The dynamic responses of a rhodium catalyst and a graphene sheet are investigated upon random excitation with 80 kV electrons. An extraordinary electron microscope stability and resolution allow studying temporary atom displacements from their equilibrium lattice sites into metastable sites across projected distances as short as 60 pm. In the rhodium catalyst, directed and reversible atom displacements emerge from excitations into metastable interstitial sites and surface states Our experiments suggest operating electron microscopes with beam currents as small as zeptoAmperes / nm 2 in a "weak-excitation" approach to improve on sample integrity and allow for time-resolved studies of conformational object changes that probe for functional behavior of catalytic surfaces or molecules.
This contribution touches on essential requirements for instrument stability and resolution that allows operating advanced electron microscopes at the edge to technological capabilities. They enable the detection of single atoms and their dynamic behavior on a length scale of picometers in real time. It is understood that the observed atom dynamic is intimately linked to the relaxation and thermalization of electron beam-induced sample excitation. Resulting contrast fluctuations are beam current dependent and largely contribute to a contrast mismatch between experiments and theory if not considered. If explored, they open the possibility to study functional behavior of nanocrystals and single molecules at the atomic level in real time.
Aberration‐corrected electron microscopy opens new ways for material characterization. In catalyst research it will enable the observation of single atom arrangements, such as the location of promoter atoms on catalyst particles. However, quantitative procedures must be developed to account for dynamic contrast changes resulting from beam‐sample interactions and incoherent instrument aberrations. We demonstrate that at low acceleration voltage (80 kV), for which knock‐on damage is suppressed, the residual intensity fluctuations can be attributed to the presence of phonons resulting in 3D low frequency atom displacements. For rhodium [110] oriented particles it was found that the catalysts are platelets with an aspect ratio of about 0.2 and a surface roughness of ±1 atom. Observation of single surface atoms requires minimization of phonon‐induced motion.
We utilize spin-casting and ultraviolet (UV) light-induced polymerization to make organic−inorganic
nanocomposite thin films. The initial mixture consists of polycaprolactone (PCL) stabilized gold nanoparticles,
reactive monomer alkoxytitanium triacrylate, and photoinitiator benzophenone, dissolved in n-butyl acetate (BuAc)
solvent. Upon spin-casting and under UV light, solvent evaporates and triacrylate monomer undergoes
polymerization, forming a hybrid film exhibiting complex morphologies on several length scales. In particular,
we observe a controlled core−shell microdomain assembly of metal nanoparticles, compatibilizer, and metal-infused photo-cross-linkable acrylate polymer host. The composite film also exhibits high electrical capacitance
due to the large effective dielectric constant of the metal nanoparticle-rich “nodules”. We characterize the
morphology of the film using both polarized light optical, transmission electron (TEM), and atomic force (AFM)
microscopy and propose a theoretical model explaining the formation of macro- and microphase-separated
structures. Our results demonstrate a route to engage molecular self-assembly in an organometallic hybrid composite
which achieves unexpected and unusual material properties that could be used in the electronics industry.
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