Abstract

A new method of direct, rapid nano- to micro-scale patterning of high purity cobalt is presented. The method utilizes a combination of electron beam induced deposition (EBID) and seeded growth at elevated temperatures below the temperature of spontaneous thermal decomposition. Dicobalt octacarbonyl $$\mathrm{Co_{2}(CO)_{8}}$$ is used as the precursor and carbon as a seed layer. Seeded deposition is carried out in the substrate temperature range from 55 to 75°C. Deposition yield is significantly higher than conventional EBID and magnetotransport measurements indicate that resistivity, $$22~\mu\Omega~\mathrm{cm}$$, and saturation magnetization, 1.55 T, are much closer to the corresponding values for bulk Co than those for standard EBID.

Abstract

A popular method for generating micron-sized aerosols is to submerge ultrasonic ( *ω* ~ MHz) piezoelectric oscillators in a water bath. The submerged oscillator atomizes the fluid, creating droplets with radii proportional to the wavelength of the standing wave at the fluid surface. Classical theory for the Faraday instability predicts a parametric instability driving a capillary wave at the subharmonic (*ω*/2) frequency. For many applications it is desirable to reduce the size of the droplets; however, using higher frequency oscillators becomes impractical beyond a few MHz. Observations are presented that demonstrate that smaller droplets may also be created by increasing the driving amplitude of the oscillator, and that this effect becomes more pronounced for large driving frequencies. It is shown that these observations are consistent with a transition from droplets associated with subharmonic ( *ω*/2) capillary waves to harmonic (*ω*) capillary waves induced by larger driving frequencies and amplitudes, as predicted by a stability analysis of the capillary waves.

Abstract

Being able to distinguish light-quark jets from gluon jets on an event-by-event basis could significantly enhance the reach for many new physics searches at the Large Hadron Collider. Through an exhaustive search of existing and novel jet substructure observables, we find that a multivariate approach can filter out over 95% of the gluon jets while keeping more than half of the light-quark jets. Moreover, a combination of two simple variables, the charge track multiplicity and the $$p_T$$-weighted linear radial moment (girth), can achieve similar results. Our study is only Monte Carlo based, so other observables constructed using different jet sizes and parameters are used to highlight areas that deserve further theoretical and experimental scrutiny. Additional information, including distributions of around 10 000 variables, can be found at http://jets.physics.harvard.edu/qvg/.

Abstract

We demonstrate the operation of a device that can produce chitosan nanoparticles in a tunable size range from 50–300 nm with small size dispersion. A piezoelectric oscillator operated at megahertz frequencies is used to aerosolize a solution containing dissolved chitosan. The solvent is then evaporated from the aerosolized droplets in a heat pipe, leaving monodisperse nanoparticles to be collected. The nanoparticle size is controlled both by the concentration of the dissolved polymer and by the size of the aerosol droplets that are created. Our device can be used with any polymer or polymer/therapeutic combination that can be prepared in a homogeneous solution and vaporized.

From the Cover…

.. epigraph:: “Helliwell achieves a rare clarity. For instance, the derivation of the standard kinematic results starting from Einstein's postulates is outstandingly clear. Throughout he shows an unusual and sympathetic appreciation of the problems that are faced by the beginning student.” -- John Taylor, University of Colorado .. epigraph:: “*Special Relativity* is definitely much better than the books I have read on this topic, and I would recommend it to any instructor who plans to teach a course on this topic. For anyone teaching special relativity as a part of a Modern Physics course, this book offers valuable supplementary reading.” -- Shirvel Stanislaus, Valparaiso University

From the Cover…

.. epigraph:: “Townsend has written an excellent book that someone needed to write for the modern physics textbook market. He has given it the same care that he gave to his excellent quantum mechanics book.” -- Jeff Dunham, Middlebury College .. epigraph:: “When I read this book I immediately adopted it for my sophomore modern physics class. This is the best introduction to quantum mechanics available.” -- B. Paul Padley, Rice University

Abstract

A new class of observables is introduced which aims to characterize the superstructure of an event, that is, features, such as color flow, which are not determined by the jet four-momenta alone. Traditionally, an event is described as having jets which are independent objects; each jet has some energy, size, and possible substructure such as subjets or heavy flavor content. This description discards information connecting the jets to each other, which can be used to determine if the jets came from decay of a color- singlet object, or if they were initiated by quarks or gluons. An example superstructure variable, pull, is presented as a simple handle on color flow. It can be used on an event-by-event basis as a tool for distinguishing previously irreducible backgrounds at the Tevatron and the LHC.

Abstract

Absorption enhancement in thin metal-backed solar cells caused by dipole scatterers embedded in the absorbing layer is studied using a semi-analytical approach. The method accounts for changes in the radiation rate produced by layers above and below the dipole, and treats incoherently the subsequent scattering of light in guided modes from other dipoles. We find large absorption enhancements for strongly coupled dipoles, exceeding the ergodic limit in some configurations involving lossless dipoles. An antireflection-coated 100-nm layer of a-Si:H on Ag absorbs up to 87% of incident above-gap light. Thin layers of both strong and weak absorbers show similar strongly enhanced absorption.

Recent Publications

Student authorFaculty author

61. L. M. Belova, James C. Eckert, J. J. L. Mulders, C. Christophersen, E. D. Dahlberg, and A. Riazanova Rapid electron beam assisted patterning of pure cobalt at elevated temperatures via seeded growth Nanotechnology 22 (2011) 145305. Andrew P. Higginbotham, Andrew J. Bernoff, Aaron M. Guillen, Thomas D. Donnelly, and Nathan Jones Evidence of the harmonic Faraday instability in ultrasonic atomization experiments with a deep, inviscid fluid Journal of the Acoustical Society of America 130 (2011) 2694-2699. Jason Gallicchio and Matthew D Schwartz Quark and Gluon Tagging at the LHC Physical Review Letters 107 (2011) 172001. Andrew P. Higginbotham, Thomas D. Donnelly, Shenda M. Baker, and Ian K. Wright Generation of Nanoparticles of Controlled Size Using Ultrasonic Piezoelectric Oscillators in Solution ACS Applied Materials and Interfaces 2 (2010) 2360-2364. Thomas Helliwell Special Relativity University Science Books, Sausalito, 2010. John S. Townsend Quantum Physics: a Fundamental Approach to Modern Physics University Science Books, Sausalito, 2010. Jason Gallicchio and Matthew D. Schwartz Seeing in Color: Jet Superstructure Physical Review Letters 105 (2010) 022001. Peter N. Saeta, Harry A. Atwater, Vivian E. Ferry, Jeremy N. Munday, and Domenico Pacifici How much can guided modes enhance absorption in thin solar cells? Optics Express 17 (2009) 20975-20990. J. Parker, David W. Mar, Joshua R. Puzey, John H. Hankinson, Kevin P. Byram, C. Lee, Michael K. Mayeda, Richard C. Haskell, Qimin Yang, S. Greenfield, and R. Epstein Thermal links for the implementation of an optical refrigerator Journal of Applied Physics 105 (2009) 013116. Andrew P. Higginbotham, Octavi E. Semonin, Sandra A. Bruce, Clarence W. Chan, David A. Mann, M. Maurer, W. Bang, I. V. Churina, J. Osterholz, I. Kim, T. Ditmire, and Thomas D. Donnelly Generation of Mie size microdroplet aerosols with applications in laser-driven fusion experiments Review of Scientific Instruments 80 (2009) 063503.