Observation of Shape, Configuration, and Density of Au Nanoparticles on Various GaAs Surfaces via Deposition Amount, Annealing Temperature, and Dwelling Time

Au-catalyzed desorption of GaAs oxides

Thermal desorption of native oxides on GaAs(100), (110) and (111)B surfaces around Au particles are studied in vacuum using in situ microspectroscopy. Two temperature-dependent desorption regimes, common to all surfaces, are identified. The low-temperature desorption regime spatially limited to the vicinity of some Au nanoparticles (NPs) is catalytically enhanced, resulting in oxide pinholes which expand laterally into macro holes many times the size of the catalyzing NPs and with shapes dictated by the underlying crystallography. The high-temperature desorption regime causes homogeneous oxides thinning and, ultimately, complete oxide desorption. The temperature difference between the two regimes is ∼25 °C-60 °C. After oxide desorption and depending on Au size and GaAs surface orientation, Au particles may dissolve the fresh GaAs surface and form mobile AuGa₂/Ga core/shell units, or form stationary AuGa₂ crystallites, or the catalyzing Au particles may run with minimal reaction with the GaAs surface. These results will add to the fundamental understanding of many Au-based nanofabrication processes, particularly the epitaxial growth of vertical and lateral nanowires.

New method for MBE growth of GaAs nanowires on silicon using colloidal Au nanoparticles

We present a new method for the deposition of colloidal Au nanoparticles on the surface of silicon substrates based on short-time Ar plasma treatment without the use of any polymeric layers. The elaborated method is compatible with molecular beam epitaxy, which allowed us to carry out the detailed study of GaAs nanowire synthesis on Si(111) substrates using colloidal Au nanoparticles as seeds for their growth. The results obtained elucidated the causes of the difference between the initial nanoparticle sizes and the diameters of the grown nanowires.

Evolution of Self-Assembled Au NPs by Controlling Annealing Temperature and Dwelling Time on Sapphire (0001)

Au nanoparticles (NPs) have been utilized in a wide range of device applications as well as catalysts for the fabrication of nanopores and nanowires, in which the performance of the associated devices and morphology of nanopores and nanowires are strongly dependent on the size, density, and configuration of the Au NPs. In this paper, the evolution of the self-assembled Au nanostructures and NPs on sapphire (0001) is systematically investigated with the variation of annealing temperature (AT) and dwelling time (DT). At the low-temperature range between 300 and 600 °C, three distinct regimes of the Au nanostructure configuration are observed, i.e., the vermiform-like Au piles, irregular Au nano-mounds, and Au islands. Subsequently, being provided with relatively high thermal energy between 700 and 900 °C, the round dome-shaped Au NPs are fabricated based on the Volmer-Weber growth model. With the increased AT, the size of the Au NPs is gradually increased due to a more favorable surface diffusion while the density is gradually decreased as a compensation. On the other hand, with the increased DT, the size and density of Au NPs decrease due to the evaporation of Au at relatively high annealing temperature at 950 °C.