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5 Jun 2006

Volume 88, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 88, 233102 (2006); http://dx.doi.org/10.1063/1.2209157 (3 pages)

Zh. M. Wang, J. H. Lee, B. L. Liang, W. T. Black, Vas. P. Kunets, Yu. I. Mazur, and G. J. Salamo
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Dependence of the IR reflectance LO absorption bands on the crystalline texture of AlN films

E. Iborra, M. Clement, L. Vergara, A. Sanz-Hervás, J. Olivares, and J. Sangrador

Appl. Phys. Lett. 88, 231901 (2006); http://dx.doi.org/10.1063/1.2209205 (3 pages) | Cited 5 times

Online Publication Date: 5 June 2006

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The infrared reflectance spectra of polycrystalline sputtered AlN films are analyzed in relation to their crystalline texture. AlN films with perfect c-axis orientation and good piezoelectric response exhibit a single peak at 887 cm−1 corresponding to the A1–longitudinal-optical (LO) vibrational mode. However, {0001}-textured films with traces of 10math1, 10math2, and 10math3 reflections in their x-ray diffraction patterns show an additional peak at 905 cm−1 that we assign to an E1-A1 quasi-LO mode due to interaction of light with non-⟨0001⟩-oriented grains. The piezoelectric response deteriorates as the amplitude of the quasi-LO mode increases with respect to the A1(LO) mode.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
77.65.-j Piezoelectricity and electromechanical effects
77.55.-g Dielectric thin films

Long wavelength emitting InAs/Ga0.85In0.15NxAs1−x quantum dots on GaAs substrate

M. Richter, B. Damilano, J.-Y. Duboz, J. Massies, and A. D. Wieck

Appl. Phys. Lett. 88, 231902 (2006); http://dx.doi.org/10.1063/1.2209879 (3 pages) | Cited 15 times

Online Publication Date: 5 June 2006

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InAs quantum dots (QDs) overgrown by a Ga0.85In0.15NxAs1−x (0 ⩽ x ⩽ 0.017) layer have been realized on GaAs substrate by molecular beam epitaxy. When the nitrogen composition increases, the photoluminescence (PL) wavelength redshifts up to 1.52 μm. It is shown that PL properties of InAs/Ga0.85In0.15N0.012As0.988 QDs are improved by thermal annealing. Finally, 1.45 μm PL emission with a 38.5 meV full width at half maximum is obtained at room temperature.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Cc Kinetics of defect formation and annealing

Detection of explosive materials by differential reflection spectroscopy

Rolf E. Hummel, Anna M. Fuller, Claus Schöllhorn, and Paul H. Holloway

Appl. Phys. Lett. 88, 231903 (2006); http://dx.doi.org/10.1063/1.2210077 (3 pages) | Cited 9 times

Online Publication Date: 6 June 2006

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It is shown that traces of 2,4,6-trinitrotoluene (TNT) display strong and distinct structures in differential reflectograms, near 420 and 250 nm. These characteristic peaks are not observed from moth balls, nail polish, polyvinyl chloride, starch, soap, paper, epoxy, aspirin, polycarbonate, aspartame, polystyrene, polyester, fertilizer, or sugar, to mention a few substances which may be in or on a suitcase. The described technique for detection of TNT is fast, inexpensive, reliable, and portable and does not require contact with the surveyed substance. Moreover, we have developed a curve recognition program for field applications of the technique. The origin of the spectra is discussed.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
78.20.-e Optical properties of bulk materials and thin films

Electronic structure and energetics of the quaternary hydride Li4BN3H10

J. F. Herbst and L. G. Hector

Appl. Phys. Lett. 88, 231904 (2006); http://dx.doi.org/10.1063/1.2210083 (3 pages) | Cited 17 times

Online Publication Date: 6 June 2006

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Li4BN3H10 has been synthesized recently from LiNH2/LiBH4 mixtures and its crystal structure determined. We have calculated the electronic structure of this complex hydride and investigated its thermodynamic stability and decomposition energetics. We find that its enthalpy of formation is −708 kJ/mole with respect to the elemental constituents and −8 kJ/mole relative to a 3:1 molar LiNH2/LiBH4 mixture, in qualitative agreement with experiment. Reaction enthalpies computed for several decomposition pathways suggest Li4BN3H10→Li3BN2+½Li2NH+½NH3+4H2 as the likely dehydriding route.
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71.20.Ps Other inorganic compounds
61.66.Fn Inorganic compounds
64.75.-g Phase equilibria
82.60.Cx Enthalpies of combustion, reaction, and formation
65.40.-b Thermal properties of crystalline solids

Inversion domain boundaries and phase separation in p-AlGaN layers with high Al contents

Hyung Koun Cho, Bo Hyun Kong, Z. Ren, J. Han, and S.-R. Jeon

Appl. Phys. Lett. 88, 231905 (2006); http://dx.doi.org/10.1063/1.2210450 (3 pages) | Cited 2 times

Online Publication Date: 6 June 2006

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The effect of Mg incorporation and Al composition on the formation of inversion domain boundaries (IDBs) and self-assembled superlattices in Mg-doped p-AlxGa1−xN epilayers grown on undoped Al0.3Ga0.7N was investigated by transmission electron microscopy. The formation, initiating position, and shape of the faceted IDBs strongly depended on the Mg and Al contents. Horizontally well-aligned self-assembled superlattices with large composition modulation by phase separation were also observed in the Mg-doped p-AlGaN before the formation of the faceted IDBs. The periodicity of the modulation obtained from the diffused streaks is ∼ 40 Å.
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68.65.Cd Superlattices
64.75.-g Phase equilibria
68.37.Lp Transmission electron microscopy (TEM)

Microstructure of relaxed InN quantum dots grown on GaN buffer layers by molecular-beam epitaxy

Lin Zhou, Tao Xu, David J. Smith, and T. D. Moustakas

Appl. Phys. Lett. 88, 231906 (2006); http://dx.doi.org/10.1063/1.2205166 (3 pages) | Cited 9 times

Online Publication Date: 6 June 2006

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Electron microscopy has been used to characterize the microstructure of InN quantum dots (QDs) grown by molecular-beam epitaxy on GaN(0001)/AlN(0001)/sapphire substrates at 425 °C under slightly group III-rich conditions. Observations in plan-view and cross-section geometries established that the large majority of the InN QDs were invariably associated with threading dislocations in the underlying GaN buffer layer having edge components. Periodic, primarily hexagonal, arrays of misfit dislocations separated by ∼ 2.8 nm were observed at the InN QD/GaN interface, indicating that the QDs were almost completely relaxed. No evidence for an InN wetting layer was obtained either in situ by reflection high-energy electron diffraction or ex situ by transmission electron microscopy.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Strong photoluminescence at 1.3 μm with a narrow linewidth from nitridized InAs/GaAs quantum dots

Y. D. Jang, N. J. Kim, J. S. Yim, D. Lee, S. H. Pyun, W. G. Jeong, and J. W. Jang

Appl. Phys. Lett. 88, 231907 (2006); http://dx.doi.org/10.1063/1.2210789 (3 pages)

Online Publication Date: 7 June 2006

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Nitridized quantum dots (QDs) were prepared by metal-organic chemical vapor deposition. These QDs all showed strong photoluminescence (PL) emission at 1.3 μm at room temperature, narrow spectral widths of 30 meV, and large separations of 98 meV between the ground and first excited states. Interestingly, the PL peak positions of the nitridized QDs were all around 1.3 μm, despite the QDs having been prepared using significantly different amounts of nitrogen. Time-resolved PL revealed no electronic coupling between the QDs. These properties could potentially make these nitridized QDs very useful candidates for the fabrication of devices emitting at 1.3 μm.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Achievement of alternative amorphous AlAs/crystalline AlGaAs multilayers

Hao Wang, Changjun Liao, Shuwen Zheng, and Songhao Liu

Appl. Phys. Lett. 88, 231908 (2006); http://dx.doi.org/10.1063/1.2210790 (3 pages)

Online Publication Date: 7 June 2006

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A hybrid multilayer, composed of ten period amorphous AlAs/crystalline GaAlAs stacks, is realized by metalorganic chemical vapor deposition method on a GaAs substrate. Cross-sectional transmission electron microscopy shows the presence of sharp amorphous/crystalline interfaces. The electron diffraction patterns reveal the coexistence of both amorphous and crystalline phases and the perfect coherence of atom arrows between substrate and crystalline AlGaAs layers was also demonstrated. Perfect crystalline AlGaAs quality was further confirmed by x-ray rocking curves. The potential application of such hybrid multilayers is discussed and its behavior as a Bragg reflector is explored with a stop band gap of 75% reflectance.
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68.65.Ac Multilayers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
42.79.Bh Lenses, prisms and mirrors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Diffusion of adatom in the selective epitaxial growth of Si(100): A molecular dynamics study

Gun-Do Lee, Sukwon Hong, Hyun-Woo Kim, and Euijoon Yoon

Appl. Phys. Lett. 88, 231909 (2006); http://dx.doi.org/10.1063/1.2210971 (3 pages)

Online Publication Date: 8 June 2006

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Tight-binding molecular dynamics simulation is performed for a Si adatom on the surface containing the {311} facet and the Si(100) surface to reproduce and explain the behavior of the {311} facet in the selective epitaxial growth of Si(100). In the simulation the adatom is observed to diffuse from the {311} facet to the Si(100) surface along the pathway of a trough between the dimer rows on Si(100) surface. By the tight-binding total energy calculation, it is also clarified that adatoms easily diffuse to the Si(100) surface because, after the adatom surmounts the first energy barrier to diffuse to the step edge near the {311} facet, there is no additional Schwoebel barrier and the other energy barriers gradually decrease to the top of the dimer row of Si(100). The pathway of the trough between dimer rows on the Si(100) surface is found to be energetically more favorable than the direct pathway to the dimer row from the tight-binding total energy calculation. Our tight-binding molecular dynamics simulation elucidates the mechanism responsible for the behavior of the {311} facet in the selective epitaxial growth of Si(100).
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68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
66.30.J- Diffusion of impurities
68.55.-a Thin film structure and morphology

First principles study of CdSe quantum dots: Stability, surface unsaturations, and experimental validation

M. Yu, G. W. Fernando, R. Li, F. Papadimitrakopoulos, N. Shi, and R. Ramprasad

Appl. Phys. Lett. 88, 231910 (2006); http://dx.doi.org/10.1063/1.2209195 (3 pages) | Cited 15 times

Online Publication Date: 9 June 2006

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Ab initio computational studies were performed for CdSe nanocrystals over a wide range of sizes and topologies. Substantial relaxations and coordination of surface atoms were found to play a crucial role in determining the nanocrystal stability and optical properties. While optimally (threefold) coordinated surface atoms resulted in stable closed-shell structures with large optical gaps, suboptimal coordination gave rise to lower stability and negligible optical gaps. These computations are in qualitative agreement with recent chemical etching experiments suggesting that closed-shell nanocrystals contribute strongly to photoluminescence quantum yield while clusters with nonoptimal surface coordination do not.
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73.21.La Quantum dots
71.15.-m Methods of electronic structure calculations
73.22.-f Electronic structure of nanoscale materials and related systems
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
61.46.Hk Nanocrystals

Dislocations in nanocrystalline grains

Xiao-Lei Wu and En Ma

Appl. Phys. Lett. 88, 231911 (2006); http://dx.doi.org/10.1063/1.2210295 (3 pages) | Cited 33 times

Online Publication Date: 9 June 2006

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Dislocation behavior inside the very small grains of nanocrystalline metals has so far eluded high-resolution transmission electron microscopy (TEM) examinations. We have identified full dislocations using high-resolution TEM, and the different ways they reside in the 20–30 nm Ni grains. The thermally activated propagation of dislocations, their interactions with twin/grain boundaries and dislocation loops, as well as their storage in nanocrystalline grains are demonstrated and discussed.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.46.Hk Nanocrystals
68.37.Lp Transmission electron microscopy (TEM)
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Mm Grain and twin boundaries
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