['Initially', ',', 'binary', 'chalcogenides', 'Bi2Te3', ',', 'Sb2Te3', 'and', 'Bi2Se3', 'have', 'been', 'identified', 'as', 'three', '-', 'dimensional', 'TIs', 'by', 'surface', 'sensitive', 'probes', 'such', 'as', 'angle', 'resolved', 'photoemission', 'spectroscopy', 'and', 'scanning', 'tunneling', 'microscopy', '/', 'spectroscopy', '.']