APL Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

2 Feb 2004

Volume 84, Issue 5, pp. 645-830

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 810 (2004); http://dx.doi.org/10.1063/1.1644924 (3 pages)

Hendrik F. Hamann, Yves C. Martin, and H. Kumar Wickramasinghe
Enlarge Image | Read More
Page 1 of 3 Pages Next Page | Jump to Page
back to top
RSS Feeds

Importance of electron-impurity scattering for electron transport in terahertz quantum-cascade lasers

Hans Callebaut, Sushil Kumar, Benjamin S. Williams, Qing Hu, and John L. Reno

Appl. Phys. Lett. 84, 645 (2004); http://dx.doi.org/10.1063/1.1644337 (3 pages) | Cited 48 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using an ensemble Monte Carlo simulation, including both electron–electron and electron–phonon scattering as well as electron-impurity scattering, the current density, population inversion, electron temperature, and gain in two THz quantum-cascade structures are investigated and compared to measurements. We find that the inclusion of electron-impurity scattering in the calculations is crucial when modeling the intersubband transport dynamics in these devices. However, the calculated gain is higher than inferred from experiments. This can be attributed to wavefunction localization caused by dephasing scattering, which is unaccounted for in the present model.© 2004 American Institute of Physics.
Show PACS
42.55.Px Semiconductor lasers; laser diodes
73.61.Ey III-V semiconductors
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Single photon emission from site-controlled pyramidal quantum dots

M. H. Baier, E. Pelucchi, E. Kapon, S. Varoutsis, M. Gallart, I. Robert-Philip, and I. Abram

Appl. Phys. Lett. 84, 648 (2004); http://dx.doi.org/10.1063/1.1643533 (3 pages) | Cited 41 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We demonstrate that a single photoexcited InGaAs semiconductor quantum dot (QD) grown by organo-metallic chemical vapor deposition on prepatterned substrates emits one photon at a time, with no uncontrolled background photon emission, making it an excellent single photon emitter. Moreover, our fabrication technique offers complete site control and small inhomogeneous broadening of QD arrays, which is essential for the practical implementation of QDs in efficient solid-state single photon emitting devices. © 2004 American Institute of Physics.
Show PACS
78.67.Hc Quantum dots
42.50.-p Quantum optics
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Tunable microdisk resonators vertically coupled to bus waveguides using epitaxial regrowth and wafer bonding techniques

Seung June Choi, Zhen Peng, Qi Yang, Sang Jun Choi, and P. Daniel Dapkus

Appl. Phys. Lett. 84, 651 (2004); http://dx.doi.org/10.1063/1.1644915 (3 pages) | Cited 3 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We demonstrate two different types of tunable microdisk resonators vertically coupled to bus waveguides: a microdisk resonator coupled to air-guided rib bus waveguides and the other one built on buried heterostructure bus lines, respectively. The latter type contacts the substrate without relying on an extra supporting structure, which affords more reliable conductive paths toward the substrate. A planarized epitaxial regrowth technology combined with wafer bonding is used to fabricate the structure. The measured transmission spectra indicate improved tuning capability of buried-bus-coupled microdisks, but the overall device performance is limited by optical leakage through the substrate. © 2004 American Institute of Physics.
Show PACS
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Parallel plate THz transmitter

S. Coleman and D. Grischkowsky

Appl. Phys. Lett. 84, 654 (2004); http://dx.doi.org/10.1063/1.1644923 (3 pages) | Cited 22 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A THz transmitter that directly excites the guided wave modes of a dielectric filled parallel plate waveguide is demonstrated. When coupled to free space, the transmitter yields a large peak time-domain THz signal. The device yields significant signal amplitudes with varying output spectra with and without a bias field applied. This transmitter provides powerful direct excitation of guided wave modes and is the next step toward an integrated guided wave transverse-electromagnetic mode THz bandwidth device. © 2004 American Institute of Physics.
Show PACS
84.40.Az Waveguides, transmission lines, striplines
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Total reflection amorphous carbon mirrors for vacuum ultraviolet free electron lasers

B. Steeg, L. Juha, J. Feldhaus, S. Jacobi, R. Sobierajski, C. Michaelsen, A. Andrejczuk, and J. Krzywinski

Appl. Phys. Lett. 84, 657 (2004); http://dx.doi.org/10.1063/1.1645320 (3 pages) | Cited 13 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Sputter-deposited amorphous carbon coatings of high optical quality and very high radiation stability will be used as reflecting optical elements for free electron laser (FEL) applications in the vacuum ultraviolet (VUV) and soft x-ray spectral regions. Their reflectivity at grazing angles of 2° is typically 94–96% for photon energies between 50 and 250 eV. Using the focused radiation (λ = 98 nm) of the VUV FEL at Deutsches Elektronen-Synchrotron DESY the damage threshold of such coatings was determined to 0.07 J/cm2. Ripples with a spatial period of 76 nm were found on the surfaces damaged by the FEL radiation. © 2004 American Institute of Physics.
Show PACS
42.79.Bh Lenses, prisms and mirrors
41.60.Cr Free-electron lasers
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Silicidation-induced band gap shrinkage in Ge epitaxial films on Si

Jifeng Liu, Douglas D. Cannon, Kazumi Wada, Yasuhiko Ishikawa, Samerkhae Jongthammanurak, David T. Danielson, Jurgen Michel, and Lionel C. Kimerling

Appl. Phys. Lett. 84, 660 (2004); http://dx.doi.org/10.1063/1.1644618 (3 pages) | Cited 17 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ge epitaxial films on Si grown at high temperatures show a shrinkage in the direct band gap EgΓ as a result of the tensile strain accumulated during the cooling process after growth, making it a promising candidate for effective photon detection in L-band telecommunications. However, because of strain relaxation at temperatures >750 °C, only about 0.20% tensile strain can be accumulated at most. This leads to a direct band gap of 0.773 eV, corresponding to 1605 nm and is not enough to cover the whole L band (1561–1620 nm). In this letter, we report the strain enhancement in epitaxial Ge films induced by the formation of C54TiSi2 on the backside of the Si wafers. The backside C54-TiSi2 layer not only forms a good electric contact, but also increases the tensile strain of the Ge film on the front side from 0.20% to 0.24% and a further direct band gap shrinkage from 0.773 to 0.765 eV, corresponding to 1620 nm, which covers the whole L band. Since the silicidation process is compatible with Si complementary metal-oxide-semiconductor technology, this technique is promising to achieve low cost L-band photon detection completely with tensile strained Ge on Si. © 2004 American Institute of Physics.
Show PACS
68.60.Bs Mechanical and acoustical properties
78.66.Db Elemental semiconductors and insulators

High transmission and single-mode operation in low-index-contrast photonic crystal waveguide devices

M. Augustin, H.-J. Fuchs, D. Schelle, E.-B. Kley, S. Nolte, A. Tünnermann, R. Iliew, C. Etrich, U. Peschel, and F. Lederer

Appl. Phys. Lett. 84, 663 (2004); http://dx.doi.org/10.1063/1.1644336 (3 pages) | Cited 9 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We investigate photonic crystal films made of low-index glass materials. Polarization-sensitive waveguiding and single-mode operation (with losses as low as 1.7 dB/mm) have been observed in wide multimode photonic crystal waveguides after propagation of some millimeters. Furthermore, single-mode operation and transmission as high as about 50% per bend has been observed experimentally in low-index photonic crystal waveguide bends. © 2004 American Institute of Physics.
Show PACS
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Visible spectrum (645 nm) transverse electric field laser operation of InP quantum dots coupled to tensile strained In0.46Ga0.54P quantum wells

G. Walter, J. Elkow, N. Holonyak, R. D. Heller, X. B. Zhang, and R. D. Dupuis

Appl. Phys. Lett. 84, 666 (2004); http://dx.doi.org/10.1063/1.1645674 (3 pages) | Cited 11 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Data are presented that demonstrate the continuous wave room-temperature transverse-electric field (TE) visible-spectrum (645 nm) heterostructure laser operation of single-layer compressively strained 3.75 monolayer equivalent InP quantum dots (QDs) coupled to 60 Å wide tensile-strained In0.46Ga0.54P quantum wells (QWs). The simple stripe geometry (200 μm×4 μm) InP QD+InGaP QW heterostructure laser is capable of high performance despite the coupling of two competing recombination systems. The InP QD+InGaP QW laser exhibits low threshold (∼31 mA), high quantum efficiency (72%, ∼1.38 mW/mA), a relatively high characteristic temperature T0 of 69 K, and a shift in wavelength at temperature of 0.19 nm/°C. © 2004 American Institute of Physics.
Show PACS
42.55.Px Semiconductor lasers; laser diodes

Enhancement of evanescent waves in waveguides using metamaterials of negative permittivity and permeability

De-Kui Qing and Gang Chen

Appl. Phys. Lett. 84, 669 (2004); http://dx.doi.org/10.1063/1.1645658 (3 pages) | Cited 20 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Electromagnetic waves in waveguides consisting of metamaterials with negative permittivity and permeability are analyzed. It is found that metamaterials can enhance the intensity of the evanescent waves in the cladding without altering the propagation constant of the waveguide for both TE and TM modes. This is a unique property of metamaterials. The enhancement factor increases with the increasing of the thickness of the metamaterial and saturates when complete surface polaritons were established at the interface between the metamaterial and the cladding. The enhancement effect can improve the performance of evanescent-wave-based waveguide devices. © 2004 American Institute of Physics.
Show PACS
84.40.Az Waveguides, transmission lines, striplines
77.22.Ch Permittivity (dielectric function)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Design of white light-emitting diodes using InGaN/AlInGaN quantum-well structures

D. Xiao, K. W. Kim, S. M. Bedair, and J. M. Zavada

Appl. Phys. Lett. 84, 672 (2004); http://dx.doi.org/10.1063/1.1644920 (3 pages) | Cited 20 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Based on the Rashba–Sheka–Pikus Hamiltonian in the vicinity of the Γ point, and taking into consideration spontaneous and piezoelectric polarization, the optical intensity of nitride-based quantum-well light-emitting diodes has been calculated. It is found that strain substantially alters the subband structure and thus the output intensity of these nitride-biased quantum-well light-emitting diodes. A design that uses AlInGaN as the quantum barrier is proposed to realize efficient red emission, which is hard to achieve if GaN is used as the barrier. In the proposed design, three different InGaN/AlInGaN quantum-well structures emit red, green, and blue light of similar intensity. Also, to achieve high efficiency, important factors related to the oscillator strength are discussed in detail. © 2004 American Institute of Physics.
Show PACS
73.21.Fg Quantum wells
78.67.De Quantum wells
85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
back to top
RSS Feeds

Nuclear reactions in copper induced by protons from a petawatt laser-foil interaction

J. M. Yang, P. McKenna, K. W. D. Ledingham, T. McCanny, S. Shimizu, L. Robson, R. J. Clarke, D. Neely, P. A. Norreys, M.-S. Wei, K. Krushelnick, P. Nilson, S. P. D. Mangles, and R. P. Singhal

Appl. Phys. Lett. 84, 675 (2004); http://dx.doi.org/10.1063/1.1645314 (3 pages) | Cited 4 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High-intensity (>1019 W cm−2) laser-plasma interactions have been shown to produce large quantities of protons with energies up to several tens of MeV. A range of laser-driven proton-induced reactions in copper have been investigated and the observed reactions quantified. The energy spectrum of the accelerated protons was determined from the reactions in a single thin copper foil and found to be in agreement with that deduced from (p,n) reactions measured in a stack of copper foils. The potential applications of this diagnostic technique are discussed. © 2004 American Institute of Physics.
Show PACS
52.38.Ph X-ray, γ-ray, and particle generation
back to top
RSS Feeds

Enhanced thermal stability of high-dielectric Gd2O3 films using ZrO2 incorporation

M.-H. Cho, D. W. Moon, S. A. Park, Y. S. Rho, Y. K. Kim, K. Jeong, C. H. Chang, J. H. Gu, J. H. Lee, and S. Y. Choi

Appl. Phys. Lett. 84, 678 (2004); http://dx.doi.org/10.1063/1.1644047 (3 pages) | Cited 2 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The thermal stability of Gd2O3 films, containing added Zr, was investigated using various techniques. The structural characteristics of epitaxial Gd2O3 are maintained on the Si(111) substrate when the Zr is codeposited along with Gd. The incorporation of ZrO2 into Gd2O3 improves the crystallinity of the film and no interfacial layers were observed. In particular, the structural stability with no deformation is greatly enhanced, and silicate formation is drastically suppressed, up to an annealing temperature of 800 °C. The interfacial defects caused by extensive interactions between Gd and Si are also minimized. © 2004 American Institute of Physics.
Show PACS
68.60.Dv Thermal stability; thermal effects
77.55.-g Dielectric thin films
81.40.Gh Other heat and thermomechanical treatments

Improved technique to determine second-order optical nonlinearity profiles using two different samples

A. Ozcan, M. J. F. Digonnet, and G. S. Kino

Appl. Phys. Lett. 84, 681 (2004); http://dx.doi.org/10.1063/1.1644622 (3 pages) | Cited 5 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
An improved inverse Fourier transform Maker fringe (MF) technique is described to retrieve the nonlinearity profile of thin films. It involves measuring the MF curve of two sandwich structures made by combining a pair of different nonlinear samples in two configurations. A simple algorithm is developed to process this data and retrieve the profile of both samples. Compared to our previous technique, which involves a single sandwich structure made of two identical samples, this technique is more flexible, it is insensitive to differences between the samples, and data processing is simpler and much faster. After a sample has been initially characterized by this technique, it can be used as a reference to characterize any other unknown sample using a single MF measurement. Experimental verification is demonstrated with a pair of thermally poled silica wafers. © 2004 American Institute of Physics.
Show PACS
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Nk Insulators
42.65.-k Nonlinear optics

Erbium-doped waveguide amplifiers fabricated using focused proton beam writing

K. Liu, E. Y. B. Pun, T. C. Sum, A. A. Bettiol, J. A. van Kan, and F. Watt

Appl. Phys. Lett. 84, 684 (2004); http://dx.doi.org/10.1063/1.1644922 (3 pages) | Cited 29 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Buried channel waveguides were fabricated in Er3+–Yb3+ codoped phosphate glasses using focused proton beam writing. Proton ion doses in the range of 1014–1015 ions/cm2 and 2.0 MeV energy were used. The waveguides were located 38 μm below the substrate surface and are in excellent agreement with the transport and range of ions in matter simulation. The waveguide properties were measured, and the fluorescence spectra and optical gain of the waveguides were characterized. The maximum net gain of the waveguide amplifiers at 1.534 μm wavelength was measured to be ∼1.72 dB/cm with 100 mW pump power at 975 nm wavelength. © 2004 American Institute of Physics.
Show PACS
42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers
42.65.Yj Optical parametric oscillators and amplifiers

Thermal conductivity of periodic microporous silicon films

David Song and Gang Chen

Appl. Phys. Lett. 84, 687 (2004); http://dx.doi.org/10.1063/1.1642753 (3 pages) | Cited 50 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This letter reports the experimental in-plane thermal conductivity of microfabricated, free-standing, single-crystal silicon thin films with periodically arranged through-film micropores. The experimental data suggest that strong size effects exist even in micro-sized porous silicon structures, particularly at low temperatures. Even at room temperature, all porous membranes show thermal conductivity values lower than expected by porosity and bulk phonon mean free path of silicon, and small-pore membranes have smaller thermal conductivity compared to the large-pore ones despite that they have close porosity values. © 2004 American Institute of Physics.
Show PACS
81.05.Rm Porous materials; granular materials
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.55.-a Thin film structure and morphology

GaN quantum dot density control by rf-plasma molecular beam epitaxy

J. Brown, F. Wu, P. M. Petroff, and J. S. Speck

Appl. Phys. Lett. 84, 690 (2004); http://dx.doi.org/10.1063/1.1645333 (3 pages) | Cited 32 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report on the growth of GaN quantum dots and the control of their density in the Stranski–Krastanov mode on AlN (0001) by rf-plasma molecular beam epitaxy at 750 °C. After depositing the equivalent of 2–3 ML GaN coverage, as limited by N fluence under Ga-droplet growth conditions, excess Ga was desorbed and Stranski–Krastanov islands formed under vacuum. We present the dependence of island density as a function of GaN coverage (for two growth rates: 0.10 and 0.23 ML/s), as estimated from atomic force microscopy and cross-sectional transmission electron microscopy. With a GaN growth rate of 0.23 ML/s, the island density was found to vary from less than 3.0×108–9.2×1010 cm−2 as the GaN coverage was varied from 2.2 (critical thickness) to 3.0 ML. For a GaN growth rate of 0.10 ML/s, the island density varied from 2.0×1010 to 7.0×1010 cm−2 over a GaN coverage range of 2.0–3.0 ML. For each growth rate, the GaN islands were found to be of nearly uniform size, independent of the quantum dot density. © 2004 American Institute of Physics.
Show PACS
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
68.43.Mn Adsorption kinetics
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)
52.77.Dq Plasma-based ion implantation and deposition

Optical properties of Cd1−xMgxTe (x = 0.00, 0.23, 0.31, and 0.43) alloy films

Y. S. Ihn, T. J. Kim, Y. D. Kim, D. E. Aspnes, and J. Kossut

Appl. Phys. Lett. 84, 693 (2004); http://dx.doi.org/10.1063/1.1639506 (3 pages) | Cited 4 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Pseudodielectric functions 〈ε〉 of Cd1−xMgxTe ternary alloy films of compositions x = 0.00, 0.23, 0.31, and 0.43 have been determined from 1.5 to 6.0 eV by spectroscopic ellipsometry. We obtain approximations to the bulk dielectric functions ε by performing wet-chemical etching to remove overlayers and using parametric modeling to remove interference oscillations below the fundamental band gap. The values of the E0, E0+Δ0, E1, E1+Δ1, E2, and E0′ critical point energies and their x dependences at room temperature were determined from numerically calculated second energy derivatives of these data. © 2004 American Institute of Physics.
Show PACS
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Air-bridged lateral growth of crack-free Al0.24Ga0.76N on highly relaxed porous GaN

R. S. Qhalid Fareed, V. Adivarahan, C. Q. Chen, S. Rai, E. Kuokstis, J. W. Yang, M. Asif Khan, J. Caissie, and R. J. Molnar

Appl. Phys. Lett. 84, 696 (2004); http://dx.doi.org/10.1063/1.1644621 (3 pages) | Cited 19 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report on the strain reduction in AlGaN layers grown on porous GaN (P-GaN) by metalorganic chemical vapor deposition (MOCVD). The P-GaN was obtained by ultraviolet radiation-enhanced electroless wet chemical etching of thick hydride vapor phase epitaxial grown GaN (HVPE-GaN) templates over (001) sapphire substrates. By optimizing the growth conditions, lateral growth of AlGaN was enhanced resulting in air-bridge formation between the P-GaN and the AlGaN layers. X-ray diffraction studies showed significant strain relaxation in AlGaN layers primarily due to the strain sharing between P-GaN and the AlGaN layers. This allowed us to grow crack-free good optical quality layers with thickness exceeding the critical limits for AlGaN deposition on the conventional MOCVD GaN or HVPE-GaN. The obtained results demonstrate the potential of this approach for the development of efficient ultraviolet light emitters. © 2004 American Institute of Physics.
Show PACS
68.60.Bs Mechanical and acoustical properties
81.05.Ea III-V semiconductors

Power-law load dependence of atomic friction

C. Fusco and A. Fasolino

Appl. Phys. Lett. 84, 699 (2004); http://dx.doi.org/10.1063/1.1644617 (3 pages) | Cited 3 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present a theoretical study of the dynamics of a tip scanning a graphite surface as a function of the applied load. From the analysis of the lateral forces, we extract the friction force and the corrugation of the effective tip-surface interaction potential. We find both the friction force and potential amplitude to have a power-law dependence on applied load with exponent ∼ 1.6. We interpret these results as characteristic of sharp undeformable tips in contrast to the case of macroscopic and elastic microscopic contacts. © 2004 American Institute of Physics.
Show PACS
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Cr2O3 surface layer and exchange bias in an acicular CrO2 particle

R. K. Zheng, Hui Liu, Y. Wang, and X. X. Zhang

Appl. Phys. Lett. 84, 702 (2004); http://dx.doi.org/10.1063/1.1644919 (3 pages) | Cited 22 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
It has been found by electron diffraction and high-resolution transmission electron microscopy that each commercial CrO2 particle is enclosed by an epitaxial Cr2O3 layer ∼2.5 nm thick. The epitaxial relationships of Cr2O3 layers on CrO2 particles have been identified. Magnetic hysteresis loops measured at different temperatures (5–300 K), after the sample was cooled from 350 K with a 50 kOe field, were found to be perfectly symmetrical, i.e., no exchange bias was observed, which is unexpected for ferromagnetic/antiferromagnetic core/shell structured particles. To gain a deeper understanding of the phenomenon, the “as-received” commercial CrO2 particles were annealed at 600 °C in air for 1 h to thicken the Cr2O3 shells. Exchange bias was clearly observed in the annealed particles with thicker Cr2O3 shells. At 5 K, the exchange bias field reached 220 Oe. These experimental observations can be explained well within the framework of the random field model. © 2004 American Institute of Physics.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
75.50.Dd Nonmetallic ferromagnetic materials
68.37.Lp Transmission electron microscopy (TEM)

Boron alloying in GaN

Laurian Escalanti and Gus L. W. Hart

Appl. Phys. Lett. 84, 705 (2004); http://dx.doi.org/10.1063/1.1644910 (3 pages) | Cited 5 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using first-principles calculations in the local density approximation, we studied effects of adding up to 6% boron to zinc-blende GaN. We found that the band gap increases monotonically with boron incorporation, in agreement with experiment. A composition-independent band-gap bowing parameter of 4.30 eV was determined, and proved to be large compared to bowing for other mixed cation systems. The formation enthalpy of mixing, ΔH, was determined for BxGa1−xN, BxGa1−xAs, and GaAs1−xNx. A comparison of enthalpies indicates that the production of BxGa1−xN films with boron concentrations of at least 5% may be possible. © 2004 American Institute of Physics.
Show PACS
65.40.G- Other thermodynamical quantities
68.43.Bc Ab initio calculations of adsorbate structure and reactions
64.75.-g Phase equilibria
71.20.Nr Semiconductor compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
82.60.Cx Enthalpies of combustion, reaction, and formation

Strain relaxation by directionally aligned precipitate nanoparticles in the growth of single-crystalline Gd-doped ceria thin films

D. X. Huang, C. L. Chen, L. Chen, and A. J. Jacobson

Appl. Phys. Lett. 84, 708 (2004); http://dx.doi.org/10.1063/1.1644035 (3 pages) | Cited 9 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Transmission electron microscopy has been used to investigate the microstructure and epitaxial behavior of gadolinium-doped ceria (Ce0.8Gd0.2O2−δ) thin films on single crystal (001) LaAlO3. The results show that the films have single-crystal cubic structure and a sharp interface with an interface relationship of (001)film∥(001)sub and [100]film∥[110]sub. Accompanying the high film crystallinity, a directionally aligned, precipitated nanoparticle structure has been observed. The precipitated particles have an average size of ∼4 nm, a Ga-rich composition of Ce0.7Gd0.3O2−δ, a rhombic shape with mainly {111} facets, and are uniformly distributed over the entire film area. The nanoparticles contribute a uniform tensile strain to the film that effectively compensates the compressive film strain induced by the substrate, and also leads to a uniform relaxation of the residual film strain by generating misfit dislocations at the film/particle interfaces. The high film crystallinity is believed to result from this uniform film strain relaxation mechanism. © 2004 American Institute of Physics.
Show PACS
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Wurtzite to zinc-blende phase transition in gallium nitride thin films

Joo Han Kim and Paul H. Holloway

Appl. Phys. Lett. 84, 711 (2004); http://dx.doi.org/10.1063/1.1640801 (3 pages) | Cited 17 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The phase transition in gallium nitride (GaN) thin films at room temperature from the thermodynamically stable wurtzite to the metastable zinc-blende structure is studied. The GaN films were grown at room temperature on (100)-oriented silicon substrates by radio-frequency planar magnetron sputtering of a GaN target in pure nitrogen atmosphere. As the nitrogen gas pressure during the film growth is decreased from 30 to 10 mTorr, the crystalline phase of GaN films changed from a hexagonal wurtzite to a cubic zinc-blende structure with (111) crystallographic planes oriented preferentially parallel to the film surface. The mechanisms responsible for the formation of the nonequilibrium cubic zinc-blende GaN phase at room temperature are suggested, in which the impact of the hyperthermal species impinging on the surface of growing films plays a key role in stabilizing the zinc-blende phase of GaN. © 2004 American Institute of Physics.
Show PACS
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
64.70.K- Solid-solid transitions

Molecular dynamics study of dislocation formation in a [001] face-centered-cubic epitaxial island under tensile stress

P. Liu, Y. W. Zhang, B. Fox, and C. Lu

Appl. Phys. Lett. 84, 714 (2004); http://dx.doi.org/10.1063/1.1644343 (3 pages) | Cited 1 time

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Dislocation formation in homoepitaxial pyramidal [001] Cu islands under tensile stress is studied using molecular dynamics simulations. It is found that 90° Shockley partial dislocations are dominant in the island strain relaxation. For a low-aspect-ratio island, the dislocations are nucleated from the island surface and propagate downwards to form misfit dislocations. For a high-aspect-ratio island, a pair of the dislocations on the same slip plane are simultaneously nucleated respectively from the two island edges, propagate inwards, and react to form a 90° Shockley misfit partial dislocation. These dislocations can form sequentially and cooperatively. © 2004 American Institute of Physics.
Show PACS
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Bb Theories and models of crystal defects

Intense blue–white luminescence from carbon-doped silicon-rich silicon oxide

Se-Young Seo, Kwan-Sik Cho, and Jung H. Shin

Appl. Phys. Lett. 84, 717 (2004); http://dx.doi.org/10.1063/1.1645989 (3 pages) | Cited 31 times

Online Publication Date: 27 January 2004

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The effect of carbon doping on the enhancement of visible luminescence from silicon-rich silicon oxide (SRSO), which consists of Si nanoclusters embedded inside a SiO2 matrix, is investigated. C-doped SRSO films were fabricated by electron cyclotron resonance-plasma enhanced chemical vapor deposition method using SiH4, O2, and CH4 source gases followed by a high-temperature anneal. Intense blue-white visible luminescence, visible to the naked eye under daylight conditions, was observed from the film with a nearly equal amount of C and excess Si (∼16 at. %) after an anneal at 950 °C. Furthermore luminescence could be tuned from 1.8 to 2.5 eV by controlling the C to excess Si ratio, the C content, and the anneal temperature. Taken together with the infrared absorption spectra, these results indicate that the luminescence is attributed to exciton recombination in C-incorporated Si nanoclusters. © 2004 American Institute of Physics.
Show PACS
78.55.Ap Elemental semiconductors
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.S- Impurities in crystals
78.30.Am Elemental semiconductors and insulators
71.35.-y Excitons and related phenomena
Page 1 of 3 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close