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20 Mar 2000

Volume 76, Issue 12, pp. 1489-1630

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Brittle-ductile relaxation kinetics of strained AlGaN/GaN heterostructures

S. J. Hearne, J. Han, S. R. Lee, J. A. Floro, D. M. Follstaedt, E. Chason, and I. S. T. Tsong

Appl. Phys. Lett. 76, 1534 (2000); http://dx.doi.org/10.1063/1.126087 (3 pages) | Cited 48 times

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We have directly measured the stress evolution during metal-organic chemical vapor deposition of AlGaN/GaN heterostructures on sapphire. In situ stress measurements were correlated with ex situ microstructural analysis to determine directly a critical thickness for cracking and the subsequent relaxation kinetics of tensile-strained AlxGa1−xN grown on GaN. Cracks appear to initiate the formation of misfit dislocations at the AlGaN/GaN interface, which account for the majority of the strain relaxation. © 2000 American Institute of Physics.
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62.20.M- Structural failure of materials
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Effects of surface resonance state on the plasmon resonance absorption of Ag nanoparticles embedded in partially oxidized amorphous Si matrix

L. Yang, G. H. Li, and L. D. Zhang

Appl. Phys. Lett. 76, 1537 (2000); http://dx.doi.org/10.1063/1.126088 (3 pages) | Cited 37 times

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Nanocomposite films consisting of nanosized Ag particles embedded in partially oxidized amorphous Si matrices were prepared by radio frequency cosputtering deposition. Subsequent heat treatment at different temperatures ranging from 200 to 500 °C and its effects on the optical absorption of the films were investigated by spectrometry in the wavelength ranging from 200 to 1200 nm. “Surface resonance state” is introduced to discuss the broadening, blue-shift, and intensity decrease of the plasmon resonance absorption peak with decreasing Ag particle size. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys
78.40.Kc Metals, semimetals, and alloys

Photoluminescence of CdSe nanocrystallites embedded in BaTiO3 matrix

Ji Zhou, Longtu Li, Zhilun Gui, S. Buddhudu, and Yan Zhou

Appl. Phys. Lett. 76, 1540 (2000); http://dx.doi.org/10.1063/1.126089 (3 pages) | Cited 18 times

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This letter reports the photoluminescence properties of CdSe quantum dots (QDs) embedded in a ferroelectric BaTiO3 matrix. The main emission from the samples has been assigned to the band–edge transition of QDs. With an increase in the heat treatment temperature, the emission peak has been shifted to a longer wavelength. This shift has been attributed due to the dielectric environment effects of the matrix on the electronic structure of the QDs. The dependences of the peak position on the heat-treatment temperature and dot size are found in agreement with the theoretical simulation results reported previously. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.46.-w Structure of nanoscale materials

Self-enhancement in the electroluminescence of a near-infrared ionic dye

Hiroyuki Suzuki

Appl. Phys. Lett. 76, 1543 (2000); http://dx.doi.org/10.1063/1.126090 (3 pages) | Cited 25 times

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This letter reports self-enhancement behavior observed in the near-infrared electroluminescence (EL) of an ionic dye, 2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methylbenzothiazolium perchlorate doped in poly(N-vinylcarbazole). The EL intensity measured under a constant current, and therefore, the external EL quantum efficiency (ϕex), increases with time both when the EL is generated continuously in a constant current mode and kept in a no-bias field, whereas it decreases in a reverse-bias field. With an enhancement factor of about 80 under a constant current of 0.1 mA/cm2, ϕex reaches the 1% photons/electron level. I conclude that the behavior originates from the enhanced electron and hole injection caused by the alignment of the doped ionic dye molecules along the bias field. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence

Recombination dynamics of carriers in an InGaN/AlGaN single-quantum-well light-emitting diode under reverse-bias voltages

Hiromitsu Kudo, Hiroki Ishibashi, Ruisheng Zheng, Yoichi Yamada, and Tsunemasa Taguchi

Appl. Phys. Lett. 76, 1546 (2000); http://dx.doi.org/10.1063/1.126091 (3 pages) | Cited 7 times

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The radiative recombination process of the blue emission band in an InGaN single-quantum-well light-emitting diode has extensively been investigated by means of the dependence of an external electric field on photoluminescence and time-resolved photoluminescence spectra. Two emission (higher and lower) components separated by about 40 meV are found in the emission band on the condition of reverse bias at 77 K. It is also found that the luminescence intensity decreases dramatically with increasing reverse-bias voltage at room temperature. The model based on field ionization of excitons cannot explain the present experimental phenomena. It is, therefore, suggested that the free-carrier recombination process is dominant at room temperature. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.47.-p Spectroscopy of solid state dynamics
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Relationship between optical properties and crystallinity of nanometer Y2O3:Eu phosphor

T. Igarashi, M. Ihara, T. Kusunoki, K. Ohno, T. Isobe, and M. Senna

Appl. Phys. Lett. 76, 1549 (2000); http://dx.doi.org/10.1063/1.126092 (3 pages) | Cited 95 times

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Y2O3-doped Eu3+ (Y2O3:Eu) nanometer particles (NPs) were synthesized via a chemical route. The particle size estimated by x-ray diffractometry and transmission electron microscopy was about 61 nm. Two photoluminescence peaks were observed at 582 and 587 nm, being attributed to the transition of 5D0→7F1a of Eu3+ in the S6 and C2 symmetry sites of Y2O3, respectively. The intensity ratio of the photoluminescence peaks at 582 nm to at 587 nm was larger for NPs than for micrometer particles (MPs). The excitation peak of NPs due to the charge-transfer band shifted toward the high-energy side as compared with that of MPs. According to x-ray diffractometry, the lattice distortion and the lattice constant were larger for NPs than for MPs, showing the restructure at the near surface and the increase in ionicity of the Eu–O bond with decreasing particle size. This explains the blueshift in the excitation peak. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
61.66.Fn Inorganic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.50.Lt Crystal binding; cohesive energy

Structures of nitridated layers on sapphire studied by x-ray reflectivity and diffraction

Ki-Sung Kim, Seon-Hyo Kim, and Dong-Ryul Lee

Appl. Phys. Lett. 76, 1552 (2000); http://dx.doi.org/10.1063/1.126093 (3 pages) | Cited 6 times

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A nitridated layer of c-plane sapphire was studied by using synchrotron x-ray reflectivity and diffraction measurements. The nitridation of the sapphire surface produced an epitaxial AlN layer with a low mosaicity (1 arcmin) normal to the surface. The nitridation temperature determined the limiting thickness for the nitridated layer. Excessive nitridation beyond the limiting thickness caused strain relaxation by a reduction of lateral domain size and an increase in lateral mosaicity. Therefore, the nitridated layer with compressive strain may provide better nucleation sites for the subsequent GaN overlayer growth than the strain-relaxed one. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Np Solid phase epitaxy; growth from solid phases
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
78.20.-e Optical properties of bulk materials and thin films

Experimental measurements of the strength of metals approaching the theoretical limit predicted by the equation of state

E. Moshe, S. Eliezer, Z. Henis, M. Werdiger, E. Dekel, Y. Horovitz, S. Maman, I. B. Goldberg, and D. Eliezer

Appl. Phys. Lett. 76, 1555 (2000); http://dx.doi.org/10.1063/1.126094 (3 pages) | Cited 29 times

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The approach to the ultimate strength of metals is determined experimentally. The ultimate strength of metals was calculated using a realistic wide-range equation of state. The strength of metals was measured using shock waves created in aluminum and copper foils with a short- (20–100 ps) pulse high-power laser. The strength of the materials was determined from the free-surface-velocity time history, which was measured with an optically recording velocity interferometer system. The strain rates in these experiments were in the range (1.5–5)×108 s−1. © 2000 American Institute of Physics.
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64.30.-t Equations of state of specific substances
62.50.-p High-pressure effects in solids and liquids
79.20.Ds Laser-beam impact phenomena
62.20.-x Mechanical properties of solids
81.40.Gh Other heat and thermomechanical treatments

Adatom condensation and quantum dot sizes in InGaAs/GaAs (001)

R. Leon, J. Wellman, X. Z. Liao, J. Zou, and D. J. H. Cockayne

Appl. Phys. Lett. 76, 1558 (2000); http://dx.doi.org/10.1063/1.126095 (3 pages) | Cited 11 times

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The sizes and concentrations of capped and surface InGaAs/GaAs quantum dots (QDs) grown under the same conditions have been investigated. Comparisons obtained with transmission electron microscopy and scanning probe microscopy imaging show a significant enlargement in the sizes of surface QDs compared with capped QDs. This discrepancy in dot dimensions increases with decreasing island surface densities and can be partially explained by thermal adatom condensation during sample cooling. These findings suggest a technique to estimate adatom concentrations and their migration lengths in strained heteroepitaxy. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.35.Fx Diffusion; interface formation
61.46.-w Structure of nanoscale materials

Bandgap closure of a flattened semiconductor carbon nanotube: A first-principles study

Mário S. C. Mazzoni and H. Chacham

Appl. Phys. Lett. 76, 1561 (2000); http://dx.doi.org/10.1063/1.126096 (3 pages) | Cited 41 times

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We investigate, through first-principles calculations, the effects of a flattening distortion on the electronic properties of a semiconductor carbon nanotube. The flattening causes a progressive reduction of the band gap from 0.92 eV to zero. The band-overlap insulator-metal transition occurs for an interlayer distance of 4.6 Å. Supposing that the flattening of the nanotube can be produced by a force applied by a scanning microscope tip, we estimate that the force per unit length of the nanotube that is necessary to reach the insulator-metal transition is 7.4 N/m. © 2000 American Institute of Physics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.05.ub Fullerenes and related materials
71.30.+h Metal-insulator transitions and other electronic transitions
71.15.-m Methods of electronic structure calculations

Coiled structure of eccentric coaxial nanocable made of amorphous boron and silicon oxide

K. Suenaga, Y. Zhang, and S. Iijima

Appl. Phys. Lett. 76, 1564 (2000); http://dx.doi.org/10.1063/1.126119 (3 pages) | Cited 14 times

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Exotic nanocable with coiled structure has been found in soot obtained by a reactive laser ablation as a byproduct of the formerly reported coaxial nanocables [Y. Zhang, K. Suenaga, C. Colliex, and S. Iijima, Science 281, 973 (1998)]. Electron energy-loss spectroscopic imaging has revealed the coaxial structure made of amorphous boron and silicon dioxide with amorphous carbon sheath. We infer that the coiled structure is attributed to a difference in the growth rate between amorphous boron and silicon dioxide that are found to comprise eccentric coaxial nanocable. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
79.20.Kz Other electron-impact emission phenomena
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