Size effects on dynamics of a p-dibromobenzene lattice

Abstract

The effect of the change in size of p-dibromobenzene nanoparticles on lattice dynamics has been studied. The nanoparticle size has been determined with an electron microscope. Experimental low-frequency Raman spectra of p-dibromobenzene particles from ∼21 µm to 50 nm in size have been taken. Frequencies of the spectrum lines decrease with the particle size. A half-width line grows with a decrease in size down to ∼400 nm and decreases with a decrease in size from ∼400 to 50 nm. The structure of nanoparticles has been simulated using the molecular dynamics method. Histograms of lattice oscillation spectra were calculated by the Dyne method. It has been found that, with a decrease in particle size to ∼400 nm, the lattice parameters increase and the orientation disorder at the lattice boundary grows. The structure of a nanoparticle is similar to that of a p-dibromobenzene single crystal. When the nanoparticle size changes from ~400 to 50 nm, the lattice parameters increase along the crystallographic a axis and decrease along the two other crystallographic axes.