Calendar of Events

Events Calendar

Quantitative Mapping of Phonon EELS Mapping in Nanoscale Structures

Date and Time: Thursday, May 02, 2019, 12:00pm -
Location: Chem 260
 

Speaker: Phil Batson

Rutgers University, Department of Physics

During the past 30 years, spatially resolved Electron Energy Loss Spectroscopy (EELS) has emerged as an important tool for the characterization of nanoscale structures designed to efficiently couple external photon fields into the bulk, using surface plasmon polariton excitations. Today, phonon vibrational modes have become accessible down to a few meV, allowing exploration of phonon surface polaritons also. Nanoscale phonon scattering includes (1) Bose-Einstein Occupation statistics that grossly distort the phonon Density of States below room temperature, (2) non-dipole, or impact scattering, by the ~1Å size keV electron beam as it passes within a few angstroms of a column of atoms, (3) scattering selection rules that compliment optical probes, allowing deeper understanding of phonon behavior in well known materials, (4) energy loss and gain scattering that obey the Principle of Detailed Balance, allowing nanoscale thermometry that is independent of specimen material, morphology, and instrumental scattering geometry. The Figure depicts an expected result when a keV electron passes near an edge of a nanoscale MgO cube. Atomic level displacements in response to the field imposed by the passing electron produce scattering that is mapped at a screen below for a 68 meV phonon polariton edge mode. A goal of this work is to extract details of the excited state from the mapped scattering of the electron beam. The molecular dynamics model also suggests that the atomic displacements are pinned at the cube corners, by the cube surfaces, as they are driven by the applied field of the swift electron. I will discuss also the use of the Fluctuation-Dissipation Theorem to access the full complex dielectric and thermal response of the nanoscale object as a function of time and space with a temporal resolution of a few attoseconds, without resorting to a laser pump. Excepting the time dependent results, this work has been published with M.J. Lagos and others in Nature (two articles Highly Cited), PRB, Ultramicroscopy, Microscopy and NanoLetters and discussed in thirteen invited presentations during 2017-2018, including seven at international conferences.

Extra Info: