Local determination of the amount of integration of an atom into a crystal surface

Abstract

Collective vibrational modes of crystal lattices, called phonons, determine fundamental material properties, such as their thermal and electrical conductivities. Bulk phonon spectra are influenced by point defects. More recently, the importance of phonons on nanostructures has come into the focus of attention. Here we show a spatially resolved phonon spectra of point defects that reveal distinctly different signatures for a cavity alone and an impurity atom fully integrated into the surface as opposed to one placed into a cavity. The spectra are indicative for delocalized phonons and localized vibrations, respectively, as confirmed by theory.

Local Probes of Graphene Lattice Dynamics

“…[ 136–141 ] In contrast, IETS of lattice vibrations has very scarcely been reported so far. Phonons of graphite, [ 142 ] Bi 2 Sr 2 CaCu 2 O 8 +δ , [ 143 ] Au(111), [ 144,145 ] Ag(100), [ 146 ] thin Pb films on Cu(111), [ 147 ] and Cu(110) [ 148 ] were previously measured using STM‐IETS. Only recently, a theoretical work has described the STM‐IETS of surface phonons of Cu(110) using a nonequilibrium Green's function method.…”

Contrast reversal in atomic-scale phonon spectroscopic imaging

“…This technical development paved the way to an experimental demonstration, supported by simulations, that changes in vibrational modes arising from defects such as interfaces, grain boundaries, and even individual atomic impurities could, in principle, be detected with atomic resolution in STEM [6]. These results offer a new tool for the study of the properties of materials at the atomic scale, complementary to surface science techniques such as inelastic tunneling microscopy, which is also able to probe phonon excitations with atomic sensitivity [7,8]. Using STEM, it was even recently shown that a single substitutional silicon impurity atom in freestanding graphene induces a characteristic, atomically localized modification of the vibrational response [9].…”

Single-atom vibrational spectroscopy in the scanning transmission electron microscope

“…Vibrational electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) has recently emerged as a powerful means of probing the vibrational response of materials at a spatial resolution that is superior to that of other experimental techniques (9,10). Tip-enhanced Raman spectroscopy (TERS) (11) and inelastic electron tunneling spectroscopy (IETS) (12,13) provide high spatial and energy resolution alternatives, but they are strictly limited to surface experiments and, therefore, present challenges for a range of applications. Vibrational STEM-EELS, on the other hand, takes advantage of versatile probe-forming optics to offer ground-breaking capabilities: nanometer-scale thermometry (14), mapping of bulk and surface-phononpolariton modes (15), establishing phonon dispersion diagrams from nano-objects (16), and site-specific isotopic labeling in molecular aggregates (17).…”