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11 Apr 2005

Volume 86, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 152101 (2005); http://dx.doi.org/10.1063/1.1897831 (3 pages)

Walid Hafez and Milton Feng
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Noncontact density measurements of liquid, undercooled, and high temperature solid boron

Paul-François Paradis, Takehiko Ishikawa, and Shinichi Yoda

Appl. Phys. Lett. 86, 151901 (2005); http://dx.doi.org/10.1063/1.1900954 (3 pages) | Cited 5 times

Online Publication Date: 4 April 2005

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Electrostatic levitation in vacuum prevented contamination and multibeam heating overcame sample position stability problems occurring when handling boron at high temperatures. This allowed the density determination of the liquid as well as the high temperature solid states. Over the 2275–2460 K interval, the density of the liquid and undercooled phases was measured as ρL(T) = 2.17×103–0.25(T–Tm)kg m−3, where Tm is the melting temperature (2360 K). Similarly, the density of the solid phase was measured as ρS(T) = 2.11×103−0.09(T–Tm)kg m−3 over the 2010–2360 K range. These data provided clear experimental evidence that boron contracts (nearly 3%) upon melting, thus settling a decade long debate.
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06.30.Dr Mass and density
64.70.D- Solid-liquid transitions
81.30.Fb Solidification

Enhanced boron diffusion in excimer laser preannealed Si

E. V. Monakhov, B. G. Svensson, M. K. Linnarsson, A. La Magna, C. Spinella, C. Bongiorno, V. Privitera, G. Fortunato, and L. Mariucci

Appl. Phys. Lett. 86, 151902 (2005); http://dx.doi.org/10.1063/1.1899765 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2005

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We have investigated boron diffusion during rapid thermal annealing in Si implanted with boron using an energy of 1 keV and a dose of 1×1016 cm−2. Two types of samples have been studied: As-implanted and pretreated with excimer laser annealing. For both types an enhanced diffusion of boron has been observed with an enhancement by a factor of 3–5 over the “standard” diffusion. It is suggested that the high concentration of implanted boron is a dominant factor for the diffusion enhancement as compared to the effect of implantation-induced damage. The data indicate that the proximity of the surface can also affect the boron diffusion enhancement.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors
61.72.uf Ge and Si
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.S- Impurities in crystals

Diffusion mechanisms of indium and nitrogen during the annealing of InGaAs quantum wells with GaNAs barriers and GaAs spacer layers

Michael M. Oye, Sridhar Govindaraju, Rubin Sidhu, Jason M. Reifsnider, and Archie L. Holmes

Appl. Phys. Lett. 86, 151903 (2005); http://dx.doi.org/10.1063/1.1900298 (3 pages) | Cited 8 times

Online Publication Date: 5 April 2005

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In this article, we discuss two indium diffusion mechanisms that are present during the rapid thermal annealing of InxGa1−xAs quantum wells (x = 0.18, 0.22, and 0.26) with GaNyAs1−y barriers (y = 0.6 or 1.2%). Samples were grown with and without a GaAs spacer layer in between the quantum well and barrier. The dominant mechanism is dependent on the amount of thermal energy applied during the annealing process. At low annealing times and temperatures, we have observed that In-Ga intra-diffusion entirely within the quantum well is dominant. For the higher times and temperatures, In-Ga inter-diffusion between the quantum well and barrier becomes dominant. These observations were confirmed by high-resolution x-ray diffraction and the peak emission wavelengths were measured by room-temperature photoluminescence. We have also observed that nitrogen had diffused from the GaNAs barriers into the InGaAs quantum wells in all of our annealed samples. In addition, the commonly observed indium-content dependent diffusion in GaInNAs-based systems was not observed with InGaAs/GaNAs-based structures.
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61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells

Shallow BF2 implants in Xe-bombardment-preamorphized Si: The interaction between Xe and F

M. Werner, J. A. van den Berg, D. G. Armour, G. Carter, T. Feudel, M. Herden, M. Bersani, D. Giubertoni, L. Ottaviano, C. Bongiorno, G. Mannino, P. Bailey, and T. C. Q. Noakes

Appl. Phys. Lett. 86, 151904 (2005); http://dx.doi.org/10.1063/1.1900305 (3 pages) | Cited 3 times

Online Publication Date: 5 April 2005

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Si(100) samples, preamorphized to a depth of ∼ 30 nm using 20 keV Xe ions to a nominal fluence of 2×1014 cm−2 were implanted with 1 and 3 keV BF2 ions to fluences of 7×1014 cm−2. Following annealing over a range of temperatures (from 600 to 1130 °C) and times the implant redistribution was investigated using medium-energy ion scattering (MEIS), secondary ion mass spectrometry (SIMS), and energy filtered transmission electron microscopy (EFTEM). MEIS studies showed that for all annealing conditions leading to solid phase epitaxial regrowth, approximately half of the Xe had accumulated at depths of 7 nm for the 1 keV and at 13 nm for the 3 keV BF2 implant. These depths correspond to the end of range of the B and F within the amorphous Si. SIMS showed that in the preamorphized samples, approximately 10% of the F migrates into the bulk and is trapped at the same depths in a ∼ 1:1 ratio to Xe. These observations indicate an interaction between the Xe and F implants and a damage structure that becomes a trapping site. A small fraction of the implanted B is also trapped at this depth. EXTEM micrographs suggest the development of Xe agglomerates at the depths determined by MEIS. The effect is interpreted in terms of the formation of a volume defect structure within the amorphized Si, leading to F stabilized Xe agglomerates or XeF precipitates.
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61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
66.30.Lw Diffusion of other defects
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.S- Impurities in crystals
68.37.Lp Transmission electron microscopy (TEM)

Misfit accommodation of compact and columnar InN epilayers grown on Ga-face GaN (0001) by molecular-beam epitaxy

Th. Kehagias, A. Delimitis, Ph. Komninou, E. Iliopoulos, E. Dimakis, A. Georgakilas, and G. Nouet

Appl. Phys. Lett. 86, 151905 (2005); http://dx.doi.org/10.1063/1.1900310 (3 pages) | Cited 19 times

Online Publication Date: 5 April 2005

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The interfacial structural properties of compact InN films and of noncoalesced three-dimensional InN islands, grown by molecular-beam epitaxy on Ga-face GaN/Al2O3 (0001) substrates, were investigated by transmission electron microscopy. Compact film growth was accomplished employing an InN nucleation layer, grown at low substrate temperatures. A 60° misfit dislocation network effectively accommodated the lattice mismatch in the InN/GaN interface in both cases of epilayers. The lattice constants of InN were determined by electron diffraction analysis, revealing a 0.28% larger in-plane parameter of the compact InN film relative to the corresponding lattice parameter of the InN islands. This is attributed to thermal tensile strain developed during post-growth cooling down of the epilayers, which also compensated the remaining compressive strain originating from the in-plane lattice mismatch of InN and GaN.
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81.05.Ea III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Pronounced photorefractive effect at wavelength over 1000 nm in monolithic organic materials

Wei You, Zhanjia Hou, and Luping Yu

Appl. Phys. Lett. 86, 151906 (2005); http://dx.doi.org/10.1063/1.1900926 (3 pages) | Cited 2 times

Online Publication Date: 5 April 2005

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Two monolithic organic materials exhibiting high photorefractive (PR) performances at a wavelength of 1064 nm were prepared and characterized. It was found that thiophene-based molecule T6 demonstrated better PR properties than benzene based molecule B6. A net optical gain of 139.1 cm−1 at a low applied field of 43.7 V/μm and a diffraction efficiency of 45.6% at 35.3 V/μm were observed for materials made from T6. Net optical gain at 1300 nm was also observed for T6. The differences in PR behavior between two materials with similar structures were explained based on dipole moment and photoconductivity differences.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.20.Ek Optical activity
72.40.+w Photoconduction and photovoltaic effects
78.40.Me Organic compounds and polymers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Exceptionally high glass-forming ability of an FeCoCrMoCBY alloy

Jun Shen, Qingjun Chen, Jianfei Sun, Hongbo Fan, and Gang Wang

Appl. Phys. Lett. 86, 151907 (2005); http://dx.doi.org/10.1063/1.1897426 (3 pages) | Cited 91 times

Online Publication Date: 5 April 2005

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It has been well documented that the maximum thickness of as-cast glassy samples attainable through conventional metallurgical routes is the decisive criteria for measuring the glass-forming ability (GFA) of bulk metallic glasses (BMGs). Here we report the exceptionally high GFA of an FeCoCrMoCBY alloy which can be fabricated in the form of glassy rods with a maximum sample thickness of at least 16 mm. It is demonstrated that, by substituting Fe with a proper amount of Co in a previously reported Fe-based BMG alloy, the glass formation of the resultant new alloy can be extensively favored both thermodynamically and kinetically. The new ferrous BMG alloy also exhibits a high fracture strength of 3500 MPa and Vickers hardness of 1253 kg mm−2.
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81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
65.40.G- Other thermodynamical quantities
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness

Nd-doped GdVO4 films prepared by pulsed-laser deposition on SiO2/Si substrate

Z. G. Dong, F. Y. Wang, Y. X. Fan, P. Lu, S. N. Zhu, P. K. Lim, and T. B. Tang

Appl. Phys. Lett. 86, 151908 (2005); http://dx.doi.org/10.1063/1.1898439 (3 pages)

Online Publication Date: 6 April 2005

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Nd-doped GdVO4(Nd:GdVO4) films with a-axis preferred orientation were fabricated on SiO2/Si substrate by pulsed-laser deposition. Fluorescences at around 1065.0 and 1342.5 nm, corresponding to math→math and math→math transitions, respectively, were excited simultaneously with an 808 nm diode laser. Waveguide behaviors in the film were investigated by using the prism coupling technique at the wavelength of 632.8 nm. Both TE and TM mode spectra revealed that favorable light confinements were achieved within the Nd:GdVO4 waveguide layer. Additionally, the optically anisotropic properties of the film were studied in detail.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Xi Diode-pumped lasers
81.15.Fg Pulsed laser ablation deposition
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
42.82.Gw Other integrated-optical elements and systems

Negative refraction of a combined double S-shaped metamaterial

Hongsheng Chen, Lixin Ran, Jiangtao Huangfu, Xianmin Zhang, Kangsheng Chen, Tomasz M. Grzegorczyk, and Jin Au Kong

Appl. Phys. Lett. 86, 151909 (2005); http://dx.doi.org/10.1063/1.1897045 (3 pages) | Cited 28 times

Online Publication Date: 6 April 2005

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We present a combined double S-shaped metamaterial structure that exhibits a left-handed property over a wide frequency band of 6 GHz. The transmission experiment, phase measurement, and prism refraction experiment from the structure confirm the presence of the negative index of refraction.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Resolving hydrogen binding sites by pressure—A first-principles prediction for ZnO

Sukit Limpijumnong and S. B. Zhang

Appl. Phys. Lett. 86, 151910 (2005); http://dx.doi.org/10.1063/1.1900935 (3 pages) | Cited 22 times

Online Publication Date: 6 April 2005

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The binding sites and vibrational frequencies ω of H in ZnO are studied by first-principles total-energy calculations. In the past, different experiments have observed different primary H vibrational modes, making the comparison with theory, and hence the identification of the most favorable H site, difficult. Here, we show that by applying a hydrostatic pressure, one should be able to make an unambiguous distinction, in particular, between the bond center sites and antibonding sites. This is because ω should increase with pressure for the former but decrease for the latter with the magnitude of calculated slopes about 4 cm−1/GPa, which should be large enough to measure.
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62.50.-p High-pressure effects in solids and liquids
63.20.Pw Localized modes
71.55.Gs II-VI semiconductors

Tb3+-doped KPb2Br5: Low-energy phonon mid-infrared laser crystal

U. N. Roy, R. H. Hawrami, Y. Cui, S. Morgan, A. Burger, Krishna C. Mandal, Caleb C. Noblitt, S. A. Speakman, K. Rademaker, and S. A. Payne

Appl. Phys. Lett. 86, 151911 (2005); http://dx.doi.org/10.1063/1.1901815 (3 pages) | Cited 7 times

Online Publication Date: 6 April 2005

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Crystals of potassium lead bromide (KPB), a moisture-insensitive low-energy phonon laser host, were synthesized and purified. High-quality undoped and Tb3+-doped (nominal doping concentration was 5 mol % TbBr3) KPb2Br5 were grown by the vertical Bridgman technique. X-ray diffraction measurements indicated that, at room temperature, the material was monoclinic with space group P21/c, while at a high temperature the phase transformed to orthorhombic form. A reversible phase transition was observed around 256 °C upon the heating and cooling cycle from differential scanning calorimetric measurements. The material was found to be transparent in the broad range from ∼ 0.4 μm to 25 μm and above. The transmission spectrum of a Tb3+-doped crystal showed different absorption bands of Tb3+ at 4.5 μm, 3 μm, 2.3 μm, and 2 μm corresponding to math–math transitions, for α = 2–5. The maximum phonon energy of undoped KPb2Br5 at room temperature was determined to be 134 cm−1 from Raman scattering spectrum.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
81.10.Fq Growth from melts; zone melting and refining
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
78.30.Hv Other nonmetallic inorganics
63.20.-e Phonons in crystal lattices
61.66.Fn Inorganic compounds

Nanoplate elasticity under surface reconstruction

Hyun Woo Shim, L. G. Zhou, Hanchen Huang, and Timothy S. Cale

Appl. Phys. Lett. 86, 151912 (2005); http://dx.doi.org/10.1063/1.1897825 (3 pages) | Cited 21 times

Online Publication Date: 7 April 2005

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Using classical molecular statics simulations, we show that nanoplate elasticity strongly depends on surface reconstruction and alignment of bond chains. Because of its well-established surface reconstructions and the readily available interatomic potential, diamond-cubic silicon is the prototype of this study. We focus on silicon nanoplates of high-symmetry surfaces, {111} and {100}; with 7×7 and 2×1 reconstructions. Nanoplates with unreconstructed {111} surfaces are elastically stiffer than bulk. In contrast, the same nanoplates with 7×7 reconstructed {111} surfaces are elastically softer than bulk. On {100} surfaces, the 2×1 surface reconstruction has little impact. The bond chains are along one of the two ⟨110⟩ directions, making the two ⟨110⟩ directions nonequivalent. The alignment of the bond chains on the opposite surfaces of a nanoplate dictates its elastic anisotropy. The sensitivity of nanoplate elasticity on details of surface atomic arrangements may impact the application of nanoplates (or nanocantilevers) as sensors.
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81.07.Bc Nanocrystalline materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.D- Elasticity

Physical kinetics and thermodynamics of phase transitions probed by dynamic nanocalorimetry

E. Château, J.-L. Garden, O. Bourgeois, and J. Chaussy

Appl. Phys. Lett. 86, 151913 (2005); http://dx.doi.org/10.1063/1.1905813 (3 pages) | Cited 8 times

Online Publication Date: 7 April 2005

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A specific ac nanocalorimeter is presented for the study of kinetics in phase transitions. This apparatus designed by means of microfabrication technologies requires a 50‐μm-thick solid or liquid sample. The use of the ac calorimetric method allows an operating frequency range around two decades combined with a very high sensitivity. The ability of this apparatus for thermal spectroscopy is illustrated by measuring the thermal behavior of a homopolymer, the polytetrafluoroethylene, which exhibits two phase transitions at room temperature. The variation of the thermal frequency allows the observation of kinetic effects directly seen on the thermodynamic properties (enthalpy and heat capacity). We demonstrate the possibility of extracting a quantitative value of the kinetic time constant occurring at a first-order phase transition and consequently the capabilities offered by highly sensitive ac calorimetry to investigate direct thermal dynamics in macromolecular samples.
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07.20.Fw Calorimeters
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Light emission and charge trapping in Er-doped silicon dioxide films containing silicon nanocrystals

A. Nazarov, J. M. Sun, W. Skorupa, R. A. Yankov, I. N. Osiyuk, I. P. Tjagulskii, V. S. Lysenko, and T. Gebel

Appl. Phys. Lett. 86, 151914 (2005); http://dx.doi.org/10.1063/1.1872208 (3 pages) | Cited 24 times

Online Publication Date: 7 April 2005

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The processes of electro- (EL) and photoluminescence (PL) and charge trapping in Er-implanted SiO2 containing silicon nanoclusters have been studied. It is shown that in Er-doped SiO2 with an excess of silicon nanoclusters of 10 at. %, a strong energy transfer from silicon nanoclusters results in a ten-fold increase of the PL peak at 1540 nm from Er luminescent centers, whereas the EL is strongly quenched by the excess silicon nanoclusters. It is further shown that the implantation of Er creates in the oxide positive charge traps with a giant cross section (σh0>10−13 cm2). Introducing subsequent silicon nanocrystals in the oxide leads to the formation of negative charge traps of a giant cross section (σe0>10−13 cm2). The possible reason for the EL quenching in the Er-doped SiO2 by silicon nanoclusters is discussed.
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78.66.Li Other semiconductors
78.60.Fi Electroluminescence
78.55.Hx Other solid inorganic materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.S- Impurities in crystals

In situ x-ray diffraction study of the thermal expansion of silver nanoparticles in ambient air and vacuum

Jinlian Hu, Weiping Cai, Cuncheng Li, Yanjie Gan, and Li Chen

Appl. Phys. Lett. 86, 151915 (2005); http://dx.doi.org/10.1063/1.1901803 (3 pages) | Cited 11 times

Online Publication Date: 7 April 2005

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The thermal expansion behavior of silver nanoparticles in ambient air and vacuum was studied by in situ x-ray diffraction (XRD) measurement of the particles dispersed within mesoporous silica in the temperature range of 25–700 °C. It has been shown that thermal expansion coefficient of Ag nanoparticles in vacuum is about 0.6×10−5/°C, only near one fourth that of bulk silver (2.2×10−5/°C). However, the coefficient in air is about 1.7×10−5/°C, about 3 times as high as that in vacuum and close to the value of bulk Ag. These were explained in terms of Ag particles’ surface energy, oxygen surface adsorption, and dissolution into lattice. This study is of importance in architectonics of future nanodevices.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
65.40.De Thermal expansion; thermomechanical effects
61.46.-w Structure of nanoscale materials
68.35.Md Surface thermodynamics, surface energies
68.43.Mn Adsorption kinetics
64.75.-g Phase equilibria
61.43.Gt Powders, porous materials

Mechanical strength of nanocrystalline/amorphous Al90Fe5Gd5 composites produced by rolling

W. H. Jiang and M. Atzmon

Appl. Phys. Lett. 86, 151916 (2005); http://dx.doi.org/10.1063/1.1897434 (3 pages) | Cited 15 times

Online Publication Date: 7 April 2005

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Mechanical deformation is expected to be an alternative route for synthesizing nanocrystalline/amorphous matrix composites. However, it is found that nanocrystalline/amorphous Al90Fe5Gd5 composites produced by cold rolling have lower hardness than the as-spun, fully amorphous, alloy. Much smaller pileups are observed around indents in rolled samples than in the as-spun sample. Combining high-resolution transmission electron microscopy with Fourier transform and image filtering, many nanovoids are observed in the shear bands near the boundary with the undeformed matrix.
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81.05.Kf Glasses (including metallic glasses)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.43.Fs Glasses
61.43.Dq Amorphous semiconductors, metals, and alloys
61.46.-w Structure of nanoscale materials
62.20.Qp Friction, tribology, and hardness
68.37.Lp Transmission electron microscopy (TEM)

Study of the photoluminescence of phosphorus-doped p-type ZnO thin films grown by radio-frequency magnetron sputtering

Dae-Kue Hwang, Hyun-Sik Kim, Jae-Hong Lim, Jin-Yong Oh, Jin-Ho Yang, Seong-Ju Park, Kyoung-Kook Kim, D. C. Look, and Y. S. Park

Appl. Phys. Lett. 86, 151917 (2005); http://dx.doi.org/10.1063/1.1895480 (3 pages) | Cited 107 times

Online Publication Date: 8 April 2005

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Phosphorus-doped p-type ZnO thin films were grown on sapphire by radio-frequency magnetron sputtering. The photoluminescence (PL) spectra revealed an acceptor bound exciton peak at 3.355 eV and a conduction band to the acceptor transition caused by a phosphorus related level at 3.310 eV. A study of the dependence of the excitation laser power density and temperature on the characteristics of the PL spectra suggests that the emission lines at 3.310 and 3.241 eV can be attributed to a conduction band to the phosphorus-related acceptor transition and a donor to the acceptor pair transition, respectively. The acceptor energy level of the phosphorus dopant was estimated to be located 127 meV above the valence band.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
78.55.Et II-VI semiconductors
68.55.A- Nucleation and growth
71.55.Gs II-VI semiconductors
61.72.uf Ge and Si
61.72.uj III-V and II-VI semiconductors
73.20.At Surface states, band structure, electron density of states

Localized exciton dynamics in nonpolar (11math0) InxGa1−xN multiple quantum wells grown on GaN templates prepared by lateral epitaxial overgrowth

T. Onuma, A. Chakraborty, B. A. Haskell, S. Keller, S. P. DenBaars, J. S. Speck, S. Nakamura, U. K. Mishra, T. Sota, and S. F. Chichibu

Appl. Phys. Lett. 86, 151918 (2005); http://dx.doi.org/10.1063/1.1900947 (3 pages) | Cited 18 times

Online Publication Date: 8 April 2005

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Beneficial effects of the localized excitons were confirmed in nonpolar (11math0) InxGa1−xN multiple quantum wells (QWs) grown on GaN templates prepared by lateral epitaxial overgrowth. Due to the absence of the polarization fields normal to the QW plane, the photoluminescence (PL) peak energy moderately shifted to the higher energy and the radiative lifetime did not change remarkably with the decrease in the well thickness. Similar to the case for polar InGaN QWs, time-resolved PL signals exhibited the nonexponential decay shape, which can be explained by thermalization and subsequent localization of excitons. Although the growth conditions were not fully optimized, values of the PL intensity at 300 K divided by that at 8 K were 25% and 17% for the peaks at 2.92 and 2.60 eV, respectively.
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81.07.St Quantum wells
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.67.De Quantum wells
78.47.-p Spectroscopy of solid state dynamics
68.65.Fg Quantum wells
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Improvement of recoverability of a nanoporous energy absorption system by using chemical admixture

X. Kong and Y. Qiao

Appl. Phys. Lett. 86, 151919 (2005); http://dx.doi.org/10.1063/1.1901830 (3 pages) | Cited 37 times

Online Publication Date: 8 April 2005

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In this paper, the behaviors of nanoporous energy absorption systems subjected to cyclic loadings are investigated. The systems consist of hydrophobic mesoporous silica particles immersed in aqueous solutions of sodium chloride (NaCl). In the first loading-unloading loop, increasing NaCl concentration, c, causes only slight increases in infiltration pressure and energy absorption efficiency. In the following loops, however, the system behaviors are strongly dependent on c. As c increases from 0% to 25.9 wt. %, the recoverability is improved by a factor of 3, indicating clearly that the addition of NaCl has a beneficial effect to promoting the outflow in the nanoenvironment.
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68.35.Md Surface thermodynamics, surface energies
68.03.Cd Surface tension and related phenomena
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