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7 Jun 2004

Volume 84, Issue 23, pp. 4599-4816

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Appl. Phys. Lett. 84, 4650 (2004); http://dx.doi.org/10.1063/1.1759390 (3 pages)

David I. Woodward, Ian M. Reaney, Gaiying Y. Yang, Elizabeth C. Dickey, and Clive A. Randall
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Enhanced strain relaxation in a two-step process of GexSi1−x/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

Yu. B. Bolkhovityanov, A. S. Deryabin, A. K. Gutakovskii, M. A. Revenko, and L. V. Sokolov

Appl. Phys. Lett. 84, 4599 (2004); http://dx.doi.org/10.1063/1.1734683 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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Two-layer GexSi1−x heterostructures, with a finite fraction of germanium up to x = 0.48 and a thickness of at most 0.65 μm, were grown by molecular-beam epitaxy. It is shown that plastic relaxation of the second step is significantly enhanced. It is assumed that threading dislocations with a density of 105–106 cm−2, which appear in the first step in the process of its plastic relaxation, are sources of misfit dislocations positioned between the first and second steps. Cross-sectional transmission electron microscopy showed the superior quality of the dislocation network in the stepped regions. Threading dislocation densities in the second step were determined with the help of etching pits and were found to be close to 105 cm−2. © 2004 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Hd Other semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Thermal diffusivity and conductivity of supercooled liquid in Zr41Ti14Cu12Ni10Be23 metallic glass

Michiaki Yamasaki, Shinya Kagao, Yoshihito Kawamura, and Kenji Yoshimura

Appl. Phys. Lett. 84, 4653 (2004); http://dx.doi.org/10.1063/1.1759768 (3 pages) | Cited 21 times

Online Publication Date: 19 May 2004

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We measured the thermal diffusivity of amorphous solid and supercooled liquid in a Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) and its crystalline counterpart alloy at temperatures ranging from room temperature to 700 K, using a laser flash method. The thermal diffusivity and conductivity of the amorphous solid were weakly temperature dependent and increased with increasing temperature up to the glass transition temperature. The thermal diffusivity of the supercooled liquid was approximately 3.5×10−6 m2 s−1 and quite constant with temperature. The amorphous solid and supercooled liquid of Zr41Ti14Cu12Ni10Be23 BMG showed lower thermal diffusivity and conductivity than the crystalline counterpart in the range from room temperature to crystallization temperature. © 2004 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
64.70.K- Solid-solid transitions

Stress profile and thermal expansion of layered materials determined from surface stresses

Jürgen Malzbender

Appl. Phys. Lett. 84, 4661 (2004); http://dx.doi.org/10.1063/1.1759773 (2 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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A simple method of inferring the stress profile and the effective difference in thermal expansion or strain in an unconstrained elastic multilayer system from a measurement of a limited number of surface stresses as obtained for example using x-ray diffraction or Raman spectroscopy is outlined. Explicit relationships are given for bilayered systems. The analysis procedure is exemplified for literature data of electronics materials, solid oxide fuel cells and thermal barrier systems. Following the outlined procedure, a determination of the stress profile and difference in thermal expansion for composites of alternating layers is also possible. © 2004 American Institute of Physics.
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65.40.De Thermal expansion; thermomechanical effects
78.30.Hv Other nonmetallic inorganics
82.47.Ed Solid-oxide fuel cells (SOFC)

Material modifications induced by laser annealing in two-dimensional structures

Antonino La Magna, Paola Alippi, Vittorio Privitera, Silvia Scalese, Salvatore Pannitteri, Guglielmo Fortunato, Luigi Mariucci, and Marco Camalleri

Appl. Phys. Lett. 84, 4738 (2004); http://dx.doi.org/10.1063/1.1759772 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2004

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The effects of the laser irradiation on metal-oxide-semiconductor structures are investigated by means of a phase-field methodology. We numerically solved the model equations in one- and two-dimensional structures also containing SiO2/amorphous-Si/crystalline-Si stacks. The simulated laser annealing processes are discussed in detail, pointing out the influence of the geometrical constraints on the irradiation effects in the samples. The simulation results are compared with the experimental two-dimensional delineation of dopant profiles. These comparisons show the importance of the joint theoretical and experimental investigations in order to fully understand the phenomena occurring in submicron sized laser irradiated structures. © 2004 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.-d Radiation effects on specific materials

Influence of buffer layers on metalorganic vapor phase epitaxy grown GaN on Si(001)

F. Schulze, A. Dadgar, J. Bläsing, and A. Krost

Appl. Phys. Lett. 84, 4747 (2004); http://dx.doi.org/10.1063/1.1760214 (3 pages) | Cited 12 times

Online Publication Date: 20 May 2004

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GaN layers grown by metalorganic vapor phase epitaxy on Si(001) substrates were investigated by x-ray analysis and scanning electron microscopy. Several sample series were grown changing the AlN/GaN buffer layer deposition temperature, sequence, and thickness. By variation of the buffer layer structure, two different growth orientations could be realized. First, GaN grows c-axis oriented on the Si(001) substrates with two rotational alignments. Second, the r plane (10math2) of the hexagonal GaN-structure is oriented parallel to the surface. In the latter case, four rotational in-plane alignments are observed. By a miscut (2°–6° off) of the Si substrates one of these alignments is preferred. © 2004 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
68.47.Fg Semiconductor surfaces
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Strain relaxation in AlN/GaN bilayer films grown on γ-LiAlO2(100) for nanoelectromechanical systems

Y. Takagaki, Y. J. Sun, O. Brandt, and K. H. Ploog

Appl. Phys. Lett. 84, 4756 (2004); http://dx.doi.org/10.1063/1.1751224 (3 pages) | Cited 4 times

Online Publication Date: 21 May 2004

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We fabricate submicrometer-wide cantilevers and beams from M-plane AlN/GaN bilayer films grown on γ-LiAlO2(100) substrates. The chemically reactive substrate is ideal for fabrication of nanoelectromechanical systems using the light, stiff, and piezoelectrically active AlN. The absence of polarization fields in M-plane quantum wells allows us to incorporate optical functionalities in the (Al,Ga)N-based nanoelectromechanical systems. Self-rolling of the cantilevers indicates that the bilayer films are strained at the AlN–GaN interface along the a axis, whereas the strain is roughly completely relaxed along the c axis. We examine the partial relaxation of the strain along the a axis when the layer thickness is varied. © 2004 American Institute of Physics.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

Rapid cryofixation/freeze fracture for the study of nanobubbles at solid–liquid interfaces

M. Switkes and J. W. Ruberti

Appl. Phys. Lett. 84, 4759 (2004); http://dx.doi.org/10.1063/1.1755837 (3 pages) | Cited 35 times

Online Publication Date: 21 May 2004

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A technique borrowed from biology, rapid cryofixation/freeze fracture, has been adapted for the study of liquid–solid interfaces. This technique allows high-resolution imaging of the interfaces between water and substrates with varying degrees of hydrophobicity. The interface between gas-saturated water and hydrophobic surfaces is covered with a network of 100 nm scale features similar to those previously reported, while degassed water produces smooth interfaces. We thus confirm that the features are indeed nanobubbles which form spontaneously from dissolved gas in the liquid. The interface of gas-saturated water and a hydrophilic surface, while showing no evidence of nanobubbles, is not as smooth as the degassed interface. © 2004 American Institute of Physics.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
64.70.D- Solid-liquid transitions
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Role of electron–phonon coupling in thermal conductance of metal–nonmetal interfaces

Arun Majumdar and Pramod Reddy

Appl. Phys. Lett. 84, 4768 (2004); http://dx.doi.org/10.1063/1.1758301 (3 pages) | Cited 85 times

Online Publication Date: 21 May 2004

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We theoretically show that the thermal conductance associated with electron–phonon coupling in a metal near a metal–nonmetal interface can be estimated as hep = math, where G is the volumetric electron–phonon coupling constant and kp is the phonon or lattice thermal conductivity of the metal. The expression suggests hep ≈ 1/math at temperatures comparable to the Debye temperature of the metal. The predicted values of hep fall within the range of conductance values experimentally observed (0.3–1 GW/m2 K), suggesting that it cannot be ignored, and could even play a dominant role at high temperatures. Predictions of the total thermal conductance, that include both electron–phonon and phonon–phonon interfacial conductances, show reasonable agreement in its temperature dependence with experimental data for TiN/MgO interfaces. © 2004 American Institute of Physics.
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63.20.K- Phonon interactions
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.35.Ja Surface and interface dynamics and vibrations

Stimulated resonance Raman scattering from epitaxially oriented crystals of biphenyl-capped thiophene

Hisao Yanagi and Atsutoshi Yoshiki

Appl. Phys. Lett. 84, 4783 (2004); http://dx.doi.org/10.1063/1.1760223 (3 pages) | Cited 14 times

Online Publication Date: 21 May 2004

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Spectrally narrowed light emission based on stimulated resonance Raman scattering has been observed for epitaxially grown needle crystals of a biphenyl-capped thiophene oligomer. Under optical pumping with a wavelength-tuned pulse laser, the crystals emitted a couple of sharp lines (full width at half maximum ∼0.3 nm) along the direction of the needle axis. In particular, the intense line with a Raman shift of 1435 cm−1 appeared at low excitation energy of a few μJ/pulse. This Raman line was assigned as the symmetric in-plane stretching mode of the molecule. The observed Raman-associated lasing suggests the presence of polaritonic interaction between the uniaxially ordered molecular excitons and emitted photons. © 2004 American Institute of Physics.
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78.30.Jw Organic compounds, polymers
78.66.Qn Polymers; organic compounds

Formation of titanium-solute clusters in alumina: A first-principles study

K. Matsunaga, T. Mizoguchi, A. Nakamura, T. Yamamoto, and Y. Ikuhara

Appl. Phys. Lett. 84, 4795 (2004); http://dx.doi.org/10.1063/1.1760598 (3 pages) | Cited 4 times

Online Publication Date: 21 May 2004

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Electronic structures and stability of substitutional Ti3+ clusters in Al2O3 were investigated by first-principles pseudopotential calculations using large supercells. It was found that a substitutional Ti3+ defect induces an extra defect level in the band gap, and the defect levels have strong bonding interactions in the cluster formation. In addition, binding energies of Ti3+ clusters increased with increasing numbers of Ti3+ ions, indicating that cluster formation is energetically favorable. The resulting impurity band within the band gap of Al2O3 will contribute to the significant electronic conduction of Ti-doped Al2O3 observed experimentally. © 2004 American Institute of Physics.
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71.20.Ps Other inorganic compounds
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.55.Ht Other nonmetals
71.15.Nc Total energy and cohesive energy calculations

Microscale polymeric helical structures produced by electrospinning

Royal Kessick and Gary Tepper

Appl. Phys. Lett. 84, 4807 (2004); http://dx.doi.org/10.1063/1.1762704 (3 pages) | Cited 22 times

Online Publication Date: 21 May 2004

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Microscale helical coils consisting of a composite of one conducting and one nonconducting polymer were produced using electrospinning. The nonconducting polymer was poly(ethylene oxide) and the conducting polymer was poly(aniline sulfonic acid). The coil structures were studied over a range of processing conditions and fiber composition. The data suggest that the helical structures are formed due to viscoelastic contraction upon partial neutralization of the charged fibers. Polymeric microcoils may find applications in microelectromechanical systems, advanced optical components, and drug delivery systems. © 2004 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Terahertz emission by InN

Ricardo Ascázubi, Ingrid Wilke, Kyle Denniston, Hai Lu, and William J. Schaff

Appl. Phys. Lett. 84, 4810 (2004); http://dx.doi.org/10.1063/1.1759385 (3 pages) | Cited 55 times

Online Publication Date: 21 May 2004

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We report on optically excited terahertz (THz) emission by indium nitride (InN) thin films. We have used 70 fs titanium–sapphire laser pulses with wavelengths at 800 nm to generate THz-radiation pulses. The InN thin films are deposited on sapphire substrates with GaN buffer layer by molecular-beam epitaxy. The THz-radiation emitted from the InN surface is significantly stronger than that of the GaN/InN interface. The origin of the THz emission are transient photocarrier currents. These results are in agreement with recent experimental results of InN which show that this material is a small band-gap semiconductor. The magnitude of the THz emission from the InN is strong compared to THz emission from previously investigated semiconductors. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
84.40.-x Radiowave and microwave (including millimeter wave) technology
78.70.Gq Microwave and radio-frequency interactions
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
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