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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Dynamic range of nanoresonators with random rough surfaces in the presence of thermomechanical and momentum exchange noise

G. Palasantzas

Appl. Phys. Lett. 91, 021901 (2007); http://dx.doi.org/10.1063/1.2751599 (3 pages) | Cited 5 times

Online Publication Date: 9 July 2007

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The authors investigate the simultaneous influence of thermomechanical and momentum exchange noise on the linear dynamic range DR of nanoresonators with random rough surfaces. The latter are characterized by the roughness amplitude w, the lateral correlation length ξ, and the roughness exponent 0<H<1. The dynamic range increases with increasing roughness (decreasing H and/or increasing roughness ratio w/ξ) if the quality factor due to gas collisions is smaller than the intrinsic quality factor associated with thermomechanical noise. The influence of the roughness ratio w/ξ on DR is significant for intermediate roughness exponents that are commonly observed in experiments.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
72.70.+m Noise processes and phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Accommodation mechanism of InN nanocolumns grown on Si(111) substrates by molecular beam epitaxy

J. Grandal, M. A. Sánchez-García, E. Calleja, E. Luna, and A. Trampert

Appl. Phys. Lett. 91, 021902 (2007); http://dx.doi.org/10.1063/1.2756293 (3 pages) | Cited 14 times

Online Publication Date: 9 July 2007

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High quality InN nanocolumns have been grown by molecular beam epitaxy on bare and AlN-buffered Si(111) substrates. The accommodation mechanism of the InN nanocolumns to the substrate was studied by transmission electron microscopy. Samples grown on AlN-buffered Si(111) show abrupt interfaces between the nanocolumns and the buffer layer, where an array of periodically spaced misfit dislocations develops. Samples grown on bare Si(111) exhibit a thin SixNy at the InN nanocolumn/substrate interface because of Si nitridation. The SixNy thickness and roughness may affect the nanocolumn relative alignment to the substrate. In all cases, InN nanocolumns grow strain- and defect-free.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.-w Structure of nanoscale materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Spectral dependence of the photoluminescence decay in disordered semiconductors

O. Rubel, W. Stolz, and S. D. Baranovskii

Appl. Phys. Lett. 91, 021903 (2007); http://dx.doi.org/10.1063/1.2755927 (3 pages) | Cited 9 times

Online Publication Date: 9 July 2007

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Kinetics of the energy transfer and the corresponding photoluminescence decay at selected photon energies in disordered semiconductors are studied theoretically. The authors show a straightforward way to arrive analytically at the solutions for the spectral and time dependences of the photoluminescence decay within a model based on the interplay between the radiative recombination and hopping energy relaxation of localized excitons. The theory is supported by comparison with experimental data, which yields valuable information on major properties of disorder in the underlying structures.
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78.55.-m Photoluminescence, properties and materials
71.35.-y Excitons and related phenomena

Spectroscopic evidence for a surface layer in CuInSe2:Cu deficiency

Sung-Ho Han, Falah S. Hasoon, Allen M. Hermann, and Dean H. Levi

Appl. Phys. Lett. 91, 021904 (2007); http://dx.doi.org/10.1063/1.2755718 (3 pages) | Cited 7 times

Online Publication Date: 9 July 2007

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The near-surface region of thin-film polycrystalline (PX) CuIn1−xGaxSe2 (CIGS) is considered important because it is the region where the electrical junction forms in a CIGS photovoltaic device. Spectroscopic ellipsometry measurements of polycrystalline CuInSe2 films reveal that there is a thin layer at the surface which has different optical and electronic properties from those of the bulk film. This surface layer of thin-film CIGS has a larger band gap and greater spin-orbit interaction energy than the bulk film. These properties indicate that the surface layer is more Cu deficient than the bulk in the nearly stoichiometric thin-film PX-CIGS used in photovoltaic devices. This work provides an insight into the importance of surface layer engineering for photovoltaic device design.
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78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.At Surface states, band structure, electron density of states
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.20.Nr Semiconductor compounds

Volume conservation in bulk metallic glasses

D. Ma, A. D. Stoica, and X.-L. Wang

Appl. Phys. Lett. 91, 021905 (2007); http://dx.doi.org/10.1063/1.2751595 (3 pages) | Cited 8 times

Online Publication Date: 10 July 2007

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The authors report that the excess molar volumes of mixing for ∼ 30 metalloid-free bulk metallic glasses (BMGs) are essentially zero, indicating that the original volumes of “mechanically mixed” constituent elemental metals are conserved after glass formation. This is attributed to the lack of solute-solute bonds and the ideal-mixing nature of solvent-solute bonding upon amorphization. The hard-sphere atomic packing fractions of most of these BMGs are found to be ∼ 0.74, comparable to the maximum packing efficiency for close-packed structures. These findings present a different perspective for understanding amorphous structures.
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61.43.Fs Glasses
61.43.Dq Amorphous semiconductors, metals, and alloys

Early stage of material movements in eutectic SnPb solder joint undergoing current stressing at 150 °C

C. E. Ho, A. Lee, K. N. Subramanian, and W. Liu

Appl. Phys. Lett. 91, 021906 (2007); http://dx.doi.org/10.1063/1.2756292 (3 pages) | Cited 6 times

Online Publication Date: 10 July 2007

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X-ray fluorescence spectroscopy was used to study movements of Sn and Pb in the eutectic SnPb solder joint undergoing electromigration with a current density of 104 A/cm2 at 150 °C. During early stages of current stressing, Sn moves toward the anode faster than Pb. However, on continued application of current stressing, both Sn and Pb will continue to accumulate at the anode. Such accumulation of conductive species facilitates the formation of hillock with associated valley near the cathode.
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66.30.Qa Electromigration
78.70.En X-ray emission spectra and fluorescence

Correlation between icosahedral short range order, glass forming ability, and thermal stability of Zr–Ti–Ni–Cu–(Be) glasses

S. Mechler, G. Schumacher, I. Zizak, M.-P. Macht, and N. Wanderka

Appl. Phys. Lett. 91, 021907 (2007); http://dx.doi.org/10.1063/1.2755924 (3 pages) | Cited 10 times

Online Publication Date: 10 July 2007

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The structure and the crystallization behavior of the bulk metallic glass Zr46.8Ti8.2Ni10Cu7.5Be27.5 and of its Be-free derivative Zr64.5Ti11.4Ni13.8Cu10.3 are analyzed by means of differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. These alloys reveal different glass forming abilities. Thermal stability and crystallization behavior of the glasses are also different. These differences are correlated with the different degrees of icosahedral short range order in the glasses. Results fit to the model of geometric frustration, which describes the structure of metallic glasses as “highly defective quasicrystals.” In the present case Be degrades the ideal quasicrystalline structure.
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61.43.Fs Glasses
64.70.K- Solid-solid transitions

Pattern formation in martensitic thin films

Y. C. Shu and J. H. Yen

Appl. Phys. Lett. 91, 021908 (2007); http://dx.doi.org/10.1063/1.2756320 (3 pages) | Cited 11 times

Online Publication Date: 10 July 2007

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Pattern formation in martensitic materials refers to the accommodation problem of how to mix martensitic variants coherently to minimize the strain energy. A framework motivated by energy-minimizing multirank laminated patterns is proposed to study this problem in martensitic films. It is found that the interfaces between the variants of martensite can be quite different in thin films than in bulk materials, and they typically have a simpler structure. Various intriguing and fascinating self-accommodation patterns are predicted for martensitic thin films with different orientations. The results are in good agreement with the Bhattacharya-James thin-film theory [ K. Bhattacharya and R. D. James, J. Mech. Phys. Solids 47, 531 (1999) ] as well as with experimental observations.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology

Effect of ion-irradiation induced defects on the nanocluster Si/Er3+ coupling in Er-doped silicon-rich silicon oxide

Se-Young Seo, Hoon Jeong, Jung H. Shin, Han Woo Choi, Hyung Joo Woo, and Joon Kon Kim

Appl. Phys. Lett. 91, 021909 (2007); http://dx.doi.org/10.1063/1.2752538 (3 pages) | Cited 2 times

Online Publication Date: 11 July 2007

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The effect of ion-irradiation induced defects on the nanocluster Si/Er3+ coupling in Er-doped silicon-rich silicon oxide (SRSO) thin film is investigated. Er-doped SRSO, which consists of silicon nanoclusters (nc-Si) in a SiO2 matrix, was fabricated using electron-cyclotron resonance plasma enhanced chemical vapor deposition using SiH4 and O2 with concurrent sputtering of Er followed by a high temperature annealing. Defects were introduced into the film via irradiation with 3 MeV Si ions and subsequently removed by high temperature annealings. The authors find that ion irradiation reduces Er3+ luminescence from SRSO films, even when the excitation cross section and luminescence efficiency of Er3+ ions are completely restored. On the other hand, ion irradiation increases the intrinsic nc-Si luminescence and has little effect on the Er3+ luminescence from a similarly prepared, Er-doped SiO2 film, indicating that the presence of irradiation induced defects in the initial amorphous film can reduce the number of Er3+ ions available for nc-Si mediated luminescence by as much as a factor of 3.
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78.55.Hx Other solid inorganic materials
78.55.Qr Amorphous materials; glasses and other disordered solids
78.66.Nk Insulators
61.80.Jh Ion radiation effects
61.82.Ms Insulators
81.40.Gh Other heat and thermomechanical treatments

Optical properties of (In,Ga)As capped InAs quantum dots grown on [11k] substrates

V. Mlinar and F. M. Peeters

Appl. Phys. Lett. 91, 021910 (2007); http://dx.doi.org/10.1063/1.2753745 (3 pages) | Cited 2 times

Online Publication Date: 11 July 2007

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Using three-dimensional k∙p calculation including strain and piezoelectricity, the authors showed that the size of the quantum dot (QD) in the growth direction determines the influence of the (In,Ga)As capping layer on the optical properties of [11k] grown InAs QDs, where k = 1,2,3. For flat dots, increase of In concentration in the capping layer leads to a decrease of the transition energy, whereas for large dots an increase of the In concentration in the capping layer is followed by an increase of the transition energy up to a critical concentration of In, after which the optical transition energy starts to decrease.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
77.65.-j Piezoelectricity and electromechanical effects
61.72.S- Impurities in crystals

Pressure-induced amorphization of quasibinary GeTe–Sb2Te3: The role of vacancies

A. V. Kolobov, J. Haines, A. Pradel, M. Ribes, P. Fons, J. Tominaga, C. Steimer, G. Aquilanti, and S. Pascarelli

Appl. Phys. Lett. 91, 021911 (2007); http://dx.doi.org/10.1063/1.2752016 (3 pages) | Cited 12 times

Online Publication Date: 12 July 2007

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The authors demonstrate that the cubic phase of quasibinary GeTe–Sb2Te3 alloys (GST), the material of choice in phase-change optical recording (such as digital versatile disk-random access memory) can be rendered amorphous by the application of hydrostatic pressure. The amorphization pressure depends on the GST composition. The pressure-induced amorphous phase possesses a local structure around Ge atoms similar to that of laser-amorphized GST. They argue that vacancies are crucial for the pressure-induced amorphization.
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64.70.K- Solid-solid transitions
61.72.J- Point defects and defect clusters
61.43.Fs Glasses

Dynamic response and reinforcement mechanism of composites embedded with tetraneedlelike ZnO nanowhiskers

M. S. Cao, W. Zhou, X. L. Shi, and Y. J. Chen

Appl. Phys. Lett. 91, 021912 (2007); http://dx.doi.org/10.1063/1.2753544 (3 pages) | Cited 26 times

Online Publication Date: 12 July 2007

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A type of glass-fiber reinforced composites was prepared by dispersing tetraneedlelike ZnO nanowhiskers in epoxy matrix. The as-prepared composites exhibited excellent dynamic mechanical properties after the effective dispersion of ZnO nanowhiskers in epoxy. Patulous and fractured reinforcement modes for the composites were proposed. The high strength of composites was attributed to the three dimensional structure of tetraneedlelike ZnO nanowhiskers and the corresponding stress transfer.
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81.05.Qk Reinforced polymers and polymer-based composites
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity

Observation of 300 K high energy magnetodielectric contrast in the bilayer manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7

J. Cao, R. C. Rai, S. Brown, J. L. Musfeldt, R. Tackett, G. Lawes, Y. J. Wang, X. Wei, M. Apostu, R. Suryanarayanan, and A. Revcolevschi

Appl. Phys. Lett. 91, 021913 (2007); http://dx.doi.org/10.1063/1.2757120 (3 pages) | Cited 6 times

Online Publication Date: 12 July 2007

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Large high energy magnetodielectric effects are observed in the bilayer manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7, a direct consequence of exploiting magnetoresistance changes associated with the field driven spin-glass insulator to ferromagnetic metal transition and its high temperature remnant. The low temperature magnetodielectric contrast is as large as ∼ 100% near 0.8 eV at 10 T and over 10 000% in selected phonon regions. The 300 K magnetodielectric contrast is ∼ 20% near 1.1 eV at 30 T. The results are potentially useful for magnetic memory applications away from the dc limit.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Lk Spin glasses and other random magnets
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Dislocation reduction in GaN grown on stripe patterned r-plane sapphire substrates

Hou-Guang Chen, Tsung-Shine Ko, Shih-Chun Ling, Tien-Chang Lu, Hao-Chung Kuo, Shing-Chung Wang, Yue-Han Wu, and Li Chang

Appl. Phys. Lett. 91, 021914 (2007); http://dx.doi.org/10.1063/1.2754643 (3 pages) | Cited 6 times

Online Publication Date: 13 July 2007

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Extended defect reduction in GaN can be achieved via direct growth on stripe patterned (1 math 02) r-plane sapphire substrates by metal organic chemical vapor deposition. The striped mesa is along [11 math 0] with two etched sides in {0001} and {1 math 01} faces. GaN grown on both etched facets in epitaxy exhibit different crystallographic relationships with sapphire substrate which are (1 math 02)sapphire‖(11 math 0)GaN and [11 math 0]sapphire‖[ math 100]GaN, and (0001)sapphire‖(0001)GaN and [11 math 0]sapphire‖[ math 100]GaN, respectively. The dislocation densities can be significantly reduced through epitaxial growth on the inclined lateral faces of mesas. Dislocation density in the order of ∼ 107 cm−2 can be achieved in the tilted GaN.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Characterization of biaxial stress and its effect on optical properties of ZnO thin films

Y. F. Li, B. Yao, Y. M. Lu, C. X. Cong, Z. Z. Zhang, Y. Q. Gai, C. J. Zheng, B. H. Li, Z. P. Wei, D. Z. Shen, X. W. Fan, L. Xiao, S. C. Xu, and Y. Liu

Appl. Phys. Lett. 91, 021915 (2007); http://dx.doi.org/10.1063/1.2757149 (3 pages) | Cited 20 times

Online Publication Date: 13 July 2007

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Biaxial stress of ZnO film deposited on quartz was measured by side-inclination x-ray diffraction technique, indicating that the film is subjected to a tensile stress. One part of the stress is induced by thermal mismatch between the ZnO and the quartz and increases with annealing temperature, while another part results from lattice mismatch and is about 1.03 GPa. The optical band gap of the ZnO film shows a blueshift with increasing biaxial tensile stress, opposed to the change of the band gap with biaxial tensile stress for GaN. The mechanism of the stress-dependent band gap is suggested in the present work.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
78.66.Hf II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
71.20.Nr Semiconductor compounds
81.40.Lm Deformation, plasticity, and creep

Photoluminescence of dome and hut shaped Ge(Si) self-assembled islands embedded in a tensile-strained Si layer

M. V. Shaleev, A. V. Novikov, A. N. Yablonskiy, Y. N. Drozdov, D. N. Lobanov, Z. F. Krasilnik, and O. A. Kuznetsov

Appl. Phys. Lett. 91, 021916 (2007); http://dx.doi.org/10.1063/1.2756291 (3 pages) | Cited 3 times

Online Publication Date: 13 July 2007

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The effect of the growth temperature (Tg) on photoluminescence of Ge(Si) self-assembled islands embedded between tensile-strained Si layers was studied. The observed redshift of the photoluminescence peak of the dome islands with a decrease of Tg from 700 to 630 °C is associated with an increase of Ge content in the islands and with the suppression of smearing of the strained Si layers. The blueshift of the photoluminescence peak with a decrease of Tg from 630 to 600 °C is associated with a change of the type of islands on surface, which is accompanied by a decrease in islands’ height.
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78.66.Li Other semiconductors
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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