Doctoral College TU-D Unravelling advanced 2D materials
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Ion irradiation of 2D materials

Fritz Aumayr, Institute of Applied Physics

Research activities in the FA group focus on the interaction of (multi-charged) ion beams and (femtosecond) laser radiation with matter (atoms, molecules, surfaces) both from a fundamental point of view and because of their relevance for applications. Impact of slow ions on surfaces and the use of highly charged ions as a tool for controlled surface modification via deposition of potential energy are studied [1] using novel experimental techniques developed in the group. We identify the basic interaction mechanisms between ions and solid surfaces from an analysis of the electron emission statistics, the energy loss of scattered projectile ions and the coincidence detection of scattered ions and emitted electrons [1]. New forms of sputtering processes (e.g. potential sputtering) are studied with a highly sensitive quartz microbalance technique [3]. State of the art scanning probe methods (AFM and STM) clarify how the potential energy deposited into the electronic system of a solid by the impact of a highly charged ion can lead to structural modifications of the surface (nano-hillocks, nano-pits or -craters) [4]. Slow highly charged ions are used as a simple tool for the fabrication of nanopores with well-defined diameters (10-20nm) in freestanding, 1nm thick carbon nanomembranes [5]. The group is currently extending its investigations from nanomembranes to single layer graphene, MoS2 and other 2D materials.

PhD Project 1: Damage formation in 2D materials due to slow ion irradiation

Co-supervisor: Gareth Parkinson

The first PhD project explores ion irradiation phenomena in free standing 2D-materials. In fundamental studies it will be investigated how a 2D-material (single layer graphene, MoS2 or hexagonal BN) behaves under a variety of irradiation conditions using slow highly charged ions in the keV region. State of the art TEM, HIM, AFM and STM instruments and thermal treatment will be used to understand damage formation and recovery in 2D-materials. The formation of nano-sized pores and the underlying physical mechanism (i.e. whether defect creation is due to the deposition of the ions potential or kinetic energy) is of specific interest. Application oriented experiments will explore the modification of 2D-materials in order to tailor their properties or to create dense arrays of small holes in 2D-materials, which might be interesting for use as molecular sieves.

 

 

 

PhD Project 2: Transmission of slow highly charged ions through freestanding single layer 2D materials

Co-supervisor: Florian Libisch

The second PhD project will obtain a fundamental understanding of the interaction processes taking place during transmission of slow highly charged ions through a freestanding 2D material (single layer graphene, MoS2 or BN). Slow, multiply charged ions extracted from an ECR-ion source will be directed onto a free standing 2D layer mounted on a TEM grid and the charge state and energy loss of the transmitted ions will be analyzed. In contrast to a 3D solid target or a conventional thin foil, a single layer of atoms are sufficient for the ions to reach charge equilibration. Strong non-equilibrium effects are to be expected like, e.g., a dramatically enhanced kinetic energy loss (stopping force) due to the high charge state of the projectile. The planned investigations will also  give access to ion neutralization times.  Additional information on the specific charge exchange and energy loss processes are addressed by coincidence measurements between the transmitted ions and the number of emitted electrons.


Literature

  1. F. Aumayr, S. Facsko, A. S. El-Said, C. Trautmann and M. Schleberger, Topical Review: Single-ion induced surface nanostructures - A comparison between slow highly-charged and swift heavy ions, Journal of Physics: Condensed Matter 23, 393001 (2011) DOI: 10.1088/0953-8984/23/39/393001
  2. R.A. Wilhelm, E, Gruber, R. Ritter, R. Heller, S. Facsko, and F. Aumayr, Charge exchange and energy loss of slow highly charged ions in 1 nm thick carbon nanomembranes, Physical Review Letters 112, 153201 (2014) DOI: 10.1103/PhysRevLett.112.153201   
  3. G. Hayderer, et al.,  Kinetically-assisted potential sputtering of insulators by highly charged ions,Physical Review Letters 86, 3530 – 3533 (2001) DOI: 10.1103/PhysRevLett.86.3530
  4. A.S. El-Said, et al. Creation of nano-hillocks on CaF2 surfaces by single slow highly charged ions,Physical Review Letters 100, 237601 (2008) DOI: 10.1103/PhysRevLett.100.237601
  5. R. Ritter, et al. Fabrication of nanopores in 1 nm thick carbon nanomembranes with slow highly charged ions, Applied Physics Letters 102, 063112 (2013) DOI: 10.1063/1.4792511