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:

Charge-Transfer Interaction between Few-Layer MoS2 and Tetrathiafulvalene. Graphene look-alike: MoS2 has a layered structure similar to graphene. Tetrathiafulvalene (TTF) interacts with thin, few-layer MoS2 material by donating an electron, resulting in the formation of TTF radical cation and n-type doping of MoS2 . Electron-withdrawing tetracyanoethylene, in contrast, does not cause p-type doping in MoS2 .
{"Chemical": ["MoS2", "Graphene", "tetracyanoethylene", "graphene", "Tetrathiafulvalene", "TTF"]}