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Journal of Applied Physics

Issue 3 • Date Feb 2003

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Displaying Results 1 - 25 of 86
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Physics and materials challenges for lead-free solders

    Page(s): 1335 - 1353
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    At present, the electronic industry is actively searching for Pb-free solders due to environmental concerns over Pb-containing solders. Solder joints are widely used to bond chips to their substrates for electrical connection and packaging. Lacking reliability data, many electronic companies will be reluctant to adopt Pb-free solders in the advanced products. Hence, it is timely to review our understanding of structure-property relationship and potential reliability issues of Pb-free solders. A brief history of solder joint processes in electronic manufacturing is presented to serve as a background for the review. It emphasizes the unique phenomenon of spalling of interfacial intermetallic compound in solder reactions. Challenges for Pb-free solders from the point of view of physics and materials are given since the reliability issues of solder joints will remain with us when advanced Cu/low k dielectric interconnect technology is introduced into microelectronic devices. © 2003 American Institute of Physics. View full abstract»

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  • Spatially resolved spectroscopic strain measurements on high-power laser diode bars

    Page(s): 1354 - 1362
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    We compare a number of strain-sensitive spectroscopic techniques, namely, micro-Raman, micro-photoluminescence, photocurrent, and electroluminescence by applying them to two AlGaAs/GaAs high-power diode laser arrays, so-called “cm-bars.” Both devices are fabricated from the same bar batch and considered “identical,” but experienced two different packaging procedures that resulted in different intentionally adjusted “packaging-induced” compressive strains along the array, namely, about -(3.0±0.5)×10-4 and -(5.0±0.7)×10-4 strain difference between edges and centers of the bars. The methods are primarily evaluated with respect to their ability to monitor and quantify the different spatial strain distributions along the devices. In addition their potential for defect detection is demonstrated. Pros and cons of the techniques are summarized and discussed. © 2003 American Institute of Physics. View full abstract»

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  • AlN/AlGaInN superlattice light-emitting diodes at 280 nm

    Page(s): 1363 - 1366
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    Ultraviolet light-emitting diodes operating at 280 nm, grown by gas source molecular-beam epitaxy with ammonia, are described. The device is composed of n- and p-type superlattices of AlN(1.2 nm thick)/AlGaInN(0.5 nm thick) doped with Si and Mg, respectively. With these superlattices, and despite the high average Al content, we obtain hole concentrations of (0.7–1.1)×1018cm-3, with the mobility of 3–4 cm2/V s and electron concentrations of 3×1019cm-3, with the mobility of 10–20 cm2/V s, at room temperature. These carrier concentrations are sufficient to form effective p–n junctions needed in UV light sources. © 2003 American Institute of Physics. View full abstract»

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  • Low-threshold lasing in a microcavity of fluorene-based liquid-crystalline polymer blends

    Page(s): 1367 - 1370
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    We report the lasing characteristics of a microcavity device made of fluorene-based luminescent polymer blends with liquid crystallinity. Poly(2,7-bis(p-stiryl)-9,9-di-n-hexylfluorene sebacate) (PBSDHFS) and poly(9,9-di-n-hexyl fluorenediylvinylene-alt-1,4-phenylenevinylene) (PDHFPPV) were used to comprise a binary blend system. We employed the Förster-type energy transfer from a liquid crystalline donor to a non-liquid-crystalline acceptor to obtain a low lasing threshold. The binary blend film of PBSDHFS/PDHFPPV (98/2 by wt) demonstrated a very low-threshold energy (∼3 nJ/cm2/pulse) for microcavity lasing, which is lower than any other values previously reported on the organic or polymeric microcavity devices with metal or dielectric mirrors. This result implies that the liquid crystalline polymer blends could be a good candidate for the gain material of photo and electrically pumped lasing devices. © 2003 American Institute of Physics. View full abstract»

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  • Magnetization-induced second-harmonic generation in electrochemically synthesized magnetic films of ternary metal Prussian blue analogs

    Page(s): 1371 - 1375
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    We observed magnetic field effects on transmitted second-harmonic generation (SHG) in electrochemically synthesized (FexIICr1-xII)1.5[CrIII(CN)6]∙7.5H2O magnetic films. These films showed a variety of temperature dependences for SH intensities below magnetic phase transition temperatures (TC). The SH intensity for x=0.25 increased monotonically with decreasing temperature and that for x=0.13 exhibited a minimum value around the magnetic compensation temperature under a zero magnetic field. These temperature dependences resembled those of the absolute value of magnetization, indicating that the magnetic strain of the films is responsible for the increase in SH below TC. In addition, the polarization of SH light was rotated by an applied external magnetic field. The observed SH rotation angle of 1.3° was much larger than the Faraday rotation angle of 0.079° at 388 nm. This SH rotation can be understood by the mechanism of magnetization-induced SHG caused by interaction between the electric polarization along the out-of-plane of film and spontaneous magnetization. The magnetic linear term ijkLmagn(1)] contributed particularly to the SH rotation. The value of the magnetic linear tensor component relative to the crystallographic tensor component [|χyyyXmagn(1)|/|χzyycr], which induced the SH rotation, was 0.023 at 50 K under 10 kOe. © 2003 American Institute of Physics. View full abstract»

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  • Inductively coupled plasma etching of SiC in SF6/O2 and etch-induced surface chemical bonding modifications

    Page(s): 1376 - 1383
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    4H silicon carbide (SiC) substrates were dry etched in an inductively coupled plasma (ICP) system, using SF6/O2 gas mixtures. Etch rate and etch mechanisms have been investigated as a function of oxygen concentration in the gas mixture, ICP chuck power, work pressure, and flow rate. Corresponding to these etch conditions, surface information of the etched SiC has been obtained by x-ray photoelectron spectroscopy measurements. The fact that no obvious Si–Si and Si–F bonds were detected on the etched surface of SiC in all our etch experiments suggests efficient removal of Si atoms as volatile products during the processes. However, various kinds of C–F bonds have been detected on the etched SiC surface and the relative intensities of these bonds vary with the etch conditions. In addition, the nature of the incorporated F atoms on the etched surface also depends strongly on etch conditions, which was identified by the change of the relative ratio between semi-ionic and covalent carbon fluorine bonds. The electrical behavior for different bond structures on the etched SiC surface can be one of the basic reasons affecting related devices. © 2003 American Institute of Physics. View full abstract»

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  • Measurement of expanding plasma sheath from a target biased by a negative pulse with a fast rise time

    Page(s): 1384 - 1388
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    The pulse rise time effect on sheath size is investigated. Experiments are carried out on a planar target biased by a negative pulse with a fast rise time in a plasma source ion implantation (PSII) system. The fast rise time of the pulse provides that the speed of sheath expansion is larger than the Bohm speed during the pulse rise time. Results show that the sheath size increases with increasing pulse voltage and pulse rise rate (the ratio of the pulse voltage and the rise time), which is a very important factor for characterizing the expanding sheath in PSII. During the rise time, sheath size is proportional to the square root of the pulse rise rate over plasma density but it is insensitive to ion mass. Experimental results are in good agreement with the developed model based on the expanding ion matrix sheath model. After the full pulse has been attained, the sheath increases linearly with a constant speed as the Bohm speed. © 2003 American Institute of Physics. View full abstract»

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  • Macromolecule formation in low density CF4 plasmas: The influence of H2

    Page(s): 1389 - 1402
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    High molecular weight fluorocarbon species are regarded as important contributors to the nucleation of films and particulates in fluorocarbon plasmas. The chemical reaction mechanisms by which fluorocarbon macromolecules form within a plasma are generally unknown. To elucidate these mechanisms, experiments were conducted in a rf capacitively coupled discharge in a Gaseous Electronics Conference reference cell. The relationships between macromolecule growth and plasma pressure, power, flow rate, and the fraction of H2 in the CF4 gas feed are identified. Macromolecule growth was found to increase with increased pressure and rf power, and decreased flow rate. A set of electron-induced dissociation and radical-recombination reactions are simulated using Chemkin–Aurora, a commercially available plasma chemistry model, and are in good agreement with the experimental results of macromolecule growth. We show that a primary mechanism by which fluorocarbon macromolecules form in a plasma occurs by electron-induced dissociation of a fluoroalkane to produce a fluoroalkyl radical and a fluorine atom, followed by a three-body radical–radical recombination reaction with CF3. Hydrogen is shown to have a profound effect on this reaction sequence by reducing the gas phase atomic fluorine concentration through the formation of HF which in turn increases the CF3 concentration available to participate in the macromolecule growth process. At moderate levels of hydrogen in the feed gas (≪20%), macromolecule growth is directly correlated with the fraction of hydrogen in the feed gas. At high concentrations of hydrogen, hydrofluorocarbon and hydrocarbon growth occurs in the plasma at the expense of fluorocarbon macromolecule growth. The conditions under which the formatio- n of these species occurs is consistent with observations in the literature of dramatic reductions in silicon dioxide etching rate. The transition between the formation of fluorocarbon macromolecules and hydrocarbon species in a CF4/H2 plasma is shown to be fundamental to understanding the growth process of each class of species within the plasma. © 2003 American Institute of Physics. View full abstract»

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  • Surface and gas-phase observations of Ar-diluted c-C4F8 plasma by using real-time infrared spectroscopy and planar laser-induced fluorescence

    Page(s): 1403 - 1408
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    Using infrared spectroscopy with attenuated-total-reflection methods and planar laser-induced fluorescence, we examined the relationship between the thickness of amorphous fluorinated carbon (a-C:F) film on the surface of a substrate and the distribution of CF2 radical density in an inductively coupled plasma (ICP) generated from an argon-diluted octafluoro-cyclo-butane (c-C4F8) gas. The axial profiles of the CF2 radical density were consistently concave, maximally close to the surface, and minimally present around the bulk plasma. The CF2 density initially increased with increasing the ICP power and then decreased as the plasma density exceeded ∼0.5×1011cm-3, while the thickness of the a-C:F films deposited on a nonbiased surface consistently increased. When bias power was applied, the thickness of the a-C:F film began to decrease constantly due to the sputtering effect while the CF2 density exhibited a stepwise increase, followed by a gradual decrease in response to the reduction in the thickness of the a-C:F film and its vanishing. The amount of the stepwise increase in the CF2 density depended only on the rate of sputtering of the a-C:F film, and it was negligible at high c-C4F8/Ar ratios. The positive and negative correlations revealed here between the thickness of the a-C:F film and the density of <- roman>CF2 radicals are discussed in comparison with mechanisms proposed in other studies. Electron-impact-induced destruction of CF2 radicals is demonstrated as the dominant factor affecting the distribution of CF2 radicals. © 2003 American Institute of Physics. View full abstract»

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  • Effect of Tl content on the growth of TlGaAs films by low-temperature molecular-beam epitaxy

    Page(s): 1409 - 1416
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    TlGaAs layers with various Tl contents have been grown on GaAs(001) substrates by solid-source molecular-beam epitaxy at a substrate temperature of 210 °C and an As/Ga beam equivalent pressure ratio of 100. The Tl content was characterized by Rutherford backscattering spectrometry, secondary-ion mass spectrometry, and electron microprobe analysis. Nomarski microscope observation revealed that the surfaces of the TlxGa1-xAs layers were mirror like until a Tl content of x=7.0% while Tl droplets appeared on the surfaces of samples with a Tl content of x=7.7%. X-ray diffraction (XRD) curves showed clearly resolved epi-layer peaks until a Tl content of x=6.4%. We estimated the epitaxial thickness hepi, at which single-crystalline growth is replaced by polycrystalline growth, by two different methods using the XRD data. In one method we measured the change in diffracted intensity of the epi-layer peak after progressive gradual etching of the TlGaAs layers grown. The other was on the basis of a simulation of the diffraction curves of the as-grown samples within dynamical diffraction theory. The values of hepi estimated by the two methods agreed well and showed a remarkable decrease with an increase in Tl content. Cross-sectional transmission electron microscopy confirmed the reliability of the estimated value of hepi. In addition, the lattice mismatch was analyzed utilizing both symmetric and asymmertic XRD data. The analysis indicated that the lattice constant of an imaginary zinc-blende type crystal of stoichiometric TlAs (aTlAs) is slightly smaller than that of InAs (aInAs). © 2003 America- n Institute of Physics.   View full abstract»

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  • Relationship between interfacial adhesion and electromigration in Cu metallization

    Page(s): 1417 - 1421
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    A relationship between the adhesion of a Cu conductor to its surrounding medium, the electromigration drift velocity, and lifetime in a conventional electromigration test has been demonstrated. Lifetime measurements demonstrate that the drift velocity and the activation energy for mass transport along an interface correlate with the measured adhesion energy of the interface as determined by a four-point bending test. The results indicate that a linear relationship is expected between the electromigration activation energy and the intrinsic work of adhesion, which is consistent with a simple model relating the two. The data indicate that interfacial cleanliness and bond character at the interface (i.e., metal/dielectric versus metal/metal bonding) have a significant impact on all measured parameters. © 2003 American Institute of Physics. View full abstract»

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  • Structure and secondary electron emission properties of MgO films deposited by pulsed mid-frequency magnetron sputtering

    Page(s): 1422 - 1427
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    A pulsed mid-frequency magnetron sputtering technique was used to deposit MgO films. Atomic force microscopy, Rutherford backscattering, x-ray diffraction, and a diode discharge device were used to characterize surface morphology, oxygen content, crystalline structure, and the secondary electron emission (γ) coefficient of the films, respectively. The oxygen content (56 at. %) in all the films remained constant. However, surface morphology, crystalline structure, and the secondary electron emission properties of the films are strongly dependent on the O2 flow rate. As the O2 flow rate is increased from 3 to 10 sccm, a sudden decrease in the grain size and the γ coefficient of the films can be observed, and the crystalline orientation evolves from a strong (200) preferred orientation continuously to a fully (220) preferred orientation. Further increase of O2 flow rate results in a slight change in the grain size and the crystalline orientation, but a considerable increase in the full width at half maximum of the x-ray diffraction peaks and a significant decrease in the γ coefficient of the films. We found that preferred orientation and crystalline quality are the main factors that influence the secondary electron emission properties of the MgO films. © 2003 American Institute of Physics. View full abstract»

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  • Indium segregation to dislocation loops induced by ion implantation damage in silicon

    Page(s): 1428 - 1431
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    Indium segregation to dislocation loops and indium co-diffusion were investigated using secondary ion mass spectrometry (SIMS) and a physically-based diffusion model. High doses of As (30 keV, 1×1015cm2) and B (5 keV, 1×1015cm2) were implanted in indium-doped Si wafers which were then annealed at 750 °C and 1000 °C in a nitrogen ambient. SIMS profiles showed indium segregation around the implantation damage in both As- and B-implanted Si samples. Indium segregation around the B implantation damage confirms that indium segregation is induced primarily by implantation damage. We present a diffusion model that describes the interaction of indium and dislocation loops and the electric field/chemical ion pairing effect. A simulation that includes this model can predict indium segregation to dislocation loops produced by As/B implantation damage. As/B implants also induce the transient enhanced diffusion of indium. A difference in diffusivity enhancement of indium is shown between As implants and B implants. It is proposed that the difference can be attributed to the difference in the amount of the net excess interstitials, primarily due to ion mass effects. © 2003 American Institute of Physics. View full abstract»

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  • Free volume coalescence and void formation in shear bands in metallic glass

    Page(s): 1432 - 1437
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    We have investigated the possibility of void nucleation from the coalescence of excess free volume generated in shear bands during deformation of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass. Excess free volume in a shear band results in excess free energy relative to a relaxed glass with less free volume. To calculate the free energy of the material in a shear band with excess free volume, we model it as having the same structure as a glass solidified at an elevated glass transition temperature, which we call the fictive temperature. This excess free energy can be correlated with a free volume chemical potential that provides a driving force for void nucleation. The results of this modeling indicate that any free volume generated in the shear band during deformation is unstable, with the consequence that voids are predicted to form spontaneously from the coalescence of free volume. These voids are then expected to coarsen. Under tension, void growth and linkage would be facilitated by a tensile stress state, perhaps leading to premature fracture, whereas a compressive stress state would hinder void growth. This may explain the common observation that failure under uniaxial tension occurs as the result of the propagation of a single shear band, whereas multiple shear bands can form under uniaxial compression without causing failure. © 2003 American Institute of Physics. View full abstract»

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  • Effect of implant temperature on defects created using high fluence of helium in silicon

    Page(s): 1438 - 1442
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    Extended defects formed by high-fluence helium implantation in silicon have been studied as a function of the implantation temperature, from room temperature up to 800 °C. Transmission electron microscopy results show that the formation of cavities created by a 50 keV He implantation with a fluence of 5×1016cm-2 can be divided into three stages. For implantation temperature up to about 300 °C the bubble size is relatively constant but the bubble density decreases due to the increase in dynamic annealing. Above 300 °C, where divacancies are no longer stable and when the helium is mobile, both the density and size of the cavities stay relatively constant. In this stage, helium starts to diffuse out and the cavities become more and more faceted as the temperature increases. Concurrently interstitial-type defects appear: small elongated rod-like defects at relatively low temperatures and large ribbon-like defects at 600 °C. Finally, for implantation at 800 °C, no cavities are formed and only dislocation loops and {113}’s (ribbon-like defects and rod-like defects), are observed depending on the deposited energy profile. At this temperature the defect annealing during implantation becomes efficient to convert ribbon-like defects into dislocation loops. © 2003 American Institute of Physics. View full abstract»

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  • Tensile failure by grain thinning in micromachined aluminum thin films

    Page(s): 1443 - 1451
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    This article reports the results of microtensile tests and transmission electron microscopy (TEM) analyses of micron-scale free-standing aluminum thin films. We fabricated the free-standing aluminum beams using micromachining procedures and tested them in a piezo-actuator-driven test apparatus. Microtensile tests revealed that the mechanical characteristics of the free-standing beams are quite different from those of the bulk material. Some unique features of our free-standing Al beams are high yield strength, low ductility, and strain softening. While the high yield strength is attributed to the typically small grain size, the strain softening and the small ductility are explained by locally thinned grains found in TEM analyses. Further TEM analyses suggested that dislocations pass through the free surfaces in the interiors of some large grains and lead to strain softening, which, in turn, results in deformation concentration in such areas and hence localized thinning. © 2003 American Institute of Physics. View full abstract»

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  • Diffusion of Si and Ge dimers on Ge (001) surfaces

    Page(s): 1452 - 1456
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    We have studied the various diffusion pathways of Si and Ge dimers on the Ge (001) surface using scanning tunneling microscopy. The adsorbed dimers can be classified into two categories: Dimers adsorbed on top of the substrate rows and dimers adsorbed in the troughs between the substrate rows. There are three different diffusion pathways for the dimers: Along the substrate rows, across the substrate rows, and in the troughs between the substrate rows. The activation barriers for diffusion of these three pathways have been determined for both Ge and Si dimers on Ge (001). The barriers for dimer diffusion of the system Ge/Ge (001) are slightly lower than for the Si/Ge (001) system. As compared to Si on Si (001) the activation barriers for dimer diffusion on Ge (001) are significantly lower. © 2003 American Institute of Physics. View full abstract»

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  • Quantitative microdiffraction from deformed crystals with unpaired dislocations and dislocation walls

    Page(s): 1457 - 1464
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    This article describes how unpaired dislocations alter white-beam Laue patterns for either isolated dislocations, dislocation walls, or combinations of dislocation walls and isolated dislocations. The intensity distribution of Laue diffraction is analyzed as a function of local misorientation. We show how to quantitatively determine the dislocation structure of single crystals and polycrystals with plastic deformation. The technique is applied to interpret the complicated plastic–elastic field in an iridium weld sample. View full abstract»

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  • Photoluminescence study of crosslinked reactive mesogens for organic light emitting devices

    Page(s): 1465 - 1467
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    We study the spectroscopic properties of luminescent liquid crystals which show a glassy nematic phase at room temperature and then form polymer networks by polymerization using ultraviolet light. The reactive mesogens possess fluorene-based aromatic cores with either diene or acrylate photoreactive groups at the end of aliphatic spacers. The photoluminescence quantum efficiency is enhanced when a rigid polymer backbone is formed by crosslinking of the diene endgroups. Spectral shifts of the vibronic transitions confirm an increase in the viscosity of the matrix following photopolymerization. Continuous and time-resolved photoluminescence measurements show that the quantum efficiency is limited by exciton diffusion to traps. Either the diffusion constant or the density of traps is reduced by photopolymerization. © 2003 American Institute of Physics. View full abstract»

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  • Formation of light-emitting FeSi2 in Fe thin films on ion-implanted (111)Si

    Page(s): 1468 - 1471
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    The formation of iron silicides on (111)Si and effects of ion implantation on phase transformation have been investigated by sheet resistance measurements, grazing-incidence x-ray diffractometry, transmission electron microscopy, energy-dispersive x-ray analysis, and secondary ion mass spectroscopy. Ion implantation was found to enhance the growth of light-emitting β-FeSi2. Phase transformation from FeSi to β-FeSi2 begins at 600 °C and completes at 700 °C. P+ implantation was found to lower the transformation temperature from 700 to 600 °C. Wider than 20 nm As-decorated grain boundaries were observed in the As+-implanted samples annealed at 600–700 °C. The As-rich grain boundaries disappeared after 800 °C annealing, leading to a decrease in resistivity. © 2003 American Institute of Physics. View full abstract»

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  • Nondestructive evaluation of dislocation structure in cyclically deformed Ni3Fe single crystals using magnetic techniques

    Page(s): 1472 - 1476
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    The deformation substructure in Ni3Fe single crystals cyclically deformed at constant plastic shear strain amplitudes pl) consisted of two phases: the matrix with planar dislocation arrangement and the persistent slip band (PSB) having a three dimensional cell structure. The saturation stress remained almost constant regardless of γpl by adjusting the volume fraction of PSB. Anisotropy of high-field susceptibility in cyclically deformed Ni3Fe single crystals was measured in the (111) discs. Two types of magnetic anisotropy caused by atom rearrangement near the antiphase boundary (APB) and internal stress around dislocations were observed in fatigued Ni3Fe single crystals. The anisotropy data were subjected to the Fourier-type transformation and were split into separate anisotropy functions depending on the type of lattice defects. The magnitude ratio of dislocation- to APB-dependent anisotropy increases linearly with increasing γpl. This strongly suggests that Winter’s two-phase model can be applied to both mechanical and magnetic properties. Thus, nondestructive evaluation of dislocation structure in cyclically deformed Ni3Fe single crystals could be done by analyzing the magnetic anisotropy induced by cyclic deformation. © 2003 American Institute of Physics. View full abstract»

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  • Morphology and crystallization kinetics in HfO2 thin films grown by atomic layer deposition

    Page(s): 1477 - 1481
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    We report the effects of annealing on the morphology and crystallization kinetics for the high-κ gate dielectric replacement candidate hafnium oxide (HfO2). HfO2 films were grown by atomic layer deposition (ALD) on thermal and chemical SiO2 underlayers. High-sensitivity x-ray diffractometry shows that the as-deposited ALD HfO2 films on thermal oxide are polycrystalline, containing both monoclinic and either tetragonal or orthorhombic phases with an average grain size of ∼8.0 nm. Transmission electron microscopy shows a columnar grain structure. The monoclinic phase predominates as the annealing temperature and time increase, with the grain size reaching ∼11.0 nm after annealing at 900 °C for 24 h. The crystallized fraction of the film has a strong dependence on annealing temperature but not annealing time, indicating thermally activated grain growth. As-deposited ALD HfO2 films on chemical oxide underlayers are amorphous, but show strong signatures of ordering at a subnanometer level in Z-contrast scanning transmission electron microscopy and fluctuation electron microscopy. These films show the same crystallization kinetics as the films on thermal oxide upon annealing. © 2003 American Institute of Physics. View full abstract»

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  • Fluorescence properties of trivalent europium doped in various niobate codoped glasses

    Page(s): 1482 - 1486
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    A series of niobate–phosphate and niobate–silicate glasses doped with Eu3+ ions were prepared. The emissions, phonon-side band spectra, and fluorescence lifetimes of these glasses were studied and the intensity parameters of Eu3+ were obtained. The temperature dependence of emission intensity of the Eu3+ ion in these niobate glasses was investigated. The temperature-quenching rates were determined. The results indicate that in niobate glasses, as the concentration of Nb2O5 increases, the covalence becomes stronger, the symmetry becomes lower and the electron-phonon coupling strength becomes stronger. Thus, the lifetimes become shorter, and the nonradiative transition processes and the temperature-quenching effect become stronger. © 2003 American Institute of Physics. View full abstract»

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  • Effect of elastic anisotropy on the elastic fields and vertical alignment of quantum dots

    Page(s): 1487 - 1492
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    The elastic fields in the self-organized quantum dot (QD) structures are investigated in details by three-dimensional finite element analysis for an array of lens shaped QDs. Emphasis is placed on the effect of elastic anisotropy of the materials with the anisotropy ratio A ranging from 0.25 to 4.0 for both the QDs and the matrix. It is found that the elastic anisotropy strongly influences the distributions of strain, stress, and strain energy density in the QD structures. It is shown that the elastic interactions among the buried QDs play crucial role in the formation of the satellite energy minima at the cap layer surface, while the materials anisotropy and the cap layer thickness also play important roles. By changing the elastic anisotropy ratio and the cap layer thickness, substantially different distributions of strain energy minima on the cap layer surface are obtained, which may result in various QD ordering phenomena such as vertical alignment, partial alignment, or complete misalignment. Based on the calculation results, a phase diagram is constructed to show the effect of material anisotropy and cap layer thickness on the vertical correlation of QDs. © 2003 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory