What we Gain with Aberration-Correctors and Monochromators — Probing Bonding, Magnetism, Temperature & Anharmonicity at the Nanoscale

DIPC Seminars

Speaker

Juan Carlos Idrobo, Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, USA

When

2017/12/19
13:00

Place

Donostia International Physics Center

Add to calendar

iCal

Subscribe to Newsletter

Until very recently, the goal of aberration-correction in STEM has been to produce the possible smallest electron probes. The reasoning is that smaller probes result in images and spectra with better spatial resolutions. However, it has been recently argued on theoretical grounds that in some cases it is desirable to have an atomic-size electron probe with customized aberrations [1]. In this talk I will discuss how one can use aberrated electron probes to detect magnetic ordering by observing a dichroic signal in the fine structure of an L-edge in a transition metal element for the case of the antiferromagnetic LaMnAsO [2]. I will also present our current efforts to study local lattice vibrations using electron energy-loss spectroscopy (EELS). The physical basis for EELS is that a high energy electron beam in a (S)TEM will interact with the electrons or phonons inside the sample, exciting them from lower to higher energy states, while losing a corresponding amount of energy. However, the opposite interaction is also possible: the fast electron can gain energy from a sample that is initially in a higher energy state, albeit with an exponentially smaller probability that depends on the temperature of the sample. Here, I will show that we can directly measure the local temperature of boron nitride flakes in the nano-environment using monochromated electron beams [3]. Finally, I will present examples of how we can detect the bonding configuration of individual atoms in monolayer graphene and even discriminate between different hydrogen isotopes in water nano drops encapsulated in monolayers of boron nitride [4]. _References_ __ [1] J. Rusz, J. C. Idrobo, and S. Bhowmick, _Phys. Rev. Lett._ **113** (2014) 145501 [2] J. C. Idrobo et al., _Advanced Structural and Chemical Imaging_ **2** (2016) 1 [3] J.C. Idrobo et al., under preparation, September (2017). [4] This research was partially supported by the Center for Nanophase Materials Sciences (CNMS), which is sponsored at ORNL by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy (JCI) **.**