Tracy Lovejoy1
Nion1
Vibrational spectroscopy in the electron microscope [1] has been made possible by stable monochromators and electron energy loss (EEL) spectrometers, and it continues to progress rapidly [2]. With modern instrumentation [3], <5 meV energy resolution can be attained at 60 keV primary energy and below. This has enabled:<br/>-Standardless temperature measurement at the nanometer (nm) scale [4]<br/>-Detecting and mapping different isotopes, e.g. <sup>13</sup>C vs <sup>12</sup>C in an amino acid (L-alanine) at a specific carbon site, and also D<sub>2</sub>O vs H<sub>2</sub>O in ice, with ~30 nm resolution [5]<br/>-Probing atomic vibrations at interfaces, and edges of nano-objects, with nm spatial resolution [6]<br/>-Efficient mapping of acoustic and optical phonons in momentum space as with nm spatial resolution using angle-resolved EELS [9]<br/>-Probing the vibrational properties of a single substitutional atom [10]<br/>Combination of these spectroscopy techniques with in-situ capabilities holds great promise. A few possible applications include:<br/>-nanometer-scale heat mapping in systems with large thermal gradients<br/>-tracking reaction pathways via the introduction of isotopes in a controlled gas-dosing experiment<br/>-studying heat propagation from phonons due to external stimuli such a strain<br/>-measuring changes in the phonon band structure of nano-objects due to temperature-induced phase transitions<br/>-seeing the spatial distribution of optical excitations of solids near surfaces, interfaces, and maybe individual atoms<br/>As an early example, we show a two-dimensional slice of the phonon band structure of boron nitride resolved as a function of temperature. The change of the phonon bands with temperature reveal the anharmonic phonon scattering in the material.<br/>References<br/>[1] O.L. Krivanek et al., Nature <b>514</b> (2014) 209; T. Miata et al., Microscopy <b>63</b> (2014) 377<br/>[2] O.L. Krivanek et al., Ultramicroscopy <b>203</b> (2019) 60-67<br/>[3] T.C. Lovejoy et al., Microsc. Microanal. <b>24</b> (Suppl 1, 2018) 446-447<br/>[4] J.-C. Idrobo et al., Phys. Rev. Lett. <b>120</b>, 095901 (2018); Lagos, Batson, Nano Lett. 18(7) p4556 (2018)<br/>[5] J. Hachtel et al., Science <b>363</b> (2019) 525–528; J. Jokisaari et al., Adv. Mater. (2018) 1802702<br/>[6] M.J. Lagos and P.E. Batson, Nature <b>543</b>, 529-532(2017); C. Dwyer et al., Phys. Rev. Lett <b>117</b> (2016) 256101<br/>[7] F.S. Hage et al., Phys. Rev. Lett <b>122</b> (2019) 016103<br/>[8] K. Venkatraman et al., Nat. Phys. <b>15</b>, 1237-1241(2019)<br/>[9] T.C. Lovejoy et al., Microsc. Microanal. <b>25</b> (Suppl 2, 2019) 628-629<br/>[10] F.S. Hage et al., Science <b>367</b>, 1124-1127 (2020)