Electrically conductive metal organic polymer: Synthesis and characterization

Abstract

Thermoelectric materials are emerging as an important type of material that address the most critical topics today, such as energy efficiency and sustainability. They are used in various applications like power generation, thermal imaging, automobiles, solar cells, electronics cooling and wireless sensors. The term metal organic framework (MOF) is used when the metal organic polymer is crystalline and highly porous. The unique properties of metal organic materials, such as low thermal conductivity, high electrical conductivity and tunability make them suitable for use as thermoelectric materials.

In this work, two synthesis methods were used to fabricate copper-ethylenetetrathiolate (Cu-ETT), which is recognized as a metal organic polymer with thermoelectric properties. Atomic Layer Deposition (ALD)/Molecular Layer Deposition (MLD) technique was used to fabricate Cu-ETT thin films. Chemical synthesis method used to synthesize Cu-ETT bulk material. Literature on synthesis methods has discussed the importance of these methods. Also, the existing literature was used to understand and interpret the results.

Bulk Cu-ETT material was synthesized using copper chloride dihydrate (CuCl2. 2H2O) as the secondary building unit (SBU) source, sodium methoxide (NaOMe) as the base and 1,3,4,6-tetrathiapentalene-2,5-dione (TPD) as the organic linker source. Thermoelectric properties of the synthesized Cu-ETT bulk material were studied in varying experimental conditions such as number of Cu equivalents, reaction temperature, and solvent. Clear differences in electrical conductivity, thermal conductivity and Seebeck coefficient were observed under various experimental conditions.

Cu-ETT thin films were fabricated using two different lithium precursors as bases: lithium tert-butoxide (Li-OtBu) and lithium bis(trimethylsilyl)amide (Li-HMDS). 1,3,4,6-tetrathiapentalene-2,5-dione (TPD) was used as the organic linker source and copper acetyl acetonate (Cu(acac)2) used as the SBU source. In ALD/MLD process, the optimized deposition temperature was 220 oC and precursor pulse/purge lengths were 4/16 s for Cu(acac)2 and Li-HMDS, 7/28 s for TPD. The electrical resistivity of the deposited Cu-ETT thin films was studied.