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15 Jul 2008

Volume 104, Issue 2, Articles (02xxxx)

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Role of C in the formation and kinetics of nanovoids induced by He+ implantation in Si

D. D’Angelo, S. Mirabella, E. Bruno, G. Pulvirenti, A. Terrasi, G. Bisognin, M. Berti, C. Bongiorno, and V. Raineri

J. Appl. Phys. 104, 023501 (2008); http://dx.doi.org/10.1063/1.2955707 (5 pages) | Cited 2 times

Online Publication Date: 16 July 2008

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The formation and growth of nanovoids in a C-doped Si layer after He+ implantation and thermal annealing are reported. A structure consisting of 240 nm of Si, 20 nm of Si doped with C at 0.8 at. %, and 240 nm of Si cap was realized by molecular beam epitaxy onto a (100) Si Czochralsky substrate. Three sets of samples were implanted with He+ at 30 keV and different doses of 8×1015, 3×1016, and 5×1016 cm−2 and subsequently annealed at 800 °C in N2 atmosphere. Cross-section transmission electron microscopy was used to determine the void size and location. The tensile strain of the C-doped layer was measured by high-resolution x-ray diffraction. Our studies report the double role of C in the formation and evolution of nanovoids. After the low dose implantation, the C-doped layer still shows tensile strain due to substitutional C, and voids are localized only within this layer. At higher implantation doses, all the C atoms have been displaced from substitutional sites. No more strain is present in the C-doped layer and the presence of large cavities in its neighborhood is strongly inhibited. This work shows how localized strain in epitaxial films can be effectively used to drive nanovoid formation and evolution.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Anisotropic diffusion of point defects in metals under a biaxial stress field simulation and theory

Wai-Lun Chan, Robert S. Averback, and Yinon Ashkenazy

J. Appl. Phys. 104, 023502 (2008); http://dx.doi.org/10.1063/1.2955786 (5 pages) | Cited 1 time

Online Publication Date: 16 July 2008

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We study the diffusion anisotropy (DA) of point defects in fcc and bcc metals in the presence of an applied biaxial stress. The DA depends sensitively on both the crystalline structure and the crystallographic direction in which the stress is applied. For example, interstitials in fcc metals diffuse faster in the plane of the compressive stress than normal to it when the stress is applied to the (001) plane, but they diffuse slower in-plane than out-of-plane when the stress is applied in the (111) plane. In contrast, an applied biaxial stress in the (001) plane of a bcc metal does not cause DA. These results can be explained by considering the interaction of the defects at their saddle point configurations with the external field, together with the constraints imposed by the crystal structure on the defect jump directions. Our calculations show that the DA can be large and lead to surprising results in a number of practical situations.
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61.72.jj Interstitials
66.30.Fq Self-diffusion in metals, semimetals, and alloys
61.66.Bi Elemental solids

Hardness of covalent compounds: Roles of metallic component and d valence electrons

Xiaoju Guo, Lei Li, Zhongyuan Liu, Dongli Yu, Julong He, Riping Liu, Bo Xu, Yongjun Tian, and Hui-Tian Wang

J. Appl. Phys. 104, 023503 (2008); http://dx.doi.org/10.1063/1.2956594 (7 pages) | Cited 32 times

Online Publication Date: 16 July 2008

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Based on the detailed analysis of chemical bonds, we present a Vickers hardness expression for the covalency-dominant crystals such as transition-metal carbides and nitrides. Hardness is dependent not only on bond length, bond density, and ionicity of bond [ F. M. Gao et al., Phys. Rev. Lett. 91, 015502 (2003) ] but also on the metallicity of bond and orbital form in the crystal structure of a compound, and all of these parameters can be determined by first-principles calculations. The calculated hardness using our expression has a good agreement with the experimental values for known monocarbides, mononitrides of transition metals, and cubic Zr3N4 with Th3P4 structure. In addition, we have predicted the Vickers hardness of the recently predicted tetragonal BC3 and tetragonal B2CN, and the recently synthesized pyrite PtN2 and marcasite OsN2. Our method offers one useful technique to search for superhard materials in transition-metal carbides and nitrides.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
61.50.Lt Crystal binding; cohesive energy

Phonon sideband recombination kinetics in single quantum dots

M. Abbarchi, M. Gurioli, A. Vinattieri, S. Sanguinetti, M. Bonfanti, T. Mano, K. Watanabe, T. Kuroda, and N. Koguchi

J. Appl. Phys. 104, 023504 (2008); http://dx.doi.org/10.1063/1.2948932 (4 pages) | Cited 3 times

Online Publication Date: 17 July 2008

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We report an experimental study on the recombination kinetics of single strain-free GaAs quantum dots (QDs) grown by modified droplet epitaxy. The different bands composing the single quantum dot emission line at high temperature show identical dynamics, proving the common origin of all contributions. Our results thus agree with the interpretation of the broad pedestal band appearing when increasing the temperature as originated from the phonon replica. Finally, the relative weight of the phonon replicas depends both on temperature and on the QD size, in agreement with the theoretical predictions.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Annealing effect on the luminescence properties of BaZrO3:Yb3+ microcrystals

J. Oliva, E. De la Rosa, L. A. Diaz-Torres, P. Salas, and C. Ángeles-Chavez

J. Appl. Phys. 104, 023505 (2008); http://dx.doi.org/10.1063/1.2954959 (6 pages) | Cited 5 times

Online Publication Date: 17 July 2008

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Yb-doped barium zirconate (BaZrO3:Yb3+) was synthesized by a hydrothermal method at 100 °C. It presents a cubic perovskite crystalline phase, which is stable between 100 and 100 °C. Upon increasing the annealing temperature, two major changes are observed. (1) The near infrared (NIR) absorption band of Yb3+ decreases, and an enhancement in both the NIR emission of Yb3+ single ion and visible emission of Yb3+ pairs occurs, which is attributed to the reduction in impurities. (2) The annealing process induces new absorption bands in the ultraviolet-visible (UV-vis) region that increase as annealing temperature increases. These results suggest that reduction in Yb3+ to Yb2+ is taking place. The visible emission is considered to be a cooperative emission from Yb3+ pairs. Under UV and visible excitation, no emission of Yb2+ ions was observed. This suggests that the broadband absorption in the UV-vis region might be related to F color centers, which are responsible for the inhibition of the Yb2+ ion emission.
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61.72.Cc Kinetics of defect formation and annealing
61.72.jn Color centers
78.55.Hx Other solid inorganic materials

Coherency effects in nanobeam x-ray diffraction analysis

Hanfei Yan, Özgür Kalenci, I. Cevdet Noyan, and Jörg Maser

J. Appl. Phys. 104, 023506 (2008); http://dx.doi.org/10.1063/1.2955714 (7 pages) | Cited 2 times

Online Publication Date: 17 July 2008

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We describe the evolution of the x-ray scattering pattern which forms on an area detector when a divergent, coherent nanobeam is diffracted from a perfect or weakly deformed single crystal. We show that the scattering can be considered as virtual diffraction from an angular aperture in reciprocal space; this is analogous to pinhole diffraction in real space. We define an angular Fresnel number, YA, which allows the categorization of the nanodiffraction image into near-field, intermediate-field, and far-field regimes. We provide equations for YA in simple geometries and show that dynamical scattering artifacts are eliminated through wave interference in the far-field image; this is the only regime where direct analysis of the charge coupled device image using geometrical formulae to transform distances to diffraction angles is possible.
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61.05.cc Theories of x-ray diffraction and scattering
61.05.cp X-ray diffraction

On the anisotropic thermal conductivity of magnetorheological suspensions

Benjamin N. Reinecke, Jerry W. Shan, Karl K. Suabedissen, and Anna S. Cherkasova

J. Appl. Phys. 104, 023507 (2008); http://dx.doi.org/10.1063/1.2949266 (7 pages) | Cited 8 times

Online Publication Date: 17 July 2008

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The thermal conductivity of an iron-based magnetorheological suspension is experimentally investigated for varying particle volume fractions and magnetic-field strengths. Under a magnetic field, the thermal-conductivity component in the field direction increases significantly (by 100% in one case), while the two components perpendicular to the field direction remain virtually unchanged. We propose and test two models for the thermal conductivity in the limiting case when the suspension’s internal structure is saturated by the imposed magnetic field. A two-level homogenization model that first uses the Bruggeman method to calculate the effective conductivity of particle chains, and then an effective-medium theory model to determine the overall conductivity of the suspension, is found to fit accurately the components of the thermal-conductivity tensor. Utilizing this modeling procedure, we determine the effective conductivity of the field-induced, iron-particle chains to be 0.966 W/mK at saturation. This conductivity is equivalent to a particle volume fraction within the chains of φint = 0.495, which is smaller than the φint = 0.698 predicted for an ideal body-centered-tetragonal arrangement of particles. This suggests that the microstructure in this case differs from perfectly aligned crystals, having either lattice defects or otherwise waviness in the particle chains.
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66.25.+g Thermal conduction in nonmetallic liquids
83.80.Gv Electro- and magnetorheological fluids
82.70.Kj Emulsions and suspensions

Modeling anisotropic damage in an encapsulated ceramic under ballistic impact

Q. H. Zuo, J. K. Dienes, J. Middleditch, and H. W. Meyer, Jr.

J. Appl. Phys. 104, 023508 (2008); http://dx.doi.org/10.1063/1.2956509 (10 pages) | Cited 2 times

Online Publication Date: 17 July 2008

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This paper presents a study of anisotropic damage and cracking in a hot isostatically pressed assembly of titanium alloy encapsulated AD-995 ceramic under ballistic impact using the statistical crack mechanics approach. Anisotropy of crack growth in the ceramic is illustrated numerically by examining the growth in crack sizes along three orientations. Comparisons with the experimental measurements of the predicted backsurface profile and the damage (cracking) in the ceramic suggest that the model predictions are consistent with the experimental data. Numerical simulation also indicates that a prestress of roughly 2 kbar (200 MPa) compensates for about 1% of initial porosity in the ceramic. A comparison is made to the Rajendran–Grove ceramic model in EPIC which assumes an isotropic crack distribution.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks

Effect of antimony incorporation on the density, shape, and luminescence of InAs quantum dots

J. F. Chen, C. H. Chiang, Y. H. Wu, L. Chang, and J. Y. Chi

J. Appl. Phys. 104, 023509 (2008); http://dx.doi.org/10.1063/1.2959598 (5 pages) | Cited 3 times

Online Publication Date: 18 July 2008

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This work investigates the surfactant effect on exposed and buried InAs quantum dots (QDs) by incorporating Sb into the QD layers with various Sb beam equivalent pressures (BEPs). Secondary ion mass spectroscopy shows the presence of Sb in the exposed and buried QD layers with the Sb intensity in the exposed layer substantially exceeding that in the buried layer. Incorporating Sb can reduce the density of the exposed QDs by more than two orders of magnitude. However, a high Sb BEP yields a surface morphology with a regular periodic structure of ellipsoid terraces. A good room-temperature photoluminescence (PL) at ∼ 1600 nm from the exposed QDs is observed, suggesting that the Sb incorporation probably improves the emission efficiency by reducing the surface recombination velocity at the surface of the exposed QDs. Increasing Sb BEP causes a blueshift of the emission from the exposed QDs due to a reduction in the dot height as suggested by atomic force microscopy. Increasing Sb BEP can also blueshift the ∼ 1300 nm emission from the buried QDs by decreasing the dot height. However, a high Sb BEP yields a quantum well-like PL feature formed by the clustering of the buried QDs into an undulated planar layer. These results indicate a marked Sb surfactant effect that can be used to control the density, shape, and luminescence of the exposed and buried QDs.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

High cluster formation tendency in Co implanted ZnO

K. Potzger, K. Kuepper, Q. Xu, S. Zhou, H. Schmidt, M. Helm, and J. Fassbender

J. Appl. Phys. 104, 023510 (2008); http://dx.doi.org/10.1063/1.2955717 (5 pages) | Cited 10 times

Online Publication Date: 18 July 2008

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ZnO(0001) single crystals have been implant doped with a maximum of 5 at. % of Co at low temperatures. While as-implanted crystals do not show ferromagnetic properties, postimplantation annealing leads to the transformation of the implanted Co ions into small metallic clusters giving rise to a pronounced hysteresis upon magnetization reversal. The dispersed Co ions are in 2+ oxidation state. Positive magnetoresistance could be observed at low temperatures.
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61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Preparation and characterization of Al2O3/Y3Al5O12/ZrO2 ternary hypoeutectic in situ composites by laser rapid solidification

Haijun Su, Jun Zhang, Junjie Tian, Lin Liu, and Hengzhi Fu

J. Appl. Phys. 104, 023511 (2008); http://dx.doi.org/10.1063/1.2955768 (7 pages) | Cited 5 times

Online Publication Date: 18 July 2008

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The directionally solidified oxide eutectic in situ composite is one of the most promising high-temperature structural materials in oxidizing environments. Pore-free rods and plates of ternary Al2O3/Y3Al5O12 (YAG)/ZrO2 hypoeutectic in situ composites with hypoeutectic composition (71 mol % Al2O3, 17 mol % Y2O3, and 12 mol % ZrO2) are prepared rapidly by the laser zone remelting technique. The hypoeutectic growth and microstructure characteristic of grown crystals are studied using the scanning electron microscopy, x-ray diffraction, and energy dispersive spectroscopy, aiming to understand well the rapid solidification behavior of the ternary oxide system of Al2O3–Y2O3–ZrO2. The rapidly solidified Al2O3/YAG/ZrO2 hypoeutectic shows a refined, interpenetrating, and irregular lamellar structure with a reticular distribution of coarse Al2O3 and yttrium aluminum garnet (YAG) and smaller ZrO2 phases. The fine ZrO2 phases are partially embedded at the Al2O3/YAG interfaces. Moreover, the typical dendrite microstructure similar to the metallic solidification is also observed. The formation of two kinds of microstructures is mainly attributed to the rapid growth during the laser zone remelting and constitutional supercooling. The Al2O3 and YAG phases grow in a typical faceted manner, and the ZrO2 phase presents a weak-faceted growth. The size of the interphase spacing obtained decreases rapidly in increasing the laser scanning rate. The fundamental investigations on the irregular growth mechanisms of the hypoeutectic are suggestive to the comprehension of the complex solidification behavior of the ternary oxide systems.
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81.05.Mh Cermets, ceramic and refractory composites
81.30.Fb Solidification
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
64.70.D- Solid-liquid transitions
81.10.Fq Growth from melts; zone melting and refining
42.62.-b Laser applications

Direct synthesis and properties of K2SiF6:Mn4+ phosphor by wet chemical etching of Si wafer

Sadao Adachi and Toru Takahashi

J. Appl. Phys. 104, 023512 (2008); http://dx.doi.org/10.1063/1.2956330 (3 pages) | Cited 16 times

Online Publication Date: 18 July 2008

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A new method of synthesizing Mn-activated phosphor is presented. The method uses only chemical etching of Si wafer in HF/H2O solution with the addition of an oxidizing agent KMnO4. The luminescence centers of red emission are ascribed to Mn4+ ions in the octahedral sites of potassium hexafluorosilicate (K2SiF6). The luminescence intensity becomes much stronger at higher temperatures, without largely changing its spectral feature.
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81.65.Cf Surface cleaning, etching, patterning
81.20.-n Methods of materials synthesis and materials processing
78.55.Hx Other solid inorganic materials

Crystallization and shear modulus of a forming biopolymer film determined by in situ x-ray diffraction and ultrasound reflection methods

Marko Peura, Timo Karppinen, Annemai Soovre, Ari Salmi, Maija Tenkanen, Edward Hæggström, and Ritva Serimaa

J. Appl. Phys. 104, 023513 (2008); http://dx.doi.org/10.1063/1.2951451 (6 pages) | Cited 3 times

Online Publication Date: 18 July 2008

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The structure and the rigidity of a forming biopolymer film were determined using concurrent x-ray diffraction and ultrasonic reflection measurements. Film formation of a xylan solution (de-ionized water, 10 g/l xylan, 4 g/l glycerol) was studied during water evaporation at 24(±2) °C, 37(±5) %RH. X-ray diffraction (XRD) data showed the crystallization and ultrasonic data the increase of the shear modulus (G) during water evaporation. Xylan crystallized into small xylan dihydrate crystallites, the number of which increased as water evaporated. Crystallization began earlier than the increase in G during film formation. The increase in G also continued after the crystallites were fully formed, indicating still ongoing structural changes in the amorphous parts. The maximum value of G was 0.1–0.5 GPa. XRD measurements performed ex situ showed a crystallinity of 16%–19% (±5%) and a fairly isotropic crystallite orientation in the surface plane of the films.
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68.60.Bs Mechanical and acoustical properties
62.65.+k Acoustical properties of solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
64.70.dg Crystallization of specific substances
68.55.am Polymers and organics

Spatially resolved residual stress assessments of GaN film on sapphire substrate by cathodoluminescence piezospectroscopy

Giuseppe Pezzotti, Alessandro Alan Porporati, Andrea Leto, and Wenliang Zhu

J. Appl. Phys. 104, 023514 (2008); http://dx.doi.org/10.1063/1.2956694 (12 pages) | Cited 3 times

Online Publication Date: 21 July 2008

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Two cathodoluminescence piezospectroscopic (CL/PS) approaches for measuring the residual stress distribution in thin films are critically examined and compared using an intrinsic GaN film sample (2.5 μm in thickness) grown on a (0001)-oriented sapphire substrate. The first approach invokes an analytical model to fit experimental stress distributions as retrieved in both film and substrate at the edge of an artificially created cross section of the sample. Such an edge-stress distribution takes into account both the thermal expansion mismatch between the film and substrate and the mechanistics of film growth process. In the second approach, we directly and nondestructively measure the bulk residual stress field from the sample top surface on the film side using an increase in electron beam voltage (maintaining a constant beam power) as a means for screening the film subsurface. In this latter case, the combined effects of self-absorption and misfit dislocations on the GaN spectrum severely affect the CL/PS assessments; therefore, they need to be analyzed separately from the effect of stress. After spectral deconvolution of the obtained stress profiles, according to either in-plane or in-depth response functions of the electron probe for both film and substrate, cross-section and top-surface stress data were compared and discussed in an effort to substantiate the feasibility of spatially resolved CL/PS approach for the examination of residual stress distributions in film structures.
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68.55.ag Semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.60.Bs Mechanical and acoustical properties
65.40.De Thermal expansion; thermomechanical effects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Structural conditions that leads to photoluminescence emission in SrTiO3: An experimental and theoretical approach

V. M. Longo, A. T. de Figueiredo, S. de Lázaro, M. F. Gurgel, M. G. S. Costa, C. O. Paiva-Santos, J. A. Varela, E. Longo, V. R. Mastelaro, F. S. DE Vicente, A. C. Hernandes, and R. W. A. Franco

J. Appl. Phys. 104, 023515 (2008); http://dx.doi.org/10.1063/1.2956741 (11 pages) | Cited 22 times

Online Publication Date: 21 July 2008

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Complex cluster [TiO5⋅VOz] and [SrO11⋅VOz] (where VOz = VOX, VO•, VO••) vacancies were identified in disordered SrTiO3 powders prepared by the polymeric precursor method, based on experimental measurements by x-ray absorption near edge structure spectroscopy. The paramagnetic complex states of [TiO5⋅VO•] and [SrO11⋅VO•] with unpaired electrons were confirmed by electron paramagnetic resonance spectroscopy. The disordered powders showed strong photoluminescence at room temperature. Structural defects of disordered powders, in terms of band diagram, density of states, and electronic charges, were interpreted using high-level quantum mechanical calculations in the density functional framework. The four periodic models used here were consistent with the experimental data and explained the presence of photoluminescence.
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78.55.Hx Other solid inorganic materials
61.72.jd Vacancies
78.70.Dm X-ray absorption spectra
61.43.Gt Powders, porous materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.20.Ck Nonmetals

Polycrystalline Si nanoparticles and their strong aging enhancement of blue photoluminescence

Shikuan Yang, Weiping Cai, Haibo Zeng, and Zhigang Li

J. Appl. Phys. 104, 023516 (2008); http://dx.doi.org/10.1063/1.2957053 (5 pages) | Cited 13 times

Online Publication Date: 21 July 2008

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Nearly spherical polycrystalline Si nanoparticles with 20 nm diameter were fabricated based on laser ablation of silicon wafer immersed in sodium dodecyl sulfate aqueous solution. Such Si nanoparticles consist of disordered areas and ultrafine grains of 3 nm in mean size and exhibit significant photoluminescence in blue region. Importantly, aging at ambient air leads to continuing enhancement of the emission (more than 130 times higher in 16 weeks) showing stable and strong blue emission. This aging enhancement is attributed to progressive passivation of nonradiative Pb centers corresponding to silicon dangling bonds on the particles’ surface. This study could be helpful in pushing Si into optoelectronic field and Si-based full color display, biomedical tagging, and flash memories.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
71.55.Cn Elemental semiconductors

Study of the phase transition and charge ordering in single-crystalline Nd1/2Sr1/2MnO3 using x-ray scattering

C.-H. Du, M. E. Ghazi, P. D. Hatton, S. P. Collins, B. M. Murphy, B. G. Kim, and S-W. Cheong

J. Appl. Phys. 104, 023517 (2008); http://dx.doi.org/10.1063/1.2957070 (4 pages)

Online Publication Date: 21 July 2008

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We report a sequent phase transition using high-resolution synchrotron x-ray scattering in a single crystal Nd1/2Sr1/2MnO3. By measuring the peak profile of Bragg reflections, upon cooling, we observed an increase in the width of the Bragg reflections around the Curie temperature (252 K) corresponding to the transition from a paramagnetic to a ferromagnetic state. Below approximately 200 K, dramatic changes in the width and integrated intensity were observed. Changes continued until the formation of charge ordering with q = (½,0,0) at TCO = 152 K. This charge ordering was observed to be the first order transition with a large hysteresis width of 10 K. This sequent transition is understood by the formation of different magnetic domains at different temperature ranges as that observed by neutron powder diffraction.
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75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.70.Ck X-ray scattering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure

Distribution and segregation of arsenic at the SiO2/Si interface

C. Steen, A. Martinez-Limia, P. Pichler, H. Ryssel, S. Paul, W. Lerch, L. Pei, G. Duscher, F. Severac, F. Cristiano, and W. Windl

J. Appl. Phys. 104, 023518 (2008); http://dx.doi.org/10.1063/1.2956700 (11 pages) | Cited 9 times

Online Publication Date: 22 July 2008

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The segregation and pile-up of arsenic atoms at the Si/SiO2 interface in steady state was investigated in detail by a combination of gracing incidence x-ray fluorescence spectroscopy (GI-XRF) measurements, electrical measurements, etching on the nanometer scale, and measurements of the step heights by interferometry. Using GI-XRF measurements and removal of the highly doped segregation layer by a sensitive etching process it was possible to distinguish clearly between the piled-up atoms and the arsenic atoms in the bulk over a large range of implantation doses, from 3×1012 to 1×1016 cm−2. The samples were annealed at different temperatures from 900 °C to 1200 °C for time periods long enough to make sure that the segregation reflects an equilibrium state. With additional step height measurements at line-space structures, the thickness of the layer with the piled-up arsenic and the shape of the segregation profile was determined. Electrical measurements indicated that the segregated arsenic atoms are deep donors with an electrical activity that increases eventually to full electrical activation for high sheet concentrations of the segregated atoms. The measured data can be modeled as a steady state of neutral arsenic atoms in the segregation layer with positively charged substitutional arsenic atoms and free electrons. For the highest concentration, a saturation of the sheet concentration of segregated arsenic atoms was observed that correlates with the increase in electrical activation. For the use in process simulation programs, a three-phase segregation model was adapted and calibrated.
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64.75.-g Phase equilibria
61.72.U- Doping and impurity implantation
73.40.-c Electronic transport in interface structures
81.40.Gh Other heat and thermomechanical treatments

Polymorphic transformation from body-centered to face-centered cubic vanadium metal during mechanosynthesis of nanostructured vanadium nitride determined by extended x-ray absorption fine structure spectroscopy

Víctor López-Flores, Manuel A. Roldán, Concepción Real, Adela Muñoz Páez, and Germán R. Castro

J. Appl. Phys. 104, 023519 (2008); http://dx.doi.org/10.1063/1.2958324 (8 pages) | Cited 4 times

Online Publication Date: 23 July 2008

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The pathway for vanadium nitride (VN) formation obtained by milling treatment has been traced out. At the initial stages of the process, the reactant, vanadium metal, showing body-centered cubic (bcc) structure, becomes highly distorted. Simultaneously, the formation of a small nucleus of the product, VN, takes place. X-ray absorption spectroscopy (XAS) has allowed the quantification of the distortion degree as well as the detection of the VN nucleus in the early stages of their formation, while other standard structural characterization techniques are unable to detect such phenomena. For increasing milling times, apart from the expected increase in the size of the VN nucleus, a polymorphic transformation from bcc to fcc vanadium metal has been recorded. This phase might play a key role in the overall synthesis process and could be a reaction intermediate in other solid state processes involving V metal. The sensitivity of XAS to noncrystalline domains and to highly distorted environments, as well as the use of high resolution x-ray diffraction, has provided the relevant information to understand the whole reaction process.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.70.Nd Structural transitions in nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
81.20.Wk Machining, milling
78.70.Dm X-ray absorption spectra

Correlation between plasticity and fragility in Mg-based bulk metallic glasses with modulated heterogeneity

E. S. Park, J. Y. Lee, D. H. Kim, A. Gebert, and L. Schultz

J. Appl. Phys. 104, 023520 (2008); http://dx.doi.org/10.1063/1.2955715 (10 pages) | Cited 11 times

Online Publication Date: 23 July 2008

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A correlation between the kinetic fragility index (m) and enhanced plasticity is presented in Mg-based bulk metallic glasses (BMGs) with modulated heterogeneity by both suitable minor addition and optimal cooling rate. As case study, with minor addition of Gd in Mg65Cu7.5Ni7.5Zn5Ag5Y10−xGdx BMG, plasticity as well as glass-forming ability improves in a wide composition range (2.5 ≤ x ≤ 7.5 at. %). Furthermore, the cooling rate can affect the structural heterogeneity and the deformability of BMGs. With increasing diameters for the alloy x = 5, the compressive fracture strain increases from 2.97% at d = 1 mm up to 3.74% at d = 2 mm and then largely decreases. In particular, the variation of heterogeneity, which can directly affect in the property of BMG, can be evaluated by comparing the m values reflecting the inherent structure of BMGs. This concept can be used as a means of guiding alloy design and processing to alleviate brittleness of BMGs.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.fq Plasticity and superplasticity
62.20.mj Brittleness
62.20.mm Fracture
61.43.Fs Glasses

Morphological evolution of voids by surface drift diffusion driven by capillary, electromigration, and thermal-stress gradients induced by steady-state heat flow in passivated metallic thin films and flip chip solder joints. I. Theory

Tarik Omer Ogurtani and Oncu Akyildiz

J. Appl. Phys. 104, 023521 (2008); http://dx.doi.org/10.1063/1.2958088 (18 pages) | Cited 5 times

Online Publication Date: 24 July 2008

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The morphological evolution of intragranular voids induced by surface drift diffusion under the actions of capillary and electromigration (EM) forces and thermal-stress gradients (TSGs) associated with steady-state heat flow is investigated in passivated metallic thin films and flip chip solder joints via computer simulation using the front-tracking method. In the mesoscopic nonequilibrium thermodynamic formulation of the generalized driving forces for the thermal-stress-induced surface drift diffusion, not only the usual elastic strain energy density contribution but also the elastic dipole tensor interaction (EDTI) between the thermal-stress field and the mobile atomic species (monovacancies) are considered using the concept of elastic interaction energy promoted in unified linear instability analysis (ULISA) [ T. O. Ogurtani, Phys. Rev. B 74, 155422 (2006) ]. According to extensive computer experiments performed on voids, which are initially cylindrical in shape, two completely different and topographically distinct behaviors are observed during the development of quasistationary state void surface morphologies, even in the presence of strong EM forces. These behaviors strictly depend on whether or not heat flux crowding occurs in the regions between the void surface layer and the sidewalls of the interconnect lines due to proximity effects of the insulating boundaries. In both morphological cases, however, one also observes two well-defined regimes, namely, the EM and TSG dominated regimes in EM versus EDTI parametric space. In the case of the TSG dominated regime, the void center of gravity (centroid) exhibits uniform displacement (drift) velocity proportional and opposite to the induced TSG exactly as predicted by ULISA theory. These domains are bounded by a threshold level curve for the EDTI parameter, above which an extremely sharp crack tip nucleation and propagation occurs in the highly localized minima in the triaxial stress regions (i.e., hot spots) surrounding the void surface layer and extending along the longitudinal and off-diagonal directions (flux crowding). The most critical configuration for interconnect failure occurs even when thermal stresses are low if the normalized ratio of interconnect width to void radius is less than 4 (which indicates the onset of heat flux crowding). In the absence of EM this regime manifests itself by the formation of two symmetrically disposed finger-shaped extrusions (pitchfork shaped slits) on the upper and lower shoulders of the void surface on the windward side. In later stages these slits extend with an almost 54° inclination toward the sidewalls, and eventually cause a fatal catastrophic interconnect breakdown due to growth by condensation of supersaturated vacancies in the bulk matrix. At high thermal-stress levels this morphology is replaced by the fracture mode of diffusive-crack formation and propagation. Outside of the heat flux crowding regime and below the TSG threshold levels, the void takes an egg shape pointed toward the high temperature region of the interconnect and steadily drifts against the heat flow (upstream direction) without causing any transgranular damage. Above the TSG threshold levels, however, these modes are replaced by a sharp crack formation regime with an accelerated propagation that may eventually cause open-circuit interconnect failure.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.60.Bs Mechanical and acoustical properties
61.72.Qq Microscopic defects (voids, inclusions, etc.)
66.30.Qa Electromigration

Morphological evolution of voids by surface drift diffusion driven by the capillary, electromigration, and thermal-stress gradient induced by the steady state heat flow in passivated metallic thin films and flip-chip solder joints. II. Applications

Tarik Omer Ogurtani and Oncu Akyildiz

J. Appl. Phys. 104, 023522 (2008); http://dx.doi.org/10.1063/1.2958303 (13 pages) | Cited 3 times

Online Publication Date: 24 July 2008

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The void growth and drift motion induced by the combined actions of the phase transformation (evaporation and condensation) and surface drift diffusion driven by the capillary and electromigration forces and thermal-stress gradients are investigated in passivated metallic thin films and flip-chip solder joints via computer simulation using the front-tracking method. As far as the device reliability is concerned, the most critical configuration for solder joint failure occurs even when thermal stresses are low if the void nucleation takes place close to the under bump metallurgy (UBM) where the heat and current flux crowding takes place due to the proximity effect associated with the confinement. The void growth induced by the condensation of excess (athermal) vacancies at the void-matrix dividing surface results in drastic spreading of pre-existing voids along transverse direction of solder joint due to the concurrently occurring heat and current crowding adjacent to the UBM. This accelerated transverse void spreading may eventually cause open-circuit interconnect failure as clearly demonstrated experimentally in literature.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.35.bd Metals and alloys
68.35.Fx Diffusion; interface formation
66.30.Qa Electromigration
64.70.F- Liquid-vapor transitions
85.40.Ls Metallization, contacts, interconnects; device isolation

Diffusion and activation of n-type dopants in germanium

Masahiro Koike, Yoshiki Kamata, Tsunehiro Ino, Daisuke Hagishima, Kosuke Tatsumura, Masato Koyama, and Akira Nishiyama

J. Appl. Phys. 104, 023523 (2008); http://dx.doi.org/10.1063/1.2958326 (5 pages) | Cited 12 times

Online Publication Date: 24 July 2008

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The diffusion and activation of n-type impurities (P and As) implanted into p-type Ge(100) substrates were examined under various dose and annealing conditions. The secondary ion mass spectrometry profiles of chemical concentrations indicated the existence of a sufficiently high number of impurities with increasing implanted doses. However, spreading resistance probe profiles of electrical concentrations showed electrical concentration saturation in spite of increasing doses and indicated poor activation of As relative to P in Ge. The relationships between the chemical and electrical concentrations of P in Ge and Si were calculated, taking into account the effect of incomplete ionization. The results indicated that the activation of P was almost the same in Ge and Si. The activation ratios obtained experimentally were similar to the calculated values, implying insufficient degeneration of Ge. The profiles of P in Ge substrates with and without damage generated by Ge ion implantation were compared, and it was clarified that the damage that may compensate the activated n-type dopants has no relationship with the activation of P in Ge.
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66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
72.80.Cw Elemental semiconductors

Anisotropic biaxial stresses in diamond films by polarized Raman spectroscopy of cubic polycrystals

T. Gries, L. Vandenbulcke, P. Simon, and A. Canizares

J. Appl. Phys. 104, 023524 (2008); http://dx.doi.org/10.1063/1.2959338 (10 pages) | Cited 1 time

Online Publication Date: 24 July 2008

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The anisotropic stresses in diamond films induced by permanent deformations of titanium tensile substrates are studied by polarized Raman spectroscopy. The influence of the in-plane orientation of each grain relative to the stress directions is shown experimentally and theoretically. Considering the dynamical equations under small strains, the solutions of the secular equation permit the determination of the triply degenerate phonon frequency of polycrystalline diamond, which splits into three singlets for each crystallite. The calculation is carried out here for six growth directions, along [001], [110], [111], [112], [113], and [331], and for all in-plane orientations normal to these textures. In the case of anisotropic stresses, it is shown how the relative values of the two stresses induce different shapes in the Raman spectra. For an isotropic polycrystalline diamond film, this Raman spectroscopy of strained cubic polycrystals approximates the complete solution for all crystallite orientations relative to the anisotropic biaxial stresses. It allows calculating theoretical Raman spectra that fairly well compare to the experimental ones. The determination of the anisotropic stresses is obtained with a better accuracy when the influence of all orientations is taken into account than with the previous average procedures used for isotropic cubic polycrystalline materials. Partially or completely textured films along one of the growth directions can also be studied. If the stresses along the two directions are identical, the particular case of isotropic biaxial stresses is also studied with a better accuracy.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.60.Bs Mechanical and acoustical properties
78.66.-w Optical properties of specific thin films
78.30.-j Infrared and Raman spectra
68.55.jm Texture

Identification of deep trap levels from thermally stimulated current spectra of semi-insulating CdZnTe detector material

M. Pavlović, M. Jakšić, H. Zorc, and Z. Medunić

J. Appl. Phys. 104, 023525 (2008); http://dx.doi.org/10.1063/1.2959354 (6 pages) | Cited 6 times

Online Publication Date: 24 July 2008

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Deep trap levels in the semi-insulating (SI) CdZnTe detector material were characterized by simultaneous multiple peak analysis based on thermally stimulated current (TSC) measurements. In our TSCs that have been published previously electron hole pairs were created through the use of proton beam irradiation. Charge carriers were captured in deep traps and afterward released by thermal emission, which was recorded in the 90–300 K range. We showed that the obtained TSC spectra could be well fitted with a unique set of 14 different deep traps, which were all simultaneously and completely characterized. The obtained trap data are in good accordance with earlier deep trap characterizations of the other authors obtained on similar SI CdZnTe materials using different methods.
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71.55.Gs II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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