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31 Dec 2001

Volume 79, Issue 27, pp. 4479-4603

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Low-resistance spin-dependent tunnel junctions with ZrAlOx barriers

Jianguo Wang, P. P. Freitas, and E. Snoeck

Appl. Phys. Lett. 79, 4553 (2001); http://dx.doi.org/10.1063/1.1428111 (3 pages) | Cited 23 times

Online Publication Date: 13 March 2002

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Spin-dependent tunnel junctions with ZrAlOx barriers were formed by natural oxidation (5 min at 10 Torr) of 7-Å-thick Zr–Al films. Resistance×area products of 6 Ω μm2 were achieved with a 15.3% tunnel magnetoresistance (TMR) signal. Bottom-pinned (MnIr) junctions were deposited on top of 600-Å-thick, ion-beam-smoothed, low-resistance, Al electrodes. Effective average barrier height and thickness are 0.28 eV and 8.2 Å, respectively, and breakdown voltage is 0.41 V for 1 μm2 junctions. The TMR signal decreases by half at a bias voltage of 210 mV. Junction TMR decreases for anneals above 250 °C. High-resolution transmission electron microscopy indicates that ZrAlOx forms an amorphous barrier that is smoother than pure crystalline ZrOx or pure amorphous AlOx barriers. These low-resistance tunnel junctions are attractive for read head applications above 100 Gbit/in.2 where competitive signal-to-noise ratios imply resistance×area products of few Ω μm2 and TMR signals near or above 20%. © 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.Ss Magnetic recording materials
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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Polarization reversal study using ultrasound

Jianhua Yin and Wenwu Cao

Appl. Phys. Lett. 79, 4556 (2001); http://dx.doi.org/10.1063/1.1428629 (3 pages) | Cited 17 times

Online Publication Date: 13 March 2002

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We found that the sound velocity changes drastically near the coercive field for a 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 ferroelectric single crystal, which reflects that domain rotation occurred during polarization switching. This velocity change associated with polarization switching provides a powerful method to study the dynamics of polarization reversal process in nontransparent ferroelectric crystals. A complete phase velocity-electric field loop was measured quasi-statically in a switching cycle and compared with the polarization hysteresis loop. In addition, two attenuation peaks were found in the switching cycle, which indicates that two domain switching processes are involved in the polarization reversal.© 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
62.65.+k Acoustical properties of solids

In situ electrical-field-induced growth and properties of Bi3TiNbO9 ferroelectric thin films

B. Yang, X. J. Zhang, S. T. Zhang, X. Y. Chen, Z. C. Wu, Y. F. Chen, Y. Y. Zhu, Z. G. Liu, and N. B. Ming

Appl. Phys. Lett. 79, 4559 (2001); http://dx.doi.org/10.1063/1.1430023 (3 pages) | Cited 5 times

Online Publication Date: 13 March 2002

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With Bi3TiNbO9 (BTN) ferroelectric samples, in situ electrical-field-induced growth of ferroelectric thin films was demonstrated to control the films’ microstructure and manipulate their ferroelectric properties. BTN films on Ti/SiO2/Si substrates were grown at a relatively low temperature (650 °C) with a biased electrical field during pulsed-laser deposition. The (001) orientation of the films, which makes no contribution to their polarization, was effectively reduced by the in situ electrical field of strength of 70 V/cm. This results in a large increase of remnant polarization from 1.1 to 6.2 μC/cm2, and reduction of the coercive field from 70 to 50 kV/cm, comparing the films grown freely under the same condition. Furthermore, the films showed an excellent fatigue-free property of up to 1010 switching cycles. © 2001 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
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Near-field optical patterning on azo-hybrid sol–gel films

N. Landraud, J. Peretti, F. Chaput, G. Lampel, J.-P. Boilot, K. Lahlil, and V. I. Safarov

Appl. Phys. Lett. 79, 4562 (2001); http://dx.doi.org/10.1063/1.1428627 (3 pages) | Cited 31 times

Online Publication Date: 13 March 2002

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We report on the near-field optical patterning of photochromic sol–gel films with subwavelength resolution. The sample containing functionalized azobenzene species is locally illuminated in the visible absorption band of these photochromes through the aperture of a metallized tapered optical fiber. The surface topography imaged by in situ shear-force microscopy reveals that, due to repeated photoisomerization cycles of the azobenzene molecules, photoinduced matter migration occurs under the tip leading to the formation of a surface relief. The shape of this structure is characteristic of the electromagnetic field distribution and strongly depends on the tip-to-sample distance. In near-field illumination conditions, protrusions of lateral dimension as small as 60 nm (≈λ/10) are currently produced. When repeating this process, compact arrays of nanodots are optically inscribed. © 2001 American Institute of Physics.
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42.70.Jk Polymers and organics
68.47.Mn Polymer surfaces
68.37.Uv Near-field scanning microscopy and spectroscopy
42.79.Dj Gratings
61.41.+e Polymers, elastomers, and plastics
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
82.30.Qt Isomerization and rearrangement

Nanobelts of the dielectric material Ge3N4

Y. H. Gao, Y. Bando, and T. Sato

Appl. Phys. Lett. 79, 4565 (2001); http://dx.doi.org/10.1063/1.1428634 (3 pages) | Cited 28 times

Online Publication Date: 13 March 2002

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Ge3N4 nanobelts 30–300 nm in width were synthesized by thermal reduction of a mixed Ge+SiO2 powder in NH3 atmosphere. These nanobelts were studied by high-resolution transmission electron microscope equipped with an x-ray energy dispersive spectrometer. In these synthesized nanobelts, the existence of α and β phases of Ge3N4 was identified. The α phase exhibiting slight difference from an ideal α-Ge3N4 phase was also found in the present Ge3N4 material. The mechanism of formation of the Ge3N4 nanobelts is discussed. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Optical gain at 1.54 μm in erbium-doped silicon nanocluster sensitized waveguide

Hak-Seung Han, Se-Young Seo, and Jung H. Shin

Appl. Phys. Lett. 79, 4568 (2001); http://dx.doi.org/10.1063/1.1419035 (3 pages) | Cited 89 times

Online Publication Date: 13 March 2002

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Optical gain at 1.54 μm in erbium-doped silicon-rich silicon oxide (SRSO) is demonstrated. Er-doped SRSO thin film was fabricated by electron-cyclotron resonance enhanced chemical vapor deposition of silicon suboxide with concurrent sputtering of erbium followed by a 5 min anneal at 1000 °C. Ridge-type single mode waveguides were fabricated by wet chemical etching. Optical gain of 4 dB/cm of an externally coupled signal at 1.54 μm is observed when the Er is excited via carriers generated in the Si nanoclusters by the 477 nm line of an Ar laser incident on the top of the waveguide at a pump power of 1.5 W cm−2. © 2001 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing

Patterned growth of single-walled carbon nanotubes on full 4-inch wafers

Nathan R. Franklin, Yiming Li, Robert J. Chen, Ali Javey, and Hongjie Dai

Appl. Phys. Lett. 79, 4571 (2001); http://dx.doi.org/10.1063/1.1429294 (3 pages) | Cited 76 times

Online Publication Date: 13 March 2002

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Patterned growth of single-walled carbon nanotubes (SWNTs) is achieved on full 4-in. SiO2/Si wafers. Catalytic islands with high uniformity over the entire wafer are obtained by a deep ultraviolet photolithography technique. Growth by chemical vapor deposition of methane is found to be very sensitive to the amount of H2 co-flow. Understanding of the chemistry enables the growth of high quality SWNTs from massive arrays (107–108) of well-defined surface sites. The scale up in patterned nanotube growth shall pave the way to large-scale molecular wire devices. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Hc Catalytic methods
81.16.Nd Micro- and nanolithography

WS2 nanotubes containing single-walled carbon nanotube bundles

R. L. D. Whitby, W. K. Hsu, P. C. P. Watts, H. W. Kroto, D. R. M. Walton, and C. B. Boothroyd

Appl. Phys. Lett. 79, 4574 (2001); http://dx.doi.org/10.1063/1.1425467 (3 pages) | Cited 6 times

Online Publication Date: 13 March 2002

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Single-walled carbon nanotubes (SWCNs) encapsulated in multiwalled WS2 nanotubes are produced by pyrolyzing a mixture of WO3−x and SWCNs in N2/H2S atmosphere. © 2001 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials

Critical lateral size for stress domain formation in InAs/GaAs square nanomesas: A multimillion-atom molecular dynamics study

Xiaotao Su, Rajiv K. Kalia, Aiichiro Nakano, Priya Vashishta, and Anupam Madhukar

Appl. Phys. Lett. 79, 4577 (2001); http://dx.doi.org/10.1063/1.1428621 (3 pages) | Cited 12 times

Online Publication Date: 13 March 2002

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Lateral size effects on the stress distribution and morphology of InAs/GaAs square nanomesas are investigated using molecular dynamics (MD) method. Two mesas with the same vertical size but different lateral sizes are simulated. For the smaller mesa, a single stress domain is observed in the InAs overlayer, whereas two stress domains are found in the larger mesa. This indicates the existence of a critical lateral size for stress domain formation in accordance with recent experimental findings. The InAs overlayer in the larger mesa is laterally constrained to the GaAs bulk lattice constant but vertically relaxed to the InAs bulk lattice constant. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
62.20.-x Mechanical properties of solids
61.46.-w Structure of nanoscale materials

Selective processing of individual carbon nanotubes using dual-nanomanipulator installed in transmission electron microscope

Toru Kuzumaki, Hidetaka Sawada, Hideki Ichinose, Yasuhiro Horiike, and Tokushi Kizuka

Appl. Phys. Lett. 79, 4580 (2001); http://dx.doi.org/10.1063/1.1430022 (3 pages) | Cited 10 times

Online Publication Date: 13 March 2002

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Nanoscale processings such as deformation, cutting off, and bonding of individual carbon nanotubes (NTs) have been selectively performed using a dual-nanomanipulation system installed in a high-resolution transmission electron microscope. These processes are directly observed in situ at a lattice resolution of 0.1 nm. At high applied electric field between the NT tip and Au tip, we have found a carbon monolayer extending out from the carbon cluster which was deposited on the NT tip. The cutting off and bonding of individual NT tips can be performed by contacting the NT tips and the opposite nanometer-sized tips at an applied bias voltage. The threshold voltage of the processing is approximately 2 V. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.16.Ta Atom manipulation
68.37.Lp Transmission electron microscopy (TEM)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Plasmon waveguide for optical far/near-field conversion

T. Yatsui, M. Kourogi, and M. Ohtsu

Appl. Phys. Lett. 79, 4583 (2001); http://dx.doi.org/10.1063/1.1428405 (3 pages) | Cited 59 times

Online Publication Date: 13 March 2002

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A plasmon waveguide was designed and fabricated using a metal-coated silicon wedge structure that converts propagating far-field light to the near field. Illumination (λ = 830 nm) of the waveguide (plateau width 150 nm) caused transverse magnetic plasmon-mode excitation. Use of a near-field microscope allowed us to determine its beam width and propagation length as 150 nm and 2.5 μm, respectively. © 2001 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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Uniaxial-stress dependence of Hall effect in an AlGaAs/GaAs modulation-doped heterojunction

Y. Liu, Z. L. Rang, A. K. Fung, C. Cai, P. P. Ruden, M. I. Nathan, and H. Shtrikman

Appl. Phys. Lett. 79, 4586 (2001); http://dx.doi.org/10.1063/1.1427753 (3 pages) | Cited 4 times

Online Publication Date: 13 March 2002

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Uniaxial compressive stress was applied to an AlGaAs/GaAs heterojunction. The uniaxial stress coefficients of sheet resistivity, sheet electron concentration, and mobility were obtained. The hydrostatic pressure coefficient of sheet resistivity was also obtained and was used to explain the different magnitude of the uniaxial stress coefficients of sheet electron concentration in the [110] and [1math0] directions. We obtain a value for the piezoelectric constant e14 of AlAs to be −0.26 C/m2, compared to the value −0.225 C/m2 calculated by K. Hübner [Phys. Status Solidi B 57, 627 (1973)]. © 2001 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.65.Bn Piezoelectric and electrostrictive constants

Polymer PBT/n-GaN metal–insulator–semiconductor structure

L. W. Tu, P. H. Tsao, K. H. Lee, Ikai Lo, S. J. Bai, C. C. Wu, K. Y. Hsieh, and J. K. Sheu

Appl. Phys. Lett. 79, 4589 (2001); http://dx.doi.org/10.1063/1.1429297 (3 pages) | Cited 14 times

Online Publication Date: 13 March 2002

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Organic poly(p-phenylenebenzobisthiazole), PBT, is spin coated on n-GaN epilayer to serve as a gate insulating layer. The GaN is grown on c sapphire by the metalorganic-chemical-vapor-deposition method. A metal-insulator-semiconductor structure is fabricated with Al ohmic contact to the n-GaN, and Au/Al gate metal on top of the PBT. High-frequency capacitance measurements are performed. A doping concentration of 8.2×1016 cm−3 is obtained from the capacitance in the depletion region as compared with a Hall value of 7.8×1016 cm−3. Another technique of max–min capacitance method is also used in the calculation of the doping concentration. The threshold voltage is calculated as −5.1 V, and negative charges with an effective charge number density of 9.3×1011 cm−2 shift the capacitance curve towards the positive voltage side. The hysteresis phenomenon is observed and analyzed. The current–voltage curve shows a low, constant current value up to 20 V. © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Effect of current direction on the lifetime of different levels of Cu dual-damascene metallization

C. L. Gan, C. V. Thompson, K. L. Pey, W. K. Choi, H. L. Tay, B. Yu, and M. K. Radhakrishnan

Appl. Phys. Lett. 79, 4592 (2001); http://dx.doi.org/10.1063/1.1428410 (3 pages) | Cited 26 times

Online Publication Date: 13 March 2002

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Electromigration in the lower metal (M1) and the upper metal (M2) of Cu dual-damascene interconnections has been studied. The failure times of M2 test structures are significantly longer than those of identical M1 structures. It is proposed that this asymmetry is the result of a difference in the location of void formation and growth, which is believed to be related to the ease of electromigration-induced void nucleation and growth at the Cu/Si3N4 interface. Asymmetric via reliability is therefore an intrinsic characteristic of current Cu interconnect technology. © 2001 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration

Photoemission spectroscopy study of Alq3 and metal mixed interfaces

Soonnam Kwon, Shin Cheul Kim, Youngkyoo Kim, Jae-Gyoung Lee, Sunwook Kim, and Kwangho Jeong

Appl. Phys. Lett. 79, 4595 (2001); http://dx.doi.org/10.1063/1.1428777 (3 pages) | Cited 6 times

Online Publication Date: 13 March 2002

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The electronic structures of mixed layers of tris (8-hydroxy-quinoline) aluminum (Alq3) and metal (Au and Al) were studied by ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). The devices with a mixed layer between Alq3 and the cathode were fabricated. The barrier height for electron injection was reduced by doping metals (Au or Al) into Alq3. The doping enhanced the performance of the device. From the XPS study, the doped Au metal did not react with Alq3 and in addition, the doped Al metal reacted slightly with Alq3. From the UPS study, the highest occupied molecular orbit shifted to a higher binding energy for both metal mixed layers. From these studies, it is concluded that the enhanced device characteristics come from the barrier height reduction by the metal doped in Alq3 rather than from the charge transfer complex induced by the reaction of Alq3 and metal. © 2001 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.20.-r Electron states at surfaces and interfaces
73.40.Ns Metal-nonmetal contacts
85.60.Jb Light-emitting devices
68.35.Fx Diffusion; interface formation
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
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Optical transport of a single cell-sized liposome

Masatoshi Ichikawa and Kenichi Yoshikawa

Appl. Phys. Lett. 79, 4598 (2001); http://dx.doi.org/10.1063/1.1430026 (3 pages) | Cited 19 times

Online Publication Date: 13 March 2002

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A closed phospholipid membrane vesicle, or giant liposome, with a diameter of ∼10 μm, constitutes a model of a living cell. Since the phospholipid membrane is about 5 nm thick, it is extremely difficult to trap an individual giant liposome with a laser. We report here the intact transport of an individual cell-sized liposome using an infrared laser. It is shown that the optical attractive potential on a liposome with an inner solution of higher refractivity is about one order of magnitude greater than that of a liposome with the same solution both inside and outside. Since this cell-sized liposome is rather stable, the optical manipulation of liposomes could be useful for the realization of a μm-scaled laboratory for use in biochemistry and molecular biology. © 2001 American Institute of Physics.
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87.80.Cc Optical trapping
87.16.D- Membranes, bilayers, and vesicles
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Formation of sprays from liquid jets by a superimposed sequence of nonaxial disturbances

Y. Zimmels and S. Sadik

Appl. Phys. Lett. 79, 4601 (2001); http://dx.doi.org/10.1063/1.1428764 (3 pages) | Cited 1 time

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A fundamental physical mechanism whereby sprays are formed is formulated. A model of nonaxial sequence of superimposed disturbances, propagating one on top of the other, is used to describe the evolution of liquid jets into sprays. It is postulated that every consecutive superimposed disturbance travels tangent to the surface that supports its propagation. Model outputs show highly nonlinear profiles of the jet surface. Fourier analysis, of the derived superimposed disturbance functions, is performed in conjunction with the basic building blocks of the classical instability theory. Starting from the first superimposed disturbance, the sum of these linear building blocks results in nonlinear intricate profiles of the jet. These profiles are shown to be the source of drops from which a spray is made.© 2001 American Institute of Physics.
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47.55.Kf Particle-laden flows
47.27.wg Turbulent jets
47.20.Dr Surface-tension-driven instability
02.30.Nw Fourier analysis
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