Michael Shaughnessy

Surface energy effects on osteoblast spatial growth and mineralization

While short-term surface energy effects on cell adhesion are relatively well known, little is revealed as regards its later stage effects on cell behavior. We examined surface energy effects on osteoblastic cell growth and mineralization by using human fetal osteoblastic (hFOB) cells cultured on plasma-treated quartz (contact angle, theta=0 degrees) and octadecyltrichlorosilane (OTS)-treated quartz (theta=113 degrees). hFOB cells formed a homogeneous cell layer on plasma-treated quartz, while those cultured on OTS-treated quartz produced randomly distributed clump-like structures that were filled with cells (confirmed by confocal microscopy). Mineral deposition by hFOB cells was spatially homogeneous when cultured on hydrophilic surfaces. Furthermore, cells on hydrophilic surfaces exhibited increased mineralized area as well as enhanced mineral-to-matrix ratio (assessed by Fourier transform infrared spectroscopy), relative to cells on hydrophobic surfaces. Experiments using other types of osteoblast-like cells (MC3T3-E1, MG63, and SAOS-2) revealed more or less similar effects in spatial growth morphology. It was concluded that hydrophilic surfaces induce homogeneous spatial osteoblastic cell growth and mineral deposition and enhance the quantity (e.g., area) and quality (e.g., mineral-to-matrix ratio) of mineralization relative to hydrophobic surfaces. Our data suggest that surface energy effects on osteoblastic cell differentiation, especially mineralization, may be correlated with surface energy dependent changes in spatial cell growth.

Stabilizing and increasing the magnetic moment of half-metals: The role of Li in half-Heusler LiMn Z ( Z = N , P , Si )

L. Damewood, ∗ B. Busemeyer, M. Shaughnessy, C. Y. Fong, L. H. Yang, and C. Felser Department of Physics, University of California, Davis, CA 95616 USA Sandia National Laboratories at Livermore, Livermore, CA 94551 USA Lawrence Livermore National Laboratory, Livermore, CA 94551 USA Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany (Dated: December 12, 2013)

Memory and Spin Injection Devices Involving Half Metals

We suggest memory and spin injection devices fabricated with half-metallic materials and based on the anomalous Hall effect. Schematic diagrams of the memory chips, in thin film and bulk crystal form, are presented. Spin injection devices made in thin film form are also suggested. These devices do not need any external magnetic field but make use of their own magnetization. Only a gate voltage is needed. The carriers are 100% spin polarized. Memory devices may potentially be smaller, faster, and less volatile than existing ones, and the injection devices may be much smaller and more efficient than existing spin injection devices.

Structural and magnetic properties of single dopants of Mn and Fe for Si-based spintronic materials

Single dopings of Mn and Fe in Si are investigated using 8-, 64-, and 216-atom supercells and a first-principles method based on density functional theory. Between the two transition metal elements (TMEs), atom sizes play an essential role in determining the contraction or the expansion of neighboring atoms around the TME dopant at a substitutional site. At a tetrahedral interstitial site, there is only expansion. Magnetic moments/TME at the two sites are calculated. Physical origins for these inter-related properties are discussed. A few suggestions about the growth of these Si-based alloys are given.

Origin of large moments in MnxSi1−x at small x

Recently, the magnetic moment/Mn, M, in MnxSi1−x was measured to be 5.0 Bohr magneton/Mn, at x=0.1%. To understand this observed M, we investigate several MnxSi1−x models of alloys using first-principles density functional methods. The only model giving M=5.0 was a 513-atom cell having the Mn at a substitutional site, and Si at a second-neighbor interstitial site. The observed large moment is a consequence of the weakened d-p hybridization between the Mn and one of its nearest neighbor Si atoms, resulting from the introduction of the second-neighbor interstitial Si. Our result suggests a way to tune the magnetic moments of transition metal doped semiconductors.

Physical origin of measured magnetic moment in MnxSi1-x with x=0.1%

A recent experiment determined the magnetic moment /Mn, M, in the dilute MnxSi1-x with x = 0.1% to be 5.0 µB/Mn. The existing calculated M values range from 2.37 to 3.1µB/Mn except the case with a fixed charge state, Mn2+, which gives 5.0µB/Mn. We address the issue: Can a single Mn at its neutral charge state in dilute MnxSi1-x alloys have M = 5.0 µB/Mn? After carrying out extensive calculations, the only model giving this M value involves a supercell having a total of 513 atoms with a Mn at a substitutional site and a Si at a tetrahedral interstitial site serving as a second neighbor to the Mn. Physically, the Mn contributes 4.0 µB due to the weakening of the d-p hybridization between the transition metal element and its nearest neighbor Si caused by the presence of the second neighbor Si. The additional 1.0 µB is the consequence of the exchange interaction through the remaining weak overlap of the wave functions between the d-state of the Mn and the sp3 state of the nearest neighbor Si atom. Evidences for the weakening of the d-p hybridization are presented.