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28 Jun 2004

Volume 84, Issue 26, pp. 5299-5475

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 5398 (2004); http://dx.doi.org/10.1063/1.1767591 (3 pages)

E. Menard, K. J. Lee, D.-Y. Khang, R. G. Nuzzo, and J. A. Rogers
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Fabrication of 5 nm linewidth and 14 nm pitch features by nanoimprint lithography

Michael D. Austin, Haixiong Ge, Wei Wu, Mingtao Li, Zhaoning Yu, D. Wasserman, S. A. Lyon, and Stephen Y. Chou

Appl. Phys. Lett. 84, 5299 (2004); http://dx.doi.org/10.1063/1.1766071 (3 pages) | Cited 192 times

Online Publication Date: 17 June 2004

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We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5 nm linewidth and 14 nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15 psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5 nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4 in. wafer were demonstrated.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography
81.07.Lk Nanocontacts
73.63.Rt Nanoscale contacts
68.55.-a Thin film structure and morphology
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Nanopillar growth mode by vapor-liquid-solid epitaxy

J. L. Taraci, J. W. Dailey, T. Clement, David J. Smith, Jeff Drucker, and S. T. Picraux

Appl. Phys. Lett. 84, 5302 (2004); http://dx.doi.org/10.1063/1.1766076 (3 pages) | Cited 8 times

Online Publication Date: 17 June 2004

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We report epitaxial growth of Ge nanopillars (NPs) on Si (100) by vapor-liquid-solid (VLS) growth from digermane. This growth morphology is characterized by short, low-aspect-ratio pillars and is markedly different from the long, narrow nanowires (NWs) previously reported for VLS growth. The NP growth mode occurs at low digermane pressures. It is attributed to surface-diffusion-induced lateral growth in combination with an insufficient Ge concentration gradient in the AuGe eutectic to catalyze NW growth. High resolution electron microscopy confirms that the NPs are epitaxial with the Si (100) substrate and are fully relaxed and strain free.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
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Structural transformation induced improved luminescent properties for LaVO4:Eu nanocrystals

Chun-Jiang Jia, Ling-Dong Sun, Feng Luo, Xiao-Cheng Jiang, Liu-He Wei, and Chun-Hua Yan

Appl. Phys. Lett. 84, 5305 (2004); http://dx.doi.org/10.1063/1.1763981 (3 pages) | Cited 54 times

Online Publication Date: 17 June 2004

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To develop a good host material for red phosphors as well as a model for clarifying the underlying correlation between structure and properties, tetragonal phased LaVO4:Eu was synthesized via an ethylenediamine tetra-acetic acid (EDTA) assisted hydrothermal method. The challenging transformation from monazite to the metastable zircon structure for LaVO4:Eu resulted in a remarkable improvement of the luminescent properties. This improvement was rationally analyzed and the impact of structure on luminescent properties was explored. Based on these results, structural transformation-induced luminescent properties improvement was proposed as an efficient means to improve the performance of doped-insulators.
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78.55.Hx Other solid inorganic materials
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.10.Dn Growth from solutions
61.72.S- Impurities in crystals

Isotopically pure 13C layer as a stress sensor in a diamond anvil cell

Wei Qiu, Nenad Velisavljevic, Paul A. Baker, Yogesh K. Vohra, and Samuel T. Weir

Appl. Phys. Lett. 84, 5308 (2004); http://dx.doi.org/10.1063/1.1766077 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2004

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Isotopically pure 13C homoepitaxial diamond layer of 20±5 microns thickness was grown on top of a brilliant cut diamond anvil by a microwave plasma chemical vapor deposition process for application as a stress sensor. This isotopically pure diamond tip was then used in conjunction with a natural abundance 12C diamond anvil to generate high pressure on a soft sample containing carbon nanotubes to 100 GPa. The 13C diamond Raman signal remained a distinct single peak showing that the mean normal stress experienced by this thin layer is uniform to the highest pressure. The stress-induced shift of the 13C layer is related to the quasihydrostatic pressure in the sample chamber using a ruby pressure sensor and shows a remarkably linear behavior to extreme pressures.
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68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Hv Other nonmetallic inorganics

Identification of native defects around grain boundary in Pr-doped ZnO bicrystal using electron energy loss spectroscopy and first-principles calculations

Yukio Sato, Teruyasu Mizoguchi, Fumiyasu Oba, Masatada Yodogawa, Takahisa Yamamoto, and Yuichi Ikuhara

Appl. Phys. Lett. 84, 5311 (2004); http://dx.doi.org/10.1063/1.1766078 (3 pages) | Cited 24 times

Online Publication Date: 17 June 2004

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Native defects and Pr dopant around grain boundaries in Pr-doped and undoped ZnO bicrystals were investigated by electron energy loss spectroscopy (EELS) with a focus on the relationship with the current–voltage characteristics. The Pr-doped bicrystal exhibited a nonlinear current–voltage characteristic, whereas the undoped bicrystal shows an ohmic characteristic. In the Pr-doped bicrystal, Pr was found to be present within 8 nm around the grain boundary. EELS investigation of native defects combined with first-principles calculations indicated the presence of zinc vacancies in the vicinity of the Pr-doped grain boundary. The formation of zinc vacancies is considered to be the origin of the nonlinear current–voltage characteristic.
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61.72.Mm Grain and twin boundaries
61.72.J- Point defects and defect clusters
68.35.Dv Composition, segregation; defects and impurities
68.49.Jk Electron scattering from surfaces
72.80.Ey III-V and II-VI semiconductors
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Controlled carbon nanotube sheathing on ultrafine InP nanowires

L. W. Yin, Y. Bando, Y. C. Zhu, and M. S. Li

Appl. Phys. Lett. 84, 5314 (2004); http://dx.doi.org/10.1063/1.1766079 (3 pages) | Cited 7 times

Online Publication Date: 17 June 2004

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Controlled carbon nanotube sheathing on ultrafine InP nanowires has been realized through a simple vapor–solid process. The synthesized InP–C nanocables were composed of crystalline InP core about 13–15 nm in diameter and parallel carbon sheath layers about several nanometers in thickness. The growth of the C layers takes place via a layer-by-layer process. The carbon tube sheathing can be controlled from several to more than 10 parallel layers by adjusting the deposition time. Both the carbon tube sheath and InP nanowire core show a higher degree of crystalline perfection. Graphitic carbon could act as chemically inert protecting layers for the ultrafine InP nanowires. This method could be applied to a wide range of materials and result in various hetrostructures, which may serve as potential building blocks in various nanodevices.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
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Dielectric relaxation in 91% Pb(Zn1/3Nb2/3)O3–9% PbTiO3 single crystal at low temperature

Peng Bao, Feng Yan, Yurong Dai, Jingsong Zhu, Yening Wang, and Haosu Luo

Appl. Phys. Lett. 84, 5317 (2004); http://dx.doi.org/10.1063/1.1766081 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2004

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The temperature dependent dielectric response of 〈001〉-oriented 91% Pb(Zn1/3Nb2/3)O3–9% PbTiO3 single crystal has been studied at various frequencies. A dielectric relaxation process with a broad distribution of time constant has been observed below 180 K. The peak temperature of the dielectric loss can be fitted well with Volger–Fulcher relation. We assume this relaxation process can be attributed to the freezing of ferroelectric macrodomain walls induced by the pinning of point defects.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
61.72.J- Point defects and defect clusters
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Optical properties of Mn4+ ions in GaN:Mn codoped with Mg acceptors

B. Han, R. Y. Korotkov, B. W. Wessels, and M. P. Ulmer

Appl. Phys. Lett. 84, 5320 (2004); http://dx.doi.org/10.1063/1.1766082 (3 pages) | Cited 11 times

Online Publication Date: 17 June 2004

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The optical properties of Mn–Mg-codoped epitaxial GaN were studied. Addition of Mg acceptors quenches the weak manganese-related photoluminescence (PL) band at 1.3 eV in GaN:Mn and a series of sharp PL peaks are observed at 1 eV in codoped epilayers. The change in PL spectra indicates that the Mg addition stabilizes the Mn4+ charge state by decreasing the Fermi level. The 1 eV PL peaks are tentatively attributed to intracenter transitions involving Mn4+ ions. Spin-allowed 3d-shell 4T2–4T1 transitions and their phonon replicas are involved. The relative intensities of the sharp peaks are strongly dependent on the excitation wavelength, indicating that the optically active Mn4+ centers involved in the separate peaks are different. The temperature dependence of the PL spectrum suggests the presence of at least three distinct Mn4+ complex centers.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors

Formation of regular arrays of submicron GaAs dots on silicon

J. D. Beach, C. Veauvy, R. Caputo, R. T. Collins, A. A. Khandekar, T. F. Kuech, C. K. Inoki, T. S. Kuan, and R. E. Hollingsworth

Appl. Phys. Lett. 84, 5323 (2004); http://dx.doi.org/10.1063/1.1766391 (3 pages)

Online Publication Date: 17 June 2004

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A combination of photolithography written with a near-field scanning optical microscope, gallium electrodeposition, and arsine annealing was used to produce regular arrays of submicron GaAs dots on a silicon substrate. Electrodeposition on a patterned Si surface produced an array of roughly hemispherical Ga dots. Annealing in arsine converted the gallium to GaAs, and caused the dots to develop faceted features. Transmission electron microscope measurements showed that the GaAs dots were polycrystalline, but had only a few grains. The dots did not have a preferred orientation relative to the substrate. Metalorganic chemical vapor deposition growth occurred selectively on these dots, forming regular arrays of GaAs disks up to 20 μm in diameter. The GaAs disks exhibited characteristic GaAs low-temperature photoluminescence. This method has application for precisely positioning semiconductor dots or tailoring the grain size of polycrystalline films.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Pq Electrodeposition, electroplating
61.72.Cc Kinetics of defect formation and annealing
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
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Decomposition of SiN interlayer during thermal annealing of HfAlOx/SiN/Si(001) structure

Manisha Kundu, Noriyuki Miyata, Yukinori Morita, Tsuyoshi Horikawa, Toshihide Nabatame, Masakazu Ichikawa, and Akira Toriumi

Appl. Phys. Lett. 84, 5326 (2004); http://dx.doi.org/10.1063/1.1766393 (3 pages) | Cited 3 times

Online Publication Date: 17 June 2004

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We investigated the effects of postdeposition annealing (PDA) on a 3.1‐nm‐HfAlOx/0.45‐nm‐SiN/Si(001) structure under ultrahigh vacuum conditions. PDA caused the SiN interlayer (IL) to decompose, which was followed by N incorporation into the HfAlOx film. A detailed assessment of temperature and time dependencies during the PDA of the structure indicated that the SiN IL decomposed with an activation energy of 0.7 eV, which was much lower than that of bulk β-phase Si3N4. We suggest that the presence of oxygen-deficient metal oxide sites at the internal dielectric interface of the structure was responsible for catalyzing IL decomposition during PDA.
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68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing
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Systematic enhancement of in-field critical current density with rare-earth ion size variance in superconducting rare-earth barium cuprate films

J. L. MacManus-Driscoll, S. R. Foltyn, Q. X. Jia, H. Wang, A. Serquis, B. Maiorov, L. Civale, Y. Lin, M. E. Hawley, M. P. Maley, and D. E. Peterson

Appl. Phys. Lett. 84, 5329 (2004); http://dx.doi.org/10.1063/1.1766394 (3 pages) | Cited 63 times

Online Publication Date: 17 June 2004

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Enhanced in-field critical current densities (Jcs) have been obtained in epitaxial superconducting (RE1,RE2) Ba2Cu3O7−x ( RE1 = rare‐earth ion 1, and RE2 = rare earth ion 2) films grown on both single crystal and buffered metallic substrates. For a constant average RE ionic radius (equal to that of yttrium), there is a systematic dependence of the in-field Jc on the RE ion size variance, with a small, but nonzero, variance being optimum. Compared to the standard YBa2Cu3O7−x composition, a factor of two improvement in Jc (75.5 K) is reproducibly observed at 0.2 T (∥c) for the composition Dy1/3Ho2/3Ba2Cu3O7−x on both single crystal and buffered-metallic substrates. Angular dependent magnetic field studies and transmission electron microscopy indicate the presence of additional pointlike random defects.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition
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Thermophysical property measurements using time-resolved photothermal deflection spectrometry with step optical excitation

Jianhua Zhao, Jianqin Zhou, and Jun Shen

Appl. Phys. Lett. 84, 5332 (2004); http://dx.doi.org/10.1063/1.1766395 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2004

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This letter reports the theoretical and experimental results of thermophysical property measurements using our recently developed time-resolved photothermal deflection spectrometry (PDS) with step optical excitation. One-dimensional heat conduction boundary conditions of the third kind were derived, and a theoretical model with the boundary conditions was proposed. Both thermal diffusivity and effusivity of two well-known samples were precisely measured simultaneously by fitting experimental data to the theory. Thermal conductivity and unit volume specific heat then can be deduced. Moreover, time-resolved PDS with step optical excitation has the advantages of simpler experimental apparatus and less time consuming measurement, compared with the traditional periodically modulated PDS.
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07.20.-n Thermal instruments and apparatus
07.60.-j Optical instruments and equipment
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Cryogenic magnetic field sensor based on the magnetoresistive effect in bulk Bi2212+USr2CaO6

M. Ionescu, B. Winton, T. Silver, S. X. Dou, and R. Ramer

Appl. Phys. Lett. 84, 5335 (2004); http://dx.doi.org/10.1063/1.1766398 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2004

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A large magnetoresistive (MR) effect was observed in melt-textured (MT) Bi2212 in which USr2CaO6 was added in a proportion of 6 wt %. The resistivity measurements of MT Bi2212+6 wt % USr2CaO6 show high sensitivity to applied dc fields, as compared to pure Bi2212, in particular at low fields, below 3 T, and in a temperature range between 45 K and 85 K. In this temperature range, the MR effect of MT Bi2212+6 wt % USr2CaO6 is two orders of magnitude larger than the MR effect in pure Bi2212, and display a maximum that may be tuned to a particular temperature within the above range, by changing the amount of added nonsuperconducting compound. A cryogenic sensor was built and tested at 77 K in low fields. It shows a good sensitivity and small ( ∼ 1%) hysteresis of resistivity when the applied field was cycled between 0 T and 1 T.
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74.81.Bd Granular, melt-textured, amorphous, and composite superconductors
74.72.-h Cuprate superconductors
07.55.-w Magnetic instruments and components
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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Sensitivity and gigahertz counting performance of NbN superconducting single-photon detectors

A. Korneev, P. Kouminov, V. Matvienko, G. Chulkova, K. Smirnov, B. Voronov, G. N. Gol’tsman, M. Currie, W. Lo, K. Wilsher, J. Zhang, W. Słysz, A. Pearlman, A. Verevkin, and Roman Sobolewski

Appl. Phys. Lett. 84, 5338 (2004); http://dx.doi.org/10.1063/1.1764600 (3 pages) | Cited 102 times

Online Publication Date: 17 June 2004

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We have measured the quantum efficiency (QE), GHz counting rate, jitter, and noise-equivalent power (NEP) of nanostructured NbN superconducting single-photon detectors (SSPDs) in the visible to infrared radiation range. Our 3.5-nm-thick and 100- to 200-nm-wide meander-type devices (total area 10×10 μm2), operating at 4.2 K, exhibit an experimental QE of up to 20% in the visible range and ∼ 10% at 1.3 to 1.55 μm wavelength and are potentially sensitive up to midinfrared ( ∼ 10 μm) radiation. The SSPD counting rate was measured to be above 2 GHz with jitter <18 ps, independent of the wavelength. The devices’ NEP varies from ∼ 10−17 W/Hz1/2 for 1.55 μm photons to ∼ 10−20W/Hz1/2 for visible radiation. Lowering the SSPD operating temperature to 2.3 K significantly enhanced its performance, by increasing the QE to ∼ 20% and lowering the NEP level to ∼ 3×10−22 W/Hz1/2, both measured at 1.26 μm wavelength.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.25.Am Superconducting device characterization, design, and modeling
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Dip-pen nanolithography with magnetic Fe2O3 nanocrystals

Gautam Gundiah, Neena Susan John, P. John Thomas, G. U. Kulkarni, C. N. R. Rao, and S. Heun

Appl. Phys. Lett. 84, 5341 (2004); http://dx.doi.org/10.1063/1.1766399 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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Dip-pen nanolithography has been employed to obtain magnetic nanopatterns of γ-Fe2O3 nanocrystals on mica and silicon substrates. The chemical and magnetic nature of the patterns have been characterized employing low-energy electron microscopy, x-ray photoemission electron microscopy, and magnetic force microscopy measurements.
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81.16.Nd Micro- and nanolithography
75.50.Dd Nonmetallic ferromagnetic materials
68.37.Nq Low energy electron microscopy (LEEM)
79.60.-i Photoemission and photoelectron spectra
68.37.Rt Magnetic force microscopy (MFM)
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Thermoelectric devices using InN and Al1−xInxN thin films prepared by reactive radio-frequency sputtering

Shigeo Yamaguchi, Ryohei Izaki, Nakaba Kaiwa, Satoshi Sugimura, and Atsushi Yamamoto

Appl. Phys. Lett. 84, 5344 (2004); http://dx.doi.org/10.1063/1.1766400 (3 pages) | Cited 20 times

Online Publication Date: 17 June 2004

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We have fabricated thermoelectric devices using InN and Al0.25In0.75N prepared by radio-frequency sputtering. The devices are composed of (a) Al0.25In0.75N–chromel of 20 pairs on SiO2 glass, (b) InN–chromel of 20 pairs on SiO2 glass, and (c) InN-chromel of 20 pairs on polyimide film. The maximum output power and the open output voltage were (a) 1.6×10−6 W and 0.21 V at the temperature difference ΔT = 345 K, 263×10−12 W and 2.7×10−3 V at ΔT = 4.8 K, (b) 3.9×10−6 W and 0.22 V at ΔT = 332 K, 282×10−12 W and 2.4×10−3 V at ΔT = 4.1 K, and (c) 0.33×10−6W and 0.089 V at ΔT = 280 K, 63×10−12W and 1.4×10−3V at ΔT = 4.5 K, respectively.
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85.80.Fi Thermoelectric devices
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
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Axial high-temperature superconducting gradiometer with a flexible flux transformer

M. Bick, K. E. Leslie, R. A. Binks, D. L. Tilbrook, S. K. H. Lam, R. Gnanarajan, J. Du, and C. P. Foley

Appl. Phys. Lett. 84, 5347 (2004); http://dx.doi.org/10.1063/1.1766401 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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An axial first-order gradiometer is formed by coupling the input coil of a flexible high-temperature superconducting flux transformer inductively to a directly coupled superconducting quantum interference device magnetometer. The transformer is patterned in a single-layer YBa2Cu3O7−x film on a flexible Hastelloy tape. The tape is bent such that the two outer pickup loops of the transformer are facing each other while perpendicular to the magnetometer plane resulting in a gradiometer baseline of 35 mm. A superconducting shield is mechanically adjusted to reduce the gradiometer response to uniform fields applied perpendicularly to both the magnetometer plane and the plane of the transformer pickup loops, by a factor of typically 7000.
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07.55.Ge Magnetometers for magnetic field measurements
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)
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Vertical alignment of printed carbon nanotubes by multiple field emission cycles

Yong C. Kim, K. H. Sohn, Y. M. Cho, and Eun H. Yoo

Appl. Phys. Lett. 84, 5350 (2004); http://dx.doi.org/10.1063/1.1766403 (3 pages) | Cited 21 times

Online Publication Date: 17 June 2004

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The effect of field emission cycles on printed carbon nanotubes was investigated using scanning electron microscopy and current–voltage measurement. After multiple emission cycles, the printed nanotubes irreversibly deformed to orient themselves parallel to the field direction and, from them, remarkably enhanced emission image with good uniformity was demonstrated. Corresponding gradual decrease in the field emission threshold and increase of field enhancement factor (β) were also observed during field emission cycles.
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61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Inherent charge transfer layer formation at La0.6Sr0.4FeO3/La0.6Sr0.4MnO3 heterointerface

H. Kumigashira, D. Kobayashi, R. Hashimoto, A. Chikamatsu, M. Oshima, N. Nakagawa, T. Ohnishi, M. Lippmaa, H. Wadati, A. Fujimori, K. Ono, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 84, 5353 (2004); http://dx.doi.org/10.1063/1.1766405 (3 pages) | Cited 26 times

Online Publication Date: 17 June 2004

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We have investigated the Mn 3d spectral function in La0.6Sr0.4FeO3(LSFO)/La0.6Sr0.4MnO3(LSMO) heterointerfaces as well as of La1−x SrxMnO3 films using Mn 2p−3d resonant photoemission spectroscopy. The strong enhancement of the Mn 3d spectra at the Mn 2p−3d threshold enables us to extract the Mn 3d spectra of LSMO layers in the vicinity of the interface with the LSFO overlayers. We have found that the spectral intensity of eg↑ states near the Fermi level is gradually reduced with increasing LSFO overlayer thickness and is finally saturated at 5–7 ML. The close similarity in reduction of the intensity of the eg↑ states between the LSFO/LSMO interface and hole-doped LSMO films indicates the occurrence of charge transfer at the interface between the LSMO and LSFO layers.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
71.20.Ps Other inorganic compounds
71.70.Gm Exchange interactions
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The use of guided surface acoustic resonances in the determination of the thin film elastic tensor

T. Wittkowski, G. Distler, K. Jung, B. Hillebrands, and J. D. Comins

Appl. Phys. Lett. 84, 5356 (2004); http://dx.doi.org/10.1063/1.1767271 (3 pages) | Cited 1 time

Online Publication Date: 17 June 2004

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A Brillouin light scattering investigation of thin supported films shows that the measurement of resonances within the continuum of excitations together with the dispersion of discrete surface acoustic modes such as the Rayleigh and Sezawa waves, yields valuable additional information. In the present study, an analysis of the combined data results in the precise determination of four independent components of the film elastic tensor of elastically anisotropic, polycrystalline tungsten carbide (W2C) films for which the single crystal elastic constants are not known.
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68.35.Iv Acoustical properties
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
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ZnMgO epilayers and ZnO–ZnMgO quantum wells for optoelectronic applications in the blue and UV spectral region

Th. Gruber, C. Kirchner, R. Kling, F. Reuss, and A. Waag

Appl. Phys. Lett. 84, 5359 (2004); http://dx.doi.org/10.1063/1.1767273 (3 pages) | Cited 32 times

Online Publication Date: 17 June 2004

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We have investigated the properties of ZnMgO epilayers and ZnO–ZnMgO quantum well structures grown by metalorganic vapor-phase epitaxy. A well-controlled incorporation of magnesium, x ⩽ 0.10, could be confirmed resulting in a blueshift of the photoluminescence emission wavelength of the Zn1−xMgxO layers up to 200 meV. Using ZnMgO as barrier material, ZnO–ZnMgO quantum well structures with different well widths have then been fabricated. The confinement effect in the ZnO quantum wells leads to the expected increase of the corresponding quantum well emission energy with decreasing well width. A comparison to calculations also suggests a further enhancement of the exciton binding energy in the quantum wells of up to 90 meV.
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78.67.De Quantum wells
68.65.Fg Quantum wells
78.55.Et II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

All-optical multiphoton absorption figures of merit: Polydiacetylene poly (bis para-toluene sulfonate) of 2,4-hexadiyne-1,6 diol

Fumiyo Yoshino, Sergey Polyakov, and George I. Stegeman

Appl. Phys. Lett. 84, 5362 (2004); http://dx.doi.org/10.1063/1.1767276 (3 pages) | Cited 4 times

Online Publication Date: 17 June 2004

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The all-optical switching figures of merit are reported for the single crystal PTS (polydiacetylene poly (bis para-toluene sulfonate) of 2,4-hexadiyne-1,6 diol). Included are the effects of the absorption mechanisms from linear up to four-photon over the wavelength range 1.2–2.2 μm.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Jk Polymers and organics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Cancer treatment by ultrasound: Increasing the depth of necrosis

David Melodelima and Dominique Cathignol

Appl. Phys. Lett. 84, 5365 (2004); http://dx.doi.org/10.1063/1.1767277 (3 pages) | Cited 7 times

Online Publication Date: 17 June 2004

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Tissue coagulation by high-intensity ultrasound is a well-established method of cancer treatment. It suffers, however, from insufficient depth of action in the case of deep-seated tumors where endoscopic or interstitial applicators are used. It is demonstrated here that this depth can be increased by temporarily creating cavitation bubbles in such a way that ultrasound attenuation becomes stronger in the zone where tissue heating is insufficient. In vitro experiments in liver tissue confirm that bubbles are indeed located in this zone and that the effective depth of coagulation necrosis is doubled.
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87.50.yt Therapeutic applications
87.50.Y- Biological effects of acoustic and ultrasonic energy
87.19.X- Diseases
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Modeling the effect of subsurface interface defects on contact stiffness for ultrasonic atomic force microscopy

A. F. Sarioglu, A. Atalar, and F. L. Degertekin

Appl. Phys. Lett. 84, 5368 (2004); http://dx.doi.org/10.1063/1.1764941 (3 pages) | Cited 2 times

Online Publication Date: 17 June 2004

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We present a model predicting the effects of mechanical defects at layer interfaces on the contact stiffness measured by ultrasonic atomic force microscopy (AFM). Defects at subsurface interfaces result in changes at the local contact stiffness between the AFM tip and the sample. Surface impedance method is employed to model the imperfections and an iterative algorithm is used to calculate the AFM tip-surface contact stiffness. The sensitivity of AFM to voids or delaminations and disbonds is investigated for film-substrate combinations commonly used in microelectronic structures, and optimum defect depth for maximum sensitivity is defined. The effect of contact force and the tip properties on the defect sensitivity are considered. The results indicate that the ultrasonic AFM should be suitable for subsurface detection and its defect sensitivity can be enhanced by adjusting the applied force as well as by judicious choice of the AFM tip material and geometry.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.37.Ps Atomic force microscopy (AFM)
68.35.Ct Interface structure and roughness
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.37.Tj Acoustic force microscopy
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Pinning phenomena in a superconducting film with a square lattice of artificial pinning centers

Z. Jiang, D. A. Dikin, V. Chandrasekhar, V. V. Metlushko, and V. V. Moshchalkov

Appl. Phys. Lett. 84, 5371 (2004); http://dx.doi.org/10.1063/1.1767278 (3 pages) | Cited 5 times

Online Publication Date: 17 June 2004

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We study the transport properties of a superconducting Nb film with a square lattice of artificial pinning centers (APCs) as a function of dc current, at a temperature close to the superconducting transition temperature of the film. We find that, at low dc currents, the differential resistance of the film shows the standard matching field anomaly, that is, the differential resistance has a local minimum at magnetic fields corresponding to an integer number of flux lines per APC. However, at higher dc currents, the differential resistance at each matching field turns to a local maximum, which is exactly opposite to the low current behavior. This effect might indicate that the flux lines in the APC system change their flow mode as the dc current is increased.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Yb Other effects
74.10.+v Occurrence, potential candidates
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