Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures

Controlling magnetic properties on the nm-scale is essential for basic research in micro-magnetism and spin-dependent transport, as well as for various applications such as magnetic recording, imaging and sensing. This has been accomplished to a very high degree by means of layered heterostructures in the vertical dimension. Here we present a complementary approach that allows for a controlled tuning of the magnetic properties of Co/Pt heterostructures on the lateral mesoscale. By means of in-situ post-processing of Pt- and Co-based nano-stripes prepared by focused electron beam induced deposition (FEBID) we are able to locally tune their coercive field and remanent magnetization. Whereas single Co-FEBID nano-stripes show no hysteresis, we find hard-magnetic behavior for post-processed Co/Pt nano-stripes with coercive fields up to 850 Oe. We attribute the observed effects to the locally controlled formation of the CoPt L1$_{0}$ phase, whose presence has been revealed by transmission electron microscopy.Comment: Accepted for publication in Beilstein J. Nanotechno

Magnetooptical Study of Zeeman Effect in Mn modulation-doped InAs/InGaAs/InAlAs Quantum Well Structures

We report on a magneto-photoluminescence (PL) study of Mn modulation-doped InAs/InGaAs/InAlAs quantum wells. Two PL lines corresponding to the radiative recombination of photoelectrons with free and bound-on-Mn holes have been observed. In the presence of a magnetic field applied in the Faraday geometry both lines split into two circularly polarized components. While temperature and magnetic field dependences of the splitting are well described by the Brillouin function, providing an evidence for exchange interaction with spin polarized manganese ions, the value of the splitting exceeds the expected value of the giant Zeeman splitting by two orders of magnitude for a given Mn density. Possible reasons of this striking observation are discussed

Epidermal Growth Factor–PEG Functionalized PAMAM-Pentaethylenehexamine Dendron for Targeted Gene Delivery Produced by Click Chemistry

Aim of this study was the site-specific conjugation of an epidermal growth factor (EGF)-polyethylene glycol (PEG) chain by click chemistry onto a poly(amido amine) (PAMAM) dendron, as a key step toward defined multifunctional carriers for targeted gene delivery. For this purpose, at first propargyl amine cored PAMAM dendrons with ester ends were synthesized. The chain terminal ester groups were then modified by oligoamines with different secondary amino densities. The oligoamine-modified PAMAM dendrons were well biocompatible, as demonstrated in cytotoxicity assays. Among the different oligoamine-modified dendrons, PAMAM-pentaethylenehexamine (PEHA) dendron polyplexes displayed the best gene transfer ability. Conjugation of PAMAM-PEHA dendron with PEG spacer was conducted via click reaction, which was performed before amidation with PEHA. The resultant PEG-PAMAM-PEHA copolymer was then coupled with EGF ligand. pDNA transfections in HuH-7 hepatocellular carcinoma cells showed a 10-fold higher efficiency with the polyplexes containing conjugated EGF as compared to the ligand-free ones, demonstrating the concept of ligand targeting. Overall gene transfer efficiencies, however, were moderate, suggesting that additional measures for overcoming subsequent intracellular bottlenecks in delivery have to be taken

First measurement of the Head-Tail directional nuclear recoil signature at energies relevant to WIMP dark matter searches

We present first evidence for the so-called Head-Tail asymmetry signature of neutron-induced nuclear recoil tracks at energies down to 1.5 keV/amu using the 1m^3 DRIFT-IIc dark matter detector. This regime is appropriate for recoils induced by Weakly Interacting Massive Particle (WIMPs) but one where the differential ionization is poorly understood. We show that the distribution of recoil energies and directions induced here by Cf-252 neutrons matches well that expected from massive WIMPs. The results open a powerful new means of searching for a galactic signature from WIMPs.Comment: 4 pages, 6 figures, 1 tabl

Antineutrinos from Earth: A reference model and its uncertainties

We predict geoneutrino fluxes in a reference model based on a detailed description of Earth's crust and mantle and using the best available information on the abundances of uranium, thorium, and potassium inside Earth's layers. We estimate the uncertainties of fluxes corresponding to the uncertainties of the element abundances. In addition to distance integrated fluxes, we also provide the differential fluxes as a function of distance from several sites of experimental interest. Event yields at several locations are estimated and their dependence on the neutrino oscillation parameters is discussed. At Kamioka we predict N(U+Th)=35 +- 6 events for 10^{32} proton yr and 100% efficiency assuming sin^2(2theta)=0.863 and delta m^2 = 7.3 X 10^{-5} eV^2. The maximal prediction is 55 events, obtained in a model with fully radiogenic production of the terrestrial heat flow.Comment: 24 pages, ReVTeX4, plus 7 postscript figures; minor formal changes to match version to be published in PR

Analysis and Modification of Amorphous and Partially-Crystalline Thin Films

Thin films of light atomic weight elements in amorphous, partially-crystalline, or crystalline forms have applications in a broad range of technologies. For example, amorphous tetrahedral carbon (a-tC) and polymeric thin films impact electronic materials technology as electron- and light-emitting device elements, respectively. A lack of crystallinity introduces complexity in the experimental and theoretical characterization of these materials but is not necessarily a limiting factor in their performance. While the growth process is clearly a major factor governing the physical properties of a film, interactions with the substrate are also important, so surface and interface analysis provides an important complement to bulk measurements. This paper focuses on several approaches in the characterization and modification of thin films made possible by recent experimental advances. The structural and electronic properties of two model systems are considered as examples: a-tC thin films grown by pulsed laser deposition (PLD) and polyaniline thin films grown by vapor deposition. First, scanning probe microscopies and X-ray scattering are used to investigate the structural aspects of a-tC films as a function of PLD growth conditions. The possible connection of nanoscale surface modification and characterization with electron emission properties will be discussed. Second, the results of inelastic scattering spectroscopy and other surface techniques will be discussed to obtain information on both interfacial aspects of the growth of polyaniline thin films and microscopic and macroscopic aspects of electrical conductivity upon doping. Comparisons will be made with other studies that address properties of analogous crystalline systems as appropriate. A brief assessment of the broader problem of analyzing these systems will be given