Laboratory for Surface Modification (LSM)

Seminars Archives

October 2018 | November 2018 | December 2018

Thursday, November 01, 2018
Nanostructures Probed with High Energy and Spatial Resolution using Scanning/Transmission Electron Microscopy
Nasim Alem
Pennsylvania State University
Materials Science and Engineering Department
12:00 Noon CHEM 260

Using ultra-high resolution aberration-corrected Scanning/Transmission Electron Microscopy (S/TEM) imaging and electron energy loss spectroscopy (EELS), this presentation will focus on our recent efforts on probing the atomic and chemical structure of nanomaterials and their plasmonic behavior in two classes of materials: complex oxides and silica nano-opals. In the first part of the talk, high resolution aberration-corrected scanning transmission electron microscopy (STEM) imaging is used to probe and quantify the ferroelectric polarization and relaxation effects resulting from Jahn-Teller effect across the domain walls and interfaces by imaging and quantifying the sub-Angstrom structural distortions. In the second part of the talk, we uncover the structure of silica nano-opal metalattices and their plasmon generation. Metalattices are artificial 3D ordered periodic nanostructured solids in the range of 1–100 nm with applications in plasmonics. The nano-meter 3D structural order in this class of materials can have a profound impact on their functional properties leading to the generation of localized surface plasmon resonances (LSPRs) and more efficient electromagnetic energy storage in nanoplasmonics. This study explores the generation and propagation of plasmons in 3D ordered interconnected silica opals filled with silver in the voids in between the Silica opals in comparison to their partner structures. This study explores the generation of LSPRs as a function of the size of the opals and their filling material using monochromated STEM and EELS.
Thursday, November 08, 2018
Modeling Thin Liquid Films: from Liquid Crystals to Liquid Metals
Lou Kondic
Department of Mathematical Sciences
12:00 Noon CHEM 260

Understanding fluid instabilities on micro and nanoscale is relevant for a variety of
reasons. From scientific point of view, modeling systems involving fluid-solid interfaces
is challenging, particularly if contact lines are present. From practical side, fluid film
evolution and resulting instabilities and crucial for making progress in the field of self
and directed assembly on nanoscale. The resulting structures may be of relevance to a
number of emerging technologies in the fields that vary from MEMS and plasmonics to
DNA analysis.
This talk will focus on recently developed models and computational techniques for
thin films. The models to be considered include long-wave asymptotic approach as
well as full Navier-Stokes based models. Both types of models have been augmented
to explicitly include fluid/solid interaction forces via disjoining pressure approach. The
simulation techniques include algorithms for GPU computing that allow for simulations
of large domains and detailed analysis of various instability mechanisms within longwave
approach, as well as volume-of-fluid based simulations of Navier-Stokes
equations. Two case studies will be discussed: (i) Liquid crystal films, for which the
challenge is to include liquid-crystalline nature of the fluid in the model in a tractable
manner, and (ii) Liquid metal films irradiated by laser pulses; in this case, one of the
challenges is to include complex thermal effects into consideration and understand
their influence on the film instability and resulting pattern formation. Particular issues
that will be considered include the influence of the initial geometry on the instability
development, Marangoni effects, and the instabilities in the case of multi-fluid
Thursday, November 29, 2018
Atomic-Scale Visualization of Charge-Lattice Order in Correlated Materials
Ismail El Baggari
Cornell University
Department of Physics
12:00 Noon CHEM 260

The coupling between charge, spin, and lattice generates complex correlated phases and, in many cases, ordered patterns that break the spatial symmetries of the crystal. Charge-order stripes are noteworthy because they occur in many material systems and cause significant electronic reconstructions such as metal-insulator transitions, suppression of superconductivity, or spin ordering. As shown by various real space measurements, visualizing electronic modulations locally is a powerful approach for understanding their formation and behavior. However, atomic-scale measurements of the lattice degrees of freedom in charge-ordered systems are lacking.

Aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) are powerful techniques for determining the structure, chemistry and bonding at atomic resolution. Due to stringent stability requirements, most efforts in the physical sciences have focused on room temperature measurements where sub-Angstrom resolution and picometer sensitivity are common. For correlated materials which exhibit electronic and structural transitions below room temperature, STEM/EELS measurements at low temperature are required.

In this talk, I will discuss cryogenic STEM measurements at sub-Å resolution and atomic tracking with picometer precision in charge-ordered materials. In manganites, we map complex picometer-scale, periodic lattice displacements and reveal nanoscale phase inhomogeneity driven by domain competition, shear deformations and topological defects in the modulation field. These phase defects govern long range ordering and incommensurate to commensurate transitions at low temperature. EELS measurements show electronic modifications commensurate with changes in the local bonding environment. Finally, recent studies of charge density waves in the layered materials TaS2 and TaTe2 will be discussed.

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