Crystallinity, Stoichiometry, and Luminescence of High Quality ZnO Nanoclusters

Abstract

Quasiperfect ZnO nanoclusters (∼6 nm in diameter) are synthesized in non steady state by an original process (the low energy cluster beam deposition, LECBD). The drastic cooling rate (10 10 K/s) of this cluster source induces an improvement of nanometric ZnO cluster quality as compared to more standard conditions of growth. The enhancement of the particle quality is justified by kinetics growth argument associated with X-ray photoelectron and Auger spectroscopies. Finally, we correlate the structural analysis to in situ cathodoluminescence spectroscopy. The study confirms the importance of the crystallinity more than the stoichiometry itself on the luminescence of the nanoparticles.

Probing the excitonic emission of ZnO nanoparticles using UV–VUV excitations

“…To support this argument it is interesting to note the presence of a broad green band in the MC emission spectra at room temperature. This band is generally attributed to oxygen vacancies or other ''volume related'' defects [11] and is not present in our NP [8]. This fact supports the hypothesis that contrary to the MC, the NP does not contain welldefined defects.…”

“…Our previous in situ study of NP cathodoluminescence reveals that contrary to the microcrystal (MC) the NP does not presents any green luminescence band [8]. The size and the crystallinity are provided by TEM characterization that has shown that the NP have a mean diameter of 6 nm and are crystallized in the wurtzite phase [8]. The MC used for the fabrication of the ablation target is 99.99% pure and calibrated at 200 mesh [9].…”

Enhanced green emission in ZnO/zinc titanate composite materials

“…The UV emission at about 380 nm attracted much attention in recent years due to its potential application in UV lasers. The broad visible emission is situated from blue to red region [1][2][3], which also has many applications in displaying, lighting, biology detector, etc.…”

Oriented Attachment of ZnO Nanocrystals

“…The buffer gas is a mixture of 75% He and 25% O 2 to ensure the resulting clusters are stoichiometric. [30] While cooling the plasma, the buffer gas induces the formation of nucleation embryos (dimers and trimers). The plasma subsequently undergoes a supersonic adiabatic expansion while moving from the nucleation chamber at 20 mbar to the high vacuum deposition chamber at 10 -7 mbar through a micrometric nozzle.…”

“…The corresponding size distribution is a log-normal law peaked at 6 nm in diameter, typical of our accretion growth process. High resolution TEM images (right panels of figure 2) show that the clusters are crystallized in the wurtzite structure and in situ XPS analyses published [30] revealed that thin films resulting from the deposition of these particles were stoichiometric. Furthermore, energy dispersive spectroscopy (EDS) has shown that there is no significant composition fluctuation from one individual particle to another (see supporting information).…”