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18 Apr 1994

Volume 64, Issue 16, pp. 2047-2180

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Coulomb blockade in a silicon tunnel junction device

D. Ali and H. Ahmed

Appl. Phys. Lett. 64, 2119 (1994); http://dx.doi.org/10.1063/1.111702 (2 pages) | Cited 44 times

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Single electron tunnel junctions have been formed in ultrathin silicon‐on‐insulator material by electron beam lithography and dry etching. Clear Coulomb blockade effects have been observed at 300 mK in the current‐voltage characteristics as a function of the voltage applied to a control sidegate. The effects are not smeared out by thermal fluctuations until temperatures greater than 4 K are reached.
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73.40.Gk Tunneling
73.90.+f Other topics in electronic structure and electrical properties of surfaces, interfaces, thin films, and low-dimensional structures (Restricted to new topics in section 73)

Neutron transmutation doping of isotopically engineered Ge

K. M. Itoh, E. E. Haller, W. L. Hansen, J. W. Beeman, J. W. Farmer, A. Rudnev, A. Tikhomirov, and V. I. Ozhogin

Appl. Phys. Lett. 64, 2121 (1994); http://dx.doi.org/10.1063/1.111703 (3 pages) | Cited 13 times

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We report a novel approach for obtaining precise control of both p‐ and n‐type dopant concentrations in bulk Ge single crystals. High‐purity Ge single crystals of controlled 74Ge/70Ge isotope composition ratios were grown and subsequently doped by the neutron transmutation doping (NTD) technique. The resulting net‐impurity concentrations and the compensation ratios were precisely determined by the thermal neutron fluence and the [74Ge]/[70Ge] ratios of the starting Ge materials, respectively. Application of NTD to seven crystals with 0≤[74Ge]/[70Ge]≤4.34 lead to p‐type Ge:Ga,As with compensation ratios in the range 0–0.76. The ability to grow crystals with accurately controlled Ge isotope mixtures allows us to obtain ratios anywhere between 0 and 1 for both p‐ and n‐type doping.
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61.72.uf Ge and Si
61.72.S- Impurities in crystals
72.20.Fr Low-field transport and mobility; piezoresistance

Photolithographic patterning of protective arsenic capping on molecular beam epitaxy grown AlxGa1−xAs(001)

H. Husby, J. K. Grepstad, and R. W. Bernstein

Appl. Phys. Lett. 64, 2124 (1994); http://dx.doi.org/10.1063/1.111704 (3 pages) | Cited 1 time

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Patterning of an arsenic capping layer deposited in situ on AlxGa1−xAs(100) epilayer surfaces is demonstrated, using standard photolithography and subsequent etching in a hydrogen radical (H∗) beam. These data suggest that the protection offered by such capping during ambient storage, may be exploited for molecular beam epitaxy overgrowth and device processing purposes. The technique needs further refinement, however, as trace amounts of surface oxide and carbon impurities were found on the H∗ etched surfaces by core‐level photoelectron spectroscopy. Moreover, the scanning electron micrographs unveil residues of the As cap along the photomask edges, after completed etching.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Resonant tunneling in AlSb‐GaSb‐AlSb and AlSb‐InGaSb‐AlSb double barrier heterostructures

J. L. Jimenez, X. Li, and W. I. Wang

Appl. Phys. Lett. 64, 2127 (1994); http://dx.doi.org/10.1063/1.111705 (3 pages) | Cited 5 times

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We report the resonant tunneling of electrons in AlSb‐GaSb‐AlSb and AlSb‐InGaSb‐AlSb double barrier heterostructures grown on different substrate orientations. We have investigated the dependence of the current voltage characteristic on barrier and well thicknesses, as well as on temperature. Resonant tunneling peak to valley (P/V) ratios of 7.6 (GaSb well) and 8.7 (InGaSb well) at 80 K have been obtained. We also report the observation of a second negative differential resistance (NDR) region with an anomalous temperature dependence, and give an experimental estimation of the band alignment in the strained GaSb/InGaSb system based on the variation of the NDR position in the tunneling structures.
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73.40.Gk Tunneling

New technique for measuring two‐dimensional oxidation‐enhanced diffusion in silicon at low temperatures

M. J. van Dort, H. Lifka, P. C. Zalm, W. B. de Boer, P. H. Woerlee, J. W. Slotboom, and N. E. B. Cowern

Appl. Phys. Lett. 64, 2130 (1994); http://dx.doi.org/10.1063/1.111706 (3 pages) | Cited 6 times

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In this letter, a new high‐resolution technique is presented for determining the lateral extent of oxidation‐enhanced diffusion (OED). A periodic grid of lines and spacings is used as an oxidation mask. It will be shown that a simple secondary ion mass spectroscopy measurement permits the extraction of parameters in the lateral direction with a resolution which can be as good as 10 nm. The lateral extent of OED is depth dependent, consistent with a physical model of point‐defect recombination at the Si/SiO2 interface.
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66.30.J- Diffusion of impurities
81.65.-b Surface treatments
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Nanometer scale patterning of silicon (100) surfaces by an atomic force microscope operating in air

Liming Tsau, Dawen Wang, and K. L. Wang

Appl. Phys. Lett. 64, 2133 (1994); http://dx.doi.org/10.1063/1.111707 (3 pages) | Cited 28 times

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Modification on silicon (100) surfaces was demonstrated by using an atomic force microscope operating in air. Field‐enhanced oxidation on silicon surfaces with protection oxide was done locally by biasing a p‐type heavily doped silicon tip between −3 and −10 V. Oxide lines of width as small as ∼10 nm were achieved. After a dip in aqueous HF solution, the oxide was etched away; the modification depth, ∼1 nm, was characterized by the same atomic force microscope. Other field induced reactions for patterning are possible.
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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
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.-b Surface treatments

Evidence of donor–acceptor pair recombination from a new emission band in semiconducting diamond

J. A. Freitas, P. B. Klein, and A. T. Collins

Appl. Phys. Lett. 64, 2136 (1994); http://dx.doi.org/10.1063/1.111710 (3 pages) | Cited 11 times

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Steady state and time resolved photoluminescence studies of type IIb boron‐doped synthetic diamond reveal a new broad red emission band that exhibits many of the features of classic donor–acceptor pair recombination. This recombination is thought to be between an as‐yet unidentified neutral donor, possibly nitrogen related, approximately 3.6 eV below the conduction band edge and neutral boron acceptors at 0.37 eV above the valence band edge.
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78.55.Hx Other solid inorganic materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Randomly oriented Angstrom‐scale microroughness at the Si(100)/SiO2 interface probed by optical second harmonic generation

J. I. Dadap, B. Doris, Q. Deng, M. C. Downer, J. K. Lowell, and A. C. Diebold

Appl. Phys. Lett. 64, 2139 (1994); http://dx.doi.org/10.1063/1.111711 (3 pages) | Cited 45 times

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Femtosecond pulses from a Kerr–Lens mode‐locked Ti:sapphire laser are used to generate second harmonic from a series of native‐oxidized Si(100)/SiO2 and hydrogen‐terminated Si(100) samples prepared with systematically varied interfacial microroughness with root‐mean‐square feature heights ranging from 0.6 to 4.3 Å. Rotationally anisotropic second harmonic signals using different polarization configurations were measured in air and correlated with atomic force microscopy measurements. The results demonstrate rapid, noncontact, noninvasive measurement of Angstrom‐level Si(100)/SiO2 interface roughness by optical second harmonic generation.  
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68.35.Fx Diffusion; interface formation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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

Reduced mass of an exciton in a monolayer‐wide‐InAs/GaAs quantum well from magnetophotoluminescence measurements

S. S. Dosanjh, E. F. Bowser, and J. J. Harris

Appl. Phys. Lett. 64, 2142 (1994); http://dx.doi.org/10.1063/1.111682 (3 pages) | Cited 1 time

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Magnetophotoluminescence experiments were conducted on samples consisting of nominally one‐monolayer‐wide InAs quantum wells (QWs) with GaAs barriers grown on (001) substrate. From these measurements, we have for the first time deduced the reduced mass of the exciton associated with the InAs QW. The reduced mass is found to be lower than that predicted theoretically using bulk effective masses, the reduction probably arising from a reduction in InAs heavy‐hole mass due to heavy‐ and light‐hole subband mixing in the QW.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

Design of ohmic contacts to p‐ZnSe

R. G. Dandrea and C. B. Duke

Appl. Phys. Lett. 64, 2145 (1994); http://dx.doi.org/10.1063/1.111683 (3 pages) | Cited 26 times

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First‐principle density functional calculations are used to design improved ohmic contacts to p‐ZnSe. Two design strategies are applied: the use of a graded semiconductor epilayer with a large valence band offset, and the imposition of an interlayer to reduce the metal/p‐ZnSe Schottky barrier. In the former strategy we study BeTe because it is lattice matched to ZnSe. We find the BeTe/ZnSe valence band offset is nearly the same as the ZnTe/ZnSe offset, so that if BeTe can be sufficiently p doped, its grading with ZnSe should lead to an ohmic contact comparable to a ZnTe‐grading contact, but without the deleterious presence of misfit dislocations. For the latter strategy we consider the use of a thin As‐Si interlayer between the II‐VI material and metal. The As effects an extra microscopic dipole at the interface that lowers the Fermi level 1 eV in the II‐VI band gap, leading to greatly decreased rectification at p‐type contacts. Applying both strategies simultaneously suggests that a metal/Si‐As/BeTe/ZnSe multilayer structure would afford a nearly ideal ohmic contact to p‐ZnSe.
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73.40.Cg Contact resistance, contact potential
73.40.Sx Metal-semiconductor-metal structures

BeTe/ZnSe graded band gap ohmic contacts to p‐ZnSe

P. M. Mensz

Appl. Phys. Lett. 64, 2148 (1994); http://dx.doi.org/10.1063/1.111684 (3 pages) | Cited 24 times

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BeTe is not a very well known wide‐band semiconductor. Due to the close lattice match to GaAs and ZnSe and p‐type as‐grown character, BexZn1−xTexSe1−x graded band‐gap layers appear an ideal candidate for ohmic contact to p‐type ZnSe based semiconductors. These contacts allow for an implementation of epitaxial structures of II‐VI compound diode lasers entirely lattice matched to the GaAs substrate. The numerical calculations predict contact resistivity of BexZn1−xTexSe1−x graded gap contacts lower than ρc=10−4 Ω cm2 at acceptor doping level 1×1018 cm−3, which corresponds to a voltage drop across the contact layer of less than 0.1 V during lasing operation.
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42.55.Px Semiconductor lasers; laser diodes
73.40.Cg Contact resistance, contact potential
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

AlxGa1−xAs‐GaAs‐InyGa1−yAs quantum well heterostructure lasers with native oxide current‐blocking windows formed on metallized devices

S. A. Maranowski, E. I. Chen, N. Holonyak, and T. A. Richard

Appl. Phys. Lett. 64, 2151 (1994); http://dx.doi.org/10.1063/1.111660 (3 pages) | Cited 6 times

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Data are presented demonstrating improved laser operation of AlxGa1−xAs‐GaAs‐InyGa1−yAs quantum well heterostructures modified with buried native oxide current‐blocking windows. The windows are formed by low temperature (425 °C) anisotropic ‘‘wet’’ oxidation of an Al0.9Ga0.1As layer exposed at the facets of metallized laser bars. These window devices operate continuously to powers as high as 248 mW/facet (uncoated, ∼10.5 μm aperture), a ∼25% improvement over nonwindow devices.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ty Semiconductor-insulator-semiconductor structures

Study of reactive‐ion‐etched silicon by a novel ultrashallow depth profiling technique

W. H. Chang, L. J. Huang, W. M. Lau, T. Abraham, and M. King

Appl. Phys. Lett. 64, 2154 (1994); http://dx.doi.org/10.1063/1.111661 (3 pages) | Cited 6 times

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Silicon treated with reactive ion etching in a CHF3/O2 plasma has been characterized by x‐ray photoelectron spectroscopy and surface charging spectroscopy, in conjunction with ozone oxidation and subsequent HF‐etching for nanodepth profiling. It was found that the residual damage mainly consisted of, from the bulk to surface, 2 nm of defective silicon where the Fermi level was pinned, 0.5 nm of silicon mainly contaminated by silicon carbide, 1 nm of silicon compounds (fluorides, oxides, and carbide), and 5 nm of fluorocarbon. After the removal of this damaged region, the Fermi level became unpinned.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Oxygen pressure dependence of in situ growth of NdCeCuO thin films by laser ablation

Wen‐Tai Lin and Yung‐Fu Chen

Appl. Phys. Lett. 64, 2157 (1994); http://dx.doi.org/10.1063/1.111662 (3 pages) | Cited 2 times

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A phase stability diagram of the NdCeCuO (NCCO) films grown by in situ laser ablation in O2 is demonstrated. The superconducting NCCO films can be grown under the deposition conditions below and close to the CuO/Cu2O transition line without vacuum annealing. On post‐deposition cooling in an oxygen pressure lower than the deposition pressure, the superconductivity of the in situ NCCO films can be significantly improved without vacuum annealing. This process may shorten the reduction step and mitigate the over‐reduction of the superconducting films. A film grown at 680 °C in 300 mTorr and then cooled down in 0.5 mTorr shows Tc(onset) of 21 K and Tc(zero) of 18 K.  
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74.78.-w Superconducting films and low-dimensional structures
81.15.Fg Pulsed laser ablation deposition

Atomic graphoepitaxy: A growth model for c‐axis in‐plane‐aligned, a‐axis oriented YBa2Cu3Ox thin films

Shintaro Miyazawa and Masashi Mukaida

Appl. Phys. Lett. 64, 2160 (1994); http://dx.doi.org/10.1063/1.111663 (3 pages) | Cited 25 times

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The simple growth model of pure a‐axis‐oriented YBa2Cu3Ox thin films on (100)‐oriented SrLaGaO4 substrates of a K2NiF4‐type structure is proposed. This is called ‘‘atomic graphoepitaxy.’’ The model is based on an atomic‐scale geometry of the (100) surface of K2NiF4‐type substrates, which is characterized by atomic‐scale grooves made of oxygen octahedra running along the 〈010〉 direction. These grooves are assumed to act as preferential nucleation sites of c‐axis in‐plane‐aligned, a‐axis‐oriented YBa2Cu3Ox. Based on this hypothesis, the pure a‐axis‐oriented thin films are successfully obtained on (100)‐oriented Nd2CuO4 substrates of K2NiF4‐type structure.
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74.78.-w Superconducting films and low-dimensional structures
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Fg Pulsed laser ablation deposition

Emission linewidth measurements of two‐dimensional array Josephson oscillators

P. A. A. Booi and S. P. Benz

Appl. Phys. Lett. 64, 2163 (1994); http://dx.doi.org/10.1063/1.111984 (3 pages) | Cited 34 times

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We have coupled emission from 10×10 arrays of Josephson junctions at 4 K to a room‐temperature mixer through a fin‐line antenna and a WR‐12 waveguide. A single voltage‐tunable peak was detected in the frequency range from 53 to 230 GHz. A stripline resonance in the antenna reduced the array’s dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data.
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74.50.+r Tunneling phenomena; Josephson effects
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Effective surface resistance of LuBa2Cu3O7−δ thin films

R. Pinto, A. G. Chourey, and P. R. Apte

Appl. Phys. Lett. 64, 2166 (1994); http://dx.doi.org/10.1063/1.111664 (3 pages) | Cited 5 times

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Superconducting LuBa2Cu3O7−δ thin films have been grown in situ on 〈100〉 LaAlO3 by pulsed laser deposition and their effective surface resistance, Reff, has been measured at 10 GHz at various temperatures and for various thicknesses using microstrip resonator technique. The results show that the films are highly c‐axis oriented with a high critical current density, Jc, in the range 4–5×106 A cm−2 at 77 K and a low value of intrinsic surface resistance Rs, of 320 μΩ for 10 GHz at 77 K. Thicker films (≳3000 Å) however, have shown degraded values presumably due to the strain caused by the small ionic radius of lutetium which, as shown by Somasundaram et al. [Mater. Res. Bull. 25, 331 (1990)], makes LuBa2Cu3O7−δ unstable in bulk.
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74.25.F- Transport properties

Thermal‐wave‐modulated superconducting quantum interference device susceptometry for thin magnetic layers

H. Enichlmair and H. Krenn

Appl. Phys. Lett. 64, 2169 (1994); http://dx.doi.org/10.1063/1.111665 (3 pages)

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Thermal waves are excited by a chopped nonresonant light wave in a 3.2 μm EuTe layer on a crystalline BaF2 substrate. The glass fiber optic sample holder is at rest within the pickup coil of a superconducting quantum interference device susceptometer. The thermal wave amplitude (simulated by a two‐dimensional heat conduction model) is a function of temperature and chop rate of illumination and modulates only the magnetic properties of the epitaxial layer. Therefore, the novel method has an enhanced dynamic range and sensitivity (resolution of magnetic moment ≤2×10−9 emu) and resolves the antiferromagnetic phase transition of the EuTe layers at TN=9.8 K even for small magnetic fields of 10 G.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.25.Dq Superconducting quantum interference devices (SQUIDs)
75.30.Cr Saturation moments and magnetic susceptibilities

Reactive ion etching of high‐aspect‐ratio 100 nm linewidth features in tungsten

W. Chu, K. W. Foster, L. M. Shirey, K. W. Rhee, J. Kosakowski, I. P. Isaacson, D. McCarthy, C. R. Eddy, E. A. Dobisz, C. R. K. Marrian, and M. C. Peckerar

Appl. Phys. Lett. 64, 2172 (1994); http://dx.doi.org/10.1063/1.111666 (3 pages) | Cited 3 times

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The subtractive patterning of fine‐linewidth (sub‐250‐nm) tungsten absorbers for x‐ray masks requires the ability to etch features with high aspect ratios and vertical sidewalls. In this letter, a reactive‐ion‐etching process which meets these requirements is described. The etch gases used are SF6 and H2. It is further shown that an intermittent etch process, whereby the sample is vented to atmosphere in between etches results in an etch profile with vertical tungsten sidewalls. This interrupted etching is compared with the results from continuous etching. The straighter sidewalls in the case of the interrupted etch suggests a passivation of the sidewalls which occurs during the venting process. Results are presented to show etching of 100 nm gratings and 200 nm dot arrays. An in situ endpoint detection method developed for the reactive‐ion‐etching system is presented.
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81.05.Bx Metals, semimetals, and alloys
85.40.Ls Metallization, contacts, interconnects; device isolation

Temporal response of a lithium nitrate electrohydrodynamic ion source

Mark Blount and J. A. Panitz

Appl. Phys. Lett. 64, 2175 (1994); http://dx.doi.org/10.1063/1.111667 (3 pages) | Cited 1 time

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The first measurements of electrohydrodynamic (EHD) ion emission from thin films of molten lithium nitrate under pulsed field conditions are presented. Pulse widths from ∼20 ns to 50 μs were used to initiate ion emission from the apex of a stainless‐steel field emitter tip coated with molten lithium nitrate. Current densities ≳100 A/cm2 were obtained from a single emission site. As the pulse width was increased from 20 ns to several microseconds the electric field required to initiate ion emission decreased and asymptotically approached the electric field value characteristic of dc operation. In contrast to dc operation, Li+ was the dominant species (≳90%) for pulse durations less than 1 μs. The abundance of Li+ was independent of pressure between 10−3 and 10−8 Torr of water vapor. The use of a lithium nitrate EHD ion source for the production of intense lithium ion beams in light‐ion inertial confinement fusion reactors is foreseen.
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41.75.Ak Positive-ion beams
79.70.+q Field emission, ionization, evaporation, and desorption

Photoconductively switched antennas for measuring target resonances

Arifur Rahman, David Kralj, Lawrence Carin, Michael R. Melloch, and Jerry M. Woodall

Appl. Phys. Lett. 64, 2178 (1994); http://dx.doi.org/10.1063/1.111668 (3 pages) | Cited 4 times

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Coplanar‐strip horn antennas are switched photoconductively to generate picosecond bursts of freely propagating electromagnetic energy with bandwidth covering 15–75 GHz. The antennas are fabricated on GaAs grown by molecular beam epitaxy at low substrate temperatures. These antennas are used to perform transient scattering measurements from slit‐coupled circular and coaxial cavities; Prony’s method [IEEE Trans. Antennas Propagat. 23, 777 (1975)] is used to extract cavity resonances from the measured late‐time scattered signal.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
72.40.+w Photoconduction and photovoltaic effects
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