Pulsed Laser Condensation of Dense Cubic ZnO with Unique Luminescence, Vibrations, and Interphase Interfaces

Abstract

Dense ZnO with a high-pressure stabilized rocksalt (R)-type structure was fabricated by pulsed laser ablation of bulk wurtzite (W)-type ZnO under a rather high peak power density for a prolonged time in a vacuum. Such dynamic synthesis of R-ZnO relies on effective six-coordination of Zn with O atoms in a laser plume for homogeneous nucleation of R-besides the W-type structure with ZnO4 tetrahedra. The deposit on amorphous silica contains ca. 10% dense R-ZnO with internal compressive stress up to 22.5 GPa based on the X-ray lattice parameter. Transmission electron microscopic observations further indicated the polymorphic condensates are (011)R, (112̅0)W, and (0001)W faceted for mutual coalescence to reach specific crystallographic orientation relationships which are different from that due to R → W transformation, all with an energetically favorable three-dimensional match of lattice planes. The R-type islands up to 100 μm in size on silica substrate showed Raman bands at 800, 1380, and 1607 cm–1 and strong photoluminescence at 545 nm due to ZnO6 octahedra in the cubic crystal field.