Reversible Phase Transfer of Luminescent ZnO Quantum Dots between Polar and Nonpolar Media

A facile and reversible phase‐transfer protocol for luminescent ZnO quantum dots (QDs) between methanol and hexane is presented. Oleylamine together with acetic acid trigger this reversible phase‐transfer process, during which the structure and optical properties of the ZnO QDs are well‐protected. ZnO QDs with a diameter of approximately 5 nm emit yellow light at 525 nm, while those with a diameter of approximately 4 nm emit green light at 510 nm. The positions of the emission peaks remain unchanged during the presented phase‐transfer process. The Pearson’s hard and soft (Lewis) acid and base principle, together with the principle that similar substances are more likely to be dissolved by each other, describes the current reversible phase‐transfer process. Herein, we circumvent the time‐consuming work required to synthesize ZnO QDs in different environments, making it possible to combine the advantages of ZnO QDs dispersed in polar and nonpolar solvents.     

Visualization of nanosecond laser-induced dewetting,ablation and crystallization processes in thin silicon films

In the present work, nanosecond pulsed laser crystallization, dewetting and ablation of thin amorphous silicon films are investigated by time-resolved imaging. Laser pulses of 532 nm wavelength and 7 ns temporal width are irradiated on silicon film. Below the dewetting threshold, crystallization process happens after 400 ns laser irradiation in the spot central region. With the increasing of laser fluence, it is observed that the dewetting process does not conclude until 300 ns after the laser irradiation, forming droplet-like particles in the spot central region. At higher laser intensities, ablative material removal occurs in the spot center. Cylindrical rims are formed in the peripheral dewetting zone due to solidification of transported matter at about 500 ns following the laser pulse exposure.