Investigation of Aging Effects in Thermoelectric Surface Anchored Metal-Organic-Framework (SURMOFs) Films Using Nanoindentation

Abstract

Thin films of Metal-organic-framework (MOF) materials are deposited using a layer-by-layer (LBL) liquid phase epitaxy (LPE) technique. The highly oriented Surface Anchored Metal-Organic Framework (SURMOFs) of Cu3(BTC)2 (BTC: benzenetricarboxylicacid), known as HKUST-1 MOF were grown on Si (100) substrates. MOF materials are designed scaffold-like compounds that consist of metal ions connected by organic ligands, forming highly ordered porous structures. MOF materials found their way to various applications including gas storage due to high storage capacity and device applications in thermoelectrics and microelectronics [1,2]. The thermoelectric application potential of HKUST-1 SURMOF films is based on their large Seebeck coefficient and the premise that the electrical properties of the otherwise insulating MOF films can be custom tailored by loading the porous MOF structure with metal clusters. For modulating the electrical conductivity of MOF films the most effective method is to infiltrate guest molecules inside the porous framework to transport ions, and hence to modulate the electrical properties of the host framework. With nanoindentation testing of the fresh and aged pristine and TCNQ loaded samples, we demonstrate that aging effects impacted the mechanical properties of the films. The aged pristine samples hardness is 0.29 GPA as compared to the fresh as-grown pristine sample of 0.16 GPA at depth of indentation/film thickness (Similarly for the TCNQ loaded samples the hardness of the aged and fresh samples is 0.22 and 0.05 GPA respectively. As hybrid organic-inorganic thermoelectric materials HKUST-1 SURMOF films are subject to aging effects. References Mazure and A.J. Auberton-Herve, Proc. of 35th European Solid-State Device Research Conf. ESSDERC, p. 29 (2005)A. Langdo, M. T. Currie, Z.-Y. Cheng, J.G. Fiorenza, M. Erdtmann, G. Braithwaite, C.W. Leitz, C.J. Vineis, J. A. Carlin, A. Lochtefeld, M. T. Bulsara, I. Lauer, D.A. Antoniadis, M. Somerville, Solid-State Electronics, 48 , 1357 (2004). Figure 1