Particles hunting. What does a particle really look like?

• Chiara Basile

Always drawn them as small dots, but particles look a little bit different when you go and look for them, they are more like a peak over a falling background. What does it mean and how such peak is measured you will know after this talk. I will tell you about how the CMS experiment at LHC, the CERN proton-proton collider, is able to detect and reconstruct particles. As an example, the study of a B meson decay into the notorious X(3872) particle is presented. Particle physicist first met X(3872) more than 20 years ago but they are still struggling in determining what is its internal structure.

Dicussion

Band gap Engineering and Single-photon Emission in Dilute Nitride GaAsN Nanowires

• Paolo De Vincenzi

Semiconductor nanowires are elongated structures with new and yet to be fully explored properties deriving from their peculiar morpholgy. In this work it has been demonstrated post-growth bandgap control of hydrogenated GaAs/GaAsN core/shell nanowires. It has been observed the passivating effect of hydrogen on nitrogen, resulting in the restoration of the emission at the gap energy of GaAs. Subsequently the wires were subjected to thermal annealing procedures to remove the hydrogen and thus restore the effect of nitrogen on the bandgap. After annealing, a huge red-shift is observed, up to 200meV, depending on the initial N concentration, leading to a degree of reversibility of the whole process. By controlling annealing parameters, such as temperature and duration, fine tuning of the emission energy of the nanowires between the characteristic frequence of hydrogenated NW and the frequence of the pristine NW is achieved. In addition, single photon light emission from single nanowires has been demonstrated. Measurements at 5K showed excitonic lines, arising from the non-hydrogenated nitrogen clusters with a g(2)(0) = 0.32 and a FWHM of 158µeV. The obtained results are the basis for the final goal of combining post-growth energy gap fine-tuning with single photon emission in nanowires, in order to create an energy-controlled and site-controlled single photon emitter.

Discussion