2,465 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
Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide
Quantum systems can provide outstanding performance in various sensing
applications, ranging from bioscience to nanotechnology. Atomic-scale defects
in silicon carbide are very attractive in this respect because of the
technological advantages of this material and favorable optical and radio
frequency spectral ranges to control these defects. We identified several,
separately addressable spin-3/2 centers in the same silicon carbide crystal,
which are immune to nonaxial strain fluctuations. Some of them are
characterized by nearly temperature independent axial crystal fields, making
these centers very attractive for vector magnetometry. Contrarily, the
zero-field splitting of another center exhibits a giant thermal shift of -1.1
MHz/K at room temperature, which can be used for thermometry applications. We
also discuss a synchronized composite clock exploiting spin centers with
different thermal response.Comment: 8 pages, 7 figure
All-optical dc nanotesla magnetometry using silicon vacancy fine structure in isotopically purified silicon carbide
We uncover the fine structure of a silicon vacancy in isotopically purified
silicon carbide (4H-SiC) and find extra terms in the spin Hamiltonian,
originated from the trigonal pyramidal symmetry of this spin-3/2 color center.
These terms give rise to additional spin transitions, which are otherwise
forbidden, and lead to a level anticrossing in an external magnetic field. We
observe a sharp variation of the photoluminescence intensity in the vicinity of
this level anticrossing, which can be used for a purely all-optical sensing of
the magnetic field. We achieve dc magnetic field sensitivity of 87 nT
Hz within a volume of mm at room temperature
and demonstrate that this contactless method is robust at high temperatures up
to at least 500 K. As our approach does not require application of
radiofrequency fields, it is scalable to much larger volumes. For an optimized
light-trapping waveguide of 3 mm the projection noise limit is below 100
fT Hz.Comment: 12 pages, 6 figures; additional experimental data and an extended
theoretical analysis are added in the second versio
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