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17 Jun 2002

Volume 80, Issue 24, pp. 4483-4665

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A study of subbands in AlGaN/GaN high-electron-mobility transistor structures using low-temperature photoluminescence spectroscopy

C. Y. Fang, C. F. Lin, Edward Yi Chang, and M. S. Feng

Appl. Phys. Lett. 80, 4558 (2002); http://dx.doi.org/10.1063/1.1485310 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2002

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Al0.15Ga0.85N/GaN high-electron-mobility transistor (HEMT) structures with various δ-doping concentrations and spacer thicknesses grown on sapphire by metalorganic chemical-vapor deposition are investigated. The Hall mobility is as high as 1333 cm2/V s at room temperature and 6330 cm2/V s at 77 K. Two-dimensional electron gas (2DEG) phenomena, which have not been clearly resolved in the literature, are observed by photoluminescence (PL) spectra at low temperature in this study. The PL spectra peaks of the interband transitions from 2DEG subbands to the valence band are in the range from 3.486 to 3.312 eV. The effects of the strain caused by different Al fractions of the top layer, and that of the spacer thickness on the 2DEG phenomena are discussed. Redshifts due to temperature variations for various HEMT structures are observed in 2DEG subbands and in the band-edge emission, which is believed to be evidence of interband transitions from 2DEG subbands to valence bands. © 2002 American Institute of Physics.
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85.30.Tv Field effect devices
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.20.At Surface states, band structure, electron density of states
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Ferromagnetic properties of Zn1−xMnxO epitaxial thin films

S. W. Jung, S.-J. An, Gyu-Chul Yi, C. U. Jung, Sung-Ik Lee, and Sunglae Cho

Appl. Phys. Lett. 80, 4561 (2002); http://dx.doi.org/10.1063/1.1487927 (3 pages) | Cited 267 times

Online Publication Date: 10 June 2002

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We report on ferromagnetic characteristics of Zn1−xMnxO (x = 0.1 and 0.3) thin films grown on Al2O3(00⋅1) substrates using laser molecular-beam epitaxy. By increasing the Mn content, the films exhibited increases in both the c-axis lattice constant and fundamental band gap energy. The Curie temperature obtained from temperature-dependent magnetization curves was 45 K for the film with x = 0.3, depending on the Mn composition in the films. The remanent magnetization and coercive field of Zn0.9Mn0.1O at 5 K were 0.9 emu/g and 300 Oe, respectively. For Zn0.7Mn0.3O, the remanent magnetization at 5 K increased to 3.4 emu/g. © 2002 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Discrete surface state related to nitrogen-vacancy defect on plasma-treated GaN surfaces

Tamotsu Hashizume and Ryusuke Nakasaki

Appl. Phys. Lett. 80, 4564 (2002); http://dx.doi.org/10.1063/1.1485309 (3 pages) | Cited 23 times

Online Publication Date: 10 June 2002

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Detailed studies on the defect-related surface states of plasma-exposed n-GaN surfaces were carried out. An anomalous flat portion appeared in the metal–insulator–semiconductor capacitance–voltage characteristics for the sample exposed to H2 plasma, corresponding to a localized peak at EC−0.5 eV in the surface state density distribution. Atomic-force microscope and x-ray photoemission studies revealed the formation of Ga droplets on H2-plasma-treated GaN surfaces, caused by the desorption of nitrogen atoms in the form of NHx. These results suggested that a nitrogen-vacancy-related state near the conduction-band edge was introduced on the H2-plasma-treated GaN surface. No such effects took place on the N2-plasma-treated GaN surfaces. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Dv Composition, segregation; defects and impurities
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
61.72.J- Point defects and defect clusters

Detection of single charges and their generation-recombination dynamics in Si nanowires at room temperature

Akira Fujiwara, Kenji Yamazaki, and Yasuo Takahashi

Appl. Phys. Lett. 80, 4567 (2002); http://dx.doi.org/10.1063/1.1487451 (3 pages) | Cited 12 times

Online Publication Date: 10 June 2002

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Detection of single electrons and single holes is demonstrated at room temperature in Si nanowire transistors using an electron-hole (e–h) system. Photogenerated carriers are stored in a quantum dot electrically formed in a Si wire by a front gate. The stored charges affect the current of the other type of carriers that flow along the bottom of the Si wire. The linear photoresponce of single-charge generation is observed. It is revealed that the recombination occurs by a bimolecular process, suggesting that it is due to the e–h interband transition. These results open up the possibility of developing single-photon devices with this system. © 2002 American Institute of Physics.
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73.63.Nm Quantum wires
73.21.Hb Quantum wires
73.63.Bd Nanocrystalline materials
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.22.-f Electronic structure of nanoscale materials and related systems
85.35.Gv Single electron devices

Defect-related density of states in low-band gap InxGa1−xAs/InAsyP1−y double heterostructures grown on InP substrates

T. H. Gfroerer, L. P. Priestley, F. E. Weindruch, and M. W. Wanlass

Appl. Phys. Lett. 80, 4570 (2002); http://dx.doi.org/10.1063/1.1487449 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2002

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We have measured the excitation-dependent radiative efficiency in a set of lattice-matched InxGa1−xAs/InAsyP1−y double heterostructures incrementally lattice mismatched to InP substrates. We find that the overall rate of defect-related recombination shows little change from the lattice-matched case. However, the excitation-dependent transition between defect-related and radiative recombination changes dramatically with mismatch. While a simple defect recombination model assuming defect levels concentrated near the middle of the band gap fits well for the lattice-matched material, the model does not fit the shape of the efficiency curve for the mismatched structures. We show that the addition of band edge exponential tails to the defect-related density of states gives a much better theoretical fit. © 2002 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.20.At Surface states, band structure, electron density of states
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
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Large low-field magnetoresistance and TC in polycrystalline (Ba0.8Sr0.2)2−xLaxFeMoO6 double perovskites

D. Serrate, J. M. De Teresa, J. Blasco, M. R. Ibarra, L. Morellón, and C. Ritter

Appl. Phys. Lett. 80, 4573 (2002); http://dx.doi.org/10.1063/1.1485119 (3 pages) | Cited 48 times

Online Publication Date: 10 June 2002

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Large low-field magnetoresistance (LFMR) together with high Curie temperatures (TC) are requirements for some applications in magnetoelectronics. In order to optimize both parameters, we have investigated double perovskites (Ba0.8Sr0.2)2−xLaxFeMoO6 (0 ⩽ x ⩽ 0.4). High-temperature neutron diffraction measurements indicate a strong increase in TC with La doping (from ≈345 K for x = 0 to ≈405 K for x = 0.4). The LFMR is very large for x = 0 (at 10 KOe ≈ 27% at 10 K and ≈7% at 290 K) and decreases with La doping. This decrease cannot be attributed to a substantial enhancement of Fe/Mo antisite disorder, which is small as tracked by means of x-ray and high-resolution neutron diffraction, but to grain boundaries modifications. © 2002 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.Mm Grain and twin boundaries

Orthogonal pinning of two ferromagnetic layers in a synthetic spin valve

Robert S. Beach, Jeffrey McCord, Patrick Webb, and Daniele Mauri

Appl. Phys. Lett. 80, 4576 (2002); http://dx.doi.org/10.1063/1.1485106 (3 pages) | Cited 5 times

Online Publication Date: 10 June 2002

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A method for pinning synthetic antiferromagnet (SAF) based spin valves is presented, which allows pinning to be established perpendicular to the setting field H. As the SAF(AP1/Ru/AP2) magnetizes, its layer moments undergo a spin–flop transition for a magnetic field H = HSF and align with H for H = HSat. The magnetization of layer AP1 is perpendicular to H for a field H = HGold. This field corresponds to the maximum giant magnetoresistance GMR on HSF<H<HSat for an unpinned SAF spin valve. SAF-pinned samples [antiferromagnet/AP1/Ru/AP2] set using H = HGold are mixed domain, with AP1 magnetized in two directions perpendicular to H, corresponding to left- and right-handed flopping. The spin–flop handedness may be controlled for a viable process. The technique offers substantial advantages to sensor stabilization schemes that rely on additional pinned ferromagnet/antiferromagnet layers, because these layers may be pinned orthogonal to the SAF without regard to the blocking temperatures of the respective antiferromagnets. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.Mg Numerical simulation studies
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.75.-c Magnetic properties of nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced transparency ramp-type Josephson contacts through interlayer deposition

Henk-Jan H. Smilde, Hans Hilgenkamp, Guus Rijnders, Horst Rogalla, and Dave H. A. Blank

Appl. Phys. Lett. 80, 4579 (2002); http://dx.doi.org/10.1063/1.1485305 (3 pages) | Cited 23 times

Online Publication Date: 10 June 2002

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A thin interlayer is incorporated in ramp-type Josephson junctions to obtain an increased transparency. The interlayer restores the surface damaged by ion milling and has the advantage of an all in situ barrier deposition between two superconductors, leading to clean and well-defined interfaces. The method has been applied to Josephson junctions between high (YBa2Cu3O7−δ) and low temperature (Nb) superconductors, separated by a Au barrier. Transmission electron microscopy images of these junctions reveal crystalline YBa2Cu3O7−δ up to the interface with the Au barrier. The junctions have improved critical current density values exceeding 20 kA/cm2, normal state resistances of 3×10−8 Ω cm2 and IcRn products of 0.7 mV at 4.2 K. Furthermore, the junction properties can be controlled by varying the Au barrier thickness. © 2002 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Spin polarized tunneling through single-crystal GaAs(001) barriers

S. Kreuzer, J. Moser, W. Wegscheider, D. Weiss, M. Bichler, and D. Schuh

Appl. Phys. Lett. 80, 4582 (2002); http://dx.doi.org/10.1063/1.1486044 (3 pages) | Cited 29 times

Online Publication Date: 10 June 2002

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We investigate spin-dependent transport through an epitaxial GaAs(001) barrier sandwiched between polycrystalline iron films. Electron transport through the barrier is dominated by quantum mechanical tunneling, demonstrated by a nonlinear I–V characteristic, an exponential dependence of the tunneling current on the barrier thickness and the temperature dependence of the current. Though small a clear tunneling magnetoresistance effect proves spin-dependent transport through the Fe–GaAs interface. The small size of the effect and the high-field magnetoresistance suggest that spin–flip scattering plays a decisive role in transport. © 2002 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
73.40.Sx Metal-semiconductor-metal structures
81.05.Ea III-V semiconductors
81.05.Bx Metals, semimetals, and alloys
73.61.Ey III-V semiconductors
75.45.+j Macroscopic quantum phenomena in magnetic systems
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
85.75.Mm Spin polarized resonant tunnel junctions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

Single-flux-quantum pump based on a three-junction superconducting quantum interference device

Yoshinao Mizugaki, Jian Chen, Satoshi Nishikata, Keiji Sugi, Kensuke Nakajima, and Tsutomu Yamashita

Appl. Phys. Lett. 80, 4585 (2002); http://dx.doi.org/10.1063/1.1485308 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2002

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We demonstrate the operation of a single-flux-quantum (SFQ) pump that is electromagnetically dual to the single-electron pump. The circuit is composed of a three-junction superconducting quantum interference device with three control lines. By applying two phase-shifted rf signals magnetically, the SFQ-pump transfers one SFQ per one cycle of the rf signals even at zero- and negatively-biased condition. The circuit was fabricated using a Nb/AlOx/Nb Josephson junction technology. When we fed rf signals of 4.5 GHz, we observed a Shapiro step crossing the zero-current axis. Periodic dependence of voltage at the zero-biasing state upon dc offset flux was also confirmed. © 2002 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Current-induced dendritic magnetic instability in superconducting MgB2 films

A. V. Bobyl, D. V. Shantsev, T. H. Johansen, W. N. Kang, H. J. Kim, E. M. Choi, and S. I. Lee

Appl. Phys. Lett. 80, 4588 (2002); http://dx.doi.org/10.1063/1.1485304 (3 pages) | Cited 21 times

Online Publication Date: 10 June 2002

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Magneto-optical imaging reveals that in superconducting films of MgB2 a pulse of transport current creates avalanche-like flux dynamics where highly branching dendritic patterns are formed. The instability is triggered when the current exceeds a threshold value, and the superconductor, shaped as a long strip, is initially in the critical state. The instability exists up to 19 K, which is a much wider temperature range than in previous experiments, where dendrites were formed by a slowly varying magnetic field. The instability is believed to be of thermomagnetic origin indicating that thermal stabilization may become crucial in applications of MgB2. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
74.25.Gz Optical properties
78.20.Ls Magneto-optical effects
68.60.Dv Thermal stability; thermal effects
74.25.Bt Thermodynamic properties

Spin-filter diode based on ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures

Yong Guo, Xin-Yi Chen, Feng Zhai, Bing-Lin Gu, and Yoshiyuki Kawazoe

Appl. Phys. Lett. 80, 4591 (2002); http://dx.doi.org/10.1063/1.1485121 (3 pages) | Cited 20 times

Online Publication Date: 10 June 2002

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We propose and demonstrate a spin-filter diode based on semimagnetic semiconductor ZnSe/Zn1−xMnxSe/Zn1−yMnySe/ZnSe heterostructures. It is found that the degree of spin polarization greatly depends on the electric field direction and its magnitude. There is significant difference of the spin polarization between under forward bias and under reverse bias. It is also found that the spin polarization will reverse under relatively small magnetic field, which is originated from resonant enhancement effect for spin-up electrons tunneling through effective steplike potential of the corresponding structure. © 2002 American Institute of Physics.
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85.75.Mm Spin polarized resonant tunnel junctions
72.25.Mk Spin transport through interfaces
75.50.Pp Magnetic semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
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Critical properties of nanoporous low dielectric constant films revealed by Brillouin light scattering and surface acoustic wave spectroscopy

C. M. Flannery, T. Wittkowski, K. Jung, B. Hillebrands, and M. R. Baklanov

Appl. Phys. Lett. 80, 4594 (2002); http://dx.doi.org/10.1063/1.1478775 (3 pages) | Cited 24 times

Online Publication Date: 10 June 2002

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Thin porous films with nanometer pore sizes are the subject of intense interest, primarily because of their reduced dielectric constant k. The lack of useful characterization tools and the reduction in film mechanical properties with increasing porosity have severely hindered their development and application. We show that both Brillouin light scattering and surface acoustic wave spectroscopy allow one to measure density, porosity and stiffness properties of nanoporous methylsilsesquioxane films of low-k value. Excellent correlations are observed among independent measurements of density, porosity and the Young’s modulus which show that the results obtained are reliable and reveal properties of the films which are difficult or impossible to obtain using other techniques. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
81.05.Rm Porous materials; granular materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
61.43.Gt Powders, porous materials
77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Qn Polymers; organic compounds
68.35.Iv Acoustical properties
62.20.D- Elasticity

On the role of interface states in low-voltage leakage currents of metal–oxide–semiconductor structures

F. Crupi, C. Ciofi, A. Germanò, G. Iannaccone, J. H. Stathis, and S. Lombardo

Appl. Phys. Lett. 80, 4597 (2002); http://dx.doi.org/10.1063/1.1487450 (3 pages) | Cited 11 times

Online Publication Date: 10 June 2002

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This work investigates the additional gate current component with respect to the direct tunneling of electrons between the conduction bands measured in ultrathin oxide metal–oxide–semiconductor field-effect transistors at low voltages, before and after the application of a high field stress. We discuss several possible conduction mechanisms on the basis of the band diagram profiles obtained by means of a one-dimensional self-consistent Poisson–Schrodinger solver and we explain why this additional leakage current is mainly due to electron tunneling involving the native and stress-induced interface states in the silicon band gap either at the cathode or at the anode. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling

Effects of ultrathin tantalum seeding layers on sol-gel-derived SrBi2Ta2O9 thin films

Ching-Chich Leu, Chao-Hsin Chien, Ming-Jui Yang, Ming-Che Yang, Tiao-Yuan Huang, Hung-Tao Lin, and Chen-Ti Hu

Appl. Phys. Lett. 80, 4600 (2002); http://dx.doi.org/10.1063/1.1486043 (3 pages) | Cited 5 times

Online Publication Date: 10 June 2002

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The effects of Ta seeding layer on the crystalline microstructure and ferroelectric properties of sol-gel-derived strontium–bismuth–tantalate (SBT) thin films were investigated. Ultrathin (<1 nm) Ta seeding layers were deposited onto Pt/TiO2/SiO2/Si substrates by magnetron sputtering at room temperature before spin coating of SBT thin films. Our results show that the presence of Ta seed layer induces significant changes in the crystallinity and microstructure of the resultant SBT thin films, resulting in improved ferroelectric properties in terms of spontaneous polarization. Interestingly, the remanent polarization (2Pr) of SBT films is also found to initially increase and then decrease with increasing Ta thickness, showing a peak value of 18.8 μC/cm2 (@5 V) at Ta thickness of around 0.23 nm. Since a stoichiometric SBT solution was employed in our experiments, the additional Ta on the Pt surface is thought to provide a Ta-rich environment for SBT films, which, in turn, results in lower nucleation activation energy for crystallization. © 2002 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
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.55.A- Nucleation and growth
77.80.-e Ferroelectricity and antiferroelectricity
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)
61.72.-y Defects and impurities in crystals; microstructure
77.22.Ej Polarization and depolarization

Degradation of the dielectric permittivity of a strongly oriented Ba0.25Sr0.75TiO3 layer by replacing a SrRuO3 electrode with an Ag one

Yu. A. Boikov and T. Claeson

Appl. Phys. Lett. 80, 4603 (2002); http://dx.doi.org/10.1063/1.1485318 (3 pages) | Cited 5 times

Online Publication Date: 10 June 2002

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Films of (Ba,Sr)TiO3 have been deposited with a quality allowing a ferroelectric Curie–Weiss behavior to be seen and a study of the influence of electrode material and interfaces in a capacitor. The measured value of the real part of the dielectric permittivity, ε′, of a 700 nm thick Ba0.25Sr0.75TiO3 layer decreased three times at temperatures around the Curie point, when one of the two SrRuO3 electrodes (the top one) was replaced with a silver one. This may be interpreted as if there were a series capacitance, Cs, at the ferroelectric-to-metal electrode. From the decreased ε′, Cs = 1.2 μF/cm2 was estimated for the Ag/Ba0.25Sr0.75TiO3 interface, corresponding to a characteristic length of about 2.6 Å for the interface layer. © 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
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point

Measurement of piezoelectric coefficients of lead zirconate titanate thin films by strain-monitoring pneumatic loading method

Gun-Tae Park, Jong-Jin Choi, Jungho Ryu, Huiqing Fan, and Hyoun-Ee Kim

Appl. Phys. Lett. 80, 4606 (2002); http://dx.doi.org/10.1063/1.1487901 (3 pages) | Cited 22 times

Online Publication Date: 10 June 2002

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A method to simultaneously measure the longitudinal (d33) and transverse (d31) piezoelectric coefficients of a lead zirconate titanate (PZT) thin film was developed. This system was based on the pneumatic loading method but was modified to monitor the radial strain when a pressurized gas was introduced into the chamber. The results of the bulk piezoelectric material measured by this system coincided with that measured by both the Berlincourt method and the resonance method. The effective d33 and the real d31 of the PZT thin film fabricated by the sol-gel multiple coating method, and poled at 300 kV/cm were 125 and −60 pC/N, respectively. The real d33 estimated upon considering the constraints by the silicon substrate was 180 pC/N. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
77.55.-g Dielectric thin films
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
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Independent optically addressable nanoparticle-polymer optomechanical composites

S. R. Sershen, S. L. Westcott, N. J. Halas, and J. L. West

Appl. Phys. Lett. 80, 4609 (2002); http://dx.doi.org/10.1063/1.1481536 (3 pages) | Cited 33 times

Online Publication Date: 10 June 2002

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We report the fabrication and characterization of optomechanically active composite materials consisting of a thermally responsive poly(NIPAAm-co-AAm) hydrogel matrix incorporating a dilute concentration of Au or silica-Au core-shell nanoparticles. Under optical illumination at the resonance absorption wavelength of the nanoparticle dopant, a dramatic volume collapse of the composite occurs due to local photothermal heating of the NIPAAm matrix. Nanoparticle dopants were chosen so that each composite was specifically optically addressable, exhibiting optomechanical behavior at independent wavelengths. Such materials can be useful as independently addressable remotely triggerable switches and gates in a wide variety of micromechanical applications. © 2002 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
81.05.Qk Reinforced polymers and polymer-based composites
61.82.Rx Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.46.-w Structure of nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
82.35.Np Nanoparticles in polymers
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Room-temperature metallic behavior in nanophase polypyrrole

S. Bhattacharyya and S. K. Saha

Appl. Phys. Lett. 80, 4612 (2002); http://dx.doi.org/10.1063/1.1486475 (2 pages) | Cited 4 times

Online Publication Date: 10 June 2002

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An ultrathin layer of polypyrrole (PPy) phase has been grown on the pore wall of a nanoporous template using oxidation polymerization technique. This thin layer of PPy phase shows metallic behavior (positive temperature coefficient of resistance) up to room temperature (300 K) and a metal-insulator transition is observed at around room temperature. © 2002 American Institute of Physics.
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72.15.Nj Collective modes (e.g., in one-dimensional conductors)
73.61.Ph Polymers; organic compounds
71.30.+h Metal-insulator transitions and other electronic transitions
73.63.Bd Nanocrystalline materials
82.35.Cd Conducting polymers
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Color-selective semiconductor nanocrystal laser

Hans-Jürgen Eisler, Vikram C. Sundar, Moungi G. Bawendi, Michael Walsh, Henry I. Smith, and Victor Klimov

Appl. Phys. Lett. 80, 4614 (2002); http://dx.doi.org/10.1063/1.1485125 (3 pages) | Cited 121 times

Online Publication Date: 10 June 2002

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Theoretical predictions of the benefits of three-dimensional quantum confinement have provided motivation for the development of quantum-dot lasers. Such lasers, developed in the case of self-assembled quantum dots, have not been successfully demonstrated with quantum-confined colloidal nanocrystals (NCs). Here, using recently developed NC-titania chemistry, we report the successful development of an optically pumped, NC-based distributed feedback laser, in which the narrow gain profiles of these nanoparticles have been matched with the feedback of a second-order distributed feedback laser. This laser, whose output color can be selected by choosing appropriately sized nanocrystals, operates at 80 K and at room temperature. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
78.45.+h Stimulated emission

Fabrication of Si single-electron transistors having double SiO2 barriers

Yuhei Ito, Tsuyoshi Hatano, Anri Nakajima, and Shin Yokoyama

Appl. Phys. Lett. 80, 4617 (2002); http://dx.doi.org/10.1063/1.1485306 (3 pages) | Cited 6 times

Online Publication Date: 10 June 2002

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We fabricated Si single-electron transistors (SETs) having double SiO2 barriers and a polycrystalline Si (poly-Si) dot. The fabrication method of this device is completely compatible with the complementary metal–oxide–semiconductor technology, and the position of the poly-Si dot is self-aligned between the source and drain regions. The device exhibits drain current (Id) oscillation against gate voltage. From the dot size dependence of the electrical characteristics, the Id oscillation is considered to be due to the Coulomb blockade effect caused by poly-Si grains in the poly-Si dot. The self-alignment of the poly-Si dot in the fabrication process also means that the SET is promising for practical use. © 2002 American Institute of Physics.
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85.35.Gv Single electron devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Kv Quantum dots
73.23.Hk Coulomb blockade; single-electron tunneling
72.70.+m Noise processes and phenomena
81.05.Cy Elemental semiconductors
81.07.Ta Quantum dots

Temperature dependence of intersublevel absorption in InAs/GaAs self-assembled quantum dots

F. Bras, P. Boucaud, S. Sauvage, G. Fishman, and J.-M. Gérard

Appl. Phys. Lett. 80, 4620 (2002); http://dx.doi.org/10.1063/1.1487446 (3 pages) | Cited 21 times

Online Publication Date: 10 June 2002

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We have studied the temperature dependence of the intersublevel absorption in n-doped InAs/GaAs self-assembled quantum dots. The investigated intersublevel transition corresponds to the optical transition between the s-type conduction ground state to the p-type first excited states. These transitions, resonant between 20 and 22 μm, are in-plane polarized along the [110] and the [math10] directions. A redshift lower than 3 meV is observed for the transition resonance from low temperature to room temperature. While the effective barrier height from the ground state is around 150 meV, the integrated absorption amplitude decreases by a factor of 4 from low temperature to room temperature. This decrease is modeled by the thermionic emission of the carriers, taking into account the density of states of the two-dimensional wetting layer, the density of states of the three-dimensional bulk layer surrounding the dots and the existence of polaron states associated with the strong electron-phonon coupling in the dots. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
73.21.La Quantum dots
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
73.20.At Surface states, band structure, electron density of states
71.38.-k Polarons and electron-phonon interactions
63.20.K- Phonon interactions

Mechanical properties of high-aspect-ratio atomic-force microscope tips

G. Jänchen, P. Hoffmann, A. Kriele, H. Lorenz, A. J. Kulik, and G. Dietler

Appl. Phys. Lett. 80, 4623 (2002); http://dx.doi.org/10.1063/1.1485307 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2002

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Focused-electron-beam-deposited carbon atomic-force microscope tips were characterized using flexural vibrations excited with piezoelectric transducers and observed directly inside a scanning electron microscope. Frequencies in the high-MHz range were measured and the elastic modulus was estimated to be 0.54±0.16 TPa. © 2002 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
81.05.U- Carbon/carbon-based materials
07.79.Lh Atomic force microscopes
68.35.Ja Surface and interface dynamics and vibrations
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
62.20.D- Elasticity

Electrically isolated SiGe quantum dots

Emma Tevaarwerk, P. Rugheimer, O. M. Castellini, D. G. Keppel, S. T. Utley, D. E. Savage, M. G. Lagally, and M. A. Eriksson

Appl. Phys. Lett. 80, 4626 (2002); http://dx.doi.org/10.1063/1.1484251 (3 pages) | Cited 2 times

Online Publication Date: 10 June 2002

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A variation of electric force microscopy (EFM) is used to measure the electrical isolation of SiGe quantum dots (QDs). The SiGe QDs are grown on mesas of ultrathin silicon on insulator. Near the mesa edges, the thin silicon layer has been incorporated into the QDs, resulting in electrically isolated QDs. Away from the edges, the silicon layer is not incorporated and has a two-dimensional resistivity of less than 800 TΩ per sq, resulting in relatively short RC times for charge flow on the mesa. The EFM technique we use here is a powerful probe of samples and devices with floating-gate geometries. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.16.Dn Self-assembly
73.63.Kv Quantum dots

Nanometer-sized optical waveguides fabricated by anodic oxidation using a scanning near-field optical microscope

T. Onuki, T. Tokizaki, Y. Watanabe, T. Tsuchiya, and T. Tani

Appl. Phys. Lett. 80, 4629 (2002); http://dx.doi.org/10.1063/1.1486479 (3 pages) | Cited 10 times

Online Publication Date: 10 June 2002

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We have fabricated an optical waveguide with a subwavelength cross section that propagates light. A metal–oxide core is partially embedded into a metal clad by anodic oxidation using the probe tip of a scanning near-field optical microscope (SNOM). Then, using the SNOM in transmission mode we have evidence of light propagating more than 5 μm in the waveguide whose core width and thickness are 300 and 70 nm, respectively. © 2002 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
81.16.Pr Micro- and nano-oxidation
07.79.Fc Near-field scanning optical microscopes
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