Transport properties of Cu-AlF3-W and Cu-AlF3-Cu heterojunctions using STS measurements and a DFT-NEGF approach

• Published in: Results in physics 2018-09, Vol.10, p.813-817
• Main Authors: Navarro, J.L., Moreno-López, J.C., Candia, A.E., Albanesi, E.A., Passeggi, M.C.G.
• Format: Article
• Language: English
• Subjects: [formula omitted] thin films; Electronic transport; Non Equilibrium Green Functions (NEGF); Scanning Tunneling Microscopy (STM); Scanning Tunneling Spectroscopy (STS)
• ISSN: 2211-3797; 2211-3797
• DOI: 10.1016/j.rinp.2018.07.035

The I-V curves for islands of AlF3 over Cu (1 0 0) were measured experimentally and compared with theoretical results obtained both with Density Functional Theory (DFT) and non equilibrium Green Functions (NEGF) leading to a good agreement between experimental and theoretical results. Also, the electronic properties like the density of states and transmission probabilities were calculated. [Display omitted] •Transport properties of heterojunctions obtained by theoretical and experimental STS.•STS measurements exhibit the insulator behavior of AlF3 on the voltage range showed.•I-V, DOS and transmission curves were obtained by DFT-NEGF calculations.•Good agreement between theoretical and experimental I-V curves showed.•The presence of states between −2 to 5eV make possible the measure of the I-V curve.•The magnitudes of obtained currents are small over AlF3 islands. To understand and to analyze the transport properties of different metal-insulator systems, we developed an experimental study of the electronic transport properties of AlF3 thin films deposited over a Cu(1 0 0) substrate, and a theoretical study to model systems composed by an AlF3 molecule between two metallic Cu(1 0 0)-W(1 0 0) and Cu(1 0 0)-Cu(1 0 0) electrodes with different geometries. The left common electrode is always a Cu(1 0 0) layer, meanwhile the right changing electrode, W(1 0 0) or Cu(1 0 0), in some cases is represented as a layer and in others as having a tip ending. Tunnelling current against voltage (I-V) characteristic curves have been obtained by Scanning Tunneling Spectroscopy (STS) measurements and computed using density functional theory (DFT) with the non equilibrium Green function method (NEGF) within a bias voltage range from −2.5 to 5.0 V. The theoretical curves show low current values, in the order of 10-9 to 10-12, in good agreement with the I-V experimental curves in the same range. This reveals that breakdown response currents begin at higher voltages than 5.0 V. The transmission spectrum, total (DOS) and partial (PDOS) density of states are also presented being the transmission variations addressed in terms of the DOS.