bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface plasmon enhanced second harmonic response from gold clusters embedded in an alumina matrix
Authors: Antoine R. , Pellarin M. , Palpant B. , Broyer M. , Prével B. , Galletto P. , Brevet P. F. , Girault H. H.
Published: July 2002

The second order nonlinear response from 4 nm diam gold clusters embedded in an alumina matrix deposited on a pure silica substrate has been recorded as a function of the wavelength of the fundamental incident beam. The spectrum exhibits a narrow resonance band peaked at 520 nm as a result of the coupling of the second harmonic field with the surface plasmon of the particles. The nonlinear second harmonic response of gold clusters is found to be blueshifted compared to the bulk, due to the finite size effects on the cluster optical properties, as already observed with the linear response. Furthermore, this nonlinear response appears to be well described with a simple free electron model where the valence electrons only participate through the screening of the ionic cores, owing to the weakness of the interband transition contribution.
X-ray phase-amplitude contrast mapping of single-crystal alloys near the absorption edge of the alloy impurity
Authors: Nikulin A. Yu. , Davis J. R. , Jones N. T. , Zaumseil P.
Published: July 2002

An experimental–analytical method for the nondestructive structural and chemical composition mapping of single-crystal alloys is proposed, implemented, and successfully tested. The technique is based on analytical measurements of phase and amplitude changes in a narrow polychromatic region near the absorption edge of the alloy impurity. Synchrotron radiation energies of 11.096–11.105 keV were used to measure the Bragg diffraction profiles near the absorption edge of germanium at 11.103 keV in SiGe/Si crystal alloy superstructures. Physical dimensions and chemical composition of SiGe alloys were determined with a spatial resolution 8.6 Å.
High-resolution x-ray diffraction and high-resolution scanning electron microscopy studies of Si-based structures with a buried amorphous layer
Authors: Ahilea T. , Zolotoyabko E. , Härtwig J. , Ohler M. , Prieur E.
Published: July 2002

Structural and geometrical parameters of Si samples with buried amorphous layers, produced by oxygen implantation and high-temperature annealings, were measured by high-resolution x-ray diffraction and high-resolution scanning electron microscopy. By using a newly developed simulation procedure precise fittings of x-ray diffraction spectra were made and important parameters were derived, such as the averaged fluctuations of the thickness of the amorphous layer (“interface roughness”) and of the interplanar spacing in the Si top layer. The data obtained revealed a reduction in interface roughness, i.e., an improvement of the samples’ quality after additional high-temperature annealing. This conclusion was supported by electron microscopy images demonstrating a more complete dissolution of SiO2 precipitates as a result of additional heat treatment. The importance of more sophisticated annealing was also confirmed by the Moiré x-ray diffraction topographs taken on the topography beamline of the European Synchrotron Radiation Facility.
Relaxor behavior of pulsed laser deposited ferroelectric (Pb1−xLax)(Zr0.65Ti0.35)O3 films
Authors: Tyunina M. , Levoska J. , Sternberg A. , Leppävuori S.
Published: July 2002

The dielectric behavior of pulsed laser deposited ferroelectric (Pb1−xLax)(Zr0.65Ti0.35)O3 films (PLZT x/65/35, x=0–9.75 at. %) has been studied experimentally. Epitaxial stoichiometric PLZT films were formed on a pulsed laser deposited layer of La0.5Sr0.5CoO3 (LSCO) on MgO (100) single-crystal substrates. The dielectric permittivity and loss tangent of the resulting heterostructures were measured in the temperature range of 20–350 °C at a frequency of 100 Hz–1 MHz. A peak around 130–350 °C was observed in the dielectric permittivity versus temperature curves. The peak exhibited a relaxor type behavior. Its position was a nonmonotonic function of the La content and depended on the microstructure of the film. The broadening of the peak of the dielectric permittivity was larger than that in the ceramic PLZT and it also depended on the La content and microstructure of the film. The broadening depended on the temperature and frequency ranges: master curves of the normalized dielectric permittivity versus normalized temperature were obtained for PLZT films. The results are discussed in terms of the random field theory for relaxor ferroelectrics and the models for finite-size ferroelectrics.
Realization of epitaxial barium ferrite films of high crystalline quality with small resonance losses
Authors: Shinde S. R. , Lofland S. E. , Ganpule C. S. , Ogale S. B. , Bhagat S. M. , Venkatesan T. , Ramesh R.
Published: July 2002

We report the results of systematic studies of the effect of thin film deposition conditions, such as deposition temperature, oxygen pressure during deposition, etc., on the microstructural, magnetic, and microwave properties of pulsed laser deposited epitaxial thin films of barium ferrite on single crystal sapphire substrates. Ferromagnetic resonance (FMR) linewidths are very sensitive to the presence of defects and inhomogeneities and therefore change markedly with the variation of deposition parameters. After careful optimization of the deposition conditions, relatively narrow resonance lines were realized in these films. For further improvement in the film quality, these films were annealed at elevated temperatures in flowing oxygen. As a result of the high degree of epitaxy, good stoichiometry, and reduced concentration of defects, FMR linewidths as small as 37 Oe were obtained in films deposited at 920 °C and subsequently annealed at 1000 °C in an oxygen atmosphere.
Gallium implantation induced deep levels in n-type 6H–SIC
Authors: Gong M. , Fung S. , Beling C. D. , Brauer G. , Wirth H. , Skorupa W.
Published: July 2002

Two Ga-acceptor levels, located at EV+0.31 eV and EV+0.37 eV, respectively, have been observed in the gallium implantation manufactured p+n diodes using deep level transient spectroscopy. The behavior of the implanted gallium is very similar to that of implanted aluminum, except that the positions of the introduced levels are different. This result strongly supports the recent model, which was used to explain the discrepant results between boron and aluminum implantation induced deep levels. Besides the two acceptor levels, a thermally stable electron trap is also observed and has been tentatively attributed to a Ga-related complex.
Misfit accommodation by compliant substrates
Authors: Jesser William A. , van der Merwe J. H. , Stoop P. M.
Published: July 2002

Experimentally it has been found that twist bonding a thin layer of epitaxially grown material to a thick substrate of the same material has the properties of being compliant with respect to the growth of a heteroepitaxial layer onto the thin layer. The benefit of the compliant substrate is that the heteroepitaxial layer is of much higher perfection when compared to the same growth but on a bulk substrate, primarily due to a very low density of threading dislocations present in the heteroepitaxial deposit. This concept has been investigated experimentally and discussed in terms of what is the operative mechanism of the compliant substrate. However, there is still much to be explained about the mechanism by which the compliant substrate accommodates misfit between itself and the heteroepitaxial layer. How the structure of the interface between the compliant substrate and the thick substrate can be tailored to derive the maximal benefit in the epilayer is the subject of the present article. The importance of a high angle of twist between the compliant substrate and the bulk substrate is in providing a high density of interfacial dislocations. Closely spaced dislocations with overlapping cores approximate the conditions of a free-standing compliant substrate by providing an easy mechanism for the complaint substrate to elastically accommodate misfit between itself and the heteroepitaxial film grown onto it. In cases which exhibit strong atomic interaction between compliant substrate and bulk substrate the approximation to a free-standing compliant substrate is not as good and the interface can be reasonably described in terms of a dense array of pure screw dislocations. In this case accommodation of misfit between the heteroepitaxial film and the compliant substrate can be accomplished by elastically changing the lattice parameter of the compliant substrate to meet that of the heteroepitaxial film. The elastic deformation of the compliant substrate can cause the dense array of pure screw dislocations to reorient thereby introducing an edge component to the interfacial dislocations which accommodates the introduced misfit between the compliant substrate and the bulk substrate. The details of this mechanism and how it can be used to design compliant substrates show that exact coincidence angles of twist should be avoided. Further, good compliant substrates may be obtained by wafer bonding thin complaint substrates of a crystal similar to that of the heteroepitaxial film rather than of a material similar to that of the substrate.
Controlled spontaneous emission of a tri(8-hydroxyquinoline) aluminum layer in a microcavity
Authors: Masenelli B. , Gagnaire A. , Berthelot L. , Tardy J. , Joseph J.
Published: July 2002

We report the fabrication of all-dielectric microcavities with a tri(8-hydroxyquinoline) aluminum (Alq3) organic layer as the emitting layer. In a first step, we characterized the materials used in the structures by ellipsometry, and ensured nondegradation of the organic material in the fabrication process. Then, by angular-resolved photoluminescence, we investigated changes in the angular emission pattern caused by the cavities and observed a sharply directed emission. We also investigated the influence of the position of the radiative layer in the cavity on normal spontaneous emission. We observed enhancements in spontaneous emission over 20 times higher than that of a single Alq3 layer. These are the highest reported for organic material based microcavities. They are mainly explained by the very small thickness of the Alq3 layer (20 nm≡0.06λ, λ being the resonant wavelength), by high-quality low-loss dielectric mirrors as well as by the narrow collecting angle of our experiment (±3°). This study corroborates analogous works and demonstrates the possibility of controlling the spontaneous emission of an emitter by a microcavity.
Microstructures of GaN1−xPx layers grown on (0001) GaN substrates by gas source molecular beam epitaxy
Authors: Seong Tae-Yeon , Bae In-Tae , Choi Chel-Jong , Noh D. Y. , Zhao Y. , Tu C. W.
Published: July 2002

Transmission electron microscope (TEM), transmission electron diffraction (TED), and synchrotron x-ray diffraction (XRD) studies have been performed to investigate microstructural behavior of gas source molecular beam epitaxial GaN1−xPx layers grown on (0001) GaN/sapphire at temperatures (Tg) in the range 500–760 °C. TEM, TED, and XRD results indicate that the samples grown at Tg⩽600 °C undergo phase separation resulting in a mixture of GaN-rich and GaP-rich GaNP with zinc-blende structure. However, the samples grown at Tg⩾730 °C are found to be binary zinc-blende GaN(P) single crystalline materials. As for the 500 °C layer, the two phases are randomly oriented and distributed, whereas the 600 °C layer consists of phases that are elongated and inclined by 60°–70° clockwise from the [0001]α-GaN direction. The samples grown at Tg⩾730 °C are found to consist of two types of microdomains, namely, GaN(P)I and GaN(P)II; the former having twin relation to the latter.
Mechanism of asymmetrical magnetoimpedance in amorphous wires
Authors: Panina L. V. , Mohri K. , Makhnovskiy D. P.
Published: July 2002

Two approaches for obtaining asymmetrical magnetoimpedance (MI) characteristics in Co-based negative magnetostrictive amorphous wires are analyzed in terms of the surface impedance tensor ζ̂, which is expressed in the form of orthogonal expansions in Bessel functions in a general case of a helical magnetization. The asymmetry in MI behavior with respect to an axial dc magnetic field can be related to either a certain asymmetric arrangement of the dc magnetic configuration or a contribution to the wire voltage due to the ac cross-magnetization process (represented by the off-diagonal component of ζ̂). The first case is realized in a wire having a helical anisotropy and subjected to an ac current superposed with a dc current. In the other approach, the asymmetric voltage response can be obtained by applying the ac current in series through the wire and the coil mounted on it. No helical anisotropy is required in this case. These kinds of asymmetrical MI are especially important for developing autobiased linear MI sensors.
Matteucci and inverse Wiedemann effects in amorphous wires with enhanced circumferential domains
Authors: Freijo J. J. , Vázquez M. , Hernando A. , Méndez A. , Ramanan V. R.
Published: July 2002

Nonmagnetostrictive CoFeSiB alloy wires were subjected to cold drawing processing followed by annealing under tension, in order to induce the formation of circular magnetic anisotropy. The axial (MZ–HZ) and circular (Mφ–Hφ) hysteresis loops indicate the existence of induced transverse anisotropy, with the magnitude of the anisotropy field being dependent on the processing conditions, while circular loops are quasibistable for samples processed under stress. Very peculiar hysteresis loops are obtained for the Matteucci (MI, Mφ–HZ) and inverse Wiedemann (IWE, MZ–Hφ) effects corresponding to those samples exhibiting the mentioned circular bistability. The circular shape of the MI loop is interpreted as produced by reversible magnetization rotation within circumferential domain. The effective hysteresis arises from the existence of a helical distribution of anisotropy in the transition region between the inner axial domain and the external shell. IWE loop confirms the presence of this helicity.
Characterization of ion beam and magnetron sputtered thin Ta/NiFe films
Authors: Mao M. , Leng Q. , Huai Y. , Johnson P. , Miller M. , Tong H.-C. , Miloslavsky L. , Qian C. , Wang J. , Hegde H.
Published: July 2002

Thin Ta/NiFe films were deposited using ion beam deposition (IBD), pulsed, and static magnetron sputtering techniques. These NiFe films show anisotropy field values ∼4 Oe, easy axis coercivities ⩽1 Oe, and hard axis coercivities ⩽0.3 Oe. IBD films exhibit higher magnetoresistance ratios (ΔR/R), while little difference is noted between different deposition techniques in the sheet resistance of NiFe films. A ΔR/R value of 1.8% has been measured for a 90 Å IBD NiFe films. X-ray diffraction measurements indicate that NiFe films of the same thickness have about the same grain size regardless of deposition technique, however, IBD films exhibit superior (111) texture and crystallinity. Our results clearly indicate that the superior magnetic properties of thin IBD Ta/NiFe films are a result of high crystallographic quality of these films.
Orientation effect on the exchange fields of NiFeO/NiFe bilayers
Authors: Lai Chih-Huang , Wang C. P. , Qian Chester
Published: July 2002

The orientation effect on the exchange field in the sputtered NiFeO/NiFe system was investigated. In-plane textured MgO films, deposited by the ion beam assisted deposition, were used as structural templates to modify the crystalline orientations of NiFeO. When the in-plane orientation of NiFeO was aligned more perfectly, the exchange field was higher. This effect may be attributable to the vector sum of moments of the NiFeO sublattice at the NiFeO/NiFe interface. The exchange field is also affected by the out-of-plane alignment, which is related to the plane anisotropic energy of NiFeO. Well-aligned out-of-plane (100) texture of NiFeO enhances the exchange field.
Effect of annealing on the grain growth and luminescent properties of SrS:Cu blue phosphors
Authors: Xin Y. B. , Tong W. , Park W. , Chaichimansour M. , Summers C. J.
Published: July 2002

Systematic studies of the postgrowth annealing of molecular beam epitaxial deposited SrS:Cu films are reported. In the as-grown SrS:Cu films, the grain size was small and the luminescence very weak. A step-annealing procedure in a H2S atmosphere was developed and found to be a very efficient way to improve the crystallinity and luminescent properties without damage to the low temperature glass substrate and insulator layer of the device. A model is presented in terms of the free energy of formation and the reaction kinetics of Cu with H2S. It was proposed that the weak luminescence in the as-grown films was attributed to Cu atoms segregated at the grain boundaries in the SrS film. The oxidation of atomic Cu by H2S and the diffusion of Cu+ into the SrS lattice during annealing were responsible for the grain growth and the improved luminescent properties.
Low-frequency noise in polycrystalline semiconducting FeSi2 thin films
Authors: Tassis D. H. , Dimitriadis C. A. , Brini J. , Kamarinos G. , Birbas A.
Published: July 2002

Low-frequency noise measurements have been carried out at room temperature in polycrystalline semiconducting iron disilicide (β-FeSi2) thin film with the current I as a parameter. The power spectral density of the current fluctuations exhibits a 1/f behavior at low frequencies (f<100 Hz) and is proportional to Iβ (β<2). The temperature dependence of the conductivity shows that, at room temperature, the measured noise is related to a thermally activated transport mechanism, which satisfies the Meyer–Neldel rule. A noise theory has been developed on the basis of trapping-detrapping of holes of the valence band and the gap states taking into account mobility inhomogeneity across the thickness of the film. Using the experimental data of Hall, conductivity, and noise measurements, the noise model provides an assessment of the distribution of traps within the energy gap of the β-FeSi2 material.
Photoluminescence microscopy imaging of tensile strained In1−xGaxAsyP1−y/InP quantum wells grown by low-pressure metalorganic vapor phase epitaxy
Authors: Bernussi A. A. , Carvalho W. , Furtado M. T. , Gobbi A. L.
Published: July 2002

The optical properties of tensile strained In1−xGaxAsyP1−y/InP single quantum wells grown by low-pressure metalorganic vapor phase epitaxy were investigated by the real-time integrated photoluminescence microscopy imaging technique at room temperature. The photoluminescence microscopy images revealed the presence of a large number of nonradiative centers (dark spots). The dark spot density was found to be strongly dependent on the tensile strain magnitude, barrier type material and cap layer thickness. High tensile strain values and thin InP cap layers resulted in an increased density of dark spots. Tensile strained structures employing lattice-matched quaternary barriers instead of InP barriers exhibited reduced defect density. Our results indicate that these defects are mainly localized close to or at the interface between the quaternary well and the upper barrier material. The reduction of the number of defects correlates quantitatively with increased radiative recombination efficiency in these structures.
Electronic states and optical properties of Si/SiO2 superlattices
Authors: Tit Nacir , Dharma-Wardana M. W. C.
Published: July 2002

We study the electronic structure of {Si}m{SiO2}n superlattices (SLs) grown along the [001] direction, using tight-binding methods. Detailed atomic models of the Si/SiO2 interface are considered. A clear feature of the results is the essentially direct band-gap structure with flat bands along the ZΓ symmetry line of the SL-Brillouin zone which has a blueshifted energy gap due to quantum confinement. The calculated densities of states are enhanced at the valence and conduction band edges, as compared with silicon. The optical properties of the SLs are calculated using a parametrization of the imaginary part of the dielectric function of bulk Si. The strong confinement of the electron–hole pairs in the Si wells and their tendency to localize at the low-dielectric {SiO2} interfaces due to the mutual Coulomb attraction lead to strong electrostatic effects. These produce an interplay of several length scales in determining possible regimes of high radiative efficiency. Our results have implications for the understanding of the luminescence in porous Si and Si-based nanostructures like the amorphous Si/SiO2 SLs studied recently.
Ge/Si self-assembled quantum dots grown on Si(001) in an industrial high-pressure chemical vapor deposition reactor
Authors: Hernandez C. , Campidelli Y. , Simon D. , Bensahel D. , Sagnes I. , Patriarche G. , Boucaud P. , Sauvage S.
Published: July 2002

We report on the structural and optical properties of Ge/Si self-assembled quantum dots epitaxially grown on Si(001). The Ge islands are grown in an industrial 200 mm single-wafer chemical vapor deposition reactor. The surface density of the Ge islands is as much as 2×1010 cm−2. The islands exhibit a maximum photoluminescence at 1.55 μm wavelength. The photoluminescence energy is correlated to the three-dimensional quantum confinement energy and to the size and geometry of the clusters, as observed by cross-section transmission electron microscopy.
Analysis of the in-plane magnetic anisotropy in amorphous ribbons obtained by torque magnetometry
Authors: Tejedor M. , Garcı́a J. A. , Carrizo J. , Elbaile L. , Santos J. D. , Mira J. , Rivas J.
Published: July 2002

The evolutions of the uniaxial torque and magnetization with the applied magnetic field allow us to discriminate the sources of in-plane magnetic anisotropy in amorphous ribbons. In order to determine the magnetic anisotropy sources, a simple model has been developed for an inhomogeneous material. We apply this model to explain the quite different behavior observed in the evolution of the uniaxial torque amplitude with the applied magnetic field of two commercial Co-based amorphous alloys.
Optimization of reflective bistable twisted nematic liquid crystal displays
Authors: Xie Z. L. , Gao H. J. , Xu S. Y. , Kwok H. S.
Published: July 2002

The contrast ratio of reflective bistable twisted nematic displays are optimized by means of a parameter space approach. By plotting the contrast ratio as a function of the twist angle and thickness-birefringence product of the display, the regions where the display shows the best contrast ratio are clearly shown. Both the absolute reflectance and wavelength dispersion of two bistable twisted states are investigated. It is confirmed that high contrast ratio of over 100 and reflectance of 100% with polarized light input are possible for such reflectance bistable displays.
Thermal stability of cobalt silicide stripes on Si (001)
Authors: Alberti A. , La Via F. , Raineri V. , Rimini E.
Published: July 2002

The effect of lateral scaling on the thermal stability of cobalt disilicide has been investigated on Si (001) substrates. Resistance measurements on four terminal resistors, with linewidth dimensions ranging from 1.3 to 0.5 μm, have been performed after annealing in the range between 900 and 1000 °C. The resistance increases faster in the stripes than in blanket regions. This degradation process has been correlated to the morphological change in the strip cross section, as analyzed by transmission electron microscopy and atomic force microscopy. Grain growth, degradation processes at the line edge, and surface and interface roughness have been observed. These analyses show that the lateral constraints of the silicide lines are mainly responsible for the lowering of the silicide thermal stability compared with blanket regions. Moreover, from measurements of agglomerated silicide grains in equilibrium with the substrate, the silicide surface free energy is 2.3 times the free energy of the CoSi2/Si interface.
Chemical vapor synthesis and luminescence properties of nanocrystalline cubic Y2O3:Eu
Authors: Konrad A. , Fries T. , Gahn A. , Kummer F. , Herr U. , Tidecks R. , Samwer K.
Published: July 2002

Nanocrystalline europium doped yttria was synthesized using a chemical vapor technique. The powder was characterized by x-ray diffraction, transmission electron microscopy, and ultraviolet spectroscopy. For the first time it was possible to obtain single phase Y2O3:Eu nanoparticles crystallized in the cubic structure with an average particle size of only 10 nm. The reflection, excitation, and emission spectra were studied. The nanoparticles show blue shifted absorption bands with respect to coarse grained material.
Vacancy-enhanced intermixing in highly strained InGaAs/GaAs multiple quantum well photodetector
Authors: Lee Alex S. W. , Li E. Herbert , Karunasiri Gamani
Published: July 2002

Impurity-free vacancy disordering techniques using rapid thermal annealing with electron-beam evaporated SiO2 encapsulant was utilized to study its effect on the optical and electrical properties of the highly strained InGaAs/GaAs quantum well infrared photodetector. The photoluminescence peak is blueshifted and its line width does not increase much, indicating the compositional disordering of the quantum well structure and there is no strain relaxation or minimal deterioration of the heterostructure quality. Both transverse electric and transverse magnetic infrared intersubband transitions are retained and observed after intermixing. The absorption peak wavelength is redshifted from the as grown 10.2 μm to the interdiffused 10.5 and 11.2 μm, for 5 and 10 s annealing at 850 °C, respectively, without appreciable degradation in absorption strength. Theoretical calculations of the absorption spectra are in good agreement with the experimental data. Annealed responsivity spectra of both 0° and 90° polarization are of comparable amplitude but with narrower spectra line width. Dark current of the annealed devices is found to be an order of magnitude larger than the as-grown one at 77 K.
Quantitative determination of effective dipole and monopole moments of magnetic force microscopy tips
Authors: Lohau J. , Kirsch S. , Carl A. , Dumpich G. , Wassermann E. F.
Published: July 2002

We present experimental results on the characterization of commercially available magnetic force microscopy (MFM) thin film tips as a function of an external magnetic field. Well defined magnetic stray fields are produced using current carrying rings with radii ranging between 603 and 2369 nm fabricated by electron-beam lithography directly imaged by MFM. Treating the MFM tip as a point probe, the analysis of the image contrast as a function of both the magnetic stray field and the lift height allows for a quantitative determination of effective magnetic dipole and monopole moments of the tip as well as their imaginary location within the real physical tip. Our systematic study gives a quantitative relationship on how absolute values of the magnetic dipole and monopole moments and their location within the tip depend on a characteristic decay length of the z component of the magnetic field being detected. From this we can estimate the effective tip volume of the real physical thin film tip relevant in MFM imaging.
Response to “Comment on ‘Dynamic analysis of the response of lateral piezoresistance gauges in shocked ceramics’ and on ‘Determination of lateral stresses in shocked solids: Simplified analysis of piezoresistance gauge data’ ” [J. Appl. Phys. 86, 3484 (1999)]
Authors: Feng R. , Gupta Y. M. , Wong M. K. W.
Published: July 2002

Contrary to the assertions in a comment by Rosenberg on our recent papers [J. Appl. Phys. 82, 2845 (1997) and J. Appl. Phys. 83, 747 (1998)], the conclusions of our work neither supported the analytic model by Rosenberg and co-workers nor validated their analysis of lateral piezoresistance gauge data. Differences in our respective approaches are emphasized, and several errors and misleading statements in the comment are pointed out.
Formation and deterioration mechanisms of low-resistance TaTi ohmic contacts for p-GaN
Authors: Suzuki Masaaki , Arai T. , Kawakami T. , Kobayashi S. , Fujita S. , Koide Yasuo , Taga Y. , Murakami Masanori
Published: July 2002

We demonstrated in our previous paper [Appl. Phys. Lett. 74, 275 (1999)] that TaTi contacts annealed at temperature of 800 °C provided a specific contact resistance (ρc) of around 3×10−5 Ω cm2 for p-GaN epilayers with hole concentration of 7.0×1017 cm−3. The reduction of the contact resistances was believed to be due to reactivation of Mg atoms doped in the GaN epilayer by removing H. In the present article, diffusion behavior of hydrogen atoms in the p-GaN was extensively studied by secondary-ion mass spectroscopy and correlated with the electrical properties of the TaTi contacts. It was found that formation of the low-resistance TaTi ohmic contacts was well explained by diffusion behavior of hydrogen in the p-GaN. Although the deterioration rates of the TaTi contacts during low temperature storage after ohmic contact formation were coincident with the diffusion rates of hydrogen atoms in the GaN, the deterioration mechanism could not be explained simply by hydrogen release from the TaTi contacts into the GaN. We believe that selection of a contact metal which would remove the hydrogen without inducing crystalline defects in the GaN after the metal and GaN reaction is a key to prepare highly reliable, low-resistance ohmic contacts for p-GaN.
Intervalence band absorption in InP and related materials for optoelectronic device modeling
Authors: Taylor Jason , Tolstikhin Valery
Published: July 2002

Intervalence band absorption spectra of InP and related materials over a range of temperatures are calculated using different k⋅p methods for band structure. It is shown that band structure models which neglect valence band intermixing effects, such as the Kane model, fail to provide any quantitative agreement with experiment. However, the Luttinger–Kohn model [Phys. Rev. 97, 869 (1955)] if properly fitted, does yield quantitatively accurate results for InP, GaAs, and InGaAs, in wide spectral and temperature ranges of interest for practical optoelectronic devices without adjusting the effective masses and split-off energy.
pn
-junction delineation in Si devices using scanning capacitance spectroscopy
Authors: Edwards Hal , Ukraintsev Vladimir A. , San Martin Richard , Johnson F. Scott , Menz Philip , Walsh Shawn , Ashburn Stan , Wills K. Scott , Harvey Ken , Chang Mi-Chang
Published: July 2002

The scanning capacitance microscope (SCM) is a carrier-sensitive imaging tool based upon the well-known scanning-probe microscope (SPM). As reported in Edwards et al. [Appl. Phys. Lett. 72, 698 (1998)], scanning capacitance spectroscopy (SCS) is a new data-taking method employing an SCM. SCS produces a two-dimensional map of the electrical pn junctions in a Si device and also provides an estimate of the depletion width. In this article, we report a series of microelectronics applications of SCS in which we image submicron transistors, Si bipolar transistors, and shallow-trench isolation structures. We describe two failure-analysis applications involving submicron transistors and shallow-trench isolation. We show a process-development application in which SCS provides microscopic evidence of the physical origins of the narrow-emitter effect in Si bipolar transistors. We image the depletion width in a Si bipolar transistor to explain an electric field-induced hot-carrier reliability failure. We show two sample geometries that can be used to examine different device properties.
Laser induced electron and sodium ion emission from single crystal NaNO3 at 1064 nm
Authors: Bandis C. , Langford S. C. , Dickinson J. T. , Ermer D. R. , Itoh Norioki
Published: July 2002

Wide band gap insulators irradiated with UV pulsed lasers have been shown to yield both photoinduced electrons and energetic positive ions suggesting occupied electronic states in the band gap. It is not obvious that similar experiments with near-IR wavelengths should yield detectable emissions. Here we report electron and Na+ ion emission from single crystal sodium nitrate (∼10 eV band gap) upon exposure to near-IR (1.16 eV) laser radiation. The fluence dependence of both ion and electron yields is highly nonlinear and the kinetic energies of the emitted ions can reach values up to 5 eV. Our data suggest that the observed emissions originate from defect sites and they are consistent with a model that requires multiple single photon charge transfer to ionize an electron trap and subsequently eject a nearby positive adion due to electrostatic repulsion. Further evidence for the role of defects in the observed ion emission are provided by two beam experiments; one beam (UV laser) is used to generate defects and the second beam (near-IR laser) is used to photodesorb the ions. Such experiments demonstrate that exposure of the sodium nitrate surfaces to UV laser radiation significantly increases the ion emission due to near-IR laser radiation.
Photoluminescence, infrared reflectivity, and Raman spectra of the ordered vacancy compound CuGa3Se5
Authors: Rincón C. , Wasim S. M. , Marı́n G. , Hernández E. , Perez G. Sanchez , Galibert J.
Published: July 2002

The photoluminescence (PL), infrared reflectivity (IR), and Raman spectra of the ordered vacancy compound CuGa3Se5 have been studied. Analysis of the data indicates that the main PL emission is due to a donor-acceptor pair recombination. Donor and acceptor levels with activation energy of 15 and 300 meV, respectively, were estimated. The lattice vibrational modes of this compound have also been obtained at 300 K by a combined analysis of IR and Raman spectra. Lines common to both spectra, observed at 48, 64, 105, 142, 187, 200, 218, 250, and 274 cm−1, were identified with E or B2 modes. The most intense peak at 166 cm−1 and those observed at 72 and 90 cm−1, which are only Raman active, are assigned to the A1 and B1 modes, respectively.
Study of ion beam induced epitaxial crystallization of SrTiO3
Authors: Oyoshi K. , Hishita S. , Haneda H.
Published: July 2002

Amorphous SrTiO3 on single crystal SrTiO3 (100) has been crystallized by He+, Ne+, or Ar+ ions with energy of 200 keV–2 MeV at a substrate temperature of 100–250 °C. Rutherford backscattering spectrometry in channeling geometry and x-ray diffraction were used to evaluate the crystallization. Ion-beam-induced epitaxial crystallization (IBIEC) of SrTiO3 was confirmed and the activation energy of IBIEC observed was about 0.1–0.3 eV, a value about 1/10 relative to thermal solid phase epitaxial crystallization. The observed IBIEC seems to be consistent with previously proposed models in which IBIEC is dominated by point defects produced by ion irradiation and their migration to the amorphous/crystal (a/c) interface. The IBIEC mechanism and point defect behavior are discussed by the use of simple models taking into account the rate limiting processes of IBIEC for both point defect diffusion and atomic rearrangement at a/c interface.
Magnetic and magneto-transport properties of γFe2O3-grain-embedded Fe3O4 thin films
Authors: Uotani M. , Taniyama T. , Yamazaki Y.
Published: July 2002

Magnetic and magneto-transport properties of γFe2O3-grain-embedded Fe3O4 thin films are investigated. The magnetoresistance (MR) abruptly changes in the intermediate oxidation state between Fe3O4 and γFe2O3. The magnetic relaxation coefficient also becomes a minimum around this oxidation state. The slow dynamics of the magnetic relaxation are associated with the disturbance of the domain wall displacement due to the embedded γFe2O3 grains with Fe2+ impurities. A possible mechanism for the change in the MR is also proposed.
The magnetic and transport properties of Fe doped La0.5Ca0.5MnO3
Authors: Chen Xin , Wang Zhihong , Li Runwei , Shen Baogen , Zhan Wenshan , Sun Jirong , Chen Jinsong , Yan Chunhua
Published: July 2002

The magnetic and transport properties of Fe doped charge ordering La0.5Ca0.5MnO3 have been studied. With the increase of the Fe ion, the ground state of the sample changes from a charge ordering state (x=0) to a spin glass state (x=0.10). The sample with x=0.04 displays a middle state, while a larger magnetoresistance of 109 at 5 K and a decrease of the critical field of charge ordering melting were found. These differences can be explained by the antiferromagnetic exchange coupling between Fe and Mn ions, the destruction of the Mn-O plane and the competition between ferromagnetic and antiferromagnetic clusters.
Growth processes of magnetic clusters studied by direct simulation Monte Carlo method
Authors: Mizuseki Hiroshi , Jin Ying , Kawazoe Yoshiyuki , Wille Luc T.
Published: July 2002

Film formation with deposited magnetic clusters has attracted strong attention as a new manufacturing technique to realize high-density magnetic recording media and to create materials with unique magnetic properties. Such clusters are typically obtained by adiabatic expansion of a metal vapor. It is therefore important to clarify the growth mechanism since this has a profound effect on the cluster magnetic moment. In this article a new simulation method based on a combination of Direct Simulation Monte Carlo (DSMC) and a cluster collision model is introduced to examine the effect of experimental conditions in cluster beam growth. We simulate the behavior of clusters and inert gas atoms in the flight path under different experimental conditions. In particular, we find a bimodal size distribution curve and a decreasing average moment as a function of flight path length.
Thermal field fluctuations in a magnetic tip / implications for magnetic resonance force microscopy
Authors: Hannay J. D. , Chantrell R. W. , Rugar D.
Published: July 2002

Thermally excited magnetic fluctuations are fundamental to the behavior of small ferromagnetic particles and have practical consequences for the proposed detection of individual spins by magnetic resonance force microscopy (MRFM). In particular, fluctuating fields from a nearby magnetic tip can increase the relaxation rate of spins in a sample if there is significant spectral density of field fluctuation at the Larmor frequency of the target spin. As an initial step toward understanding this issue, magnetic field fluctuations have been simulated which emanate from a magnetic tip with dimensions 60 nm×60 nm×2 μm. It was found that the fluctuations in a cobalt magnetic tip were too strong for MRFM experiments aimed at detecting individual electron spins. However, the results obtained for a PrFeB tip fell within the tolerance required.
Alternating current susceptibility of a gadolinium crystal
Authors: Coey J. M. D. , Gallagher K. , Skumryev V.
Published: July 2002

The complex ac susceptibility of long bar-shaped crystals of gadolinium cut parallel or perpendicular to the c axis does not exhibit the expected divergence at the Curie point TC=293 K. However, χ′ does diverge to the demagnetization-limited value 1/N≈70 at the spin reorientation transition temperature Tsr=225 K, where the first anisotropy constant K1 changes sign. The c-axis susceptibility χ∥′(T) shows a step to reach a value of 10 at Tc which is essentially independent of measuring field in the ranges 10 Hz–1 kHz and 8–800 A/m. However, there is a peak in the perpendicular susceptibility χ⊥′(T) near TC, which reaches 45. A superimposed 50 Hz depinning field does not influence the ac response. It is proposed that gadolinium exhibits long-period sinusoidally modulated c-axis order below TC, analogous to that of erbium. The period of the modulation is estimated as 70 Å.
Single spin ensemble model for the change of unidirectional anisotropy constant by annealing on polycrystalline ferromagnetic/ antiferromagnetic bilayers
Authors: Tsunoda Masakiyo , Takahashi Migaku
Published: July 2002

A model for the exchange coupled polycrystalline ferromagnetic/antiferromagnetic (F/AF) bilayers is proposed in order to discuss the mechanism of the change of the unidirectional anisotropy constant (JK) of the bilayers by thermal annealing. The AF layer is treated as an aggregation of the AF grains whose magnetic anisotropy axes lay in the film plane with two-dimensionally random distribution. Two stable states concerning the direction of the AF spins are calculated for the AF grain. Determining the populations of the AF grains in each state in thermal equilibrium, total energy of the system is obtained, which provides the magnetization curves and the magnetic torque curves of the F/AF bilayers. The calculated results show the reduction of JK with increasing the equilibrium temperature, which is due to the changes of the probability functions for the respective spin alignments of the AF grain. We conclude that the changes in JK do not necessarily need any changes of the microstructure and the intrinsic physical quantities of the F/AF bilayers.
Enhancement of room temperature magnetoresistance in double perovskite ferrimagnets
Authors: Zhou J. P. , Dass R. , Yin H. Q. , Zhou J.-S. , Rabenberg L. , Goodenough J. B.
Published: July 2002

The double perovskite Sr2FeMoO6 is a half-metallic ferrimagnet exhibiting significant magnetoresistance (MR) at 300 K in a magnetic field H<2 kOe. A preliminary study of the influence of isovalent and aliovalent substitutions for Sr2+ on the magnitude of the room-temperature MR is reported. Of the polycrystalline samples, Sr1.9A0.1FeMoO6 (A=Ca, Ba, La or Pr), the best result was obtained with the Ba(0.1) sample, which showed a factor of 2 enhancement of the MR over that previously reported for Sr2FeMoO6.
Structure and magnetic properties of melt-spun PrFe10Mo2Nx compounds
Authors: Jin Z. Q. , Zhang J. R. , Tang S. L. , Du Y. W.
Published: July 2002

The structure and magnetic properties of PrFe10Mo2Nx compounds prepared by melt spinning have been investigated. A single-phase structure of ThMn12-like has been obtained in ribbons quenched at velocities vs below 40 m/s. The desired ThMn12 structure is considerably more stable for Pr(Fe, Mo)12 compounds than for Nd(Fe, Mo)12 compounds. Only at higher speeds than 50 m/s the PrFe10Mo2 ribbons quench into TbCu7-like compound of which Curie temperature is about 580 K. Annealing temperatures in excess of 1023 K are required to form ThMn12 crystal structure for the ribbons melt spun at 50 m/s. Upon nitrogenation at 723 K, the Curie temperatures increase to 663 and 580 K for TbCu7- and ThMn12-like nitrides, respectively. A coercivity of 3.3 kOe with a magnetization up to 118 emu/g at a field of 20 kOe has been obtained in the present ribbons.
Design optimization for a SmCo-biased colossal magnetoresistive thin film device
Authors: Neu V. , Anane A. , Wirth S. , Xiong P. , Shaheen S. A. , Cadieu F. J.
Published: July 2002

A device structure composed primarily of a film made from colossal magnetoresistive (CMR) material and a permanent magnet (PM) film used for biasing the CMR film is proposed as a sensor for magnetic objects. The PM film provides a magnetic field through the CMR film, which is substantially decreased when a magnetic object approaches the device, as part of the magnetic flux is now diverted through the object. To test the feasibility of this concept, we performed simulations of the magnetic field distribution with a three-dimensional finite boundary program. Our vertical model structure consists of a strip of CMR material covered by a PM strip with magnetic in-plane texture and magnetized along its width. The maximum possible biasing field through the CMR material is mainly controlled by the thickness to width ratio of the PM material and cannot be improved by the use of a soft magnetic cladding. The same effect is observed on the flux reduction by approaching a magnetic object. Preliminary results on an experimental realization of the device are given.
A heating model including effects on magnetoresistance (MR) in MR and giant MR heads
Authors: Gibbons M. R. , Liu F. , Stoev K. , Shi X. , Yan X. , Saha R.
Published: July 2002

An analytic model is presented that describes current induced heating effects in giant magnetoresistive (GMR) heads. Unlike previous transmission line models, the model includes temperature effects on the measured GMR response of the head in addition to changes in the temperature and the resistance. The response of the head will decrease with temperature in part due to the negative thermal coefficient for the GMR. The model predicts that the measured GMR response does not decrease as much as indicated by the thermal coefficient since the signal is enhanced by the change in temperature due to the GMR response to the applied field.
Resistance as a reliability indicator in lifetime testing of thin film magnetic recording heads
Authors: Macchioni Curtis V. , Doan Vincent V. , He Qing
Published: July 2002

It is demonstrated that the resistance rise observed during lifetime testing of magnetoresistive heads is primarily due to interlayer diffusion of Ta into the Au, NiFe, and NiFeRh layers, not electromigration damage to the sensor. 3.2 Gb/in.2 production heads which were preannealed at 275 °C for 168 h without bias current prior to lifetime testing showed no increase in resistance, or evidence of electromigration, after 200 h at 150 °C with a current density of 7.6×107 A/cm2. In contrast, identical heads, which were not preannealed, showed an average 14% resistance rise during the same lifetime test. Step annealing of heads and sheet films of Cr/CoCrPt/Ta/Au/Ta and NiFeRh/Ta/NiFe/Ta showed that the resistance rise was linear in t1/2, where t is the annealing time, in the earliest stages of the anneal cycle. This behavior is indicative of diffusion processes in the heads.
Magnetically soft and electrically resistive CoNiFeS alloy films prepared by electrodeposition
Authors: Kim Young Keun , Son Hee Young , Choi Young Sik , Moon Ki-Seok , Sunwoo Kuk Hyun
Published: July 2002

Magnetic properties of electrodeposited CoNiFeS films were studied to seek their feasibility for applications in microelectromagnetic devices such as high areal density recording heads. We started with NiFe and then expanded experiments to a CoNiFe system. Finally, we added a fourth element, sulfur, to further improve physical properties. A small amount of sulfur inclusion has induced grain size refinement and offered magnetic softness to the film accompanying with increased electrical resistivity. Grain size was found to be in the order of 10 nm. Co73Ni17Fe9S1 (in wt. %) films with thickness of 2.5 μm exhibit superior properties compared with currently utilized Ni45Fe55: high saturation magnetic flux density (Bs∼17 kG), low coercivity (Hc∼0.4 Oe), near zero saturation magnetostriction (λs∼1.0×10−6), high permeability (μ∼1300 at 100 MHz), and high electrical resistivity (ρ∼55 μΩ cm). From a processing standpoint, we were able to control film thickness uniformity by adjusting current distributions between the auxiliary electrode and cathode across 100 mm wafers.
Simulation of the write field for T-shaped pole heads
Authors: Narumi S. , Kawato Y. , Tsuchiya Y. , Kawabe T. , Fukui H. , Ito T.
Published: July 2002

The write field distributions of T-shaped pole heads are presented. The maximum head field in the medium plane for T-shaped heads was larger than that for conventional structure heads. However, the field from the edges of the upper pole is not negligible for the T-shaped heads. As a result, neighboring bit patterns may be affected. To decrease the edge field, it is effective to make the throat height longer and recess the edges of the upper pole from the air bearing surface. Actual T-shaped heads were fabricated and their characterizations were investigated. The results agreed with simulations for longer throat height and for the recessed pole edge effect.
Prospects for performing neutron scattering in intense pulsed magnetic fields (invited)
Authors: Robinson R. A.
Published: July 2002

Present dc split-pair superconducting magnets designed for neutron scattering studies can reach fields up to 14.5 T. Prospects for achieving pulsed magnetic fields up to 30 T in conjunction with spallation neutron sources are reviewed, along with a number of scientific questions that can be addressed with such a capability.