The plasmon resonance-based optical trapping (PREBOT) method is used to achieve stable trapping of metallic nanoparticles of different shapes and composition, including Au bipyramids and Au/Ag core/shell nanorods. In all cases the longitudinal plasmon mode of these anisotropic particles is used to enhance the gradient force of an optical trap, thereby increasing the strength of the trap potential. Specifically, the trapping laser is slightly detuned to the long-wavelength side of the longitudinal plasmon resonance where the sign of the real component of the polarizability leads to an attractive gradient force. A second (femtosecond pulsed) laser is used to excite two-photon fluorescence for detection of the trapped nanoparticles. Two-photon fluorescence time trajectories are recorded for up to 20 minutes for single and multiple particles in the trap. In the latter case, a stepwise increase reflects sequential loading of single Au bipyramids. The nonlinearity of the amplitude and noise with step number are interpreted as arising from interactions or enhanced local fields amongst the trapped particles and fluctuations in the arrangements thereof.

The vibrational properties of CrI3 single crystals were investigated using Raman spectroscopy and were analyzed with respect to the changes of the crystal structure. All but one mode are observed for both the low-temperature R3 and the high-temperature C2/m phase. For all observed modes the energies and symmetries are in good agreement with DFT calculations. The symmetry of a single-layer was identified as p31/m. In contrast to previous studies we observe the transition from the R3 to the C2/m phase at 180 K and find no evidence for coexistence of both phases over a wide temperature range.

We present the Raman scattering results on layered semiconducting ferromagnetic compound CrSiTe3. Four Raman active modes, predicted by symmetry, have been observed and assigned. The experimental results are supported by DFT calculations. The self-energies of the A 3 g and the E 3 g symmetry modes exhibit unconventional temperature evolution around 180 K. In addition, the doubly degenerate E 3 g mode shows clear change of asymmetry in the same temperature region. The observed behaviour is consistent with the presence of the previously reported short-range magnetic order and the strong spin-phonon coupling.