Showing papers by "John B Ketterson published in 2007"
TL;DR: In this article, an opposing radio frequency (RF) magnetron sputtering approach was proposed for the preparation of HA thin films on various substrates at low power levels, showing that as-sputtered films are nearly stoichiometric, highly crystalline, and strongly bound to the substrate.
49 citations
TL;DR: In vitro experiments, using murine osteoblasts, showed that cells rapidly adhere, spread and proliferate over the thin coating surface, while simultaneously generating strong in-plane stresses, as observed on SEM images, demonstrating that RAMS is a promising coating technique for biomedical applications.
Abstract: Right angle magnetron sputtering (RAMS) was used to produce hydroxyapatite (HA) film coatings on pure titanium substrates and oriented silicon wafer (Si(0 0 1)) substrates with flat surfaces as well as engineered surfaces having different forms. Analyses using synchrotron XRD, AFM, XPS, FTIR and SEM with EDS showed that as-sputtered thin coatings consist of highly crystalline hydroxyapatite. The HA coatings induced calcium phosphate precipitation when immersed in simulated body fluid, suggesting in vivo bioactive behavior. In vitro experiments, using murine osteoblasts, showed that cells rapidly adhere, spread and proliferate over the thin coating surface, while simultaneously generating strong in-plane stresses, as observed on SEM images. Human osteoblasts were seeded at a density of 2500 cells cm−2 on silicon and titanium HA coated substrates by RAMS. Uncoated glass was used as a reference substrate for further counting of cells. The highest proliferation of human osteoblasts was achieved on HA RAMS-coated titanium substrates. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.
44 citations
TL;DR: In this paper, the eigenmodes of a ferromagnetic particle of arbitrary shape, as well as the absorption in the presence of an inhomogeneous radio-frequency field, are extended to treat infinite lattices of such particles.
Abstract: Recently developed techniques to find the eigenmodes of a ferromagnetic particle of arbitrary shape, as well as the absorption in the presence of an inhomogeneous radio-frequency field, are extended to treat infinite lattices of such particles. The method is applied to analyze the results of recent ferromagnetic resonance experiments and yields substantially good agreement between theory and experiment.
20 citations
TL;DR: In this paper, a single dipole approximation is used to analyze the behavior of anisotropy-dominated magnetic nanoparticles subjected to an external r.f. field and identify the steady state oscillations and analyze their stability.
Abstract: We use a single dipole approximation to analyze the behavior of anisotropy-dominated magnetic nanoparticles subjected to an external r.f. field. We identify the steady state oscillations and analyze their stability. We also analyze the case when the external r.f. field has a time-dependent frequency which insures the most effective switching of the magnetization.
19 citations
TL;DR: In this paper, a detailed comparison between the results of FMR measurements on a square array of permalloy nanodots and a numerical simulation based on the eigenvalues of the linearized Landau-Lifshitz equation is presented.
15 citations
TL;DR: In this paper, the angular dependence of the orthoexciton-polariton luminescence under resonant two-photon excitation at 0.3em was measured.
Abstract: Near the orthoexciton resonance in ${\mathrm{Cu}}_{2}\mathrm{O}$, light propagating through the medium is accompanied by a quadrupolar polarization, a quadrupole polariton. However, these orthoexciton-polaritons can lose their initial coherence because the excitonic component of the mode, a tightly bound electron-hole pair, is subject to wide-angle scattering by atomic-scale imperfections within the crystal. In order to examine this scattering by ambient impurities, we measured the angular dependence of the orthoexciton-polariton luminescence under resonant two-photon excitation at $2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. A rather broad angular distribution is obtained at higher impurity concentrations. We provide a simplified polariton scattering model in order to describe the observed angular distribution. Various experimental data obtained from two natural-growth samples indicate that the orthoexciton-polariton propagation can strongly depend on the local impurity concentration.
9 citations
TL;DR: In this article, the authors measured the angular dependence of the molecule luminescence under resonant two-photon excitation and found that the observed photoluminescence is highly directional and well correlated with the propagation direction of the incident laser.
Abstract: Unlike the conventional theory of giant oscillator strength, the recently proposed bipolariton model describes two-photon excitation of an excitonic molecule in terms of resonant polariton-polariton Coulomb scattering. Using angle-resolved spectroscopy, we directly measure the angular dependence of the molecule luminescence under resonant two-photon excitation. We find that the observed photoluminescence is highly directional and well correlated with the propagation direction of the incident laser. This observation unambiguously supports the core idea of this model that replaces the idea of a biexciton by that of a mutually bound propagating polariton molecule.
4 citations
05 Sep 2007
TL;DR: In this paper, the authors measured the optical force on isolated par ticles trapped in an optical lattice generated by the interference of two coherent laser beams by a method based on the equipartition theorem and by an independent method using hydrodynamic-dr ag.
Abstract: We have measured the optical force on isolated par ticles trapped in an optical lattice generated by the interference of two coherent laser beams by a method based on the equipartition theorem and by an independent method based on hydrodynamic-dr ag. The experimental results show that the optical force on a particle in this type of optical lattice depends strongly on the ratio of the particle diameter to the period of the lattice. By tuning this ratio, the force due to the optical lattice can be made to vanish. We also formed optical lattices involving two independent standing waves with different spatial periods formed by tightly focusing four laser beams which are pair wise coherent. By shifting the relative phases of the interfering beams we can advance the two waves in opposite directions. Depending on the spacing and the translation speed of the two interference patterns, appropriately sized particles can be translated in opposite directions; using this approach we succeeded in separating two different sizes of particles in the presence of a simulated fluid flow.
3 citations
TL;DR: In this paper, the magnetic properties of Ge/MnAs digital heterostructures grown by molecular beam epitaxy were investigated using the highly precise all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA).
Abstract: Magnetic properties of Ge/MnAs digital heterostructure grown by molecular beam epitaxy are reported. A Ge (1 nm)/MnAs (0.15 nm) digital heterostructure exhibited ferromagnetic ordering below 335 K. More importantly, the Ge (1 nm)/MnAs (0.15 nm) heterostructure shows an n-type conductivity and an anomalous Hall effect at room temperature. Concurrently, the magnetic phase stabilities of the Ge (1 nm)/MnAs (0.15 nm) digital heterostructure have been investigated using the highly precise all-electron full-potential linearized augmented plane-wave (FLAPW) method within the generalized gradient approximation (GGA). A total energy calculations reveal that the ferromagnetic coupling between the Mn atoms is energetically favored over the antiferromagnetic (100) and (110) coupling. The Ge (1 nm)/MnAs (0.15 nm) digital heterostructure also showed a possible half-metallic ferromagnetic phase with a 0.25 eV band gap for the minority spin channel, which indicates a promising possible spintronic application
3 citations
TL;DR: In this article, a novel opposing RF magnetron sputtering approach at room temperature was used to prepare crystalline hydroxyapatite thin coatings for bioimplant materials and in vitro cell culture experiments showed that murine osteoblast cells attach and grow well on the as-sputtered coatings.
Abstract: Crystalline hydroxyapatite thin coatings have been prepared using a novel opposing RF magnetron sputtering approach at room temperature. X-ray diffraction (XRD) analysis shows that all the principal peaks are attributable to HA, and the as-deposited HA coatings are made up of crystallites in the size range of 50-100nm. Fourier transform infrared spectroscopy (FTIR) studies reveal the existence of phosphate, carbonate and hydroxyl groups, suggesting that HA coatings are carbonated. Finally, in vitro cell culture experiments have demonstrated that murine osteoblast cells attach and grow well on the as-sputtered coatings. These results encourage further studies of hydroxyapatite thin coatings prepared by the opposing RF magnetron sputtering approach as a promising candidate for next-generation bioimplant materials.
2 citations
TL;DR: In this article, a spin valve was used to reverse the magnetization in a magnetic nanoparticle using a current that specifically excites a uniform spin wave in the spin valve, and the current was swept such that the chirped-frequency generated by the valve matched the angular-dependent resonant frequency of the anisotropy-dominated magnetic nanoparticles, as a result of which magnetization reversal occurred.
Abstract: Using micromagnetics, we demonstrate that the RF field produced by a spin valve can be used to reverse the magnetization in a magnetic nanoparticle. The RF field is generated using a current that specifically excites a uniform spin wave in the spin valve. This current is swept such that the chirped-frequency generated by the valve matches the angular-dependent resonant frequency of the anisotropy-dominated magnetic nanoparticle, as a result of which the magnetization reversal occurs. The switching is fast, requires currents similar to those used in recent experiments with spin valves, and is stable with respect to small perturbations. This phenomenon can potentially be employed in magnetic information storage devices or recently discussed magnetic computing schemes
TL;DR: In this paper, the authors demonstrate that the r.f.m. field produced by a spin valve can be used to reverse the magnetization in a magnetic nanoparticle using a current that specifically excites a uniform spin wave in the spin valve, and this current is swept such that the chirped-frequency generated by the valve matches the angular dependent resonant frequency of the anisotropy-dominated magnetic nanoparticles.
Abstract: Using micromagnetics we demonstrate that the r.f. field produced by a spin valve can be used to reverse the magnetization in a magnetic nanoparticle. The r.f. field is generated using a current that specifically excites a uniform spin wave in the spin valve. This current is swept such that the chirped-frequency generated by the valve matches the angular dependent resonant frequency of the anisotropy-dominated magnetic nanoparticle, as a result of which the magnetization reversal occurs. The switching is fast, requires currents similar to those used in recent experiments with spin valves, and is stable with respect to small perturbations. This phenomenon can potentially be employed in magnetic information storage devices or recently discussed magnetic computing schemes.
TL;DR: In this paper, the authors used an opposing RF magnetron sputtering approach at room temperature to obtain a high-resolution X-ray diffraction (XRD) analysis and showed that all the principal peaks are attributable to HA, and the as-deposited HA coatings are made up of crystallites in the size range of 50-100nm.
Abstract: Crystalline hydroxyapatite thin coatings have been prepared using a novel opposing RF magnetron sputtering approach at room temperature. X-ray diffraction (XRD) analysis shows that all the principal peaks are attributable to HA, and the as-deposited HA coatings are made up of crystallites in the size range of 50-100nm. Fourier transform infrared spectroscopy (FTIR) studies reveal the existence of phosphate, carbonate and hydroxyl groups, suggesting that HA coatings are highly crystalline. To study the biocompatibility of these coatings, murine osteoblast cells were seeded onto various substrates. Cell density counts using fluorescence microscopy show that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.
TL;DR: A right-angle radio frequency magnetron sputtering (RAMS) approach has been developed to deposit hydroxyapatite coatings on various substrates at low power levels.
Abstract: Hydroxyapatite coatings have been widely recognized for their biocompatibility and utility in promoting biointegration of implants in both osseous and soft tissue. Conventional sputtering techniques have shown some advantages over the commercially available plasma spraying method; however, the as-sputtered coatings are usually non-stoichiometric and amorphous which can cause some serious problems such as poor adhesion and excessive coating dissolution rate. A versatile right-angle radio frequency magnetron sputtering (RAMS) approach has been developed to deposit HA coatings on various substrates at low power levels. Using this alternative magnetron geometry, as-sputtered HA coatings are nearly stoichiometric, highly crystalline, and strongly bound to the substrate, as evidenced by analyses using x-ray diffraction (XRD), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). In particular, coatings deposited on oriented substrates show a polycrystalline XRD pattern but with some strongly preferred orientations, indicating that HA crystallization is sensitive to the nature of the substrate. Post deposition heat treatment under high temperature does not result in a marked improvement in the degree of crystallinity of the coatings. To study the biocompatibility of these coatings, murine osteoblast cells were seeded onto various substrates. Cell density counts using fluorescence microscopy show that the best osteoblast proliferation is achieved on an HA RAMS-coated titanium substrate. These experiments demonstrate that RAMS is a promising coating technique for biomedical applications.
TL;DR: In this article, the effect of nonlinear coupling of the two subjunctions due to the electric current controlled by the proximity effect in the N layer has been studied in multiterminal SINIS devices.
Abstract: In a multiterminal SINIS $(\mathrm{Nb}∕\mathrm{Al}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Al}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Al}∕\mathrm{Nb})$ device (where S, I, and N denote a superconductor, insulator, and normal metal), which has electrical leads connected to the middle N (Al) layer, a current passing through one of the subjunctions (NIS) modulates the supercurrent through the other subjunction (SIN), so that, at some injection levels, the supercurrent increases above its steady state value. A theoretical model is given that describes the effect in terms of nonlinear coupling of the two subjunctions due to the electric current controlled by the proximity effect in the N layer.
TL;DR: A large, reentrant, JosephsonCurrent is observed in SINIS junctions at a finite voltage close to Delta/e and a bias current exceeding the zero-voltage Josephson current.
Abstract: A large, reentrant, Josephson current is observed in SINIS (Nb/Al/AlOx/Al/AlOx/Al/Nb) junctions at a finite voltage close to Delta/e (where Delta is the superconducting energy gap in S) and a bias current exceeding the zero-voltage Josephson current. The effect is studied using a multiterminal device configuration. A theoretical interpretation in terms of quantized electron states in the N layer is provided.