Showing papers by "John B Ketterson published in 1984"
TL;DR: In this paper, the authors used X-ray diffraction at glancing angles to find that in Langmuir-Blodgett films of lead stearate the lead atoms form plane arrays identical to one set of planes in a bulk crystal, but with little correlation between the planes.
41 citations
TL;DR: In this article, an UHV evaporator with two electron beam guns and a heated substrate turntable is used for the preparation of composition-modulated structures (CMSs).
Abstract: We describe the construction of an UHV evaporator with two electron beam guns and a heated substrate turntable which is used for the preparation of composition‐modulated structures (CMS’s). Using a suitably controlled stepping motor, up to 20 different CMS’s can be prepared in the same run. The system has been used to deposit V/Fe CMS’s and preliminary structural measurements indicate the samples are of high quality.
22 citations
TL;DR: In this article, X-ray θ-2θ scans showed that the samples had a bcc (110) texture with a strong composition modulation, which is expected for the Bloch spin wave contribution to the magnetization of a 2D ferromagnet.
Abstract: V/Fe composition‐modulated structures have been grown on the (0001) surface of a sapphire substrate in an UHV evaporator. X‐ray θ‐2θ scans showed that the samples had a bcc (110) texture with a strong composition modulation. Samples with three atomic planes of Fe separated by thick layers of V showed a linear temperature dependence of the saturation magnetization over the range 5–400 K. This behavior is expected for the Bloch spin wave contribution to the magnetization of a 2D ferromagnet. Hysteresis measurements also confirmed that the samples were ferromagnetic. Superconductivity has been seen in samples with very thick V layers.
21 citations
TL;DR: In this paper, a technique for preparing compositionally modulated PbTe/Bi films on mica with a well-defined epitaxy by evaporation is described, where the bismuth layers of the film approached a quasi-simple cubic structure.
19 citations
TL;DR: In this paper, compositionally modulated structures (CMS) of PbTe-Bi with wavelengths between 38-140 A were prepared by thermal evaporation on muscovite mica substrates.
Abstract: Compositionally modulated structures (CMS) of PbTe–Bi with wavelengths between 38–140 A were prepared by thermal evaporation on muscovite mica substrates. There was a well defined epitaxy with the (111) plane and the [110] axis of the CMS parallel to (001) and [100] of the mica. The dc resistivity, Hall coefficient, and magnetoresistance were measured in the temperature range of 1.8 to 300 K and for magnetic fields up to 50 kG. All samples displayed an anomalous logarithmic increase in the resistance at low temperature. The magnetoresistance increased logarithmically with magnetic field H in large fields for the samples with thick PbTe layers (≳45 A), while it went as H1/2 for the samples with thin PbTe layers (≲30 A). The sign of the Hall coefficient changed from negative to positive with increasing Bi layer thickness and the positive Hall coefficient could be changed in sign by increasing the PbTe layer thickness.
18 citations
01 Dec 1984
TL;DR: In this paper, it has been shown that the large, modulation wavelength dependent enhancement of the biaxial modulis in composition modulated foils is due to the changes in the primary elastic constants.
Abstract: From measurements of independent elastic moduli it has been shown that the large, modulation wavelength dependent enhancement of the biaxial modulis in composition modulated foils is due to the changes in the primary elastic constants. These results provide an explanation for some of the apparently conflicting data in the literature. The plastic and thermoelectric properties of these materials were also found to be anomalous and wavelength dependent.
14 citations
TL;DR: In this article, the growth and structural characteristics of three semiconductor-semimetal superlattices were presented, which were prepared by thermal evaporation in high vacuum, and only a small lattice mismatch was observed.
11 citations
TL;DR: In this article, the authors proposed a method to solve the problem of low-dimensional laser rangefinders using the Northwestern Materials Research Center (NMC) and the Office of Naval Research under Grant No. N00014-82-K-52-98 and National Science Foundation grant No. DMR79-23573.
Abstract: This work was supported by the Office of Naval Research under Grant No. N00014-82-K-52-98 and the Northwestern Materials Research Center under National Science Foundation Grant No. DMR79-23573
8 citations
TL;DR: In this paper, the surface wave velocity in SnTe/Sb superlattices has been determined using Brillouin scattering and the velocity is independent of modulation wavelength over the range studied but is lower than would be expected if the layers of Sb and SnTe possessed their bulk properties.
Abstract: The surface wave velocity in SnTe/Sb superlattices has been determined using Brillouin scattering. The velocity is independent of modulation wavelength over the range studied but is lower than would be expected if the layers of Sb and SnTe possessed their bulk properties. This is consistent with x‐ray data which can be interpreted as evidence of a cubic polymorph of Sb which is unstable in bulk form.
7 citations
TL;DR: In this paper, a new composition modulated structure composed of semiconducting SnTe and semimetallic Sb has been grown epitaxially on mica substrates with differing SnTe to Sb ratios.
Abstract: A new composition modulated structure composed of semiconducting SnTe and semimetallic Sb has been grown epitaxially on mica substrates with differing SnTe to Sb ratios. The samples were characterized by x‐ray diffraction using the transmission Laue patterns and θ‐2θ diffractometer scans with scattering vectors both normal and in the plane of the film. We observed that the modulation satellites were 180° out of phase for films with short modulation wavelengths, but were in phase for long wavelengths. This change in the phase of the modulation can be understood by assuming that Sb adopts a quasicubic structure at short modulation wavelength, due to the coherency strain, but relaxes back to a distorted rhombohedral structure, with the loss of coherency, at long wavelengths. A simple 1‐D model was used to estimate the modulation wavelength dependence of the sublattice displacement of Sb.
7 citations
TL;DR: In this paper, an apparatus has been designed, assembled, and employed in experiments to determine, as a function of molecular areal density, the viscoelastic behavior of insoluble monolayers spread on water.
Abstract: An apparatus has been designed, assembled, and employed in experiments to determine, as a function of molecular areal density, the viscoelastic behavior of insoluble monolayers spread on water. The apparatus has several unique features: (1) surface tension can be monitored constantly without touching the monolayer; (2) compression of the film is isotropic in an annular space entirely free of obstructions; (3) the stress transducer, located at the geometric center, defines the inner wall of the annulus and the trough wall defines the outer wall of the annulus. A wide range of viscosity and shear modulus can be measured by controlling the stress or strain applied to the film. The apparatus can be used to study the air/water interface of surfactant solutions as well as the surface of water covered by an insoluble monolayer. 14 references, 4 figures.