Chiral helicene, a fully conjugated system without stereogenic carbon, can filter spins effectively at room temperature, a consequence of the chiral-induced spin-selectivity effect. The chirality dictates the spin of the electrons transferred through helicene, and magnetoresistance devices based on these molecules show antisymmetric magnetoresistance versus H plots.
The
production of hydrogen through water splitting in a photoelectrochemical
cell suffers from an overpotential that limits the efficiencies. In
addition, hydrogen-peroxide formation is identified as a competing
process affecting the oxidative stability of photoelectrodes. We impose
spin-selectivity by coating the anode with chiral organic semiconductors
from helically aggregated dyes as sensitizers; Zn-porphyrins and triarylamines.
Hydrogen peroxide formation is dramatically suppressed, while the
overall current through the cell, correlating with the water splitting
process, is enhanced. Evidence for a strong spin-selection in the
chiral semiconductors is presented by magnetic conducting (mc-)AFM
measurements, in which chiral and achiral Zn-porphyrins are compared.
These findings contribute to our understanding of the underlying mechanism
of spin selectivity in multiple electron-transfer reactions and pave
the way toward better chiral dye-sensitized photoelectrochemical cells.
We report on the observation of chirality induced spin selectivity for electrons transmitted through monolayers of oligopeptides, both for energies above the vacuum level as well as for bound electrons and for electrons conducted through a single molecule. The dependence of the spin selectivity on the molecular length is measured in an electrochemical cell for bound electrons and in a photoemission spectrometer for photoelectrons. The length dependence and the absolute spin polarization are similar for both energy regimes. Single molecule conductance studies provide an effective charge transport barrier between the two spin channels and it is found to be on the order of 0.5 eV
Ferromagnets are commonly magnetized by either external magnetic fields or spin polarized currents. The manipulation of magnetization by spin-current occurs through the spin-transfer-torque effect, which is applied, for example, in modern magnetoresistive random access memory. However, the current density required for the spin-transfer torque is of the order of 1 × 106 A·cm−2, or about 1 × 1025 electrons s−1 cm−2. This relatively high current density significantly affects the devices' structure and performance. Here we demonstrate magnetization switching of ferromagnetic thin layers that is induced solely by adsorption of chiral molecules. In this case, about 1013 electrons per cm2 are sufficient to induce magnetization reversal. The direction of the magnetization depends on the handedness of the adsorbed chiral molecules. Local magnetization switching is achieved by adsorbing a chiral self-assembled molecular monolayer on a gold-coated ferromagnetic layer with perpendicular magnetic anisotropy. These results present a simple low-power magnetization mechanism when operating at ambient conditions.
We show that in an electrochemical
cell, in which the photoanode
is coated with chiral molecules, the overpotential required for hydrogen
production drops remarkably, as compared with cells containing achiral
molecules. The hydrogen evolution efficiency is studied comparing
seven different organic molecules, three chiral and four achiral.
We propose that the spin specificity of electrons transferred through
chiral molecules is the origin of a more efficient oxidation process
in which oxygen is formed in its triplet ground state. The new observations
are consistent with recent theoretical works pointing to the importance
of spin alignment in the water-splitting process.
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