18 research outputs found
Imaging of isotope diffusion using atomic-scale vibrational spectroscopy
The spatial resolutions of even the most sensitive isotope analysis
techniques based on light or ion probes are limited to a few hundred
nanometres. Although vibration spectroscopy using electron probes has achieved
higher spatial resolution, the detection of isotopes at the atomic level has
been challenging so far. Here we show the unambiguous isotopic imaging of 12C
carbon atoms embedded in 13C graphene and the monitoring of their
self-diffusion via atomic level vibrational spectroscopy. We first grow a
domain of 12C carbon atoms in a preexisting crack of 13C graphene, which is
then annealed at 600C for several hours. Using scanning transmission electron
microscopy electron energy loss spectroscopy, we obtain an isotope map that
confirms the segregation of 12C atoms that diffused rapidly. The map also
indicates that the graphene layer becomes isotopically homogeneous over 100
nanometre regions after 2 hours. Our results demonstrate the high mobility of
carbon atoms during growth and annealing via selfdiffusion. This imaging
technique can provide a fundamental methodology for nanoisotope engineering and
monitoring, which will aid in the creation of isotope labels and tracing at the
nanoscale
Position and momentum mapping of vibrations in graphene nanostructures in the electron microscope
Propagating atomic vibrational waves, phonons, rule important thermal,
mechanical, optoelectronic and transport characteristics of materials. Thus the
knowledge of phonon dispersion, namely the dependence of vibrational energy on
momentum is a key ingredient to understand and optimize the material's
behavior. However, despite its scientific importance in the last decade, the
phonon dispersion of a freestanding monolayer of two dimensional (2D) materials
such as graphene and its local variations has still remained elusive because of
experimental limitations of vibrational spectroscopy. Even though electron
energy loss spectroscopy (EELS) in transmission has recently been shown to
probe the local vibrational charge responses, these studies are yet limited to
polar materials like boron nitride or oxides, in which huge signals induced by
strong dipole moments are present. On the other hand, measurements on graphene
performed by inelastic x-ray (neutron) scattering spectroscopy or EELS in
reflection do not have any spatial resolution and require large microcrystals.
Here we provide a new pathway to determine the phonon dispersions down to the
scale of an individual freestanding graphene monolayer by mapping the distinct
vibration modes for a large momentum transfer. The measured scattering
intensities are accurately reproduced and interpreted with density functional
perturbation theory (DFPT). Additionally, a nanometre-scale mapping of selected
momentum (q) resolved vibration modes using graphene nanoribbon structures has
enabled us to spatially disentangle bulk, edge and surface vibrations
Atomic Resolution Imaging at an Ultralow Accelerating Voltage by a Monochromatic Transmission Electron Microscope
Diffractive imaging of the dumbbell structure in silicon by spherical-aberration-corrected electron diffraction
The dumbbell structure in crystalline silicon as known with the separation of 0.136 nm has been reconstructed clearly by diffractive imaging using an electron beam. The spatial resolution in the result is estimated at about 0.1 nm. By utilizing the selected area diffraction technique in a spherical-aberration-corrected transmission electron microscope, one can reconstruct nanostructures with atomic resolution, even if they are not surrounded by empty space such as localized structures embedded in thin film samples. This means that the present method has a unique potential to expand the versatility of diffractive imaging by electron beams drastically