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  • 1
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy energy of antiferromagnetic coupled Fe/Cr/Fe layers (abstract) : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5321-5321 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of Fe with interleaved Cr have generated considerable interest because of the antiferromagnetic coupling between the Fe layers. This coupling has been examined using ferromagnetic resonance and other measurements. The results have been explained on the basis of the phenomenological expression for the magnetic free energy. We have determined the magnetic free energy for a single-crystal Fe/Cr/Fe(001) sandwich grown by molecular beam epitaxy using torque magnetometry. At fields below the anisotropy field, both the torque and free energy show a complex switching of the antiferromagnetically coupled Fe moments (Fig. 1). Preliminary calculations show that the exchange and the angle between the antiferromagnetically coupled Fe moments can be determined directly from these curves. We shall discuss our measurements and calculations and compare our results with the earlier ferromagnetic resonance results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348065
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  • 2
    Electronic Resource
    Electronic Resource
    Hole trapping phenomena in the gate insulator of As-fabricated insulated gate field effect transistors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4620-4633 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hole trapping phenomena in SiO2 were examined using an optically assisted hot carrier injection technique on p-channel insulated gate field effect transistors. It was found that only a single, field-dependent, capture-cross-section hole trap is present. The capture cross section of these hole traps at a field of 4 mV/cm across the gate insulator, corresponding to a gate voltage just above the threshold voltage, was found to be 8.5×10−14 cm2. Injected holes were found to trap with an initial efficiency of approximately 60% at this gate field. Depopulation of trapped holes at room temperature was also examined, and found to be significant. The neutral hole trap density in unirradiated device gate insulators after post-metal annealing was found to be approximately 7.0×1012 cm−2. Based on a study of the threshold voltage shift as a function of gate insulator thickness, coupled with the model recently proposed by Walters and Reisman for determining charge centroid, it appears that for oxides with thicknesses greater than 10 nm, the hole traps lie in a band of finite thickness with a charge centroid 5 nm from the substrate-SiO2 interface. In addition, there exists a layer approximately 3.7 nm thick at each interface that appears void of trapped charge. Therefore, oxides less than 7.4 nm thick should not trap charge, which was found to be the case experimentally. This implies that as devices are scaled down, hole trapping will disappear, which is of particular significance in oxides subjected to ionizing irradiation, either during processing or during use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346172
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  • 3
    Electronic Resource
    Electronic Resource
    The magnetic and structural properties of pulsed laser deposited epitaxial Mn1−xZnxFe2O4 ferrite films (abstract) : 37th annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6312-6312 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Since modern high frequency device technology is shifting towards planar miniaturization, ferrite films will play an important role in facilitating the design and fabrication nonreciprocal monolithic integrated devices such as isolators and circulators. The authors have examined magnetic and structural properties for a series of pulsed laser deposited (PDL) single crystal MnZn-ferrite films. The films were epitaxially grown on (001) MgO at substrate temperatures of 300 °C, 400 °C, 600 °C, and 800 °C in an oxygen partial pressure of 30 mTorr. The film microstructure, crystal structure, and composition were characterized by SEM, x-ray diffraction and atomic absorption spectroscopy, respectively. The magnetocrystalline anisotropy constant K1, uniaxial anisotropy constant Ku, saturation magnetization Ms, and coercive force Hc were examined by torque and vibrating sample magnetometry. Ferrimagnetic resonance measurements were made on the films to obtain the linewidth ΔH. A comparison of the magnetic, structural, and chemical properties shows that K1 and Ms scale with the Fe2+ ion concentration and that Ku, Ms, and ΔH are very sensitive to the microstructure. The values of K1, Ms, and ΔH obtained for films deposited at 800 °C were compared with those of bulk MnZn-ferrite and found to exceed the bulk values (Table I), thus making PLD ferrite films very attractive for nonreciprocal device applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352681
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  • 4
    Electronic Resource
    Electronic Resource
    Molecular dynamics studies of polar/nonpolar fluid mixtures. II. Mixtures of Stockmayer and polarizable Lennard-Jones fluids (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5113-5120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of canonical ensemble molecular dynamics simulations of mixtures of equisized Stockmayer and polarizable Lennard-Jones fluids are reported. The excess free energy of mixing shows a decrease with increasing polarizability reflecting an increased miscibility. For sufficiently large values of the polarizability, the miscibility gap, observed previously for mixtures of nonpolarizable Lennard-Jones and Stockmayer fluids, is shown to disappear. The results can be explained qualitatively with perturbation theory. The structure and orientational correlation functions of the mixture are discussed. The marked increase in local ordering at low concentrations of the polar component, so prominent in the nonpolarizable case, diminishes with increasing polarizability. As a result the asymmetry of excess properties with respect to composition becomes less pronounced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463833
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of the crystal-field spectra of the actinide tetrafluorides. I. UF4, NpF4, and PuF4 (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7194-7203 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An interpretation of the low-temperature absorption spectra of AnF4 (An=U, Np, Pu) is presented. Using an effective operator Hamiltonian with orthogonalized free-ion operators and initializing crystal-field parameter values based on a superposition model calculation for An4+ sites with C2 symmetry, good agreement between the model calculations and experimentally observed absorption band structure could be obtained. Correlations with published magnetic and heat capacity measurements are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461396
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular dynamics studies of polar/nonpolar fluid mixtures. I. Mixtures of Lennard-Jones and Stockmayer fluids (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 2704-2714 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of canonical ensemble molecular dynamics calculations of mixtures of Lennard–Jones and Stockmayer fluids are reported. To study solely the influence of the polarity, the Lennard-Jones parameters were identical for both components. The excess mixing properties show a strong asymmetry with respect to composition for large dipolar strength. The free energy of mixing is obtained through a thermodynamic integration procedure. The results strongly suggest that, for reduced dipolar strengths μ2〉3.15, demixing occurs into a phase rich in polar component and an almost pure Lennard-Jones fluid. It is shown that perturbation theory yields fairly accurate results for the dipolar energy and free energy of the mixture. For the free energy of mixing, qualitatively correct results are obtained. The structure and orientational correlation functions of the mixture are discussed. The radial distribution function for pairs of polar molecules show a marked increase in local ordering with dipolar strength for low concentrations of the polar component, indicating that strong clustering of polar molecules occurs at these concentrations. The orientational order is also seen to increase very strongly with dipole moment at these concentrations. The pair correlation function for pairs of Lennard-Jones atoms shows little dependence on dipolar strength of Stockmayer molecules at these concentrations. The distribution function for pairs of unlike molecules reflects the increasingly dissimilar character of these molecules as the dipolar strength increases. For large concentrations of Stockmayer molecules, the opposite effect is observed, albeit less pronounced, in that the pair-correlation function for Lennard-Jones atoms shows an increase in local ordering as μ increases, whereas the radial distribution function for Stockmayer pairs remains relatively unaffected with increasing μ. These results are interpreted in terms of a frustation model. Results are given for the variation of the dielectric constant of the mixture with composition and dipolar strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458909
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic properties of bulk Eu2/3Ca1/3MnO3 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5387-5389 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic and structural properties of the bulk manganite Eu2/3Ca1/3MnO3 are characterized using Mössbauer spectroscopy, magnetization measurements, x-ray diffraction, and resistivity measurements. Here it is demonstrated that one can investigate the magnetic properties of manganites using Mössbauer spectroscopy by doping with europium at the rare earth site and using rays from Eu151 as a probe. Mössbauer measurements were performed at several temperatures between 15 and 293 K using a 151Eu source. The spectrum at room temperature is a single line demonstrating paramagnetism with an isomer shift of 0.60±0.02 mm/s. Measurements at room temperature show the Eu to be trivalent and single phase with a linewidth of 2.933±0.004 mm/s, which is comparable to that found for the Mössbauer standard EuF3. Measurements below 100 K show a much broader linewidth which at 15 K is more than twice that found at 293 K and is associated with a magnetic phase transition. Magnetization as a function of magnetic field measurements up to 5 T show the system to be paramagnetic at 300 K and ferromagnetic-like at 50 K. Magnetic susceptibility measurements made between 300 and 4.2 K show the sample to be paramagnetic down to 100 K, where it undergoes a magnetic phase transition. Mössbauer, resistivity, and magnetic measurements all indicate a change in the paramagnetic state around 230 K. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369986
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  • 8
    Electronic Resource
    Electronic Resource
    Advances in experimental technique for quantitative two-dimensional dopant profiling by scanning capacitance microscopy (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 158-164 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several advances have been made toward the achievement of quantitative two-dimensional dopant and carrier profiling. To improve the dielectric and charge properties of the oxide–silicon interface, a method of low temperature heat treatment has been developed which produces an insulating layer with consistent quality and reproducibility. After a standard polishing procedure is applied to cross-sectional samples, the samples are heated to 300 °C for 30 min under ultraviolet illumination. This additional surface treatment dramatically improves dielectric layer uniformity, scanning capacitance microscopy (SCM) signal to noise ratio, and C–V curve flat band offset. Examples of the improvement in the surface quality and comparisons of converted SCM data with secondary ion mass spectrometry (SIMS) data are shown. A SCM tip study has also been performed that indicates significant tip depletion problems can occur. It is shown that doped silicon tips are often depleted by the applied SCM bias voltage causing errors in the SCM measured profile. Worn metal coated and silicided silicon tips also can cause similar problems. When these effects are tested for and eliminated, excellent agreement can be achieved between quantitative SCM profiles and SIMS data over a five-decade range of dopant density using a proper physical model. The impact of the tip size and shape on SCM spatial accuracy is simulated. A flat tip model gives a good agreement with experimental data. It is found that the dc offset used to compensate the C–V curve flat band shift has a consistently opposite sign on p- and n-type substrates. This corresponds to a positive surface on p-type silicon and to a negative surface on n-type silicon. Rectification of the large capacitance probing voltage is considered as a mechanism responsible for the apparent flat band shift of (0.4–1) V measured on the samples after heating under UV irradiation. To explain the larger flat band shift of (1–5) V, tip induced charging of water-related traps is proposed and discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149558
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  • 9
    Electronic Resource
    Electronic Resource
    A combined thermal dissociation and electron impact ionization source for radioactive ion beam generation (abstract)a) : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1189-1189 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for radioactive ion beam (RIB) applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, in principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility, now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147233
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  • 10
    Electronic Resource
    Electronic Resource
    A combined thermal dissociation and electron impact ionization source for radioactive ion beam generationa) (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1626-1629 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecular feed materials with conventional, hot-cathode, electron-impact ion sources is low and consequently, the ion beams from these sources often appear as mixtures of several molecular sideband beams. This fragmentation process leads to dilution of the intensity of the species of interest for radioactive ion beam (RIB) applications where beam intensity is at a premium. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high ionization efficiency characteristics of an electron impact ionization source that will, in principle, overcome this handicap. The source concept will be evaluated as a potential candidate for use for RIB generation at the Holifield Radioactive Ion Beam Facility, now under construction at the Oak Ridge National Laboratory. The design features and principles of operation of the source are described in this article. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146903
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