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22 Sep 2003

Volume 83, Issue 12, pp. 2303-2490

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 2396 (2003); http://dx.doi.org/10.1063/1.1613038 (3 pages)

A. Rida, V. Fernandez, and M. A. M. Gijs
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Magnetic photonic band-gap material at microwave frequencies based on ferromagnetic nanowires

A. Saib, D. Vanhoenacker-Janvier, I. Huynen, A. Encinas, L. Piraux, E. Ferain, and R. Legras

Appl. Phys. Lett. 83, 2378 (2003); http://dx.doi.org/10.1063/1.1610798 (3 pages) | Cited 28 times

Online Publication Date: 15 September 2003

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We present an experimental investigation of a class of microwave photonic band-gap (PBG) materials, in which the magnetic permeability μ varies periodically within the material. This material is fabricated using a periodic arrangement of arrays of magnetic nanowires. As for dielectric or metallic PBG, the band-gap behavior varies with the geometrical parameters fixing the spatial periodicity of the magnetic structure. The magnetic photonic band gap is induced by the presence of a ferromagnetic resonance effect in the vicinity of the band gap. © 2003 American Institute of Physics.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
42.70.Qs Photonic bandgap materials

60 ns time scale short pulse interlayer tunneling spectroscopy for Bi2Sr2CaCu2O8+δ

Kenkichi Anagawa, Yoshiharu Yamada, Takasada Shibauchi, Minoru Suzuki, and Takao Watanabe

Appl. Phys. Lett. 83, 2381 (2003); http://dx.doi.org/10.1063/1.1612891 (3 pages) | Cited 26 times

Online Publication Date: 15 September 2003

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We utilize the short pulse interlayer tunneling spectroscopy on a 60 ns time scale for the Bi2Sr2CaCu2O8+δ system. The results indicate that the influence of self-heating is negligible up to an injection current density of ∼ 60 kA/cm2 and an injection power areal density of ∼ 90 kW/cm2. By means of this technique, we are able to observe the superconducting gap, the pseudogap, and the dip-and-hump structure precisely with little influence from the self-heating. © 2003 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.50.+r Tunneling phenomena; Josephson effects
74.25.Jb Electronic structure (photoemission, etc.)

Enhanced intergrain magnetoresistance in bulk Sr2FeMoO6 through controlled processing

A. Sharma, A. Berenov, J. Rager, W. Branford, Y. Bugoslavsky, L. F. Cohen, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 83, 2384 (2003); http://dx.doi.org/10.1063/1.1613358 (3 pages) | Cited 21 times

Online Publication Date: 15 September 2003

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Enhanced low field magnetoresistance (LFMR) values have been obtained in bulk Sr2FeMoO6 through controlled processing. MR values, R(H)/R(0) of ∼ 60% [(R(H)−R(H = 0)/R(H = 0) = 40%] were achieved at 50 K, in 1 T, and R(H)/R(0) ∼ 8% [(R(H)−R(H = 0)/R(H = 0) = 92%] at 290 K, in 1 T. For a ∼ 1 μm starting particle size, the optimum sintering temperature was 1300 °C, 100 °C higher than normally used. The optimum sintering time in Ar/H2 was only 5 h, much shorter than normally used. The magnitude of the LFMR appears to depend strongly on grain boundary oxygen content, controlled through optimization of sintering temperature and time. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.Mm Grain and twin boundaries
81.40.Rs Electrical and magnetic properties related to treatment conditions

Design of realistic switches for coupling superconducting solid-state qubits

Markus J. Storcz and Frank K. Wilhelm

Appl. Phys. Lett. 83, 2387 (2003); http://dx.doi.org/10.1063/1.1612901 (3 pages) | Cited 7 times

Online Publication Date: 15 September 2003

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Superconducting flux qubits are a promising candidate for solid-state quantum computation. One of the reasons is that implementing a controlled coupling between the qubits appears to be relatively easy, if one uses tunable Josephson junctions. We evaluate possible coupling strengths and show how much extra decoherence is induced by the subgap conductance of a tunable junction. In light of these results, we evaluate several options of using intrinsically shunted junctions and show that based on available technology, Josephson field effect transistors and high-Tc junctions used as π shifters would be a good option, whereas the use of magnetic junctions as π shifters severely limits quantum coherence. © 2003 American Institute of Physics.
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85.25.Cp Josephson devices
85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
74.81.Fa Josephson junction arrays and wire networks

High-Tc interferometers using all YBa2Cu3O7−δ trilayer junctions

H. Sato, E. Fujimoto, T. Yamada, H. Akoh, T. Nakajima, K. Hohkawa, H. Nakagawa, and M. Aoyagi

Appl. Phys. Lett. 83, 2390 (2003); http://dx.doi.org/10.1063/1.1613037 (3 pages)

Online Publication Date: 15 September 2003

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We have demonstrated high-Tc interferometers using YBaCuO trilayer junctions, which are two-junction-type interferometers with a direct current injection. In order to realize a small loop inductance value without a ground plane, the interferometers were designed to have loop inductance with a vertical stacked structure by overlapping junction bridges on base electrodes. The interferometers showed clear threshold characteristics in the control current dependence of the gate current at temperatures below 70 K. The temperature dependence of the loop inductance showed good agreement with a calculation result based on a strip-line model. The sheet inductance was estimated to be 0.85 pH/□ at 4.2 K from the threshold characteristics of the interferometers by changing the bridge length between the two junctions, which was in good agreement with the design value. © 2003 American Institute of Physics.
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85.25.-j Superconducting devices
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

Molecular-beam-epitaxy growth of ferromagnetic Ni2MnGe on GaAs(001)

J. Lu, J. W. Dong, J. Q. Xie, S. McKernan, C. J. Palmstrøm, and Y. Xin

Appl. Phys. Lett. 83, 2393 (2003); http://dx.doi.org/10.1063/1.1612900 (3 pages) | Cited 10 times

Online Publication Date: 15 September 2003

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Single-crystal Heusler alloy Ni2MnGe thin films have been grown on GaAs(001) by molecular-beam epitaxy. X-ray diffraction and transmission electron microscopy were used for postgrowth structural characterization. The Ni2MnGe grew in a tetragonally distorted L21-like structure (a = 5.65 Å, c = 5.96 Å) with the c axis perpendicular to the film surface. An in-plane ordering with 2× periodicity and an out-of-plane ordering with 3× periodicity was observed for the as-grown films. Magnetometry measurements performed at 50 K indicate that the films are ferromagnetic and have a weak in-plane anisotropy with a coercivity ∼5.5 Oe and saturation magnetization of ∼450 emu/cm3. The Curie temperature was measured to be ∼320 K. © 2003 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Long-range transport of magnetic microbeads using simple planar coils placed in a uniform magnetostatic field

A. Rida, V. Fernandez, and M. A. M. Gijs

Appl. Phys. Lett. 83, 2396 (2003); http://dx.doi.org/10.1063/1.1613038 (3 pages) | Cited 44 times

Online Publication Date: 15 September 2003

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We propose an approach for magnetic microbead transport in microfluidic channels over long-range distances using an array of simple planar coils. The latter are placed in a uniform static magnetic field, the role of which is to impose a permanent magnetic moment to the microbeads. The very small magnetic field gradient of a simple planar coil is then sufficient to displace the microbeads. The long-range displacement is assured by arranging adjacent coils in the array with spatial overlap in a three-phase actuation scheme. © 2003 American Institute of Physics.
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85.70.-w Magnetic devices
84.32.Hh Inductors and coils; wiring
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
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Temperature effect on ultrathin SiO2 time-dependent-dielectric-breakdown

Kin P. Cheung

Appl. Phys. Lett. 83, 2399 (2003); http://dx.doi.org/10.1063/1.1613367 (3 pages) | Cited 2 times

Online Publication Date: 15 September 2003

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The unusually high temperature acceleration in ultrathin oxide time-dependentdielectric-breakdown and the non-Arrhenius behavior are one of the current outstanding puzzles in oxide reliability research. In this letter, both phenomena are explained using the recently developed kinetic model. It is found that in thick oxide the degradation kinetic is controlled by hole trapping while in thin oxide it is controlled by the consumption of trapped holes. The consumption of trapped holes is further found to be a competition between hole detrapping and electron capturing, leading to the observed non-Arrhenius behavior. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Jp Dielectric breakdown and space-charge effects
71.55.Ht Other nonmetals
73.61.Ng Insulators

Nonlinear-optical probing of nanosecond ferroelectric switching

E. D. Mishina, N. E. Sherstyuk, V. I. Stadnichuk, A. S. Sigov, V. M. Mukhorotov, Yu. I. Golovko, A. van Etteger, and Th. Rasing

Appl. Phys. Lett. 83, 2402 (2003); http://dx.doi.org/10.1063/1.1612905 (3 pages) | Cited 17 times

Online Publication Date: 15 September 2003

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It is demonstrated that the switching dynamics of the ferroelectric polarization in thin Ba(SrTi)O3 (BST) films can be followed by optical second harmonic generation with a time resolution that is only limited by the gating electronics. It is shown that the characteristic time of electric-field induced polarization switching in 70 nm BST films is less than τ = 5 ns. © 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.Fm Switching phenomena
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
77.22.Ej Polarization and depolarization

Low-temperature atomic-layer-deposition lift-off method for microelectronic and nanoelectronic applications

M. J. Biercuk, D. J. Monsma, C. M. Marcus, J. S. Becker, and R. G. Gordon

Appl. Phys. Lett. 83, 2405 (2003); http://dx.doi.org/10.1063/1.1612904 (3 pages) | Cited 41 times

Online Publication Date: 15 September 2003

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We report a method for depositing patterned dielectric layers with submicron features using atomic layer deposition. The patterned films are superior to sputtered or evaporated films in continuity, smoothness, conformality, and minimum feature size. Films were deposited at 100–150 °C using several different precursors and patterned using either electron-beam or photoresist. The low deposition temperature permits uniform film growth without significant outgassing or hardbaking of resist layers. A lift-off technique presented here gives sharp step edges with edge roughness as low as ∼10 nm. We also measure dielectric constants (κ) and breakdown fields for the high-κ materials aluminum oxide (κ∼8–9), hafnium oxide (κ∼16–19), and zirconium oxide (κ∼20–29), grown under similar low temperature conditions. © 2003 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.35.B- Structure of clean surfaces (and surface reconstruction)

Large piezoelectric response in (111)-oriented epitaxial Pb(Zr,Ti)O3 films consisting of mixed phases with rhombohedral and tetragonal symmetry

Shintaro Yokoyama, Yoshihisa Honda, Hitoshi Morioka, Takahiro Oikawa, Hiroshi Funakubo, Takashi Iijima, Hirofumi Matsuda, and Keisuke Saito

Appl. Phys. Lett. 83, 2408 (2003); http://dx.doi.org/10.1063/1.1611273 (3 pages) | Cited 14 times

Online Publication Date: 15 September 2003

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Pb(Zr,Ti)O3 films with a Zr/(Zr+Ti) ratio of 0.48 having 1.5 μm in thickness were grown on (100)c-, (110)c-, and (111)c-oriented SrRuO3//SrTiO3 substrates by metalorganic chemical vapor deposition. It was ascertained by θ–2θ scans of x-ray diffraction that (001)T-/(100)T-/(100)R-, {110}-, and {111}-oriented films were epitaxially grown on (100)c-, (110)c-, and (111)c-oriented substrates. Polarization and field-induced strain in these films were simultaneously observed through a scanning probe microscope that was attached to a ferroelectric test system. About three times larger field-induced strain than that on other substrates was observed together with the largest spontaneous polarization for a film grown on a (111)cSrRuO3//(111)SrTiO3 substrate. High-resolution x-ray diffraction analysis suggested that the film grown on the (111)cSrRuO3//(111)SrTiO3 substrate consisted of rhombohedral and tetragonal mixture phases. Its crystal structure possibly contributed to the large piezoelectric response. © 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
77.65.-j Piezoelectricity and electromechanical effects
68.55.Nq Composition and phase identification
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ej Polarization and depolarization
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Low-loss, tunable bismuth zinc niobate films deposited by rf magnetron sputtering

Jiwei Lu and Susanne Stemmer

Appl. Phys. Lett. 83, 2411 (2003); http://dx.doi.org/10.1063/1.1613036 (3 pages) | Cited 75 times

Online Publication Date: 15 September 2003

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Near-stoichiometric Bi1.5Zn1.0Nb1.5O7 (BZN) films were deposited by rf magnetron sputtering. The relative permittivity and dielectric loss of BZN films were measured with frequencies up to 100 MHz using planar Al2O3/Pt/BZN/Pt and Si/SiO2/Pt/BZN/Pt capacitor structures. BZN films with thicknesses in the range of 160 to 170 nm exhibited electric field tunable permittivities up to 220, and dielectric loss tangents less than 0.0005. A maximum applied bias field of 2.4 MV/cm resulted in a ∼ 55% tunability of the dielectric constant. The permittivity was independent of the measurement frequency over a wide frequency range (10 kHz–100 MHz). Above 1 MHz, losses were increasingly dominated by conductor losses of the Pt bottom electrode. Their excellent dielectric properties make BZN films attractive candidates for low-loss, medium-permittivity integrated device applications. © 2003 American Institute of Physics.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering
77.22.Gm Dielectric loss and relaxation

Orientation dependence of ferroelectric properties of pulsed-laser-ablated Bi4−xNdxTi3O12 films

A. Garg, Z. H. Barber, M. Dawber, J. F. Scott, A. Snedden, and P. Lightfoot

Appl. Phys. Lett. 83, 2414 (2003); http://dx.doi.org/10.1063/1.1613052 (3 pages) | Cited 84 times

Online Publication Date: 15 September 2003

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Epitaxial (001)-, (118)-, and (104)-oriented Nd-doped Bi4Ti3O12 films have been grown by pulsed-laser deposition from a Bi4−xNdxTi3O12 (x = 0.85) target on SrRuO3 coated single-crystal (100)-, (110)-, and (111)-oriented SrTiO3 substrates, respectively. X-ray diffraction illustrated a unique epitaxial relationship between film and substrate for all orientations. We observed a strong dependence of ferroelectric properties on the film orientation, with no ferroelectric activity in an (001)-oriented film; a remanent polarization 2Pr of 12 μC/cm2 and coercive field Ec of 120 kV/cm in a (118)-oriented film; and 2Pr = 40 μC/cm2, Ec = 50 kV/cm in a (104)-oriented film. The lack of ferroelectric activity along the c-axis is consistent with the orthorhombic nature of the crystal structure of the bulk material, as determined by powder neutron diffraction. © 2003 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology

Contribution of interface capacitance to the electric-field breakdown in thin-film Al–AlOx–Al capacitors

Guneeta Singh-Bhalla, Xu Du, and Arthur F. Hebard

Appl. Phys. Lett. 83, 2417 (2003); http://dx.doi.org/10.1063/1.1613802 (3 pages) | Cited 7 times

Online Publication Date: 15 September 2003

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We present a systematic study of the dependence of breakdown voltages on oxide thickness d in Al–AlOx–Al thin-film capacitor structures. For sufficiently thin dielectrics, we find that a significant portion of the measured breakdown potential Vb occurs across the electrode interfaces, thereby leading to an overestimate (Vb/d) of the true breakdown electric field Eb across the dielectric. By modeling this interface contribution as an “interface” capacitance in series with the geometric “bulk” capacitance, we find for high-quality rf magnetron-sputtered AlOx dielectrics that Eb is independent of d over the range 30–300 Å. © 2003 American Institute of Physics.
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77.22.Jp Dielectric breakdown and space-charge effects
84.32.Tt Capacitors
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
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Optical detection of quasi-static actuation of nanoelectromechanical systems

Christine Meyer, Heribert Lorenz, and Khaled Karrai

Appl. Phys. Lett. 83, 2420 (2003); http://dx.doi.org/10.1063/1.1608491 (3 pages) | Cited 8 times

Online Publication Date: 15 September 2003

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An all optical method designed to test the functionality of nanoelectromechanical systems is presented. Silicon tweezers consisting of freestanding nanometer-sized prongs are prepared using electron beam lithography. Images of the tweezers structures are taken by scanning confocal microscopy while the prongs are electrostatically actuated under a low frequency ac voltage. The images, which are demodulated at the actuation frequency and its higher harmonics, clearly resolve the actuating parts of the tweezers. An actuation amplitude down to 6 pm (rms)/math can be detected. © 2003 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
81.16.Ta Atom manipulation
07.79.Fc Near-field scanning optical microscopes
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Self-assembled Co nanorods in diamond-like carbon thin films synthesized by plasma-assisted magnetron sputtering

F. L. Wang, J. C. Jiang, and E. I. Meletis

Appl. Phys. Lett. 83, 2423 (2003); http://dx.doi.org/10.1063/1.1610813 (3 pages) | Cited 6 times

Online Publication Date: 15 September 2003

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We report on self-assembled, high-aspect-ratio nanostructures of Co rods in diamond-like carbon (DLC) thin films synthesized by plasma-assisted magnetron sputtering. Cross-sectional and plan-view transmission electron microscopy investigations show that the nanorods continuously grow vertically to the substrate and have a relatively narrow distributed lateral size. The nanorods in the as-deposited thin films are found to have an ε-Co structure with a high density of defects and are encapsulated by 1–2 nm of an amorphous DLC matrix. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
81.15.Cd Deposition by sputtering
81.16.Dn Self-assembly

Fluorination of carbon nanotubes in CF4 plasma

N. O. V. Plank, Liudi Jiang, and R. Cheung

Appl. Phys. Lett. 83, 2426 (2003); http://dx.doi.org/10.1063/1.1611621 (3 pages) | Cited 54 times

Online Publication Date: 15 September 2003

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The effect of CF4 gaseous plasma exposure to single-wall carbon nanotubes (CNTs) has been studied. Raman spectroscopy results show that CNTs have gained more disordered sp3 bonds associated with functionalization, as both the flow rates of gas in the plasma and exposure time in the plasma are increased. Scanning electron microscopy images indicate the CNTs have been preserved after CF4 plasma exposure. X-ray photoelectron spectroscopy provides evidence of carbon to fluorine bonds (C–F) on the CNTs samples after CF4 plasma exposure. Semi-ionic and covalent C–F bonds are prevalent on the CNTs after CF4 exposure with the intensity ratio of the semi-ionic to covalent C–F bond decreasing as the flow rate of CF4 and exposure time in the CF4 plasma is increased. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
78.67.Ch Nanotubes
78.30.Hv Other nonmetallic inorganics
79.60.-i Photoemission and photoelectron spectra

Schottky barriers at metal-finite semiconducting carbon nanotube interfaces

Yongqiang Xue and Mark A. Ratner

Appl. Phys. Lett. 83, 2429 (2003); http://dx.doi.org/10.1063/1.1613355 (3 pages) | Cited 14 times

Online Publication Date: 15 September 2003

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Electronic properties of metal-finite semiconducting carbon nanotube interfaces are studied as a function of the nanotube length using a self-consistent tight-binding theory. We find that the shape of the potential barrier depends on the long-range tail of the charge transfer, leading to an injection barrier thickness comparable to half of the nanotube length until the nanotube reaches the bulk limit. The conductance of the nanotube junction shows a transition from tunneling to thermally activated transport with increasing nanotube length. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.63.Fg Nanotubes
73.30.+y Surface double layers, Schottky barriers, and work functions

Germanium nanowire field-effect transistors with SiO2 and high-κ HfO2 gate dielectrics

Dunwei Wang, Qian Wang, Ali Javey, Ryan Tu, Hongjie Dai, Hyoungsub Kim, Paul C. McIntyre, Tejas Krishnamohan, and Krishna C. Saraswat

Appl. Phys. Lett. 83, 2432 (2003); http://dx.doi.org/10.1063/1.1611644 (3 pages) | Cited 148 times

Online Publication Date: 15 September 2003

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Single-crystal Ge nanowires are synthesized by a low-temperature (275 °C) chemical vapor deposition (CVD) method. Boron doped p-type GeNW field-effect transistors (FETs) with back-gates and thin SiO2 (10 nm) gate insulators are constructed. Hole mobility higher than 600 cm2/V s is observed in these devices, suggesting high quality and excellent electrical properties of as-grown Ge wires. In addition, integration of high-κ HfO2 (12 nm) gate dielectric into nanowire FETs with top-gates is accomplished with promising device characteristics obtained. The nanowire synthesis and device fabrication steps are all performed below 400 °C, opening a possibility of building three-dimensional electronics with CVD-derived Ge nanowires. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.63.Nm Quantum wires
77.22.Ch Permittivity (dielectric function)
61.46.-w Structure of nanoscale materials

Drain voltage scaling in carbon nanotube transistors

M. Radosavljević, S. Heinze, J. Tersoff, and Ph. Avouris

Appl. Phys. Lett. 83, 2435 (2003); http://dx.doi.org/10.1063/1.1610791 (3 pages) | Cited 59 times

Online Publication Date: 15 September 2003

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Decreasing the oxide thickness in carbon nanotube field-effect transistors (CNFETs) improves the turn-on behavior. However, we demonstrate that this also requires scaling the range of the drain voltage. This scaling is needed to avoid an exponential increase in off-current with drain voltage, due to modulation of the Schottky barriers at both the source and drain contact. We illustrate this with results for bottom-gated ambipolar CNFETs with oxides of 2 and 5 nm, and give an explicit scaling rule for the drain voltage. Above the drain voltage limit, the off-current becomes large and has equal electron and hole contributions. This allows the recently reported light emission from appropriately biased CNFETs. © 2003 American Institute of Physics.
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85.35.Kt Nanotube devices
85.30.Tv Field effect devices
85.60.Jb Light-emitting devices

Optical properties of organic dyes in nanoporous zeolite crystals

Irene L. Li, Z. K. Tang, X. D. Xiao, C. L. Yang, and W. K. Ge

Appl. Phys. Lett. 83, 2438 (2003); http://dx.doi.org/10.1063/1.1613033 (3 pages) | Cited 8 times

Online Publication Date: 15 September 2003

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Organic dye molecules of styryl 7 were introduced into the channels of AlPO4-5 single crystals. Polarized absorption and photoluminescence spectra of the dye molecules were investigated. The polarization angle dependence of the absorption and photoluminescence intensity indicates that the dye molecules are highly oriented in the channels. The hexagonal-shaped AlPO4-5 single crystal serves as a natural microcavity for lasing action of the dye molecules. The microcavity modes of the lasing action were also demonstrated. © 2003 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.25.Ja Polarization
81.05.Rm Porous materials; granular materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.55.Mb Porous materials
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
82.75.-z Molecular sieves, zeolites, clathrates, and other complex solids
42.70.Hj Laser materials
42.60.By Design of specific laser systems
42.55.Mv Dye lasers

Pattern uniformity control in room-temperature imprint lithography

Pil S. Hong and Hong H. Lee

Appl. Phys. Lett. 83, 2441 (2003); http://dx.doi.org/10.1063/1.1613363 (3 pages) | Cited 7 times

Online Publication Date: 15 September 2003

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Nonuniformity in patterning that can arise in room-temperature imprint lithography is analyzed and a condition is presented under which the uniformity is assured. The condition is developed in such a way that the elastic recovery of stain-hardened polymer after the mold is removed does not cause the nonuniformity. Experimental testing of the condition reveals that it is a reliable criterion for uniform patterning. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
68.37.Ps Atomic force microscopy (AFM)

Nanoscroll formation from strained layer heterostructures

Marius Grundmann

Appl. Phys. Lett. 83, 2444 (2003); http://dx.doi.org/10.1063/1.1613366 (3 pages) | Cited 42 times

Online Publication Date: 15 September 2003

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Nanoscrolls develop when thin, strained semiconductor multilayers are peeled off from their substrate. We model the strain relaxation using continuum strain theory and predict that the scroll diameter depends on the winding direction if the cubic symmetry of zinc blende semiconductors is taken into account, 〈100〉 being the preferred winding direction. The effects of nonlinear strain and third order elastic coefficients are considered, the latter leading to smaller scroll diameter. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
62.20.D- Elasticity
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Effect of thermal annealing of Ni/Au ohmic contact on the leakage current of GaN based light emitting diodes

Chin-Yuan Hsu, Wen-How Lan, and YewChung Sermon Wu

Appl. Phys. Lett. 83, 2447 (2003); http://dx.doi.org/10.1063/1.1601306 (3 pages) | Cited 28 times

Online Publication Date: 15 September 2003

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The effect of thermal annealing on current–voltage properties of GaN light emitting diodes (LEDs) has been studied. At annealing temperatures above 700 °C, the p–n junction of the diodes became very leaky and Ga-contained metallic bubbles were observed on the surface of Ni/Au p-ohmic contact. Transmission electron microscopy and energy dispersive x-ray spectrometer studies revealed that these metallic bubbles resided directly on top of the threading dislocations in GaN and both Ni and Au were indiffused into the LED structure along the cores of the TDs. The conducting paths formed by the metal containing dislocation cores are believed to be the cause for the observed short circuit behavior of p–n junctions at high annealing temperatures. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.60.Jb Light-emitting devices
61.72.Cc Kinetics of defect formation and annealing
73.61.Ey III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
61.72.Lk Linear defects: dislocations, disclinations

On the origin of shot noise in CdTe detectors

G. Ferrari, M. Sampietro, G. Bertuccio, G. Gomila, and L. Reggiani

Appl. Phys. Lett. 83, 2450 (2003); http://dx.doi.org/10.1063/1.1611648 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2003

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Semi-insulating CdTe-based detectors exhibit shot noise at normal operating applied voltage, in spite of their linear symmetric current–voltage characteristic. In the present letter, we provide theoretical and experimental evidence that the origin of shot noise in these detectors under dark conditions can be explained in terms of a diffusion model. The physical reason for this behavior is that the dielectric relaxation time can become longer than the dynamic transit time depending on the applied bias, thus allowing carriers to cross the sample in an independent way. The predictions of the model are confirmed by detailed current noise measurements performed at different temperatures. © 2003 American Institute of Physics.
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29.40.Wk Solid-state detectors
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
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