Surface science using radioactive ions at ISOLDE: from metal surfaces to two-dimensional materials

K Potzger,A S Fenta,T E Mølholt,L M C Pereira

doi:10.1088/1361-6471/aa659e

Abstract

We review the research carried out using the apparatus for surface physics and interfaces (ASPIC), at ISOLDE, CERN. We give an overview of the research highlights since 2000, focusing on magnetic and non-magnetic metallic surfaces, and introduce the scientific program that will follow the upgrade which is currently underway, focusing on two-dimensional materials. ASPIC was formerly used for the growth of ultrathin metallic films and their characterization by means of perturbed angular correlation spectroscopy. Past research has mainly focused on the determination of the magnetic hyperfine field at the probe atom located on different sites at the surface such as terraces, kinks, steps as well as on the investigation of the static magnetic polarization at the interface between ferromagnetic and paramagnetic layers. Future research on two-dimensional materials using ASPIC is foreseen to focus on the investigation of structural and electronic properties of adatoms (adsorption sites, hybridization effects, intra-atomic charge transfer, magnetic moments, etc). We emphasize, in this context, the exceptional capabilities of ASPIC in terms of broad applicability, high precision and low detection limits.

Highlights

Reduced dimensionality is a rich playground for contemporary solid state physics, made accessible by continuous progress in experimental techniques which can probe ever smaller amounts of matter
We review the research carried out using the apparatus for surface physics and interfaces (ASPIC), at ISOLDE, CERN
Experimentally investigating structural and electronic properties of 2D systems implies probing a small amount of material, confined within one or few atomic monolayers. This raises a number of challenges, because it requires detecting a small amount of material, and distinguishing it from the macroscopic counterpart associated with the 2D system: the bulk corresponding to the surface; the materials above and below the interface; the substrate in which the two-dimensional material is supported, etc

Summary

Introduction

Reduced dimensionality is a rich playground for contemporary solid state physics, made accessible by continuous progress in experimental techniques which can probe ever smaller amounts of matter. Experimentally investigating structural and electronic properties of 2D systems (surfaces, interfaces and two-dimensional materials) implies probing a small amount of material, confined within one or few atomic monolayers. Using radioactive probes makes it possible to probe small amounts of atoms, orders of magnitude below the monolayer regime of ∼1015 atoms per cm2 This low detection limit is a general consequence of the fact that, within one half-life, half of the probes emit radiation which can contribute to a spectrum. This is in contrast with experimental techniques based on external beams (of photons, electrons, ions, neutrons) which depend on (generally small) cross sections for interaction between the probed atoms and the beam particles. We review the research carried out using ASPIC since 2000, on metal surfaces (section 2), and introduce the scientific program that will follow the upgrade which is currently underway, focusing on two-dimensional materials (section 3)

Research at ASPIC since 2000: surfaces of metals

Magnetic hyperfine fields and anisotropies of ferromagnetic Ni surfaces

Magnetic polarization of a Pd layer induced by a ferromagnetic Ni substrate

Future physics at ASPIC: adatoms on 2D materials

Summary and conclusion