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19 Oct 1998

Volume 73, Issue 16, pp. 2233-2380

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Ultraviolet cathodoluminescence from diamond layers after doping by means of boron-ion implantation

Johan F. Prins

Appl. Phys. Lett. 73, 2308 (1998); http://dx.doi.org/10.1063/1.121806 (3 pages) | Cited 2 times

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Boron-doped diamond layers have been generated in insulating (type IIa) diamonds by means of ion implantation. Cathodoluminescence measurements were used to monitor the layers during this process. It was found that the activation of the boron acceptors, followed by suitable annealing, gave rise to the appearance of two ultraviolet luminescence bands around 3.5 and 4.6 eV. These same bands had been observed previously in natural, as well as synthetically grown, boron-doped, type IIb diamonds. The results reported in this study, support the conclusion that these bands are related to the presence of boron acceptors and show, in addition, that the acceptor density NA need not be more than the density of the compensating donors ND, as had been postulated. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.up Other materials
61.80.Jh Ion radiation effects
81.05.ub Fullerenes and related materials
81.05.Cy Elemental semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Db Elemental semiconductors and insulators
61.72.Cc Kinetics of defect formation and annealing
71.55.Cn Elemental semiconductors
73.61.Cw Elemental semiconductors

Void-like defects in annealed Czochralski silicon

M. Gao, X. F. Duan, L.-M. Peng, and J. Li

Appl. Phys. Lett. 73, 2311 (1998); http://dx.doi.org/10.1063/1.121807 (2 pages) | Cited 1 time

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Void-like defects of octahedron structure having {111} facets were observed in annealed Czochralski silicon. The amorphous coverage of SiOx and SiCx on the inner surface of the defects was identified using transmission electron microscopy and electron energy-loss spectroscopy. It is suggested that these defects are a kind of amorphous precipitate origin. A mechanism for the generation of these defects and the previously reported solid amorphous precipitates is proposed. © 1998 American Institute of Physics.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.05.Cy Elemental semiconductors
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing
79.20.Kz Other electron-impact emission phenomena

Refractive index and absorption of GaAs quantum wells across excitonic resonances

M. V. Marquezini, J. Tignon, T. Hasche, and D. S. Chemla

Appl. Phys. Lett. 73, 2313 (1998); http://dx.doi.org/10.1063/1.121808 (3 pages) | Cited 7 times

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We present simultaneous measurement of the refractive index and absorption coefficient in a AlGaAs/GaAs multiple quantum well structure near the band gap by Fourier transform spectral interferometry. Both quantities were measured across heavy- and light-hole excitons for temperatures ranging from liquid helium to room temperature. The experimental results are analyzed using an analytical expression for the complex dielectric function of Wannier excitons in fractional dimension. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Observation of a leaky wave guide resonance mode in polycrystalline silicon structures using infrared spectroscopic ellipsometry

F. Ferrieu

Appl. Phys. Lett. 73, 2316 (1998); http://dx.doi.org/10.1063/1.122506 (3 pages)

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Optical constants of polycrystalline silicon, used as the gate electrode material in semiconductor technology, have been analyzed by infrared spectroscopic ellipsometry. In the optical refractive indices n, k of the polycrystalline silicon material, we observed an unexpected absorption resonance at 1280 cm−1. The same effect is seen with different layer thicknesses and different polycrystalline texture. The absorption peak is not seen with an additional capping silicon oxide layer on top of the stack. This effect does not arise from an intrinsic absorption of the polysilicon but rather because of a longitudinal mode excitation present in the underlying silicon oxide layer. In the oxide infrared reststrahlen band, the incident electromagnetic radiation is totally reflected at the polysilicon/oxide interface. Further evidence for the mechanism is obtained from observation of a polysilicon/nitride/silicon sample. © 1998 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.40.Ty Semiconductor-insulator-semiconductor structures
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
42.79.Gn Optical waveguides and couplers

Photoinduced and thermal stress in silicon microcantilevers

Panos G. Datskos, Slobodan Rajic, and Irene Datskou

Appl. Phys. Lett. 73, 2319 (1998); http://dx.doi.org/10.1063/1.121809 (3 pages) | Cited 26 times

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The photogeneration of free charge carriers in a semiconductor gives rise to mechanical strain. We measured the deflection of silicon microcantilevers resulting from photoinduced stress. The excess charge carriers responsible for the photoinduced stress, were produced via photon irradiation from a diode laser with wavelength λ = 780 nm. For Si microcantilevers, the photoinduced stress is of opposite direction and about four times larger than the stress resulting from only thermal excitation. In this letter we report on our study of the photoinduced stress in silicon microcantilevers and discuss their temporal and photometric response. © 1998 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
72.40.+w Photoconduction and photovoltaic effects
81.05.Cy Elemental semiconductors
62.20.F- Deformation and plasticity
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Structure and photoluminescence of single AlGaAs/GaAs quantum dots grown in inverted tetrahedral pyramids

Arno Hartmann, Yann Ducommun, Laurent Loubies, Klaus Leifer, and Eli Kapon

Appl. Phys. Lett. 73, 2322 (1998); http://dx.doi.org/10.1063/1.121810 (3 pages) | Cited 20 times

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Arrays of single GaAs/AlGaAs quantum dot (QD) heterostructures grown by organometallic chemical vapor deposition in inverted tetrahedral pyramids on {111}B GaAs substrates are investigated. Cross-sectional atomic force microscopy images evidence a pronounced thickening of the GaAs quantum well layer at the tip of the pyramid, giving rise to a lens-like QD structure. Low-temperature photoluminescence and cathodoluminescence spectra show distinct luminescence from the dots, exhibiting filling of QD states separated by 33 meV at increased carrier densities. Luminescence linewidths of 15 meV and line energy variations of less than 5 meV are obtained across mm2 sample areas. © 1998 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Cr III-V semiconductors
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors

Number of Cu atom(s) in the 1.014 eV photoluminescence copper center and the center’s model in silicon crystal

M. Nakamura, S. Ishiwari, and A. Tanaka

Appl. Phys. Lett. 73, 2325 (1998); http://dx.doi.org/10.1063/1.121811 (3 pages) | Cited 21 times

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Number of Cu atom(s) in the 1.014 eV copper center in silicon crystal was determined from an accurately measured relationship between the photoluminescence (PL) intensity of the center and Cu concentration in the crystal. For Cu concentrations lower than about 1×1014 atom/cm3, the PL intensity increased linearly with increasing Cu concentration. From this result and the law of mass action, it was concluded that the Cu center had only one Cu atom in it, contradicting the long-believed pair Cu model. Based on already published data and the present result, a structural model in which the Cu atom was bonded at the center of the Si–Si bond was presented for the Cu center. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
71.55.Cn Elemental semiconductors

Effect of curvature and stress on reaction rates at solid interfaces

J. Tersoff, Yuhai Tu, and G. Grinstein

Appl. Phys. Lett. 73, 2328 (1998); http://dx.doi.org/10.1063/1.121812 (3 pages) | Cited 11 times

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We analyze the effect of interface curvature and stress on reaction rates at solid–solid or solid–fluid interfaces. Curvature affects the forward and reverse reactions differently, and cannot be related simply to an interface energy. To describe the effect of stress requires at least two parameters each for forward and reverse reactions. The distribution of local configurations may be ignored to linear order; but beyond the linear regime, this effect can cause large deviations from the expected exponential dependence. © 1998 American Institute of Physics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.-w Chemical kinetics and dynamics
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies

Energy levels of Zn in Si1−XGeX alloys

S. Voß, H. Bracht, N. A. Stolwijk, P. Kringhøj, and A. Nylandsted Larsen

Appl. Phys. Lett. 73, 2331 (1998); http://dx.doi.org/10.1063/1.121813 (3 pages) | Cited 4 times

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Deep level transient spectroscopy measurements were performed on Zn-doped Si1−XGeX with X between 0 and 0.34. Our investigations reveal two deep hole traps which are attributed to the acceptor states Zn0/− and Zn−/2− of substitutional Zn. Taking into account band-offset data for Si1−XGeX, we have found that the energy level related to Zn0/− is horizontally aligned across the composition-dependent band gap which gives evidence for a highly localized defect state. The defect level related to the second hole trap decreases with increasing Ge content. © 1998 American Institute of Physics.
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71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photoluminescence decay dynamics of ion-irradiated porous silicon: Evidence for the absence of carrier migration

Satoshi Tanaka, Hideki Koyama, and Nobuyoshi Koshida

Appl. Phys. Lett. 73, 2334 (1998); http://dx.doi.org/10.1063/1.122453 (3 pages) | Cited 4 times

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We have measured the photoluminescence (PL) decay properties of porous silicon (PS) samples subjected to ion irradiation up to a dose of 1015 cm−2 at 30 kV. It is found that while the PL intensity decreases down to 1/100 of the initial value due to induced nonradiative recombination centers, its decay constant is unchanged. This observation is inconsistent with the hypothesis that photoexcited carriers migrate among the Si nanocrystallites in PS. The results are compared with those of PS samples subjected to thermal annealing instead of ion irradiation, where the PL quenching in this case is accompanied by a large reduction in the decay constant. Infrared absorption spectra of ion-irradiated samples show essentially no chemical bonding change. In contrast, those of the annealed samples show loss of hydrogen bonding and increase of surface oxidation. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
81.05.Cy Elemental semiconductors
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
61.50.Lt Crystal binding; cohesive energy
78.30.Am Elemental semiconductors and insulators
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.-p Spectroscopy of solid state dynamics
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Electrical properties of wafer-bonded GaAs/Si heterojunctions

Y. C. Zhou, Z. H. Zhu, D. Crouse, and Y. H. Lo

Appl. Phys. Lett. 73, 2337 (1998); http://dx.doi.org/10.1063/1.122454 (3 pages) | Cited 16 times

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This letter reports on the fabrication and electrical characterization of wafer-fused GaAs/Si heterojunctions. A detailed study of the effect of surface preparation on bonding GaAs to Si was performed. The current–voltage (I–V) characteristics of both n-GaAs/n-Si and p-GaAs/p-Si were measured from 77 K to room temperature. The forward I–V characteristics were analyzed using a numerical model that includes thermionic emission across the heterojunction. Specifically, a p-GaAs/p-Si heterointerface of high electrical quality was obtained by direct hydrophobic bonding. © 1998 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
81.05.Cy Elemental semiconductors
81.65.-b Surface treatments
68.35.Gy Mechanical properties; surface strains

Gettering of Cu and Ni in mega-electron-volt ion-implanted epitaxial silicon

Sergei Koveshnikov and Oleg Kononchuk

Appl. Phys. Lett. 73, 2340 (1998); http://dx.doi.org/10.1063/1.122455 (3 pages) | Cited 14 times

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Gettering of Cu and Ni by 2.3 MeV Si ion-implantation-induced defects has been investigated in epitaxial silicon as a function of annealing temperature, time, and cooling rate. Secondary ion mass spectrometry revealed two distinct gettering regions, the position of which correlated with the ion projected range Rp and approximately half of Rp. Gettering experiments performed on samples with low metal impurity concentration have shown that capture of Cu and Ni in the two gettering regions occurred during high-temperature annealing, indicating a segregation-induced gettering mechanism. The binding energies of Cu and Ni are higher in the shallow Rp/2 region than in the Rp region. © 1998 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
81.05.Cy Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.80.Jh Ion radiation effects
61.72.uf Ge and Si
71.55.Cn Elemental semiconductors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.Cc Kinetics of defect formation and annealing
81.65.Tx Gettering

Origin of the charge to breakdown distributions in thin silicon dioxide films

S. Okhonin and P. Fazan

Appl. Phys. Lett. 73, 2343 (1998); http://dx.doi.org/10.1063/1.121686 (2 pages) | Cited 2 times

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This letter shows that in thin silicon dioxide films the charge to breakdown distribution can have two origins. It can be related to the oxide thickness variation across the wafer or to the statistical nature of the breakdown event. The oxide nonuniformity is a major factor in the case of stress-induced-bulk-charge enhanced breakdown. © 1998 American Institute of Physics.  
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77.22.Jp Dielectric breakdown and space-charge effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
73.61.Ng Insulators
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Direct-coupled second-order superconducting quantum interference device gradiometer from single layer of high temperature superconductor

Soon-Gul Lee, Yunseok Hwang, Byung-Chang Nam, Jin-Tae Kim, and In-Seon Kim

Appl. Phys. Lett. 73, 2345 (1998); http://dx.doi.org/10.1063/1.122456 (3 pages) | Cited 14 times

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We developed a noble design of the planar-type single-layer second-order superconducting quantum interference device (SQUID) gradiometer, and demonstrated that the gradiometer did not respond to a uniform field or the first-order gradient of the field but responded sensitively to the second-order gradient. The device consisted of three parallel-connected pickup loops, each of which is directly coupled to the step-edge junction SQUID. The entire structure was made from a single layer of YBa2Cu3O7 patterned by photolithography with ion milling technique. Response of the device to the field was tested with three identical wire-wound coils coupled to each loop and balancing was achieved by using a small piece of superconductor placed in the center loop. Measured off balance was about 0.6% for the uniform field and 1.4% for the first-order gradient, which were believed not due to intrinsic imbalance but mostly due to slight difference in alignment of the test coils. © 1998 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
74.72.-h Cuprate superconductors

Demonstration of a current-controlled three-terminal Nb–InxGa1−xAs/InP Josephson contact

Th. Schäpers, J. Malindretos, K. Neurohr, S. Lachenmann, A. van der Hart, G. Crecelius, H. Hardtdegen, H. Lüth, and A. A. Golubov

Appl. Phys. Lett. 73, 2348 (1998); http://dx.doi.org/10.1063/1.122457 (3 pages) | Cited 25 times

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The supercurrent in a Nb–In0.53Ga0.47As/In0.77Ga0.23As/InP weak link structure is controlled by means of a current injected into the two-dimensional electron gas. For small injection currents the critical current to control current ratio is as large as 20. The measured features can be qualitively explained in terms of a modification of the Andreev level occupation by the injected carriers. © 1998 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
85.30.-z Semiconductor devices
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.05.Ea III-V semiconductors
74.25.Sv Critical currents
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Flux pinning in ternary (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy melt-processed superconductors

M. R. Koblischka, M. Muralidhar, and M. Murakami

Appl. Phys. Lett. 73, 2351 (1998); http://dx.doi.org/10.1063/1.122458 (3 pages) | Cited 36 times

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The flux pinning characteristics of ternary melt-processed (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG) superconductors are studied in the temperature range 60 ⩽ T ⩽ 90 K. NEG samples exhibit a strongly developed peak effect in the dependence of the critical current densities on the external field, Ha. The scaling of the pinning forces versus the reduced field h = Ha/Hirr (where Hirr denotes the irreversibility field) yields a peak at h0 = 0.5 which is an indication of pinning provided by a spatial variation of the transition temperature. The presence of a weaker superconducting second phase is demonstrated by means of field cooling and warming experiments in fields up to 7 T. Furthermore, we discuss the possible effect of the magnetic moments of Gd and Nd on the flux pinning. © 1998 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.62.Yb Other effects

Superconductor–normal–superconductor Josephson junctions fabricated by oxygen implantation into YBa2Cu3O7−δ

F. Kahlmann, A. Engelhardt, J. Schubert, W. Zander, Ch. Buchal, and J. Hollkott

Appl. Phys. Lett. 73, 2354 (1998); http://dx.doi.org/10.1063/1.122459 (3 pages) | Cited 13 times

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We report Josephson junctions in YBa2Cu3O7−δ  films, fabricated by oxygen irradiation through a 50 nm wide slit in an implantation mask. After annealing the irradiated microbridges at 500 °C in an oxygen atmosphere, this process creates a homogeneous barrier region with a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of ⩽15 K. Over the entire temperature range of Josephson coupling these junctions show resistively shunted junction behavior. The exponential dependence of the critical current on temperature is in good agreement with conventional superconductor–normal–superconductor proximity effect theory. © 1998 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Cp Josephson devices
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
81.40.Gh Other heat and thermomechanical treatments
61.72.up Other materials
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
74.10.+v Occurrence, potential candidates
74.62.Dh Effects of crystal defects, doping and substitution
74.25.Sv Critical currents

Numerical modeling of superconducting coplanar resonators for radio frequency superconducting quantum interference devices

H. R. Yi, Y. Zhang, and A. I. Braginski

Appl. Phys. Lett. 73, 2357 (1998); http://dx.doi.org/10.1063/1.122460 (3 pages) | Cited 5 times

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We have simulated the superconducting coplanar resonators of different designs that we have fabricated and tested as the tank circuit of radio frequency superconducting quantum interference devices. The coplanar resonator is formed by two microstrip lines surrounding a flux concentrator with each line having a slit. The simulated resonant frequencies agreed well with the experimental values, where frequencies decreased with an increasing mutual angular position between the two microstrip slits, and with a short circuit between the two microstrip lines. The simulation also showed that the loss in the system is mainly contributed by the dielectric loss of the substrate materials. © 1998 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.40.Az Waveguides, transmission lines, striplines
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Strain-induced large low-field magnetoresistance in Pr0.67Sr0.33MnO3 ultrathin films

H. S. Wang and Qi Li

Appl. Phys. Lett. 73, 2360 (1998); http://dx.doi.org/10.1063/1.122461 (3 pages) | Cited 70 times

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We report magnetoresistance (MR) measurements in very thin Pr0.67Sr0.33MnO3 films (5–15 nm) grown on LaAlO3 (001) substrates. The films are under compressive strain imposed by the lattice mismatch with the substrate. The MR ratio [R(H)−R0]/R0 is ∼92% at H = 800 Oe and T = 70 K when the magnetic field is applied perpendicular to the film plane and is much smaller when the magnetic field is parallel to the film plane. We suggest that the large low-field MR is due to strain-induced magnetic anisotropy and spin-dependent scattering at domain boundaries. © 1998 American Institute of Physics.
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73.61.-r Electrical properties of specific thin films
75.70.Ak Magnetic properties of monolayers and thin films
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.De Giant magnetoresistance
68.60.Bs Mechanical and acoustical properties
75.30.Gw Magnetic anisotropy

Dielectric breakdown of ferromagnetic tunnel junctions

W. Oepts, H. J. Verhagen, W. J. M. de Jonge, and R. Coehoorn

Appl. Phys. Lett. 73, 2363 (1998); http://dx.doi.org/10.1063/1.122462 (3 pages) | Cited 44 times

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The time-dependent dielectric breakdown of Co/Al2O3/Co(-Fe) magnetic tunnel junctions is investigated. At voltages larger than 1.2 V, almost immediate breakdown of the junction is observed, leading to a decreased (magneto)resistance. The shorts, which are local hot spots, were visualized by making use of a liquid crystal film on top of the junction. The breakdown voltages of a series of nominally identical tunnel junctions measured in a voltage-ramp experiment are shown to increase with increasing ramp speed. The results are analyzed in the framework of several models for the voltage dependent breakdown probability. © 1998 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance
73.40.Rw Metal-insulator-metal structures
77.22.Jp Dielectric breakdown and space-charge effects
75.50.Cc Other ferromagnetic metals and alloys
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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Solvent-driven chemical motor

Tetsu Mitsumata, Kazuo Ikeda, Jian Ping Gong, and Yoshihito Osada

Appl. Phys. Lett. 73, 2366 (1998); http://dx.doi.org/10.1063/1.122505 (3 pages) | Cited 15 times

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A solvent-driven chemical motor using amphiphilic polymer gel has been fabricated. The driving force of the gel originates from the surface tension of spreading organic fluid which is pumped out by osmotic and hydrostatic pressures in the gel. A tetrahydrofurane-swollen gel equipped with a spouting hole made a controlled translational motion with a velocity of 77 mm/s or rotational motion with a maximum speed of 400 rpm and a torque of 10−9–10−7 Nm on the water surface. A generator to produce an electric power with a maximum electromotive force of 15 mV and electric power of 0.2 μW has also been constructed. The successful fabrication of gel motor may produce a new era of soft machine systems which work without pollution and unnecessary intermediates. © 1998 American Institute of Physics.  
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84.60.-h Direct energy conversion and storage
82.70.Gg Gels and sols
68.03.Cd Surface tension and related phenomena
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
83.80.Tc Polymer blends

Fabrication and characterization of small tunnel junctions through a thin dielectric membrane

A. Aassime, A. J. Manninen, and J. P. Pekola

Appl. Phys. Lett. 73, 2369 (1998); http://dx.doi.org/10.1063/1.122463 (3 pages)

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We show that a small tapered hole through a thin silicon nitride membrane provides a mask for tunnel junction structures. Our experiments imply, unlike in the conventional planar electron beam lithography, that tunnel junctions are well voltage biased in this structure with vanishingly small on-chip impedance. Our technique allows fabrication of double junctions, and even multijunction linear arrays, with small metallic islands in between. © 1998 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Ds Quantum interference devices
85.40.Hp Lithography, masks and pattern transfer
73.40.Gk Tunneling

An optoelectronic thyristor-based analog-to-digital converter for parallel processing

J. Cai and G. W. Taylor

Appl. Phys. Lett. 73, 2372 (1998); http://dx.doi.org/10.1063/1.122464 (3 pages)

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A single pixel optoelectronic analog-to-digital converter is described which is suitable for two-dimensional (2D) arrays as would be required for a digital optical signal processor. The conversion is based upon the use of an optoelectronic thyristor in the form of the double heterostructure optoelectronic switch as a comparator. Using the switch configured as a VCSEL and one field-effect transistor load device, the comparator delivers the binary output optically and, at the same time, provides an electrical output to combine with the input signal to determine the next lower order bit. The function is similar to the algorithmic electrical converter with several optoelectronic advantages. Resolution of 10 bits is expected at speeds of 100 MHz with scaled transistor technology. The compact size of the circuit and the algorithm suggest a viable approach for conversion of 2D data arrays in real time. © 1998 American Institute of Physics.
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85.60.-q Optoelectronic devices
42.79.Hp Optical processors, correlators, and modulators
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
07.68.+m Photography, photographic instruments; xerography

Controlled ink-jet printing and deposition of organic polymers and solid particles

Gökhan Perçin, Thomas S. Lundgren, and Butrus T. Khuri-Yakub

Appl. Phys. Lett. 73, 2375 (1998); http://dx.doi.org/10.1063/1.122465 (3 pages) | Cited 36 times

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In this letter, we present a technique for the deposition of inks, organic polymers and solid particles, using a fluid ejector. The ejector design is based on a flextensional transducer that excites axisymmetric resonant modes in a clamped circular membrane. It is constructed by bonding a thin piezoelectric annular ring to a thin, edge supported, circular membrane. Liquids or solid particles are placed behind one face of the membrane which has a small orifice (50–200 μm diam) at its center. By applying an ac signal across the piezoelectric element, continuous or drop-on-demand ejection of photoresist (Shipley Microposit S1400-21, S1400-27, S1805, and S1813), oil-based ink, water, or talcum powder [Mg3Si4O10(OH)2] has been achieved. Successful deposition of photoresist has been accomplished without spinning, and thus without waste. Patterning of 10 μm features, by baking, exposure, and developing, has revealed no defects in the deposition process. A boundary integral method was used to numerically simulate drop formation from the vibrating orifice. Simulations have been used to optimize ejection performance. © 1998 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.40.Sz Deposition technology
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.40.Hp Lithography, masks and pattern transfer
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
07.07.Mp Transducers
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Comment on “Germanium dots with highly uniform size distribution grown on Si(100) substrate by molecular beam epitaxy” [Appl. Phys. Lett. 71, 3543 (1997)]

P. De Padova, P. Perfetti, R. Pizzoferrato, and M. Casalboni

Appl. Phys. Lett. 73, 2378 (1998); http://dx.doi.org/10.1063/1.122466 (2 pages) | Cited 4 times

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Abstract Unavailable
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
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