Design of a miniature picosecond low-energy electron gun for time-resolved scattering experiments

Abstract

High power, high uniformity strip electron gun design, simulation and performance Rev.We present the design and performance tests of a miniaturized pulsed low-energy electron gun. Electrons photoemitted from a gold cathode are accelerated over a distance of 75 m and then collimated by a microchannel plate. According to calculations, this novel concept will allow the time spread of the electron pulses to be kept below 5 ps for kinetic energies as low as 100 eV. The achievement of a minimum angular beam divergence ͑Ϸ1°͒ along with an energy resolution of 1.1 eV has to be paid for by low signal intensities. We demonstrate the performance of the gun and the high electron-beam coherence by presenting low-energy-electron diffraction images taken from a submonolayer of lead adsorbed on the germanium ͑111͒ surface. We anticipate that this electron gun will open up new possibilities for following structural changes on solid surfaces in real time.

Development of an Ultrafast Low-Energy Electron Diffraction Setup

“…An implementation of ultrahigh temporal resolution into a LEED system using a laserpump / electron-probe scheme as described below is mainly limited by the capability to deliver short electron pulses at low energies [46,47,141,142]. In particular, electrons with kinetic energies typically employed in LEED are highly susceptible to spatiotemporal broadening from velocity dispersion and space charge effects.…”

“…However, many of the proposed ideas make compromises in either low signal intensity [142] or grazing incidence geometry [143], which ultimately complicates the quantitative analysis, as well as limits the achievable pulse duration.…”

“…In perspective of a stable long-term operation 4 , we therefore limited the maximum emission current to about 10 electrons per pulse. As will be shown later, the resulting few million electrons on the detector per second allow for a real-time observation of diffraction patterns with reasonable contrast and necessitate long integration times only for high-accuracy measurements or low repetition rates [142].…”

An Efficient Procedure to Identify and Quantify New Molecules for Insulating Gas Mixtures

“…Usually, photocathodes are operated in vacuum [33,34,35]. However, in PT experiments [36,37,38,39], the photocathode necessarily operates in the presence of gases at 100 Pa to 100 kPa total pressure.…”

Nanotip-based photoelectron microgun for ultrafast LEED

“…Some drawbacks of RHEED are enhanced volume contributions for stepped and imperfect surfaces and its restriction to map a limited angular fraction of reciprocal space. Ultrafast low-energy electron diffraction (ULEED), on the other hand, is highly desirable due to LEED's outstanding ability to map atomic-scale surface structures 18 but has remained particularly challenging experimentally 19,20 . A main obstacle in the implementation of ULEED lies in achieving ultrashort electron probe pulses at low energies, which are extremely susceptible to pulse spreading in the propagation from the electron source to the sample 19,21 .…”