Unique compositional profile at the interface between Bi2Te3 and aluminium produced via room-temperature bonding

• Room-temperature bonding of the Bi-Te alloy to Al was performed. • Two materials in contact with clean Al and Bi-Te alloy surfaces at room temperature bonded. • A unique compositional profile was formed at the interface. • The bonded interface was analysed using ADFD-STEM, HR-TEM, and EDS. • The formation mechanism was clarified by examining the oxygen diffusion processes. Room-temperature bonding between a Bi 2 Te 3 Peltier element and aluminium wiring was successfully achieved using a surface activation technique. This method involves activation of bonding surfaces in vacuum, enabling direct adhesion between dissimilar materials. STEM, HR-TEM, and EDS analyses revealed a unique interface structure composed of two layers: a ∼2 nm crystalline layer on the aluminium side containing Te and a 4.5– to 6-nm-thick amorphous Al₂O₃ layer containing crystalline nanoparticles on the Bi 2 Te 3 side. To interpret the observed concentration profile, the formation enthalpy of possible reactions and the oxygen source were investigated. It was hypothesised that upon contact, aluminium and Bi₂Te₃ react to form a thermodynamically stable Al₂Te₃ layer. Oxygen inside Bi 2 Te 3 then diffuses toward this layer, causing selective oxidation of aluminium at the Bi₂Te₃–Al₂Te₃ interface. In cases of limited oxygen availability, the Al₂Te₃ layer near the aluminium remains unoxidised. This results in a concentration profile of Al, Te segregates, Al₂O₃, and Bi₂Te₃ from the aluminium side, while Bi concentration increases at the Bi₂Te₃ interface due to Te consumption. The study demonstrates the feasibility of room-temperature bonding for these materials and highlights the critical role of oxygen in forming complex interfacial structures.