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11 Mar 2002

Volume 80, Issue 10, pp. 1683-1849

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Simultaneous measurements of Seebeck coefficient and thermal conductivity across superlattice

B. Yang, J. L. Liu, K. L. Wang, and G. Chen

Appl. Phys. Lett. 80, 1758 (2002); http://dx.doi.org/10.1063/1.1458693 (3 pages) | Cited 37 times

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A method is developed to simultaneously measure the Seebeck coefficient and thermal conductivity in the cross-plane direction of thin films and applied to an n-type Si/Ge quantum-dot superlattice. In this method, an Au/Cr pattern serves as both a heater and a thermometer, and a microprobe is prepared between the heater and the thin film to extract the Seebeck voltage. Using a differential measurement between the thin films with different thickness, the temperature and voltage drops across the thin film are determined to deduce its cross-plane thermal conductivity and Seebeck coefficient. At room temperature, the cross-plane Seebeck coefficient and thermal conductivity are 312 μV/K and 2.92 W/mK, respectively, for the n-type Si(75 Å)/Ge(15 Å) quantum-dot superlattice doped to 8.7×1019 cm−3. © 2002 American Institute of Physics.
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73.63.Kv Quantum dots
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.20.-n Thermal instruments and apparatus

Electron transport measurements of Schottky barrier inhomogeneities

L. E. Calvet, R. G. Wheeler, and M. A. Reed

Appl. Phys. Lett. 80, 1761 (2002); http://dx.doi.org/10.1063/1.1456257 (3 pages) | Cited 25 times

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We report nonmonotonicities in the low-temperature current versus gate voltage characteristics of PtSi/Si Schottky Barrier metal–oxide–semiconductor field-effect transistors. Direct tunneling through the Schottky barrier is shown to limit the current and be superimposed with resonant peaks and oscillations. These structures are attributed to resonant tunneling through impurities located close to the interface and nonuniformities of the heterojunction. We thus demonstrate barrier height variations in electron transport through a relatively large metal/semiconductor contact area. The inhomogeneities result in different average Schottky barrier heights between devices, and cause height variations as a function of carrier concentration within a metal/semiconductor interface. © 2002 American Institute of Physics.
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85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
73.40.Gk Tunneling
73.61.Cw Elemental semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Band discontinuity in the GaAs/AlAs interface studied by in situ photoemission spectroscopy

J. Okabayashi, K. Ono, T. Mano, M. Mizuguchi, K. Horiba, K. Nakamura, A. Fujimori, and M. Oshima

Appl. Phys. Lett. 80, 1764 (2002); http://dx.doi.org/10.1063/1.1455695 (3 pages) | Cited 1 time

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In order to investigate the valence-band discontinuity of the GaAs/AlAs interface, the thickness dependence of the photoemission spectra of a GaAs layer in situ deposited on AlAs by molecular-beam epitaxy has been studied. Although the interface is atomically abrupt, the electronic structure in the interface region displays Al1−xGaxAs alloy-like behaviors. The valence-band maximum as well as the Ga 3dcore level show a gradual shift as a function of GaAs layer thickness of less than 2 nm (8 monolayers), which indicates that interface formation needs about 2 nm thickness for the electronic structure of the GaAs layer to become that of bulk GaAs. © 2002 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
79.60.Dp Adsorbed layers and thin films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Thermal quenching effect of an infrared deep level in Mg-doped p-type GaN films

Keunjoo Kim and Sang Jo Chung

Appl. Phys. Lett. 80, 1767 (2002); http://dx.doi.org/10.1063/1.1456547 (3 pages) | Cited 6 times

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The thermal quenching of an infrared deep level of 1.2–1.5 eV has been investigated on Mg-doped p-type GaN films, using one- and two-step annealing processes and photocurrent measurements. The deep level appeared in the one-step annealing process at a relatively high temperature of 900 °C, but disappeared in the two-step annealing process with a low-temperature step and a subsequent high-temperature step. The persistent photocurrent was residual in the sample including the deep level, while it was terminated in the sample without the deep level. This indicates that the deep level is a neutral hole center located above a quasi-Fermi level, estimated with an energy of EpF = 0.1–0.15 eV above the valence band at a hole carrier concentration of 2.0–2.5×1017/cm3. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.66.Fd III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Current transport in InP/In0.5(Al0.6Ga0.4)0.5P self-assembled quantum dot heterostructures using ballistic electron emission microscopy/spectroscopy

C. V. Reddy, V. Narayanamurti, J. H. Ryou, and R. D. Dupuis

Appl. Phys. Lett. 80, 1770 (2002); http://dx.doi.org/10.1063/1.1458689 (3 pages) | Cited 4 times

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Ballistic electron emission microscopy/spectroscopy (BEEM/S) has been employed to image, inject, and investigate the current transport through self-assembled InP quantum dots embedded in InAlGaP barriers. The spectroscopy performed on the dot and off the dot revealed that the charge confinement within the dots is more effective than the leakage through the quasibound states. Evidence for the charge accumulation in the quantum dots is presented with the help of BEEM imaging as a function of the tip bias. © 2002 American Institute of Physics.
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73.63.Kv Quantum dots
73.21.La Quantum dots
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Improving SiO2/SiGe interface of SiGe p-metal–oxide–silicon field-effect transistors using water vapor annealing

T. Ngai, X. Chen, J. Chen, and S. K. Banerjee

Appl. Phys. Lett. 80, 1773 (2002); http://dx.doi.org/10.1063/1.1445806 (3 pages) | Cited 3 times

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SiGe p-metal–oxide–silicon field-effect transistors (p-MOSFETs) were fabricated with ultrathin thin (∼20 Å) remote plasma chemical vapor deposition gate oxides deposited directly on SiGe. A low temperature water vapor annealing was used to improve the SiO2/SiGe interface and performance of SiGe p-MOSFETs. After the wet annealing, dangling Si and Ge bonds at the interface are passivated by atomic hydrogen, the threshold voltage of SiGe p-MOSFETs decreases from −0.39 to −0.20 V, the subthreshold slope from 117 to 87 mV/dec, and more than 20% output current enhancement is observed in these SiGe p-MOSFETs compared with Si control devices. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing
81.65.Rv Passivation
71.55.Ht Other nonmetals
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Local contactless measurement of the ordinary and extraordinary Hall effect using near-field microwave microscopy

M. Abu-Teir, F. Sakran, M. Golosovsky, D. Davidov, and A. Frenkel

Appl. Phys. Lett. 80, 1776 (2002); http://dx.doi.org/10.1063/1.1456541 (3 pages) | Cited 3 times

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We report a polarization-sensitive scanning microwave microscope based on a bimodal dielectric resonator with a cross-slit aperture. The microscope operates at ∼26 GHz in the reflection mode and has a subwavelength spatial resolution. It allows contactless mapping of the conductivity tensor, including magnetic-field-induced terms such as the Hall effect. We demonstrate local contactless measurement of the ordinary Hall effect in semiconducting wafers and of the extraordinary Hall effect in thin ferromagnetic Ni films. The latter yields out-of-plane magnetization. The microwave measurements are in good agreement with the dc Hall-effect measurements. © 2002 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
73.61.At Metal and metallic alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
72.20.My Galvanomagnetic and other magnetotransport effects
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Transition from negative magnetoresistance behavior to positive behavior in Co20(Cu1−xGex)80 ribbons

J. He, Z. D. Zhang, J. P. Liu, and D. J. Sellmyer

Appl. Phys. Lett. 80, 1779 (2002); http://dx.doi.org/10.1063/1.1458682 (3 pages) | Cited 1 time

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We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co20(Cu1−xGex)80 ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co3Ge2 compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co3Ge2/Co junctionlike configuration. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
73.23.Hk Coulomb blockade; single-electron tunneling
75.47.De Giant magnetoresistance

Low voltage I–V characteristics in magnetic tunneling junctions

G. G. Cabrera and N. García

Appl. Phys. Lett. 80, 1782 (2002); http://dx.doi.org/10.1063/1.1433168 (3 pages) | Cited 16 times

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We show that elastic currents, which take into account variations of the tunneling transmission with voltage and a large ratio of majority to minority spin densities of states of the conduction band at the Fermi level, can account for the low voltage current anomalies observed in magnet–oxide–magnet junctions. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.Mk Spin transport through interfaces
75.47.De Giant magnetoresistance
75.10.Lp Band and itinerant models

Balistic magnetoresistance in nanocontacts electrochemically grown between macro- and microscopic ferromagnetic electrodes

N. García, G. G. Qiang, and I. G. Saveliev

Appl. Phys. Lett. 80, 1785 (2002); http://dx.doi.org/10.1063/1.1459108 (3 pages) | Cited 16 times

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Our results prove the local origin of magnetoresistance in electrochemically deposited Ni nanocontacts. Experiments have been done using a complex setup for both in situ growth and ballistic magnetoresistance (BMR) measurements. Nanocontacts have been grown between two macroscopic Ni wires. In situ experiments with variation of the nanocontact diameter from 3 to 20 nm have been done using the same pair of wires. BMR values from 0.5% to 100% have been observed but no correlation of BMR value with the sample resistance, i.e., with the nanocontact cross section, has been found. These results show that the BMR in the nanometric size contact is determined by local geometrical and magnetic structures near the nanocontact rather than by the contact cross section itself. The hypothesis of existence of the intrinsic nonmagnetic dead layer in the ferromagnetic nanocontact is proposed to account for the BMR properties of the nanometric size contacts. Additionally, we report a BMR value of 200% in a Ni nanocontact (5 nm diameter) electrochemically grown between two nonmagnetic macroscopic gold wires. An external magnetic field has been used during the electrochemical deposition to fix the easy magnetic axis of the deposited Ni layer. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
73.40.Jn Metal-to-metal contacts
73.61.At Metal and metallic alloys
75.50.Cc Other ferromagnetic metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Pq Electrodeposition, electroplating

Quantum-confined magneto-Stark effect in diluted magnetic semiconductor coupled quantum wells

Kai Chang, J. B. Xia, H. B. Wu, S. L. Feng, and F. M. Peeters

Appl. Phys. Lett. 80, 1788 (2002); http://dx.doi.org/10.1063/1.1459491 (3 pages) | Cited 2 times

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The magneto-Stark effect in a diluted magnetic semiconductor (DMS) coupled quantum well (CQW) induced by an in-plane magnetic field is investigate theoretically. Unlike the usual electro-Stark effects, in a DMS CQW the Lorenz force leads to a spatially separated exciton. The in-plane magnetic field can shift the ground state of the magnetoexciton from a zero in-plane center of mass (CM)/momentum to a finite CM momentum, and render the ground state of magnetoexciton stable against radiative recombination due to momentum conservation. © 2002 American Institute of Physics.
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78.67.De Quantum wells
75.50.Pp Magnetic semiconductors
78.20.Ls Magneto-optical effects
71.35.Ji Excitons in magnetic fields; magnetoexcitons
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.Fg Quantum wells

Phase diagram of three contrasting magnetization reversal phases in uniaxial ferromagnetic thin films

Sug-Bong Choe and Sung-Chul Shin

Appl. Phys. Lett. 80, 1791 (2002); http://dx.doi.org/10.1063/1.1457527 (3 pages) | Cited 17 times

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We present an analytical description of a magnetization reversal phase diagram of ferromagnetic thin films that have uniaxial perpendicular anisotropy. The phase equilibrium lines were calculated from a micromagnetic consideration of equilibrium conditions of the wall motion, dendritic growth, and nucleation processes. The phase diagram characterizes well simulated domain evolution patterns: typical domain evolution patterns are predicted accurately in the corresponding phases accompanied by gradual phase transitions across the phase equilibrium lines. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Jk Magnetization reversal mechanisms
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy

Spin polarization contrast observed in GaAs by force-detected nuclear magnetic resonance

Kent R. Thurber, Lee E. Harrell, Raúl Fainchtein, and Doran D. Smith

Appl. Phys. Lett. 80, 1794 (2002); http://dx.doi.org/10.1063/1.1458688 (3 pages) | Cited 12 times

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We applied the technique of force-detected nuclear magnetic resonance to observe 71Ga, 69Ga, and 75As in GaAs. The nuclear spin-lattice relaxation time is 21±5 min for 69Ga at ∼5 K and 4.6 T. We have exploited this long relaxation time to first create and then observe spatially varying nuclear spin polarization within the sample, demonstrating a form of contrast for magnetic resonance force microscopy. Such nuclear spin contrast could be used to indirectly image electron spin polarization in GaAs-based spintronic devices. © 2002 American Institute of Physics.
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76.60.Es Relaxation effects
76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
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Electrical and dielectric behavior of MgO doped Ba0.7Sr0.3TiO3 thin films on Al2O3 substrate

S. Y. Lee and T. Y. Tseng

Appl. Phys. Lett. 80, 1797 (2002); http://dx.doi.org/10.1063/1.1458067 (3 pages) | Cited 41 times

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In this letter, we present the results of the fabrication and characterization of 5 mol % MgO doped Ba0.7Sr0.3TiO3 (BST) films grown on Pt/TiN/SiO2 coated on Al2O3 substrates using the rf magnetron sputtering technique. The dielectric and electrical properties of Ba0.7Sr0.3TiO3 thin film were found to improve obviously by means of MgO doping. The leakage current density of BST thin film decreased about 1 order of magnitude on MgO doping, while BST film with MgO doping had a higher dielectric constant than that without MgO doping. The dielectric constant of the films increased with increasing annealing temperature due to the consistent increase in grain size and crystallinity. The 750 °C annealed, 100 nm thick film indicated a high dielectric constant of 440 at 100 kHz and the lattice constant of 3.986 Å. The improvement of the electrical properties of BST films was associated with the reduced oxygen vacancies due to improved oxygenation of BST films in the presence of MgO. The MgO doped BST films exhibited a high tunability of 25% and dc resistivity of 6×1010 Ω cm at an applied electric field of 200 kV/cm. The time-dependent dielectric breakdown studies indicated that the films had a longer lifetime of over 10 yrs on operation at the electric field of 0.4 MV/cm which is better than undoped BST film. © 2002 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
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)
81.15.Cd Deposition by sputtering
77.22.Jp Dielectric breakdown and space-charge effects
61.72.J- Point defects and defect clusters

Electrical characterization of metal–insulator–semiconductor capacitors with xerogel as dielectric

E. Anulekha Manjari, A. Subrahmanyam, N. DasGupta, and A. DasGupta

Appl. Phys. Lett. 80, 1800 (2002); http://dx.doi.org/10.1063/1.1458065 (3 pages) | Cited 2 times

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Xerogel films have been prepared on p-type silicon (pSi) substrates by the sol–gel process using hexamethyldisilazane for surface modification. The dielectric constants of the films are in the range of 1.9–2.5. Detailed electrical characterization has been carried out using an aluminum–xerogel–pSi metal–insulator–semiconductor structure. Low values of fixed oxide charges, mobile oxide charges, and interface state densities have been obtained. The low leakage current density and high breakdown field strength of these films make them suitable for intermetal isolation. Very little degradation of the film properties was observed even after 40 days without any capping layer. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
77.55.-g Dielectric thin films
81.05.Rm Porous materials; granular materials
82.70.Gg Gels and sols
81.05.Cy Elemental semiconductors
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
85.30.Tv Field effect devices
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects
81.05.Bx Metals, semimetals, and alloys
85.40.Ls Metallization, contacts, interconnects; device isolation
73.20.At Surface states, band structure, electron density of states

Direct observation of atomic disordering at the SrTiO3/Si interface due to oxygen diffusion

V. Shutthanandan, S. Thevuthasan, Y. Liang, E. M. Adams, Z. Yu, and R. Droopad

Appl. Phys. Lett. 80, 1803 (2002); http://dx.doi.org/10.1063/1.1456261 (3 pages) | Cited 11 times

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The stability of epitaxially grown single crystal SrTiO3(001) thin films on Si(100) substrates was studied as a function of temperature under vacuum and oxygen-rich environments using Rutherford backscattering spectrometry in channeling geometry, nuclear reaction analysis, and x-ray photoelectron spectroscopy. During vacuum annealing, it was found that interfacial silica formed due to diffusion of oxygen from the film to Si. This was further accompanied by the atomic disordering of Sr, Ti, and O sublattices in the film due to reduction reactions. Although the interfacial degradation process is similar during heating in oxygen environment, no disordering of the film was observed. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.Cc Kinetics of defect formation and annealing

Scanning probe microscopy of well-defined periodically poled ferroelectric domain structure

M. Shvebelman, P. Urenski, R. Shikler, G. Rosenman, Y. Rosenwaks, and M. Molotskii

Appl. Phys. Lett. 80, 1806 (2002); http://dx.doi.org/10.1063/1.1456967 (3 pages) | Cited 14 times

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We analyze and determine the factors governing the contrast in contact mode atomic force microscopy of domain-structured ferroelectric crystals. The analysis is applied to measurements conducted on KTiOPO4 crystals with artificially created well-defined domain structure. It is found that the amplitude contrast is due to difference in the work functions of the antiparallel domains. © 2002 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
77.22.Ej Polarization and depolarization

In situ x-ray scattering study of PbTiO3 chemical-vapor deposition

M. V. Ramana Murty, S. K. Streiffer, G. B. Stephenson, J. A. Eastman, G.-R. Bai, A. Munkholm, O. Auciello, and Carol Thompson

Appl. Phys. Lett. 80, 1809 (2002); http://dx.doi.org/10.1063/1.1458530 (3 pages) | Cited 15 times

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We present in situ surface x-ray scattering measurements of PbTiO3 epitaxy by metal–organic chemical-vapor deposition. Oscillations in crystal truncation rod intensity corresponding to layer-by-layer growth are observed under a variety of growth conditions. At lower PbO overpressures, we observe a transition to step-flow growth and an increased rate of recovery after growth, indicating a higher surface mobility. © 2002 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
61.05.cf X-ray scattering (including small-angle scattering)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.70.Ck X-ray scattering
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
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Dispersion, refinement, and manipulation of single silicon nanowires

J. Z. He, J. B. Xu, M. S. Xu, Z. Xie, I. H. Wilson, X. L. Ma, Q. Li, N. Wang, L. S. Hung, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 80, 1812 (2002); http://dx.doi.org/10.1063/1.1456966 (3 pages) | Cited 1 time

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We have successfully dispersed silicon nanowires in liquid by a mild etching treatment. A transmission electron microscopic study reveals that the etching occurs selectively at the defect sites of the wires. This implies that the treated wires have much fewer defects than those of the raw material. We have adopted an electrophoresis method, which is usually used in biosciences, to mount single nanowires onto chosen electrodes of a prototype device. The mounting of the wires was checked using scanning probe microscopes. Compared with the commonly used microactuation method, our method is far more applicable to industrial device fabrication, which may require simultaneous manipulation of a large number of wires. © 2002 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
81.15.Pq Electrodeposition, electroplating
81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
61.46.-w Structure of nanoscale materials
68.37.Ps Atomic force microscopy (AFM)
68.37.Lp Transmission electron microscopy (TEM)

Simple method to prepare individual suspended nanofibers

Gyu-Tae Kim, Gang Gu, Ulrike Waizmann, and Siegmar Roth

Appl. Phys. Lett. 80, 1815 (2002); http://dx.doi.org/10.1063/1.1458533 (3 pages) | Cited 26 times

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A simple and general technique for producing a suspended nanofiber has been developed using coordinate markers and a sacrificial layer of poly(methylmethacrylate). The simple procedure does not involve etching processes or chemical vapor deposition and makes it easier to investigate the physical properties of nanofibers in a suspended configuration. As a demonstration, a suspended carbon nanotube rope was fabricated and Young’s modulus was determined to be 0.4 TPa from the force calibration of an atomic force microscope. © 2002 American Institute of Physics.
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81.07.De Nanotubes
81.07.Bc Nanocrystalline materials
62.20.D- Elasticity
61.46.-w Structure of nanoscale materials

Strongly capacitively coupled quantum dots

I. H. Chan, R. M. Westervelt, K. D. Maranowski, and A. C. Gossard

Appl. Phys. Lett. 80, 1818 (2002); http://dx.doi.org/10.1063/1.1456552 (3 pages) | Cited 5 times

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Double quantum dots were formed in a gated GaAs/AlGaAs heterostructure with negligible interdot tunneling; strong capacitive coupling was provided by a floating interdot capacitor. The interdot capacitance was measured to be 0.28CΣ, where CΣ is the single-dot capacitance. Coulomb blockade conductance images for both dots versus side gate voltages at 70 mK show a hexagonal pattern of peaks; the double dot acts as a single-electron current switch. For weak tunneling, the conductance peaks of both dots fit thermally broadened line shapes. Charge fluctuations produced by strong tunneling on one dot are induced on the second, filling in its peak splitting. © 2002 American Institute of Physics.
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73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling

Field emission from well-aligned carbon nanotips grown in a gated device structure

C. L. Tsai, C. F. Chen, and C. L. Lin

Appl. Phys. Lett. 80, 1821 (2002); http://dx.doi.org/10.1063/1.1459109 (2 pages) | Cited 13 times

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Vertically well-aligned, high-aspect-ratio carbon nanotips have been directly grown upward on the gated device structure with 4 μm gate aperture. The nanotips rapidly nucleate and grow without any catalyst. In addition, selected area deposition of nanotips is achieved by using a Pt layer as inhibitor in the bias-assisted microwave plasma chemical vapor deposition. The field emission current of nanotips on the gated structure is 154 μA (at a gate-to-cathode voltage of Vgc = 50 V). This results from the following reasons: (i) short gate-tips spacing, (ii) small gate aperture, and (iii) the high-aspect ratio of nanotips. © 2002 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters
81.07.De Nanotubes
85.35.Kt Nanotube devices
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes

Growth and properties of Cu3N films and Cu3N/γ′-Fe4N bilayers

D. M. Borsa, S. Grachev, C. Presura, and D. O. Boerma

Appl. Phys. Lett. 80, 1823 (2002); http://dx.doi.org/10.1063/1.1459116 (3 pages) | Cited 34 times

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Copper nitride films were grown by molecular-beam epitaxy of copper in the presence of nitrogen from a radio-frequency atomic source on (001) γ′-Fe4N/(001)MgO or directly on MgO substrates. The structural properties of the Cu3N films were found to be very dependent on the substrate and on the deposition temperature. At optimal growth conditions, the Cu3N films grow epitaxial on both substrates. The Cu3N films grown on MgO were characterized optically to be insulators with an energy gap of 1.65 eV. On γ′-Fe4N, Cu3N films with a thickness of only 6 nm, were grown as closed layers, epitaxial and rather smooth (root-mean-square roughness of 0.7 nm). This material has ideal properties to be used as a barrier in low resistance magnetic tunnel junctions. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.61.Ng Insulators
78.66.Nk Insulators
68.35.B- Structure of clean surfaces (and surface reconstruction)

Resonant light scattering from individual Ag nanoparticles and particle pairs

Hiroharu Tamaru, Hitoshi Kuwata, Hideki T. Miyazaki, and Kenjiro Miyano

Appl. Phys. Lett. 80, 1826 (2002); http://dx.doi.org/10.1063/1.1461072 (3 pages) | Cited 93 times

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Light scattering by individual Ag nanoparticles and structures have been studied spectroscopically. Individual particles were selected and manipulated with a micromanipulator installed inside a scanning electron microscope (SEM). With typical particle dimensions of some 100 nm, the plasma resonances of particles and the coupled modes of particle pairs were observed in the visible region. The polarization dependence of the resonance frequencies strongly reflects the shape anisotropy; the effect that would be averaged out for experiments on ensembles. With a simple approximation to take the glass substrate into account, the results are in good agreement with the analytical calculations by Mie scattering, and with numerical calculations by the finite-difference time-domain method, both of which are performed with the morphological parameters obtained from the SEM observation for the corresponding particle or particle pair. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.35.+c Brillouin and Rayleigh scattering; other light scattering
73.22.Lp Collective excitations
78.40.Kc Metals, semimetals, and alloys
61.46.-w Structure of nanoscale materials

Correlation of surface molecular composition to nanoscale elastic behavior and topography of stretched polyurethane films

E. Amitay-Sadovsky, K. Komvopoulos, Y. Tian, and G. A. Somorjai

Appl. Phys. Lett. 80, 1829 (2002); http://dx.doi.org/10.1063/1.1458526 (3 pages) | Cited 4 times

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Correlation of the surface molecular composition with the nanoscale elastic behavior and topography of stretched polyurethane films was examined by surface-specific techniques, such as sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM). Identification of the SFG spectra of the soft and hard copolymer segments elucidated changes in the molecular composition due to stretching. The surface molecular composition is correlated to AFM results for the roughness and elastic modulus. It is shown that, in addition to molecular reorientation, stretching promotes exposure of hard segments at the surface, and that this is a continuous time-dependent process at constant elongation. © 2002 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
68.37.Ps Atomic force microscopy (AFM)
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
63.50.-x Vibrational states in disordered systems
62.20.D- Elasticity
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