Single-molecule photo-spintronics

Lead Research Organisation: University of Liverpool
Department Name: Chemistry

Abstract

Spintronics is like electronics except that it uses the spin of the electron (a quantum mechanical property that behaves like angular momentum and is closely linked to magnetism) as well as the electron's electric charge. Using spin and charge together could lead to computers that use much less energy, for example. Photo-spintronics adds light to the mix. This is very useful because light can easily carry information over long distances (think of optic fibres). Light and spin are also key to future quantum technologies such as quantum computing and quantum information.

Our research is to find ways of using organic molecules, based on chains and rings of carbon atoms, in photo-spintronics. This is an exciting prospect because carbon has a low atomic number which reduces the chances of losing spin information, and because there are so many different organic molecules and ways of linking them that the opportunities to find new and useful phenomena are practically endless. Our plan is to study single molecules linking a semiconductor and a magnetic metal. Single molecule experiments are difficult but not impossible, and we have made them successfully in the past using a modified scanning tunnelling microscope. Single molecule studies have helped greatly in understanding molecular electronics because studying molecules individually reveals information that is lost when they are measured in a large group.

Ours will be the first single molecule studies in photo-spintronics. We will create a population of excited electrons in the semiconductor by illuminating it and use the polarization of the light to control the spin of the electrons. We will then measure the current between the semiconductor and the ferromagnetic metal. If the current depends on the polarization of the light and the direction in which the metal is magnetized, that will be evidence that spin is being transported through the molecules. Once we show that we can make photo-spintronic measurements through a single molecule, we will investigate how the spin transport depends on the type of semiconductor, the metal, the voltage between the two (known as the bias), and the types of chemical bond between the molecule and the semiconductor and metal. This will show us how best to use organic molecules in future spintronic and photo-spintronic devices.

Publications

10 25 50
 
Description Using a scanning tunnelling microscopy (STM) technique we have shown that single molecules attaching and detaching can be detected via the conductance of a metal - molecule - compound semiconductor junction. We have shown how the choice of molecule modifies the rectifying properties of the junction and provide new knowledge concerning charge flow in such junctions at the single molecule level. This fabrication of metal - molecule - compound semiconductor junctions opens a new route to integrating devices, such as sensors, incorporating a small number of molecules and conventional semiconductor technology. We have further shown that metal - few molecule - compound semiconductor junctions generate a photocurrent that depends on both the choice of molecule and the doping density of the semiconductor, and have provided a qualitative explanation of this dependence. The photocurrent shows transient effects, which we explain as due to hole-trapping. We have also shown that molecular junctions with nickel contacts can respond to both electrical and chemical stimuli simultaneously, which is extremely important for sensor applications.
Exploitation Route Our work will further the development of new, ultrasensitive and ultracompact sensors. The transient photo-response detected could form the basis of a new local probe of the electronic structure of molecule-semiconductor junctions.
Sectors Chemicals,Education,Electronics,Environment,Pharmaceuticals and Medical Biotechnology

 
Description Collaboration with Bristol University 
Organisation University of Bristol
Department School of Social and Community Medicine
Country United Kingdom 
Sector Academic/University 
PI Contribution Bilateral collaboration with Bristol University on molecular electronics, spintronics and single molecule electronics and measurements and electrochemistry.
Collaborator Contribution Bilateral collaboration with Bristol University on molecular electronics, spintronics and single molecule electronics and measurements and electrochemistry. Collaboration with group of Walther Schwarzacher.
Impact A series of scientific publications.
Start Year 2007
 
Description Danish Technical University 
Organisation Technical University of Denmark
Department Department of Photonics Engineering
Country Denmark 
Sector Academic/University 
PI Contribution Collaboration in molecular electronics (theory) with Prof. Ulstrup group.
Collaborator Contribution Collaboration in molecular electronics (experiment)
Impact Scientific publications, see publication list.
 
Description Univeristy of Georgia, Athens, USA 
Organisation University of Georgia
Department Department of Chemistry
Country United States 
Sector Academic/University 
PI Contribution Molecular electronics collaboration (synthesis and measurements)
Collaborator Contribution Molecular electronics collaboration (measurements)
Impact Publications.
Start Year 2014
 
Description Univeristy of Zaragoza 
Organisation University of Zaragoza
Department Department of Chemistry
Country Spain 
Sector Academic/University 
PI Contribution Bilateral collaboration with Zaragoza University (Spain) on molecular electronics, LB films, single molecule electronics and electrochemistry.
Collaborator Contribution Bilateral collaboration with Zaragoza University (Spain) on molecular electronics, LB films, single molecule electronics and electrochemistry.
Impact See publications attributed.
Start Year 2007
 
Description University of Durham 
Organisation Durham University
Department Department of Biosciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Molecular Electronics (synthesis)
Collaborator Contribution Molecular Electronics (measurements and characterisation)
Impact Scientific publications.
Start Year 2006
 
Description University of Madrid 
Organisation Autonomous University of Madrid
Country Spain 
Sector Academic/University 
PI Contribution Collaboration in single molecule electronics
Collaborator Contribution Collaboration in single molecule electronics
Impact Publications in preparation.
Start Year 2015
 
Description University of Western Australia (UWA) 
Organisation University of Western Australia
Country Australia 
Sector Academic/University 
PI Contribution Molecular electronics (synthesis)
Collaborator Contribution Molecular electronics (measurements and characterisation)
Impact Scientific publications (see list)
Start Year 2014
 
Description Bristol-Liverpool Workshop on Single-Molecule Electron Transport 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Bristol-Liverpool Workshop on Single-Molecule Electron Transport involving academic and industrial attendees and outreach.
Year(s) Of Engagement Activity 2018