Shape- and phase-controlled ZnS nanostructures and their optical properties

Single-crystalline ZnS nanoparticles with a zinc-blende crystal structure have some microdefects such as stacking faults and nanotwins. In contrast, ZnS nanorods have a wurtzite crystal structure, which grows along the [0 0 0 1] direction, although some nanorods display the intergrowth of a minor zinc-blende phase and the major wurtzite phase, which forms stacking faults or zinc-blende/wurtzite ZnS nanotwins. Raman spectroscopy measurements reveal surface phonons and longitudinal optical phonons in the nanoparticles, nanorods and doublet phonons that are associated with the transversal optical phonons of the A1 and E1 modes in only the nanorods. The first-order longitudinal optical phonon mode exhibits a blueshift of 6 cm−1 when the particle size increases from 5 to 15 nm, but there is no shift in the range of 15–30 nm because of quantum confinement and microdefects.