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24 Nov 2003

Volume 83, Issue 21, pp. 4279-4450

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 4294 (2003); http://dx.doi.org/10.1063/1.1629140 (3 pages)

Han-Youl Ryu, Masaya Notomi, and Yong-Hee Lee
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Native hole traps of ferromagnetic Ga1−xMnxAs layers on (100) GaAs substrates

I. T. Yoon, C. J. Park, H. Y. Cho, T. W. Kang, K. H. Kim, and D. J. Kim

Appl. Phys. Lett. 83, 4354 (2003); http://dx.doi.org/10.1063/1.1629398 (3 pages) | Cited 1 time

Online Publication Date: 18 November 2003

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Dominant hole traps of ferromagnetic Ga1−xMnxAs and epilayers with an Mn mole fraction of x ≈ 2.2% and 4.4% were identified employing deep-level transient spectroscopy. Three hole traps with binding energies of EA = 0.38±0.01 eV at 140 K, EB = 0.43±0.01 eV at 220 K, and EC = 0.65±0.01 eV at 300 K above the top of the valence band were observed. Comparing with theoretical data of GaAs, it appears most likely that the trap with EA is associated with a gallium vacancy (VGa) or the arsenic antisite complex (GaAs+VAs), whereas the traps with EB and EC are associated with two charge states of arsenic antisite (AsGa) defect. The hole capture cross sections were determined as σp(A) = 3.7×10−11, σp(B) = 1.5×10−14, and σp(C) = 1.1×10−14 cm2, respectively. The samples with x ≈ 2.2% and x ≈ 4.4% show typical behavior for metallic Ga1−xMnxAs and insulator Ga1−xMnxAs, respectively, through Hall measurements. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.50.Pp Magnetic semiconductors
61.72.J- Point defects and defect clusters
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Transition from granular to dilute magnetic semiconducting multilayers in ion-beam-deposited ZnO/Co

A. B. Pakhomov, Bradley K. Roberts, and Kannan M. Krishnan

Appl. Phys. Lett. 83, 4357 (2003); http://dx.doi.org/10.1063/1.1629369 (3 pages) | Cited 32 times

Online Publication Date: 18 November 2003

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Multilayers of Co/ZnO, with varying nominal thickness of metal (2–10 Å) and semiconductor (2–20 Å), were prepared by ion-beam sputtering. Magnetic, transport, and magnetotransport measurements were carried out over a temperature range of 2.5 to 300 K. Upon decreasing Co thickness and increasing ZnO thickness in the multilayer stack, the properties of the samples undergo a crossover from those of granular metallic Co/semiconductor multilayers to a dilute magnetic semiconductor superlattice. We interpret ferromagnetism in the latter case as due to ordering in the Co-rich layers, mediated by carriers from lightly doped, high carrier concentration layers. © 2003 American Institute of Physics.
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68.65.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
75.50.Pp Magnetic semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ga II-VI semiconductors
75.50.Cc Other ferromagnetic metals and alloys

Temperature dependence of the trapped magnetic field in MgB2 bulk superconductors

R. V. Viznichenko, A. A. Kordyuk, G. Fuchs, K. Nenkov, K.-H. Müller, T. A. Prikhna, and W. Gawalek

Appl. Phys. Lett. 83, 4360 (2003); http://dx.doi.org/10.1063/1.1629148 (3 pages)

Online Publication Date: 18 November 2003

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Based on dc magnetization measurements, the temperature dependencies of the trapped magnetic field have been calculated for two MgB2 samples prepared by two different techniques: high-pressure sintering and hot pressing. Experimentally measured trapped field values for the first sample coincide remarkably well with calculated ones over the whole temperature range. This shows, on one hand, the validity of the introduced calculation approach, and demonstrates, on the other hand, the great prospects of the hot pressing technology for large scale superconducting applications of the MgB2. © 2003 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
74.25.Sv Critical currents

Magnetic coercivity patterns for magnetic recording on patterned media

M. Albrecht, C. T. Rettner, M. E. Best, and B. D. Terris

Appl. Phys. Lett. 83, 4363 (2003); http://dx.doi.org/10.1063/1.1630153 (3 pages) | Cited 18 times

Online Publication Date: 18 November 2003

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Magnetic patterns were created by locally altering the magnetic coercivity of a perpendicular anisotropy film by ion irradiation. The resulting pattern, after dc magnetizing, consists of regions having alternating up/down magnetization patterns in remanence. In this case, the magnetization of the soft magnetic material in the exposed segments is reversed and stabilized by the demagnetization fields of the adjacent unexposed media. A magnetic pattern generated in this manner can be used as a type of servo pattern for recording head positioning. An accuracy in positioning of better than 10 nm was demonstrated and deliberate magnetic patterns were written and read back by addressing individual 80 nm single-domain nanostructures. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
61.80.Jh Ion radiation effects
75.70.Ak Magnetic properties of monolayers and thin films
61.82.Ms Insulators

Influence of interfacial bonding on giant magnetoelectric response of multiferroic laminated composites of Tb1−xDyxFe2 and PbZrxTi1−xO3

Ce-Wen Nan, Gang Liu, and Yuanhua Lin

Appl. Phys. Lett. 83, 4366 (2003); http://dx.doi.org/10.1063/1.1630157 (3 pages) | Cited 70 times

Online Publication Date: 18 November 2003

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The influence of interfacial bonding on the magnetoelectric response in multiferroic laminated composites of Tb1−xDyxFe2 (Terfenol-D) and lead–zirconate–titanate (PZT) by using the recent Green’s function technique was studied. Numerical results demonstrate that a giant magnetoelectric response is produced in the simple sandwiched composites of thick Terfenol-D layers and thin PZT layers. The interfacial epoxy binders used for bonding PZT and Terfenol-D together are very critical to the giant magnetoelectric response of the composites. A thicker interfacial epoxy film and, in particular, a sliding interfacial bonding by a very flexible epoxy would result in a significant drop in the magnetoelectric response. © 2003 American Institute of Physics.
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68.35.Np Adhesion
82.35.Gh Polymers on surfaces; adhesion
75.80.+q Magnetomechanical effects, magnetostriction
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Bb Fe and its alloys

Effects of transition curvature on perpendicular magnetic recording performance

P. A. A. van der Heijden, T. W. Clinton, and M. F. Erden

Appl. Phys. Lett. 83, 4369 (2003); http://dx.doi.org/10.1063/1.1629375 (3 pages) | Cited 2 times

Online Publication Date: 18 November 2003

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The effect of magnetic transition curvature has been studied for a perpendicular recording system. The curvature of the medium transitions is varied in a controlled manner by altering the write poles using a focused ion beam. Tracks are written using these write heads and are characterized with a magnetic force microscope, which demonstrates the ability to manipulate transition shape and even correct the curvature. The effect of transition curvature on the perpendicular recording performance is characterized by spinstand measurements and bit error rate simulations. These results show a significant performance loss, demonstrating that transition curvature degrades perpendicular recording performance. © 2003 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Using antiferromagnetic/ferromagnetic bilayers as detection layers in magnetic tunnel junctions

G. Malinowski, M. Hehn, M. Sajieddine, F. Montaigne, E. Jouguelet, F. Canet, M. Alnot, D. Lacour, and A. Schuhl

Appl. Phys. Lett. 83, 4372 (2003); http://dx.doi.org/10.1063/1.1630171 (3 pages) | Cited 10 times

Online Publication Date: 18 November 2003

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It is shown that the association of an antiferromagnetic material with a ferromagnetic material in an exchange-coupled bilayer, often used in spintronic devices as a magnetic reference or pinned system, can be used as a detection layer in magnetoresistive sensors. The magnetic response is shown to be reversible and linear in an adjustable field window. The sensitivity is studied as a function of temperature. © 2003 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
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Anomalous electro-optic effect in Sr0.6Ba0.4Nb2O6 single crystals and its application in two-dimensional laser scanning

L. Tian, D. A. Scrymgeour, Alok Sharan, and Venkatraman Gopalan

Appl. Phys. Lett. 83, 4375 (2003); http://dx.doi.org/10.1063/1.1627475 (3 pages) | Cited 8 times

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We report an anomalous electro-optic effect that results in laser scanning along the polarization direction of strontium barium niobate (Sr0.6Ba0.4Nb2O6, or SBN:60) single crystals under external fields. The origin of such unusual phenomenon is believed to arise from inhomogeneous index gradients near the crystal surfaces, possibly arising from space-charge fields. Based on this effect, two-dimensional scanning is demonstrated by using a combination of SBN:60 single crystal (for vertical scanning; full scan angle of 0.79°±0.07°) and lithium tantalate (LiTaO3) (for horizontal scanning; full scan angle of 3.68°±0.14°). © 2003 American Institute of Physics.
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78.20.Jq Electro-optical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Jp Dielectric breakdown and space-charge effects

Enhanced electrical properties of c-axis epitaxial Nd-substituted Bi4Ti3O12 thin films

S. T. Zhang, X. J. Zhang, H. W. Cheng, Y. F. Chen, Z. G. Liu, N. B. Ming, X. B. Hu, and J. Y. Wang

Appl. Phys. Lett. 83, 4378 (2003); http://dx.doi.org/10.1063/1.1629372 (3 pages) | Cited 36 times

Online Publication Date: 18 November 2003

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High-quality c-axis epitaxial ferroelectric thin films of Bi4Ti3O12 (BTO) and Nd-substituted BTO, Bi3.15Nd0.85Ti3O12 (BNT), were prepared on (001)-LaNiO3-coated (001) LaAlO3 substrates by pulsed-laser deposition. The epitaxial alignments were established by the x-ray diffraction, including θ–2θ and ϕ scans. Compared to the BTO films, the BNT films have significantly improved electrical properties with about 2 times larger remanent polarization, 0.6 times lower coercive field, better fatigue-resisting characteristics, and 1.7 times larger dielectric constant. These results showed experimentally that Nd substitution could enhance the c-axis electrical properties of BTO. The reason for the improved properties of BNT films was discussed. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.22.Ch Permittivity (dielectric function)

Thickness dependence of leakage currents in high-permittivity thin films

Herbert Schroeder and Sam Schmitz

Appl. Phys. Lett. 83, 4381 (2003); http://dx.doi.org/10.1063/1.1629141 (3 pages) | Cited 11 times

Online Publication Date: 18 November 2003

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The leakage current through high-permittivity perovskite thin films in the nanometer range is of great technological interest because of the possible applications of these insulating films in future submicroelectronic devices such as dielectrics in Gbit dynamic random access memories or gate oxides in metal–oxide–semiconductor field-effect transistors. The experimental result of decreasing leakage current with decreasing thickness of the dielectric for the same externally applied field can be described by using a model combining thermionic emission at the electrode/dielectric interface and a low-mobility, high-permittivity dielectric with low-permittivity layers at the interfaces, the so-called dead layers. © 2003 American Institute of Physics.
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73.61.Ng Insulators
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.22.Ch Permittivity (dielectric function)
85.30.Tv Field effect devices

Phase transition in relaxor ferroelectrics studied by mechanical measurements

Feng Yan, Peng Bao, and Yening Wang

Appl. Phys. Lett. 83, 4384 (2003); http://dx.doi.org/10.1063/1.1629383 (3 pages) | Cited 8 times

Online Publication Date: 18 November 2003

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We report the mechanical properties of [(1−x)%]Pb(Mg1/3Nb2/3)O3−x%PbTiO3 ceramics with PbTiO3 content changed from 23% to 0% measured at the vibration frequency of about 1 kHz. Two modulus kinks can be observed in any of the samples. The kink appears at higher temperature can be attributed to the stress-induced relaxation of nanodomains. Another modulus kink at a lower temperature appears near the Vogel–Fulcher freezing temperature. An associated internal friction peak can also be observed at this temperature. This kink and the internal friction peak can be explained to be due to a ferroelectric phase transition, which becomes weaker with the decrease of PbTiO3 content. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Effects of in-plane compressive stress on electrical properties of (Ba,Sr)TiO3 thin film capacitors prepared by on- and off-axis rf magnetron sputtering

Woo Young Park, Kun Ho Ahn, and Cheol Seong Hwang

Appl. Phys. Lett. 83, 4387 (2003); http://dx.doi.org/10.1063/1.1629790 (3 pages) | Cited 24 times

Online Publication Date: 18 November 2003

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This study investigated the structural and electrical properties of (Ba,Sr)TiO3 (BST) thin film capacitors with thicknesses ranging from 18 to 215 nm, which were prepared by on- and off-axis rf magnetron sputtering technique on Pt/SiO2/Si substrates. The deposition rate and cation composition ratios of the films were controlled to be the same regardless of the sputtering geometry. All the films show elongations in the out-of-plane lattice spacing, suggesting the presence of compressive stress with a smaller value by on-axis sputtering than by the off-axis system. There was no thickness dependence of the strain in the polycrystalline BST films. The BST films deposited using the on-axis system showed a higher bulk dielectric constant with a higher interfacial capacitance and a lower leakage current level than the films produced by the off-axis system. The strain effect was proposed to explain the correlations between the structural and electrical properties. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.32.Tt Capacitors
81.15.Cd Deposition by sputtering
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.-e Ferroelectricity and antiferroelectricity
68.55.-a Thin film structure and morphology
61.66.Fn Inorganic compounds

Evidence of short-range antiferroelectric local states in lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric ceramics

H. Amorín, J. Pérez, A. Fundora, J. Portelles, F. Guerrero, M. R. Soares, E. Martínez, and J. M. Siqueiros

Appl. Phys. Lett. 83, 4390 (2003); http://dx.doi.org/10.1063/1.1629377 (3 pages) | Cited 2 times

Online Publication Date: 18 November 2003

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Structural and electrical measurements were performed on lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric (FE) ceramics. Dielectric properties show a well-defined relaxor anomaly around −50 °C with double-loop hysteresis curves from this point to the transition temperature. The thesis of short-range antiferroelectric (AFE) local states having incommensurate (INC) structure embedded in the FE polar matrix is proposed to explain the observed behavior. Structural lattice parameters show negative expansion coefficients and INC superlattice diffraction spots were observed through the selected-area diffraction patterns in the [110] zone for this minority local states. The titanium modification of this system seems to be the key fact in the coupling of the INC structure to the AFE local states in the FE–AFE coexistence region. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
61.66.Fn Inorganic compounds
64.70.Rh Commensurate-incommensurate transitions
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Crystal structure and polarization phenomena of epitaxially grown Pb(Zr,Ti)O3 thin-film capacitors

M. Tsukada, H. Yamawaki, and M. Kondo

Appl. Phys. Lett. 83, 4393 (2003); http://dx.doi.org/10.1063/1.1630371 (3 pages) | Cited 9 times

Online Publication Date: 18 November 2003

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{100} oriented Pb(Zr,Ti)O3 (PZT) thin films were deposited by metalorganic chemical vapor deposition on both Ir/MgO(100) and Ir/MgAl2O4/SiO2/Si(100) substrates. The x-ray Φ-scan spectra for the (202) reflections revealed each film had fourfold symmetry, which was epitaxially grown as cube-on-cube. The switchable polarization (Qsw) of the PZT capacitor on the MgO substrate attained 100 μC/cm2 at 1.8 V; however, PZT capacitors on Si had a Qsw of 23 μC/cm2. This difference in Qsw is attributed to the volume fraction of (001) orientation of each PZT film. The difference in orientation between the two kinds of PZT films does not seem to depend on misfit of lattice parameters between PZT and Ir, but on the stress caused by the difference in the thermal expansion coefficients of MgO and Si. © 2003 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Temperature dependence of the electrical and electromechanical properties of lead zirconate titanate thin films

Hiroshi Maiwa, Seung-Hyun Kim, and Noboru Ichinose

Appl. Phys. Lett. 83, 4396 (2003); http://dx.doi.org/10.1063/1.1629786 (3 pages) | Cited 14 times

Online Publication Date: 18 November 2003

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The temperature dependence of the electrical and electromechanical properties of Pb(Zr,Ti)O3 (PZT) (Zr/Ti=30/70, 52/48, and 70/30) thin films are investigated. The 1-μm-thick PZT thin films were prepared on (111)Pt/Ti/SiO2/Si substrates by chemical solution deposition. The temperature dependence of the dielectric and ferroelectric properties of the films were measured in the temperature range from −250 to 150 °C. The temperature-dependent strain loops from PZT films were measured using scanning probe microscopy in the temperature range from −100 to 150 °C. The field-induced displacement increased with increase of the temperature; however, their temperature dependence was relatively small, compared with that reported for bulk PZT ceramics. The results indicate that a thermally activated extrinsic ferroelastic contribution is not predominant in thin PZT films. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.65.-j Piezoelectricity and electromechanical effects
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.60.Bs Mechanical and acoustical properties
77.22.Ch Permittivity (dielectric function)
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Contactless electroreflectance of CdSe/ZnSe quantum dots grown by molecular-beam epitaxy

Martín Muñoz, Shiping Guo, Xuecong Zhou, Maria C. Tamargo, Y. S. Huang, C. Trallero-Giner, and A. H. Rodríguez

Appl. Phys. Lett. 83, 4399 (2003); http://dx.doi.org/10.1063/1.1628393 (3 pages) | Cited 15 times

Online Publication Date: 18 November 2003

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The interband transitions of a capped CdSe quantum-dot structure have been investigated using contactless electroreflectance. The electroreflectance spectrum shows transitions originating from all the portions of the sample including the quantum dots and the wetting layer. The transitions of the two-dimensional layers have been modeled using an envelope approximation calculation which takes into account the biaxial strain in the wetting layer. A good agreement was found between the experimental values for the transition energies and the calculated ones. From atomic force microscopy measurements, a lens shape was observed for the uncapped quantum dots. Taking into account the lens shape geometry and assuming that the effective height-to-radius ratio is preserved, the size of the capped quantum dots was determined using the observed electroreflectance transitions, in the framework of the effective mass approximation. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.20.Jq Electro-optical effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.08.Bc Wetting

Dynamic and atomistic deformation of sp2-bonded boron nitride nanoarrays

C. Iwamoto, H. S. Yang, S. Watanabe, and T. Yoshida

Appl. Phys. Lett. 83, 4402 (2003); http://dx.doi.org/10.1063/1.1629139 (3 pages) | Cited 6 times

Online Publication Date: 18 November 2003

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With the aim of developing a nanostructure, we produced an sp2-bonded boron nitride nanoarray (BNNA), and observed its dynamic deformation behavior using high-resolution transmission electron microscopy with a piezoceramic tube for three-axis positioning of an indenter. The BNNA has remarkable flexibility and resiliency, such that no permanent deformation occurred when it was bent repeatedly to the minimum radius of curvature of about 4 nm. Even in repeated bends to the minimum radius of curvature of about 0.3 nm, the BNNA underwent no catastrophic failure. © 2003 American Institute of Physics.
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62.25.-g Mechanical properties of nanoscale systems
62.20.F- Deformation and plasticity
61.46.-w Structure of nanoscale materials

Amplitude-modulated electrostatic nanolithography in polymers based on atomic force microscopy

Sergei F. Lyuksyutov, Pavel B. Paramonov, Shane Juhl, and Richard A. Vaia

Appl. Phys. Lett. 83, 4405 (2003); http://dx.doi.org/10.1063/1.1629787 (3 pages) | Cited 21 times

Online Publication Date: 18 November 2003

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Amplitude modulated electrostatic lithography using atomic force microscopy (AFM) on 20–50 nm thin polymer films is discussed. Electric bias of AFM tip increases the distance over which the surface influences the oscillation amplitude of an AFM cantilever, providing a process window to control tip-film separation. Arrays of nanodots, as small as 10–50 nm wide by 1–10 nm high are created via a localized Joule heating of a small fraction of polymer above the glass transition temperature, followed by electrostatic attraction of the polarized viscoelastic polymer melt toward the AFM tip in the strong (108–109 V/m) nonuniform electric field. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
81.16.Ta Atom manipulation
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics
85.40.Hp Lithography, masks and pattern transfer
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
68.37.Ps Atomic force microscopy (AFM)

Transfer of nanoporous pattern of anodic porous alumina into Si substrate

Hidetaka Asoh, Mamoru Matsuo, Megumi Yoshihama, and Sachiko Ono

Appl. Phys. Lett. 83, 4408 (2003); http://dx.doi.org/10.1063/1.1629385 (3 pages) | Cited 35 times

Online Publication Date: 18 November 2003

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Nanohole arrays in a Si substrate with a self-ordered configuration having a 100 nm hole periodicity were fabricated by the pattern transfer of the hole configuration of anodic porous alumina. The self-ordered anodic porous alumina used as a mask was directly prepared by anodizing an aluminum film sputtered on a Si substrate. The transfer of the nanoporous pattern of anodic alumina into the Si substrate could be achieved by removing silicon oxide, which was produced by the anodic oxidation of the local part of the Si substrate underneath the barrier layer corresponding to the pore base. In addition, we confirmed that the transformation of the nanostructure of porous alumina grown on a Si substrate is comparable to the current transient during alumina film formation. © 2003 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation

Thickness and temperature dependence of stress relaxation in nanoscale aluminum films

S. Hyun, W. L. Brown, and R. P. Vinci

Appl. Phys. Lett. 83, 4411 (2003); http://dx.doi.org/10.1063/1.1629381 (3 pages) | Cited 9 times

Online Publication Date: 18 November 2003

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We have found that stress relaxation of nanoscale Al thin films is strongly dependent on both film thickness and temperature. Films 33, 107, and 205 nm thick prepared by evaporation onto a silicon nitride membrane substrate were studied using membrane resonance. A single thermal cycle to 300 °C was used to establish a stress, after which the time dependence of the stress was measured for the three film thicknesses at 50, 75, and 100 °C. The relaxation rate is highest for the highest temperature and the thinnest film. A dislocation locking mechanism is suggested as a possible explanation for the observed thickness dependence. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Two-dimensional micrometer-sized single-crystalline ZnO thin nanosheets

J. Q. Hu, Y. Bando, J. H. Zhan, Y. B. Li, and T. Sekiguchi

Appl. Phys. Lett. 83, 4414 (2003); http://dx.doi.org/10.1063/1.1629788 (3 pages) | Cited 88 times

Online Publication Date: 18 November 2003

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Two-dimensional micrometer-sized single-crystalline ZnO thin nanosheets were achieved on a large scale, in which Zn thin nanosheets (precursor) were first grown via a thermal decomposition and reduction of the starting ZnS powder, and then converted to the ZnO nanosheets via a simple oxidation process. The ZnO nanosheets, growing along [100] or [010] direction and enclosed by ± (001) facets, have lateral dimensions up to several hundreds of microns, and thicknesses of 30–70 nm. Both room-temperature cathodoluminescence and photoluminescence measurements reveal that the present ZnO nanosheets have visible emission bands ranging from the green to red. © 2003 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors

Ultrafast patterning of nanostructures in polymers using laser assisted nanoimprint lithography

Qiangfei Xia, Chris Keimel, Haixiong Ge, Zhaoning Yu, Wei Wu, and Stephen Y. Chou

Appl. Phys. Lett. 83, 4417 (2003); http://dx.doi.org/10.1063/1.1630162 (3 pages) | Cited 22 times

Online Publication Date: 18 November 2003

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We propose and demonstrate a nanopatterning technique, laser-assisted nanoimprint lithography (LAN), in which the polymer is melted by a single excimer laser pulse and then imprinted by a mold made of fused quartz. LAN has been used to pattern nanostructures in various polymer films on a Si or quartz substrate with high fidelity over the entire mold area. Here we show 200 nm pitch gratings with 100 nm linewidth and 90 nm height. The entire imprint from melting the polymer to completion of the imprint is less than 500 ns. The mold has been used multiple times without cleaning between each imprint. LAN not only greatly shortens the imprint processing time, but also significantly reduces the heating and expansion of the substrate and mold, leading to better overlay alignment between the two. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation

Nanoscale surface and subsurface defects induced in lithium niobate by a femtosecond laser

Eric A. Stach, Velimir Radmilovic, Devesh Deshpande, Ajay Malshe, Dennis Alexander, and David Doerr

Appl. Phys. Lett. 83, 4420 (2003); http://dx.doi.org/10.1063/1.1629797 (3 pages) | Cited 17 times

Online Publication Date: 18 November 2003

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In this letter, electron and ion microscopy techniques have been used to characterize the changes that result when single crystals of lithium niobate are processed using a focused femtosecond laser. The prevailing observation is that of competing processes—ablation and partial redeposition, thermal shock, and extreme quenching, as well as effects associated with shock wave propagation, resulting in both amorphization and heavily defective regions at the focal point of the laser pulse. The observed microstructural defects have a direct implication in optical memory or waveguide writing, where the goal is to realize consistent structural features with uniform optical properties. © 2003 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
42.62.Cf Industrial applications
42.70.Ln Holographic recording materials; optical storage media
42.79.Gn Optical waveguides and couplers
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena
62.50.-p High-pressure effects in solids and liquids
61.43.Er Other amorphous solids
68.37.Lp Transmission electron microscopy (TEM)
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.86.+b Optical workshop techniques
61.82.Ms Insulators

Patterned growth of coiled carbon nanotubes by a template-assisted technique

D. Y. Zhong, S. Liu, and E. G. Wang

Appl. Phys. Lett. 83, 4423 (2003); http://dx.doi.org/10.1063/1.1630164 (3 pages) | Cited 12 times

Online Publication Date: 18 November 2003

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A method for controlled synthesis of coiled carbon nanotubes (CNTs) is demonstrated, in which three-dimensional columns of aligned CNTs are used as a template. The coiled CNTs with pitches and coil diameters from 100 to 300 nm are regrown on the straight CNT arrays and the mesoporous structure between the CNT arrays produces an asymmetric growth condition for the coil formation. As observed using transmission electron microscopy, the graphitic layers on the tube wall are stacking-disordered due to the coil geometry. The growth mechanism of the coiled CNTs is also proposed. © 2003 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Hc Catalytic methods
68.37.Lp Transmission electron microscopy (TEM)

Nonlinear current-voltage characteristics of Pt nanowires and nanowire transistors fabricated by electron-beam deposition

L. Rotkina, J.-F. Lin, and J. P. Bird

Appl. Phys. Lett. 83, 4426 (2003); http://dx.doi.org/10.1063/1.1629382 (3 pages) | Cited 41 times

Online Publication Date: 18 November 2003

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We have fabricated Pt/C composite nanowires and nanowire transistors, using the technique of electron-beam-induced deposition. The current-voltage characteristics of the granular nanowires are strongly nonlinear at 4.2 K, and evidence for this nonlinearity is found to persist to room temperature. A voltage gap of order 0.1–0.2 V is observed at the lowest temperatures, and we suggest that this feature is consistent with single-electron tunneling via Pt nanocrystals that form in the wires during their fabrication. In order to further explore this possibility, we incorporate the nanowires into three-terminal transistor structures and find evidence for a gate-induced modulation of their voltage gap. © 2003 American Institute of Physics.
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85.35.Gv Single electron devices
73.63.Nm Quantum wires
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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