 3 times

Online Publication Date: 8 August 2008

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Conceptual design and numerical simulation of two polarization dependent planar optical switches based on the electro-optic effect in ferroelectrics operating at 1.55 μm wavelength are presented. The first design is a 3×3 optical switch based entirely on electro-optic beam steering (prism) elements and ion-exchanged lenses for collimation. The second design is a 1×N optical switch based on a combination of electro-optic beam steering and electro-optic focusing (lens) elements. The scalability of this device has been improved by compensating the in-plane divergence of the laser. Analytical expressions for the dependence of scalability are presented.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
42.70.-a Optical materials
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Large pyroelectric effect in undoped epitaxial Pb(Zr,Ti)O3 thin films on SrTiO3 substrates

Bo Xiao, Vitaliy Avrutin, Huiyong Liu, Ümit Özgür, Hadis Morkoç, and Changzhi Lu

Appl. Phys. Lett. 93, 052913 (2008); http://dx.doi.org/10.1063/1.2969778 (3 pages) | Cited 5 times

Online Publication Date: 8 August 2008

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We have studied pyroelectric and ferroelectric properties of Pb(Zr,Ti)O3 thin films grown epitaxially on SrTiO3(001) substrates by rf magnetron sputtering. The pyroelectric coefficient was measured in the temperature range from 280 to 370 K using the Byer–Roundy method. Values as high as 48 nC/cm2 K have been obtained at 300 K. The PZT thin films exhibited a remanent polarization of 45–58 μC/cm2. The improved pyroelectric coefficient was attributed to a high crystalline quality of the films, as revealed by x-ray diffraction that showed only (001)-oriented perovskite PZT phase and a ω-rocking curve full width at half maximum value as low as 4.2 arc min for 300 nm thick films.
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77.55.-g Dielectric thin films
77.70.+a Pyroelectric and electrocaloric effects
77.80.-e Ferroelectricity and antiferroelectricity
77.65.-j Piezoelectricity and electromechanical effects
81.15.Cd Deposition by sputtering
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Zr-metal adhesion on graphenic nanostructures

Y. Sanchez-Paisal, D. Sanchez-Portal, N. Garmendia, R. Muñoz, I. Obieta, J. Arbiol, L. Calvo-Barrio, and A. Ayuela

Appl. Phys. Lett. 93, 053101 (2008); http://dx.doi.org/10.1063/1.2966373 (3 pages) | Cited 7 times

Online Publication Date: 4 August 2008

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Our high resolution transmission electronic microscopy studies of multiwall carbon nanotubes show, after the growth of zirconia nanoparticles by a hydrothermal route, the presence of surface Zr, forming an atomically thin layer. Using first-principles calculations we investigate the nature of the Zr–C interaction, which is neither ionic nor covalent, and the optimal coverage for the Zr metal in a graphene flake. This preferred coverage is in agreement with that deduced from electron energy loss spectra experiments. We show also that the amount of charge transferred to the C layer saturates as the Zr coverage increases and the Zr–C bond becomes weaker.
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68.35.Np Adhesion
61.46.Fg Nanotubes
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
79.20.Uv Electron energy loss spectroscopy

Carrier relaxation through two-electron process during photoconduction in highly UV sensitive quasi-one-dimensional ZnO nanowires

A. Bera and D. Basak

Appl. Phys. Lett. 93, 053102 (2008); http://dx.doi.org/10.1063/1.2968131 (3 pages) | Cited 28 times

Online Publication Date: 5 August 2008

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We have investigated the carrier relaxation process during photoconduction in quasi-one-dimensional (Q1D) ZnO nanowires (NWs) of diameters 29–36 nm on different substrates using photocurrent transient measurements. Ultraviolet (UV) sensitive NWs show around three to four orders of change in the photo-to-dark current ratio. Under steady UV illumination, the photocarrier relaxation occurs through two-electron process—carrier loss due to the trapping by the surface states and recombination at the deep defect states. The results demonstrate that the carrier relaxation during photoconduction in Q1D NWs of diameter comparable to the Debye length is also dominated by the surface states.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.55.Gs II-VI semiconductors
73.20.At Surface states, band structure, electron density of states

A nuclear magnetic resonance study on rubrene-cobalt nanocomposites

Masashi Shiraishi, Haruka Kusai, Ryo Nouchi, Takayuki Nozaki, Teruya Shinjo, Yoshishige Suzuki, Makoto Yoshida, and Masashi Takigawa

Appl. Phys. Lett. 93, 053103 (2008); http://dx.doi.org/10.1063/1.2966149 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2008

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We implemented a nuclear magnetic resonance (NMR) study on rubrene (C42H28)−Co nanocomposites that exhibit an enhanced magnetoresistance (MR) ratio of 80%. The 59Co NMR spin echo experiment enabled clarification of the hyperfine field of Co at the interface between the ferromagnet and the molecules, which has not been investigated for molecular spintronics. An enhanced hyperfine field of the Co was observed in the rubrene-Co nanocomposites, which may be related to the enhancement of the MR ratio. This study demonstrates the importance of microscopic investigation of the interface between molecules and ferromagnets that governs spin-dependent transport in molecular spin devices.
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76.60.Lz Spin echoes
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Xx Molecular magnets
75.50.Dd Nonmetallic ferromagnetic materials

Atomic resolution study of the interfacial bonding at Si3N4/CeO2−δ grain boundaries

W. Walkosz, R. F. Klie, S. Öğüt, A. Borisevich, P. F. Becher, S. J. Pennycook, and J. C. Idrobo

Appl. Phys. Lett. 93, 053104 (2008); http://dx.doi.org/10.1063/1.2968683 (3 pages) | Cited 5 times

Online Publication Date: 6 August 2008

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Using a combination of atomic-resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope, we examine the atomic and electronic structures at the interface between Si3N4 (10math0) and CeO2−d intergranular film (IGF). Ce atoms are observed to segregate to the interface in a two-layer periodic arrangement, which is significantly different from the structure observed in a previous study. Our EELS experiments show (i) oxygen in direct contact with the terminating Si3N4 open-ring structures, (ii) a change in the Ce valence from a nominal oxidation state of +3 to almost +4 moving from the interface into the IGF, and (iii) a uniform concentration of Si in the film.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
61.72.Mm Grain and twin boundaries
71.20.Ps Other inorganic compounds
64.75.-g Phase equilibria

High-performance nanowire complementary metal-semiconductor inverters

R. M. Ma, L. Dai, C. Liu, W. J. Xu, and G. G. Qin

Appl. Phys. Lett. 93, 053105 (2008); http://dx.doi.org/10.1063/1.2967725 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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We demonstrated the construction of complementary metal-semiconductor (CMES) inverters with single n- and p-type nanowires (NWs) on the same chip. A single p-type NW was assembled by the side of an n-type NW via the electric field assembly method. n- and p-channel metal-semiconductor field-effect transistors were fabricated with n- and p-type NWs, respectively. Based on this, high-performance NW CMES NOT logic gate (inverter) was built. The NW CMES inverters have low operating voltage ( ≤ 2 V), high voltage gain ( ≥ 7), and low static power dissipation ( ≤ 0.3 nW).
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Excitation enhancement of CdSe quantum dots by single metal nanoparticles

Yeechi Chen, Keiko Munechika, Ilan Jen-La Plante, Andrea M. Munro, Sara E. Skrabalak, Younan Xia, and David S. Ginger

Appl. Phys. Lett. 93, 053106 (2008); http://dx.doi.org/10.1063/1.2956391 (3 pages) | Cited 36 times

Online Publication Date: 6 August 2008

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We study plasmon-enhanced fluorescence from CdSe/CdS/CdZnS/ZnS core/shell quantum dots near a variety of Ag and Au nanoparticles. The photoluminescence excitation (PLE) spectrum of quantum dots closely follows the localized surface plasmon resonance (LSPR) scattering spectrum of the nanoparticles. We measure excitation enhancement factors of ∼ 3 to 10 for different shapes of single metal nanoparticles.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.68.+m Optical properties of surfaces
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Carbon nanotubes on carbon fabrics for flexible field emitter arrays

Kenichi Suzuki, Hidetoshi Matsumoto, Mie Minagawa, Akihiko Tanioka, Yasuhiko Hayashi, Kazuyuki Fukuzono, and Gehan A. J. Amaratunga

Appl. Phys. Lett. 93, 053107 (2008); http://dx.doi.org/10.1063/1.2967868 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2008

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Flexible carbon fabrics (CFs) prepared by electrospray deposition were used for the substrate of carbon nanotube (CNT) field emitter arrays. CNTs were grown on the CFs by chemical vapor deposition. The CNT field emitter arrays on CFs produced a higher current density at a lower turn-on voltage compared to ones on a Si substrate.
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81.07.De Nanotubes
85.45.Db Field emitters and arrays, cold electron emitters
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Two-dimensional growth of lattice matched Nd-doped (Gd,Lu)2O3 films on Y2O3 by pulsed laser deposition

Teoman Gün, Andreas Kahn, Bilge İleri, Klaus Petermann, and Günter Huber

Appl. Phys. Lett. 93, 053108 (2008); http://dx.doi.org/10.1063/1.2967870 (3 pages) | Cited 7 times

Online Publication Date: 6 August 2008

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This letter focuses on epitaxial growth of a 1-μm-thick lattice matched Nd-doped monocrystalline (Gd,Lu)2O3 film deposited on a {100} oriented Y2O3 substrate by pulsed laser deposition. Layer-by-layer growth indicated by in situ reflection high energy electron diffraction was observed up to film thicknesses of 100 nm. The subsequent growth behavior could be explained by a multilevel growth mode. Thus, the growth mode was two-dimensional and epitaxial. Lattice matching of up to 99.3% was achieved. The evolution of the structural and topographical properties of the films was verified by ex situ x-ray diffraction analysis and atomic force microscopy, respectively.
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81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
68.55.jd Thickness
68.37.Ps Atomic force microscopy (AFM)
42.70.Hj Laser materials

Synthesis of horizontally aligned ZnO nanowires localized at terrace edges and application for high sensitivity gas sensor

J. Y. Son, S. J. Lim, J. H. Cho, W. K. Seong, and Hyungjun Kim

Appl. Phys. Lett. 93, 053109 (2008); http://dx.doi.org/10.1063/1.2967871 (3 pages) | Cited 29 times

Online Publication Date: 6 August 2008

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We developed step edge decoration method for the fabrication of semiconductor ZnO nanodots and nanowires using pulsed laser deposition. We synthesized high quality ZnO nanowires with the small diameter of about 20 nm and the uniform interval of about 80 nm between each nanowire, which has a simple structure for the formation of contact electrodes. The ZnO nanowire-based sensor was prepared only with the simple process of a gold electrode formation. The ZnO nanowire-based sensor exhibited the high surface-to-volume ratio of 58.6 μm−1 and the significantly high sensitivity of about 10 even for the low ethanol concentration of 0.2 ppm.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Nearly intrinsic exciton lifetimes in single twin-free GaAs/AlGaAs core-shell nanowire heterostructures

S. Perera, M. A. Fickenscher, H. E. Jackson, L. M. Smith, J. M. Yarrison-Rice, H. J. Joyce, Q. Gao, H. H. Tan, C. Jagadish, X. Zhang, and J. Zou

Appl. Phys. Lett. 93, 053110 (2008); http://dx.doi.org/10.1063/1.2967877 (3 pages) | Cited 18 times

Online Publication Date: 6 August 2008

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CW and time-resolved photoluminescence measurements are used to investigate exciton recombination dynamics in GaAs/AlGaAs heterostructure nanowires grown with a recently developed technique which minimizes twinning. A thin capping layer is deposited to eliminate the possibility of oxidation of the AlGaAs shell as a source of oxygen defects in the GaAs core. We observe exciton lifetimes of ∼ 1 ns, comparable to high quality two-dimensional double heterostructures. These GaAs nanowires allow one to observe state filling and many-body effects resulting from the increased carrier densities accessible with pulsed laser excitation.
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71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
61.72.Mm Grain and twin boundaries
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Nano-optical microlens with ultrashort focal length using negative refraction

B. D. F. Casse, W. T. Lu, Y. J. Huang, and S. Sridhar

Appl. Phys. Lett. 93, 053111 (2008); http://dx.doi.org/10.1063/1.2968873 (3 pages) | Cited 12 times

Online Publication Date: 7 August 2008

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We have experimentally realized an ultrashort focal length planoconcave microlens in an InP/InGaAsP semiconductor two-dimensional (2D) photonic crystal with negative index of refraction (−0.7). At λ = 1.5 μm, the lens exhibits ultrashort focal lengths of 12 μm ( ∼ 8λ) and numerical aperture close to unity. The focused beam has a near diffraction-limited spot size of 1.05 μm ( ∼ 0.68λ) at full width at half maximum. The negative refractive index and focusing properties of the microlens are confirmed by 2D finite-difference time-domain simulations. Such ultrarefractive negative-index nano-optical microlenses can be integrated into existing semiconductor heterostructure platforms for next-generation optoelectronic applications.
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42.79.Bh Lenses, prisms and mirrors
42.82.Gw Other integrated-optical elements and systems

High-density horizontally aligned growth of carbon nanotubes with Co nanoparticles deposited by arc-discharge plasma method

D. Phokharatkul, Y. Ohno, H. Nakano, S. Kishimoto, and T. Mizutani

Appl. Phys. Lett. 93, 053112 (2008); http://dx.doi.org/10.1063/1.2969290 (3 pages) | Cited 16 times

Online Publication Date: 7 August 2008

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High-density horizontally aligned single-walled carbon nanotubes are grown on a quartz substrate using Co nanoparticles deposited by arc-discharge plasma method. The Co nanoparticles with a density as high as 6.0×1010 cm−2 are formed by a single pulse of arc discharge at room temperature. The density of the aligned nanotubes is ∼ 8 μm−1 in average. Multichannel nanotube field-effect transistors with a high-k top-gate structure are fabricated with aligned nanotubes. The devices show high-performance, normally on, and n-type conduction property without any doping process. A high on current of 1.3 mA and a large transconductance of 0.23 mS for a channel width of 100 μm are obtained. The normally on and n-type property is attributed to fixed positive charges in the HfO2 gate insulator and at the interfaces.
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81.07.De Nanotubes
85.35.Kt Nanotube devices
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Current-voltage characteristics and transport mechanism of solar cells based on ZnO nanorods/In2S3/CuSCN

T. Dittrich, D. Kieven, M. Rusu, A. Belaidi, J. Tornow, K. Schwarzburg, and M. Lux-Steiner

Appl. Phys. Lett. 93, 053113 (2008); http://dx.doi.org/10.1063/1.2969291 (3 pages) | Cited 17 times

Online Publication Date: 8 August 2008

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Temperature dependent current-voltage characteristics in the dark and under illumination have been analyzed on up to 3.2% efficient solar cells with extremely thin absorber based on ZnO nanorods/In2S3/CuSCN structures. The diode ideality factor and the open circuit voltage are strongly influenced on a thermal activation process. Significant enhancement of the devices efficiency by annealing at moderate temperatures has been demonstrated. After this annealing, the activation energy of the saturation current increased from 1.00 to 1.46 eV (in the dark). Transport mechanisms at the In2S3/CuSCN interface region are discussed.
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84.60.Jt Photoelectric conversion
61.72.Cc Kinetics of defect formation and annealing

Microwave absorption properties of conducting polymer composite with barium ferrite nanoparticles in 12.4–18 GHz

Anil Ohlan, Kuldeep Singh, Amita Chandra, and S. K. Dhawan

Appl. Phys. Lett. 93, 053114 (2008); http://dx.doi.org/10.1063/1.2969400 (3 pages) | Cited 29 times

Online Publication Date: 8 August 2008

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Conducting polymer nanocomposites of polyphenyl amine with barium ferrite nanoparticles (50–70 nm) have been synthesized via emulsion polymerization. The complex permittivity, permeability, and microwave absorption properties of the composite were studied in the 12.4–18 GHz (Ku band) frequency range. The composite has shown high shielding effectiveness due to absorption (SEA) of 28.9 dB ( ∼ 99.9%), which strongly depends on dielectric loss, magnetic permeability, and volume fraction of barium ferrite nanoparticles. The high value of SEA suggests that these composites can be used as a promising radar absorbing materials.
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78.70.Gq Microwave and radio-frequency interactions
72.80.Tm Composite materials
84.40.-x Radiowave and microwave (including millimeter wave) technology
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Gm Dielectric loss and relaxation
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Hybrid metal-base transistor with base of sulfonated polyaniline and fullerene emitter

Wilson J. da Silva, Ivo A. Hümmelgen, Regina M. Q. Mello, and Dongge Ma

Appl. Phys. Lett. 93, 053301 (2008); http://dx.doi.org/10.1063/1.2967731 (3 pages) | Cited 10 times

Online Publication Date: 4 August 2008

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We demonstrate hybrid vertical architecture transistors that operate like metal-base transistors, using n-type silicon as the collector, sulfonated polyaniline as the base, and C60 fullerene as the emitter. Electrical measurements suggest that the sulfonated polyaniline base effectively screens the emitter from electric field variations occurring in the collector leading to the metal-base transistor behavior. These devices operate at low voltages and show common-emitter current gain equal to 8, which is independent of the base current up to values of ∼ 1.5 μA and constant at collector voltages between 1 and 5 V.
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85.30.Tv Field effect devices
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