Multidimensional Contact Potential Difference Measurements at the Nanoscale in Inorganic Oxides

Inorganic oxide-based sample systems are popular for applications in catalysis, sensing, renewable energy, and fuel cells in which electronic properties play important roles. Environmental conditions, e.g., temperature, can greatly impact the electronic properties and thereby the performance. The lack of basic knowledge of the local variation of electronic properties as a function of temperature limits the fundamental understanding of systems and hampers their robustness. Here, we demonstrate the multidimensionality of contact potential difference (CPD, i.e., the difference in the work functions of the gold-coated probe and the sample when they are in proximity and under thermodynamic equilibrium, a.k.a., volta potential) at the nanoscale in inorganic perovskites and metal-oxides with scanning probe microscopy (SPM) measurements [1, 2]. We concentrated on single-crystal, inorganic perovskites (<i>e.g.</i>, strontium titanate, SrTiO₃) and metal-oxides (<i>e.g.</i>, titanium dioxide, TiO₂) to have the least amount of uncertainty of sample properties. We employed an undoped SrTiO₃ and TiO₂, as they are vastly utilized due to their ideal lattice match for similar systems, cost efficiency, stability, and technological and scientific importance. Our experiments reveal three important results: (I) the CPD of both SrTiO₃ and TiO₂ evolve with temperature, (II) the measured CPD is dominated by the local surface state at small tip-sample separations (<i>i.e.</i>, tip-sample distance &lt; 10 nm), and (III) the thermodynamically driven intrinsic doping of the material is the governing mechanism of the variation of the CPD for these sample systems. These results clearly show that care must be given to identify the temperature-dependent change of electronic properties to attain and preserve the desired performance of inorganic oxide-based sample systems.<br/> <br/>[1] <b> Bugrahan Guner </b>and Omur E. Dagdeviren, ACS Applied Electronic Materials <b>4</b> (8), 4085 (2022).<br/>[2] <b> Bugrahan Guner</b>, Simon Laflamme, and Omur E. Dagdeviren, Review of Scientific Instruments <b>94</b> (6) (2023).<br/> <br/>Funding information:<br/>This work was supported by the Canada Economic Development Fund, Natural Sciences and Engineering Research Council of Canada, and Le Fonds de Recherche du Québec - Nature et Technologies.