Annealing of Au, Ag and Au–Ag alloy nanoparticle arrays on GaAs (100) and (111)B

Abstract

Part of developing new strategies for fabrications of nanowire structures involves in many cases the aid of metal nanoparticles (NPs). It is highly beneficial if one can define both diameter and position of the initial NPs and make well-defined nanowire arrays. This sets additional requirement on the NPs with respect to being able to withstand a pre-growth annealing process (i.e. de-oxidation of the III-V semiconductor surface) in an epitaxy system.Recently, it has been demonstrated that Ag may be an alternative to using Au NPs as seeds for particle-seeded nanowire fabrication. This work brings light onto the effect of annealing of Au, Ag and Au-Ag alloy NP arrays in two commonly used epitaxial systems, the Molecular Beam Epitaxy (MBE) and the Metalorganic Vapor Phase Epitaxy (MOVPE). The NP arrays are fabricated with the aid of Electron Beam Lithography on GaAs 100 and 111B wafers and the evolution of the NPs with respect to shape, size and position on the surfaces 2 are studied after annealing using Scanning Electron Microscopy (SEM). We find that while the Au NP arrays are found to be stable when annealed up to 600 °C in a MOVPE system, a diameter and pitch dependent splitting of the particles are seen for annealing in a MBE system. The Ag NP arrays are less stable, with smaller diameters (≤ 50 nm) dissolving during annealing in both epitaxial systems. In general, the mobility of the NPs is observed to differ between the two the GaAs 100 and 111B surfaces. While the initial pattern is found be intact on the GaAs 111B surface for a particular annealing process and particle type, the increased mobility of the NP on the 100 may influence the initial pre-defined positions at higher annealing temperatures. The effect of annealing on Au-Ag alloy NP arrays suggests that these NP can withstand necessary annealing conditions for a complete de-oxidation of GaAs surfaces.

Growth of Boron-Doped Diamond Films on Gold-Coated Substrates with and without Gold Nanoparticle Formation

“…Analysis of the anneal-ing temperature and cooling rate on the crystallographic orientation of AuNPs has shown that annealing at lower temperature yields more faceted, larger particles with a wider size distribution. 58 The surface orientation of the substrates appears to affect the mobility and crystal structure of AuNPs, 59 however AuNPs formed on amorphous SiO 2 -glass substrates also show faceting, preferring the {111} orientation. 58 The formation of nanoparticles (NPs) by annealing occurs as a result of the processes of coalescence, Ostwald ripening, or as a combination of the two.…”

Growth of InAs Wurtzite Nanocrosses from Hexagonal and Cubic Basis

“…We find that a relatively high V/III ratio combined with an oxide masked substrate 39,40 increases the yield of these inclined NWs. However, the initial growth depends on the details of the catalyst interaction with the substrate 41,42 , which also 9 influence the preferential NW morphology and crystal structure. We also find that the NW crystal structure changes from ZB to pure WZ during the initial growth stage, under the given growth conditions 13,43,44 .…”

“…We find that a relatively high V/III ratio combined with an oxide masked substrate , increases the yield of these inclined NWs. However, the initial growth depends on the details of the catalyst interaction with the substrate, , which also influence the preferential NW morphology and crystal structure. We also find that the NW crystal structure changes from ZB to pure WZ during the initial growth stage, under the given growth conditions. ,, Growth of two NWs along the opposite ⟨111⟩B directions, stemming from seed particles positioned along the [0–11] direction, then results in the formation of the vertical X-shaped WZ/ZB/WZ NCs (Figure a, left panel).…”

Exploring Au Droplet Motion in Nanowire Growth: A Simple Route toward Asymmetric GaP Morphologies

“…Recently, the spontaneous motion of Au droplets on III–V surfaces has been studied due to the role of this metal particle in vapor–liquid–solid mechanism, usually employed in III–V nanowire growth. − In particular, the ability to control droplet crawling opens up the possibility to create novel structures and to facilitate nanowire integration in device fabrication, through a process totally determined by an in situ mechanism, which can reach similar size limits as electron beam lithography. The fabrication of oxide free surfaces by Au droplet crawling has already been observed; however, the direct impact of Au droplet motion in nanowire growth to create novel morphologies has not been determined yet.…”

“…Spontaneous temperature-activated motion of liquid metal droplets on III–V semiconductor surfaces has already been reported, especially for Ga droplets. − In this case, droplet dynamics have been shown to be intrinsically associated with differences in surface roughness on solid surfaces, such as the local step density; , in general, the motion can be interpreted as a result of the surface free energy gradient under nonequilibrium conditions, caused by changes in surface roughness . Recently, the crawling of liquid droplets has been observed and studied in more detail for Au nanoparticles, where vacuum conditions and the introduction of water vapor during the heating step have been demonstrated to affect droplet stability. Despite chemical and surface energy differences for Ga and Au droplets on III–V surfaces, we can expect some common features.…”