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29 Mar 2004

Volume 84, Issue 13, pp. 2223-2459

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 2244 (2004); http://dx.doi.org/10.1063/1.1690471 (3 pages)

David R. Smith, David Schurig, Jack J. Mock, Pavel Kolinko, and Patrick Rye
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Electromagnetic radiation produced by avalanches in the magnetization reversal of Mn12-acetate

J. Tejada, E. M. Chudnovsky, J. M. Hernandez, and R. Amigó

Appl. Phys. Lett. 84, 2373 (2004); http://dx.doi.org/10.1063/1.1691501 (3 pages) | Cited 25 times

Online Publication Date: 23 March 2004

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Electromagnetic radiation produced by avalanches in the magnetization reversal of Mn12-acetate has been measured. Short bursts of radiation have been detected, with intensity significantly exceeding the intensity of the blackbody radiation from the sample. A model based upon superradiance from inversely populated spin levels has been suggested. © 2004 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
78.45.+h Stimulated emission
75.50.Xx Molecular magnets

Ferromagnetism and magnetoresistance of Co–ZnO inhomogeneous magnetic semiconductors

Shi-shen Yan, C. Ren, X. Wang, Y. Xin, Z. X. Zhou, L. M. Mei, M. J. Ren, Y. X. Chen, Y. H. Liu, and H. Garmestani

Appl. Phys. Lett. 84, 2376 (2004); http://dx.doi.org/10.1063/1.1690881 (3 pages) | Cited 44 times

Online Publication Date: 23 March 2004

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Co–ZnO inhomogeneous magnetic semiconductor thin films were synthesized on the subnanometer scale by sputtering. Room temperature ferromagnetism with high magnetization was found. Large negative magnetoresistance of 11% was found at room temperature, and its value increased with a decrease in temperature up to 36% at 4.8 K. The mechanism for large negative magnetoresistance is discussed. © 2004 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Pq Other materials
72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
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Effect of interfaces in Monte Carlo computer simulations of ferroelectric materials

D. Bolten, U. Böttger, and R. Waser

Appl. Phys. Lett. 84, 2379 (2004); http://dx.doi.org/10.1063/1.1687455 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2004

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In this article, Monte Carlo simulation methods were used to investigate the influence of interface layers between the ferroelectric core material and the electrodes on the hysteresis loop in ferroelectric thin films. The hysteresis loops were calculated using an existing Monte Carlo model. For certain interface configurations, the simulations resulted in asymmetric hysteresis loops, similar to imprinted loops, due to asymmetric nucleation kinetics. Although the results might not offer a new explanation for imprint in ferroelectric thin films, they provide insight into the often observed phenomenon of initially imprinted hysteresis loops of as-prepared thin-film samples. © 2004 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
02.70.Uu Applications of Monte Carlo methods

Three-dimensional ferroelectric domain imaging of bulk Pb(Zr,Ti)O3 by atomic force microscopy

Seungbum Hong, Bastien Ecabart, Enrico L. Colla, and Nava Setter

Appl. Phys. Lett. 84, 2382 (2004); http://dx.doi.org/10.1063/1.1655695 (3 pages) | Cited 16 times

Online Publication Date: 23 March 2004

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We report on the ferroelectric domain evolution as a function of the depth of the surface of 100 μm thick bulk Pb(Zr,Ti)O3 (PZT) doped with 2% Nb. Ferroelectric domain imaging (FDI) was performed by piezoelectric detection assisted by atomic force microscopy (AFM). The depth evolution of the polarization orientation was obtained by repeated surface chemical etching followed by FDI. It was observed that backswitching mainly occurred close to 90° domain and grain boundaries. The depth of these domains was estimated to be about 500 nm. This indicates that nonpenetrating domains of opposite polarity can retain their polarization vector near the surface region without the help of a top electrode interface. It also supports the idea that they act as preferential nucleation sites for polarization reversal. We suggest that AFM FDI combined with proper etching methods could be used to construct a three-dimensional image of the whole domain structure by stacking two-dimensional images layer by layer. © 2004 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
68.37.Ps Atomic force microscopy (AFM)
81.65.Cf Surface cleaning, etching, patterning
61.72.Mm Grain and twin boundaries

Crossover between extrinsic and intrinsic dielectric loss mechanisms in SrTiO3 thin films at microwave frequencies

K. F. Astafiev, V. O. Sherman, A. K. Tagantsev, N. Setter, T. Kaydanova, and D. S. Ginley

Appl. Phys. Lett. 84, 2385 (2004); http://dx.doi.org/10.1063/1.1690878 (3 pages) | Cited 9 times

Online Publication Date: 23 March 2004

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The dc bias field dependence of the dielectric loss in SrTiO3 thin films deposited onto MgO substrate is investigated. The experimental data obtained at different frequencies of the ac field (8 and 16 GHz) from differently processed films (as deposited and oxygen annealed) strongly suggest the occurrence of a crossover in the dominant loss mechanism. The crossover is driven by the dc bias field: at weak fields the loss is governed by an extrinsic mechanism(s) whereas, at higher fields, the contribution of an intrinsic mechanism (dc field-induced quasi-Debye loss) becomes predominant. © 2004 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Gm Dielectric loss and relaxation

Direct evidence of ferroelastic participation in 180° polarization switching and fatigue for 111 oriented rhombohedral ferroelectric 0.955 Pb(Zn1/3Nb2/3)O3:0.045 PbTiO3 single crystals

Wenyi Zhu and L. Eric Cross

Appl. Phys. Lett. 84, 2388 (2004); http://dx.doi.org/10.1063/1.1690869 (3 pages) | Cited 3 times

Online Publication Date: 23 March 2004

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Direct elastic deformation measurements taken during polarization reversal in 111 oriented 0.955 Pb(Zn1/3Nb2/3)O3–0.045 PbTiO3 single crystals confirm the observation by W. Cao [Ferroelectrics 290, 107 (2003)] that a ferroelastic reorientation of the domain polarization vectors is involved, and the observed strain changes are consistent with the model he proposed. First cycle nonrecoverable fatigue occurring in our crystals and the associated changes of shape in polarization and strain hysteresis are suggested to be due to microcracking associated with the large very rapid strain changes associate with the ferroelastic switching mode. © 2004 American Institute of Physics.
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77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
77.22.Ej Polarization and depolarization
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Super-resolution in laser annealing and ablation

Ivan Avrutsky, Daniel G. Georgiev, Dmitry Frankstein, Gregory Auner, and Golam Newaz

Appl. Phys. Lett. 84, 2391 (2004); http://dx.doi.org/10.1063/1.1688995 (3 pages) | Cited 12 times

Online Publication Date: 23 March 2004

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This letter reports observation of ablated holes as small as 0.7 μm fabricated by single 25 ns pulses of KrF (λ = 248 nm) laser focused onto a 5.6 μm spot. Samples with high thermal conductivity films with respect to that of the substrate (Si/silica, Al/glass) repeatedly showed considerable reduction in the size of the ablated spot (0.7- and 1.2-μm-diam holes, respectively). This letter also presents a likely mechanism of the observed super-resolution and the criteria necessary to achieve super-resolution. Due to the nonoptical origin of this effect it is expected that a tightly focused (<0.5 μm) laser beam can be used to ablate with nanoscale (<100 nm) resolution. © 2004 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.20.Wk Machining, milling
07.10.Cm Micromechanical devices and systems
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)

Direct observation of metal complex nanoparticles doped in sol-gel silica glasses using transmission electron microscopy

M. Baba, M. Ichihara, R. A. Ganeev, M. Suzuki, H. Kuroda, M. Morita, D. Rau, T. Ishii, and M. Iwamura

Appl. Phys. Lett. 84, 2394 (2004); http://dx.doi.org/10.1063/1.1688980 (3 pages) | Cited 5 times

Online Publication Date: 23 March 2004

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Sol-gel silica glasses are good nanoporous matrices and are able to confine various phosphors as dopants, so these are quite interesting and strategic materials and show phenomena such as surface-enhanced quantum confinement effects: high luminescence quantum efficiency and ultrafast decay times. We observed directly clear images of metal complex nanoparticles in those with transmission electron microscopy. This can easily improve the quality of uniformly doped sol-gel silica glasses. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
78.55.Qr Amorphous materials; glasses and other disordered solids
78.55.Mb Porous materials
68.37.Lp Transmission electron microscopy (TEM)

Space-resolved photoluminescence of ZnS:Cu,Al nanocrystals fabricated by sequential ion implantation

Atsushi Ishizumi, C. W. White, and Yoshihiko Kanemitsu

Appl. Phys. Lett. 84, 2397 (2004); http://dx.doi.org/10.1063/1.1689738 (3 pages) | Cited 19 times

Online Publication Date: 23 March 2004

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We report on photoluminescence (PL) properties of Cu- and Al-doped ZnS nanocrystals fabricated by sequential implantation of Zn+, S+, Cu+, and Al+ ions into Al2O3 matrices. The spatially resolved PL spectrum has been studied by a scanning near-field optical microscope (SNOM). In the SNOM image, bright spots are observed on the sample surface. The PL spectrum at each bright spot is broad and is not sensitive to the monitored positions. The broad SNOM-PL spectrum at each spot is very similar to the macroscopic PL spectrum measured by conventional optics. The donor-acceptor pair luminescence process in nanocrystals is discussed. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Photoelectronic transport imaging of individual semiconducting carbon nanotubes

Kannan Balasubramanian, Yuwei Fan, Marko Burghard, Klaus Kern, Marcel Friedrich, Uli Wannek, and Alf Mews

Appl. Phys. Lett. 84, 2400 (2004); http://dx.doi.org/10.1063/1.1688451 (3 pages) | Cited 42 times

Online Publication Date: 23 March 2004

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Photoconductivity in individual semiconducting single-wall carbon nanotubes was investigated using a confocal scanning optical microscope. The magnitude of the photocurrent was found to increase linearly with the laser intensity, and to be maximum for parallel orientation between the light polarization and the tube axis. Larger currents were obtained upon illuminating the tubes at 514.5 nm in comparison to those at 647.1 nm, consistent with the semiconducting tubes having a resonant absorption energy at the former wavelength. Moreover, the determination of the photoresponse as a function of position along single nanotubes has proven to be a useful tool to monitor local electronic structure effects. © 2004 American Institute of Physics.
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73.63.Fg Nanotubes
61.46.-w Structure of nanoscale materials
72.40.+w Photoconduction and photovoltaic effects
78.30.Hv Other nonmetallic inorganics

Single graphene sheet detected in a carbon nanofilm

Shigeo Horiuchi, Takuya Gotou, Masahiro Fujiwara, Toru Asaka, Tadahiro Yokosawa, and Yoshio Matsui

Appl. Phys. Lett. 84, 2403 (2004); http://dx.doi.org/10.1063/1.1689746 (3 pages) | Cited 37 times

Online Publication Date: 23 March 2004

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In order to clarify the existence of a single sheet of carbon six-membered-ring plane (graphene) this letter presents a method by which the stacking number of the sheets in a carbon nanofilm (CNF) can be exactly counted, based on the quantitative analysis of electron diffraction intensity. Using the method we can detect a single graphene sheet in a CNF. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
82.80.-d Chemical analysis and related physical methods of analysis

Nanoscale thin single-crystal silicon and its application to electronics

Uygar Avci and Sandip Tiwari

Appl. Phys. Lett. 84, 2406 (2004); http://dx.doi.org/10.1063/1.1689745 (3 pages) | Cited 4 times

Online Publication Date: 23 March 2004

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We demonstrate a method for achieving thin (tens of nanometers) single-crystal silicon films with electronic-quality bulk and surface properties, atomic-scale surface roughness, and suitable for use in complex multilayered structures. The thin silicon film is achieved by defining thickness through the use of oxidation depth as a reference, transfer of film structure by exfoliation, and chemical-mechanical polishing for selective thin film definition. Such structures are useful in a variety of directions: in electronic devices such as field-effect transistors, in characterization studies such as those utilizing vertical transport using thicknesses of the order of mean free path length, etc. We demonstrate its use in a silicon metal-oxide-semiconductor transistor with two gates, one on each side of the thin silicon film on a planar substrate. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
85.30.Tv Field effect devices
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Mq Oxidation
81.65.Ps Polishing, grinding, surface finishing
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Direct carrier multiplication due to inverse Auger scattering in CdSe quantum dots

Marco Califano, Alex Zunger, and Alberto Franceschetti

Appl. Phys. Lett. 84, 2409 (2004); http://dx.doi.org/10.1063/1.1690104 (3 pages) | Cited 40 times

Online Publication Date: 23 March 2004

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Many optoelectronic devices could achieve much higher efficiencies if the excess energy of electrons excited well above the conduction band minimum could be used to promote other valence electrons across the gap rather than being lost to phonons. It would then be possible to obtain two electron–hole pairs from one. In bulk materials, this process is inherently inefficient due to the constraint of simultaneous energy and momentum conservation. We calculated the rate of these processes, and of selected competing ones, in CdSe colloidal dots, using our semi-empirical nonlocal pseudopotential approach. We find much higher carrier multiplication rates than in conventional bulk materials for electron excess energies just above the energy gap Eg. We also find that in a neutral dot, the only effective competing mechanism is Auger cooling, whose decay rates can be comparable to those calculated for the carrier multiplication process. © 2004 American Institute of Physics.
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73.21.La Quantum dots
73.63.Kv Quantum dots

Double-wall carbon nanotube field-effect transistors: Ambipolar transport characteristics

Takashi Shimada, Toshiki Sugai, Yutaka Ohno, Shigeru Kishimoto, Takashi Mizutani, Hiromichi Yoshida, Toshiya Okazaki, and Hisanori Shinohara

Appl. Phys. Lett. 84, 2412 (2004); http://dx.doi.org/10.1063/1.1689404 (3 pages) | Cited 48 times

Online Publication Date: 23 March 2004

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Double-wall carbon nanotubes (DWNTs) have been used as channels of field-effect transistors (FETs) to obtain information on their transport characteristics. DWNTs-FETs show metallic or semiconducting behavior depending on the tube diameters. All the semiconducting DWNTs have exhibited both p- and n-type characteristics, the so-called ambipolar behavior which is absent in normal SWNTs-FETs. Comparisons between the subthreshold swing (S) factor of DWNTs and that of SWNTs indicate that DWNTs are better FET channels than SWNTs. © 2004 American Institute of Physics.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices

Photonic bandgaps in patterned waveguides of silicon-rich silicon dioxide

R. T. Neal, M. E. Zoorob, M. D. Charlton, G. J. Parker, C. E. Finlayson, and J. J. Baumberg

Appl. Phys. Lett. 84, 2415 (2004); http://dx.doi.org/10.1063/1.1690106 (3 pages) | Cited 7 times

Online Publication Date: 23 March 2004

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We describe waveguides of photoluminescent silicon-rich silicon dioxide, which have been patterned by triangular two-dimensional (2D) photonic crystals to give higher-order photonic bandgaps occurring within the luminescence band of the core material. Photonic crystal modification of the photoluminescence spectrum allows identification of angle-tuned photonic bandgaps, in close agreement with 2D plane wave expansion and finite-difference time domain simulations. We discuss the importance of these findings for the development of integrated optical circuitry based on silicon-compatible microelectronics. © 2004 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Local switching properties of dense nanocrystalline BaTiO3 ceramics

Liliana Mitoseriu, Catalin Harnagea, Paolo Nanni, Andrea Testino, Maria Teresa Buscaglia, Vincenzo Buscaglia, Massimo Viviani, Zhe Zhao, and Mats Nygren

Appl. Phys. Lett. 84, 2418 (2004); http://dx.doi.org/10.1063/1.1695201 (3 pages) | Cited 25 times

Online Publication Date: 23 March 2004

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The switching properties of dense BaTiO3 ceramics with 50 nm average grain size were investigated at local scale by piezoresponse force microscopy. Large areas with low piezoelectrical activity beside islands with strong piezoresponse were found. The application of electric fields induces stable domain structures and changes in the polarization state far away from the probing area, probably via trans-granular dipole interactions. Piezoelectric hysteresis loops were recorded on various positions, even in regions with initial zero piezoresponse, which possibly showed a superparaelectric behavior. The results are incontestable proof that 50 nm BaTiO3 ceramics retain ferroelectricity at a local scale. © 2004 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)

Formation of embedded Co nanoparticles by reaction in Al/Co multilayers and impact on phase sequence

P. Gas, C. Bergman, J. L. Lábár, P. B. Barna, and F. M. d’Heurle

Appl. Phys. Lett. 84, 2421 (2004); http://dx.doi.org/10.1063/1.1690466 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2004

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The analysis of solid-state reaction in Al/Co multilayers shows that, after the first reaction step which is the formation of Al9Co2, the remaining Co “layer” can either be continuous or formed of Co nanoparticles. Simultaneously with this formation of Co nanoparticles we observe a bifurcation in the phase sequence, the second reaction product is different and its formation takes place at different temperatures. Thermodynamic considerations, namely modification of free energy by curvature and stress are used to explain that the change in the phase sequence is a result of the nanostructuration of the Co layer. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
82.40.Bj Oscillations, chaos, and bifurcations
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
66.30.Ny Chemical interdiffusion; diffusion barriers
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Preparation of organic bulk heterojunction photovoltaic cells by evaporative spray deposition from ultradilute solution

Takamasa Ishikawa, Makiko Nakamura, Katsuhiko Fujita, and Tetsuo Tsutsui

Appl. Phys. Lett. 84, 2424 (2004); http://dx.doi.org/10.1063/1.1690493 (3 pages) | Cited 19 times

Online Publication Date: 23 March 2004

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An organic bulk heterojunction photovoltaic cell (OPC) having a thin layer consisting of a functionalized fullerene and a poly-p-phenylenevinylene (PPV) derivative was prepared from a highly diluted tetrahydrofuran solution at the concentration below 1 ppm by the evaporative spray deposition from ultradilute solution (ESDUS) technique. The power conversion efficiency of the OPC prepared from 1:1 mixture solution of fullerene/PPV derivative at the concentration of 1 ppm was 0.69%, which was almost comparable to that prepared by the conventional spin coating technique from 0.5 wt % chlorobenzene solution of the mixture. Although the bulk heterojunction OPCs are known to show relatively high power conversion efficiency, they have two major problems for development of higher device performance. One is a solubility problem of used materials and the other is a strong dependence of the device performance on the preparation solvent. The former has been a stumbling block to improve the performance by examining various combinations of organic materials. The latter has compelled to use relatively toxic solvents such as a chlorobenzene to prepare the devices. Those problems could be solved by the ESDUS technique to fabricate an organic film of almost insoluble materials. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Rs Spray coating techniques
85.60.Bt Optoelectronic device characterization, design, and modeling

Experimental analysis and theoretical model for anomalously high ideality factors in ZnO/diamond p-n junction diode

Cheng-Xin Wang, Guo-Wei Yang, Hong-Wu Liu, Yong-Hao Han, Ji-Feng Luo, Chun-Xiao Gao, and Guang-Tian Zou

Appl. Phys. Lett. 84, 2427 (2004); http://dx.doi.org/10.1063/1.1689397 (3 pages) | Cited 22 times

Online Publication Date: 23 March 2004

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High-quality heterojunctions between p-type diamond single-crystalline films and highly oriented n-type ZnO films were fabricated by depositing the p-type diamond single-crystal films on the Io-type diamond single crystal using a hot filament chemical vapor deposition, and later growing a highly oriented n-type ZnO film on the p-type diamond single-crystal film by magnetron sputtering. Interestingly, anomalously high ideality factors (n≫2.0) in the prepared ZnO/diamond p–n junction diode in the interim bias voltage range were measured. For this, detailed electronic characterizations of the fabricated p–n junction were conducted, and a theoretical model was proposed to clarify the much higher ideality factors of the special heterojunction diode. © 2004 American Institute of Physics.
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85.30.Kk Junction diodes
81.15.Cd Deposition by sputtering
85.30.De Semiconductor-device characterization, design, and modeling

Boron nitride nanotubes: Pronounced resistance to oxidation

Ying Chen, Jin Zou, Stewart J. Campbell, and Gerard Le Caer

Appl. Phys. Lett. 84, 2430 (2004); http://dx.doi.org/10.1063/1.1667278 (3 pages) | Cited 138 times

Online Publication Date: 23 March 2004

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Boron nitride (BN) nanotubes have the same nanostructure as carbon nanotubes but are found to exhibit significant resistance to oxidation at high temperatures. Our systematic study has revealed that BN nanotubes are stable at 700 °C in air and that some thin nanotubes (diameter less than 20 nm) with perfect multiwalled cylindrical structure can survive up to 900 °C. Thermogravimetric analysis reveals an onset temperature for oxidation of BN nanotubes of 800 °C compared with only 400 °C for carbon nanotubes under the same conditions. This more pronounced resistance of BN nanotubes to oxidation is inherited from the hexagonal BN and also depends on the nanocrystalline structure. This high level of resistance to oxidation allows promising BN nanotube applications at high temperatures. © 2004 American Institute of Physics.
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81.65.Kn Corrosion protection
61.46.-w Structure of nanoscale materials
81.07.De Nanotubes

Modeling of an equivalent circuit for dye-sensitized solar cells

Liyuan Han, Naoki Koide, Yasuo Chiba, and Takehito Mitate

Appl. Phys. Lett. 84, 2433 (2004); http://dx.doi.org/10.1063/1.1690495 (3 pages) | Cited 181 times

Online Publication Date: 23 March 2004

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Internal resistance in a dye-sensitized solar cell (DSC) was investigated using electrochemical impedance spectroscopy measurements. Four resistance elements were observed in the impedance spectra, and their dependencies on the applied bias voltage were characterized. It is found that the resistance element related to charge transport at the TiO2/dye/electrolyte interface displays behavior like that of a diode, and the series resistance elements largely correspond to the sum of the other resistance elements. An equivalent circuit for DSCs is proposed based on these results. © 2004 American Institute of Physics.
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84.60.Jt Photoelectric conversion
82.80.Fk Electrochemical methods
82.45.Gj Electrolytes

Application of the compatibility factor to the design of segmented and cascaded thermoelectric generators

G. Jeffrey Snyder

Appl. Phys. Lett. 84, 2436 (2004); http://dx.doi.org/10.1063/1.1689396 (3 pages) | Cited 35 times

Online Publication Date: 23 March 2004

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Using thermoelectric compatibility, efficient thermoelectric generators are rationally designed. With examples, compatible and incompatible systems are explained and materials proposed for targeted development. The compatibility factor explains why segmentation of (AgSbTe2)0.15(GeTe)0.85 (TAGS) with SnTe or PbTe produces little extra power, while filled skutterudite increases the efficiency from 10.5% to 13.6%. High efficiency generators are designed with compatible n-type La2Te3, and similar p-type material, while incompatible SiGe alloys actually reduce the efficiency. A refractory metal with high p-type thermopower (>100 μV/K) is required for development. Cascaded generators avoid the compatibility problem. The thermoelectric potential provides a simple derivation of the cascading ratio. © 2004 American Institute of Physics.
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84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion
72.15.Jf Thermoelectric and thermomagnetic effects
72.20.Pa Thermoelectric and thermomagnetic effects

Accelerated photopolymerization and increased mobility in C60 field-effect transistors studied by ultraviolet photoelectron spectroscopy

T. Shimada, T. Suetsugu, T. Miyadera, Y. Yamamoto, A. Koma, K. Saiki, and K. Kudo

Appl. Phys. Lett. 84, 2439 (2004); http://dx.doi.org/10.1063/1.1691487 (3 pages) | Cited 5 times

Online Publication Date: 23 March 2004

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Ultraviolet photoelectron spectroscopy (UPS) of C60 thin-film field-effect transistors was measured with biasing gate voltages. A time-dependent change in the electronic structure of the C60 film was observed during the UPS measurement, which has never been observed in a C60 film grown on a conductive substrate. The change was attributed to the accelerated polymerization of C60 by comparing the UPS with that of the photopolymerized C60. The polymerization was associated with the increase in the field-effect electron mobility. This result indicates that mobile carriers produce reactive radicals in organic semiconductors. © 2004 American Institute of Physics.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
79.60.Fr Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
82.35.Cd Conducting polymers

Dielectric/metal sidewall diffusion barrier for Cu/porous ultralow-k interconnect technology

Zhe Chen, K. Prasad, C. Y. Li, P. W. Lu, S. S. Su, L. J. Tang, D. Gui, S. Balakumar, R. Shu, and Rakesh Kumar

Appl. Phys. Lett. 84, 2442 (2004); http://dx.doi.org/10.1063/1.1695205 (3 pages) | Cited 8 times

Online Publication Date: 23 March 2004

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With the acknowledged insufficiency of traditional Ta or TaN barriers, deposited by physical vapor deposition (PVD), in the Cu/porous ultralow-k intermetal dielectric integration, an amorphous hydrogenated SiC (a-SiC:H)/Ta bilayer sidewall diffusion barrier has been fabricated using 0.13 μm Cu/porous ultralow-k [Porous-SiLK (Proprietary product from Dow Chemical Corporation, USA), k ∼ 2.2] single damascene process. The electrical tests show that the line-to-line leakage current and the electrical breakdown field (EBD) of samples with this a-SiC:H/Ta dielectric/metal bilayer structure are significantly improved compared to the conventional PVD multi-stacked Ta(N) sidewall barrier. This improvement is mostly due to surface roughness modification after the deposition of a-SiC:H film, which, in addition to being a good barrier to Cu diffusion, can effectively “seal” the weak points on the surface of porous low-k material that are responsible for the sidewall barrier failure. © 2004 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)
66.30.J- Diffusion of impurities
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Band-stop magnetostatic waves micromachined resonators

Romolo Marcelli, George Sajin, Alina Cismaru, and Florea Craciunoiu

Appl. Phys. Lett. 84, 2445 (2004); http://dx.doi.org/10.1063/1.1690866 (3 pages) | Cited 2 times

Online Publication Date: 23 March 2004

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Show Abstract
Band-stop magnetostatic wave (MSW) resonators based on microstrip transducers realized on low-resistivity silicon (LRS) wafers and on micromachined silicon membranes have been studied. Frequency tunable MSW straight edge resonators made of yttrium–iron–garnet film have been used as selective frequency components. The frequency tunability ranged between 5 and 7.5 GHz for bulk devices and between 3.5 and 9.5 GHz for the membrane supported ones, with better rejection and wider bandwidth with respect to the bulk configuration. From measurements of the transmission parameter suppression of more than 20 dB of high-order modes and a rejection ratio better than 20 dB for the membrane supported resonators have been obtained. As a result, the possibility to manufacture microwave resonators characterized by high rejection ratios on low-cost, LRS membranes is demonstrated. © 2004 American Institute of Physics.
Show PACS
84.40.Az Waveguides, transmission lines, striplines
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
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