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  • 1
    Electronic Resource
    Electronic Resource
    Scattering mechanisms and defects in InP epitaxially grown on (001) Si substrates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4705-4712 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carrier concentration and mobility of unintentionally doped InP layers, grown directly on Si using metal-organic vapor-phase epitaxy, have been studied. The formation of antiphase domains (APDs) was found to depend on annealing of the Si substrate in an AsH3 flow prior to epitaxial growth. Dislocation densities determined by the wet chemical delineation technique were (8±1)×107 cm−3, seemingly uncorrelated to APDs in the layers. In addition to a shallow donor and a compensating acceptor, a deep donor was observed affecting the temperature dependence of the free-electron concentration between 77 and 300 K. The electron mobility in this temperature range could be described in terms of the scattering mechanisms which are dominant in homoepitaxial InP, namely, scattering due to polar optical phonons, to ionized impurities, and to space charges. Electron scattering due to either of these mechanisms was strongly influenced by the occurrence of antiphase boundaries (APBs). The space-charge density as well as the degree of compensation of the epitaxial layers increases with the density of APBs. Degraded 300 K mobilities were obtained indicating the effect of local stress at the APB.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358445
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic degrees of freedom and unimolecular rate constants in metal clusters (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10481-10484 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We calculate the modifications of the unimolecular rate constants for free metallic clusters due to thermally exited electronic degrees of freedom. The effect is essentially taken into account by substituting Helmholtz's free energy of the electronic system for the ground state energy. The activation energy pertaining to the electronic ground states of the mother and daughter cluster is then replaced by the first difference in Helmholtz's free energy. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467866
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  • 3
    Electronic Resource
    Electronic Resource
    Spontaneous abortion following mid-trimester amniocentesis. Clinical significance of placental perforation and blood-stained amniotic fluid (1987)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 94 (1987), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Summary. The clinical significance of placental perforation and bloodstained amniotic fluid was studied in a group of 7238 Danish women undergoing mid-trimester amniocentesis for prenatal diagnosis under ultrasound guidance. The risk of spontaneous abortion was significantly increased both in pregnancies where the placenta was perforated and in those with blood-stained amniotic fluid. The risk estimate nearly doubled after placental perforation and more than doubled with a bloody tap. It is concluded that for women at relatively low risk of a fetal genetic abnormality, the indication of the amniocentesis should be reconsidered if a placental perforation is unavoidable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1987.tb02252.x
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  • 4
    Electronic Resource
    Electronic Resource
    Fast and accurate current-voltage curves of metallic quantum point contacts (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1793-1803 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present an experimental setup for measuring the electrical conductance through metallic quantum point contacts (QPCs) under constant or time-dependent bias voltage conditions. The response time of the setup is as short as 25 ns and typical bias voltages range from 10 mV to 2 V. A function generator is used as bias voltage supply. With this, voltage bursts with a frequency of up to 100 kHz can be applied to the QPCs, whereby current-to-voltage (I–V) curves can be acquired using a homebuilt, 30 MHz bandwidth I–V converter, and a 100 Msamples/s digital storage oscilloscope. Test experiments on resistors show that nonlinear contributions to the I–V curves are always less than 1% of the current for all applied voltages. From the slope of the I–V curves, the conductance can be determined with an accuracy better than 1%. The QPCs are formed between a single-crystal metal sample and the tip of a scanning tunneling microscope under clean ultrahigh vacuum conditions. We demonstrate how the setup can be used to capture the I–V curves of several metastable states in a Au QPC, as it breaks during a period of 200 μs at room temperature. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150539
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  • 5
    Electronic Resource
    Electronic Resource
    Computer controlled probe diagnostic system and applications in a magnetized laboratory plasma (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2615-2622 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A computer controlled acquisition and evaluation system for electrostatic probes is presented. Fully automatic evaluation of the probe characteristics yields electron temperature, plasma potential, and density during the recording. Two-dimensional probe positioning is accomplished with stepping motors. The system is characterized by 12-bit probe current resolution and extremely wide probe voltage range (±130 V). It is tested in a collisionless argon magnetoplasma and compared to standard wave diagnostic techniques for magnetized plasmas, i.e., the resonance cone technique. The influence of the probe radius on the electron current in a magnetized plasma is studied experimentally. The two techniques yield identical density and temperature values within 20% accuracy and therefore show the reliable applicability of the automatic evaluation system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144660
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  • 6
    Electronic Resource
    Electronic Resource
    On the concept of temperature for a small isolated system (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 6518-6525 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The microcanonical temperature is shown to be a useful concept in calculations of the decay of a small isolated system with well defined energy. A simpler and more transparent description is obtained than in Klots' formulation of finite-heat-bath theory, where the system is represented by a canonical ensemble. As a further illustration of the utility of the microcanonical temperature concept, we discuss a formula derived by Dunbar for the probabilities for excitation of a single oscillator in a collection of harmonic oscillators with well defined total energy. This formula expresses the excitation probabilities in terms of the temperature for a canonical ensemble with mean energy equal to the energy of the system. However, a much improved accuracy is obtained if the canonical temperature and heat capacity are replaced by their microcanonical values. We justify this replacement through a modified derivation, in which the microcanonical temperature appears as the canonical temperature of a fictitious system with level density ρ′(E), the derivative of the level density ρ(E) of the collection of oscillators. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357794
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  • 7
    Electronic Resource
    Electronic Resource
    The LIDAR Thomson scattering diagnostic on JET (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1451-1456 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: By combining the time-of-flight or LIDAR principle with a Thomson backscatter diagnostic, spatial profiles of the electron temperature and density are measured in a magnetically confined fusion plasma. This technique was realized for the first time on the JET tokamak. A ruby laser (3-J pulse energy, 300-ps pulse duration, 0.5-Hz repetition rate) together with a 700-MHz bandwidth detection and registration system yields a spatial resolution of about 12 cm. A spectrometer with six channels in the wavelength range 400–800 nm gives a dynamic range of the temperature measurements of 0.3–20 keV. The stray light problem in the backscatter geometry is overcome by spectral discrimination and gating of the photomultipliers. A ruby filter in the spectral channel containing the laser wavelength allows calibration of the vignetting along the line of sight by means of Raman scattering, enabling the measurement of density profiles. The low level of background signal due to the short integration time for a single spatial point yields low statistical errors (ΔTe /Te ≈6%, Δne /ne ≈4% at Te =6 keV, ne =3×1019 m−3 ). Goodness-of-fit tests indicate that the systematic errors are within the same limits. The system is described and examples of measurements are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139686
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  • 8
    Electronic Resource
    Electronic Resource
    Electronics for microchannel photomultipliers in the LIDAR Thomson scattering diagnostic on JET (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 3265-3269 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The electronics for the microchannel plate photomultiplier tubes used in the LIDAR (Light Detection and Ranging) Thomson scattering diagnostic on the JET tokamak are described. It is shown how the microchannel plate photomultiplier tubes are gated with a very small coupling between gate signal and output, and how ≈300 V transient pulses with rise times of 230 ps are clipped to safe levels of ≈40 V.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140563
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  • 9
    Electronic Resource
    Electronic Resource
    Submicrometer-resolution photoelectron-spectroscopy at MAX Lab : INTERNATIONAL CONFERENCE ON SYNCHROTRON RADIATION INSTRUMENTATION (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2168-2171 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design of a photoemission microprobe beamline at the MAX laboratory is presented. The beamline will utilize the radiation from a 26 period undulator on the 550-MeV MAX storage ring. The beamline will be capable of providing about 1010 photons/s of monochromatized radiation (bandwidth better than 0.25 eV) in the energy range of 20 to 150 eV focused into a submicrometer focal spot. It will be used for scanning photoemission experiments with a lateral resolution better than 1 μm. The optical system is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a specially designed ellipsoidal focusing mirror.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140812
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  • 10
    Electronic Resource
    Electronic Resource
    Current-voltage curves of gold quantum point contacts revisited (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 708-710 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present measurements of current–voltage (I–V) curves on gold quantum point contacts (QPCs) with a conductance up to 4 G0 (G0=2e2/h is the conductance quantum) and voltages up to 2 V. The QPCs are formed between the gold tip of a scanning tunneling microscope and a Au(110) surface under clean ultra-high-vacuum conditions at room temperature. The I–V curves are found to be almost linear in contrast to previous reports. Tight-binding calculations of I–V curves for one- and two-atom contacts are in excellent agreement with our measurements. On the other hand, clearly nonlinear I–V curves are only observed when the sample has been cleaned in air. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.127093
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