Spontaneous Growth of Gallium-Filled Microcapillaries on Ion-Bombarded GaN

Abstract

Bottom-up growth of microscopic pillars is observed at room temperature on GaN irradiated with a Ga þ beam in a gaseous XeF 2 environment. Ion bombardment produces Ga droplets which evolve into pillars, each comprised of a spherical Ga cap atop a Ga-filled, gallium fluoride tapered tube (sheath). The structures form through an interdependent, self-ordering cycle of liquid cap growth and solid sheath formation. The sheath and core growth mechanisms are not catalytic, but instead consistent with a model of ion-induced Ga and F generation, Ga transport through surface diffusion, and heterogeneous sputtering caused by self-masking of the tapered pillars.

Advances in gas-mediated electron beam-induced etching and related material processing techniques

“…Recent applications of electron beam writing techniques have blurred the distinction between EBIE and related deposition methods by demonstrating that precursors which have conventionally been used for etching can also be used to functionalize surfaces [69,89] and to grow complex, non-planar microstructures [90]. These developments, and other examples of surface activation [91][92][93][94][95][96][97] and nanostructure editing through nonchemical pathways [99], highlight the wide diversity of processes that can be exploited by electron beam processing techniques.…”

“…However, the models neglect numerous physical and chemical mechanisms and can not describe effects such as surface roughening and the simultaneous evolution of surface topology, internal nanos-tructure and composition of materials fabricated or restructured by charged particle beams. Future work will likely address these shortcomings, and lead to a better understanding of the full potential of EBIE and related material restructuring [69,[90][91][92][93][94][95][96][97] and characterization [87,31,88] Fig. 2 Potential energy diagrams for physisorption (a) and activated chemisorption (b) used in models of gas-mediated electron beam induced processing [68,69].…”

“…This has been demonstrated most dramatically using XeF 2 , which can be used to realize three distinct processes (Fig. 4(a-c)): electron beam induced fluorination of surfaces [69,89], conventional EBIE, and growth of GaF 3 -containing microstructures [90]. Fluorination (Fig.…”

“…Similarly, the spontaneous growth of the Ga-filled microstructures shown in Fig. 3(i) and 4(c) was simulated by a mass transport model that helped explain the self-organized structure formation mechanism [90]. However, this new form of bottom-up growth has not been incorporated into standard models of particle beam processing (such as Eqns.…”

“…4(c)) through a spontaneous, chemicallyassisted structure formation mechanism driven by a charged particle beam [90]. Specifically, a focused Ga + ion beam is used to induce bottom-up growth of Gafilled, GaF 3 microcapillaries by irradiating a GaN substrate in the presence of XeF 2 precursor gas.…”