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2 Jun 2003

Volume 82, Issue 22, pp. 3811-3991

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 3958 (2003); http://dx.doi.org/10.1063/1.1579125 (3 pages)

E. Zussman, D. Rittel, and A. L. Yarin
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Mode analysis in He+-implanted lithium fluoride planar waveguides

V. Mussi, F. Somma, P. Moretti, J. Mugnier, B. Jacquier, R. M. Montereali, and E. Nichelatti

Appl. Phys. Lett. 82, 3886 (2003); http://dx.doi.org/10.1063/1.1577822 (3 pages) | Cited 5 times

Online Publication Date: 27 May 2003

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The depth refractive index profiles of broadband visible-emitting planar waveguides produced in LiF crystals with 1.5- and 2-MeV He+ ions at different doses have been derived from mode analysis. They show that there are two competitive mechanisms responsible for positive and negative modifications of the refractive index in the irradiated volume associated with different processes of energy deposition of the incident ions, so as to induce a complex coloration profile along the penetration direction, which is strongly dependent on the irradiation dose. © 2003 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
61.72.up Other materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Jh Ion radiation effects
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers
61.82.Ms Insulators

Energy level evolution at a silole/magnesium thin-film interface

A. J. Mäkinen, M. Uchida, and Z. H. Kafafi

Appl. Phys. Lett. 82, 3889 (2003); http://dx.doi.org/10.1063/1.1579558 (3 pages) | Cited 12 times

Online Publication Date: 27 May 2003

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Photoemission spectroscopy of an interface formed through step-by-step deposition of Mg onto a film of a silole derivative, 2,5-bis[6′-(2′,2″-bipyridyl)]-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy), reveals the formation of gap states arising from electron transfer from the metal to the organic. In addition, a 0.3-eV rigid shift of the molecular orbitals toward higher binding energy is observed, while the work function of the Mg-rich PyPySPyPy surface is reduced by 0.6 eV. The observed energy level evolution elucidates how the electronic structure of the Mg/PyPySPyPy interface depends on the chemical interaction between the metal and the organic. This is important for understanding and optimizing electron injection at the Mg/PyPySPyPy interface, which can be incorporated in electronic, electro-optic, and optoelectronic devices. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
79.60.Jv Interfaces; heterostructures; nanostructures
73.30.+y Surface double layers, Schottky barriers, and work functions

GaAs film on Si substrate transplanted from GaAs/Ge structure by direct bonding

N. Chandrasekaran, T. Soga, and T. Jimbo

Appl. Phys. Lett. 82, 3892 (2003); http://dx.doi.org/10.1063/1.1581976 (3 pages) | Cited 8 times

Online Publication Date: 27 May 2003

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A process to transplant GaAs film from a Ge substrate to Si substrate using a direct bonding method is proposed. The scanning electron microscopy picture shows that the GaAs film is uniformly transplanted from Ge to Si. The high-resolution transmission electron microscopy image shows that GaAs is connected to Si by the covalent bonds. The stress of the bonded GaAs on Si is compared with GaAs/GaAs and heteroepitaxially grown GaAs/Ge(before bonding) by a 4.2 K photoluminescence method. The difference in the residual stress between the bonded GaAs/Si sample and GaAs/Si grown by two-step growth is explained by a thermal stress relaxation mechanism during the cooling process. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.05.Ea III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.47.Fg Semiconductor surfaces
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
68.35.Np Adhesion
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Temperature dependence of photoreflectance in InAs/GaAs quantum dots

C. M. Lai, F. Y. Chang, C. W. Chang, C. H. Kao, H. H. Lin, G. J. Jan, and Johnson Lee

Appl. Phys. Lett. 82, 3895 (2003); http://dx.doi.org/10.1063/1.1581003 (3 pages) | Cited 6 times

Online Publication Date: 27 May 2003

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Temperature dependent photoreflectance (PR) and photoluminescence experiments of the InAs/GaAs quantum dot (QD) structures were performed. At 20 K, effective band-gap transitions due to the InAs QDs, wetting layers, and GaAs buffer and cap layers were identified. Transition energies of the ground state and four excited states with nearly equal interlevel spacings (75–80 meV) were observed. The linewidth of the ground-state transition decreased as the temperature increased from 20 K to 100 K while the linewidth became broader at temperatures above 100 K. Energy features of the PR spectra originating from QDs and relating to the in-plane parabolic potentials were discussed. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots

The effect of the surface layer of tetrahedral amorphous carbon films on their tribological and electron emission properties investigated by atomic force microscopy

Dongping Liu, Günther Benstetter, and Werner Frammelsberger

Appl. Phys. Lett. 82, 3898 (2003); http://dx.doi.org/10.1063/1.1581367 (3 pages) | Cited 19 times

Online Publication Date: 27 May 2003

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The nanowear resistance, tribological, and field emission properties of tetrahedral amorphous carbon (ta-C) films have been analyzed by atomic force microscope (AFM)-based wear testing technique, lateral force microscope, and conducting AFM. The ta-C films grown by filtered pulsed cathodic arc discharge were found to have soft surface layers, 1.1±0.1 nm thick, which contribute to an improvement of their field emission properties. The low friction coefficient between the nanotip and film surface is correlated to one or two graphite-like atomic layers at the ta-C film surfaces. The analysis of Fowler–Nordheim tunneling currents indicates the formation of filament-like emission channels in amorphous carbon films. © 2003 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
81.40.Pq Friction, lubrication, and wear
68.60.Bs Mechanical and acoustical properties
62.20.Qp Friction, tribology, and hardness
68.37.Ps Atomic force microscopy (AFM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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High electron mobility of epitaxial ZnO thin films on c-plane sapphire grown by multistep pulsed-laser deposition

E. M. Kaidashev, M. Lorenz, H. von Wenckstern, A. Rahm, H.-C. Semmelhack, K.-H. Han, G. Benndorf, C. Bundesmann, H. Hochmuth, and M. Grundmann

Appl. Phys. Lett. 82, 3901 (2003); http://dx.doi.org/10.1063/1.1578694 (3 pages) | Cited 171 times

Online Publication Date: 27 May 2003

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A multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 μm on c-plane sapphire substrates. We obtain reproducibly high electron mobilities from 115 up to 155 cm2/V s at 300 K in a narrow carrier concentration range from 2 to 5×1016 cm−3. The key issue of the multistep PLD process is the insertion of 30-nm-thin ZnO relaxation layers deposited at reduced substrate temperature. The high-mobility samples show atomically flat surface structure with grain size of about 0.5–1 μm, whereas the surfaces of low-mobility films consist of clearly resolved hexagonally faceted columnar grains of only 200-nm size, as shown by atomic force microscopy. Structurally optimized PLD ZnO thin films show narrow high-resolution x-ray diffraction peak widths of the ZnO(0002) ω- and 2Θ-scans as low as 151 and 43 arcsec, respectively, and narrow photoluminescence linewidths of donor-bound excitons of 1.7 meV at 2 K. © 2003 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
81.05.Dz II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
71.35.-y Excitons and related phenomena

Cyclotron resonance of terahertz photoresponse in two-dimensional polar semiconductors at high temperatures

X. L. Lei and S. Y. Liu

Appl. Phys. Lett. 82, 3904 (2003); http://dx.doi.org/10.1063/1.1579853 (3 pages) | Cited 2 times

Online Publication Date: 27 May 2003

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Far infrared photoresponse of magnetoresistivity ΔRxx of two-dimensional electron systems is investigated theoretically at high temperatures. Photon-assisted impurity and phonon scatterings, rather than the electron heating, are shown to be the dominant mechanisms for high-temperature photoresponse at cyclotron resonance. Based on the theory developed for electron magnetotransport driven by intense terahertz radiations, we have calculated the far infrared photoresistivity of a GaAs/AlGaAs heterostructure at temperature T = 150 K, predicting notable cyclotron resonance of ΔRxx, in agreement with the experimental finding. Contrary to low temperature case, where the electron heating is almost solely responsible for the cyclotron resonance of ΔRxx, at T = 150 K electron-heating contribute at most a small fraction of the total response. © 2003 American Institute of Physics.
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76.40.+b Diamagnetic and cyclotron resonances
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
72.40.+w Photoconduction and photovoltaic effects

Morphology and electronic transport of polycrystalline pentacene thin-film transistors

D. Knipp, R. A. Street, and A. R. Völkel

Appl. Phys. Lett. 82, 3907 (2003); http://dx.doi.org/10.1063/1.1578536 (3 pages) | Cited 108 times

Online Publication Date: 27 May 2003

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Temperature-dependent measurements of thin-film transistors were performed to gain insight in the electronic transport of polycrystalline pentacene. Devices were fabricated with plasma-enhanced chemical vapor deposited silicon nitride gate dielectrics. The influence of the dielectric roughness and the deposition temperature of the thermally evaporated pentacene films were studied. Although films on rougher gate dielectrics and films prepared at low deposition temperatures exhibit similar grain size, the electronic properties are different. Increasing the dielectric roughness reduces the free carrier mobility, while low substrate temperature leads to more and deeper hole traps. © 2003 American Institute of Physics.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.37.Ps Atomic force microscopy (AFM)

Improved morphology for ohmic contacts to AlGaN/GaN high electron mobility transistors using WSix- or W-based metallization

B. Luo, F. Ren, R. C. Fitch, J. K. Gillespie, T. Jenkins, J. Sewell, D. Via, A. Crespo, A. G. Baca, R. D. Briggs, D. Gotthold, R. Birkhahn, B. Peres, and S. J. Pearton

Appl. Phys. Lett. 82, 3910 (2003); http://dx.doi.org/10.1063/1.1579845 (3 pages) | Cited 18 times

Online Publication Date: 27 May 2003

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A comparison was made of specific contact resistivity and morphology of Ti/Al/Pt/WSi/Ti/Au and Ti/Al/Pt/W/Ti/Au ohmic contacts to AlGaN/GaN heterostructures relative to the standard Ti/Al/Pt/Au metallization. The W- and WSi-based contacts show comparable specific resistivities to that of the standard contact on similar layer structures, reaching minimum values of ∼ 10−5 Ω cm2 after annealing in the range 850–900 °C. However, the W- and WSi-based contacts exhibit much smoother surface morphologies, even after 950 °C annealing. For example, the root-mean-square roughness of the Ti/Al/Pt/WSi/Ti/Au contact annealed at 950 °C was unchanged from the as-deposited values whereas the Ti/Al/Pt/Au contact shows significant deterioration of the morphology under these conditions. The improved thermal stability of the W- and WSix-based contacts is important for maintaining edge acuity during high-temperature operation. © 2003 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

Ion-implanted In0.53Ga0.47As for ultrafast optoelectronic applications

C. Carmody, H. H. Tan, C. Jagadish, A. Gaarder, and S. Marcinkevičius

Appl. Phys. Lett. 82, 3913 (2003); http://dx.doi.org/10.1063/1.1579565 (3 pages) | Cited 28 times

Online Publication Date: 27 May 2003

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Undoped In0.53Ga0.47As epilayers were implanted with 2-MeV Fe+ ions at doses of 1×1015 and 1×1016 cm−2 at room temperature and annealed at temperatures between 500 and 800 °C. Hall-effect measurements show that after annealing, layers with resistivities on the order of 105 Ω/square can be achieved. Carrier lifetimes as short as 300 fs are observed for samples annealed at 500 and 600 °C. For higher annealing temperatures, characteristic times of the optical response are on the order of a few picoseconds. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
61.80.Jh Ion radiation effects
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.82.Fk Semiconductors

Thickness-dependent stress effect in p-type metal–oxide–semiconductor structure investigated by substrate injection current

Chao-Chi Hong, Wei-Jian Liao, and Jenn-Gwo Hwu

Appl. Phys. Lett. 82, 3916 (2003); http://dx.doi.org/10.1063/1.1581004 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2003

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The effects of oxide, Si wafer, and gate Al thicknesses on the substrate injection currents (Jsub) of p-type metal–oxide–semiconductor structures with ultrathin oxides are studied. Jsub is reported to be both trap-related (interface and Si bulk) and Si band gap-related (intrinsic carrier concentration). Both mechanisms have given rise to the stress near the Si/SiO2 interface. Current–voltage and capacitance–voltage characterizations reveal that Jsub increases with oxide thickness, which is suggested to be dominated by the trap-related mechanism. A stronger dependence of Jsub on a change in oxide thickness is observed for a thicker Si wafer, which is proposed to be mainly caused by the band gap-related mechanism. Furthermore, a thicker gate Al introduces a higher Jsub, which is proposed to be due to both the trap-related and the band gap-related mechanisms. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Observation of a scanning tunneling microscopy induced photocurrent during ballistic electron emission microscopy

E. R. Heller and J. P. Pelz

Appl. Phys. Lett. 82, 3919 (2003); http://dx.doi.org/10.1063/1.1579844 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2003

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We report that a scanning tunneling microscope induced photocurrent (STM–PC) can occur during ballistic electron emission microscopy (BEEM) measurements on Schottky-barrier samples with typical efficiency of 10−4–10−6 and apparent BEEM threshold slightly above the substrate semiconductor band gap. This STM–PC resembles normal BEEM current, and hence, can interfere with BEEM measurements of structures with intrinsically low signal and/or intrinsic BEEM threshold voltage larger than the substrate band gap. We discuss a simple test for the existence of STM–PC during BEEM measurements. © 2003 American Institute of Physics.
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68.37.Vj Field emission and field-ion microscopy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Pz Photoconduction and photovoltaic effects

Hot-electron spectroscopy in parallel magnetic fields

M. Kast, W. Boxleitner, C. Pacher, G. Strasser, and E. Gornik

Appl. Phys. Lett. 82, 3922 (2003); http://dx.doi.org/10.1063/1.1579119 (3 pages) | Cited 1 time

Online Publication Date: 27 May 2003

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Hot-electron spectroscopy in the presence of magnetic fields applied parallel to the current direction is studied. Inter-Landau-level transitions are observed due to scattering processes in the drift region of the hot-electron transistor. In high magnetic fields, the reduced phase space of elastic/inelastic scattering is directly observed as a decrease of the energetic widths of ballistic/phonon-replica peaks. This results in an increased resolution of the hot-electron spectroscopy to be well below ΔE = 10 meV. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Determination of the electron capture time in quantum-well infrared photodetectors using time-resolved photocurrent measurements

S. Steinkogler, H. Schneider, M. Walther, and P. Koidl

Appl. Phys. Lett. 82, 3925 (2003); http://dx.doi.org/10.1063/1.1579855 (3 pages) | Cited 5 times

Online Publication Date: 27 May 2003

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We have investigated the transport properties of optically excited electrons in a 100 period InGaAs/GaAs-quantum well infrared photodetector. The electrons were excited by femtosecond-infrared laser pulses and the transient photocurrent was recorded in the picosecond regime. We have carefully analyzed the measured photocurrent transients taking into account both the capture time τc and the transit time τtrans. Our experimental results allow us to determine τc, which increases from 10 ps at 5 kV/cm to about 20 ps at 20 kV/cm. We have also measured the noise gain in order to determine the transit time and the drift velocity. The dynamic parameters extracted from our measurements are consistent with values from the literature. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Hs Quantum wells
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
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Spin-torque transistor

Gerrit E. W. Bauer, Arne Brataas, Yaroslav Tserkovnyak, and Bart J. van Wees

Appl. Phys. Lett. 82, 3928 (2003); http://dx.doi.org/10.1063/1.1579122 (3 pages) | Cited 28 times

Online Publication Date: 27 May 2003

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A magnetoelectronic thin-film transistor is proposed that can display negative differential resistance and gain. The working principle is the modulation of the soure–drain current in a spin valve by the magnetization of a third electrode, which is rotated by the spin-torque created by a control spin valve. The device can operate at room temperature, but in order to be useful, ferromagnetic materials with polarizations close to unity are required. © 2003 American Institute of Physics.
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85.75.Hh Spin polarized field effect transistors
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.30.Tv Field effect devices
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Al2O3/Si3N4 stacked insulators for 0.1 μm gate metal–oxide–semiconductor transistors realized by high-density Si3N4 buffer layers

Yoshihisa Fujisaki, Kunie Iseki, Hiroshi Ishiwara, Ming Mao, and Randhir Bubber

Appl. Phys. Lett. 82, 3931 (2003); http://dx.doi.org/10.1063/1.1579850 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2003

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We developed Al2O3/Si3N4 stacked insulators suitable for the advanced metal–oxide–semiconductor (MOS) devices. Ultrathin Si3N4 was prepared by direct nitridation of Si substrate using atomic nitrogen radicals. With this process, the film obtained was less defective compared to conventional Si3N4. Al2O3 was then deposited by atomic layer deposition on Si3N4 and oxidized to eliminate defects in the film. Since the buffer Si3N4 does not contain a large amount of hydrogen, we could perform high-temperature oxidation without any additional interfacial layer formation in the Si substrate. We achieved high capacitance density and low leakage current that are acceptable for the gate insulator in advanced MOS devices with a 0.1 μm gate length by exploiting this buffering technique. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Ng Insulators
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Mq Oxidation

Nanodomain engineering in RbTiOPO4 ferroelectric crystals

G. Rosenman, P. Urenski, A. Agronin, A. Arie, and Y. Rosenwaks

Appl. Phys. Lett. 82, 3934 (2003); http://dx.doi.org/10.1063/1.1578693 (3 pages) | Cited 13 times

Online Publication Date: 27 May 2003

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A high voltage atomic force microscope has been applied for tailoring strip-like nanodomains in RbTiOPO4 ferroelectric crystal. Highly anisotropic nanodomain propagation has been observed owing to the difference in lattice constants along the principal axes of the RbTiOPO4 crystal. Studying the influence of the applied high voltage, and tip velocity on the domain strips has allowed us to fabricate fine nanodomain gratings, which is useful for backward-propagating quasi-phase-matched frequency conversion. © 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.Dj Domain structure; hysteresis
42.70.Mp Nonlinear optical crystals
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Dj Gratings

Effects of scaling the film thickness on the ferroelectric properties of SrBi2Ta2O9 ultra thin films

J. Celinska, V. Joshi, S. Narayan, L. McMillan, and C. Paz de Araujo

Appl. Phys. Lett. 82, 3937 (2003); http://dx.doi.org/10.1063/1.1579559 (3 pages) | Cited 8 times

Online Publication Date: 27 May 2003

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We have investigated the effect of reducing the thickness of strontium bismuth tantalate film to as low as 25 nm on its ferroelectric characteristics. A degradation of ferroelectric properties such as significant reduction in remanent polarization is generally observed with reduction in film thickness, in particular below 100 nm. This has been overcome by using a modified deposition process sequence and a crystallization technique based completely on the rapid thermal annealing process. The resulting ultrathin films show good remanent polarization, low-voltage saturation, low leakage current, high breakdown strength, and good endurance. These films demonstrate the potential for scaling and are excellent candidates for several generations of ferroelectric random access memory applications. © 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
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ej Polarization and depolarization

High-temperature ferroelastic phase transitions in Li–Na niobate compounds

B. Jiménez, A. Castro, and L. Pardo

Appl. Phys. Lett. 82, 3940 (2003); http://dx.doi.org/10.1063/1.1580648 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2003

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Measurements of mechanoelastic properties as a function of the temperature of (LixNa1−x)NbO3 (x ⩽ 0.12) ceramics in the paraelectric phase show a sequence of anomalies in the complex Young’s modulus Y∗. These anomalies are associated with structural phase transitions of the ferro–ferroelastic and ferro–paraelastic type, where strong elastic softening due to the order-parameter–spontaneous-strain coupling of linear quadratic character takes place. The existence of NbO6 octahedra tilts and the lack of significant volume change in the phase transition temperatures of the studied compositions allows considering the order parameters in the same way as that invoked in the case of the strontium titanate. © 2003 American Institute of Physics.
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64.70.K- Solid-solid transitions
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
65.40.De Thermal expansion; thermomechanical effects
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Tomography in the multiple scattering regime of the scanning transmission electron microscope

Zachary H. Levine

Appl. Phys. Lett. 82, 3943 (2003); http://dx.doi.org/10.1063/1.1579116 (3 pages) | Cited 10 times

Online Publication Date: 27 May 2003

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To date, nearly all tomography based on electron microscopy has been performed on samples 1 μm or less thick. It has also relied on Beer’s Law. In this work, tomographic reconstructions of simulated scans of a photonic band-gap crystal based on bright-field imaging with a scanning transmission electron microscope are made assuming (1) multiple scattering or (2) the standard Beer’s Law model. The results suggest that it should be possible to treat systems several times larger than those which appear in literature, albeit at a worse resolution. The multiple scattering theory leads to high-quality reconstructions. Beer’s Law does only a little worse despite being applied outside its range of validity.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
68.37.Lp Transmission electron microscopy (TEM)

Single-electron charging of a self-assembled II–VI quantum dot

J. Seufert, M. Rambach, G. Bacher, A. Forchel, T. Passow, and D. Hommel

Appl. Phys. Lett. 82, 3946 (2003); http://dx.doi.org/10.1063/1.1580632 (3 pages) | Cited 13 times

Online Publication Date: 27 May 2003

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We have studied single-electron injection into individual self-assembled CdSe/ZnSe quantum dots. Using nanostructured contacts to apply a vertical electric field, excess electrons are promoted to the single-quantum-dot ground state in a controlled fashion. Spatially-resolved photoluminescence spectroscopy is applied to demonstrate single-quantum-dot charging via the formation of single zero-dimensional charged excitons with a binding energy on the order of 10 meV. © 2003 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
73.63.Kv Quantum dots
71.35.Pq Charged excitons (trions)
78.55.Et II-VI semiconductors
81.07.Ta Quantum dots

Electronic structure of GaN nanowire studied by x-ray-absorption spectroscopy and scanning photoelectron microscopy

J. W. Chiou, J. C. Jan, H. M. Tsai, W. F. Pong, M.-H. Tsai, I.-H. Hong, R. Klauser, J. F. Lee, C. W. Hsu, H. M. Lin, C. C. Chen, C. H. Shen, L. C. Chen, and K. H. Chen

Appl. Phys. Lett. 82, 3949 (2003); http://dx.doi.org/10.1063/1.1579871 (3 pages) | Cited 13 times

Online Publication Date: 27 May 2003

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X-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been employed to obtain information on the electronic structures of the GaN nanowires and thin film. The comparison of the XANES spectra revealed that the nanowires have a smaller (larger) N (Ga) K edge XANES intensity than that of the thin film, which suggests an increase (decrease) of the occupation of N 2p (Ga 4p) orbitals and an increase of the N (Ga) negative (positive) effective charge in the nanowires. The SPEM spectra showed that the Ga 3d band for the nanowires lies about 20.8 eV below the Fermi level and has a chemical shift of about −0.9 eV relative to that of the thin film. © 2003 American Institute of Physics.
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73.22.Dj Single particle states
78.70.Dm X-ray absorption spectra
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Xy Scanning Auger microscopy, photoelectron microscopy

Nonlocal resonant interaction between coupled quantum wires

T. Morimoto, Y. Iwase, N. Aoki, T. Sasaki, Y. Ochiai, A. Shailos, J. P. Bird, M. P. Lilly, J. L. Reno, and J. A. Simmons

Appl. Phys. Lett. 82, 3952 (2003); http://dx.doi.org/10.1063/1.1579851 (3 pages) | Cited 34 times

Online Publication Date: 27 May 2003

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We study the transport in a system of coupled quantum wires and show evidence for a resonant interaction that occurs whenever one of them is biased close to pinch off. Measuring the conductance of one of the wires, as the width of the other is varied, we observe a resonant peak in the conductance that is correlated to the point at which the other wire pinches off. The origin of this interaction remains undetermined at present, although its characteristics appear consistent with predictions that a correlated many-body state should form in narrow wires as their conductance vanishes. © 2003 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
73.63.Nm Quantum wires
73.21.Hb Quantum wires
73.63.Rt Nanoscale contacts

Photovoltaic effect on differential capacitance profiles of low-energy-BF2+-implanted silicon wafers

M. N. Chang, C. Y. Chen, F. M. Pan, J. H. Lai, W. W. Wan, and J. H. Liang

Appl. Phys. Lett. 82, 3955 (2003); http://dx.doi.org/10.1063/1.1581987 (3 pages) | Cited 12 times

Online Publication Date: 27 May 2003

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Using scanning capacitance microscopy (SCM), we have studied the photovoltaic effect on differential capacitance (dC/dV) signals of low-energy-BF2+-implanted silicon wafers. The surface photovoltage induced by the stray light of the atomic force microscope laser beam leads to distorted dC/dV profiles and hence perturbs the contrast of SCM images. Due to the photovoltaic effect on the junction region, the observed junction image also exhibits a narrower junction width. According to this study, the photovoltaic effect not only significantly affects the dC/dV signals but also deteriorates the accuracy of junction characterization, in particular for ultrashallow junctions and lower band-gap semiconductors. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
72.40.+w Photoconduction and photovoltaic effects
68.37.Ps Atomic force microscopy (AFM)

Failure modes of electrospun nanofibers

E. Zussman, D. Rittel, and A. L. Yarin

Appl. Phys. Lett. 82, 3958 (2003); http://dx.doi.org/10.1063/1.1579125 (3 pages) | Cited 33 times

Online Publication Date: 27 May 2003

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Failure modes of electrospun polymer nanofibers are reported. The nanofibers have diameters in the range of 80–400 nm and lengths greater then several centimeters. The nanofibers fail by a multiple necking mechanism, sometimes followed by the development of a fibriliar structure. This phenomenon is attributed to a strong stretching of solidified nanofibers by the tapered accumulating wheel (electrostatic lens), if its rotation speed becomes too high. Necking has not been observed in the nanofibers collected on a grounded plate. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
62.25.-g Mechanical properties of nanoscale systems
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
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