Laura Nuccio

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer

Spintronics has shown a remarkable and rapid development, for example from the initial discovery of giant magnetoresistance in spin valves to their ubiquity in hard-disk read heads in a relatively short time. However, the ability to fully harness electron spin as another degree of freedom in semiconductor devices has been slower to take off. One future avenue that may expand the spintronic technology base is to take advantage of the flexibility intrinsic to organic semiconductors (OSCs), where it is possible to engineer and control their electronic properties and tailor them to obtain new device concepts. Here we show that we can control the spin polarization of extracted charge carriers from an OSC by the inclusion of a thin interfacial layer of polar material. The electric dipole moment brought about by this layer shifts the OSC highest occupied molecular orbital with respect to the Fermi energy of the ferromagnetic contact. This approach allows us full control of the spin band appropriate for charge-carrier extraction, opening up new spintronic device concepts for future exploitation.

Muon spin spectroscopy: magnetism, soft matter and the bridge between the two

LS would like to acknowledge financial support from the Swiss National Science Foundation, grant numbers PBFRP2-138632 and PBFRP2-142820. AD would like to acknowledge financial support from the UK Engineering and Physical Sciences Research Council, grant number EP/G054568/1, the European Union Seventh Framework Programme project NMP3-SL- 2011-263104 ‘HINTS’ and the European Research Council project ‘Muon Spin Spectroscopy of Excited States (MuSES)’ proposal number 307593

Importance of intramolecular electron spin relaxation in small molecule semiconductors

Electron spin relaxation rate (eSR) is investigated on several organic semiconductors of different morphologies and molecular structures, using avoided level crossing muon spectroscopy as a local spin probe. We find that two functionalized acenes (polycrystalline tri(isopropyl)silyl-pentacene and amorphous 5,6,11,12-tetraphenyltetracene) exhibit eSRs with an Arrhenius-like temperature dependence, each with two characteristic energy scales similar to those expected from vibrations. Polycrystalline tris(8-hydroxyquinolate)gallium shows a similar behavior. The observed eSR for these molecules is no greater than 0.85 MHz at 300 K. The variety of crystal structures and transport regimes that these molecules possess, as well as the local nature of the probe, strongly suggest an intra-molecular phenomenon general to many organic semiconductors, contrasting the commonly assumed spin relaxation models based on inter-molecular charge carrier transport.

Temporal mapping of photochemical reactions and molecular excited states with carbon specificity

Photochemical reactions are essential to a large number of important industrial and biological processes. A method for monitoring photochemical reaction kinetics and the dynamics of molecular excitations with spatial resolution within the active molecule would allow a rigorous exploration of the pathway and mechanism of photophysical and photochemical processes. Here we demonstrate that laser-excited muon pump-probe spin spectroscopy (photo-μSR) can temporally and spatially map these processes with a spatial resolution at the single-carbon level in a molecule with a pentacene backbone. The observed time-dependent light-induced changes of an avoided level crossing resonance demonstrate that the photochemical reactivity of a specific carbon atom is modified as a result of the presence of the excited state wavefunction. This demonstrates the sensitivity and potential of this technique in probing molecular excitations and photochemistry.

Future directions of μSR—laser excitation

We discuss the general principles of laser-excited muon pump–probe spin spectroscopy (photo-μSR), including the historical origins of the technique, and discuss the overall experimental method. We review examples of past work using this technique, then discuss the future upgrade of the HiFi spectrometer with a high-power laser system. In particular, we note that performing photo-μSR experiments at high field around avoided level crossing resonances in unsaturated organic materials, offers advantages over the work previously performed at lower magnetic fields. We then present some results from some preliminary modelling of a rather simple two-electron spin system, where we see quite a complicated behaviour of the avoided level crossings. Finally, we discuss some potential applications in the biosciences, such as electron transfer in peptides and photochemistry of carotenoids, as well as magnetism which is a more traditional area for study with muons.

Electron spin relaxation in organic semiconductors probed through μSR

Muon spin spectroscopy and in particular the avoided level crossing technique is introduced, with the aim of showing it as a very sensitive local probe for electron spin relaxation in organic semiconductors. Avoided level crossing data on TMS-pentacene at different temperatures are presented, and they are analysed to extract the electron spin relaxation rate, that is shown to increase on increasing the temperature from 0.02 MHz to 0.33 MHz at 3 K and 300 K respectively.

Measurement of hyperfine coupling constants of muoniated radicals in small molecule semiconductors

We report the hyperfine coupling constants of muoniated radicals formed in a number of organic semiconductors, via transverse field measurements taken in the Paschen Back limit, and compare the results to avoided level crossing resonances. Five muoniated radicals are found in tetracene, despite there only being three potential non-equivalent bonding sites, and we suggest that this might be down to crystal packing effects. For 6,13-bis(triisopropylsilylethynyl) pentacene and 6,13-bis(trimethlsilylethynyl)-pentacene, we demonstrate that the transverse field data supports the previously published avoided level crossing resonances.

Future directions of ?SR?laser excitation

We discuss the general principles of laser-excited muon pump–probe spin spectroscopy (photo-μSR), including the historical origins of the technique, and discuss the overall experimental method. We review examples of past work using this technique, then discuss the future upgrade of the HiFi spectrometer with a high-power laser system. In particular, we note that performing photo-μSR experiments at high field around avoided level crossing resonances in unsaturated organic materials, offers advantages over the work previously performed at lower magnetic fields. We then present some results from some preliminary modelling of a rather simple two-electron spin system, where we see quite a complicated behaviour of the avoided level crossings. Finally, we discuss some potential applications in the biosciences, such as electron transfer in peptides and photochemistry of carotenoids, as well as magnetism which is a more traditional area for study with muons.

Future directions ofμSR—laser excitation

We discuss the general principles of laser-excited muon pump–probe spin spectroscopy (photo-μSR), including the historical origins of the technique, and discuss the overall experimental method. We review examples of past work using this technique, then discuss the future upgrade of the HiFi spectrometer with a high-power laser system. In particular, we note that performing photo-μSR experiments at high field around avoided level crossing resonances in unsaturated organic materials, offers advantages over the work previously performed at lower magnetic fields. We then present some results from some preliminary modelling of a rather simple two-electron spin system, where we see quite a complicated behaviour of the avoided level crossings. Finally, we discuss some potential applications in the biosciences, such as electron transfer in peptides and photochemistry of carotenoids, as well as magnetism which is a more traditional area for study with muons.