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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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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 21 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 23 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 142 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 190 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 36 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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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.
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84.40.Az Waveguides, transmission lines, striplines
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
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