Nucleation kinetics of SrTiO3 3D islands and nanorings on Si substrates.

The nucleation of SrTiO3 three-dimensional (3D) islands and nanorings on Si substrates via a novel metalorganic decomposition (MOD) process has been investigated as a function of temperature and solution concentration of the SrTi(OC3H7)6 precursor. Quantitative analysis of island density and size distribution by atomic force microscopy (AFM) has revealed the existence of a nucleation regime at solution concentrations below 5 × 10(-3) M, in which the critical nucleus is a trimer and a coalescence regime at higher concentrations, dominated by growth of immobile clusters. Nanorings form preferentially under high supersaturation conditions and their size distribution is consistent with a dynamic coalescence. On the basis of recent theoretical models (Gill, 2012), we have proposed that the island-to-nanoring transition in the SrTiO3/Si system occurs above a critical size as a result of a competition between energetic and kinetic factors. The combination of high-resolution transmission electron microscopy (HRTEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) has shown that the monocrystalline SrTiO3 nanoclusters grow pseudomorphically on the Si substrate and exhibit a strain-induced tetragonal lattice distortion.

Thermal stability of HfO2-on-GaAs nanopatterns.

We have evaluated the effect of thermal annealing on the morphology, crystalline phase and elemental composition of high-k dielectric HfO(2)-on-GaAs nanopatterns at 500-620 °C by using atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). While the HfO(2)-GaAs interface continues to be atomically abrupt at 620 °C, we have found a gradual shrinkage in the pattern linewidth and period with increasing temperature. Facet formation triggered by a nanoscale-modulated sequence of tensile and compressive stresses on the GaAs substrate, observed at 620 °C, has been attributed to a volumetric expansion of the HfO(2) nanostructures, caused by the tetragonal/cubic to monoclinic HfO(2) phase transformation and, to a lesser extent, by solid-state diffusion of As into HfO(2).

Fabrication of HfO2 patterns by laser interference nanolithography and selective dry etching for III-V CMOS application.

Nanostructuring of ultrathin HfO2 films deposited on GaAs (001) substrates by high-resolution Lloyd's mirror laser interference nanolithography is described. Pattern transfer to the HfO2 film was carried out by reactive ion beam etching using CF4 and O2 plasmas. A combination of atomic force microscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy microanalysis was used to characterise the various etching steps of the process and the resulting HfO2/GaAs pattern morphology, structure, and chemical composition. We show that the patterning process can be applied to fabricate uniform arrays of HfO2 mesa stripes with tapered sidewalls and linewidths of 100 nm. The exposed GaAs trenches were found to be residue-free and atomically smooth with a root-mean-square line roughness of 0.18 nm after plasma etching.PACS: Dielectric oxides 77.84.Bw, Nanoscale pattern formation 81.16.Rf, Plasma etching 52.77.Bn, Fabrication of III-V semiconductors 81.05.Ea.