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19 Sep 2005

Volume 87, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 87, 123111 (2005); http://dx.doi.org/10.1063/1.2053370 (3 pages)

Xianghui Zhang, Ye Zhang, Jun Xu, Zhe Wang, Xihong Chen, Dapeng Yu, Peng Zhang, Hanhong Qi, and Yongjun Tian
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High performance reflection gratings in nematiclike photorefractive polymers

O-Pil Kwon, Seong-Ji Kwon, Mojca Jazbinsek, Peter Günter, and Suck-Hyun Lee

Appl. Phys. Lett. 87, 121910 (2005); http://dx.doi.org/10.1063/1.2053363 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2005

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Photorefractive materials based on the nematiclike photoconductive polymers PPT-TPA consisting of the rigid backbone poly(p-phenyleneterephthalate), PPT, and pendent photoconducting triphenylamine (TPA) groups were studied in reflection grating geometry and compared to the layered photorefractive composites PPT-CZs with photoconducting carbazole (CZ) groups. The order level of the mesophase structure has a crucial influence on the trapping characteristics of the composites. The nematiclike composites although of lower photoconductivity exhibit one order of magnitude faster response than in the layered composites in the reflection grating regime. This is attributed to the increased trapping rate as a result of the specific mesophase structure.
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42.70.Jk Polymers and organics
42.70.Gi Light-sensitive materials
42.79.Dj Gratings
72.40.+w Photoconduction and photovoltaic effects

Strengthening TiN diffusion barriers for Cu metallization by lightly doping Al

L. C. Yang, C. S. Hsu, G. S. Chen, C. C. Fu, J. M. Zuo, and B. Q. Lee

Appl. Phys. Lett. 87, 121911 (2005); http://dx.doi.org/10.1063/1.2056583 (3 pages) | Cited 9 times

Online Publication Date: 14 September 2005

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Thin films of Ti1−xAlxN were deposited on (100) Si by ultrahigh-vacuum dual-target reactive sputtering, and the impact of lightly doping Al of x as small as 0.09 on altering the films’s microstructure upon thermal annealing, and hence the performance of the films (40 nm thick) as diffusion barriers for Cu metallization was evaluated. The results of transmission electron microscopy, Rutherford backscattering spectroscopy, and grazing-incidence x-ray diffraction show that the TiN barrier layer gives the commonly observed voided, columnar grains composed of 5 nm sized subgrains. Upon annealing, the subgrains tend to coalesce into 20 nm sized equiaxed grains full of crystalline defects, initiating an inward penetration of Cu and a partial dissociation of TiN, transforming themselves, respectively, into pyramidal (or columnar) Cu3Si precipitates and a dendritic Ti5Si3 layer just after 550 °C, 10 min annealing. However, the lightly doped Al not only overrides the tendency to form intercolumnar voids inherent in sputter deposition by self-shadowing and statistical roughening, but also substantially enhances the microstructural and thermochemical stability, hence significantly improving barrier property, as evidenced from an annealing test at an elevated temperature (600 °C) for a prolonged period of 30 min.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
66.30.-h Diffusion in solids
61.72.up Other materials
81.15.Cd Deposition by sputtering
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
81.40.Gh Other heat and thermomechanical treatments
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Intermixing and phase separation at the atomic scale in Co-rich (Co,Fe) and Cu multilayered nanostructures

Peter F. Ladwig, Jesse D. Olson, Joseph H. Bunton, David J. Larson, Robert M. Ulfig, Richard L. Martens, Tye T. Gribb, Thomas F. Kelly, Martin C. Bonsager, Allan E. Schultz, Bharat B. Pant, and Y. Austin Chang

Appl. Phys. Lett. 87, 121912 (2005); http://dx.doi.org/10.1063/1.2032593 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2005

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Despite the fact that Co-rich (Co,Fe) alloys and Cu are immiscible materials in bulk form, evidence of thermally induced mixing at the atomic scale has been observed in thin-film multilayers of (Co,Fe) and Cu. However, long term anneals at lower temperatures produced a breakup of the multilayers into a two-phase mixture of (Co,Fe) and Cu particles. The observations were made with the use of the three-dimensional atom probe technique, with supporting evidence from differential scanning calorimetry and x-ray diffraction. Besides their scientific importance, these results are of interest where these (Co,Fe) and Cu thin films are used to produce the giant magnetoresistive effect.
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68.35.Fx Diffusion; interface formation
64.75.-g Phase equilibria
66.30.Ny Chemical interdiffusion; diffusion barriers
81.40.Gh Other heat and thermomechanical treatments
75.50.Tt Fine-particle systems; nanocrystalline materials
75.47.De Giant magnetoresistance

“Bridge Model” of nanoparticles deposited on pores area of the substrate during a membrane fabrication

Zhongliang Shi, Shanqiang Wu, and Jerzy A. Szpunar

Appl. Phys. Lett. 87, 121913 (2005); http://dx.doi.org/10.1063/1.2056587 (3 pages)

Online Publication Date: 15 September 2005

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The initial observations of a palladium membrane deposited by an electroless process and an aluminium membrane deposited by a sputtering process on the porous stainless steel substrates illustrate that the membranes are made of their nanoparticles and the pore areas at the surface of the substrate are covered by palladium or aluminium nanoparticles, which are like building bridges there. A “Bridge Model” is presented to illustrate the deposition progress of the fabrication of a membrane on the porous substrate. Scanning electron microscope micrographs from the cross section of the the palladium membrane deposited on the substrate confirm the presence of this bridge. The result will be beneficial for the design and fabrication of various nanomembranes and micromembranes on the porous substrates as well the effective control of them by the deposition processes.
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81.07.Bc Nanocrystalline materials
81.15.Pq Electrodeposition, electroplating
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology

Lateral phase separation in AlGaN grown on GaN with a high-temperature AlN interlayer

Q. Sun, Y. Huang, H. Wang, J. Chen, R. Q. Jin, S. M. Zhang, H. Yang, D. S. Jiang, U. Jahn, and K. H. Ploog

Appl. Phys. Lett. 87, 121914 (2005); http://dx.doi.org/10.1063/1.2056588 (3 pages) | Cited 10 times

Online Publication Date: 15 September 2005

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The influences of a high-temperature (HT) AlN interlayer (IL) on the phase separation in crack-free AlGaN grown on GaN have been studied. The depth-dependent cathodoluminescence (CL) spectra indicate a relatively uniform Al distribution in the growth direction, but the monochromatic CL images and the CL spectra obtained by line scan measurements reveal a lateral phase separation in AlGaN grown on relatively thick HT-AlN ILs. Moreover, when increasing the thickness of HT-AlN IL, the domain-like distribution of the AlN mole fraction in AlGaN layers is significantly enhanced through a great reduction of the domain size. The morphology of mesa-like small islands separated by V trenches in the HT-AlN IL, and the grain template formed by the coalescence of these islands during the subsequent AlGaN lateral overgrowth, are attributed to be responsible for the formation of domain-like structures in the AlGaN layer.
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81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Integration of carbon nanotubes into diluted magnetic semiconductor

Yun-Hi Lee, J. M. Yoo, J. Ah Lee, S. Y. Ahn, J. Joo, S. Lee, D. H. Kim, B. K. Ju, and K. J. Song

Appl. Phys. Lett. 87, 121915 (2005); http://dx.doi.org/10.1063/1.2045557 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2005

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Carbon nanotubes (CNTs) were grown using catalytic pyrolysis of acetylene on a thin-film-diluted magnetic semiconductor (Co-8 at. % doped TiO2) without consuming the host layer of semiconductor TiO2. Effects of the thickness of the diluted magnetic semiconductor layer and the stacking structure on the growth of the carbon nanotubes were examined. The external diameter and crystalline structure of the nanotubes showed correlation with the structure of the magnetic catalyst Co within the nanotubes or at the end of the tube. After the growth of CNTs, the TiO2 layer still maintained its semiconducting properties in view of the temperature dependent resistance behavior. Moreover, we studied the influence of the electrical resistivity, i.e, the thickness as a process parameter, of the diluted magnetic semiconductor underlayer, which determines the growth height and the crystalline quality of the carbon nanotubes, on the nanotubes’ growth behavior. Finally, we measured the magnetic behavior of the heterosystem and interpreted the results due to the action of the properties of the catalytic diluted magnetic semiconductor underlayer. Our result shows a promising recipe for the fabrication of one-dimensional CNT—two-dimensional magnetic-metal-doped magnetic semiconductor and/or wide-band-gap insulator.
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81.07.De Nanotubes
75.50.Pp Magnetic semiconductors
61.46.-w Structure of nanoscale materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
75.70.Ak Magnetic properties of monolayers and thin films
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Surface stability and evolution of biaxially strained epitaxial thin films

Y. W. Zhang

Appl. Phys. Lett. 87, 121916 (2005); http://dx.doi.org/10.1063/1.2053367 (3 pages) | Cited 4 times

Online Publication Date: 16 September 2005

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First-order perturbation analysis has been performed to investigate the stability and the fastest growth mode of a biaxially strained epitaxial thin film surface by stress-induced surface diffusion. It is found that the normalized critical wavelength along one principal direction depends on the Poisson’s ratio of the film, and also the perturbed wavelength and stress level along the other principal direction. The fastest growth analysis shows that when the absolute value of the ratio of the two principal stresses deviates from unity, a gradual transition from nanoisland formation to nanowire formation occurs. The larger the deviation, the stronger the tendency for the formation of a nanowire; finite element simulations confirm the tendency.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.35.Fx Diffusion; interface formation
68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Atomic-scale manipulation of potential barriers at SrTiO3 grain boundaries

Pradyumna Prabhumirashi, Vinayak P. Dravid, Andrew R. Lupini, Matthew F. Chisholm, and Stephen J. Pennycook

Appl. Phys. Lett. 87, 121917 (2005); http://dx.doi.org/10.1063/1.2046734 (3 pages) | Cited 8 times

Online Publication Date: 16 September 2005

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In oxide grain boundaries (GBs), oxygen ions and their vacancies serve as a common denominator in controlling properties such as GB barrier height and capacitance. Therefore, it is critical to analyze, control and manipulate oxygen and vacancies at oxide interfaces as most of the practical devices are almost always influenced by the presence of electrostatic potential barriers at interfaces. Here, we report adjustment of a single GB potential barrier via manipulation of oxygen vacancy concentration using simple oxidation and reduction treatments. We validate our analysis with aberration-corrected HAADF imaging and column-by-column EELS coupled with macroscopic transport measurements of isolated GBs to gain important insight into the physical attributes of GB potential barriers.
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61.72.Mm Grain and twin boundaries
79.20.Uv Electron energy loss spectroscopy
81.65.Mq Oxidation
68.37.Lp Transmission electron microscopy (TEM)
61.72.J- Point defects and defect clusters

Impact of metal silicide precipitate dissolution during rapid thermal processing of multicrystalline silicon solar cells

T. Buonassisi, A. A. Istratov, S. Peters, C. Ballif, J. Isenberg, S. Riepe, W. Warta, R. Schindler, G. Willeke, Z. Cai, B. Lai, and E. R. Weber

Appl. Phys. Lett. 87, 121918 (2005); http://dx.doi.org/10.1063/1.2048819 (3 pages) | Cited 20 times

Online Publication Date: 16 September 2005

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Synchrotron-based analytical x-ray microprobe techniques were employed to study the dissolution of iron, copper, and nickel silicide precipitates at structural defects in cast multicrystalline silicon in response to rapid thermal processing (RTP). A direct correlation was observed between iron silicide precipitate dissolution, increased minority carrier recombination, and decreased device performance after high-temperature (1000 °C) RTP. In contrast, iron precipitates comparable in size to as-grown material remained after lower-temperature RTP (860 °C); in this case the material exhibited higher minority carrier diffusion length and better solar cell performance. RTP at both temperatures effectively dissolved nickel and copper silicide precipitates. It is concluded that iron dissolved from structural defect reservoirs detrimentally affects the cell performance, likely by forming distributed point defects and smaller precipitates. For cast multicrystalline silicon, higher performance can be expected by inhibiting the dissolution of these precipitates, i.e., by reducing the time and/or temperature of processing steps.
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84.60.Jt Photoelectric conversion
64.75.-g Phase equilibria
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
66.30.-h Diffusion in solids
61.72.J- Point defects and defect clusters
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Bistable resistance switching of poly(N-vinylcarbazole) films for nonvolatile memory applications

Yi-Sheng Lai, Chia-Hsun Tu, Dim-Lee Kwong, and J. S. Chen

Appl. Phys. Lett. 87, 122101 (2005); http://dx.doi.org/10.1063/1.2051801 (3 pages) | Cited 76 times

Online Publication Date: 12 September 2005

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Poly(N-vinylcarbazole) (PVK) has been fabricated by spin-coating to show the bistable resistance switching characteristics. Various resistance states can be made by controlling the on-state current through the PVK films. The resistance of the on-state PVK films also affects the turn-off current, which needs to erase the on state. The filament theory is used to elucidate the observed phenomenon. We demonstrate that the PVK films exhibit good retention and stable “read-write-read-erase” cyclic switching characteristics. The PVK films also show a good switching behavior with on-off ratio of 104, which will be a potential material for nonvolatile memory application.
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73.61.Ph Polymers; organic compounds
68.55.A- Nucleation and growth
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Oxygen vacancies in ZnO

Anderson Janotti and Chris G. Van de Walle

Appl. Phys. Lett. 87, 122102 (2005); http://dx.doi.org/10.1063/1.2053360 (3 pages) | Cited 200 times

Online Publication Date: 14 September 2005

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The electronic properties of ZnO have traditionally been explained by invoking intrinsic defects. In particular, the frequently observed unintentional n-type conductivity has often been attributed to oxygen vacancies. We report first-principles calculations showing that the oxygen vacancy VO is not a shallow donor, but has a deep ε(2+/0) level at ∼ 1.0 eV below the conduction band. The negative-U behavior that causes the 1+charge state to be unstable is associated with large local lattice relaxations. We present a detailed configuration coordinate diagram, which allows us to provide a detailed interpretation of recently reported ODEPR (optically detected electron paramagnetic resonance) measurements [ L. S. Vlasenko and G. D. Watkins, Phys. Rev. B 71, 125210 (2005) ].
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61.72.J- Point defects and defect clusters
71.55.Gs II-VI semiconductors
71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
76.30.-v Electron paramagnetic resonance and relaxation

Growth of nominally undoped p-type ZnO on Si by pulsed-laser deposition

Min-Suk Oh, Sang-Ho Kim, and Tae-Yeon Seong

Appl. Phys. Lett. 87, 122103 (2005); http://dx.doi.org/10.1063/1.2056576 (3 pages) | Cited 21 times

Online Publication Date: 14 September 2005

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We report on the growth of nominally undoped p-type ZnO films on Si(111) substrates by pulsed-laser deposition. Hall effect measurements show that the undoped ZnO films change from n-type to p-type material when the oxygen pressure changes from 6×10−5 to 3×10−4 Torr during growth. Ti/Au contacts produce ohmic behavior to n-type ZnO ( ∼ 1017 cm−3), but leaky Schottky behavior to p-type ZnO ( ∼ 1018 cm−3). Electrical and photoluminescence results indicate that native defects, such as oxygen and zinc vacancies, could play an important role in determining the conductivity of these nominally undoped ZnO films.
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81.05.Dz II-VI semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ga II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.J- Point defects and defect clusters
73.40.Ns Metal-nonmetal contacts
68.55.-a Thin film structure and morphology

Field and temperature dependence of the photocurrent in polymer/fullerene bulk heterojunction solar cells

H. H. P. Gommans, M. Kemerink, J. M. Kramer, and R. A. J. Janssen

Appl. Phys. Lett. 87, 122104 (2005); http://dx.doi.org/10.1063/1.2056609 (3 pages) | Cited 19 times

Online Publication Date: 14 September 2005

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The photocurrent in polymer/fullerene blends is characterized as a function of bias at temperatures ranging from 125 to 300 K. Assuming a constant generation rate and bimolecular recombination, the results are numerically modeled within the drift-diffusion approximation. Bimolecular recombination is found to be a dominant factor in the field dependence of the photocurrent in the entire measured voltage range. Inclusion of field dependent geminate pair dissociation and recombination via the Onsager expressions gives a much stronger field dependence than experimentally observed. From the temperature dependence of the extracted mobilities, we can simultaneously estimate the broadening of the transporting highest occupied and lowest unoccupied molecular orbital levels.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds

Yellow and green bands in GaN by resolved spectral photoconductivity

A. Castaldini, A. Cavallini, and L. Polenta

Appl. Phys. Lett. 87, 122105 (2005); http://dx.doi.org/10.1063/1.2045547 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2005

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Defect-related bands and their properties are widely investigated in gallium nitride, especially by luminescence techniques, which evidenced a broad yellow band, and seldom, a green band. We present here a study of the visible portion of the photoconductivity spectra obtained in samples of different thicknesses and doping. The superior resolution of photoconductivity with respect to luminescence techniques allows for clearly distinguishing green and yellow bands, both showing a double peak structure. Moreover, while the yellow band shape results were unchanged with sample properties, the green band is sensitive to the growth conditions. Hence some hypotheses about their microscopic origin can be proposed.
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81.05.Ea III-V semiconductors
78.40.Fy Semiconductors
72.40.+w Photoconduction and photovoltaic effects
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
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Exchange spring structures and coercivity reduction in FePt/FeRh bilayers: A comparison of multiscale and micromagnetic calculations

F. Garcia-Sanchez, O. Chubykalo-Fesenko, O. Mryasov, R. W. Chantrell, and K. Yu. Guslienko

Appl. Phys. Lett. 87, 122501 (2005); http://dx.doi.org/10.1063/1.2051789 (3 pages) | Cited 16 times

Online Publication Date: 12 September 2005

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Calculations of magnetization reversal mechanism and coercivity reduction in exchange coupled FePt/FeRh bilayers are presented. It is shown by comparison with atomistic model calculations that the use of a standard micromagnetic model leads to an underestimation of the exchange energy at the interface, leading to a reduced coercivity decrease for small interfacial exchange energy constant. This is due to the failure of the domain wall (DW) to penetrate the hard FePt phase in the micromagnetic calculations. A multiscale model is proposed based an atomic level simulation in the interface region coupled with a micromagnetic approach elsewhere. This leads to improved calculations of DW structures at the interface, allowing a detailed study of the magnetization reversal mechanism. The new approach predicts a saturation in the coercivity reduction as a function of interface exchange energy at 4% of the bulk value, which is associated with complete continuity of the DW across the interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Enhanced flux pinning in YBa2Cu3O7−δ films by nanoscaled substrate surface roughness

Zu-Xin Ye, Qiang Li, Y. Hu, W. D. Si, P. D. Johnson, and Y. Zhu

Appl. Phys. Lett. 87, 122502 (2005); http://dx.doi.org/10.1063/1.2051794 (3 pages) | Cited 6 times

Online Publication Date: 12 September 2005

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Nanoscaled substrate surface roughness is shown to strongly influence the critical current density (Jc) in YBa2Cu3O7−δ (YBCO) films made by pulsed-laser deposition on the crystalline LaAlO3 substrates consisting of two separate twin-free and twin-rich regions. The nanoscaled corrugated substrate surface was created in the twin-rich region during the deposition process. Using magneto-optical imaging techniques coupled with optical and atomic force microscopy, we observed an enhanced flux pinning in the YBCO films in the twin-rich region, resulting in a ∼ 30% increase in Jc, which was unambiguously confirmed by the direct transport measurement.
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74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents

Bias-controlled hole degeneracy and implications for quantifying spin polarization

G. Kioseoglou, A. T. Hanbicki, B. T. Jonker, and A. Petrou

Appl. Phys. Lett. 87, 122503 (2005); http://dx.doi.org/10.1063/1.2051790 (3 pages) | Cited 4 times

Online Publication Date: 13 September 2005

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We report on a spin injection study from an Fe Schottky tunnel contact into n‐AlGaAs/GaAs/p‐AlGaAs light-emitting diodes with a bulk-like GaAs recombination region. The spectral composition and circular polarization of the electroluminescence allowed us to monitor changes in the band structure induced by the applied bias voltage. At low bias conditions, the holes are confined at the GaAs/p‐AlGaAs interface and have two-dimensional (2D) character with nondegenerate heavy- and light-hole subbands. Increasing the bias voltage moves the structure towards a flatband condition, making the holes three-dimensional (3D)-like. The results are discussed in terms of the quantum selection rules describing radiative recombination in 2D and 3D systems.
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72.25.Dc Spin polarized transport in semiconductors
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
78.60.Fi Electroluminescence

[Bi3Fe5O12/Gd3Ga5O12]m magneto-optical photonic crystals

S. I. Khartsev and A. M. Grishin

Appl. Phys. Lett. 87, 122504 (2005); http://dx.doi.org/10.1063/1.2053359 (3 pages) | Cited 26 times

Online Publication Date: 16 September 2005

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A series of one-dimensional heteroepitaxial all-garnet magneto-optical photonic crystals has been synthesized and optically characterized. They are composed of alternating magneto-optically active Bi3Fe5O12 (BIG) and Gd3Ga5O12 (GGG) quarter-wave length layers pulsed laser deposited on to the GGG(001) substrate. Photonic crystals, as designed, exhibit stop band structure and the band gap with the transmittance central peak caused by the light localization in the half-wave length BIG cavity. Compared to previously reported [Bi3Fe5O12/Y3Fe5O12]m photonic crystal [ Appl. Phys. Lett. 84, 1438 (2004) ], the replacement of optically dense Y3Fe5O12 garnet by transparent Gd3Ga5O12 enables significant enhancement of light rejection within the stop band. Photonic crystals spectra experience “blue” shift in oblique incidence geometry thus demonstrating feasibility to use this effect for tunable magneto-optical filters.
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42.70.Qs Photonic bandgap materials
75.50.Gg Ferrimagnetics
78.20.Ls Magneto-optical effects
78.40.Ha Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Charge trapping and detrapping characteristics in hafnium silicate gate dielectric using an inversion pulse measurement technique

Rino Choi, S. C. Song, C. D. Young, Gennadi Bersuker, and Byoung Hun Lee

Appl. Phys. Lett. 87, 122901 (2005); http://dx.doi.org/10.1063/1.2043252 (3 pages) | Cited 14 times

Online Publication Date: 16 September 2005

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Threshold voltage (VTH) instability in metal oxide semiconductor field transistors (MOSFETs) with high dielectric constant (k) gate dielectrics has been investigated with an inversion pulse measurement technique, which can detect fast dielectric charging/discharging within microseconds (μs). The results indicate that VTH instability can be significantly underestimated by conventional VTH measurement techniques. Based on temperature-dependent stress data, it is suggested that charging and discharging are determined by direct tunneling and thermally assisted processes, respectively.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
85.30.Tv Field effect devices
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Effects of radial breathing mode phonons on charge transport in semiconducting zigzag carbon nanotubes

A. Verma, M. Z. Kauser, and P. P. Ruden

Appl. Phys. Lett. 87, 123101 (2005); http://dx.doi.org/10.1063/1.2043244 (3 pages) | Cited 11 times

Online Publication Date: 12 September 2005

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We report ensemble Monte Carlo transport simulation results for single-wall semiconducting zigzag carbon nanotubes. The effects of electron scattering by radial breathing mode phonons are investigated. The basis for the Monte Carlo simulations is provided by electronic structure calculations in the framework of the tight-binding model. Scattering mechanisms considered are due to electron-phonon interactions involving longitudinal acoustic, longitudinal optical, and radial breathing mode phonons. The steady-state velocity is lower for low and moderate electric fields when radial breathing mode phonons are taken into account. Electron scattering by radial breathing mode phonons does not appear to affect strongly the steady-state electron transport within a carbon nanotube at high electric fields. Oscillations in the transient velocity show increased damping.
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73.63.Fg Nanotubes
72.20.Fr Low-field transport and mobility; piezoresistance
63.20.K- Phonon interactions
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.61.Cw Elemental semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.22.-f Electronic structure of nanoscale materials and related systems

Chlorophyll-layer-inserted poly(3-hexyl-thiophene) solar cell having a high light-to-current conversion efficiency up to 1.48%

Je-Jung Yun, Ho-Seok Jung, Sung-Han Kim, Eun-Mi Han, Veeramuthu Vaithianathan, and Samson A. Jenekhe

Appl. Phys. Lett. 87, 123102 (2005); http://dx.doi.org/10.1063/1.2051804 (3 pages) | Cited 10 times

Online Publication Date: 12 September 2005

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We report the fabrication of a chlorophyll-layer-inserted poly(3-hexyl-thiophene) (P3HT) solar cell. A significant enhancement in the light-to-current conversion efficiency of up to 1.48% with a fill factor of 0.32 was achieved in a solar cell with a device structure of indium tin oxide anode/poly (3,4-ethylene dioxy-thiophene):poly(styrene sulfonate)/P3HT/chlorophyll/Al cathode under the standard air mass 1.5 irradiation (20 mW/cm2). These results suggest that the generation of an internal electric field is mainly due to a difference between the highest occupied molecular orbital of the P3HT (donor) and the lowest unoccupied molecular orbital of the chlorophyll (acceptor), which permits the transfer of photoinduced electrons from P3HT to chlorophyll.
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84.60.Jt Photoelectric conversion
71.55.Ht Other nonmetals

Microwave attenuation of multiwalled carbon nanotube-fused silica composites

Changshu Xiang, Yubai Pan, Xuejian Liu, Xingwei Sun, Xiaomei Shi, and Jingkun Guo

Appl. Phys. Lett. 87, 123103 (2005); http://dx.doi.org/10.1063/1.2051806 (3 pages) | Cited 39 times

Online Publication Date: 12 September 2005

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Multiwalled carbon nanotubes (MWCNTs) were used to convert radome materials to microwave absorbing materials. Dense MWCNT-fused silica composites were prepared by hot-pressing technique. The composites exhibit high complex permittivities at X-band frequencies, depending on the content of MWCNTs. The value of the loss tangent increases three orders over pure fused silica only by incorporating 2.5 vol % MWCNTs into the composites. The average magnitude of microwave transmission reaches −33 dB at 11–12 GHz in the 10 vol % MWCNT-fused silica composites, which indicates the composites have excellent microwave attenuation properties. The attenuation properties mainly originate from the electric loss of MWCNTs by the motion of conducting electrons.
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81.05.Pj Glass-based composites, vitroceramics
84.40.-x Radiowave and microwave (including millimeter wave) technology
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.80.Tm Composite materials
73.63.-b Electronic transport in nanoscale materials and structures
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

Pattern preserving deposition: Experimental results and modeling

Marcos F. Castez, Mariano H. Fonticelli, Omar Azzaroni, Roberto C. Salvarezza, and Hernán G. Solari

Appl. Phys. Lett. 87, 123104 (2005); http://dx.doi.org/10.1063/1.2053368 (3 pages) | Cited 4 times

Online Publication Date: 12 September 2005

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In this work we discuss pattern-preserving growth during metal deposition from the vapor on micro/nano-structured metal substrates. Experimental results for Cu deposition on patterned Cu substrates show pattern preserving growth or pattern destruction depending on the incident angle. We introduce a mesoscopic 1+1 dimensional model including deposition flow (directed and isotropic), surface diffusion and shadowing effects that account for the experimental growth data. Moreover, simulations on post-deposition annealing, for high aspect-ratio patterns show departures from the predictions of the linear theory for surface diffusion.
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68.55.A- Nucleation and growth
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
81.16.Rf Micro- and nanoscale pattern formation

Surface-enhanced Raman scattering sensor based on D-shaped fiber

Y. Zhang, C. Gu, A. M. Schwartzberg, and J. Z. Zhang

Appl. Phys. Lett. 87, 123105 (2005); http://dx.doi.org/10.1063/1.2051799 (3 pages) | Cited 22 times

Online Publication Date: 13 September 2005

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Fiber surface-enhanced Raman scattering (SERS) sensors show great potential for in vivo and in vitro detection. However, current probes based on end-polished fibers suffer from small signal due to their small active region. To overcome this, we propose and demonstrate a D-shaped fiber configuration to increase the detection area. Initial modeling has shown that most of the light can be absorbed by the SERS active layer coated on the polished fiber surface. A several orders of magnitude increase in surface area leads to substantially more detectable Raman scattered photons than those in end-tip configurations. The SERS sensor based on D-shaped fibers has been demonstrated with excellent results using rhodamine 6G.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.30.Jw Organic compounds, polymers
82.80.-d Chemical analysis and related physical methods of analysis

Nanoindentation study of nanofibers

E. P. S. Tan and C. T. Lim

Appl. Phys. Lett. 87, 123106 (2005); http://dx.doi.org/10.1063/1.2051802 (3 pages) | Cited 27 times

Online Publication Date: 13 September 2005

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Nanoindentation study of a single poly(L-lactic acid) nanofiber produced by the phase separation method was performed using an atomic force microscope (AFM) cantilever tip. Issues concerning the use of AFM for nanoindentation of polymer nanofibers were discussed. The Hertz theory of contact mechanics was used to analyze the indentation results. It was found that the elastic modulus was comparable to that obtained from the nanoscale three-point bend test done in our previous study, after roughness correction was made.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
62.25.-g Mechanical properties of nanoscale systems
68.35.Gy Mechanical properties; surface strains
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.46.-w Structure of nanoscale materials
64.75.-g Phase equilibria
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Mn Polymer surfaces
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