We study the patterns formed on
Ar+
ion-sputtered Si surfaces at room temperature as a function of the control parameters ion
energy and incidence angle. We observe the sensitivity of pattern formation to artifacts
such as surface contamination and report the procedures we developed to control them. We
identify regions in control parameter space where holes, parallel mode ripples and
perpendicular mode ripples form, and identify a region where the flat surface is stable. In
the vicinity of the boundaries between the stable and pattern-forming regions, called
bifurcations, we follow the time dependence from exponential amplification to
saturation and examine the amplification rate and the wavelength in the exponential
amplification regime. The resulting power laws are consistent with the theory of
nonequilibrium pattern formation for a type I (constant wavelength) bifurcation at low
angles and for a type II (diverging wavelength) bifurcation at high angles. We
discuss the failure of all sputter rippling models to adequately describe these
aspects of the simplest experimental system studied, consisting of an elemental,
isotropic amorphous surface in the simplest evolution regime of linear stability.
Methods for the fabrication of large areas of nanoscale features with controlled period and intraperiod organization are of interest because of the potential for high-throughput mass production of nanoscale devices. Due to their potential in this regard, much recent attention has been devoted to self-organization processes, [1][2][3][4][5] in which processing causes the spontaneous emergence of a nanoscale pattern. The short-range order can be quite high [2][3][4] but some envisaged applications require long-range order, which is destroyed by uncontrolled topological defects arising spontaneously from the self-organization process. A potentially successful hierarchical fabrication strategy is the fabrication of controlled features at a small, but lithographically tractable, length scale by methods such as conventional mask or optical-standing-wave lithography, in order to guide a self-organization process at the finest length scale. [6][7][8] Topographic patterning has been used for templating the local disorder in two-dimensional (2D) self-assembled monolayers [9] and for templating defect organization or elimination in three-dimensional (3D) colloidal crystallization.[10] Topography has also been used to manipulate semiconductor quantum-dot placement, composition, and strain, through its effect on stress, [11] surface energy, and mobility.[12]3D short-range ordering of grown-in quantum-dot short-period superlattices can result from multilayer growth; [1,4] nanoscale topographic templating of the first layer could dramatically accelerate the development of order and lead to true long-range order. Lithographically and focused ion beam (FIB)-patterned topographies have recently been used to template quantum-dot growth in linear chains, [8] periodic 2D lattices, [7] and in more complex configurations that are promising for novel nanoelectronic architectures, such as quantum cellular automata.[13] The finest features have been templated by serial writing with a FIB, a prohibitively expensive process for mass production that might be circumvented by using a hierarchical fabrication strategy. Here we report the influence of patterned boundaries on the primary material of complementary metal oxide semiconductor (CMOS) technology, i.e., a Si(001) substrate, in guiding self-organized topographic ripples spontaneously appearing during uniform irradiation with low energy Ar + ions. We show that the long-range order of the features can be greatly enhanced by this lateral-templating approach. The emerging pattern can be manipulated by changing the boundary spacing and misorientation with respect to the projected ion-beam direction. We develop a scalar figure of merit, a dimensionless topological defect density, to characterize the degree of order of the pattern. At small boundary separation, greatest order is observed when the separation is near an integer multiple of the spontaneously arising feature size. The defect density is exceedingly low up to a critical misorientation angle, beyond which topological defects develop i...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.