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24 Dec 2001

Volume 79, Issue 26, pp. 4271-4458

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Observation of orientation dependence of electrorheology effect in ferroelectric liquid crystal using shear horizontal wave

M. Inoue, K. Yoshino, H. Moritake, and K. Toda

Appl. Phys. Lett. 79, 4345 (2001); http://dx.doi.org/10.1063/1.1424472 (3 pages) | Cited 1 time

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The electrorheology (ER) effect of ferroelectric liquid crystals is observed under shear-horizontal (SH) wave propagation. The ER effect is strongly dependent on the orientation direction of the liquid-crystal molecule. The apparent viscosity is evaluated through the numerical analysis result on the propagation characteristics of a SH wave in a trilayer structure including a ferroelectric liquid-crystal (Chisso, CS1014) layer between two glass plates. The ER effect is examined by the relation between the orientation of smectic layers and the propagation direction of the SH wave. © 2001 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
02.60.-x Numerical approximation and analysis
66.20.-d Viscosity of liquids; diffusive momentum transport
62.30.+d Mechanical and elastic waves; vibrations

Nitrogen bonding structure in carbon nitride thin films studied by soft x-ray spectroscopy

Niklas Hellgren, Jinghua Guo, Conny Såthe, Akane Agui, Joseph Nordgren, Yi Luo, Hans Ågren, and Jan-Eric Sundgren

Appl. Phys. Lett. 79, 4348 (2001); http://dx.doi.org/10.1063/1.1428108 (3 pages) | Cited 49 times

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Soft x-ray absorption (SXAS) and emission (SXES) spectroscopies were applied to study the nitrogen bonding structure in magnetron sputtered CNx thin films. By comparing with calculated spectra of N in different model systems, N in three main bonding environments can be identified: (i) C�N bonds, with a sharp SXAS peak at 399.5 eV, (ii) pyridine-like N (i.e., N bonded to two C atoms), with an x-ray absorption resonance at ∼398.5 eV, and (iii) N substituted in graphite, possibly with one sp3 carbon as a neighbor (SXAS energy ∼401 eV). These bondings are present in all CNx films analyzed; however, as shown earlier, the relative intensities between the peaks may vary with the growth conditions. Differences in the coordination of the nearest or second nearest C neighbors only cause slight changes in the peak positions and spectrum shape. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra
78.70.En X-ray emission spectra and fluorescence
61.50.Lt Crystal binding; cohesive energy

Lattice parameters of wurtzite Al1−xSixN ternary alloys

Yoshitaka Taniyasu, Makoto Kasu, and Naoki Kobayashi

Appl. Phys. Lett. 79, 4351 (2001); http://dx.doi.org/10.1063/1.1428768 (3 pages) | Cited 8 times

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Lattice constants and bond lengths of wurtzite Al1−xSixN ternary alloys (0 ⩽ x ⩽ 0.08) were determined by reciprocal lattice maps around Al1−xSixN (0002) and (11–24) reflections. The measured lattice constants obtained directly from as-grown Al1−xSixN layers were scattered because they include the factor of residual strain. Therefore, the lattice constants in the strain-free case were calculated from the measured lattice constants taking the residual strain into account. We found that the a-axis and c-axis lattice constants of the strain-free Al1−xSixN linearly decreased with the Si content as a0 = 3.1113−0.1412x (Å) and c0 = 4.9814−0.2299x (Å). Further, we obtained the bond length as d0 = 1.86818−0.0862x (Å). The bond length is nearly equal to the interpolation between the Al–N bond and the Si–N bond. © 2001 American Institute of Physics.
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61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology
61.50.Lt Crystal binding; cohesive energy
68.60.Bs Mechanical and acoustical properties
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Excitation mechanisms in dye-doped organic light-emitting devices

F. Pschenitzka and J. C. Sturm

Appl. Phys. Lett. 79, 4354 (2001); http://dx.doi.org/10.1063/1.1427746 (3 pages) | Cited 25 times

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In an organic light-emitting device with a polymeric matrix concurrently doped with two different dyes, the photoluminescence (PL) and electroluminescence (EL) spectra are observed to be very different, with both dyes emitting in PL and only one in EL at room temperature. A simple model based on charge trapping and thermal excitation is introduced to explain this observation. The EL spectral change of a device at 77 K is consistent with this model. In addition, using the same model, the strong dependence of the EL efficiency (but not PL) on the concentration of a single dye in an organic film can be understood. The materials used in this experiment are the polymer poly(9-vinylcarbazole) combined with electron transport molecules, and the dyes coumarin 47, coumarin 6, and Nile red. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics

Boron carbide/n-silicon carbide heterojunction diodes

S. Adenwalla, P. Welsch, A. Harken, J. I. Brand, A. Sezer, and B. W. Robertson

Appl. Phys. Lett. 79, 4357 (2001); http://dx.doi.org/10.1063/1.1426257 (3 pages) | Cited 21 times

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The fabrication, initial structural characterization, and diode measurements are reported for a boron carbide/silicon carbide heterojunction diode. Current–voltage curves are obtained for operation at temperatures from 24 to 351 °C. Plasma-enhanced chemical-vapor deposition (PECVD) -deposited undoped boron carbide material is highly crystalline and consists of a variety of polytypes of boron carbide (BC) with crystal sizes as large as 110 nm. Crystal phases are similar to those for PECVD BC on Si but only partially match known boron and boron-rich BC phases. © 2001 American Institute of Physics.
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85.30.Kk Junction diodes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
68.35.Ct Interface structure and roughness

Stacking fault band structure in 4H–SiC and its impact on electronic devices

M. S. Miao, Sukit Limpijumnong, and Walter R. L. Lambrecht

Appl. Phys. Lett. 79, 4360 (2001); http://dx.doi.org/10.1063/1.1427749 (3 pages) | Cited 62 times

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First principles calculations of the stacking fault (SF) in 4H–SiC indicate the occurrence of an interface band in the gap with maximum depth of 0.2–0.3 eV below the conduction band minimum at the math point. The energy of formation of SFs in 3C–, 4H–, and 6H–SiC on the other hand is found to be of order a few meV/pair. Thus, there is a thermodynamic driving force promoting growth of SF area in an n-type sample. Radiationless recombination of electrons trapped at the SF with holes is proposed to provide sufficient energy to overcome the partial dislocation motion barriers towards formation of additional SF area in a device under forward bias. © 2001 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Time domain measurement of spin-dependent recombination

Christoph Boehme and Klaus Lips

Appl. Phys. Lett. 79, 4363 (2001); http://dx.doi.org/10.1063/1.1428623 (3 pages) | Cited 11 times

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A defect characterization method is presented, the time domain measurement of spin-dependent recombination (TSR). Recombination between paramagnetic states is changed rapidly by electron spin resonant excitation through strong nanosecond microwave pulses. After the pulse, a slow relaxation of the recombination rate towards its steady state takes place. By measuring the current transient after the resonant pulse, information about dissociation and recombination probabilities of spin pairs is directly obtained for a distinct recombination path. Dangling bond recombination in microcrystalline silicon was used as model process for the demonstration of TSR. © 2001 American Institute of Physics.
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76.30.-v Electron paramagnetic resonance and relaxation
71.55.-i Impurity and defect levels

Ab initio study of quantum confined unpassivated ultrathin Si films

B. K. Agrawal and S. Agrawal

Appl. Phys. Lett. 79, 4366 (2001); http://dx.doi.org/10.1063/1.1427420 (3 pages)

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An ab initio study of the electronic structure of the one-dimensional quantum-confined crystalline ultrathin Si (100) films both with the unreconstructed p(1×1) and the reconstructed c(2×2) film surfaces in a large thickness range of 2.7–29.7 Å has been made after employing a self-consistent full potential linear muffin tin orbital method along with the density functional theory in local approximation. A relatively large unit cell of 28 layers has been employed. In the case of the unreconstructed p(1×1) surface, the dangling bond states fill the fundamental energy gap completely and these states are weakly localized, i.e., the wave functions of these states die out in the inner region of the film slowly. After the c(2×2) surface reconstruction, the bonding and the antibonding dangling bond states are seen to lie near the valence band maximum and the conduction band minimum in the fundamental energy gap, respectively, and are again weakly localized. There remain dangling bond states within the gap after reconstruction. The separation between the two surface Si atoms in a dimer shows quite an appreciable change of about 36–40%. The band gaps of the various films remain practically unchanged after surface reconstruction; the changes lie well within 6%. The present results give convincing theoretical evidence for the occurrence of the weakly localized dangling bond states and the absence of too much localized states in quantum-confined systems, which may be responsible for the occurrence of luminescence observed in a comparatively low energy region in the quantum-confined nanostructures, e.g., in the infrared region in porous silicon. The presently predicted exponential rise of the band gap with the decrease in the quantum-confined size in the ultrathin film region is in sharp contrast to an approximate linear rise in the band gap observed in the spectroellipsometric measurements. © 2001 American Institute of Physics.
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71.20.Mq Elemental semiconductors
73.20.At Surface states, band structure, electron density of states
73.20.Fz Weak or Anderson localization
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Synthesis and characterization of luminescent ZrO2:Mn, Cl powders

M. García-Hipólito, C. Falcony, M. A. Aguilar-Frutis, and J. Azorín- Nieto

Appl. Phys. Lett. 79, 4369 (2001); http://dx.doi.org/10.1063/1.1428110 (3 pages) | Cited 10 times

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ZrO2:Mn, Cl luminescent powders have been synthesized at temperatures ranging from 250 to 500 °C. X-ray diffraction measurements indicate changes in the crystallinity of the material as a function of the processing temperature. The photoluminescence spectra show bands associated with transitions from the 4T1 level to the 6A1 levels of the Mn2+ ions. An impurity concentration quenching is observed with the Mn contents. In addition, the presence of Cl in the synthesized material has been found to have an important role on the photoluminescence intensity emission. Preliminary results on cathodoluminescent emission are also reported. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices

A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, A. V. Osinsky, P. E. Norris, S. J. Pearton, J. Van Hove, A. Wowchak, and P. Chow

Appl. Phys. Lett. 79, 4372 (2001); http://dx.doi.org/10.1063/1.1429754 (3 pages) | Cited 10 times

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Electrical and optical properties of modulation-doped p-AlGaN/GaN superlattices are compared to those of similarly doped p-GaN films. It is shown that modulation doping increases the sheet hole concentration by several times. In p-AlGaN/GaN superlattices grown on GaN underlayers, this increase is accompanied by a significant increase in hole mobility which results in a remarkable decrease in sheet resistivity of the structure compared to p-GaN films and this decrease in sheet resistivity should hold up to temperatures exceeding 350 °C. For superlattices prepared on AlGaN underlayers, the mobility decreases compared to p-GaN. In such superlattices, one also observes a strong redshift and a strong broadening of the band edge luminescence peak coming most probably from increased mosaicity and strain which would also explain the observed deterioration of mobility. The magnitude of the redshift in the position of the band edge luminescence band slightly increased upon application of reverse bias which is interpreted as a manifestation of quantum-confined Stark effect. © 2001 American Institute of Physics.
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73.63.-b Electronic transport in nanoscale materials and structures
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.21.Cd Superlattices
68.65.Cd Superlattices
61.72.uj III-V and II-VI semiconductors
78.20.Jq Electro-optical effects
78.60.Hk Cathodoluminescence, ionoluminescence

Localization of carriers and polarization effects in quaternary AlInGaN multiple quantum wells

E. Kuokstis, J. Zhang, M.-Y. Ryu, J. W. Yang, G. Simin, M. Asif Khan, R. Gaska, and M. S. Shur

Appl. Phys. Lett. 79, 4375 (2001); http://dx.doi.org/10.1063/1.1429753 (3 pages) | Cited 10 times

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We report on observing a long-wavelength band in low-temperature photoluminescence (PL) spectrum of quaternary Al0.22In0.02Ga0.76N/Al0.38In0.01Ga0.61N multiple quantum wells (MQWs), which were grown over sapphire substrates by a pulsed atomic-layer epitaxy technique. By comparing the excitation-power density and temperature dependence of the PL spectra of MQWs and bulk quaternary AlInGaN layers, we show this emission band to arise from the carrier and/or exciton localization at the quantum well interface disorders. PL data for other radiative transitions in MQWs indicate that excitation-dependent spectra position is determined by screening of the built-in electric field. © 2001 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
81.07.St Quantum wells
71.35.Gg Exciton-mediated interactions
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Spin-polarized scanning tunneling microscopy on half-metallic manganite thin film with half-metallic manganite tip

R. Akiyama, H. Tanaka, T. Matsumoto, and T. Kawai

Appl. Phys. Lett. 79, 4378 (2001); http://dx.doi.org/10.1063/1.1375832 (3 pages) | Cited 15 times

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Spin-polarized tunneling was demonstrated on La0.7Sr0.3MnO3 epitaxial thin film with a La0.7Sr0.3MnO3-coated PtIr tip at room temperature. A magnetic-field-dependent gap structure was found in the differential tunneling spectra due to the spin-valve effect. The spatial mapping of the differential tunneling conductance shows strongly contrasting variations, which demonstrates the presence of magnetic domains with different spin alignments. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
72.15.Gd Galvanomagnetic and other magnetotransport effects

Quantum-well effect in magnetic tunnel junctions with ultrathin single-crystal Fe(100) electrodes

T. Nagahama, S. Yuasa, Y. Suzuki, and E. Tamura

Appl. Phys. Lett. 79, 4381 (2001); http://dx.doi.org/10.1063/1.1424068 (3 pages) | Cited 17 times

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We studied the tunnel spectra of magnetic tunnel junctions with a single-crystal ultrathin Fe(100) electrode. The tunnel spectra show oscillations of the differential conductivity and the differential tunnel magnetoresistance. The positions of the maxima of the oscillations move systematically with the change in the Fe(100) electrode’s thickness, indicating that the oscillations originate from the quantum-well states in the ultrathin Fe(100) electrode. This effect provides us with an opportunity to create voltage-controlled spin functional devices. © 2001 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Micromagnetic disorder in antiparallel biased spin valves

C. H. Marrows, G. L. Creeth, F. E. Stanley, B. J. Hickey, P. R. Aitchison, M. Crawford, and J. N. Chapman

Appl. Phys. Lett. 79, 4384 (2001); http://dx.doi.org/10.1063/1.1421641 (3 pages)

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The reorientation of antiferromagnetically coupled Co layers comprising the pinned layers of an antiparallel biased spin valve is reported. Initially, the lower Co layer is saturated in the growth field in the deposition chamber, but it reorients as the upper Co layer grows to be thicker than the lower one. We have investigated the nature of this reorientation by ex situ transport measurements and Lorentz microscopy, and found it highly inhomogeneous, leading to a complex in-plane domain pattern. This results in a reduction of the giant magnetoresistance of the spin valves close to the balance point, where the benefits of the antiparallel biasing are greatest. © 2001 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Ee Antiferromagnetics
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Spin-dependent tunnel junctions with ZrOx barriers

Jianguo Wang, P. P. Freitas, E. Snoeck, P. Wei, and J. C. Soares

Appl. Phys. Lett. 79, 4387 (2001); http://dx.doi.org/10.1063/1.1421232 (3 pages) | Cited 24 times

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Spin-dependent tunnel junctions with crystalline ZrOx barriers were fabricated, with tunnel magnetoresistance (TMR) reaching 20% and a resistance×area product of 24 k Ω μm2, after annealing at 260 °C. Effective barrier height and thickness are 1.6 eV and 10.6 Å, respectively. The ZrOx barriers were fabricated by rf plasma oxidation of a 5 Å thick Zr layer. High-resolution transmission electron microscopy and Rutherford backscattering spectrometry were used to characterize the as-deposited barrier. Both ZrO and ZrO2 phases are present, together with (CoFe)Ox. Upon annealing, the interfacial oxygen moves into the barrier, resulting in an increase of TMR from 2% to 19.2%, an increase of barrier height from 0.3 to 1.6 eV, and a reduction of barrier thickness from 18.5 to 10.5 Å. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
61.72.Cc Kinetics of defect formation and annealing

Continuous reel-to-reel measurement of critical currents of coated conductors

G. Grimaldi, M. Bauer, and H. Kinder

Appl. Phys. Lett. 79, 4390 (2001); http://dx.doi.org/10.1063/1.1428771 (3 pages) | Cited 5 times

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We demonstrate that magnetization measurements by Hall probe arrays are well suited for the reel-to-reel determination of critical currents along long lengths of coated conductors. The technique is contact-free, fast, simple, and it has a high spatial resolution. A quantitative measure of the critical current as a function of position was obtained by fitting a simple critical state model to the field distribution. The technique is demonstrated for YBa2Cu3O7 films on single-crystal substrates and then applied to samples of coated conductors. © 2001 American Institute of Physics.
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74.25.Sv Critical currents
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena

Thermal effects in self-assembled FePt nanoparticles with partial chemical ordering

J. W. Harrell, S. Wang, D. E. Nikles, and M. Chen

Appl. Phys. Lett. 79, 4393 (2001); http://dx.doi.org/10.1063/1.1427751 (3 pages) | Cited 33 times

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We have studied the thermal stability of self-assembled FePt nanoparticles with partial chemical ordering. The magnetic viscosity was measured at zero field after partial dc demagnetization as a function of the initial remanent magnetization. The viscosity curves are in good agreement with a calculation using a noninteracting Stoner–Wohlfarth, Arrhenius–Néel model with a broad distribution of anisotropy fields and randomly oriented easy axes. The shape of the zero field viscosity curve differs from curves measured for thin film media with in-plane and perpendicular anisotropy, in which interactions are known to be important. © 2001 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Lr Magnetic aftereffects
61.46.-w Structure of nanoscale materials

Magnetic, structural, and transport properties of thin film and single crystal Co2MnSi

M. P. Raphael, B. Ravel, M. A. Willard, S. F. Cheng, B. N. Das, R. M. Stroud, K. M. Bussmann, J. H. Claassen, and V. G. Harris

Appl. Phys. Lett. 79, 4396 (2001); http://dx.doi.org/10.1063/1.1428625 (3 pages) | Cited 49 times

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The magnetic, structural, and transport properties of the Heusler alloy Co2MnSi are reported for sputtered thin films and a single crystal. X-ray diffraction reveals a phase pure L21 structure for all films grown between 573 and 773 K. Films grown at 773 K display a four-fold decrease in the resistivity relative to those grown at lower temperatures and a corresponding 30% increase in the residual resistivity ratio (ρ300 K/ρ5 K). We show that the higher growth temperature results in lattice constants, room temperature resistivities, and magnetic properties that are comparable to that of the bulk single crystal. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
73.61.At Metal and metallic alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Effect of lattice strain and defects on the superconductivity of MgB2

A. Serquis, Y. T. Zhu, E. J. Peterson, J. Y. Coulter, D. E. Peterson, and F. M. Mueller

Appl. Phys. Lett. 79, 4399 (2001); http://dx.doi.org/10.1063/1.1428109 (3 pages) | Cited 61 times

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The influence of lattice strain and Mg vacancies on the superconducting properties of MgB2 samples has been investigated. High quality samples with sharp superconducting transitions were synthesized. The variations in lattice strain and Mg vacancy concentrations were obtained by varying the synthesis conditions. It was found that high strain (∼1%) and the presence of Mg vacancies (∼5%) resulted in lowering the Tc by only 2 K. © 2001 American Institute of Physics.
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74.62.Dh Effects of crystal defects, doping and substitution
61.72.J- Point defects and defect clusters
74.10.+v Occurrence, potential candidates
74.72.-h Cuprate superconductors

The effect of uniaxial quartic anisotropy on thermal stability of magnetic nanograins

H. Neal Bertram and Vladimir L. Safonov

Appl. Phys. Lett. 79, 4402 (2001); http://dx.doi.org/10.1063/1.1425469 (3 pages) | Cited 13 times

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The effect of quartic anisotropy (K2) for nanograins with hexagonal crystalline structure on thermal stability has been studied. For reversal field parallel to the anisotropy axis, the presence of K2 increases the energy barrier in small fields but does not change the nucleation field. The mean first passage time was calculated from the stochastic differential equation. Reversal field at a finite temperature versus field pulse time showed very little effect at short times but thermal stability at long times was significantly extended. This effect was shown to be appreciable only for fields oriented within about 15° to the anisotropy axis. © 2001 American Institute of Physics.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.50.Ss Magnetic recording materials

Fabrication of highly balanced directly coupled YBa2Cu3Oy gradiometers and their noise properties in an unshielded environment

A. Tsukamoto, T. Fukazawa, K. Takagi, K. Yokosawa, D. Suzuki, and K. Tsukada

Appl. Phys. Lett. 79, 4405 (2001); http://dx.doi.org/10.1063/1.1429291 (3 pages) | Cited 10 times

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We fabricated directly coupled gradiometers made of YBa2Cu3Oy thin films on bicrystal substrates. The parasitic effective area of the gradiometric pickup coil was found to be comparable with that of the superconducting quantum interference devices (SQUIDs) in each gradiometer. A gradiometer balance of below 10−3 was achieved by selecting the coupling direction of the SQUID so as to cancel the parasitic effective area of the pickup coil by the effective area of the SQUID itself. The noise of the gradiometers measured in an unshielded environment decreased in proportion to the improvement in the gradiometer balance; however, the noise of the gradiometer with a balance of 0.03% was limited by the gradient-field component of the environmental noise. © 2001 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
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Electrical characteristics of a TaOxNy/ZrSixOy stack gate dielectric for metal–oxide–semiconductor device applications

Hyungsuk Jung, Hyundoek Yang, Kiju Im, and Hyunsang Hwang

Appl. Phys. Lett. 79, 4408 (2001); http://dx.doi.org/10.1063/1.1427155 (3 pages) | Cited 4 times

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In this letter, we describe a process for the preparation of high-quality tantalum oxynitride (TaOxNy) with zirconium silicate (ZrSixOy) as an interfacial layer for use in gate dielectric applications. Compared with conventional chemical oxide and nitride as interfacial layers, TaOxNy metal–oxide–semiconductor capacitors using ZrSixOy as an interfacial layer exhibit lower leakage current levels at the same oxide thickness and a lower interface state density. We were able to confirm the TaOxNy/ZrSixOy stack structure by Auger electron spectroscopy and transmission electron microscopy analyses. Zirconium silicate is a promising interfacial layer for future high-k gate dielectric applications. © 2001 American Institute of Physics.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
77.55.-g Dielectric thin films
79.20.Fv Electron impact: Auger emission

Multimode quantitative scanning microwave microscopy of in situ grown epitaxial Ba1−xSrxTiO3 composition spreads

K. S. Chang, M. Aronova, O. Famodu, I. Takeuchi, S. E. Lofland, J. Hattrick-Simpers, and H. Chang

Appl. Phys. Lett. 79, 4411 (2001); http://dx.doi.org/10.1063/1.1427438 (3 pages) | Cited 33 times

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We have performed variable-temperature multimode quantitative microwave microscopy of in situ epitaxial Ba1−xSrxTiO3 thin-film composition spreads fabricated on (100) LaA1O3 substrates. Dielectric properties were mapped as a function of continuously varying composition from BaTiO3 to SrTiO3. We have demonstrated nondestructive temperature-dependent dielectric characterization of local thin-film regions. Measurements are simultaneously taken at multiple resonant frequencies of the microscope cavity. The multimode measurements allow frequency dispersion studies. We observe strong composition-dependent dielectric relaxation in Ba1−xSrxTiO3 at microwave frequencies. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
07.79.-v Scanning probe microscopes and components
68.37.-d Microscopy of surfaces, interfaces, and thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
68.55.-a Thin film structure and morphology

Electromigration in multilevel interconnects with polymeric low-k interlevel dielectrics

P. Justison, E. Ogawa, P. S. Ho, M. Gall, C. Capasso, D. Jawarani, J. Wetzel, and H. Kawasaki

Appl. Phys. Lett. 79, 4414 (2001); http://dx.doi.org/10.1063/1.1421426 (3 pages) | Cited 1 time

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The impact of low-k dielectrics on the reliability of advanced Cu interconnects is of growing importance. As a first step to understanding this impact, we have investigated the effect of two types of polymeric low-k materials on the electromigration (EM) behavior of multilevel Al(Cu) interconnects. The two polymers used as interlevel dielectrics in this work are a fluorinated polyimide and a poly(aryl) ether. Joule heating experiments and microstructural analysis were both conducted on Al(Cu) to ensure that there were no significant microstructural or thermal differences between the polymer samples and their oxide counterparts. The resulting EM behavior can then be directly attributed to differences in the mechanical properties of the low-k and oxide interlevel dielectrics. We have observed that the low-k samples had a higher steady-state drift rate and did not reach saturation, resulting in shorter EM lifetimes. These results indicate that the short length is greatly modified with the incorporation of mechanically weaker dielectrics and can potentially alter reliability design strategies as Cu/Low-k integration moves into the production stage. © 2001 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration

Polarization reversal in a perovskite ferroelectric by molecular-dynamics simulation

M. Sepliarsky, S. R. Phillpot, S. K. Streiffer, M. G. Stachiotti, and R. L. Migoni

Appl. Phys. Lett. 79, 4417 (2001); http://dx.doi.org/10.1063/1.1428122 (3 pages) | Cited 10 times

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We characterize the microscopic processes that take place during polarization reversal in the tetragonal phase of a monodomain order–disorder perovskite ferroelectric using molecular-dynamics simulation. Microscopically the polarization of each unit cell reorients from an [001] orientation to an [00math] orientation through intermediate states with polarization parallel to [011] and [01math]. For low electric field and low temperature, chains of polarization reverse in a spatially coherent manner, resulting in macroscopic intermediate states with orthorhombic symmetry. At high electric field and high temperature the process is completely incoherent and there is no well-defined macroscopic intermediate state. © 2001 American Institute of Physics.
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77.80.Fm Switching phenomena
02.70.Ns Molecular dynamics and particle methods
77.22.Ej Polarization and depolarization
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