A low energy ion source for electron capture spectroscopy

Hole doping effect of MoS2 via electron capture of He+ ion irradiation

Beyond the general purpose of noble gas ion sputtering, which is to achieve functional defect engineering of two-dimensional (2D) materials, we herein report another positive effect of low-energy (100 eV) He⁺ ion irradiation: converting n-type MoS₂ to p-type by electron capture through the migration of the topmost S atoms. The electron capture ability via He⁺ ion irradiation is valid for supported bilayer MoS₂; however, it is limited at supported monolayer MoS₂ because the charges on the underlying substrates transfer into the monolayer under the current condition for He⁺ ion irradiation. Our technique provides a stable and universal method for converting n-type 2D transition metal dichalcogenides (TMDs) into p-type semiconductors in a controlled fashion using low-energy He⁺ ion irradiation.

Development of 1.2-GHz ECR ion source and Wien filter for inexpensive ion beam processing system

A desktop-sized ion beam processing system with an inexpensive electron cyclotron resonance (ECR) ion source has been developed for industrial applications at the National Institute of Technology, Toyama College. A commercially available 1.2- to 1.3-GHz transceiver is adopted as a microwave source to generate the ECR plasma. The minimum-B magnetic field is formed by arranging small rectangular permanent magnets. A Wien filter with orthogonal electric and magnetic fields is employed as a beam separator. At the end of the beam line, a processing chamber with a substrate stage for ion beam applications, such as ion implantation and microfabrication, is installed. Here, we report the results of the first experiment. Ar ion beams with a current of approximately 62 µA were obtained at an extraction voltage of 4 kV. In addition, we demonstrate that Ar and Xe ions can be separated by the Wien filter.

Imaging properties of hemispherical electrostatic energy analyzers for high resolution momentum microscopy

Hemispherical deflection analyzers are the most widely used energy filters for state-of-the-art electron spectroscopy. Due to the high spherical symmetry, they are also well suited as imaging energy filters for electron microscopy. Here, we review the imaging properties of hemispherical deflection analyzers with emphasis on the application for cathode lens microscopy. In particular, it turns out that aberrations, in general limiting the image resolution, cancel out at the entrance and exit of the analyzer. This finding allows more compact imaging energy filters for momentum microscopy or photoelectron emission microscopy. For instance, high resolution imaging is possible, using only a single hemisphere. Conversely, a double pass hemispherical analyzer can double the energy dispersion, which means it can double the energy resolution at certain transmission, or can multiply the transmission at certain energy resolution.

Correlated Electron Dynamics at Surfaces Investigated via He^{2+} Ion Neutralization

The neutralization of a single He^{2+} ion near a Ir surface leads to the emission of an electron pair. Via coincidence spectroscopy we give evidence that a sizable amount of these electron pairs originate from a correlated single step neutralization of the ion involving a total of four electrons from the metal. These correlated electron pairs cannot be explained in the common picture of two consecutive and independent neutralization steps. We infer a characteristic time scale for the correlated electron dynamics in the metal of 40-400  as.