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1 Feb 2007

Volume 101, Issue 3, Articles (03xxxx)

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Raman piezospectroscopic evaluation of intergrowth ferroelectric polycrystalline ceramic in biaxial bending configuration

Wanyin Ge, Wenliang Zhu, Marco Deluca, Keshu Wan, Zhiguo Yi, Yongxiang Li, and Giuseppe Pezzotti

J. Appl. Phys. 101, 033501 (2007); http://dx.doi.org/10.1063/1.2402586 (8 pages)

Online Publication Date: 1 February 2007

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The piezospectroscopic (PS) effect was studied in an intergrowth bismuth layer-structure ferroelectric ceramic Bi5TiNbWO15 according to a micro-Raman spectroscopic evaluation. By using a ball-on-ring flexure configuration, a biaxial stress was generated in a Bi5TiNbWO15 plate-like specimen and in situ collected Raman spectra were acquired and analyzed under several loading conditions. As the observed spectral line contained signals arising from the whole illuminated in-depth region, the laser probe information was deconvoluted (by means of an in-depth probe response function obtained according to the defocusing method) in order to deduce biaxial PS coefficients for the three Raman bands of Bi5TiNbWO15 located at 763, 857, and 886 cm−1, respectively. The biaxial PS coefficients of these bands were derived to be −1.74±0.16, −2.51±0.16, and -2.64±0.31 cm−1/GPa, respectively, and should be referred to the c axis of the Bi5TiNbWO15 crystal.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
78.30.Hv Other nonmetallic inorganics
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Structural and optical properties of single crystal Zn1−xMgxO nanorods—Experimental and theoretical studies

Yu-Sheng Chang, Chih-Tao Chien, Chun-Wei Chen, Ta-Ya Chu, Hsuen-Han Chiang, Chen-Hao Ku, Jih-Jen Wu, Chao-Sung Lin, Li-Chyong Chen, and Kuei-Hsien Chen

J. Appl. Phys. 101, 033502 (2007); http://dx.doi.org/10.1063/1.2429729 (7 pages) | Cited 18 times

Online Publication Date: 1 February 2007

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Structural and optical properties of single crystal Zn1−xMgxO nanorods (0 ≤ x ≤ 0.17) are studied experimentally and theoretically. Structural analyses indicate that the nanorods grown on Si substrates are oriented in the c-axis direction and the nanorods possess the single-crystalline hexagonal structure with the Mg incorporated within the ZnO nanorods by means of substituting Zn. A blueshift of the near-band edge emission in the photoluminescence spectra by increasing Mg content is observed. Two distinct emission bands are found in the photoluminescence spectra; one is mainly attributed to the delocalized exciton recombination and the other is originating from localized excitons due to the incorporation of foreign impurity of Mg. Enhanced exciton localization with increasing Mg content in Zn1−xMgxO nanorods is mainly due to large ionic characters of Mg-O bonding. Structural stability, band structures, projected density of states, and charge distribution in various Zn1−xMgxO alloy compounds were further investigated by first-principles calculations. A good agreement between experimental and theoretical results is found.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.46.Hk Nanocrystals
73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Nr Semiconductor compounds
71.35.-y Excitons and related phenomena

Analysis of defect mode switching response in one-dimensional photonic crystal with a nematic liquid crystal defect layer

Ryotaro Ozaki, Hiroshi Moritake, Katsumi Yoshino, and Masanori Ozaki

J. Appl. Phys. 101, 033503 (2007); http://dx.doi.org/10.1063/1.2432877 (6 pages) | Cited 9 times

Online Publication Date: 1 February 2007

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We analyze the dynamic response and optical properties of a high-speed defect mode switching that is based on a tunable defect mode in a one-dimensional photonic crystal with a nematic liquid crystal defect layer. The electro-optic responses of the defect mode switching are calculated considering the director distributions in the defect layer, which are determined using continuum theory. The calculated defect mode switching exhibits a response on the order of microseconds in spite of the use of the reorientation of nematic liquid crystal molecules. From the calculation, it is found that the fast response is realized using a narrow peak shift and a fast part of the molecular reorientation. Furthermore, the dependences of the switching response are clarified on several physical parameters.
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42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
78.20.Jq Electro-optical effects

Electron spin-resonance studies of conduction electrons in phosphorus-doped silicon nanocrystals

Kazuaki Sumida, Keiichi Ninomiya, Minoru Fujii, Kazuyoshi Fujio, Shinji Hayashi, Masafumi Kodama, and Hitoshi Ohta

J. Appl. Phys. 101, 033504 (2007); http://dx.doi.org/10.1063/1.2432377 (5 pages) | Cited 10 times

Online Publication Date: 2 February 2007

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The properties of conduction electrons in P-doped Si nanocrystals embedded in insulating glass matrices have been studied by electron spin-resonance spectroscopy. For heavily P-doped samples, a broad conduction electron signal is observed at low temperatures. The width of the signal is found to be much broader than that of P-doped bulk Si crystals. The temperature dependence of the signal intensity obeys the Curie law even when the P concentration is very high. This suggests that in P-doped nanocrystals donor levels do not merge into the conduction band even at very high P concentration, and also provides evidence that Si nanocrystals smaller than a certain threshold size do not become metallic, at least when they are prepared under an equilibrium condition.
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76.30.Pk Conduction electrons
73.22.-f Electronic structure of nanoscale materials and related systems
71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors

Comparison of preferred orientation and stress in silver thin films on different substrates using x-ray diffraction

Yeongseok Zoo and T. L. Alford

J. Appl. Phys. 101, 033505 (2007); http://dx.doi.org/10.1063/1.2401654 (6 pages) | Cited 5 times

Online Publication Date: 5 February 2007

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Silver thin films were deposited on SiO2 and polyethylene naphthalate (PEN) using e-beam evaporation. X-ray diffraction techniques were used to investigate the influence of substrate morphology on the Ag film’s texture. Different modes of texture were observed in Ag thin films on SiO2 and PEN. Detailed information regarding spatial distribution of specific {hkl} planes was obtained by conducting pole figure analyses. A typical stress measurement technique for thin films, sin2 ψ analysis, was performed to study how the surface morphology of the various substrates affected the stress induced during the texture evolution of the thin films. Based on the data from this study, the preferred orientation and stress of Ag thin films on SiO2 and PEN were discussed.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

The effect of order and dose of H and He sequential implantation on defect formation and evolution in silicon

Phuong Nguyen, K. K. Bourdelle, T. Maurice, N. Sousbie, A. Boussagol, X. Hebras, L. Portigliatti, F. Letertre, A. Tauzin, and N. Rochat

J. Appl. Phys. 101, 033506 (2007); http://dx.doi.org/10.1063/1.2432380 (4 pages) | Cited 4 times

Online Publication Date: 5 February 2007

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In this paper we study the effect of the order and dose of H and He sequential implantation on H interaction with Si lattice defects. We use systematic infrared absorption measurements to investigate the evolution of hydrogenated point defects complexes during isothermal annealing. This analysis combined with the electron microscopy data led to the identification of the infrared absorption modes corresponding to the formation of the partially amorphized layer. The obtained results provide an important input for the optimization of the implantation conditions in order to achieve fracture in Si in the wide temperature range.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.30.Am Elemental semiconductors and insulators

Grain size effect on nanomechanical properties and deformation behavior of copper under nanoindentation test

Shou-Yi Chang and Ting-Kui Chang

J. Appl. Phys. 101, 033507 (2007); http://dx.doi.org/10.1063/1.2432873 (8 pages) | Cited 13 times

Online Publication Date: 5 February 2007

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The mechanical properties and deformation behaviors of copper with different grain sizes have been investigated in this study by instrumented nanoindentation. Following the Hall-Petch relation, the hardness of copper specimens increased as the grain size decreased. Dislocations were clearly observed in deformed regions around indent marks, indicating plastic deformation by dislocation formation and sliding. However, the hardness of electroless copper films with an ultrafine grain size of only 10 nm dropped. Voiding at grain boundaries and triple grain junctions was observed as a consequence of grain-boundary sliding and grain rotation, which was expected as the dominant deformation mechanism resulting in the reduced hardness. The critical shear stresses for the initiation of plastic deformation in the copper specimens with large grain sizes were close to the theoretical value and comparatively much lower for electroless copper films with an ultrafine grain size.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
62.20.Qp Friction, tribology, and hardness
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Excess vacancies in high energy ion implanted SiGe

R. Kögler, A. Mücklich, W. Skorupa, A. Peeva, A. Yu. Kuznetsov, J. S. Christensen, and B. G. Svensson

J. Appl. Phys. 101, 033508 (2007); http://dx.doi.org/10.1063/1.2433122 (5 pages) | Cited 5 times

Online Publication Date: 5 February 2007

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Excess vacancies generated by high energy implantation with 1.2 MeV Si+ and 2 MeV Ge+ ions in SiGe were investigated after rapid thermal annealing at 900 °C. Excess vacancies were probed by decoration with Cu and measuring the Cu profile by secondary ion mass spectrometry. Cross section transmission electron microscopy of cleaved specimen enabled to visualize nanocavities resulting from agglomeration of excess vacancies. The ion-induced damage in SiGe increases with increasing Ge fraction of the alloy. The amorphization threshold decreases and the extension of a buried amorphous layer increases for given implantation and annealing conditions. In contrast to ballistic simulations of excess defect generation where perfect local self-annihilation is assumed the concentrations of excess vacancies and excess interstitials in SiGe increase with increasing Ge fraction. The main contribution to the high excess vacancy concentration in SiGe results from the inefficient recombination of vacancies and interstitials. The widely used +1 model describing the ion-induced damage in Si is not valid for SiGe.
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61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Effects of barrier growth temperature ramp-up time on the photoluminescence of InGaN/GaN quantum wells

Y. Wang, X. J. Pei, Z. G. Xing, L. W. Guo, H. Q. Jia, H. Chen, and J. M. Zhou

J. Appl. Phys. 101, 033509 (2007); http://dx.doi.org/10.1063/1.2433700 (6 pages) | Cited 6 times

Online Publication Date: 6 February 2007

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The influence of ramp-up time of barrier growth temperature on optical properties is investigated for InGaN/GaN quantum wells deposited on sapphire substrate by metal organic chemical vapor deposition. Three ramp-up times are used from the low and high growth temperatures for the well and barrier, respectively. The results indicate that increasing the ramp-up time leads to a blueshift of the photoluminescence (PL) peak position and a broadening of the PL emission linewidth. Similarly, “S-shaped” temperature dependences of the PL peak energy are observed in all the samples. However, very different temperature dependences of PL linewidth, such as the conventional shaped, “U-shaped,” and S-shaped, are observed in the samples with different ramp-up time. These effects are attributed to the redistribution of the In-rich clusters in the wells. Small quantum-dot-like In-rich clusters with high density are considered to be formed in the wells for the sample with a long ramp-up time, leading to the unconventional PL linewidth behavior and enhanced internal quantum efficiency.
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78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Cr III-V semiconductors

Surface amorphization in conductors by using skin effect: Model and experiment

A. Vinogradov, S. G. Lazarev, A. L. Mozgovoi, S. A. Gornostai-Polskii, R. Okumura, and S. Hashimoto

J. Appl. Phys. 101, 033510 (2007); http://dx.doi.org/10.1063/1.2431858 (7 pages) | Cited 1 time

Online Publication Date: 6 February 2007

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An approach to amorphization and/or nanostructurization of a metal surface layer is proposed utilizing a skin effect induced by a high power electric pulse. Modeling electric and magnetic fields and heat transfer in a metallic cylinder predicts that melting followed by rapid quenching can occur in a thin skin layer if the amplitude of a passing electric pulse is high enough. The quenching rates can reach 108–109 K/s, giving rise to an opportunity of surface amorphization and spectacular surface structure modification in a wide range of metallic systems. Justifying the approach, a glassylike structure has been found experimentally in ordinary stainless steel subjected to the treatment proposed. Furthermore, specific ultradispersed structures containing nanocrystalline particles embedded into amorphous matrix or twin lamellar structures with nanodimensions can be produced in the subsurface layer.
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68.35.Rh Phase transitions and critical phenomena
61.43.Dq Amorphous semiconductors, metals, and alloys
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.70.K- Solid-solid transitions
81.30.Fb Solidification
64.70.D- Solid-liquid transitions

Ceramic liquid droplets stabilized in vacuum

R. Takahashi, Y. Tsuruta, Y. Yonezawa, T. Ohsawa, H. Koinuma, and Y. Matsumoto

J. Appl. Phys. 101, 033511 (2007); http://dx.doi.org/10.1063/1.2433123 (5 pages) | Cited 4 times

Online Publication Date: 6 February 2007

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We have studied the ceramic liquid droplet of CuOx-added BiOx at high temperature in vacuum. CuOx always floated on the BiOx as a surfactant and suppressed the evaporation of volatile BiOx liquid droplets. A clear liquid behavior of the BiOx droplets was directly observed by in situ laser microscope, with numerous liquid droplets growing by the coalescences in accordance with Marangoni’s [Nuovo Cimento Ser. 2, 239 (1872)] effect involved with the precursor film. We have also found a unique absorption of CaO into the BiOx liquid droplets, based on which a reliable process has been established for an atomically flat surface of MgO(001). These results open a broad window of opportunity to tailor not only a chemical interaction on oxide surface but also a liquid droplet dynamics in vacuum.
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68.03.Fg Evaporation and condensation of liquids

Buried amorphous layers by electronic excitation in ion-beam irradiated lithium niobate: Structure and kinetics

J. Olivares, A. García-Navarro, G. García, F. Agulló-López, F. Agulló-Rueda, A. García-Cabañes, and M. Carrascosa

J. Appl. Phys. 101, 033512 (2007); http://dx.doi.org/10.1063/1.2434801 (8 pages) | Cited 12 times

Online Publication Date: 7 February 2007

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The formation of buried heavily damaged and amorphous layers by a variety of swift-ion irradiations (F at 22 MeV, O at 20 MeV, and Mg at 28 MeV) on congruent LiNbO3 has been investigated. These irradiations assure that the electronic stopping power Se(z) is dominant over the nuclear stopping Sn(z) and reaches a maximum value inside the crystal. The structural profile of the irradiated layers has been characterized in detail by a variety of spectroscopic techniques including dark-mode propagation, micro-Raman scattering, second-harmonic generation, and Rutherford backscattering spectroscopy∕channeling. The growth of the damage on increasing irradiation fluence presents two differentiated stages with an abrupt structural transition between them. The heavily damaged layer reached as a final stage is optically isotropic (refractive index n = 2.10, independent of bombarding ion) and has an amorphous structure. Moreover, it has sharp profiles and its thickness progressively increases with irradiation fluence. The dynamics under irradiation of the amorphous-crystalline boundaries has been associated with a reduction of the effective amorphization threshold due to the defects created by prior irradiation (cumulative damage). The kinetics of the two boundaries of the buried layer is quite different, suggesting that other mechanisms aside from the electronic stopping power should play a role on ion-beam damage.
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61.82.Ms Insulators
61.80.Jh Ion radiation effects
61.43.Er Other amorphous solids
78.30.-j Infrared and Raman spectra
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Mn2+ concentration manipulated red emission in BaMg2Si2O7:Eu2+,Mn2+

Song Ye, Jiahua Zhang, Xia Zhang, Shaozhe Lu, Xinguang Ren, and Xiaojun Wang

J. Appl. Phys. 101, 033513 (2007); http://dx.doi.org/10.1063/1.2431684 (5 pages) | Cited 16 times

Online Publication Date: 8 February 2007

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The luminescent properties of concentration dependence are reported in BaMg2Si2O7:Eu2+,Mn2+ red phosphor. It is observed that the broad red emission of Mn2+ consists of two bands, located at 620 and 675 nm, respectively, which are attributed to two different Mn2+ centers [Mn2+(I) and Mn2+(II)] substituting for two nonidentical Mg2+ sites [Mg2+(I) and Mg2+(II)] in the host. It is also found that the relative emission intensity of the Mn2+(II) to the Mn2+(I) increases with increasing Mn2+ concentration, leading to a red-shift of the overall emission. A detail analysis on the energy transfer from Eu2+ to the two Mn2+ centers is presented, which indicates that the number ratio of Mn2+(II) to Mn2+(I) increases with increasing Mn2+ concentration. This result is interpreted by the preferential formation of Mn2+(I) substituting for Mg2+(I) site. Based on energy transfer, the emission intensity ratios of Mn2+(I) to Eu2+ and Mn2+(II) to Eu2+, which is Mn2+ concentration dependent, are calculated using related fluorescence lifetimes. The calculated results are in good agreement with that obtained experimentally in the emission spectra.
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78.60.-b Other luminescence and radiative recombination
61.72.S- Impurities in crystals

Simultaneous measurement of Young’s and shear moduli of multiwalled carbon nanotubes using atomic force microscopy

Ganesh Guhados, Wankei Wan, Xueliang Sun, and Jeffrey L. Hutter

J. Appl. Phys. 101, 033514 (2007); http://dx.doi.org/10.1063/1.2433125 (5 pages) | Cited 5 times

Online Publication Date: 8 February 2007

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Carbon nanotubes (CNTs) are widely hailed as the strongest material known to mankind. However, experimental measurements—and even theoretical estimates—of their mechanical properties span a wide range. We present an atomic force microscopy study of multiwalled CNTs, which, unlike previous such studies, measures the tube compliance as a function of position along suspended tubes. This permits a simultaneous determination of the effective Young’s and shear moduli of CNTs: 350±110 and 1.4±0.3 GPa, respectively.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Scintillation characteristics of Lu3Al5O12:Ce optical ceramics

Martin Nikl, Jiri A. Mares, Natasha Solovieva, Hui-Li Li, Xue-Jian Liu, Li-Ping Huang, Ilaria Fontana, Mauro Fasoli, Anna Vedda, and Carmelo D’Ambrosio

J. Appl. Phys. 101, 033515 (2007); http://dx.doi.org/10.1063/1.2433706 (5 pages) | Cited 12 times

Online Publication Date: 8 February 2007

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Optical absorption, luminescence, and scintillation characteristics of Lu3Al5O12:Ce optical ceramics were measured and compared with an analogous high quality single crystal. Optical absorption of the former shows an additional light scattering loss due to nanovoids and/or refraction index inhomogeneities. Even though radioluminescence intensity of the optical ceramics prepared by a coprecipitation route exceeds that of single crystal, its scintillation light yield is lower due to the charge carrier retrapping in the process of energy transfer towards the Ce3+ emission centers. Retrapping processes are evidenced by thermoluminescence measurements below room temperature. Lu3Al5O12:Ce optical ceramics does not show the presence of the LuAl antisite defects which decreases the scintillation figure of merit in single crystals grown from the melt [ M. Nikl, Phys. Status Solidi A 202, 201 (2005) ]. Furthermore, using the ceramic technology, one can achieve both the homogeneous doping and higher Ce concentration. Similar to Y3Al5O12:Ce, the optical ceramics may therefore become competitive to the Lu3Al5O12:Ce single crystals, if trapping phenomena at other defects can be further reduced.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials

High photoluminescence quantum efficiency InGaN multiple quantum well structures emitting at 380 nm

D. M. Graham, P. Dawson, G. R. Chabrol, N. P. Hylton, D. Zhu, M. J. Kappers, C. McAleese, and C. J. Humphreys

J. Appl. Phys. 101, 033516 (2007); http://dx.doi.org/10.1063/1.2434823 (5 pages) | Cited 5 times

Online Publication Date: 8 February 2007

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In this paper we report the design of high room temperature photoluminescence internal efficiency InGaN-based quantum well structures emitting in the near ultraviolet at 380 nm. To counter the effects of nonradiative recombination the quantum wells were designed to have a large indium fraction, high barriers, and a small quantum well thickness. To minimize the interwell and interbarrier thickness fluctuations we used Al0.2In0.005Ga0.795N barriers, where the inclusion of the small fraction of indium was found to lead to fewer structural defects and a reduction in the layer thickness fluctuations. This approach has led us to achieve, for an In0.08Ga0.92N/Al0.2In0.005Ga0.795N multiple quantum well structure with a well width of 1.5 nm, a photoluminescence internal efficiency of 67% for peak emission at 382 nm at room temperature.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Red luminescence of Cr in β‐Ga2O3 nanowires

Emilio Nogales, José A. García, Bianchi Méndez, and Javier Piqueras

J. Appl. Phys. 101, 033517 (2007); http://dx.doi.org/10.1063/1.2434834 (4 pages) | Cited 14 times

Online Publication Date: 8 February 2007

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Red luminescence emission from chromium doped β‐Ga2O3 nanowires has been studied by means of photoluminescence (PL) techniques. PL excitation shows several bands in the ultraviolet-visible region. Time decay values, obtained by time resolved PL, at different temperatures fit a three level model with thermal population of the upper level from the middle one. From the results, the origin of the emission is assigned to Cr3+ ions in the β‐Ga2O3 host, and values for the energy level separation and Huang-Rhys factor of the broad 4T2‐4A2 emission are estimated.
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78.67.Lt Quantum wires
78.55.Hx Other solid inorganic materials
78.40.Fy Semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.21.Hb Quantum wires

Deficiencies of the kinetics order method for the study of thermoluminescence

Zheng Xu, Fujun Zhang, Suling Zhao, Liwei Wang, A. N. Georgobiani, and Xurong Xu

J. Appl. Phys. 101, 033518 (2007); http://dx.doi.org/10.1063/1.2433764 (3 pages)

Online Publication Date: 9 February 2007

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Luminescence is a widespread fundamental physical phenomenon. It has a broad application in the field of illumination, display, dosimeter, mining, archaeology, various analyses, etc. Trap and decay are two important, inseparable factors in luminescence dynamic processes, and thermoluminescence, in particular. Of the two most popular techniques of studying the dynamics of this process, the method based on kinetics order has serious deficiencies: (1) a fixed parameter to represent an evolving process and (2) an assumed value, instead of an experimental value, disagrees with reality. We proposed a method of simultaneous determination of trap depth and decay parameters from the glow curve of ZnS:Cu,Co, obtaining the trap depth ε = 0.86 eV and decay parameter math = 2.6 simultaneously. From these data, we have shown dependence of trap depth ε on decay parameter, which clearly shows the error of ε for any assumed decay parameter. If we treat the case of kinetics order α = 1 as α = 2, the error might be as large as 100%.
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78.60.Kn Thermoluminescence

Subsurface modifications in indium phosphide induced by single and multiple femtosecond laser pulses: A study on the formation of periodic ripples

M. Couillard, A. Borowiec, H. K. Haugen, J. S. Preston, E. M. Griswold, and G. A. Botton

J. Appl. Phys. 101, 033519 (2007); http://dx.doi.org/10.1063/1.2423136 (8 pages) | Cited 14 times

Online Publication Date: 9 February 2007

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We use cross-sectional transmission electron microscopy to study the damage induced below the surface of indium phosphide (InP) samples by single and multiple femtosecond laser pulses with a photon energy lower than the InP band gap. Single-pulse irradiation creates a ∼ 100 nm deep crater with a resolidified surface layer consisting of quasiamorphous indium phosphide. The resolidified layer has a thickness of ∼ 60 nm at the center and extends laterally beyond the edge of the crater rim. Exposure to multiple femtosecond pulses of 2050 nm center wavelength results in the formation of laser-induced periodic surface structures (LIPSS) with two different periods, one ( ∼ 1730 nm) less than but close to the laser wavelength and one ( ∼ 470 nm) four times smaller. Segregation beneath both types of ripples leads to the formation of In-rich particles embedded in the resolidified surface layer. Extended defects are detected only below the center of the multiple-pulse crater and their distribution appears to be correlated with the LIPSS modulation. Finally, LIPSS formation is discussed in terms of the observed subsurface microstructures.
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81.05.Ea III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.30.Mh Solid-phase precipitation
81.30.Fb Solidification

Measurement of the shear strength of pure tungsten during one-dimensional shock loading

J. C. F. Millett, G. T. Gray, III, and N. K. Bourne

J. Appl. Phys. 101, 033520 (2007); http://dx.doi.org/10.1063/1.2427096 (6 pages) | Cited 12 times

Online Publication Date: 9 February 2007

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The behavior of a pure tungsten under conditions of one-dimensional shock loading has been monitored using Manganin stress gauges, in longitudinal and lateral orientations. The shock induced equation of state, in terms of stress and particle velocity (from the longitudinal gauges), shows that the Hugoniot of this pure material agrees with the results of previous workers, both in pure tungsten and tungsten alloys. Lateral stress traces show an increase in stress (and hence decrease in shear strength) behind the shock front, in a manner similar to that observed in a tungsten heavy alloy and pure tantalum. It has been proposed that this is due to the high Peierl’s stress initially restricting dislocation generation, followed by a later increased in dislocation density. However, the brittle manner in which tungsten fails under shock loading indicates that other mechanisms are in operation. It has been suggested that the shock front nucleates cracking, which progressively grows behind it, which in combination with the proposed dislocation mechanisms reduces shear strength. Finally, we show that the variation of shear strength with shock stress is in agreement with a number of other workers until a stress level of ∼ 10 GPa, where it is significantly higher. We have suggested that this is due to the higher strength of pure tungsten compared to the liquid phase sintered materials studied previously.
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62.50.-p High-pressure effects in solids and liquids
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Composition effects on the early-stage oxidation kinetics of (001) Cu–Au alloys

G.-W. Zhou, J. A. Eastman, R. C. Birtcher, P. M. Baldo, J. E. Pearson, L. J. Thompson, L. Wang, and J. C. Yang

J. Appl. Phys. 101, 033521 (2007); http://dx.doi.org/10.1063/1.2433714 (6 pages) | Cited 10 times

Online Publication Date: 9 February 2007

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An in situ environmental transmission electron microscopy study of the nucleation and growth of oxide islands during the early-stage oxidation of (001) Cu1−xAux alloys (x ⩽ 38 at. %) was undertaken in order to investigate the effects of alloying on oxide island nucleation behavior and growth kinetics. The kinetic data reveal that Au enhances the nucleation density of oxide islands and suppresses their growth rate. Our results provide insight into reasons for the decreased passivation properties of Cu when alloyed with Au.
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81.05.Bx Metals, semimetals, and alloys
81.65.Mq Oxidation
81.65.Rv Passivation
68.35.B- Structure of clean surfaces (and surface reconstruction)

Enhanced thermal stability in organic light-emitting diodes through nanocomposite buffer layers at the anode/organic interface

D. Grozea, A. Turak, Y. Yuan, S. Han, Z. H. Lu, and W. Y. Kim

J. Appl. Phys. 101, 033522 (2007); http://dx.doi.org/10.1063/1.2434943 (6 pages) | Cited 9 times

Online Publication Date: 9 February 2007

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The effect of doped buffer layers at the anode/organic interface in small molecule organic light-emitting diodes was investigated. Appropriate doping of N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and Cu-phthalacyanine (CuPc) layers using LiF or C60 molecules leads to improved interfacial morphology and thermal stability for both standard indium tin oxide or metals anodes, such as Au and Ag. Graded interfaces remain stable at temperatures well above the hole transport layer (i.e., NPB) glass transition temperature.
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85.60.Jb Light-emitting devices

Optical and magneto-optical properties of gadolinium

Sapan Mohan Saini, Nirpendra Singh, Tashi Nautiyal, and Sushil Auluck

J. Appl. Phys. 101, 033523 (2007); http://dx.doi.org/10.1063/1.2434800 (6 pages) | Cited 2 times

Online Publication Date: 12 February 2007

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We report calculations of the optical and magneto-optical properties of elemental rare earth gadolinium using the full potential linear augmented plane wave method and including spin-orbit coupling. Calculations are performed within the local spin density approximation (LSDA) and Coulomb corrected local spin density approximation (LSDA+U). While LSDA+U gives better agreement for density of states and magnetic moments, a comparison with the experimental data shows that both LSDA and LSDA+U are at par in representing the diagonal components of the optical conductivity. For the much smaller off-diagonal components, interestingly, the LSDA results have an edge over the LSDA+U results.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Ls Magneto-optical effects
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.20.Eh Rare earth metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Field emission from nanoforest carbon nanotubes grown on cobalt-containing amorphous carbon composite films

Y. B. Zhang, S. P. Lau, and H. F. Li

J. Appl. Phys. 101, 033524 (2007); http://dx.doi.org/10.1063/1.2434830 (5 pages)

Online Publication Date: 12 February 2007

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Nanoforest carbon nanotubes (CNTs) were synthesized by biased thermal chemical vapor deposition on cobalt-containing amorphous carbon composite films. The composite films were deposited on silicon by filtered cathodic vacuum arc using a Co-containing graphite target and then CNTs were grown at 580 °C using the composite film as a catalyst layer. The nanoforest multiwalled CNTs have thin diameters between 10 and 20 nm. Their tips point upwards while the rest is densely tangled. They exhibit good field emission properties with a low threshold field of 1.6 V/μm and a high current density of 2.1 mA/cm2 at 3 V/μm.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.46.Fg Nanotubes

Dispersion of confined optical phonons in semiconductor nanowires in the framework of a continuum approach

F. Comas, I. Camps, G. E. Marques, and Nelson Studart

J. Appl. Phys. 101, 033525 (2007); http://dx.doi.org/10.1063/1.2433149 (7 pages) | Cited 1 time

Online Publication Date: 12 February 2007

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Confined optical phonons are discussed for a semiconductor nanowire of the Ge (Si) prototype on the basis of a theory developed some years ago. In the present work this theory is adapted to a nonpolar material and generalized to the case when the phonon dispersion law involves both linear and quadratic terms in the wave vector. The treatment is considered along the lines of a continuous medium model and leads to a system of coupled differential equations describing oscillations of mixed nature. The nanowire is modeled in the form of an infinite circular cylinder and the solutions of the fundamental equations are found. We are thus led to a description of long-wavelength optical phonons, which should show a closer agreement with experimental data and with calculations along atomistic models. The presented theory is applied to the calculation of optical phonons in a Ge nanowire. We have found the dispersion curves for various optical phonon modes. We also normalize the modes and discuss the electron-phonon interaction within the deformation potential approximation.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.38.-k Polarons and electron-phonon interactions
61.46.-w Structure of nanoscale materials
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