You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Self-assembly of ordered epitaxial nanostructures on polygonal nanowires. We study the self-assembly of ordered nanostructures, that is, nanorings (NRs) and quantum dots (QDs), epitaxially grown on a polygonal cross-section nanowire (PCS-NW) using both theoretical and phase-field modeling. Our studies show that, by increasing the PCS-NW size, transitions from ordered NRs to ordered QDs on facets and further to ordered QDs on ridges occur. The predicted morphologies and their transitions are in excellent agreement with existing experiments. Our study suggests a novel approach to fabricate ordered nanostructures on nanowires.
{"Chemical": []}