Indentation fracture toughness of single-crystal Bi 2 Te 3 topological insulators Caterina Lamuta 1 (  ), Anna Cupolillo 2 , Antonio Politano 2 , Ziya S. Aliev 3,4,5 , Mahammad B. Babanly 3 , Evgueni V. Chulkov 5,6,7,8,9 , and Leonardo Pagnotta 1 1 Department of Mechanical, Energy and Management Engineering, University of Calabria, Ponte P. Bucci, Cubo 44C, 87036 Rende, Italy 2 Department of Physics, University of Calabria, Ponte P. Bucci, Cubo 31C, 87036 Rende, Italy 3 Institute of Catalysis and Inorganic Chemistry, ANAS, AZ1143 Baku, Azerbaijian 4 Institute of Physics, ANAS, AZ1143 Baku, Azerbaijian 5 Donostia International Physics Center (DIPC), Paseo de Manuel Lardizabal 4, 20018 San Sebastián/Donostia, Spain 6 Departamento de Fisica de Materiales, Universidad del Pais Vasco, Apartado 1072, 20080 San Sebastián/Donostia, Spain 7 Centro de Fisica de Materiales CFM-Materials Physics Center MPC, Centro Mixto CSIC-UPV/EHU, Paseo de Manuel Lardizabal 5, 20018 San Sebastián/Donostia, Spain 8 Saint Petersburg State University, 198504 Saint Petersburg, Russian Federation 9 Tomsk State University, 634050 Tomsk, Russian Federation Received: 29 September 2015 Revised: 28 December 2015 Accepted: 31 December 2015 © Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2016 KEYWORDS topological insulators, bismuth telluride (Bi 2 Te 3 ), fracture toughness, nanoindentation ABSTRACT Bismuth telluride (Bi 2 Te 3 ) is one of the most important commercial thermoelectric materials. In recent years, the discovery of topologically protected surface states in Bi chalcogenides has paved the way for their application in nanoelectronics. Determination of the fracture toughness plays a crucial role for the potential application of topological insulators in flexible electronics and nanoelectro- mechanical devices. Using depth-sensing nanoindentation tests, we investigated for the first time the fracture toughness of bulk single crystals of Bi 2 Te 3 topological insulators, grown using the Bridgman−Stockbarger method. Our results highlight one of the possible pitfalls of the technology based on topological insulators. 1 Introduction Bismuth telluride (Bi 2 Te 3 ) is a well-known thermo- electric material [1–5]. It is particularly suitable for thermoelectric solar cells [6], waste heat recovery units [7, 8], and power generation [7, 9]. In recent years, Bi chalcogenides have attracted renewed interest because they represent a new phase of quantum matter with innovative electronic properties. These materials, also referred to as “topological insulators” [10–12], are Nano Research 2016, 9(4): 1032–1042 DOI 10.1007/s12274-016-0995-z Address correspondence to caterinalamuta@gmail.com