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1 Mar 2004

Volume 84, Issue 9, pp. 1435-1613

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 1558 (2004); http://dx.doi.org/10.1063/1.1651641 (3 pages)

DongWeon Lee, Adrian Wetzel, Roland Bennewitz, Ernst Meyer, Michel Despont, Peter Vettiger, and Christoph Gerber
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Self-assembled InAsSb quantum dots on (001) InP substrates

Yueming Qiu and David Uhl

Appl. Phys. Lett. 84, 1510 (2004); http://dx.doi.org/10.1063/1.1655690 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2004

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Self-assembled InAsSb quantum dots (QD) on (001) InP substrates have been grown using metalorganic vapor phase epitaxy. The dot density and size are found to be strongly dependent on the presence of arsine. Direct deposition of InSb on InP and GaSb substrates formed large islands of InSb with low density of less than 5×109/cm2, however, InAsSb QDs of density as high as 4×1010/cm2 could be self-assembled by alternating group III and group V precursors, and high density almost pure InSb QDs were achieved on In0.53Ga0.47As/InP. The formation of high density InAsSb QDs is a result of a local nonequilibrium process and a reduction in mobility of In adatoms on the growth surface due to the presence of arsenic atoms, and in the case of high density almost pure InSb QDs on InGaAs/InP, the InAs interface layer is believed to be responsible. Photoluminescence shows that InSb QDs emit light at room temperature in the range of 1.7–2.2 μm. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Hc Quantum dots

Highly-efficient blue electroluminescence based on two emitter isomers

Ying Kan, Liduo Wang, Lian Duan, Yuanchuan Hu, Guoshi Wu, and Yong Qiu

Appl. Phys. Lett. 84, 1513 (2004); http://dx.doi.org/10.1063/1.1651653 (3 pages) | Cited 39 times

Online Publication Date: 25 February 2004

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Highly-efficient blue organic light-emitting devices with a nondoped device structure have been fabricated with two anthracene derivatives, 2,3,6,7-tetramethyl-9,10-(1-dinaphthyl)-anthracene (α-TMADN) and 2,3,6,7-tetramethyl-9,10-(2-dinaphthyl)-anthracene (β-TMADN). The homemade α-TMADN, β-TMADN, or their blend were used as the light-emitting materials, and 4,7-diphenyl-1,10-phenanthroline was used as the hole blocking and electron transporting material, N,N′-biphenyl-N,N′-bis-(1-naphenyl)-[1,1′-biphenyl]-4,4′-diamine was used as the hole transporting material. The brightness of the device with β-TMADN as the light-emitting material is up to 10 000 cd/m2 at 12 V with the maximum efficiency of 4.5 cd/A, which is better than that of the device with α-TMADN as the light-emitting material. The brightness of the same structure device with the blend of α-TMADN and β-TMADN as the light-emitting material, in which the ratio of α-TMADN to β-TMADN is 9:1, is more than 12 000 cd/m2 at 15 V with the maximum efficiency of 5.2 cd/A. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
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Switching current versus magnetoresistance in magnetic multilayer nanopillars

S. Urazhdin, Norman O. Birge, W. P. Pratt, and J. Bass

Appl. Phys. Lett. 84, 1516 (2004); http://dx.doi.org/10.1063/1.1651645 (3 pages) | Cited 53 times

Online Publication Date: 25 February 2004

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We study current-driven magnetization switching in nanofabricated magnetic trilayers, varying the magnetoresistance in three different ways. First, we insert a strongly spin-scattering layer between the magnetic trilayer and one of the electrodes, giving increased magnetoresistance. Second, we insert a spacer with a short spin-diffusion length between the magnetic layers, decreasing the magnetoresistance. Third, we vary the angle between layer magnetizations. In all cases, we find an approximately linear dependence between magnetoresistance and inverse switching current. We give a qualitative explanation for the observed behaviors, and suggest some ways in which the switching currents may be reduced. © 2004 American Institute of Physics.
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68.65.Ac Multilayers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.15.Qm Scattering mechanisms and Kondo effect
75.50.Bb Fe and its alloys

Writing and reading bits on pre-patterned media

J. Moritz, L. Buda, B. Dieny, J. P. Nozières, R. J. M. van de Veerdonk, T. M. Crawford, and D. Weller

Appl. Phys. Lett. 84, 1519 (2004); http://dx.doi.org/10.1063/1.1644341 (3 pages) | Cited 32 times

Online Publication Date: 25 February 2004

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We have written and read back bits on perpendicular pre-patterned media prepared by electron-beam lithography. Using a contact tester equipped with a standard longitudinal head, we are able to write different bit lengths on 100×200 nm2 dots spaced 100 nm apart. These tests demonstrate the role played by the distribution of the coercive fields of the dots during the write process. Signal-to-noise ratios (SNRs) are obtained by numerical analysis and are found to be on the same order of magnitude as in continuous perpendicular media, but remain constant at decreasing bit lengths. This property of the SNR is due to a partial reduction of transition noise. The potential to pattern these media with nanoimprint lithography and their good recording performance make them candidates for ultrahigh density recording. © 2004 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer

Inhomogeneous magnetization of a superconducting film measured with a gradiometer

H. Stalzer, A. Cosceev, C. Sürgers, H. v. Löhneysen, J.-M. Brosi, G.-A. Chakam, and W. Freude

Appl. Phys. Lett. 84, 1522 (2004); http://dx.doi.org/10.1063/1.1655706 (3 pages) | Cited 2 times

Online Publication Date: 25 February 2004

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The magnetic flux generated by the screening currents of a superconducting Nb film in the Meissner state is measured with a coaxial gradiometer in a weak magnetic field B. A peculiar position dependence is found when the sample surface is only slightly tilted away from the parallel field orientation and shifted with respect to the center axis of the gradiometer. This is due to the inhomogeneous magnetization with a strong out-of-plane contribution measured by the two pick-up coils as confirmed by numerical finite-element calculations. The unusual position dependence has important consequences for interpreting the diamagnetic screening of superconducting films measured by a coaxial gradiometer near the parallel-field orientation. © 2004 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.78.-w Superconducting films and low-dimensional structures
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Nanotube magnetism

Y. C. Sui, R. Skomski, K. D. Sorge, and D. J. Sellmyer

Appl. Phys. Lett. 84, 1525 (2004); http://dx.doi.org/10.1063/1.1655692 (3 pages) | Cited 68 times

Online Publication Date: 25 February 2004

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FePt and Fe3O4 nanotubes are produced by hydrogen reduction in nanochannels of porous alumina templates and investigated by electron microscopy, x-ray diffraction analysis, and magnetic measurements. Loading the templates with a Fe chloride and Pt chloride mixture followed by hydrogen reduction at 560 °C leads to the formation of ferromagnetic FePt nanotubes in the alumina pores. Using a Fe nitrate solution, thermally decomposed at 250 °C and reduced in hydrogen for 2.5 h at the same temperature, yields Fe3O4 tubes. The length of the nanotubes is about 50 μm and their diameters range from about 150 to 220 nm, depending on the thickness of the template film and the pore diameter distribution. Reflecting the different magnetocrystalline anisotropies of the compounds, the coercivities range from 0.61 kOe for Fe3O4 to 20.9 kOe for FePt. The hysteresis is explained in terms of a tubular random-anisotropy model, which yields a diameter and anisotropy dependent transition from a curling-type mode (Fe3O4) to a localized mode (FePt). © 2004 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.50.Dd Nonmetallic ferromagnetic materials
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Cy Elemental semiconductors
75.30.Gw Magnetic anisotropy
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
75.70.Rf Surface magnetism
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effects of magnetic field on the manganite-based bilayer junction

J. R. Sun, C. M. Xiong, T. Y. Zhao, S. Y. Zhang, Y. F. Chen, and B. G. Shen

Appl. Phys. Lett. 84, 1528 (2004); http://dx.doi.org/10.1063/1.1664032 (3 pages) | Cited 81 times

Online Publication Date: 25 February 2004

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An oxide bilayer junction has been fabricated by growing a La0.32Pr0.35Ca0.33MnO3 film on 0.5 wt % Nb-doped SrTiO3 crystal, and its behavior under magnetic field is experimentally studied. It is found that external field greatly affected the rectifying property and the resistance of the junction, causing an extremely large magnetoresistance. The most striking observation of the present work is that the magnetoresistance of the junction can be either positive or negative, depending on temperature and applied current, and is asymmetric with respect to the direction of the bias current. These results reveal the great potential of the manganites in configuring artificial devices. © 2004 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.Lx Magnetic oxides
71.20.Ps Other inorganic compounds
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Turnaround of hysterisis for capacitance–voltage characteristics of hafnium oxynitride dielectrics

J. C. Wang, D. C. Shie, T. F. Lei, and C. L. Lee

Appl. Phys. Lett. 84, 1531 (2004); http://dx.doi.org/10.1063/1.1644616 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2004

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The capacitance–voltage (C–V) characteristics of hafnium oxynitride gate dielectrics for silicon metal-oxide-semiconductor (MOS) capacitors with different sweep voltage were investigated. It was found that, for the p-type substrate MOS capacitor, the C–V hysterisis has a turnaround characteristic as the applied voltage exceeds −3.0 V. The phenomenon is explained by electron trappings at the low electric field and hole trappings, which resulted from the impact ionization, at the high electric field in the dielectrics. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Ht High-field and nonlinear effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Slow relaxation of field-induced piezoelectric resonance in paraelectric barium stannate titanate

Xiaoyong Wei, Yujun Feng, and Xi Yao

Appl. Phys. Lett. 84, 1534 (2004); http://dx.doi.org/10.1063/1.1655694 (3 pages) | Cited 16 times

Online Publication Date: 25 February 2004

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A kind of slow relaxation of field-induced piezoelectric resonance is observed in paraelectric barium stannate titanate ceramics. The piezoelectric resonance peaks vanish in several minutes when bias field is either applied or removed. These phenomena may be universal for dielectrics and can be explained by a model of slow dipoles composed of injected homocharges. With this model, the authors predict a negative piezoelectric modulus of d33 when just the bias field is removed, and verify it by experimental results. © 2004 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
77.80.B- Phase transitions and Curie point
77.65.Fs Electromechanical resonance; quartz resonators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Experimental confirmation of negative refractive index of a metamaterial composed of Ω-like metallic patterns

Jiangtao Huangfu, Lixin Ran, Hongsheng Chen, Xian-min Zhang, Kangsheng Chen, Tomasz M. Grzegorczyk, and Jin Au Kong

Appl. Phys. Lett. 84, 1537 (2004); http://dx.doi.org/10.1063/1.1655673 (3 pages) | Cited 95 times

Online Publication Date: 25 February 2004

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A one-dimensional metamaterial is realized using three connected Ω rings printed back-to-back and reversed on two sides of a dielectric substrate. Both transmission and prism experiments are reported, yielding concordant results of the presence of a left-handed frequency band. Experiments show reduced losses and an enlarged left-handed frequency band. © 2004 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Gi Light-sensitive materials
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Field emission from gallium-doped zinc oxide nanofiber array

C. X. Xu, X. W. Sun, and B. J. Chen

Appl. Phys. Lett. 84, 1540 (2004); http://dx.doi.org/10.1063/1.1651328 (3 pages) | Cited 107 times

Online Publication Date: 25 February 2004

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Gallium-doped nanostructural zinc oxide fibers have been fabricated by vapor-phase transport method of heating the mixture of zinc oxide, gallium oxide, and graphite powders in air. The zinc oxide fibers grew along [002] direction, forming a vertically aligned array that is predominantly perpendicular to the substrate surface. With a gallium doping concentration of 0.73 at. %, the corresponding carrier concentration and resistivity were 3.77×1020 cm−3 and 8.9×10−4 Ω cm, respectively. The field emission of these vertically aligned ZnO fiber arrays showed a low field emission threshold (2.4 V/μm at a current density of 0.1 μA/cm2), high current density, and high field enhancement factor (2317). The dependence of emission current density on the electric field followed Fowler–Nordheim relationship. The enhanced field emission is attributed to the aligned structure, good crystal quality, and especially, the improved electrical properties (increased conductivity and reduced work function) of the nanofibers due to gallium doping. © 2004 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
72.80.Ey III-V and II-VI semiconductors
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Energy-level splitting of ligand-stabilized Au55 clusters observed by scanning tunneling spectroscopy

H. Zhang, U. Hartmann, and G. Schmid

Appl. Phys. Lett. 84, 1543 (2004); http://dx.doi.org/10.1063/1.1652227 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2004

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A monolayer of Au55 clusters stabilized by [P(C6H5)3]12Cl6 ligands was investigated at 7 K using a low-temperature ultrahigh vacuum scanning tunneling microscope. The topography of single clusters shows the actual arrangement of the C6H5 rings of ligand molecules. Characteristic charge-quantization phenomena usually obtained for metal particles were observed by current–voltage measurements. Spectroscopic data acquired at different locations within a cluster reveal energy levels with average spacing of 170 meV which can be attributed to the Au55 core. © 2004 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Synthesis of InN/InP core/sheath nanowires

Long-Wei Yin, Yoshio Bando, Ying-Chun Zhu, Dmitri Golberg, and Mu-Sen Li

Appl. Phys. Lett. 84, 1546 (2004); http://dx.doi.org/10.1063/1.1651331 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2004

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Bulk quantities of InN/InP core/sheath nanowires with a diameter of 60–90 nm and a length of several micrometers were synthesized through a vapor reaction route. The nanowires consisted of single-crystalline InN core with 30–40 nm in diameter and amorphous InP sheath with a thickness of 20–25 nm. High-resolution transmission electron microscopy images indicated that most of the InN core is perfect crystalline; there also exists a high density of stacking faults and twins in the crystalline InN core in some of the synthesized nanowires. Indium nanoparticles found at the tip of the nanowires indicated a vapor-liquid-solid growth mechanism for formation of the InN/InP nanostructures. This type of InN/InP nanowire is important and may be further developed to be utilized as nanoscale field effect transistor and light-emitting diode. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.05.Gc Amorphous semiconductors
61.46.-w Structure of nanoscale materials
61.72.Nn Stacking faults and other planar or extended defects
61.72.Mm Grain and twin boundaries

Resonance Raman scattering of boron carbonitride nanotubes

C. Y. Zhi, X. D. Bai, and E. G. Wang

Appl. Phys. Lett. 84, 1549 (2004); http://dx.doi.org/10.1063/1.1652237 (3 pages) | Cited 8 times

Online Publication Date: 25 February 2004

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Resonance Raman spectra of boron carbonitride (BCN) nanotubes synthesized by hot-filament chemical vapor deposition were investigated. The intensity of the D band is insensitive to laser excitation energy (Elaser), while the intensity of the G and G′ bands increases as Elaser increases, and saturates at Elaser = 2.67 eV. This particular resonance behavior is ascribed to an electronic transition process different from the π–π∗ transition that occurs in carbon materials. The dispersive behavior of the D-related bands also shows an inflection at Elaser = 2.67 eV and different ∂ω/∂Elaser compared to carbon materials. These results indicate there are special electronic and phonon structures in BCN nanotubes. © 2004 American Institute of Physics.
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78.67.Ch Nanotubes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Na Fullerenes and related materials

Field emission from vertically aligned conductive IrO2 nanorods

Reui-San Chen, Ying-Sheng Huang, Ya-Min Liang, Chim-Sung Hsieh, Dah-Shyang Tsai, and Kwong-Kau Tiong

Appl. Phys. Lett. 84, 1552 (2004); http://dx.doi.org/10.1063/1.1655703 (3 pages) | Cited 46 times

Online Publication Date: 25 February 2004

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We report on the preparation and field-emission properties of vertically aligned conductive IrO2 nanorods. The unique geometrical features of IrO2 nanorods, including nanosized structure and self-assembled sharp tip, exhibit a strong effect on field enhancement (β∼40 000), which result in a low threshold field (Eth ∼ 0.7 V/μm) defined at the beginning of emission. A low turn-on field for driving a current of 10 μA/cm2 is about 5.6 V/μm, which is comparable with the carbon nanotube, diamond, and amorphous carbon. The potential of using IrO2 nanorods as an emitter material has been demonstrated. © 2004 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

A 7-nm nanocolumn structure fabricated by using a ferritin iron-core mask and low-energy Cl neutral beams

Tomohiro Kubota, Tomohiro Baba, Seiji Samukawa, Hiroyuki Kawashima, Yukiharu Uraoka, Takashi Fuyuki, and Ichiro Yamashita

Appl. Phys. Lett. 84, 1555 (2004); http://dx.doi.org/10.1063/1.1655701 (3 pages) | Cited 25 times

Online Publication Date: 25 February 2004

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A 7-nm silicon column structure was fabricated by using a Cl neutral beam we developed. The neutral beam achieved a high etching selectivity to a ferritin iron-core mask by using charge-free and damage-free etching processes. The silicon etching selectivity ratio to the iron core was measured to be about 59. The iron core in the ferritin was 7 nm in diameter, which was identical to that of the etched nanocolumn. This indicates that neutral-beam etching transferred the structure and size of the iron core to the silicon substrate. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Switchable cantilever for a time-of-flight scanning force microscope

DongWeon Lee, Adrian Wetzel, Roland Bennewitz, Ernst Meyer, Michel Despont, Peter Vettiger, and Christoph Gerber

Appl. Phys. Lett. 84, 1558 (2004); http://dx.doi.org/10.1063/1.1651641 (3 pages) | Cited 10 times

Online Publication Date: 25 February 2004

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We have developed a cantilever device for applying a time-of-flight scanning force microscope (TOF–SFM) system. The cantilever device consists of a switchable cantilever with an integrated bimorph actuator, an integrated extraction electrode to minimize the ion extraction voltage, and an interlocking structure for precise tip–EE alignment. The TOF–SFM with the cantilever device allows quasisimultaneous topographical and chemical analyses of solid surfaces to be performed in the same way as with the conventional scanning probe technique. The switching properties of the bimorph actuator are demonstrated for use in two operating systems. Field emission measurements and a TOF analysis of a Pt-coated tip are conducted with the TOF–SFM. © 2004 American Institute of Physics.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.80.-d Chemical analysis and related physical methods of analysis
79.70.+q Field emission, ionization, evaporation, and desorption

Investigation of azobenzene side group orientation in polymer surface relief gratings by means of photoelectron spectroscopy

O. Henneberg, Th. Geue, U. Pietsch, M. Saphiannikova, and B. Winter

Appl. Phys. Lett. 84, 1561 (2004); http://dx.doi.org/10.1063/1.1651654 (3 pages) | Cited 4 times

Online Publication Date: 25 February 2004

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The molecular orientation of azobenzene side groups in polymer films before (nonpatterned) and after (patterned) development of a surface relief grating has been investigated by photoelectron spectroscopy using synchrotron radiation. The photoemission spectra obtained for 60–100 eV photons of a patterned and a nonpatterned surface are similar when the polarization vector of the synchrotron light is parallel to the grating vector. However, for perpendicular excitation, considerable spectral intensity differences can be observed for 9–14 eV electron binding energy. The observed changes are attributed to the formation of well-oriented azobenzenes at the surface. © 2004 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
79.60.Ht Disordered structures
78.66.Qn Polymers; organic compounds

Phonon confinement in oxide-coated silicon nanowires

Somnath Bhattacharyya and Saumyadip Samui

Appl. Phys. Lett. 84, 1564 (2004); http://dx.doi.org/10.1063/1.1651648 (3 pages) | Cited 20 times

Online Publication Date: 25 February 2004

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Raman spectroscopy of micron-long crystalline Si nanowires covered with a thick SiO2 layer showed a downshift and asymmetric broadening of the Raman first order TO phonon peak when compared with the bulk (q = 0) mode. The Raman shift and broadening were attributed to phonon confinement in the nanowires. A phenomenological phonon confinement model, incorporating the effects of nanowire diameter distribution, is presented. This model is shown to accurately describe the broadening of the Raman peak and is consistent with the microstructure of Si nanowires. In addition to the work a distribution of the phonon wave vector was directly taken into consideration replacing the diameter distribution to fit the Raman TO peak. The effects of the nano-Si:SiO2 boundary on the Raman spectra are discussed in terms of softening of the phonon confinement. © 2004 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Am Elemental semiconductors and insulators
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

2H nuclear magnetic resonance spectroscopy of deuterium adsorption on single-walled carbon nanotubes

Kai Shen and Tanja Pietraß

Appl. Phys. Lett. 84, 1567 (2004); http://dx.doi.org/10.1063/1.1652231 (3 pages) | Cited 2 times

Online Publication Date: 25 February 2004

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2H nuclear magnetic resonance (NMR) spectroscopy was employed to study the interaction between deuterated hydrogen gas and single walled carbon nanotubes before and after purification. Transmission electron micrographs revealed strong bundling of the tubes. After purification, very little amorphous carbon and no graphitic particles were present, implying that the interactions observed are truly due to the nanotubes. In the parent material, the NMR signal is dominated by interaction of hydrogen with residual metal catalyst particles. For purified material, hydrogen in the gas phase is discernible from adsorbed hydrogen. The two phases do not exchange with each other on a ms time scale. The hydrogen molecules move among different adsorption sites, presumably outer tube surfaces and interstitial channels. This process is diffusion limited in the pressure range investigated. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.43.Mn Adsorption kinetics
76.60.Es Relaxation effects
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
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Anomalous charge transport behavior of Fullerene based diodes

G. J. Matt, N. S. Sariciftci, and T. Fromherz

Appl. Phys. Lett. 84, 1570 (2004); http://dx.doi.org/10.1063/1.1651642 (3 pages) | Cited 14 times

Online Publication Date: 25 February 2004

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We observed an anomalous voltage–current (V–I) characteristics of fullerene based diodes in the low temperature regime. The diodes exhibit a negative differential resistance and voltage hysteresis for opposite current sweep directions. This behavior is directly observable at temperatures below 95 K and indicates the formation of highly conductive filaments in the fullerene thin films. © 2004 American Institute of Physics.
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85.30.Kk Junction diodes
77.80.Dj Domain structure; hysteresis

Thin-film field-effect transistors based on La-doped SrTiO3 heterostructures

Feng Pan, David Olaya, John C. Price, and Charles T. Rogers

Appl. Phys. Lett. 84, 1573 (2004); http://dx.doi.org/10.1063/1.1651647 (3 pages) | Cited 10 times

Online Publication Date: 25 February 2004

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Field-effect transistors have been fabricated from epitaxial perovskite strontium titanate heterostructures. Lanthanum-doped SrTiO3 was used as the semiconducting channel while insulating SrTiO3 was used as a gate insulator. Both depletion and accumulation effects in the channel have been studied from 300 to 4 K. Hall effect measurements indicate a temperature independent n-type carrier density around 5×1019 cm−3. At 300 K, typical mobilities are 2–3 cm2 V−1 s−1 while low temperature mobilities are as high as 15 cm2 V−1 s−1. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Electron-beam-induced current observed for dislocations in diffused 4H-SiC P–N diodes

S. Maximenko, S. Soloviev, D. Cherednichenko, and T. Sudarshan

Appl. Phys. Lett. 84, 1576 (2004); http://dx.doi.org/10.1063/1.1652229 (3 pages) | Cited 7 times

Online Publication Date: 25 February 2004

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The electron-beam-induced current (EBIC) method was employed to investigate the electrical activity of dislocations in silicon carbide Schottky and diffused p–n diodes. Dislocations in Schottky diodes appear as dark spots with the EBIC current signal at the dislocations reduced with respect to the background. However, in p–n diodes, the same dislocations exhibited characteristic bright halos, with the EBIC current higher than that of the background. These bright halos were attributed to a nonuniform impurity distribution around dislocations caused by the high-temperature (∼2000 °C) diffusion process. © 2004 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
66.30.Lw Diffusion of other defects
85.30.Kk Junction diodes

Bulk-acoustic waves radiated from low-loss surface-acoustic-wave resonators

J. V. Knuuttila, J. J. Vartiainen, J. Koskela, V. P. Plessky, C. S. Hartmann, and M. M. Salomaa

Appl. Phys. Lett. 84, 1579 (2004); http://dx.doi.org/10.1063/1.1650557 (3 pages) | Cited 6 times

Online Publication Date: 25 February 2004

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The bulk-acoustic conductance in low-loss surface-acoustic-wave filters utilizing leaky surface-acoustic waves is significant for the device operation. Here we directly measure the bulk acoustic wave radiation pattern on the backside of the piezoelectric substrate with the help of a scanning laser-interferometer probe. For the case studied, a leaky surface-acoustic wave resonator on 36°YX–LiTaO3, a numerical calculation is carried out and the different bulk-wave modes arriving at the substrate bottom are identified by comparing the measured and computed energy-flow angles. The results are expected to lead to improved models for describing the operation of low-loss surface-acoustic-wave filters. © 2004 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.35.Iv Acoustical properties
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics

Organic thin-film transistors fabricated by microcontact printing

M. Leufgen, A. Lebib, T. Muck, U. Bass, V. Wagner, T. Borzenko, G. Schmidt, J. Geurts, and L. W. Molenkamp

Appl. Phys. Lett. 84, 1582 (2004); http://dx.doi.org/10.1063/1.1652233 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2004

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We have fabricated organic thin-film transistors (OTFTs) using a microcontact printing technique (μCP) that employs thin polydimethylsiloxane stamps on a rigid silicon substrate in order to reduce macroscopic distortions. Systematic variation of the printing pressure, printing time, and concentration of eicosanethiol, the “molecular ink” in the μCP process, permits the fabrication of devices with smaller channel lengths (Leff) than nominally defined by the stamp. Interdigitated Ti/Au electrode structures with Leff down to 100 nm could be fabricated which, after additional surface treatment and vacuum deposition of αα′-dihexylquaterthiophene, yield OTFTs with excellent characteristics. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
81.65.Ps Polishing, grinding, surface finishing
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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