Atomic vibrations control all thermally activated processes in materials including ionic, atomic and electron diffusion, heat transport, phase transformations and surface chemical reactions. The jump frequency characterizing thermally activated processes is of great practical importance and is determined by the local phonon and molecular vibrational modes of the system. Atomic and molecular heterogeneities and defects such as vacancies, interstitials, dislocations and grain boundaries often regulate kinetic pathways and are associated with vibrational modes which are substantially different from bulk modes. High spatial resolution vibrational spectroscopy is required to probe these defect modes.Recent developments in aberration corrected, monochromated, scanning transmission electron microscopy (STEM) have enabled nanoscale probing of vibrational modes via electron energy-loss spectroscopy (EELS) 1,2 . Nanoscale vibrational spectroscopy is already impacting a wide range of important scientific problems such as measurement of surface and bulk vibrational excitations in MgO nanocubes 3 , probing hyperbolic phonon polaritons in nanoflakes of hBN 4 , measuring temperature in nanometer-sized areas with 1°K precision 5,6 and determining phonon dispersion in nanoparticles 7 . The delocalized nature of certain vibrational signals allows damagefree nanoscale detection for a variety of organic and inorganic material-systems 8-11 . This progress has been impressive, however, to date there have been no experimental methods to spectroscopically probe individual vibrational modes in materials with atomic resolution. Theoretical treatments have explored the question of spatial resolution 12,13 with some treatments suggesting that atomic resolution vibrational EELS should be possible [14][15][16] . Here we demonstrate atomic resolution vibrational spectroscopy in STEM for signals predominantly excited by impact scattering. The resulting order of magnitude advance in spatial resolution will

Palladium is one of the few metals capable of forming hydrides, with the catalytic properties being dependent on the elemental composition and spatial distribution of H atoms in the lattice. Herein, we report a facile method for the complete transformation of Pd nanocubes into a stable phase made of PdH0.706 by treating them with aqueous hydrazine at a concentration as low as 9.2 mM. Using formic acid oxidation (FAO) as a model reaction, we systematically investigated the structure–catalytic property relationship of the resultant nanocubes with different degrees of hydride formation. The current density at 0.4 V was enhanced by four times when the nanocubes were completely converted from Pd to PdH0.706. On the basis of a set of slab models with PdH(100) overlayers on Pd(100), we conducted density functional theory calculations to demonstrate that the degree of hybrid formation could influence both the activity and selectivity toward FAO by modulating the relative stability of formate (HCOO) and carboxyl (COOH) intermediates. This work provides a viable strategy for augmenting the performance of Pd-based catalysts toward various reactions without altering the loading of this scarce metal.

High-resolution monochromated electron energy-loss spectroscopy has the potential to map vibrational modes at nanometer resolution. Using the SiO2/Si interface as a test case, we observe an initial drop in the SiO2 vibrational signal when the electron probe is 200 nm from the Si due to long-range nature of the Coulomb interaction. However, the distance from the interface at which the SiO2 integrated signal intensity drops to half its maximum value is 5 nm. We show that nanometer resolution is possible when selecting the SiO2/Si interface signal which is at a different energy position than the bulk signal. Calculations also show that, at 60 kV, the signal in the SiO2 can be treated non-relativistically (no retardation) while the signal in the Si, not surprisingly, is dominated by relativistic effects. For typical transmission electron microscope specimen thicknesses, surface coupling effects must also be considered.

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