Dr Tim Albrecht

Biography

• Surface modification and functionalisation on single-crystal electrodes
• Single-molecule conductance and molecular electronics
• Electrochemical scanning tunnelling microscopy (EC-STM)
• Chip-based nanoscale electrodes
• Theory of interfacial charge transfer at the nanoscale

Research interests

I am interested in various aspects of electrochemical charge transfer, in particular at the single-molecule level. This includes redox systems as diverse as small transition metal complexes, metal nanoparticles and biomolecules. We mainly employ electrochemical scanning tunnelling microscopy (ECSTM), which combines ultimate spatial resolution (atoms!) with the detection of ultra-low currents (~ pA). Other approaches are chip-based nanoelectrodes and various electrochemical techniques using single-crystal metal substrates and microelectrodes. Such a well-equipped toolbox gives the opportunity to study both fundamental and applied aspects of single-molecular electron transport. How does the immediate environment of a molecule influence its electron transport properties? Can one use such a configuration as device components in nanoscale electronic circuitry ("molecular electronics")? Is it possible to use such a concept in innovative sensor applications?

Other activities

I have been involved in teaching at undergraduate and postgraduate levels, for example in a “nanochemistry” course for 1st year students. Furthermore, I am reviewer for a number of scientific journals in the field of electrochemistry, physical chemistry, and chemical physics. I am member of the Royal Society of Chemistry and of the International Society of Electrochemistry.

Research Highlights
Electrochemical tunnelling sensors and their potential applications - Nature Communications, May 2012

Recent publications

• Scanning Tunneling Spectroscopy in an Ionic Liquid, Tim Albrecht, Kasper Moth-Poulsen, Jørn B. Christensen, Johan Hjelm, Thomas Bjørnholm, Jesn Ulstrup J. Am. Chem. Soc., 2006, 128(20) pp 6574 - 6575, (Communication) DOI: 10.1021/ja061993p [available for download from the publisher's site]

For the first time ever, we could demonstrate single-molecule diode, transistor, and switching characteristics in an ionic liquid.

• Mechanism of Electrochemical Charge Transport in Individual Transition Metal Complexes, Tim Albrecht, Adrian Guckian, Alexander M. Kuznetsov, Johannes G. Vos, and Jens Ulstrup, J. Am. Chem. Soc.; 2006; 128(51) pp 17132 - 17138; (Article) DOI: 10.1021/ja066213r [available for download from the publisher's site]

This is a detailed study of redox-mediated single-molecule charge transport in aqueous electrolyte. We determine the conductance per molecule, interfacial tunnelling rate constants, and bridge the gap between monolayer and single-molecule charge transport.

• Transistor-like Behavior of Transition Metal Complexes, Tim Albrecht, Adrian Guckian, Jens Ulstrup and Johannes G. Vos, Nano Lett., 5 (7), 1451 -1455, 2005 . (Letter) DOI: 10.1021/nl050818o [available for download from the publisher's site]

We identify inorganic transition metal complexes as a new class of redox-active switch molecules and show that the electron transport mechanism is hopping.

Biography

• Chemistry studies at the University of Duisburg-Essen, Germany (1995-2000)
• Master thesis in Atmospheric Chemistry (2000), after visits at UC Berkeley and the EU Joint Research Center in Ispra, Italy
• PhD studies at the Max-Planck Institute for Radiation Chemistry (now Bioinorganic Chemistry), working on heterogeneous charge transfer processes of proteins on metal surfaces (2000-2003)
• Visits to the Instituto de Tecnologia Química e Biológica in Oeiras, Portugal, and Prof. Jens Ulstrup’s group at the Technical University of Denmark in Lyngby (2001, 2002)
• PhD degree from the Technical University of Berlin (2003)
• Research Assistant Professor with Prof. Jens Ulstrup at the Technical University of Denmark (2003-2006)
• Appointed to a lecturer position at Imperial College London, Chemistry Department (2006-)

Research
Redox molecules can be brought to display tunnelling current characteristics that are reminiscent of electronic device components, such as diodes, transistors, and switches. These features could thus be exploited in nanoscale and molecular electronics on the way to ever smaller electronic circuitry. The figure illustrates the experimental setup, an electrochemical scanning tunnelling microscope (STM), along with the expected tunnelling current response for different tunnelling experiments. To the left is an example of diode-like behaviour in bias spectroscopy. The tunnelling current is recorded while the difference between tip and substrate potentials is changed (called “bias voltage”).
The figure describes the tunnelling current characteristics similar to a transistor for an electrochemical gate configuration. Both tip and substrate potentials are changed at the same time, keeping the bias voltage constant. These experiments can be performed on individual molecules bound to a conducting substrate. While it remains to be seen if the performance of electrochemically controlled devices can compete with established electronic components and circuit architectures, the above features open up the perspective of true single-molecule electrochemistry. This includes the study of fundamental charge transport in a wide range of electrochemically active systems and their exploitation in innovative sensor and catalyst design.