PbTe quantum dots grown by femtosecond laser ablation

Laser ablation (LA) is a thin film fabrication technique which has generated a lot of interest in the past few years as one of the simplest and most versatile methods for the deposition of a wide variety of materials. With the rapid development experienced in the generation of ultra short laser pulses, new possibilities were opened for the laser ablation technique, using femtosecond lasers as ablation source. It is commonly believed that when the temporal length of the laser pulse became shorter than the several picoseconds required to couple the electronic energy to the lattice of the material, thermal effects could not play a significant role. Since the pulse width is too short for thermal effects to take place, with each laser pulse a few atom layers of material are direct vaporized away from the target surface and a better control in the quantum dots (QDs) fabrication could be achieved. In this work we report the fabrication of PbTe QDs by femtosecond laser ablation of a PbTe target in argon atmosphere. Experiments were carried out using a typical LA configuration comprising a deposition chamber and an ultra short pulsed laser (100 fs; 30 mJ) at a central wavelength of 800 nm. PbTe was chosen because its QDs absorption band can be controlled by its size to fall in the spectral window of interest for optical communications (1.3-1.5 μm). This, together with the QD high optical nonlinearity, makes this material an excellent candidate for development of photonic devices. It was investigated the influence of the number of laser pulses in the formation of the nanoparticles. The structural parameters and the surface density of the nanoparticles were studied by high resolution transmission electron microscopy (HRTEM)..