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18 Feb 2008

Volume 92, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 073101 (2008); http://dx.doi.org/10.1063/1.2840574 (3 pages)

N. W. Gong, M. Y. Lu, C. Y. Wang, Y. Chen, and L. J. Chen
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Crystal rotation in Cu single crystal micropillars: In situ Laue and electron backscatter diffraction

R. Maaß, S. Van Petegem, D. Grolimund, H. Van Swygenhoven, D. Kiener, and G. Dehm

Appl. Phys. Lett. 92, 071905 (2008); http://dx.doi.org/10.1063/1.2884688 (3 pages) | Cited 31 times

Online Publication Date: 21 February 2008

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In situ microdiffraction experiments were conducted on focused ion beam machined single crystal Cu pillars oriented for double slip. During deformation, the crystal undergoes lattice rotation on both the primary and critical slip system. In spite of the initial homogeneous microstructure of the Cu pillar, rotation sets in already at yield and is more important at the top of the pillar than at the bottom, demonstrating the inhomogeneous stress state during a microcompression experiment. The rotation results are confirmed by electron backscatter diffraction measurements.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
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ZnO epitaxy on (111) Si using epitaxial Lu2O3 buffer layers

W. Guo, A. Allenic, Y. B. Chen, X. Q. Pan, W. Tian, C. Adamo, and D. G. Schlom

Appl. Phys. Lett. 92, 072101 (2008); http://dx.doi.org/10.1063/1.2841667 (3 pages) | Cited 13 times

Online Publication Date: 19 February 2008

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We report the growth and characterization of single-crystalline, crack-free, epitaxial (0001) ZnO films on (111) Si substrates using intervening epitaxial Lu2O3 buffer layers. The epitaxial orientation relationships are (0001)ZnO∥(111)Lu2O3∥(111)Si and [1math10]ZnO∥[math10]Lu2O3∥[1math0]Si. X-ray diffraction and transmission electron microscopy reveal that the ZnO films have high structural quality and an atomically sharp ZnO/Lu2O3 interface. Temperature-dependent photoluminescence measurements show optical properties comparable to ZnO single crystals. The films have a resistivity of 0.31 Ω cm, an electron concentration of 2.5×1017 cm−3, and a mobility of 80 cm2/V⋅s at room temperature. The epitaxial growth of ZnO on Si represents a significant step toward the integration of ZnO-based multifunctional devices with Si electronics.
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68.55.ag Semiconductors
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors

Magnetotransport, noise, and x-ray magnetic circular dichroism studies of pulsed laser deposited Fe3O4 film on Si substrates

R. J. Choudhary, Shailja Tiwari, D. M. Phase, Ravi Kumar, P. Thakur, K. H. Chae, and W. K. Choi

Appl. Phys. Lett. 92, 072102 (2008); http://dx.doi.org/10.1063/1.2884267 (3 pages) | Cited 2 times

Online Publication Date: 21 February 2008

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Electrical fluctuation, magnetic, and magneto-transport properties of the (111) oriented Fe3O4 thin film deposited by pulsed laser deposition on technologically important silicon substrate have been studied. Low frequency conduction noise follows the trend of resistivity behavior with respect to temperature and the normalized value of noise drops by two orders of magnitude below the Verwey transition. At room temperature, magnetoresistance of the film is 5% at 8 T. X-ray magnetic circular dichroism measurements performed on 10 nm thick film of Fe3O4 indicate a single crystal-like uniform distribution of Fe ions in its crystal or magnetic structure.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
78.20.Ls Magneto-optical effects
73.61.Ng Insulators

Doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide

P. Achatz, J. Pernot, C. Marcenat, J. Kacmarcik, G. Ferro, and E. Bustarret

Appl. Phys. Lett. 92, 072103 (2008); http://dx.doi.org/10.1063/1.2885081 (3 pages) | Cited 7 times

Online Publication Date: 21 February 2008

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We report an experimental determination of the doping-induced metal-insulator transition in aluminum-doped 4H silicon carbide. Low temperature transport measurements down to 360 mK and temperature dependent Raman experiments down to 5 K, together with secondary ion mass spectroscopy profiling, suggest a critical aluminum concentration lying between 6.4 and 8.7×1020 cm−3 for the metal-insulator transition in these epilayers grown by the vapor-liquid-solid technique. Preliminary indications of a superconducting transition in the metallic sample are presented.
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72.60.+g Mixed conductivity and conductivity transitions
73.61.Le Other inorganic semiconductors
61.72.up Other materials

Electronic transport properties of amorphous indium-gallium-zinc oxide semiconductor upon exposure to water

Jin-Seong Park, Jae Kyeong Jeong, Hyun-Joong Chung, Yeon-Gon Mo, and Hye Dong Kim

Appl. Phys. Lett. 92, 072104 (2008); http://dx.doi.org/10.1063/1.2838380 (3 pages) | Cited 72 times

Online Publication Date: 21 February 2008

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The effect of water exposure on amorphous indium-gallium-zinc oxide (a-IGZO) semiconductors was reported. It was found that water can diffuse in and out of the a-IGZO film, reversibly affecting the transistor properties. Two competing mechanisms depending on the thickness of the active channel were clarified. The electron donation effect caused by water adsorption dominated for the thicker a-IGZO films ( ≥ 100 nm), which was manifested in the large negative shift (>14 V) of the threshold voltage. However, in the case of the thinner a-IGZO films ( ⩽ 70 nm), the dominance of the water-induced acceptorlike trap behavior was observed. The direct evidence for this behavior was that the subthreshold swing was greatly deteriorated from 0.18 V/decade (before water exposure) to 4.4 V/decade (after water exposure) for the thinnest a-IGZO films (30 nm). These results can be well explained by the screening effect of the intrinsic bulk traps of the a-IGZO semiconductor.
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85.30.Tv Field effect devices
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360° domain wall generation in the soft layer of magnetic tunnel junctions

M. Hehn, D. Lacour, F. Montaigne, J. Briones, R. Belkhou, S. El Moussaoui, F. Maccherozzi, and N. Rougemaille

Appl. Phys. Lett. 92, 072501 (2008); http://dx.doi.org/10.1063/1.2838455 (3 pages) | Cited 3 times

Online Publication Date: 21 February 2008

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High spatial resolution x-ray photoemission electron microscopy technique has been used to study the influence of the dipolar coupling taking place between the NiFe and the Co ferromagnetic electrodes of micron sized, elliptical shaped magnetic tunnel junctions. The chemical selectivity of this technique allows us to observe independently the magnetic domain structure in each ferromagnetic electrode. The combination of this powerful imaging technique with micromagnetic simulations allows us to evidence that a 360° domain wall can be stabilized in the NiFe soft layer. In this letter, we discuss the origin and the formation conditions of those 360° domain walls evidenced experimentally and numerically.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.40.Mg Numerical simulation studies
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Epitaxial Ni–Mn–Ga films deposited on SrTiO3 and evidence of magnetically induced reorientation of martensitic variants at room temperature

O. Heczko, M. Thomas, J. Buschbeck, L. Schultz, and S. Fähler

Appl. Phys. Lett. 92, 072502 (2008); http://dx.doi.org/10.1063/1.2883961 (3 pages) | Cited 17 times

Online Publication Date: 21 February 2008

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Epitaxial Ni–Mn–Ga films were grown on SrTiO3 by sputter deposition. The films deposited at 673 K are ferromagnetic and martensitic at room temperature. Pole figure measurements indicate that the twinned orthorhombic martensite microstructure of the film has a lower symmetry compared to bulk. Magnetically induced reorientation or magnetic shape memory effect is indicated by magnetization curve measurements. Though the overall extension of the film is constrained by a rigid substrate, the reorientation is possible due to the additional degree of freedom in the orthorhombic phase.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
81.30.Kf Martensitic transformations

Over 40% transverse Kerr effect from Ni80Fe20

D. A. Allwood, P. R. Seem, S. Basu, P. W. Fry, U. J. Gibson, and R. P. Cowburn

Appl. Phys. Lett. 92, 072503 (2008); http://dx.doi.org/10.1063/1.2884332 (3 pages) | Cited 3 times

Online Publication Date: 21 February 2008

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We show how mixed s- and p-polarized light incident on a ferromagnetic surface yields large transverse magneto-optical Kerr effect (MOKE) signals. Fractional MOKE signals of over 40% could be achieved from transverse magnetization changes in 35 nm thick Ni80Fe20, an increase of over two orders of magnitude compared with the standard MOKE configuration. Transverse MOKE signals from patterned structures were also improved by an order of magnitude. Calculations of the magneto-optical interaction show how changing the incident polarization controls the Kerr rotation and reflected beam intensity for opposite magnetization orientations.
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78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys

Giant room-temperature magnetocaloric effect in Mn1−xCrxAs

N. K. Sun, W. B. Cui, D. Li, D. Y. Geng, F. Yang, and Z. D. Zhang

Appl. Phys. Lett. 92, 072504 (2008); http://dx.doi.org/10.1063/1.2884524 (3 pages) | Cited 17 times

Online Publication Date: 21 February 2008

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A giant magnetocaloric effect was observed at room temperature in Mn1−xCrxAs compounds with x = 0.006 and 0.01. The Cr dopant reduces (or even eliminates) the large thermal hysteresis of MnAs, while it lowers the first-order transition temperature from 313 K for MnAs to 265 K for Mn0.99Cr0.01As. Near the Curie temperature, a magnetic field induces a first-order phase transition from a ferromagnetic hexagonal phase to a paramagnetic orthorhombic phase, leading to a maximum value of ΔSM of 20.2 J/kg K at 267 K for a 5 T field change for Mn0.99Cr0.01As. The study on the Mn1−xCrxAs system may open an important field in searching proper materials for room-temperature magnetic refrigeration.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
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Atomic-layer-deposited HfO2 on In0.53Ga0.47As: Passivation and energy-band parameters

Y. C. Chang, M. L. Huang, K. Y. Lee, Y. J. Lee, T. D. Lin, M. Hong, J. Kwo, T. S. Lay, C. C. Liao, and K. Y. Cheng

Appl. Phys. Lett. 92, 072901 (2008); http://dx.doi.org/10.1063/1.2883967 (3 pages) | Cited 43 times

Online Publication Date: 19 February 2008

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Atomic-layer-deposited high κ dielectric HfO2 films on air-exposed In0.53Ga0.47As/InP (100), using Hf(NCH3C2H5)4 and H2O as the precursors, were found to have an atomically sharp interface free of arsenic oxides, an important aspect for Fermi level unpinning. A careful and thorough probing, using high-resolution angular-resolved x-ray photoelectron spectroscopy (XPS) with synchrotron radiation, however, observed the existence of Ga2O3, In2O3, and In(OH)3 at the interface. The current transport of the metal-oxide-semiconductor capacitor for an oxide 7.8 nm thick follows the Fowler–Nordheim tunneling mechanism and shows a low leakage current density of ∼ 10−8 A/cm2 at VFB+1 V. Well behaved frequency-varying capacitance-voltage curves were measured and an interfacial density of states of 2×1012 cm−2 eV−1 was derived. A conduction-band offset of 1.8±0.1 eV and a valence-band offset of 2.9±0.1 eV have been determined using the current transport data and XPS, respectively.
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77.55.-g Dielectric thin films
81.65.Rv Passivation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
84.32.Tt Capacitors

Ferroelectric 90° domain structure in a thin film of BaTiO3 fine ceramics observed by 300 kV electron holography

Takao Matsumoto, Masanari Koguchi, Keigo Suzuki, Hitoshi Nishimura, Yasuhiro Motoyoshi, and Nobuyuki Wada

Appl. Phys. Lett. 92, 072902 (2008); http://dx.doi.org/10.1063/1.2857469 (3 pages) | Cited 2 times

Online Publication Date: 19 February 2008

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We observed 90° ferroelectric domain structure in a thin film of BaTiO3 by 300 kV electron holography, especially paying attention to beam-induced influence on the polarization and diffraction effect. The beam-induced influence was minimized by recording holograms on high-resolution films at low electron-optical magnification. As for the diffraction effect, we chose such an orientation of the specimen as to minimize the corresponding amplitude contrast. Furthermore, to minimize any phase shifts that are not intrinsic to ferroelectricity, such as the mean-inner potential of the material or the electron-beam-induced charging under the illumination condition, we calculated the difference between phase images taken below and above the Curie temperature of the material to obtain a consistent value for the spontaneous polarization.
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77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.66.-w Optical properties of specific thin films

Magnetoelectric characteristics of a dual-mode magnetostrictive/piezoelectric bilayered composite

Lei Li and Xiang Ming Chen

Appl. Phys. Lett. 92, 072903 (2008); http://dx.doi.org/10.1063/1.2840177 (3 pages) | Cited 11 times

Online Publication Date: 20 February 2008

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The magnetoelectric characteristics of a Terfenol-D/Pb(Zr,Ti)O3 bilayered composite were investigated, and an additional bending vibration mode due to the asymmetrical structure was observed besides the length vibration mode which also acted in the symmetrical trilayered composites. The module of magnetoelectric coefficient for the bilayered composite at 1 kHz was significantly lower than those for the trilayered composites, and one more resonant peak was observed at a lower frequency of 15.57 kHz. The combination of bending and length vibration modes was responsible for the unique magnetoelectric characteristics of the dual-mode bilayered composite. Moreover, theoretical discussion indicated that the shape of the lower-frequency resonant peak was variable and determined by the module and phase differences for the two vibration modes.
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75.80.+q Magnetomechanical effects, magnetostriction
77.65.Bn Piezoelectric and electrostrictive constants

Effect of dc bias on pressure-induced depolarization of Pb(Nb,Zr,Sn,Ti)O3 ceramics

Zhonghua Dai, Zhuo Xu, and Xi Yao

Appl. Phys. Lett. 92, 072904 (2008); http://dx.doi.org/10.1063/1.2883972 (3 pages) | Cited 8 times

Online Publication Date: 20 February 2008

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The polarization and depolarization of antiferroelectric Pb(Nb,Zr,Sn,Ti)O3 (PNZST) ceramics under a dc bias were studied in a hydraulic pressure from 0 to 250 MPa. It is found that the antiferroelectric ceramic can be induced to a metastable ferroelectric state and that the ceramic at this ferroelectric state can be switched to the antiferroelectric state using hydraulic pressure. The hydraulic pressure to induce the transition from the ferroelectric to the antiferroelectric states increases with the positive and decreases with the negative dc bias. Based on the results, the pressure–electric field phase diagram for polarized PNZST ceramics was established.
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77.22.Ej Polarization and depolarization
77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Precision nanoscale domain engineering of lithium niobate via UV laser induced inhibition of poling

C. L. Sones, A. C. Muir, Y. J. Ying, S. Mailis, R. W. Eason, T. Jungk, Á. Hoffmann, and E. Soergel

Appl. Phys. Lett. 92, 072905 (2008); http://dx.doi.org/10.1063/1.2884185 (3 pages) | Cited 17 times

Online Publication Date: 20 February 2008

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Continuous wave ultraviolet laser irradiation at λ = 244 nm on the +z face of undoped and MgO doped congruent lithium niobate single crystals has been observed to inhibit ferroelectric domain inversion. The inhibition occurs directly beneath the illuminated regions, in a depth greater than 100 nm during subsequent electric field poling of the crystal. Domain inhibition was confirmed by both differential domain etching and piezoresponse force microscopy. This effect allows the formation of arbitrarily shaped domains in lithium niobate and forms the basis of a high spatial resolution microstructuring approach when followed by chemical etching.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Dielectric properties of MgO-doped compositionally graded multilayer barium strontium titanate films

M. W. Cole, E. Ngo, S. Hirsch, M. B. Okatan, and S. P. Alpay

Appl. Phys. Lett. 92, 072906 (2008); http://dx.doi.org/10.1063/1.2870079 (3 pages) | Cited 31 times

Online Publication Date: 20 February 2008

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We have grown 5 mol % MgO-doped multilayered Ba1−xSrxTiO3 (BST) films having a nominal thickness of 220 nm with compositions of each layer as BST60/40, BST75/25, and BST90/10 (upgraded). We also fabricated undoped upgraded BST and uniform BST60/40 films for comparison. Results show that Mg-doping improves dielectric loss (tan δ = 0.008) and yields better surface roughness ( ∼ 3.1 nm) compared to undoped upgraded BST. Mg-doped films displayed excellent temperature stability with temperature coefficient of capacitances of −0.94 and 1.14 ppt/°C from 20 to 90 °C and 20 to −10 °C, respectively. Mg doping resulted in a moderate dielectric tunability (29%) compared to undoped BST (65.5%) at 444 kV/cm.
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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
61.72.up Other materials
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Effect of postdeposition annealing on the interfacial and electrical properties of high-k NdOxNy gate dielectrics

Tung-Ming Pan and Sung-Ju Hou

Appl. Phys. Lett. 92, 072907 (2008); http://dx.doi.org/10.1063/1.2884333 (3 pages) | Cited 3 times

Online Publication Date: 21 February 2008

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The authors proposed a high-k NdOxNy gate dielectric grown on silicon substrate by reactive rf sputtering. It is found that the NdOxNy gate dielectric after annealing at 700 °C exhibits excellent electrical properties such as high capacitance value, small interface state, low leakage current, and almost no hysteresis in the capacitance-voltage curves. This indicates that annealing at 700 °C treatment can suppress the interfacial layer and silicate formation, reduce interface traps, and anneal out defects.
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81.40.Gh Other heat and thermomechanical treatments
73.61.Ng Insulators
72.20.Fr Low-field transport and mobility; piezoresistance
77.55.-g Dielectric thin films
81.15.Cd Deposition by sputtering
68.55.aj Insulators

Leakage mechanisms in bismuth ferrite-lead titanate thin films on Pt/Si substrates

Mikael A. Khan, Tim P. Comyn, and Andrew J. Bell

Appl. Phys. Lett. 92, 072908 (2008); http://dx.doi.org/10.1063/1.2839598 (3 pages) | Cited 22 times

Online Publication Date: 21 February 2008

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(1−x)BiFeO3–xPbTiO3 (0.5<x<0.3) thin films have been reported to exhibit high remanent polarizations but device integration is hindered by the presence of leakage currents. An insight into the nature of leakage mechanisms in the films is presented. Films with x = 0.4 and 0.5 exhibit lower leakage currents as compared to x = 0.3 films. At applied fields above 190 kV cm−1, in the region of the coercive field of these films, x = 0.4 and 0.5 exhibit a Poole–Frenkel mechanism while films with x = 0.3 exhibit a combination of space charge limited current and the Schottky effect.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Fq High-field and nonlinear effects
73.30.+y Surface double layers, Schottky barriers, and work functions
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Au(Si)-filled β-Ga2O3 nanotubes as wide range high temperature nanothermometers

N. W. Gong, M. Y. Lu, C. Y. Wang, Y. Chen, and L. J. Chen

Appl. Phys. Lett. 92, 073101 (2008); http://dx.doi.org/10.1063/1.2840574 (3 pages) | Cited 9 times

Online Publication Date: 19 February 2008

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Au(Si)-filled β-Ga2O3 nanotubes were fabricated by an effective one-step chemical vapor deposition method. The Au(Si) interior was introduced by capillarity. Linear thermal expansion of Au(Si) with a coefficient of thermal expansion (CTE) as high as 1.5×10−4(1/K) within single crystal Ga2O3 shell up to 800° C was observed by in situ transmission electron microscopy. The high CTE is correlated to partial melting of Au(Si). As Ga2O3 possesses excellent thermal and chemical stability, the structure can be used as a wide range high-temperature nanothermometer within localized regions of nanosystems.
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61.46.Fg Nanotubes
65.40.De Thermal expansion; thermomechanical effects
81.16.-c Methods of micro- and nanofabrication and processing

High density platinum nanocrystals for non-volatile memory applications

J. Dufourcq, S. Bodnar, G. Gay, D. Lafond, P. Mur, G. Molas, J. P. Nieto, L. Vandroux, L. Jodin, F. Gustavo, and Th. Baron

Appl. Phys. Lett. 92, 073102 (2008); http://dx.doi.org/10.1063/1.2840188 (3 pages) | Cited 22 times

Online Publication Date: 19 February 2008

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High density self-assembled platinum nanodots are elaborated using a radio frequence sputtering technique and embedded in memory structures. Electronic microscopy methods are used to characterize the morphology. Scanning electron microscopy and scanning transmission electron microscopy observations allow quantification of the density (>3×1012 cm−2) and size (2–3 nm) of the nanocrystals, whereas their crystallinity is investigated using high-resolution transmission electron microscopy. Then, capacitance-voltage sweep measurements give excellent memory characteristics with a 7.1 V maximal memory window. Promising retention performances and an estimation of the number of electrons stored in the metallic nanodots are also given in this paper.
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81.16.Dn Self-assembly
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Temperature dependent photoluminescence study on phosphorus doped ZnO nanowires

C. X. Shan, Z. Liu, and S. K. Hark

Appl. Phys. Lett. 92, 073103 (2008); http://dx.doi.org/10.1063/1.2884312 (3 pages) | Cited 29 times

Online Publication Date: 21 February 2008

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We report temperature dependent photoluminescence studies on phosphorus doped ZnO nanowires. The shape of the spectra is very similar to those of phosphorus doped ZnO films. The photoluminescence spectrum at 10 K is dominated by neutral acceptor bound exciton (A 0X) emissions. The acceptor binding energy determined also agrees with the corresponding value in phosphorus doped films. Studies on the A 0X intensity show two quenching channels, associated with the thermal dissociations of A 0X to a free exciton and of shallow residual donors. The residual donors revealed provide a clue for the difficulty in p doping of ZnO.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena

Maskless electrodeposited contact for conducting polymer nanowires

Carlos M. Hangarter, Mangesh Bangar, Sandra C. Hernandez, Wilfred Chen, Marc A. Deshusses, Ashok Mulchandani, and Nosang V. Myung

Appl. Phys. Lett. 92, 073104 (2008); http://dx.doi.org/10.1063/1.2883923 (3 pages) | Cited 8 times

Online Publication Date: 25 February 2008

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This letter reports a simple and scalable method to create mechanical joints and electrical contacts of conducting polymer nanowires to electrodes by selective maskless metal electrodeposition on electrodes. This is an attractive route for contacting nanowires as it bypasses harsh processing conditions of conventional methods. The electrodeposition conditions and initial resistance of the nanowires were found to have a significant impact on the selective maskless deposition. Different dopants were also investigated to understand the polymer reduction during cathodic deposition of metal. A single dodecyl sulfate doped polypyrrole nanowire with maskless electrodeposited nickel contacts was shown to have improved sensitivity toward ammonia gas.
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73.40.Ns Metal-nonmetal contacts
73.63.Nm Quantum wires
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
82.45.Fk Electrodes
82.30.-b Specific chemical reactions; reaction mechanisms
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Lithium cobalt oxide as electron injection material for high performance organic light-emitting diodes

Deqiang Zhang, Yang Li, Guohui Zhang, Yudi Gao, Lian Duan, Liduo Wang, and Yong Qiu

Appl. Phys. Lett. 92, 073301 (2008); http://dx.doi.org/10.1063/1.2828859 (3 pages) | Cited 7 times

Online Publication Date: 19 February 2008

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Lithium cobalt oxide was introduced into organic light-emitting diodes as the electron injection layer. The device with tris(8-hydroxyquinolato) aluminum doped with 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one as the light-emitting layer and LiCoO2 as the electron injection layer showed promising efficiency (10.74 cd/A at 11 V) and longer lifetime (2.8 times as much as LiF/Al control device). Lithium cobalt oxide proved to be thermally decomposed in vacuum to form lithium oxide, which was responsible for the enhanced electron injection.
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85.60.Jb Light-emitting devices
FREE

Light scattering from an ordered array of needle-shaped organic nanoaggregates: Evidence for optical mode launching

J. Fiutowski, V. G. Bordo, L. Jozefowski, M. Madsen, and H.-G. Rubahn

Appl. Phys. Lett. 92, 073302 (2008); http://dx.doi.org/10.1063/1.2839396 (3 pages) | Cited 1 time

Online Publication Date: 19 February 2008

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Pronounced peaks in both photoluminescence and light scattering from an array of almost parallel oriented, needle-shaped organic nanoaggregates on mica are observed as a function of angle of incidence. Within the framework of a simple theoretical model, we identify those peaks as originating from the launching of normal modes in the nanofibers, both radiative and waveguiding. Quantitative information is obtained about the mode spectrum and morphology of nanoscaled objects from a simple far field scattering measurement.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Kz Solid organic materials
81.07.Nb Molecular nanostructures
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Passivated p-type silicon: Hole injection tunable anode material for organic light emission

W. Q. Zhao, G. Z. Ran, W. J. Xu, and G. G. Qin

Appl. Phys. Lett. 92, 073303 (2008); http://dx.doi.org/10.1063/1.2857543 (3 pages) | Cited 2 times

Online Publication Date: 19 February 2008

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We find that hole injection can be enhanced simply by selecting a lower-resistivity p-Si anode to match an electron injection enhancement for organic light emitting diodes with ultrathin-SiO2-layer-passivated p-Si anode (Si-OLED). For a Si-OLED with ordinary AlQ electron transport layer, the optimized resistivity of the p-Si anode is 40 Ω cm; for that with n-doped Bphen electron transport layer, it decreases to 5 Ω cm. Correspondingly, the maximum power efficiency increases from 0.3 to 1.9 lm/W, even higher than that of an indium tin oxide control device (1.4 lm/W). This passivated p-type silicon is a hole injection tunable anode material for OLED.
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85.60.Jb Light-emitting devices
81.65.Rv Passivation
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Electroluminescence imaging and microstructure of organic light-emitting field-effect transistors

Jana Zaumseil, R. Joseph Kline, and Henning Sirringhaus

Appl. Phys. Lett. 92, 073304 (2008); http://dx.doi.org/10.1063/1.2836790 (3 pages) | Cited 13 times

Online Publication Date: 20 February 2008

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The effect of morphology and microstructure on the emission characteristics of ambipolar light-emitting field-effect transistors is studied using the polyfluorene copolymer F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)] as a model system. Different intensity distributions of the emission zones of amorphous, polycrystalline, and aligned F8BT films are demonstrated. Electroluminescence maps of the channel region are produced by overlaying a series of images recorded during gate voltage sweeps. They show a correlation to the microcrystalline structure of the F8BT and are assumed to visualize the current density distribution within the transistor channel.
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85.60.Jb Light-emitting devices
85.30.Tv Field effect devices
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