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24 Dec 2007

Volume 91, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages)

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu
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A large-area bent crystal shield for deflection of high-energy ions

M. B. H. Breese

Appl. Phys. Lett. 91, 261901 (2007); http://dx.doi.org/10.1063/1.2824457 (3 pages)

Online Publication Date: 26 December 2007

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A large-area bent crystal shield which is capable of deflecting high-energy ions of all atomic numbers is described. Its effect on the transmitted angular distribution of high-energy ions is characterized using Monte Carlo channeling simulations. Ions up to an energy limit set by the bent crystal curvature radius are deflected by the full bend angle. A shield with a surface area of 1×1 cm2 which is capable of deflecting ions with energies up to 100 GeV/nucleon has been fabricated in which the lattice planes across the entrance surface are uniformly aligned.
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61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
81.20.-n Methods of materials synthesis and materials processing

Interface electronic structure of the organic light-emitting devices: Photoemission and x-ray absorption studies of Al/KF/Alq3 interface

J. Lee, J. S. Lim, H. J. Shin, and Y. Park

Appl. Phys. Lett. 91, 261902 (2007); http://dx.doi.org/10.1063/1.2824464 (3 pages) | Cited 3 times

Online Publication Date: 26 December 2007

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The chemistry of organic light-emitting diode interface composed of KF sandwiched between the Al and Alq3 was investigated using near-edge x-ray absorption fine structure (NEXAFS) as well as x-ray and ultraviolet photoelectron spectroscopy techniques. At the earliest stages of KF deposition on Alq3, changes in F K-edge NEXAFS spectra indicated a strong chemical reaction, which is responsible for the dipole layer formation seen in valence-band spectra. For Al deposition on KF/Alq3, the reactions inferred from observed spectral changes are not consistent with the commonly believed KF dissociation and AlF3 formation scenarios.
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85.60.Jb Light-emitting devices

Effects of plasma surface modification on interfacial behaviors and mechanical properties of carbon nanotube-Al2O3 nanocomposites

Yan Guo, Hoonsung Cho, Donglu Shi, Jie Lian, Yi Song, Jandro Abot, Bed Poudel, Zhifeng Ren, Lumin Wang, and Rodney C. Ewing

Appl. Phys. Lett. 91, 261903 (2007); http://dx.doi.org/10.1063/1.2824865 (3 pages) | Cited 9 times

Online Publication Date: 26 December 2007

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The effects of plasma surface modification on interfacial behaviors in carbon nanotube (CNT) reinforced alumina (Al2O3) nanocomposites were studied. A unique plasma polymerization method was used to modify the surfaces of CNTs and Al2O3 nanoparticles. The CNT-Al2O3 nanocomposites were processed by both ambient pressure and hot-press sintering. The electron microscopy results showed ultrathin polymer coating on the surfaces of CNTs and Al2O3 nanoparticles. A distinctive stress-strain curve difference related to the structural interfaces and plasma coating was observed from the nanocomposites. The mechanical performance and thermal stability of CNT-Al2O3 nanocomposites were found to be significantly enhanced by the plasma-polymerized coating.
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61.46.Fg Nanotubes
52.40.Hf Plasma-material interactions; boundary layer effects
82.35.Np Nanoparticles in polymers
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Jj Elasticity and anelasticity, stress-strain relations

Precise measurements of electron and hole g factors of single quantum dots by using nuclear field

R. Kaji, S. Adachi, H. Sasakura, and S. Muto

Appl. Phys. Lett. 91, 261904 (2007); http://dx.doi.org/10.1063/1.2827572 (3 pages) | Cited 10 times

Online Publication Date: 26 December 2007

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We demonstrated the cancellation of the external magnetic field by the nuclear field at one edge of the nuclear polarization bistability in single InAlAs quantum dots. The cancellation for the electron Zeeman splitting gives the precise value of the hole g factor. In combination with the exciton g factor that is obtained from the Zeeman splitting for linearly polarized excitation, the magnitude and the sign of the electron and hole g factors in the growth direction are evaluated.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.35.-y Excitons and related phenomena
81.05.Dz II-VI semiconductors

Effects of carbon on ion-implantation-induced disorder in GaN

S. O. Kucheyev, J. E. Bradby, C. P. Li, S. Ruffell, T. van Buuren, and T. E. Felter

Appl. Phys. Lett. 91, 261905 (2007); http://dx.doi.org/10.1063/1.2827587 (3 pages) | Cited 9 times

Online Publication Date: 26 December 2007

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Wurtzite GaN films bombarded with 40 keV C ions to high doses (5×1017 and 1×1018 cm−2) are studied by a combination of Rutherford backscattering/channeling spectrometry, transmission electron microscopy, and soft x-ray absorption spectroscopy. Results show that, contrary to other ion species, implanted C forms nitrilelike carbon-nitride bonds (–C≣N) and suppresses ion-beam-induced material decomposition involving the formation and agglomeration of ≳5-nm-large N2 gas bubbles.
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81.05.Ea III-V semiconductors
79.20.Kz Other electron-impact emission phenomena
78.70.Dm X-ray absorption spectra

Mechanical properties of carbon nanocones

J. X. Wei, K. M. Liew, and X. Q. He

Appl. Phys. Lett. 91, 261906 (2007); http://dx.doi.org/10.1063/1.2813017 (3 pages) | Cited 11 times

Online Publication Date: 26 December 2007

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In this paper, the elastic and plastic properties of single-walled carbon nanocones (CNCs) under tension are investigated employing molecular dynamics simulation. The force-deformation responses of CNCs are obtained and compared with those of carbon nanotubes (CNTs). CNCs with a larger apex angle present a larger failure strength but a smaller maximum strain under tension. Following this law, CNTs exhibit the smallest failure strength but greatest maximum strain due to their zero conical angles. The mechanical properties such as Young’s modulus, elastic strain limit, and ultimate force are determined and discussed.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep

Strong excitonic transition of Zn1−xMgxO alloy

H. Tampo, H. Shibata, K. Maejima, A. Yamada, K. Matsubara, P. Fons, S. Niki, T. Tainaka, Y. Chiba, and H. Kanie

Appl. Phys. Lett. 91, 261907 (2007); http://dx.doi.org/10.1063/1.2828031 (3 pages) | Cited 16 times

Online Publication Date: 26 December 2007

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A strong excitonic optical transition in a Zn1−xMgxO alloy grown by radical source molecular beam epitaxy was observed using both optical reflectivity measurements and photoluminescence (PL) measurements. Clear and strong reflectance peaks at room temperature (RT) were observed from 3.42 eV (x = 0.05) to 4.62 eV (x = 0.61) from ZnMgO layers at RT. Distinct clear PL spectra at RT were also observed for energies up to 4.06 eV (x = 0.44). The peak intensity of the reflected signal increased for x values up to x ∼ 0.2 simultaneously with an increase in PL intensity; however, a Stokes shift between the reflectance peak and the PL peak was not observed for x values below 0.2. These facts suggest that the oscillator strength of ZnMgO is enhanced by alloying, and the underlying mechanism is discussed. Furthermore, we demonstrate that the strong reflectance properties even at RT provide an easy method to determine the Mg composition of a thin ZnMgO layer in a ZnMgO/ZnO heterostructure.
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71.35.-y Excitons and related phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Characterization of fatigue-induced free volume changes in a bulk metallic glass using positron annihilation spectroscopy

R. S. Vallery, M. Liu, D. W. Gidley, M. E. Launey, and J. J. Kruzic

Appl. Phys. Lett. 91, 261908 (2007); http://dx.doi.org/10.1063/1.2825427 (3 pages) | Cited 6 times

Online Publication Date: 26 December 2007

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Depth-profiled Doppler broadening spectroscopy of positron annihilation on the cyclic fatigue-induced fracture surfaces of three amorphous Zr44Ti11Ni10Cu10Be25 metallic glass specimens reveals the presence of a 30–50 nm layer of increased free volume that is generated by the propagating fatigue crack tip. The presence and character of this fatigue transformation zone is independent of the initial amount of bulk free volume, which was varied by structural relaxation via annealing, and the voids generated in the zone by intense cyclic deformation are distinct from those typical of the bulk.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.43.Fs Glasses
78.70.Bj Positron annihilation
81.40.Gh Other heat and thermomechanical treatments
81.40.Lm Deformation, plasticity, and creep

Friction of soft elastomeric surfaces with a defect

Charles J. Rand and Alfred J. Crosby

Appl. Phys. Lett. 91, 261909 (2007); http://dx.doi.org/10.1063/1.2828136 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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We consider a simple problem that provides insight into the building blocks of friction for topographically patterned surfaces and fundamental understanding into the general friction of coatings. The problem focuses on the effect of a line defect, such as a pattern’s edge, on the lateral force of a sliding soft interface. The line defect presents a discontinuity in the stress at the sliding interface, changing the lateral stiffness and decreasing the sliding force. We relate the decrease in sliding shear force to the changes in lateral stiffness through relationships that account for contact splitting and lateral confinement effects.
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68.35.Af Atomic scale friction
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations

Crack-free GaN grown on AlGaN/(111)Si micropillar array fabricated by polystyrene microsphere lithography

Guan-Ting Chen, Jen-Inn Chyi, Chia-Hua Chan, Chia-Hung Hou, Chii-Chang Chen, and Mao-Nan Chang

Appl. Phys. Lett. 91, 261910 (2007); http://dx.doi.org/10.1063/1.2828137 (3 pages) | Cited 6 times

Online Publication Date: 26 December 2007

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The authors report on the growth of GaN on AlGaN/(111)Si micropillar array by metal-organic chemical vapor deposition. Using the substrates with micropillar array, 2-μm-thick GaN films without cracks can be achieved. Transmission electron microscopy, atomic force microscopy, and micro-Raman studies indicate that the dislocation density and residual stress of the GaN grown on micropillar array are also reduced. The results reveal the potential of this type of substrates for growing GaN-based devices as well as preparing GaN freestanding substrates.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties

Complicated three-dimensional photonic crystals fabricated by holographic lithography

Wei-Dong Mao, Guan-Quan Liang, Yi-Ying Pu, He-Zhou Wang, and Zhaohua Zeng

Appl. Phys. Lett. 91, 261911 (2007); http://dx.doi.org/10.1063/1.2827565 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2007

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We have fabricated a kind of three-dimensional photonic crystal in a single exposure by two sets of conventional laser holographic configurations. Specific structural features, such as a kagomelike lattice with p6mm symmetry on the top surface and a chainlike lattice on a cleavage plane, are possessed in this large-area and high-quality complicated microstructure, and many interesting properties such as skyrocketlike diffraction pattern exist. This work demonstrates that holographic lithography is a good method for the fabrication of photonic materials with crystal structure differing from the electronic crystals.
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42.70.Qs Photonic bandgap materials
42.40.My Applications
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