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  • 1
    Electronic Resource
    Electronic Resource
    Electroreflectance and deep-level transient spectroscopy studies of metal/n-InP interfaces (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3137-3140 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electroreflectance (ER) and deep-level transient spectroscopy (DLTS) were used to study the effect of surface treatment and substrate temperature on the characteristics of metal/n-InP. The Franz–Keldysh oscillations (FKO) were observed for all samples. From the period of the FKO, the surface electric field ξ was calculated and found to be a function of reverse dc bias, Vdc, but not ac modulating voltage, Vac. Surface potential and carrier concentration were determined from the plot of ξ2 vs Vdc. The Schottky barrier height φB and surface carrier concentration were found to be 0.46 eV and 8.0×1015/cm3 for the metal-semiconductor (MS) diode deposited at room temperature (RT=300 K). With a thin layer of thermal oxide, the φB was increased to 0.70 eV. For a MS diode deposited at low temperature (LT=77 K), φB was found to be as high as 0.96 eV. DLTS studies of InP MS diodes revealed two extra interface traps on RT diodes and a much higher trap density compared with the LT diode. The results clearly show the effect of surface treatment and substrate temperature during metal deposition on the behavior of MS and metal-insulator-semiconductor interfaces. It is demonstrated that the ER technique can be utilized as an optical Mott–Schottky method. It permits an independent confirmation of surface electric field, doping concentration, and barrier height.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349293
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  • 2
    Electronic Resource
    Electronic Resource
    Current transport in Pd/n-InP diodes formed at room and low temperature (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3803-3807 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Schottky contacts to n-InP have been made by deposition on substrates cooled to low temperature (LT=77 K) with a vacuum close to 10−7 Torr. The Schottky barrier height, φB, was found to be as high as 0.96 eV with Pd metal. This indicated an 0.4 to 0.5 eV increase in φB compared with the room temperature (RT=300 K) deposition. For the diode fabricated at room temperature, the reverse saturation current density, J0, decreased sharply with the decrease of measuring temperature. The φB was increased from 0.48 to 0.71 eV, with the testing temperature decreased from 300 to 100 K, with a temperature coefficient of −6.1×10−4 eV/K. The conduction mechanism was controlled by thermionic emission. For the LT diode, the value of J0 was about six orders smaller than for the RT diode at the same temperature. As testing temperature decreased, the barrier height was increased from 0.96 to 1.15 eV, with a temperature coefficient of −3.2×10−4 eV/K. The forward current had a saturation trend at a larger forward bias. In this region, the current was almost temperature independent and the transport mechanism was controlled by thermionic field emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352278
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  • 3
    Electronic Resource
    Electronic Resource
    Elucidating the origin of magic numbers: Trends in the relative binding energies of xenon cluster ions and their implications (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8604-8607 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Metastable decay fractions of Xe〈lu〉n〈bu〉+〈lux〉, n=5–39, are measured using a reflectron time-of-flight mass spectrometry technique. Employing these data, the relative binding energies of Xe〈lu〉n〈bu〉+〈lux〉, n=12–39, are deduced by applying the latest evaporative ensemble model. An excellent correlation is found between the relative binding energies and the intensity anomalies observed in the mass spectrum. Importantly, however, are findings that magic numbers of size n are related to the ratio of the cluster-ion band energies ΔEn/ΔEn+1, and hence are not only influenced by the bonding of this size, but also of n+1 and even n+2! Our results show that magic numbers in the mass spectra alone do not conclusively lead to knowledge of the stabilities and structures of the cluster ions, but consideration of the relative bond energies which can be derived from the new approach are required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460043
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  • 4
    Electronic Resource
    Electronic Resource
    Mixed cluster ions as a structure probe: Experimental evidence for clathrate structure of (H2O)20H+ and (H2O)21H+ (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3268-3270 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: First direct experimental evidence for clathrate structures of (H2O)nH+ (n=20,21) is reported based on a technique allowing the number of nonhydrogen-bonded surface hydrogens to be counted. Neutral clusters (H2O)n⋅((CH3)3N)m, prepared in a pulsed nozzle supersonic expansion, are ionized by multiphoton ionization and investigated with a reflectron time-of-flight mass spectrometry technique. The magic numbers (n,m) in the ion intensity distributions of (H2O)n⋅((CH3)3N)m⋅H+ studied under various experimental conditions are well correlated to the stable hydrogen-bonding structures. For the mixed cluster ion (H2O)20⋅((CH3)3N)m⋅H+, the intensity distribution displays an abrupt intensity drop after the magic number at (20,11), while for (H2O)21⋅((CH3)3N)m⋅H+ the magic number appears at (21,10). The findings provide experimental evidence for a stable clathrate structure of (H2O)20H+, with the proton residing on the surface, while for (H2O)21H+, the H3O+ ion is encaged inside the clathrate structure of (H2O)20; the latter structure provides a total of 10 hydrogen-bonding sites for (CH3)3N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459796
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  • 5
    Electronic Resource
    Electronic Resource
    Water clusters: Contributions of binding energy and entropy to stability (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8009-8015 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The binding energies of water cluster cations are obtained by measuring decay fractions of metastable dissociation and employing Klots' model of evaporative dissociation. Their variation with degree of solvation shows the commonly observed decrease, followed by a slow rise in magnitude, which typifies the trend found for solvated cations. There is no observed abrupt change in the vicinity of the well-known magic number (H2O)21⋅H+ corresponding to (H2O)20⋅H3O+. Other data are used to deduce free energies for water clusters up to size n=28, allowing a determination of entropy changes with size. All of the thermochemical data, including prior literature values, are assessed in terms of calculations made using the liquid drop model and standard statistical mechanical equations. It is concluded that entropic rather than energetic effects give rise to the referred to magic number.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465678
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal imaging by atomic force microscopy using thermocouple cantilever probes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3584-3592 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Thermocouple cantilever probes are used in the atomic force microscope (AFM) to simultaneously obtain thermal and topographical images of surfaces with submicrometer scale spatial resolution. Three designs of thermocouple AFM probes and the thermal images obtained by each of them are presented here. Experiments show that the dominant mechanism for sample-probe heat transfer is gas conduction. If probes are not properly designed, this could lead to image distortion and loss of temperature and spatial resolution. The steady state probe behavior is dominated by the gas thermal conductivity whereas the transient effects are dominated by the thermal mass of the probe. Thermal images of single transistors show their thermal characteristics under different biasing conditions. In addition, hot spots created by short-circuit defects within a transistor can be located by this technique. Efforts are underway to improve the spatial resolution from 0.4 to 0.05 μm by careful probe design. The results suggest that this can be achieved when the size of the thermal sensor at the tip of an AFM cantilever probe is of the order of the tip radius. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145474
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  • 7
    Electronic Resource
    Electronic Resource
    Temporal changes in the spatial distributions of some soil properties on a temperate grassland site (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 18 (2002), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Precision Agriculture seeks to match resource application and agronomic practice with soil and crop requirements as they vary in both space and time. Therefore, an understanding of both the temporal and the spatial components of variability is essential before decisions can be made about the feasibility of site-specific management. In the present study, the spatial and the temporal components of variability in certain key soil properties of a grassland field were evaluated to assess the likely feasibility of adopting a site-specific approach to grassland management. A 7.9 ha grassland field was selected for the study and soil samples were taken three times at regular 25 m intervals across the field over a two year period, and chemically analysed. Classical and geostatistical procedures were used to evaluate the spatial variability and the temporal stability of soil property distributions. Soil extractable P and K had the greatest within-field variability and soil pH the least. Soil K distributions were also highly unstable over time and it was concluded that the optimal risk aversion strategy would be to apply uniform dressings of this nutrient to the entire field. In contrast, soil pH, P, Mg and sulphate distributions were not only temporally stable, but were also spatially correlated over reasonably large ranges. It was concluded that these properties might be managed in a site-specific way based on the results of periodic soil testing in three clearly defined management sub-units within the field. Over the two year period, C and N accumulated in the soil at surprisingly high rates on certain parts of the field but not in others.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.2002.tb00252.x
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  • 8
    Electronic Resource
    Electronic Resource
    Paramagnetism and scaling behavior of volume flux pinning force density in a GdBa2Cu3O6+x thin film (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3287-3292 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic measurements have been performed on a GdBa2Cu3O6+x superconducting thin film. The paramagnetism carried by rare earth Gd3+ ions in the film tilts the magnetic hysteresis loop and broadens the width of the magnetic hysteresis ΔM, then the magnetization critical current density and the volume flux pinning force density based on the Bean critical state model deviate from intrinsic values. Therefore, in order to get useful information on the pinning mechanism, correction for the paramagnetism is essential. And after correction for the paramagnetism, a scaling law of the volume flux pinning force density is obtained as f(b)=(b/4)0.5(1−b/4)1.5, based on which the possible pinning mechanism in the film is discussed. In the end, deviation from the scaling law at high fields is interpreted by the collective pinning theory. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360019
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  • 9
    Electronic Resource
    Electronic Resource
    Study of magnetization relaxation on zone-melted YBa2Cu3O6+x superconductors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2618-2624 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The analytical magnetization versus time expressions for several flux-pinning models for high-Tc superconductors are deduced. Magnetic relaxation and hysteresis studies have been performed on a zone-melted YBa2Cu3O6+x sample by SQUID. Nonlogarithmic magnetization decay is observed at relatively high temperatures; we attribute this to the nonlinear U(J) relationship which may arise from the local pinning potential Up(x), rather than collective pinning. At 70 K, the experimental data fits extremely well to the expression M(t)=M0+a(T)ln ln(t/τ) which is the result of the exponential U(J) relationship. Based on this U(J) law, the local pinning potential is determined to be Up(x)=U0(x/x0)[1−ln (x/x0)]. The voltage–current E(J) resulting from the observed U(J) relationship, as well as the role of the Y2BaCuO5 (211) phase in zone-melted YBCO is discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358726
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetization relaxation in YBa2Cu3O7−δ (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1671-1675 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time and field sweep rate dependencies of magnetization in high temperature superconductors are derived from a combined view based on the thermally activated flux creep. The τ0 in the magnetization relaxation expression M=M0+M1 ln(1+t/τ0) is a macroscopic quantity related primarily to the sample geometry and other experimental conditions via the effective activation energy U(J0). This activation energy provides an alternative interpretation to the nearly inverse proportionality of τ0 to the field sweep rate. The values of τ0 in the magnetization relaxation of single crystal YBa2Cu3O7−δ are consistent with the calculated ones. As the nonlinear U(J) is taken into account, the curvature in the ||M||-ln t plot may change from negative to positive over a sufficiently long time window, and the magnetization hysteresis M(H) depends on the field sweep rate H(overdot) by const+A ln H(overdot)+B ln2 H(overdot), where A is slightly larger than M1 and B(approximately-greater-than)0. A discussion of the temperature dependency of the normalized flux creep rate is at the conclusion of the article.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356352
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