Cheng K. Saw

Dimensional attributes in enhanced hardness of nanocrystalline Ta–V nanolaminates

The scaling of microstructure to the nanoscale is a well-known method of enhancing the physical properties of many materials. New findings reveal a 10-fold enhancement in the hardness of nanocrystalline Ta and V nanolaminates is attributable to grain size effects, more so than the layer pair spacing. A Hall–Petch relationship of hardness with grain size appears in these body-centred-cubic nanocrystalline structures.

Properties of GaAs nanoclusters deposited by a femtosecond laser

The properties of femtosecond pulsed laser deposited GaAs nanoclusters were investigated. Nanoclusters of GaAs were produced by laser ablating a single crystal GaAs target in vacuum or Ar gas. Atomic force and transmission electron microscopies showed that most of the clusters were spherical and ranged in diameter from 1 nm to 50 nm, with a peak size distribution between 5 nm and 9 nm, depending on the Ar gas pressure or laser fluence. X-ray diffraction, solid-state nuclear magnetic resonance, Auger electron spectroscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy revealed that these nanoclusters were randomly oriented GaAs crystallites. An oxide outer shell of ∼2 nm developed subsequently on the surfaces of the nanocrystals as a result of transportation in air. Unpassivated GaAs nanoclusters exhibited no detectable photoluminescence. After surface passivation, these nanoclusters displayed photoluminescence energies less than that of bulk GaAs from which they were made. Our photoluminescence experiments suggest an abundance of sub-band gap surface states in these GaAs nanocrystals.