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15 Feb 2012

Volume 111, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 043501 (2012); http://dx.doi.org/10.1063/1.3680881 (8 pages)

Gregory J. McGraw and Stephen R. Forrest
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back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Fluid dynamics and mass transport in organic vapor jet printing

Gregory J. McGraw and Stephen R. Forrest

J. Appl. Phys. 111, 043501 (2012); http://dx.doi.org/10.1063/1.3680881 (8 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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Organic vapor jet printing (OVJP) is a high-resolution mask and solvent-free organic thin film deposition and patterning technique. In this work, we analyze factors that affect the material deposition rate and the dynamics of gas flow through an OVJP print head consisting of an array of micron-sized nozzles. Scaling laws governing carrier gas flow dynamics through a system of microchannels and nozzles are developed. From these laws, we predict the deposition rate and doping ratio of organic material as a function of carrier gas flow. The analysis is applied to an experimental print head, and is compared to results obtained via a more complex, direct simulation Monte Carlo model. The print head is used to grow efficient green phosphorescent organic light emitting diodes having an external quantum efficiency and luminance comparable to analogous devices grown by vacuum thermal evaporation.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.U- Doping and impurity implantation
68.55.aj Insulators

Determination of the composition and thickness of semi-polar and non-polar III-nitride films and quantum wells using X-ray scattering

M. E. Vickers, J. L. Hollander, C. McAleese, M. J. Kappers, M. A. Moram, and C. J. Humphreys

J. Appl. Phys. 111, 043502 (2012); http://dx.doi.org/10.1063/1.3678631 (13 pages)

Online Publication Date: 16 February 2012

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There is increasing interest in III-nitride films and multiple quantum well structures grown in non-polar or semi-polar orientations for application in light-emitting devices. We describe a method to obtain the compositions and the thicknesses of layers within III-nitride quantum well or superlattice structures grown in non-polar or semi-polar orientations, based on X-ray scattering. For each new crystallographic orientation considered, new axes were obtained and both the lengths and angles of these new axes calculated relative to the original conventional reference axes. These angles provide the coefficients of the matrix to transform the elastic constants published in the conventional setting (as used for polar c-plane oriented III-nitrides) into the appropriate new values. The new characteristic lengths and new elastic constants are then put into the general equation that relates the composition of a fully strained layer to the experimentally measured out-of-plane alloy d-spacing. Thus we have (a) determined the alloy composition from the difference between the experimentally measured alloy d-spacing and that of the substrate and (b) calculated the strained d-spacing for a given alloy composition for input to simple kinematical simulation software. In addition for quantum well structures the thickness ratio of well-to-barrier must be determined. Here we use the minima in the low angle reflectivity data. The repeat thickness and thus the thicknesses of the well and barrier layers, can be obtained from either the low or the high-angle data. We then cross-check by comparing the experimental and the simulated high-angle diffraction data. This method has been applied successfully to heteroepitaxial non-polar and semi-polar GaN/AlGaN and InGaN/GaN multiple quantum well structures and may also be used to find the composition of epilayers. The method works even in the presence of tilt between the superlattice and the GaN “template’, although in this case additional high-angle diffraction data at different settings must be collected.
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78.70.Ck X-ray scattering
81.07.St Quantum wells
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
68.55.ag Semiconductors
68.65.Cd Superlattices
68.65.Fg Quantum wells

Phase transformation and crystallization kinetics of a-Ge/Cu bilayer for blue-ray recording under thermal annealing and pulsed laser irradiation

Yung-Chiun Her, Wei-Ting Tu, and Ming-Hsin Tsai

J. Appl. Phys. 111, 043503 (2012); http://dx.doi.org/10.1063/1.3684966 (6 pages)

Online Publication Date: 16 February 2012

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Similar phase formation and crystallization behaviors have been observed in the a-Ge/Cu bilayer under thermal annealing and pulsed laser irradiation. The Cu3Ge phase would form prior to the crystallization of a-Ge. The crystallization temperature and activation energy for crystallization of a-Ge were reduced to 310 °C and 2.75 eV, respectively, due to the fast Ge diffusion in the already formed germanide phases. The reaction exponent m of ∼2.0 for the a-Ge/Cu bilayer corresponds to a crystallization process in which grain growth occurs with nucleation, and the nucleation rate decreases with the progress of the grain growth process. Under pulsed laser irradiation, the maximum data-transfer-rates of 44, 56, 74, and 112 Mbit/s can be achieved in the write-once blue-ray disk at the recording powers of 3, 4, 5, and 6 mW, respectively. The a-Ge/Cu bilayer also demonstrated sufficient optical contrast and adequate absorptance for low power and high speed write-once blue-ray recording.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
66.30.-h Diffusion in solids
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.60.Q- Nucleation

Femtosecond electron diffraction: Preparation and characterization of (110)-oriented bismuth films

Gustavo Moriena, Masaki Hada, Germán Sciaini, Jiro Matsuo, and R. J. Dwayne Miller

J. Appl. Phys. 111, 043504 (2012); http://dx.doi.org/10.1063/1.3684975 (4 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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Here, we present a new approach to synthesize (110)-oriented ultrathin membranes of bismuth (Bi). This rather exotic orientation was achieved by directing the growth through rationale control of lattice matching. Bi films were hetero-epitaxially grown on the (100)-surface of freshly cleaved potassium chloride crystals. The sample orientation was characterized by x-ray and electron diffraction. In addition, high quality free-standing films were obtained after dissolution of the substrate in water and controlled evaporation. Femtosecond electron diffraction (FED) was, therefore, used to monitor the coherent shear acoustic phonons in (110)-oriented free-standing Bi films produced by impulsive femtosecond optical excitation. The small de Broglie wavelength (flat Ewald sphere) of keV-electrons combined with an off-Bragg detection scheme provided a magnified view of shear atomic motions, i.e., lattice distortions in the transverse direction. All-optical pump-probe experiments are usually insensitive to shear displacements, a fact that makes FED a unique non-contact method to achieve the complete characterization of elastic properties of nanoscale materials.
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81.05.Bx Metals, semimetals, and alloys
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
68.55.A- Nucleation and growth
63.22.Dc Free films

Optimization on a three-level heat engine working with two noninteracting fermions in a one-dimensional box trap

Jianhui Wang and Jizhou He

J. Appl. Phys. 111, 043505 (2012); http://dx.doi.org/10.1063/1.3681295 (6 pages) | Cited 2 times

Online Publication Date: 16 February 2012

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We setup a three-level heat engine model that works with two noninteracting fermions in a one-dimensional box trap. Besides two quantum adiabatic processes, the quantum heat engine cycle consists of two isoenergetic processes, along which the particles are coupled to energy baths at a high constant energy EH and a low constant energy EC, respectively. Based on the assumption that the potential wall moves at a very slow speed and there exists a heat leakage between two energy baths, we derive the expressions of the power output and the efficiency, and then obtain the optimization region for the heat engine cycle. Finally, we present a brief performance analysis of a Carnot engine between a hot and a cold bath at temperatures TH and TC, respectively. We demonstrate that under the same conditions, the efficiency η = 1-(EC/EH) of the engine cycle is bounded from above the Carnot efficiency ηc = 1-(TC/TH).
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05.30.Fk Fermion systems and electron gas
05.70.-a Thermodynamics

Damage property of incompletely spalled aluminum under shock wave loading

Meilan Qi, Chao Luo, Hongliang He, Yonggang Wang, Duan Fan, and Shilin Yan

J. Appl. Phys. 111, 043506 (2012); http://dx.doi.org/10.1063/1.3681301 (6 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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The nucleation, growth, and coalescence of microscopic voids are induced inside ductile metal when it is subjected to dynamic tension, and this eventually results in a catastrophic fracture of the specimen. In the present work, this failure property is studied by using ultrapure aluminum (99.999%) as a representative candidate for the ductile metal and, further, the micro-void growth behavior (or the damage evolution) before the catastrophic fracture has been investigated. Measurements of the free surface velocity profile and statistical analysis of micro-voids were used to determine the spall characteristic and damage evolution behavior of dynamic tensile fracture in ultrapure aluminum. Through comparison of the differences between the incompletely and completely spalled signals, the spall characteristics of ultrapure aluminum from incomplete to complete spall were analyzed. Moreover, an obvious critical characteristic is found on the basis of the association between the maximum damage caused within samples and the product of peak stress and tensile duration. The damage variable slowly increased in a linear manner in the initial stages but changed to nonlinear growth and rapidly approached a fracture state as the damage variable extended beyond the critical value, which is approximately 0.09. A physical explanation for this transition is discussed and implicates micro-void linkage behavior during the dynamic failure.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.50.Ef Shock wave effects in solids and liquids
64.60.qj Studies of nucleation in specific substances
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Identification of electrically active defects in thin dielectric films by spectroscopic ellipsometry

J. Price, G. Bersuker, and P. S. Lysaght

J. Appl. Phys. 111, 043507 (2012); http://dx.doi.org/10.1063/1.3684605 (6 pages)

Online Publication Date: 17 February 2012

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A study of resonant photo-absorption features in high-k dielectric film stacks using vacuum ultraviolet spectroscopic ellipsometry demonstrates that all optically observable dielectric-related defects are located in the interfacial SiO2 layer rather than in the bulk high-k film. The defects, located at 2.9 eV, 3.6 eV, 3.9 eV, and 4.75 eV within the bandgap of this bottom interface, are found to be strongly affected by processing conditions. These results are supported by both electrical and physical characterization measurements that identify a consistent trend in the evolution of charge trapping defects for samples subjected to identical processing conditions. In addition, evidence is provided correlating the optically active 2.9 eV defect to positively charged oxygen vacancies in the bottom interfacial layer that have recently been proposed as contributing to the flatband voltage roll-off phenomenon. The close connection between these results and both ab initio calculations and experimental findings substantiate the use of spectroscopic ellipsometry as a unique characterization method for identifying process-induced defects during development and fabrication of dielectric film stacks.
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77.55.D- High-permittivity gate dielectric films
61.72.jd Vacancies

Structural and optical evaluation of InGaN/GaN multi-quantum wells on template consisting of in-plane alternately arranged relaxed InGaN and GaN

Narihito Okada, Yoichi Yamada, and Kazuyuki Tadatomo

J. Appl. Phys. 111, 043508 (2012); http://dx.doi.org/10.1063/1.3684606 (5 pages)

Online Publication Date: 21 February 2012

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Templates consisting of in-plane alternately arranged relaxed InGaN and GaN were obtained by (11–22) facet growth and mass transport via metal-organic vapor phase epitaxy. InGaN/GaN multi-quantum wells (MQWs) were grown on the novel templates, and their optical and structural properties were investigated. From photoluminescence measurement, longer and shorter peak emission wavelengths were observed from the MQWs on the InGaN and GaN regions, respectively. The discrepancy of the peak emission wavelength for the MQWs on the alternately arranged relaxed InGaN and GaN was caused by the compositional-pulling effect, which contributed to the InN molar fraction and the thickness of the InGaN quantum well. The reduction of the quantum-confined Stark effect on the InGaN region of the template was confirmed by revealing the structural and optical properties of the MQWs.
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81.07.St Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Effect of interface alloying and band-alignment on the Auger recombination of heteronanocrystals

J. I. Climente, J. L. Movilla, and J. Planelles

J. Appl. Phys. 111, 043509 (2012); http://dx.doi.org/10.1063/1.3684981 (5 pages) | Cited 1 time

Online Publication Date: 21 February 2012

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We report a numerical study of the effect of interface alloying and band alignment on the Auger recombination processes of core/shell nanocrystals. Smooth interfaces are found to suppress Auger recombination, the strength of the suppression being very sensitive to the core size. The use of type-II structures constitutes an additional source of suppression, especially when the shell confines electrons rather than holes. We show that “magic” sizes leading to negligible Auger recombination [Cragg and Efros, Nano Letters 10, 313 (2010)] should be easier to realize experimentally in nanocrystals with extended interface alloying and wide bandgap.
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79.20.Fv Electron impact: Auger emission

Evolution of SiHx hydrides during the phase transition from amorphous to nanocrystalline silicon films

C. Garozzo, R. A. Puglisi, C. Bongiorno, C. Spinella, S. Mirabella, R. Reitano, S. Di Marco, M. Foti, and S. Lombardo

J. Appl. Phys. 111, 043510 (2012); http://dx.doi.org/10.1063/1.3686136 (8 pages)

Online Publication Date: 21 February 2012

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This paper investigates the morphological evolution of hydrogenated amorphous silicon layers obtained by plasma enhanced chemical vapor deposition at different H dilutions in the regime close to the formation of the nanocrystalline phase. The role of hydrogen in the transition from the amorphous to the crystalline phase is investigated by accurate structural and chemical characterization, from the early stages of nucleation, where the nuclei present size slightly larger than the critical nucleus, i.e., about 0.8 nm in radius, up to the formation of crystalline grains larger than 30 nm in radius. A correlation between the structural characteristics of such crystalline phase and the bonding mechanism of Si with H through multiple hydrides, such as Si-H2 and Si-H3 is found, particularly the tri-hydrides are found to be directly correlated to the shape and the size of the nanocrystallites present in the films. The multiple hydrides are found to play a role also in the electrical characteristics of p-i-n a-Si:H solar cells whose intrinsic layer is realized in the above H dilution conditions. An explanation of the experimental data in terms of the different bonding mechanism of H in the Si matrix is provided.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kg Semiconductors
73.61.Cw Elemental semiconductors
64.70.Nd Structural transitions in nanoscale materials
64.60.qj Studies of nucleation in specific substances
88.40.jj Silicon solar cells

In situ study of the growth properties of Ni-rare earth silicides for interlayer and alloy systems on Si(100)

J. Demeulemeester, W. Knaepen, D. Smeets, A. Schrauwen, C. M. Comrie, N. P. Barradas, A. Vieira, C. Detavernier, K. Temst, and A. Vantomme

J. Appl. Phys. 111, 043511 (2012); http://dx.doi.org/10.1063/1.3681331 (13 pages) | Cited 1 time

Online Publication Date: 21 February 2012

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We report on the solid-phase reaction of thin Ni-rare earth films on a Si(100) substrate, for a variety of rare earth (RE) elements (Y, Gd, Dy, and Er). Both interlayer (Ni/RE/〈Si〉) and alloy (Ni-RE/〈Si〉) configurations were studied. The phase sequence during reaction was revealed using real-time x-ray diffraction whereas the elemental diffusion and growth kinetics were examined by real-time Rutherford backscattering spectrometry. All RE elements studied exert a similar influence on the solid phase reaction. Independent of the RE element or its initial distribution a ternary Ni2Si2RE phase forms, which ends up at the surface after NiSi growth. With respect to growth kinetics, the RE metal addition hampers the Ni diffusion process even for low concentrations of 2.5 at. %, resulting in the simultaneous growth of Ni-rich silicide and NiSi. Moreover, the formation of Ni2Si2RE during NiSi growth alters the Ni diffusion mechanism in the interlayer causing a sudden acceleration of the Ni silicide growth. Besides a significant effect on the silicide growth, we have found that adding 5 at. % Er (relative to Ni) lowers the NiSi Schottky barrier height on n-type Si(100) by approximately 0.1 eV for the interlayer and alloy configuration.
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68.55.A- Nucleation and growth
68.35.Fx Diffusion; interface formation
73.30.+y Surface double layers, Schottky barriers, and work functions

Effect of Si and C concentration on the microstructure, and the mechanical, tribological and electrochemical properties of nanocomposite TiC/a-SiC:H/a-C:H coatings prepared by plasma enhanced chemical vapor deposition

Duanjie Li, Salim Hassani, Suzie Poulin, Jerzy A. Szpunar, Ludvik Martinu, and Jolanta E. Klemberg-Sapieha

J. Appl. Phys. 111, 043512 (2012); http://dx.doi.org/10.1063/1.3684602 (9 pages) | Cited 1 time

Online Publication Date: 22 February 2012

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The nanocomposite TiC/a-SiC:H/a-C:H (presented as Ti-Si-C) coatings attract considerable interest due to their possible applications such as wear protective coatings, diffusion barriers, and materials for solar cells and electrical contacts. In order to explore new film properties and open new opportunities, in the present work, we prepare a series of C-rich Ti-Si-C coatings with different Si and C concentrations using plasma enhanced chemical vapor deposition, and we systematically investigate the effect of elemental composition on the microstructure, and on the mechanical, tribological and electrochemical properties. XRD and XPS analyses demonstrate that the Ti-Si-C coatings mainly consist of nanocrystalline (nc-) TiC embedded in amorphous (a-) SiC:H and a-C:H matrices. Ti-Si-C coatings with a high Si concentration possess enhanced mechanical properties (high hardness), while those with additional C exhibit superior tribological behaviors. The increase of Si and/or C concentrations leads to a grain size refinement of the TiC nanocrystals and to an expansion of the amorphous phase. This in turn substantially enhances their corrosion resistance. Ti-Si-C coatings with the highest Si or C contents exhibit the best corrosion performance among the tested samples by improving the corrosion resistance of the SS410 substrate by a factor of ∼400.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Kn Corrosion protection
81.40.Pq Friction, lubrication, and wear
81.40.Rs Electrical and magnetic properties related to treatment conditions
68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness

Formation of fullerene superlattices by interlayer bonding in twisted bilayer graphene

Andre R. Muniz and Dimitrios Maroudas

J. Appl. Phys. 111, 043513 (2012); http://dx.doi.org/10.1063/1.3682475 (6 pages) | Cited 1 time

Online Publication Date: 22 February 2012

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Based on first-principles density functional theory calculations, we report a novel class of carbon nanostructures consisting of superlattice arrangements of caged fullerene configurations of various sizes embedded within planes of twisted bilayer graphene. Formation of these structures is the outcome of interlayer C-C bonding between pairs of graphene planes chemically modified with certain patterns of chemisorbed hydrogen and rotated with respect to each other by angles around 30°. A specific subclass of these nanostructures preserves the main features of the electronic structure of pristine single-layer graphene. Our study proposes possible functionalization strategies to systematically tailor the electronic properties of bilayer graphene.
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71.20.Tx Fullerenes and related materials; intercalation compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.21.Cd Superlattices
81.16.Rf Micro- and nanoscale pattern formation
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Study on the effect of pressure on the properties of intrinsic point defects in monoclinic zirconia: Ab initio calculations

Shijun Zhao, Jianming Xue, Yugang Wang, and Sha Yan

J. Appl. Phys. 111, 043514 (2012); http://dx.doi.org/10.1063/1.3682766 (10 pages)

Online Publication Date: 22 February 2012

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First-principles calculations were performed to investigate the effects of external pressure on the properties of intrinsic point defects in monoclinic zirconia. Our results show that when the applied external pressure increases from atmospheric pressure to 14.9 GPa, the formation energies of oxygen vacancies decrease with increasing pressure, while the formation energies of the cation and anion interstitials increase all over the pressure regime investigated. Among them the most remarkable change occurs in neutral zirconium interstitial with an increase of 2.21 eV. In particular, the formation energy of zirconium vacancy depends strongly on its charge state. For all the chemical potential and Fermi level considered, the cation and anion vacancies are the most stable defects in all cases. The present calculations also reveal that the formation energies of Frenkel defects could be raised by external pressures, while the energetics of Schottky defects are not much affected. Moreover, the charge state transition of defects is found to be greatly influenced by the external pressures, and thus the stability diagram of defects in ZrO2 is strongly dependent on external pressures. Our findings suggest that external pressures should raise the concentration of oxygen vacancies significantly.
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61.72.jj Interstitials
61.72.jd Vacancies

Size dependent melting behaviors of nanocrystalline in particles embedded in amorphous matrix

J. Mu, Z. W. Zhu, H. F. Zhang, H. M. Fu, A. M. Wang, H. Li, and Z. Q. Hu

J. Appl. Phys. 111, 043515 (2012); http://dx.doi.org/10.1063/1.3686624 (4 pages)

Online Publication Date: 23 February 2012

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The composites of In nanoparticles embedded in Al-based amorphous matrix were synthesized. As the content of In increases, the average size of In nanoparticles increases. The melting behaviors of embedded In nanoparticles were investigated, indicating that the melting temperature is suppressed, and the smaller the size is, the lower the melting temperature is. It is confirmed by comparing the differential scanning calorimetry curves with those of the size distribution. The size dependent melting behaviors of nanoparticles were discussed with the thermodynamic model.
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64.70.D- Solid-liquid transitions
81.07.Wx Nanopowders

Ab initio many-body study of the electronic and optical properties of MgAl2O4 spinel

Shengli Jiang, Tiecheng Lu, Yao Long, and Jun Chen

J. Appl. Phys. 111, 043516 (2012); http://dx.doi.org/10.1063/1.3686727 (7 pages) | Cited 4 times

Online Publication Date: 23 February 2012

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The electronic structure and optical properties of MgAl2O4 spinel with and without oxygen vacancies have been studied in the framework of many-body perturbation theory. By considering the self-energy of electrons, we reasonably describe the bandgap of perfect MgAl2O4 and the defect energy levels of MgAl2O4 containing oxygen vacancies. With the inclusion of electron-hole interaction by solving Bethe-Salpeter equation, the calculated dielectric functions and reflectivity spectrum all are in agreement well with the experimental results for perfect MgAl2O4. Our results show that the sharp peak near 7.8 eV in the experimental absorption spectrum is attributed to the excitonic states. The oxygen vacancies produce some new defect energy levels in the forbidden gap. The optical absorption peaks at 5.3 eV, 4.75 eV and 3.2 eV are induced by the VO0 and VO1+ vacancies.
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71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.jd Vacancies
71.15.-m Methods of electronic structure calculations

Dissolution of Sn in a SnPb solder bump under current stressing

Ying-Ta Chiu, Kwang-Lung Lin, and Yi-Shao Lai

J. Appl. Phys. 111, 043517 (2012); http://dx.doi.org/10.1063/1.3682480 (8 pages)

Online Publication Date: 24 February 2012

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An in situ SEM/energy dispersive spectroscopy (EDS) analysis revealed that the dispersed Sn-rich phase of the 95Pb-5Sn solder in a 95Pb-5Sn/63Sn-37Pb composite solder bump dissolved under current stressing. The dissolution was not prominent until the current density reached a threshold value of between 3.3 × 104 and 4.2 × 104 A/cm2. Supersaturation over thermal solubility of Sn-in-Pb was detected with current stressing. A polarity dissolution model was proposed for the dissolution behavior of the Sn-rich phase under current stressing. The dissolution mechanism under current stressing was discussed in relation to electromigration and thermomigration behavior of SnPb solders.
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64.75.Bc Solubility
66.30.Qa Electromigration
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Structural study of GaP layers on misoriented silicon (001) substrates by transverse scan analysis

H. Jussila, S. Nagarajan, T. Huhtio, H. Lipsanen, T. O. Tuomi, and M. Sopanen

J. Appl. Phys. 111, 043518 (2012); http://dx.doi.org/10.1063/1.3686711 (6 pages) | Cited 4 times

Online Publication Date: 24 February 2012

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This paper examines the structural properties of gallium phosphide layers by high resolution x-ray diffraction and atomic force microscopy measurements. GaP layers are grown on misoriented and nominally exactly oriented silicon (001) substrates by metalorganic vapor phase epitaxy. Structural characterization is performed by reciprocal lattice map and transverse scan measurements of (00l)-reflections (l = 2, 4, 6). Transverse scan line profiles of GaP layers on exactly oriented and misoriented substrates are compared thoroughly and antiphase disorder related satellite peaks are observed on exactly oriented substrates. In addition, results imply that antiphase disorder is self-annihilated on misoriented substrates. The dependence of crystallographic tilt on growth temperature indicates structural coherence. Williamson-Hall-like plot of transverse scans reveals the lateral correlation length of crystalline defects of 79 nm which gives the average size of the mosaic crystallites. In addition, the mosaicity of the GaP layer is 0.042°.
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68.47.Fg Semiconductor surfaces
61.72.Mm Grain and twin boundaries
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors

CdS nanofilms: Synthesis and the role of annealing on structural and optical properties

Suresh Kumar, Pankaj Sharma, and Vineet Sharma

J. Appl. Phys. 111, 043519 (2012); http://dx.doi.org/10.1063/1.3688042 (6 pages) | Cited 3 times

Online Publication Date: 27 February 2012

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Cadmium sulfide (CdS) nanofilms have been deposited on the glass substrate using the chemical bath technique. Cadmium chloride and thiourea have been used as Cd2+ and S2− ion sources with ammonia as a complexing agent in the presence of a nonionic surfactant. The deposited films have been annealed in air at 373 K, 473 K, 573 K, and 673 K ± 5 K temperature. The effect of the annealing on the structure, morphology, and optical properties of CdS nanofilms has been studied. CdS films have been characterized by X-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and UV-Vis-NIR spectrophotometer. The CdS films have been found to be nanocrystalline in nature with the zinc blende structure. The direct bandgap has been determined. Various parameters, viz. the grain size, inter-planer spacing, lattice constant, dislocation density, microstrain, surface morphology, absorption coefficient, and optical bandgap has been calculated and found to vary with annealing. The results have been explained on the basis of structural, surface, and optical changes.
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68.55.ag Semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
68.55.J- Morphology of films
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effects of P implantation and post-implantation annealing on defect formation in ZnO

X. J. Wang, W. M. Chen, F. Ren, S. Pearton, and I. A. Buyanova

J. Appl. Phys. 111, 043520 (2012); http://dx.doi.org/10.1063/1.3687919 (7 pages) | Cited 3 times

Online Publication Date: 27 February 2012

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Photoluminescence (PL) and optically detected magnetic resonance (ODMR) techniques are utilized to examine the effects of P implantation and post-implantation annealing on defect formation in ZnO single crystals. From ODMR, the main defects created by ion implantation include oxygen and zinc vacancies as a well as a deep donor labeled as PD. The formation of the PD defect is likely promoted by the presence of P as it could only be detected in the P-containing ZnO. The VO and PD centers are found to exhibit low thermal stability and can be annealed out at 800 °C. On the other hand, a new set of defects, such as Z, T, and D* centers, is detected after annealing. Based on measured spectral dependences of the ODMR signals, the VO, VZn, and PD centers are shown to participate in spin-dependent recombination processes related to red emissions, whereas the Z, T, and D* centers are involved in radiative recombination over a wide spectral range of 1.55–2.5 eV. From the PL measurements, combined effects of implantation and annealing also lead to appearance of a new PL band peaking at ∼3.156 eV, likely due to donor-acceptor-pair recombination. The formation of the involved deep acceptor is concluded to be facilitated by the presence of P.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies
78.55.Et II-VI semiconductors

Refractive index of sodium iodide

G. E. Jellison, Jr., L. A. Boatner, J. O. Ramey, J. A. Kolopus, L. A. Ramey, and D. J. Singh

J. Appl. Phys. 111, 043521 (2012); http://dx.doi.org/10.1063/1.3689746 (4 pages) | Cited 1 time

Online Publication Date: 28 February 2012

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The refractive index of sodium iodide, an important scintillator material that is widely used for radiation detection, is based on a single measurement made by Spangenberg at one wavelength using the index-matching liquid immersion method (Z. Kristallogr. 57, 494 (1923)). In the present paper, we present new results for the refractive index of sodium iodide as measured by the minimum deviation technique at six wavelengths between 436 nm (n = 1.839 ± 0.002) and 633 nm (n = 1.786 ± 0.002). These six measurements can be fit to a Sellmeier model, resulting in a χ2 of 1.02, indicating a good fit to the data. In addition, we report on ellipsometry measurements, which suggest that the near-surface region of the air sensitive NaI crystal seriously degrades, even in a moisture-free environment, resulting in a significantly lower value of the refractive index near the surface. First-principles theoretical calculations of the NaI refractive index that agree with the measured values within 0.025-0.045 are also presented and discussed.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.70.Ps Scintillation
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