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15 Feb 2008

Volume 103, Issue 4, Articles (04xxxx)

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Ultrafast crystallization and thermal stability of In–Ge doped eutectic Sb70Te30 phase change material

Mei Ling Lee, Xiang Shui Miao, Lee Hou Ting, and Lu Ping Shi

J. Appl. Phys. 103, 043501 (2008); http://dx.doi.org/10.1063/1.2841724 (5 pages) | Cited 8 times

Online Publication Date: 20 February 2008

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Effect of In and Ge doping in the form of In2Ge8Sb85Te5 on optical and thermal properties of eutectic Sb70Te30 alloys was investigated. Crystalline structure of In2Ge8Sb85Te5 phase change material consists of a mixture of phases. Thermal analysis shows higher crystallization temperature and activation energy for crystallization. Isothermal reflectivity-time measurement shows a growth-dominated crystallization mechanism. Ultrafast crystallization speed of 30 ns is realized upon irradiation by blue laser beam. The use of ultrafast and thermally stable In2Ge8Sb85Te5 phase change material as mask layer in aperture-type super-resolution near-field phase change disk is realized to increase the carrier-to-noise ratio and thermal stability.
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64.70.dg Crystallization of specific substances
61.66.Dk Alloys
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.-e Optical properties of bulk materials and thin films

Structural, elastic, and electronic properties of Fe3C from first principles

C. Jiang, S. G. Srinivasan, A. Caro, and S. A. Maloy

J. Appl. Phys. 103, 043502 (2008); http://dx.doi.org/10.1063/1.2884529 (8 pages) | Cited 28 times

Online Publication Date: 20 February 2008

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Using first-principles calculations within the generalized gradient approximation, we predicted the lattice parameters, elastic constants, vibrational properties, and electronic structure of cementite (Fe3C). Its nine single-crystal elastic constants were obtained by computing total energies or stresses as a function of applied strain. Furthermore, six of them were determined from the initial slopes of the calculated longitudinal and transverse acoustic phonon branches along the [100], [010], and [001] directions. The three methods agree well with each other; the calculated polycrystalline elastic moduli are also in good overall agreement with experiments. Our calculations indicate that Fe3C is mechanically stable. The experimentally observed high elastic anisotropy of Fe3C is also confirmed by our study. Based on electronic density of states and charge density distribution, the chemical bonding in Fe3C was analyzed and was found to exhibit a complex mixture of metallic, covalent, and ionic characters.
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61.66.Fn Inorganic compounds
71.15.-m Methods of electronic structure calculations
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations
71.20.Ps Other inorganic compounds
63.20.dk First-principles theory

Spirobifluorene molecular films investigated by means of near infrared-vacuum ultraviolet spectroscopic ellipsometry

Simona D. Silaghi, Till Spehr, Christoph Cobet, Tobat P. I. Saragi, Christoph Werner, Josef Salbeck, and Norbert Esser

J. Appl. Phys. 103, 043503 (2008); http://dx.doi.org/10.1063/1.2884582 (4 pages)

Online Publication Date: 20 February 2008

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Thin films of spirobifluorene-type materials, namely, spiro-octo1 and spiro-octo2, were investigated by means of spectroscopic ellipsometry in a broad spectral range from near-infrared to vacuum ultraviolet. The optical response of the amorphous organic films was described by an isotropic layer model based on Tauc–Lorentz functions. The dielectric functions of both types of organic films were determined. The strongest light absorption occurs around 6 eV for both types of organic films. The more effective π-conjugation of spiro-octo2 redshifts by 160 meV the absorption edge compared to Spiro-Octo1.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
61.43.-j Disordered solids
07.60.Fs Polarimeters and ellipsometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

Systematic investigation on structure and excitonic-related transitions: An evidence for Zn1−xCoxO alloy film as a wide gap semiconductor

Zhiyan Xiao, Hiroaki Matsui, Noriyuki Hasuike, Hiroshi Harima, and Hitoshi Tabata

J. Appl. Phys. 103, 043504 (2008); http://dx.doi.org/10.1063/1.2841769 (5 pages) | Cited 7 times

Online Publication Date: 21 February 2008

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Systematic investigations were performed concerning the crystal structure and excitonic-related transitions of Zn1−xCoxO layers. The substitution of Co atoms for Zn sites was initially identified from the intra-emissions originating from the 3d levels of the Co2+ ions. Microresonant Raman scattering (μ‐RRS) revealed that the local crystal structure of the host was disordered even at Co concentrations of a few percent, as determined by monitoring the A1(LO) mode and also supported by the ω-rocking curves obtained from x-ray diffraction. A critical point (Γ-edge) derived from magnetic circular dichroism systematically shifted to higher energy with increasing x, representing clear evidence for a widening of the band gap, and that the photoluminescent peaks correlated closely with absorption peaks related to excitonic transitions. The obvious excitonic structures gradually became diffuse with the appearance of photoexcited charge-transfer levels of Co2+ ions when x exceeded 2%. This allowed for observations of excitonic luminescence of samples with a Co content not exceeding 0.8%. The excitonic luminescence for all Co-doped ZnO layers was superimposed distinctly with Stokes and anti-Stokes LO phonons. This was attributed to outgoing multiphonon resonance Raman scattering due to a Fröhlich interaction based on strong coupling between photoexcited carriers and LO phonons, and further supported by the results of μ‐RRS.
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61.66.Fn Inorganic compounds
71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.20.Ls Magneto-optical effects
78.55.Et II-VI semiconductors

Deposition of controllable preferred orientation silicon films on glass by inductively coupled plasma chemical vapor deposition

Junshuai Li, Jinxiao Wang, Min Yin, Pingqi Gao, Deyan He, Qiang Chen, Yali Li, and Hajime Shirai

J. Appl. Phys. 103, 043505 (2008); http://dx.doi.org/10.1063/1.2885158 (7 pages) | Cited 10 times

Online Publication Date: 21 February 2008

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An inductively coupled plasma (ICP) system with the adjustable distance between the inductance coil and substrates was designed to effectively utilize the spatial confinement of ICP discharge, and then control the gas-phase transport process. The effects of the gas phase processes on the crystallinity and preferred orientation of silicon films deposited on glass were systematically investigated. The investigation was conducted in the ICP-chemical vapor deposition process with the precursor gas of a SiH4/H2 mixture at a substrate temperature of 350 °C. Highly crystallized silicon films with different preferred orientations, (111) or (220), could be selectively deposited by adjusting the SiH4 dilution ratio [R = [SiH4]/([SiH4]+[H2])] or total working pressure. When the total working pressure is 20 Pa, the crystallinity of the silicon films increases with the increase of the SiH4 dilution ratio, while the preferred orientation was changed from (111) to (220). In the case of the fixed SiH4 dilution (10%), the silicon film with I(220)/I(111) of about 3.5 and Raman crystalline fraction of about 89.6% has been deposited at 29.7 nm/min when the total working pressure was increased to 40 Pa. At the fixed SiH4 partial pressure of 2 Pa, the film crystallinity decreases and the preferred orientation is always (111) with increasing the H2 partial pressure from 18 to 58 Pa. Atomic force microscope reveals that the film deposited at a relatively high H2 partial pressure has a very rough surface caused by the devastating etching of H atoms to the silicon network.
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68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.jm Texture
68.37.Ps Atomic force microscopy (AFM)
68.35.bj Amorphous semiconductors, glasses

Pseudocrystallization of SiO2 and superhardness effects of AlN/SiO2 nanomultilayers

Wenji Zhao, Ming Kong, Ying Wu, and Geyang Li

J. Appl. Phys. 103, 043506 (2008); http://dx.doi.org/10.1063/1.2844316 (5 pages) | Cited 2 times

Online Publication Date: 21 February 2008

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AlN/SiO2 nanomultilayers with different SiO2 thicknesses were synthesized by reactive magnetron sputtering. X-ray diffraction and high-resolution transmission electron microscopy were used to characterize the microstructure, and nanoindentation technology was used to measure the mechanical properties of the multilayers. The crystallization of SiO2 as well as its influences on the growth and mechanical properties of the multilayers was studied. Results showed that due to the template effects of hcp AlN, amorphous SiO2 was forced to crystallize to a hcp pseudocrystal structure when its thickness was below 0.6 nm. The SiO2 epitaxially grew with AlN in the multilayer with coherent interfaces. At this time, a tensile and compressive alternate stress field was developed corresponding to the modulation structure. The hardness of the multilayers was enhanced as a result. Calculation revealed that alternate stress field played an important role in multilayers’ reinforcement. As thickness increases, SiO2 grew into amorphous again, resulting in the blockade of epitaxial growth in the multilayers and disappearing of the hardness enhancement.
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62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
81.15.Cd Deposition by sputtering
68.65.Ac Multilayers
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Influence of film thickness on texture and electrical and optical properties of room temperature deposited nanocrystalline V2O5 thin films

Preetam Singh and Davinder Kaur

J. Appl. Phys. 103, 043507 (2008); http://dx.doi.org/10.1063/1.2844438 (9 pages) | Cited 18 times

Online Publication Date: 21 February 2008

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Nanocrystalline V2O5 thin films have been grown at low temperature on glass substrates by dc magnetron sputtering using a vanadium metal target. Film thickness was found to have a great impact on the orientation, shape, and size of the crystallites of these films. X-ray diffraction (XRD) patterns of the films with a thickness of 110 nm show a strong c-axis orientated crystal structure with a preferred (001) orientation, while those with a thickness of 315 nm show mixed orientations (a-axis+c-axis). With further increase in film thickness, an a-axis orientation with predominant (200) reflection was observed in the XRD pattern. The shape of the crystallite changes from a rodlike to a bricklike structure with change in crystallographic orientation from (001) to (200). Atomic force microscopy results were also in agreement with the field emission scanning electron microscopy and XRD results. A direct correlation has been established between the semiconductor to metal transformation of V2O5 films and their crystallite size and orientation. The optical measurement also revealed a systematic band gap variation (from 2.50 to 2.20 eV) with variation in film thickness.
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68.55.jd Thickness
68.55.jm Texture
73.61.Ng Insulators
78.66.Nk Insulators
81.15.Cd Deposition by sputtering
68.60.-p Physical properties of thin films, nonelectronic

Investigation of the V-pit related morphological and optical properties of InGaN/GaN multiple quantum wells

F. Lin, N. Xiang, P. Chen, S. Y. Chow, and S. J. Chua

J. Appl. Phys. 103, 043508 (2008); http://dx.doi.org/10.1063/1.2884534 (5 pages) | Cited 4 times

Online Publication Date: 26 February 2008

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In this work, the effects of large V-pits on the morphological and optical properties of InGaN/GaN multiple quantum wells (MQWs) were studied using scanning electron microscopy, transmission electron microscopy, and photoluminescence. InGaN/GaN MQWs with high-density large V-pits were grown by metal organic chemical vapor deposition. In addition to the regular c-plane MQWs, the MQWs grown on the {10math1} faceted sidewalls of the V-pits were also observed, which gave much higher emission energies than those of the c-plane MQWs. Furthermore, when the low-temperature GaN buffer was very thin, the {11mathm} (m ≥ 2) faceted sidewalls of the V-pits were observed. It was then found that MQWs grown on such sidewalls had emission energies between those of the c-plane MQWs and those of the {10math1} faceted sidewall MQWs.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Energy band alignment at TiO2/Si interface with various interlayers

M. Perego, G. Seguini, G. Scarel, M. Fanciulli, and F. Wallrapp

J. Appl. Phys. 103, 043509 (2008); http://dx.doi.org/10.1063/1.2885109 (6 pages) | Cited 12 times

Online Publication Date: 27 February 2008

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Anatase TiO2 films are grown on Si (100) by atomic layer deposition. Three different interlayers (Si3N4, Al2O3, and Ti-rich SiOx) between the TiO2 films and the Si substrate have been considered. The band alignment of the titanium oxide films with the silicon substrate is investigated by x-ray photoelectron spectroscopy (XPS), internal photoemission (IPE) spectroscopy, and optical absorption (OA) measurements. XPS analysis indicates that TiO2/Si heterojunctions with different interlayers (ILs) have different valence-band offsets (VBOs). A VBO value of 2.56±0.09 eV is obtained for the TiO2/Ti-rich SiOx/Si sample. Similarly, we obtain a VBO value of 2.44±0.09 and 2.73±0.10 eV for the TiO2/Si3N4/Si and TiO2/Al2O3/Si samples, respectively. According to IPE and OA measurements, the band gap of the as-grown TiO2 films is 3.3±0.1 eV for all the samples. Combining the XPS and IPE data, the conduction band offset values at the TiO2/Si heterojunction are found to be −0.2±0.1, −0.4±0.1, and −0.5±0.1 eV for the TiO2/Si3N4/Si, TiO2/Ti-rich SiOx/Si, and TiO2/Al2O3/Si samples, respectively. According to our experimental results, the band alignment of a TiO2 film with the underlying Si (100) substrate is clearly affected by the presence of an IL, suggesting the possibility to tune the band structure of a TiO2/Si heterojunction by selecting the proper IL.
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71.20.-b Electron density of states and band structure of crystalline solids
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Influence of laser beam size on measurement sensitivity of thermophysical property gradients in layered structures using thermal-wave techniques

Chinhua Wang, Andreas Mandelis, Hong Qu, and Zhuying Chen

J. Appl. Phys. 103, 043510 (2008); http://dx.doi.org/10.1063/1.2872462 (8 pages) | Cited 6 times

Online Publication Date: 28 February 2008

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The influence of the photothermal laser source beam size on the measurement sensitivity of layered systems using photothermal radiometry (PTR) is presented. Based on an appropriate theoretical model, widely different behaviors of the photothermal amplitude and phase in terms of combinations of thermophysical properties (i.e., thermal conductivity and thermal diffusivity) between a thin coating and the substrate are observed. The beam size effect on PTR measurement sensitivity is theoretically examined and experimentally demonstrated using a carbonitrided C1018 steel sample. The experimental results of using a variable size laser beam for the carbonitrided C1018 sample validate the theoretical prediction, in which an expanded beam exhibits a much larger magnitude change in both amplitude and phase as a function of frequency than measurements with a focused beam. The fitted thermal conductivity and thermal diffusivity based on the assumed industrially relevant range of effective hardness case depth gives the approximate range of the change in thermal conductivity and thermal diffusivity of C1018 steels after the carbonitriding process.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
66.70.Df Metals, alloys, and semiconductors
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Ablation-induced explosion of metal using a high-power Nd:YAG laser

Jack J. Yoh, Hyunhee Lee, Jihee Choi, Kyung-cheol Lee, and Ki-hong Kim

J. Appl. Phys. 103, 043511 (2008); http://dx.doi.org/10.1063/1.2884532 (6 pages) | Cited 7 times

Online Publication Date: 28 February 2008

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The interaction of a high-power pulsed-laser beam with metal targets in air from a 1.06 μm, 5 ns, 3 J/pulse, Nd:YAG pulsed laser is investigated together with hydrodynamic theories of laser-supported blast wave and multimaterial reactive Euler equations. The high-speed blast wave generated by the laser ablation of metal reaches a maximum velocity of several thousand meters per second. The apparently similar flow conditions to those of reactive shock wave allow one to apply the equations of motion for energetic materials and to understand the explosive behavior of metal vaporization upon laser ablation. The characteristic time at which the planar to spherical wave transition occurs is investigated at low (20 mJ/pulse) to high (200 mJ/pulse) beam intensities. The flow structure behind the leading shock wave during the early planar shock state is confirmed by the high-resolution multimaterial hydrocode originally developed for shock compression of condensed matter. A repeatable lab-scale blast wave experiment is conducted at various energy levels with three different ablative targets, and both theoretical and computational analyses are used to verify the flow structures behind the leading shock front that remains spherically symmetric until all the momentum transferred from the absorbed intensity dissipates into open air a few microseconds later.
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79.20.Ds Laser-beam impact phenomena
62.50.Ef Shock wave effects in solids and liquids
42.62.-b Laser applications

Indentation depth dependence of the mechanical strength of Ni films

Zengsheng Ma, Shiguo Long, Yong Pan, and Yichun Zhou

J. Appl. Phys. 103, 043512 (2008); http://dx.doi.org/10.1063/1.2885090 (6 pages) | Cited 8 times

Online Publication Date: 29 February 2008

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The indentation depth effect has been systematically examined on the mechanical properties of electrodeposited nickel films under 0% and 10% tensile strains. It is found that the indentation depth is proportional to the square root of the loads applied and the depth profiles of hardness and elastic modulus follow the similar trend of change with maximal values at the surface skins. The hardness and modulus then attenuate to a value of about half of the maximum, which follows the model proposed by Graca et al., Surf. Coat. Technol. (in press) with the mechanism of geometrically necessary dislocations and surface free energy. We suggest that the effect of surface oxidation and surface bond contraction [ C. Q. Sun, Prog. Solid State Chem. 35, 1 (2007) ] contributes intrinsically to the anomalous skin strengthening because of the local strain and energy trapping caused by surface bonds breaking.
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68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations

Spectral and polarization responses of femtosecond laser-induced periodic surface structures on metals

A. Y. Vorobyev and Chunlei Guo

J. Appl. Phys. 103, 043513 (2008); http://dx.doi.org/10.1063/1.2842403 (3 pages) | Cited 14 times

Online Publication Date: 29 February 2008

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We study, for the first time, the spectral responsivity of femtosecond laser-induced periodic surface structures (FLIPSSs) in the UV, vis, and IR wavelength ranges. We find that FLIPSSs are an effective technique for controlling the optical properties of metals in the UV, vis, and near-IR spectral regions. In contrast to previous studies of FLIPSSs produced over an area of only a single irradiation spot on metals, we demonstrate that FLIPSSs can be produced over an extended area by scanning laser beam. This FLIPSS technique has potential applications in photonics, plasmonics, optoelectronics, thermal radiation sources, and bio-optical devices.
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78.47.-p Spectroscopy of solid state dynamics
68.35.bd Metals and alloys
78.40.Kc Metals, semimetals, and alloys
78.30.Er Solid metals and alloys

An angle-resolved study of early oxidation (<3.0 nm) of Si–Ge alloys

S. J. Kilpatrick and R. J. Jaccodine

J. Appl. Phys. 103, 043514 (2008); http://dx.doi.org/10.1063/1.2885340 (7 pages)

Online Publication Date: 29 February 2008

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A study was completed involving the mechanisms of Si1−xGex oxidation. Either pure or mixed oxides of Si and Ge were grown. All oxides were grown in situ in a Scienta ESCA-300 system designed for oxidation. Angle-resolved x-ray photoelectron spectroscopy was the principal tool in assessing interfacial chemistry. The sub-bonded species of both Si and Ge were investigated as a function of composition. Values for the number of interfacial states were determined in addition to their spatial extension in the actual oxidation interface. The role of interfacial cleaning and the initiation of growth in thin films were determined.
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81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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