Physics Commons^™

Temperature Dependence Of Metal-Organic Heteroepitaxy, Geoffrey Rojas, Xumin Chen, Donna Kunkel, Matthias Bode, Axel Enders

Axel Enders

The nucleation and growth of 2D layers of tetraphenyl porphyrin molecules on Ag(111) are studied with variable-temperature scanning tunneling microscopy. The organic/metal heteroepitaxy occurs by strict analogy to established principles for metal heteroepitaxy. A hierarchy of energy barriers for diffusion on terraces and along edges and around corners of adislands is established. The temperature is key to activating these barriers selectively, thus determining the shape of the organic aggregates, from a fractal shape at lower temperatures to a compact shape at higher temperatures. The energy barriers for the terrace diffusion of porpyrins and the molecule-molecule binding energy were determined to …

Stress And Structure Of Ni Monolayers On W(110): The Importance Of Lattice Mismatch, D. Sander, C. Schmidthals, Axel Enders, J. Kirschner

Axel Enders

The combination of in situ stress measurements, low-energy electron diffraction, and scanning tunneling microscopy reveals the intimate relation between film structure and film stress for epitaxial growth of Ni on W(110) in the monolayer range. In contradiction to lattice mismatch considerations, we measure tremendous compressive stress in the pseudomorphic Ni film, where tensile film stress is expected from strain arguments. Surface stress of the film-substrate composite is proposed to be much more relevant for the description of film stress in the submonolayer range than lattice mismatch arguments are.

Cobalt Nanoclusters On Metal-Supported Xe Monolayers: Influence Of The Substrate On Cluster Formation Kinetics And Magnetism, V. Sessi, K. Kuhnke, J. Zhang, J. Honolka, K. Kern, Axel Enders, P. Bencok, S. Bornemann, J. Minár, H. Ebert

Axel Enders

The growth dynamics of submonolayer coverages of cobalt during buffer layer assisted growth on Ag(111) and Pt(111) substrates is investigated by variable temperature scanning tunneling microscopy in the temperature range between 80 and 150 K. It is found that attractive cluster-substrate interactions can govern the cluster formation on the Xe buffer layer if the Xe layer is sufficiently thin. The interpretation of the microscopy results is supported by x-ray magnetic circular dichroism data which monitor the effect of cluster-substrate interactions on the formation of magnetic moments and magnetic anisotropy of Co nanocluster during the different stages of growth. Ab initio …

Structure And Magnetism Of Atomically Thin Fe Layers On Flat And Vicinal Pt Surfaces, D. Repetto, T. Lee, S. Rusponi, J. Honolka, K. Kuhnke, V. Sessi, U. Starke, H. Brune, P. Gambardella, C. Carbone, Axel Enders, K. Kern

Axel Enders

Ultrathin Fe films on Pt substrates have been investigated under ultrahigh vacuum conditions by scanning tunneling microscopy, low energy electron diffraction, magneto-optical Kerr effect, x-ray magnetic circular dichroism measurements, and Kerr microscopy. We present a comparison between Fe films on flat Pt(111) and stepped Pt(997), with particular focus on the magnetic anisotropy in the submonolayer thickness range below 0.2 monolayer coverage, and above the spin reorientation transition at 3 monolayer thickness. The comparison of structure and magnetism suggests that the perpendicular easy axis found for films thinner than three monolayers is due to dominating contributions from both film interfaces to …

Stress Evolution During The Growth Of Ultrathin Layers Of Iron And Iron Silicide On Si(111), D. Sander, Axel Enders, J. Kirschner

Axel Enders

Using a simple optical deflection technique, we measured continuously the mechanical stress during the growth of Fe films of 0.1–1.5 nm thickness on Si(111) in ultrahigh vacuum (UHV). The stress versus coverage dependence is discussed in view of the different growth modes during the various stages of Fe deposition. The deposition of up to 0.3 nm Fe induces a compressive stress of -1 N/m. We assign this stress to the formation of a reactive Fe–Si interface layer with a silicide-like structure. Subsequent Fe deposition at 300 K leads to a small tensile stress of 0.7 N/m, whereas the deposition at …

Self-Assembled Nanometer-Scale Magnetic Networks On Surfaces: Fundamental Interactions And Functional Properties, Carlo Carbone, Sandra Gardonio, Paolo Moras, Samir Lounis, Marcus Heide, Gustav Bihlmayer, Nicolae Atodiresei, Peter Dederichs, Stefan Blügel, Sergio Vlaic, Anne Lehnert, Safia Ouazi, Stefano Rusponi, Harald Brune, Jan Honolka, Axel Enders, Klaus Kern, Sebastian Stepanow, Cornelius Krull, Timofey Balashov, Aitor Mugarza, Pietro Gambardella

Axel Enders

Nanomagnets of controlled size, organized into regular patterns open new perspectives in the fields of nanoelectronics, spintronics, and quantum computation. Self-assembling processes on various types of substrates allow designing fine-structured architectures and tuning of their magnetic properties. Here, starting from a description of fundamental magnetic interactions at the nanoscale, we review recent experimental approaches to fabricate zero-, one-, and two-dimensional magnetic particle arrays with dimensions reduced to the atomic limit and unprecedented areal density. We describe systems composed of individual magnetic atoms, metal-organic networks, metal wires, and bimetallic particles, as well as strategies to control their magnetic moment, anisotropy, and …

Temperature Dependence Of The Magnetism In Fe/Cu(001), Axel Enders, D. Repetto, D. Peterka, K. Kern

Axel Enders

The correlation between morphology and magnetism of ultrathin epitaxial films is investigated by a combined study of variable temperature scanning tunneling microscopy, magneto-optical Kerr effect measurements, and Kerr microscopy under ultrahigh vacuum condition. The magnetization reversal of the films was studied as a function of temperature by imaging the propagation of Bloch domain walls in situ. It is demonstrated on the example of fcc Fe films grown at 120 K on Cu(001) that changes in the morphology of the films during annealing are directly reflected in modified magnetic properties. Competing pinning mechanisms for the domain wall propagation are identified. The …

Computational Design Optimization For Microfluidic Magnetophoresis, Brian Plouffe, Laura Lewis, Shashi Murthy

Shashi K. Murthy

Current macro- and microfluidic approaches for the isolation of mammalian cells are limited in both efficiency and purity. In order to design a robust platform for the enumeration of a target cell population, high collection efficiencies are required. Additionally, the ability to isolate pure populations with minimal biological perturbation and efficient off-chip recovery will enable subcellular analyses of these cells for applications in personalized medicine. Here, a rational design approach for a simple and efficient device that isolates target cell populations via magnetic tagging is presented. In this work, two magnetophoretic microfluidic device designs are described, with optimized dimensions and …

Electron Beam Induced Luminescence Of Sio2 Optical Coatings, Jr Dennison, Amberly Evans, Gregory Wilson, Justin Dekany, Charles Bowers, Robert Meloy

Justin Dekany

Optical coatings of disordered thin film SiO2/SiOx dielectric samples on reflective metal substrates exhibited cathodoluminescence under electron beam irradiation. Measurements of the absolute radiance and emission spectra as functions of incident electron energy, flux and power over a range of sample temperatures are reported. Radiance reached a saturation plateau at high incident electron power. Well below saturation radiance scaled with deposited power, that is linearly with incident power for lower-energy non-penetrating electrons and decreasing with increasing energy for penetrating radiation. Four bands were observed in spectral measurements from 300 nm to 1000 nm. Changes in peak intensity and shifts in …

Extending The Band Model Of Disordered Sio2 Through Cathodoluminescence Studies, Amberly Evans, Gregory Wilson, Jr Dennison, Justin Dekany

Justin Dekany

Optical coatings of disordered thin film SiO2/SiOx dielectric samples on reflective metal substrates exhibited electron-induced luminescence (cathodoluminescence) under electron beam irradiation in an ultrahigh vacuum chamber at the USU facilities,. These experiments provided measurements of the absolute radiance and emission spectra as functions of incident electron energy, flux and power over a range of sample temperatures (300 K to 40 K). Early results from these experiments have led to a preliminary model of the band structure of highly disordered trapped states within the band gap of SiO2. We now extend this model to further describe the excitation of electrons from …

Muon Contribution To Cathodoluminescence Tests?, Justin Dekany, Allen Andersen, Jr Dennison

Justin Dekany

Tests of composites incorporating highly disordered insulating materials that were bombarded with low-flux keV electron beams exhibited three distinct forms of light emission: short-duration (<<1 s), high intensity luminous electrostatic discharges between the insulator and ground--termed “arcs”; intermediate-duration (10-100 s), intense surface emissions—termed “flares”; and lower intensity, continuous surface cathodoluminescent “glow”. During long-duration experiments at temperatures <150 K, relatively intense flare events occurred at rates of ~2 per min. Rapid increase in photon emission and electron displacement current were observed, with long exponential decay times >1 min. We propose that the source of the flares is the interactions of high energy muons—of cosmic ray origin—with the highly-charged insulating components of the composite materials, which trigger avalanche electrostatic discharge and subsequent recharging along with concomitant light emission. We review evidence from the insulator conductivity at low temperatures, the rates and magnitude of surface charging, the flare frequency, and the magnitude and time-dependence of currents and light emission with regard to this …

Power And Charge Deposition In Multilayer Dielectrics From Monoenergetic Electron Bombardment, Gregory Wilson, Amberly Evans, Justin Dekany, Jr Dennison

Justin Dekany

Power and charge deposition in multilayer dielectrics from electron bombardment is dependent upon the flux and electron range of the electron beam, where the range,--a lso known as the penetration depth—is dependent upon the incident beam energy. Using the Continuous Slow Down Approximation (CSDA), a composite analytical formula has been developed to relate the electron range to the dose rate and subsequently to the deposited power in each subsequent layer. Based on the constituent layer geometry and material , the deposited charge can also be inferred. To validate these models two separate experiments were conducted, one based on the net …

Hfco7-Based Rare-Earth-Free Permanent-Magnet Alloys, Bhaskar Das

B. Das

This study presents the structural and magnetic properties of melt-spun HfCo7,HfCo7-xFex (0.25 ≤ × ≤ 1) and HfCo7Six(0.2 ≤ × ≤1.2) alloys. Appreciable permanent-magnet properties with a magnetocrystalline anisotropy of about 9.6-16.5 Mergs/cm3, a magnetic polarization Js ≈ 7.2-10.6 kG, and coercivities Hc = 0.5-3.0 kOe were obtained by varying the composition of these alloys. Structural analysis reveals that the positions of x-ray diffraction peaks of HfCo7 show good agreement with those corresponding to an orthorhombic structure having lattice parameters of about α = 4.719 Å, b = 4.278 Å, and c = 8.070 Å. Based on these results, a …

Proofs Of The Kochen-Specker Theorem Based On The N-Qubit Pauli Group, Padmanabhan Aravind, Mordecai Waegell

Padmanabhan K. Aravind

We present a number of observables-based proofs of the KochenSpecker (KS) theorem based on the N-qubit Pauli group for N ≥ 4, thus adding to the proofs that have been presented earlier for the 2- and 3-qubit groups. These proofs have the attractive feature that they can be presented in the form of diagrams from which they are obvious by inspection. They are also irreducible in the sense that they cannot be reduced to smaller proofs by ignoring some subset of qubits and/or observables in them. A simple algorithm is given for transforming any observables-based KS proof into a large …

Assembly Of Uniaxially Aligned Rare-Earth-Free Nanomagnets, B. Balamurugan, B. Das, V. R. Shah, Ralph Skomski, X. Z. Li, David Sellmyer

B. Das

We report HfCo7 nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K1≈10 Mergs/cm3, coercivity Hc ≈ 4.4 kOe, and magnetic polarization Js≈10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having Js as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This study suggests HfCo7 as a promising rare-earth-free permanent-magnet alloy, which is …

Simultaneous Quantum-State Measurements Using Array Detection, Andrew Dawes, Mark Beck

Andrew M C Dawes

We have simultaneously measured the quantum states of two different spatial modes of the same optical beam by performing quantum-state tomography with an array detector. Both modes are well described by coherent states, but the projection of the signal onto the local oscillator mode contains a mean of 0.09 photons, while a more complicated mode has a mean of 4.3 photons. This demonstrates that for this particular mode the effective detection efficiency when using array detection is over 40 times greater than when using single detectors.

Optical Switching With Cold Atoms, Andrew Dawes

Andrew M C Dawes

A Viewpoint on: Efficient All-Optical Switching Using Slow Light within a Hollow Fiber M. Bajcsy, S. Hofferberth, V. Balic, T. Peyronel, M. Hafezi, A. S. Zibrov, V. Vuletic, and M. D. Lukin Phys. Rev. Lett. 102, 203902 (2009) – Published May 18, 2009

A Graphical Introduction To Special Relativity Based On A Modern Approach To Minkowski Diagrams, Thushara Perera, Boxiang Liu, '14

Thushara A. Perera

No abstract provided.

Parametric Resonance Enhancement In Neutron Interferometry And Application For The Search For Non-Newtonian Gravity, Vladimir Gudkov, Hirohiko Shimizu, Geoffrey Greene

Geoffrey Greene

The parametric resonance enhancement of the phase of neutrons due to non-Newtonian anomalous gravitationis considered. The existence of such resonances is confirmed by numerical calculations. A possible experimentalscheme for observing this effect is discussed based on an existing neutron interferometer design.

Neutron Interferometric Method To Provide Improved Constraints On Non-Newtonian Gravity At The Nanometer Scale, Geoffrey Greene, Vladimir Gudkov

Geoffrey Greene

In recent years, an energetic experimental program has set quite stringent limits on a possible “non-1/r2” dependence on gravity at short length scales. This effort has been largely driven by the predictions of theories based on compactification of extra spatial dimensions. It is characteristic of many such theories that the strength and length scales of such anomalous gravity are not clearly determined from first principles. As a result, it is productive to extend the current limits the range and strength of such hypothetical interactions. As a heavy, neutral, and (almost) stable particle, the neutron provides an ideal probe for the …

Laminar Flow Of Two Miscible Fluids In A Simple Network, Casey Karst, Brian Storey, John Geddes

John B. Geddes

When a fluid comprised of multiple phases or constituents flows through a network, nonlinear phenomena such as multiple stable equilibrium states and spontaneous oscillations can occur. Such behavior has been observed or predicted in a number of networks including the flow of blood through the microcirculation, the flow of picoliter droplets through microfluidic devices, the flow of magma through lava tubes, and two-phase flow in refrigeration systems. While the existence of nonlinear phenomena in a network with many inter-connections containing fluids with complex rheology may seem unsurprising, this paper demonstrates that even simple networks containing Newtonian fluids in laminar flow …

Usu Grad Student, Researchers Collect Project Data At South Pole, Kevin Opsahl

Jonathan Pugmire

No abstract provided.

Usu Grad Student Travels To South Pole, Kylie Conway

Jonathan Pugmire

No abstract provided.

Usu Team Travels To South Pole To Measure Gravity Waves, Nancy Van Valkenburg

Jonathan Pugmire

No abstract provided.

Photoexcitation And Photoionization From The 2p53p[5/2]2,3 Levels In Neon, M. Baig, I. Bokhari, M. Rafiq, M. Kalyar, T. Hussian, Raheel Ali, Naveed Piracha

Naveed K. Piracha

We present measurements of the excitation spectra from the 2p53p [5/2]3,2 levels in neon using two-step laser excitation and ionization in conjunction with an optogalvanic detection in dc and rf discharge cells. The 2p53p [5/2]3,2 intermediate levels have been approached via the collisionally populated 2p53s [3/2]2 metastable level. The Rydberg series 2p5(2P3/2)nd [7/2]4 (12 ⩽ n ⩽ 44), 2p5(2P3/2)ns [3/2]2 (13 ⩽ n ⩽ 35) and the parity forbidden transitions 2p5(2P3/2)np [5/2]3 (13 ⩽ n ⩽ 19) have been observed from the 2p53p [5/2]3 level, whereas the 2p5(2P3/2)nd [7/2]3 (12 ⩽ n ⩽ 44), 2p5(2P3/2)ns [3/2]2 (13 ⩽ n ⩽ …

South Australian Historical Earthquakes In The Pre-Instrumental Period 1837-1963: A Comprehensive Chronicle And Analysis Of Available Intensity Data, Katherine Dix

Dr Katherine Dix

Synthesis Of Al2tio5 And Its Effect On The Properties Of Chitosan-Nh4scn Polymer Electrolytes, Siti Rohana Majid, Hassan F., Woo H. J., Aziz N. A., Kufian M. Z.

Siti Rohana Majid

In this paper, Al2TiO5 ceramic material has been synthesised and used as filler in polymer electrolyte system to enhance the conductivity. The precursor sintered at 1,050 A degrees C and contained 0.08 mole of aluminium nitrate gives the best and complete formation of Al2TiO5. Composite polymer electrolytes of chitosan-NH4SCN containing different amount of home-made Al2TiO5 were prepared by solution casting. The addition of filler has enhanced the conductivity of polymer electrolyte. The sample 57 wt% chitosan-38 wt% NH4SCN-5 wt% Al2TiO5 exhibited the highest electrical conductivity of 2.10 x 10(-4) S cm(-1) at room temperature. The presence of the Al2TiO5 creates …

The Effect Of Antimony Trioxide On Poly (Vinyl Alcohol)-Lithium Perchlorate Based Polymer Electrolytes, Siti Rohana Majid, Lim C. S., Ramesh S.

Siti Rohana Majid

A new type of inorganic filler antimony trioxide (Sb2O3) is used to prepare composite polymer electrolytes based on poly (vinyl alcohol) (PVA) and lithium perchlorate (LiClO4) by solution casting technique. The incorporation of Sb2O3 enhances the ionic conductivity at ambient temperature and exhibits the highest ionic conductivity value of 9.51 x 10(-5) S cm(-1) upon the addition of 6 wt% Sb2O3. Thermogravimetric analyses (TGA) reveal that the second weight loss is reduced. This shows the improvement in thermal stability of electrolyte film upon addition of Sb2O3. Differential scanning calorimetry (DSC) analyses show that the glass transition temperature (T-g) value decreases …

Vortex-Glass Phase Transition And Enhanced Flux Pinning In C 4+-Irradiated Bafe1.9ni0.1as2 Superconducting Single Crystals, M Shahbazi, X Wang, S Ghorbani, M Ionescu, Olga Shcherbakova, Frederick Wells, Alexey Pan, S Dou, K Choi

Frederick S Wells

We report the effects of C4+-irradiation on the superconducting properties of BaFe1.9Ni0.1As2 single crystal. The BaFe1.9Ni0.1As2 single crystal before and after C4+-irradiation was characterized by magnetic, magneto-transport and magneto-optical techniques over a wide range of magnetic fields (0-13 T) and temperatures (2-200 K). We demonstrate that the C 4+-irradiation significantly enhances the in-field critical current density (by a factor of up to 1.5 at 5 K) and induces enhanced flux jumping at 2 K, with only a small degradation (by 0.5 K) of the critical temperature, T c. The vortex phase diagram describing the evolution of the vortex-glass transition temperature …