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31 May 2004

Volume 84, Issue 22, pp. 4361-4576

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4409 (2004); http://dx.doi.org/10.1063/1.1757648 (3 pages)

Azita Soleymani, Piroz Zamankhan, and William Polashenski
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Atomic-scale observation of interfacial roughness and As–P exchange in InGaAs/InP multiple quantum wells

I. Yamakawa, R. Oga, Y. Fujiwara, Y. Takeda, and A. Nakamura

Appl. Phys. Lett. 84, 4436 (2004); http://dx.doi.org/10.1063/1.1758784 (3 pages) | Cited 8 times

Online Publication Date: 12 May 2004

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Cross-sectional scanning tunneling microscopy (XSTM) has been used to study interfacial properties of InP-on-InGaAs interfaces in InGaAs/InP multiple quantum wells grown by metalorganic vapor phase epitaxy with a growth interruption. XSTM has enabled us to separately identify step-like roughness and distributions of As atoms incorporated in the InP layer near the interface. The As composition profile along the growth direction analyzed from distributions of As atoms in XSTM images shows an exponential variation with distance from the InP-on-InGaAs interface. It is found that the growth interruption of 30 s reduces considerably the roughness amplitude to 0.45 nm from 1.1 nm and increases the coherent length from 22 to 27 nm. © 2004 American Institute of Physics.
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68.65.Fg Quantum wells
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Ct Interface structure and roughness
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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Quantum grid infrared spectrometer

K. K. Choi, G. Dang, J. W. Little, K. M. Leung, and T. Tamir

Appl. Phys. Lett. 84, 4439 (2004); http://dx.doi.org/10.1063/1.1758785 (3 pages) | Cited 3 times

Online Publication Date: 12 May 2004

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We have designed and characterized an infrared spectrometer, which uses a linear array of quantum grid infrared photodetectors (QGIPs) as its spectral sensing elements. Each QGIP element shares the same detector material but has a different grid geometry. The detector material, which is based on a binary superlattice design, provides an 8–14 μm broadband absorption medium for the spectrometer. The geometry of the grid, which is the light coupling structure under normal incidence, selects individual absorption wavelength for each element. Using a linear array of QGIPs of different geometries, multiple wavelengths can be detected simultaneously, and the array thus forms a spectrometer. Multicolor infrared imaging can then be achieved by integrating such QGIPs in unit cells of a two-dimensional array. © 2004 American Institute of Physics.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
78.67.De Quantum wells
85.60.Gz Photodetectors (including infrared and CCD detectors)
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Structure of grain boundaries in nanostructured ZnO

Zhihao Wu, Yingxue Zhou, Xinyi Zhang, Shiqiang Wei, and Dongliang Chen

Appl. Phys. Lett. 84, 4442 (2004); http://dx.doi.org/10.1063/1.1759060 (3 pages) | Cited 9 times

Online Publication Date: 12 May 2004

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The grain boundary (GB) of nanocrystalline ZnO films is investigated using the x-ray absorption fine structure technique. With the advantage of the dominant GB volume fraction in our samples, the GB structure is found to be neither simply “gas-like” nor “similar to that of coarse-grained phase,” but experiences a transition from the modestly ordered innermost coordination shell around centered atoms to partly disordered second coordination shell and then to completely disordered higher coordination shells. © 2004 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
61.46.-w Structure of nanoscale materials
78.70.Dm X-ray absorption spectra
68.55.-a Thin film structure and morphology

Influence of pulse duration on the amorphization of GeSb thin films under ultrashort laser pulses

S. M. Wiggins, J. Solis, and C. N. Afonso

Appl. Phys. Lett. 84, 4445 (2004); http://dx.doi.org/10.1063/1.1759062 (3 pages) | Cited 9 times

Online Publication Date: 12 May 2004

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Laser-induced amorphization of crystalline, 25-nm-thick, Sb-rich GeSb films has been studied for pump pulse durations in the range from 100 fs up to 6 ns. The dynamics of the phase change has been investigated using real-time reflectivity measurements with picosecond time resolution performed with a streak camera. For pulses in the femtosecond regime, the time required to complete the transformation is of the order of ∼10–15 ns. When the pulse duration is increased to the 1.5–20 ps range, the transformation time decreases to values as short as 400 ps, while for nanosecond laser pulses amorphization is not achievable. This behavior is discussed in terms of the heat flow dynamics of the system and the influence of pulse duration on the initial supercooling and nucleation rate. © 2004 American Institute of Physics.
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64.70.K- Solid-solid transitions
81.40.Wx Radiation treatment (particle and electromagnetic)

Crystal nucleation and growth processes in Ge2Sb2Te5

S. Privitera, C. Bongiorno, E. Rimini, and R. Zonca

Appl. Phys. Lett. 84, 4448 (2004); http://dx.doi.org/10.1063/1.1759063 (3 pages) | Cited 28 times

Online Publication Date: 12 May 2004

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The kinetics of the amorphous-to-crystal transition in Ge2Sb2Te5 thin films have been studied through in situ transmission electron microscopy analyses. By following the time evolution of the grain density and size, the growth velocity and the nucleation rate have been separately measured at different annealing temperatures. Activation energies of 2.9±0.5 eV and 2.3±0.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG∗ has been evaluated, and the scalability of phase change nonvolatile memories has been estimated. © 2004 American Institute of Physics.
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68.55.A- Nucleation and growth
68.60.Wm Other nonelectronic physical properties
64.70.K- Solid-solid transitions
68.37.Lp Transmission electron microscopy (TEM)

Stable extremely-high-damping discrete viscoelastic systems due to negative stiffness elements

Yun-Che Wang and Roderic S. Lakes

Appl. Phys. Lett. 84, 4451 (2004); http://dx.doi.org/10.1063/1.1759064 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2004

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Systems with negative stiffness constituents can have extreme material properties greatly exceeding those of either constituent. We show that a discrete system with a viscoelastic damping element and a negative stiffness element can be made with overall viscoelastic damping orders of magnitude higher than that of any constituent, or of the system with all elements of positive stiffness. The product of stiffness and damping, important for vibration damping, is also enhanced by orders of magnitude. We show this system is unconditionally stable in the high damping regime. The singularity in damping can be made arbitrarily close to the stability boundary. © 2004 American Institute of Physics.
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46.35.+z Viscoelasticity, plasticity, viscoplasticity
46.40.Ff Resonance, damping, and dynamic stability

Random laser action in self-organized para-sexiphenyl nanofibers grown by hot-wall epitaxy

F. Quochi, F. Cordella, R. Orrù, J. E. Communal, P. Verzeroli, A. Mura, G. Bongiovanni, A. Andreev, H. Sitter, and N. S. Sariciftci

Appl. Phys. Lett. 84, 4454 (2004); http://dx.doi.org/10.1063/1.1759384 (3 pages) | Cited 41 times

Online Publication Date: 12 May 2004

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We report on the observation of amplified spontaneous emission and random lasing in self-organized crystalline para-sexiphenyl nanofibers. Using subpicosecond excitation, a lasing threshold is observed on the 0–1 emission band near 425 nm at excitation fluences as low as 0.5 μJ/cm2 (6×1016 cm−3 equivalent density), near the onset of density-dependent recombination processes. The dependence of the nonlinear emission spectrum on both the pump intensity and position of the excitation area are attributed to the interplay between random lasing and amplified spontaneous emission occurring along the nanofibers. © 2004 American Institute of Physics.
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42.55.Wd Fiber lasers
42.55.Zz Random lasers
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
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White organic light-emitting devices using 2,5,2′,5′-tetrakis(4′-biphenylenevinyl)-biphenyl as blue light-emitting layer

Gang Cheng, Yi Zhao, Yingfang Zhang, Shiyong Liu, Feng He, Haiquan Zhang, and Yuguang Ma

Appl. Phys. Lett. 84, 4457 (2004); http://dx.doi.org/10.1063/1.1738179 (3 pages) | Cited 26 times

Online Publication Date: 14 May 2004

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White organic light-emitting devices (OLEDs) have been fabricated using a trimeric phenylenvinylene derivative, 2,5,2′,5′-tetrakis(4′-biphenylenevinyl)-biphenyl (TBVB), as blue light-emitting layer. The structure of devices is simple, in which tris(8-hydroxyquinoline) aluminum (Alq), N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine, TBVB, and an ultrathin layer of 5,6,11,12-tetraphenylnaphthacene (rubrene), which is inserted between Alq and TBVB layers, are used as electron-transporting, hole-transporting, blue, and yellow light-emitting layers, respectively. A fairly pure white OLED with Commission Internationale De L’Eclairage coordinates of (0.33,0.34) at 4000 cd/m2 is realized when the thickness of TBVB is 10 nm and that of rubrene is 0.15 nm. The maximum luminance and efficiency of this device are 4025 cd/m2 and 3.2 cd/A, respectively. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
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Integrated optical devices design by genetic algorithm

L. Sanchis, A. Håkansson, D. López-Zanón, J. Bravo-Abad, and José Sánchez-Dehesa

Appl. Phys. Lett. 84, 4460 (2004); http://dx.doi.org/10.1063/1.1738931 (3 pages) | Cited 34 times

Online Publication Date: 14 May 2004

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In this work, we use multiple scattering in conjunction with a genetic algorithm to reliably determine the optimized photonic-crystal-based structure able to perform a specific optical task. The genetic algorithm operates on a population of candidate structures to produce new candidates with better performance in an iterative process. The potential of this approach is illustrated by designing a spot size converter that has a very low F number (F = 0.47) and a conversion ratio of 11:1. Also, we have designed a coupler device that introduces the light from the optical fiber into a photonic-crystal-based waveguide with a coupling efficiency over 87% for a wavelength that can be tuned to 1.5 μm. © 2004 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.82.Bq Design and performance testing of integrated-optical systems
42.81.Qb Fiber waveguides, couplers, and arrays
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High-mobility thin InSb films grown by molecular beam epitaxy

T. Zhang, S. K. Clowes, M. Debnath, A. Bennett, C. Roberts, J. J. Harris, R. A. Stradling, L. F. Cohen, T. Lyford, and P. F. Fewster

Appl. Phys. Lett. 84, 4463 (2004); http://dx.doi.org/10.1063/1.1748850 (3 pages) | Cited 23 times

Online Publication Date: 14 May 2004

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The problem of preparing high-mobility thin InSb films is revisited for magnetoresistive and spintronic sensor applications. We introduce a growth process that significantly improves the electrical properties of thin unintentionally doped InSb layers (60–300 nm) epitaxially grown on GaAs(100) substrates by reducing the density of dislocations within the interfacial layer. The epilayer properties are well described by a differential two-layer model. This model confirms that the contribution of the interface can only be donor-like. Moreover, the electrical properties of the InSb layers change continuously away from the interface up to sample thickness of the order of 1 μm. © 2004 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ey III-V semiconductors
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Room-temperature ferromagnetism in ion-implanted Co-doped TiO2(110) rutile

V. Shutthanandan, S. Thevuthasan, S. M. Heald, T. Droubay, M. H. Engelhard, T. C. Kaspar, D. E. McCready, L. Saraf, S. A. Chambers, B. S. Mun, N. Hamdan, P. Nachimuthu, B. Taylor, R. P. Sears, and B. Sinkovic

Appl. Phys. Lett. 84, 4466 (2004); http://dx.doi.org/10.1063/1.1753652 (3 pages) | Cited 30 times

Online Publication Date: 14 May 2004

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Ferromagnetic Co-doped rutile TiO2 single crystals were synthesized by high-temperature ion implantation and characterized by a variety of techniques. Co is uniformly distributed to a depth of ∼300 nm with an average concentration of ∼2 at. %, except in the near-surface region, where the concentration is ∼3 at. %. Ferromagnetic behavior is exhibited at room temperature with an effective saturation magnetization of ∼ 0.6 μB/Co atom. The Co is in a formal oxidation state of +2 throughout the implanted region, and no Co(O) is detected. © 2004 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
61.72.up Other materials
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.65.Mq Oxidation
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Ultrasensitive nanoelectromechanical mass detection

K. L. Ekinci, X. M. H. Huang, and M. L. Roukes

Appl. Phys. Lett. 84, 4469 (2004); http://dx.doi.org/10.1063/1.1755417 (3 pages) | Cited 115 times

Online Publication Date: 14 May 2004

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We describe the application of nanoelectromechanical systems (NEMS) to ultrasensitive mass detection. In these experiments, a modulated flux of atoms was adsorbed upon the surface of a 32.8 MHz NEMS resonator within an ultrahigh-vacuum environment. The mass-induced resonance frequency shifts by these adsorbates were then measured to ascertain a mass sensitivity of 2.53×10−18 g. In these initial measurements, this sensitivity is limited by the noise in the NEMS displacement transducer; the ultimate limits of the technique are set by fundamental phase noise processes. Our results and analysis indicate that mass sensing of individual molecules will be realizable with optimized NEMS devices. © 2004 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
06.30.Dr Mass and density
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Three-photon excited band edge and trap emission of CdS semiconductor nanocrystals

James W. M. Chon, Min Gu, Craig Bullen, and Paul Mulvaney

Appl. Phys. Lett. 84, 4472 (2004); http://dx.doi.org/10.1063/1.1755420 (3 pages) | Cited 25 times

Online Publication Date: 14 May 2004

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We report on three-photon excited band edge and trap emission of CdS semiconductor nanocrystals. While the band edge emission intensity clearly shows a cubic dependence on excitation intensity, demonstrating three-photon absorption process, the trap emission does not exhibit such a cubic dependence. A simple theoretical model based on the assumption that there exist a limited number of trap states in nanocrystals shows good agreement with the experiment, suggesting that the number of trap states play an important role in their emission intensity dependence of multiphoton excitation. The three-photon absorption cross section of CdS nanocrystals is measured to be ∼ 10−79 cm6 s2 photon−2, which is three to four orders of magnitude higher than those of the previously reported common UV fluorescent dyes. © 2004 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
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Radial superlattices and single nanoreactors

Ch. Deneke, N.-Y. Jin-Phillipp, I. Loa, and O. G. Schmidt

Appl. Phys. Lett. 84, 4475 (2004); http://dx.doi.org/10.1063/1.1755835 (3 pages) | Cited 40 times

Online Publication Date: 14 May 2004

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We investigate the wall structure and thermal stability of individual freestanding rolled-up nanotubes (RUNTs) using micro-Raman spectroscopy, transmission electron microscopy, and selected area electron diffraction. Our studies reveal that the walls of the InAs/GaAs RUNTs consist of a radial superlattice comprising alternating crystalline and noncrystalline layers. Furthermore, we locally heated individual RUNTs with a laser beam, and Raman spectroscopy was used in situ to monitor any structural changes. At about 300 °C the heated part of a RUNT starts to oxidize and eventually transforms into crystalline β-Ga2O3. This result shows that RUNTs can serve as nanoreactors that locally synthesize material at intentional places on a substrate surface. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.05.jm Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction
68.37.Lp Transmission electron microscopy (TEM)
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Blue-light emission from molecular-beam-epitaxially grown GaN/Al0.5Ga0.5N multiple quantum wells with a perturbating layer of Al0.5Ga0.5N monolayers

Y. S. Park, Seung-Ho Lee, Jae-Eung Oh, Chang-Mo Park, and Tae-Won Kang

Appl. Phys. Lett. 84, 4478 (2004); http://dx.doi.org/10.1063/1.1755836 (3 pages) | Cited 8 times

Online Publication Date: 14 May 2004

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We have studied the influence of AlGaN inserting layer into GaN well region on the light emission from a strained GaN/AlGaN multiple-quantum-well system. We have found that, by simply inserting thin AlGaN layer, the luminescence is dramatically redshifted with respect to that of the normal GaN/AlGaN quantum well, which is centered at 2.96 eV, nearly 0.52 eV below the bulk GaN band gap. We attribute this enormous redshift to an additional 0.7 MV/cm field present in the well due to the perturbation of the well region by inserting AlGaN layer. The result is revealed to be of great importance in the design and analysis of nitride heterostructure devices which can be exploited to advantage in nitride materials and device engineering. © 2004 American Institute of Physics.
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78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
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Carbon nanotube-enhanced performance of microplasma devices

S.-J. Park, J. G. Eden, and K.-H. Park

Appl. Phys. Lett. 84, 4481 (2004); http://dx.doi.org/10.1063/1.1755845 (3 pages) | Cited 23 times

Online Publication Date: 14 May 2004

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Incorporating multiwall carbon nanotubes (CNTs) directly into the cylindrical cathode of Ni screen/BN/Ni microplasma devices significantly improves all device performance parameters—operating and ignition voltages, as well as radiative efficiency. Having a cathode diameter of 200 μm, these devices exhibit operating voltages as much as 30 V (∼22%) lower than those required for an identical structure without CNTs. For Ne pressures of 100–300 Torr, ignition voltages are reduced by 14%–18% with the introduction of CNTs. In contrast, radiative efficiencies in the 300–800 nm spectral region are increased with CNTs by 6%–9% over the entire pressure range studied (200–600 Torr Ne). Voltage–current characteristics for two device configurations suggest that electrons generated within the cathode microcavity by CNT field emission are most effective in impacting device performance. © 2004 American Institute of Physics.
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85.60.Pg Display systems
85.45.Fd Field emission displays (FEDs)
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Nanomachining carbon nanotubes with ion beams

M. S. Raghuveer, P. G. Ganesan, J. D’Arcy-Gall, G. Ramanath, M. Marshall, and I. Petrov

Appl. Phys. Lett. 84, 4484 (2004); http://dx.doi.org/10.1063/1.1756191 (3 pages) | Cited 32 times

Online Publication Date: 14 May 2004

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We demonstrate the use of 10 and 30 keV focused beams of Ga+ ions to thin, slice, weld, and alter the structure and composition of multiwalled carbon nanotubes at precise locations along the nanotube axis. This strategy of harnessing ion-beam-induced defect generation and doping could be attractive for modulating chemical and electrical properties along the nanotube length, and fabricate nanotube heterostructures and networks for device applications. © 2004 American Institute of Physics.
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61.82.Rx Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.80.Jh Ion radiation effects
81.65.-b Surface treatments
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
81.05.ub Fullerenes and related materials
61.72.up Other materials
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Wave interactions in buckling: Self-organization of a metal surface on a structured polymer layer

S. Joon Kwon, Pil J. Yoo, and Hong H. Lee

Appl. Phys. Lett. 84, 4487 (2004); http://dx.doi.org/10.1063/1.1756194 (3 pages) | Cited 15 times

Online Publication Date: 14 May 2004

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We report on self-organized metal surface patterns that result when a thin bilayer of a metal on a periodically corrugated polymer layer is annealed. A theoretical basis is provided for the self-organization that is verified by experiment. The wave number of the surface pattern is determined by a square law relationship involving the corrugation wave number and the intrinsic wave number of the bilayer. The phase shift between the wave on the ridge and that on the groove is related to an uncertainty in the corrugation wave number. Free energy minimization dictates connectivity of the two waves and fidelity of the metal surface pattern. © 2004 American Institute of Physics.
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68.35.Rh Phase transitions and critical phenomena
68.35.Gy Mechanical properties; surface strains
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Characterization of laser-produced aluminum plasma in ambient atmosphere of nitrogen using fast photography

A. K. Sharma and R. K. Thareja

Appl. Phys. Lett. 84, 4490 (2004); http://dx.doi.org/10.1063/1.1756199 (3 pages) | Cited 13 times

Online Publication Date: 14 May 2004

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We report on the pulsed-laser ablation of aluminum in ambient pressure of nitrogen varying from 0.01 to 70 Torr using images of the expanding plasma plume. At pressures ≥ 1 Torr plasma–gas interface showed severe distortion in the front of the expanding plume. The plasma expansion velocity showed oscillatory behavior with delay time beyond 260 ns and is attributed to Rayleigh–Taylor instability. The effect of background gas on inducing polarization in the ablated plasma is also reported. At low pressure of 0.1 Torr the degree of polarization of Al III transition 4s 2S1/2–4p 2P3/20 at 569.6 nm increased with delay time. At pressures ≥ 1 Torr it showed an oscillatory behavior. The observed steep pressure gradient at the plasma–gas interface may result in strong self-generated magnetic field due to Rayleigh–Taylor instability. © 2004 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.65.Kj Magnetohydrodynamic and fluid equation
52.35.Tc Shock waves and discontinuities
52.38.Mf Laser ablation
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Temperature-dependent emptying of grain-boundary charge traps in chemical vapor deposited diamond

S. M. Hearne, D. N. Jamieson, E. Trajkov, S. Prawer, and J. E. Butler

Appl. Phys. Lett. 84, 4493 (2004); http://dx.doi.org/10.1063/1.1756201 (3 pages) | Cited 9 times

Online Publication Date: 14 May 2004

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We have used the technique of ion beam induced charge with a 2 MeV He+ microprobe to image particle detectors fabricated from polycrystalline chemical vapor deposited diamond as a function of temperature. We find that detectors which display a thermally stimulated current peak at 190 °C display increased charge collection efficiency when heated above that temperature. The probability of detecting the impact of a single ion at room temperature was less than 2%, but this probability rises to over 80% at 170 °C. We model this effect by showing that charge trapped at grain boundaries is liberated at elevated temperatures and this results in an increased electric field within the detector volume and hence a raised charge collection efficiency. © 2004 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
29.40.Wk Solid-state detectors
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High-quality radio-frequency inductors on silicon using a hybrid ferrite technology

M. Saidani and M. A. M. Gijs

Appl. Phys. Lett. 84, 4496 (2004); http://dx.doi.org/10.1063/1.1756677 (3 pages) | Cited 10 times

Online Publication Date: 14 May 2004

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We have realized millimeter-size rf inductors on silicon using a polyimide mold–copper electroplating coil technology. Subsequently, the coils are assembled with magnetic cover plates of commercially available bulk Ni–Zn ferrites of high resistivity. Using the magnetic flux-amplifying ferrite plates, we obtain a 40% enhancement of the inductance and a 25% enhancement of the quality factor (Q = 10–20) for frequencies up to 0.2 GHz. Our results indicate the large potential of using bulk ferrites for rf applications in a hybrid inductor assembly process. © 2004 American Institute of Physics.
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84.32.Hh Inductors and coils; wiring
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Scanning ferromagnetic resonance microscopy and resonant heating of magnetite nanoparticles: Demonstration of thermally detected magnetic resonance

F. Sakran, A. Copty, M. Golosovsky, D. Davidov, and P. Monod

Appl. Phys. Lett. 84, 4499 (2004); http://dx.doi.org/10.1063/1.1756682 (3 pages) | Cited 7 times

Online Publication Date: 14 May 2004

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We report a 9 GHz microwave scanning probe based on a slit aperture for spatially resolved magnetic resonance detection. We use patterned layers of dispersed magnetite Fe3O4 nanoparticles and demonstrate low-field ferromagnetic resonance images with a spatial resolution of 15 μm. We also demonstrate localized heating of magnetite nanoparticles via ferromagnetic resonance absorption which can be controlled by an external dc magnetic field. Using our microwave probe as a transmitter and a temperature sensor (thermocouple or infrared detector), we show thermally detected magnetic resonance at room temperature. © 2004 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
07.79.-v Scanning probe microscopes and components
75.50.Dd Nonmetallic ferromagnetic materials
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Generation of silicon nanoparticles via femtosecond laser ablation in vacuum

S. Amoruso, R. Bruzzese, N. Spinelli, R. Velotta, M. Vitiello, X. Wang, G. Ausanio, V. Iannotti, and L. Lanotte

Appl. Phys. Lett. 84, 4502 (2004); http://dx.doi.org/10.1063/1.1757014 (3 pages) | Cited 66 times

Online Publication Date: 14 May 2004

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We demonstrate that femtosecond laser ablation of silicon targets in vacuum is a viable route to the generation and deposition of nanoparticles with radii of ≈5–10 nm. The nanoparticles dynamics during expansion has been analyzed through their structureless continuum optical emission, while atoms and ions, also present in the plume, have been identified by their characteristic emission lines. Atomic force microscopy analysis of the material deposited at room temperature has allowed the characterization of the nanoparticles size distribution. Taking into account the emissivity of small particles we show that the continuum emission is a blackbody-like radiation from the nanoparticles. Our results suggest that nanoclusters are generated as a result of relaxation processes of the extreme material state reached by the irradiated target surface, in agreement with recently published theoretical studies. © 2004 American Institute of Physics.
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81.07.De Nanotubes
81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces
61.82.Rx Nanocrystalline materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.16.Mk Laser-assisted deposition
78.55.Ap Elemental semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.82.Fk Semiconductors
61.46.-w Structure of nanoscale materials
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Dielectric characterization of Bi3.25La0.75Ti3O12 thin films

Di Wu, Aidong Li, and Naiben Ming

Appl. Phys. Lett. 84, 4505 (2004); http://dx.doi.org/10.1063/1.1757631 (3 pages) | Cited 23 times

Online Publication Date: 14 May 2004

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Dielectric properties of Pt/Bi3.25La0.75Ti3O12(BLaT)/Pt ferroelectric thin film capacitors were studied as functions of frequency (40–106 Hz) and temperature (30–590 °C). BLaT thin films showed a first-order para-ferroelectric transition around 400 °C. Pt/BLaT/Pt capacitors post-annealed in Ar exhibited broadened transition with larger losses, which was interpreted in terms of increased oxygen vacancies. Via complex impedance spectroscopy study, the conduction activation energy of the space charges was determined to be ∼ 1.1 eV, close to that of oxygen vacancies in perovskite materials. The impedance characteristics of Pt/BLaT/Pt were compared with those of Pt/SrBi2Ta2O9(SBT)/Pt capacitors. The impact of dielectric characteristics on fatigue resistance of BLaT films was briefly discussed in comparison with SBT films. © 2004 American Institute of Physics.
Show PACS
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Jp Dielectric breakdown and space-charge effects
77.80.Dj Domain structure; hysteresis
81.40.Gh Other heat and thermomechanical treatments
77.80.B- Phase transitions and Curie point
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GaInN light-emitting diodes with RuO2/SiO2/Ag omni-directional reflector

Jong Kyu Kim, Thomas Gessmann, Hong Luo, and E. Fred Schubert

Appl. Phys. Lett. 84, 4508 (2004); http://dx.doi.org/10.1063/1.1757634 (3 pages) | Cited 42 times

Online Publication Date: 14 May 2004

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A GaInN light-emitting diode (LED) employing an omni-directional reflector (ODR) is presented. The ODR consists of a RuO2 ohmic contact to p-type GaN, a quarter-wave thick SiO2 low-index layer perforated by an array of micro-contacts, and an Ag layer. Calculations predict a 98% angle-averaged reflectivity at λ = 450 nm for an GaN/SiO2/Ag ODR, much higher than that for a 20 period Al0.25Ga0.75N/GaN distributed Bragg reflector (49%) and an Ag reflector (94%). It is shown that the RuO2/SiO2/Ag ODR has higher reflectivity than Ni/Au and even Ag reflectors, leading to a higher light extraction efficiency of GaInN LEDs with ODR. The electrical properties of the ODR-LED are comparable to those LEDs with a conventional Ni/Au contact. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.82.Gw Other integrated-optical elements and systems
73.40.Ns Metal-nonmetal contacts
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