5 research outputs found
Explosive Formation and Dynamics of Vapor Nanobubbles around a Continuously Heated Gold Nanosphere
We form sub-micrometer-sized vapor bubbles around a single laser heating gold
nanoparticle in a liquid and monitor them through optical scattering of a probe
laser. The fast, inertia-governed expansion is followed by a slower contraction
and disappearance after some tens of nanoseconds. In a narrow range of
illumination powers, bubble time traces show a clear echo signature. We
attribute it to sound waves released upon the initial explosion and reflected
by flat interfaces, hundreds of microns away from the particle. Echoes can
trigger new explosions. A steady state of nanobubble with a vapor shell
surrounding the heated nanoparticle can be reached by a proper time profile of
the heating intensity. Stable nanobubbles could have original applications for
light modulation and for enhanced optical-acoustic coupling in photoacoustic
microscopy
Design and synthesis of aromatic molecules for probing electric-fields at the nanoscale
We propose using halogenated organic dyes as nanoprobes for electric field
and show their greatly enhanced Stark coefficients using density functional
theory (DFT) calculations. We analyse halogenated variants of three molecules
that have been of interest for cryogenic single molecule spectroscopy,
perylene, terrylene, and dibenzoterrylene, with the zero-phonon optical
transitions at blue, red, and near infrared. Out of all the combinations of
halides and binding sites that are calculated, we have found that fluorination
of the optimum binding site induces a dipole difference between ground and
excited states larger than 0.5 D for all three molecules with the highest value
of 0.69 D for fluoroperylene. We also report on synthesis of 3-fluoroterrylene
and bulk spectroscopy of this compound in liquid and solid organic
environments.Comment: Article presented in Faraday Discussions on September 201
Intersystem crossing rates of single perylene molecules in ortho-dichlorobenzene
Triplet states can be interesting for optical switching of molecular fluorescence as well as quantum experiments relying on the manipulation of spin states. However, the ground state of molecules is usually a singlet state. It is therefore interesting to study the intersystem crossing (ISC) rates between singlet and triplet states. We have measured the autocorrelation function of the fluorescence from single perylene molecules in an ortho-dichlorobenzene host matrix at cryogenic temperatures (1.3 K). We observed two time scales in the autocorrelation function corresponding to intersystem crossing to two indistinguishable triplet states (TX and TY) and a third triplet state (TZ). By studying the power dependence of the correlation times and contrasts in the autocorrelation functions of single molecules, we determine the ISC rates of perylene for the first time