We have studied single-shot femtosecond laser ablation of graphite by combining a variety of experimental techniques including Raman spectroscopy, atomic force microscopy as well as time of flight spectrometry. The comprehensive analysis reveals insights into the ablation process by exploring the surface structure, the fluence dependence, and the structural dynamics of the detachment. The results show formation and detachment of charged carbon products (such as graphene nanoflakes) from the surface. Time-resolved measurements of ion yields and velocities reveal strong quenching and revival of Coulomb explosion as a function of delay time in the range of 100–200 fs, suggesting a displacive motion between the topmost surface layers which regulates the optical properties of the system.

A new 3D composite substrate for on-chip surface enhanced Raman spectroscopy made of nanoporous silicon with embedded gold plasmonic nanoparticles – demonstration of 10 ⁹ enhancement factor.

The authors report single-shot femtosecond laser ablation experiments on the highly oriented pyrolitic graphite surface. The yield of positively charged carbon clusters has been measured by time-of-flight mass spectrometry. The reconstructed velocity distribution of atomic carbon ions indicates that the observed Coulomb explosion is most pronounced for fluences slightly above the damage threshold. Atomic force microscopy studies of the damage spots indicate nanoscopic removal of intact monolayers. The results imply a significant degree of charge localization on the surface graphite layers.

The production of atomically dispersed metal catalysts remains a significant challenge in the field of heterogeneous catalysis due to coexistence with continuously packed sites such as nanoclusters and nanoparticles. This work presents a comprehensive guidance on how to increase the degree of atomization through a selection of appropriate experimental conditions and supports. It is based on a rigorous macro-kinetic theory that captures relevant competing processes of nucleation and formation of single atoms stabilized by point defects. The effects of metal-support interactions and deposition parameters on the resulting single atom to nanocluster ratio as well as the role of metal centers formed on point defects in the kinetics of nucleation have been established, thus paving the way to guided synthesis of single atom catalysts. The predictions are supported by experimental results on sputter deposition of Pt on exfoliated hexagonal boron nitride, as imaged by aberration-corrected scanning transmission electron microscopy.

We demonstrate for the first time the possibility of all-optical modulation of self-standing porous Silicon (pSi) membrane in the Mid-Wavelength Infrared (MWIR) range using femtosecond pump-probe techniques. To study optical modulation, we used pulses of an 800 nm, 60 femtosecond for pump and a MWIR tunable probe in the spectral range between 3.5 and 4.4 μm. We show that pSi possesses a natural transparency window centred around 4 μm. Yet, about 55% of modulation contrast can be achieved by means of optical excitation at the pump power of 60 mW (4.8 mJ/cm²). Our analysis shows that the main mechanism of the modulation is interaction of the MWIR signal with the free charge carrier excited by the pump. The time-resolved measurements showed a sub-picosecond rise time and a recovery time of about 66 ps, which suggests a modulation speed performance of ~15 GHz. This optical modulation of pSi membrane in MWIR can be applied to a variety of applications such as thermal imaging and free space communications.