76 research outputs found
Spin Signatures of Photogenerated Radical Anions in Polymer-[70]Fullerene Bulk Heterojunctions: High Frequency Pulsed EPR Spectroscopy
Charged polarons in thin films of polymer-fullerene composites are
investigated by light-induced electron paramagnetic resonance (EPR) at 9.5 GHz
(X-band) and 130 GHz (D-band). The materials studied were
poly(3-hexylthiophene) (PHT), [6,6]-phenyl-C61-butyric acid methyl ester
(C60-PCBM), and two different soluble C70-derivates: C70-PCBM and
diphenylmethano[70]fullerene oligoether (C70-DPM-OE). The first experimental
identification of the negative polaron localized on the C70-cage in
polymer-fullerene bulk heterojunctions has been obtained. When recorded at
conventional X-band EPR, this signal is overlapping with the signal of the
positive polaron, which does not allow for its direct experimental
identification. Owing to the superior spectral resolution of the high frequency
D-band EPR, we were able to separate light-induced signals from P+ and P- in
PHT-C70 bulk heterojunctions. Comparing signals from C70-derivatives with
different side-chains, we have obtained experimental proof that the polaron is
localized on the cage of the C70 molecule
Sedentary Behavior among National Elite Rowers during Off-Training—A Pilot Study
The aim of this pilot study was to analyze the off-training physical activity (PA) profile in national elite German U23 rowers during 31 days of their preparation period. The hours spent in each PA category (i.e., sedentary: <1.5 metabolic equivalents (MET); light physical activity: 1.5–3 MET; moderate physical activity: 3–6 MET and vigorous intense physical activity: >6 MET) were calculated for every valid day (i.e., >480 min of wear time). The off-training PA during 21 weekdays and 10 weekend days of the final 11-week preparation period was assessed by the wrist-worn multisensory device Microsoft Band II (MSBII). A total of 11 rowers provided valid data (i.e., >480 min/day) for 11.6 week days and 4.8 weekend days during the 31 days observation period. The average sedentary time was 11.63 ± 1.25 h per day during the week and 12.49 ± 1.10 h per day on the weekend, with a tendency to be higher on the weekend compared to weekdays (p = 0.06; d = 0.73). The average time in light, moderate and vigorous PA during the weekdays was 1.27 ± 1.15, 0.76 ± 0.37, 0.51 ± 0.44 h per day, and 0.67 ± 0.43, 0.59 ± 0.37, 0.53 ± 0.32 h per weekend day. Light physical activity was higher during weekdays compared to the weekend (p = 0.04; d = 0.69). Based on our pilot study of 11 national elite rowers we conclude that rowers display a considerable sedentary off-training behavior of more than 11.5 h/day
Sub-nanoscale Temperature, Magnetic Field and Pressure sensing with Spin Centers in 2D hexagonal Boron Nitride
Spin defects in solid-state materials are strong candidate systems for
quantum information technology and sensing applications. Here we explore in
details the recently discovered negatively charged boron vacancies () in
hexagonal boron nitride (hBN) and demonstrate their use as atomic scale sensors
for temperature, magnetic fields and externally applied pressure. These
applications are possible due to the high-spin triplet ground state and bright
spin-dependent photoluminescence (PL) of the . Specifically, we find
that the frequency shift in optically detected magnetic resonance (ODMR)
measurements is not only sensitive to static magnetic fields, but also to
temperature and pressure changes which we relate to crystal lattice parameters.
Our work is important for the future use of spin-rich hBN layers as intrinsic
sensors in heterostructures of functionalized 2D materials.Comment: 9 pages, 4 figures, 2 table
Direct Detection of Photoinduced Charge Transfer Complexes in Polymer:Fullerene Blends
We report transient electron paramagnetic resonance (trEPR) measurements with
sub-microsecond time resolution performed on a P3HT:PCBM blend at low
temperature. The trEPR spectrum immediately following photoexcitation reveals
signatures of spin-correlated polaron pairs. The pair partners (positive
polarons in P3HT and negative polarons in PCBM) can be identified by their
characteristic g-values. The fact that the polaron pair states exhibit strong
non-Boltzmann population unambiguously shows that the constituents of each pair
are geminate, i.e. originate from one exciton. We demonstrate that coupled
polaron pairs are present even several microseconds after charge transfer and
suggest that they embody the intermediate charge transfer complexes which form
at the donor/acceptor interface and mediate the conversion from excitons into
free charge carriers
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