Search

Atomic-resolution electron microscopy is a crucial tool to elucidate the structure of matter. Recently, fast electron cameras have added the time domain to high-resolution imaging, allowing static images to be acquired as movies from which sample drift can later be removed computationally and enabling real-time observations of atomic-scale dynamics on the millisecond time scale. Even higher time resolution can be achieved with short electron pulses, yet their potential for atomic-resolution imaging remains unexplored. Here, we generate high-brightness microsecond electron pulses from a Schottky emitter whose current we briefly drive to near its limit. We demonstrate that drift-corrected imaging with such pulses can achieve atomic resolution in the presence of much larger amounts of drift than with a continuous electron beam. Moreover, such pulses enable atomic-resolution observations on the microsecond time scale, which we employ to elucidate the crystallization pathways of individual metal nanoparticles as well as the high-temperature transformation of perovskite nanocrystals.

Reshaping plasmonic nanoparticles with laser pulses has been extensively researched as a tool for tuning their properties. However, in the absence of direct observations of the processes involved, important mechanistic details have remained elusive. Here, we present an in situelectron microscopy study of one such process that involves Coulomb fission of plasmonic nanoparticles under femtosecond laser irradiation. We observe that gold nanoparticles encapsulated in a silica shell fission by emitting progeny droplets comprised of about 10–500 atoms, with ejection preferentially occurring along the laser polarization direction. Under continued irradiation, the emitted droplets coalesce into a second core within the silica shell, and the system evolves into a dual-core particle. Our findings are consistent with a mechanism in which electrons are preferentially emitted from the gold core along the laser polarization direction. The resulting anisotropic charge distribution in the silica shell then determines the direction in which progeny droplets are ejected. In addition to yielding insights into the mechanism of Coulomb fission in plasmonic nanoparticles, our experiments point toward a facile method for forming surfaces decorated with aligned dual-gold-core silica shell particles.

A frequency calibration in the tuning range of the ArF excimer laser near 193 nm was performed. Different electronic spectra of NO were measured by laser-induced fluorescence in a cell and in an oxyacetylene flame. Spectra were measured with a frequency-doubled and Raman-shifted dye laser system and with a tunable ArF excimer laser with a modified configuration. A list of absolute frequencies of the B^2Π(υ′ = 7) ? X^2Π(υ″ = 0) and D^2Σ^+(υ′ = 0) ? X^2Π(υ″ = 1) transitions in this spectral region is given, including a more comprehensive assignment of the latter excitation spectrum.

An atomic streak camera has been constructed that operates from the near to the far infrared. The photocathode used in conventional streak cameras for the conversion of photons to electrons has been replaced by gas-phase atoms in a Rydberg state. The low binding energy of the electron in a Rydberg atom combined with the large photoionization cross section of a Rydberg atom makes Rydberg atoms suitable for use in an infrared streak camera. Operation of the streak camera is demonstrated at 2.6 µm, well beyond the spectral range of any conventional streak camera.