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RF Nano-Spectroscopy

Head of group: Prof. Stefan Müllegger

Our Research:

Single Atom Radio Frequency Fingerprinting: The "6th Sense" for STM

Modern nanoscience approaches the atomic scale: Individual atoms, rather than ensembles, carry the functionalities of man-made devices (switching, storing, calculating, catalyzing, etc). While single-atom imaging is routine since the advent of the scanning tunneling microscope (STM) in the ‘80s, their chemical identification is difficult. My group develops a “6th sense” that turns the STM from an imaging- to an identification tool with atomic resolution.

Low-temperature scanning tunneling microscopy and -spectroscopy (STS) are the methods of choice for studying electronic and geometric properties of matter at the atomic scale. We develop the low-temperature STM technique towards the detection of radio frequency signals up to several GHz. Our present focus is single-spin spectroscopy with sub-nanometer spatial resolution.

Keywords:

  • Radio Frequency Scanning Tunneling Spectroscopy (rf-STS)
  • Molecule-Based Hybrid Nanostructures
  • Experimental Nanophysics

Single-Spin Microscopy and Spectroscopy- Radio Frequency Scanning Tunneling Microscopy and -Spectroscopy (rf-STS):
Low-temperature (LT) scanning tunneling microscopy (STM) and -spectroscopy (STS) are the methods of choice for studying electronic and geometric properties of matter at the atomic scale. We develop the low-temperature STM technique towards the detection of radio frequency (rf) signals up to several GHz. Our present focus is Single-Spin Spectroscopy with sub-nanometer spatial resolution.

 

Molecule-based Hybrid Nanostructures:
We utilize STM's capabilities of imaging, spectroscopy and manipulation of matter at atomic precision to explore self-aligned and artificial nanostructures formed by a small number (< 10) of molecules on single crystal surfaces. We study the change of molecular properties upon structure formation as well as properties of the ordered molecular ensemble. Recently, we discovered that one-dimensional molecular chains assemblies act as nanomechanical resonators. The image shows the World's Smallest (Man-Made) Mechanical Resonators.

 

Molecular Functionality:
Supporting functional molecules on crystal factes is an established technique in nanotechnology. We apply STM and STS to clarify specific aspects of molecular functionality with immediate importance to spintronics and catalysis. Conductance spectroscopy with sub-nanometer spatial resolution reveals electronic and magnetic properties of the frontier molecular orbitals; the latter are most relevant for the chemical reactivity of agent molecules.

 

Selected publications:

Single-molecule chemical reduction induced by low-temperature scanning tunneling microscopy: a case study of Gold-porphyrin on Au(111),
S. Müllegger, M. Rashidi, W. Schöfberger, and R. Koch,
Surf. Sci. (2018). DOI: 10.1016/j.susc.2018.04.018

Radio frequency surface plasma oscillations: electrical excitation and detection by Ar/Ag(111),
G. Serrano, S. Tebi, S. Wiespointner-Baumgarthuber, S. Müllegger, and R. Koch,
Sci. Rep. 7, 9708 (2017). http://dx.doi.org/10.1038/s41598-017-10170-y

Radio Frequency Scanning Tunneling Spectroscopy for Single-Molecule Spin Resonance,
S. Müllegger, S. Tebi, A.K. Das, W. Schöfberger, F. Faschinger, and R. Koch,
Phys. Rev. Lett. 113, 133001 (2014)

Radio-wave oscillations of molecular-chain resonators,
S. Müllegger, M. Rashidi, K. Mayr, M. Fattinger, A. Ney and R. Koch,
Phys. Rev. Lett. 112, 117201 (2014)
Featured article. Selected for a viewpoint in Physics 7, 26 (2014)

Radio-Frequency Excitation of Single Molecules by Scanning Tunnelling Microscopy,
S. Müllegger, A. K. Das, K. Mayr and R. Koch,
Nanotechnology, 25, 135705 (2014)

Preserving Charge and Oxidation State of Au(III) Ions in an Agent-Functionalized Nanocrystal Model System,
S. Müllegger, W. Schoefberger, M. Rashidi, T. Lengauer, F. Klappenberger, K. Diller, K. Kara, J. V. Barth, E. Rauls, W. G. Schmidt and R. Koch,
ACS Nano 5, 6480 (2011)

Equipment:

The experiments are carried out at ultrahigh vacuum conditions (base pressure below 10-10 mbar) in a low-temperature (LT) scanning tunneling microscopy (STM) system (Createc). The sample temperature is typically at 5 K. The system features a separate UHV chamber for sample preparation including QMS and LEED systems for sample quality checks. We have adapted the STM with a home-built high-frequency excitation and detection system. It is capable of performing a novel type of conductance spectroscopy with simultaneous resonant excitation at radio-frequencies (< 5 GHz).

 

Team:

Former group members:
Lukas Haidinger (Master, 2019)
Dominik Farka (PostDoc, 2018)
Jeffrey Schuster (Master, 2018)
Giulia Serrano (PostDoc, 2016). Thereafter postdoc fellow in Roberta Sessoli's group at University of Firenze.
Stefano Tebi (PhD 2016)
Stefan Wiespointner (Master, 2016)
Karlheinz Mayr (Bachelor, 2013)
Michael Fattinger (Master, 2013)
Thomas Lengauer (Diploma, 2010)
Mohammad Rashidi (PhD, 2009-2013). Thereafter postdoc fellow in Bob Wolkow's group at University of Alberta.

Collaborations:

Join us:

I am constantly looking for proactive and enthusiastic students to join my group. I offer various possibilities for conducting bachelor, master or PhD thesis. At your request I am able to offer flexible working conditions and multidisciplinary topics. For further inquiries please write to stefan.muellegger@jku.at

Open positions:

  • 2 PhD student positions (3 years) on radio-frequency scanning tunneling microscopy, see EURAXESS #381263
  • Postdoc position on radio-frequency scanning tunneling microscopy, see EURAXESS #381333