Le Professeur Carl Daniel Frisbie de l’université de Minnesota, Minneapolis, MN (USA) , donnera un séminaire le vendredi 5 juillet à 11h, en salle 774 (Bât. Lavoisier, 15 rue Jean-Antoine de Baïf, 75013, Paris) :
" Extracting Quantitative Information from Molecular Junction I-V Characteristics using a Compact Analytical Model "
One of the central challenges of molecular electronics is to establish clear connections between molecular structure, the ensuing electronic structure, and the current-voltage (I-V) characteristics of molecular junctions. In particular, the offset ε h of the Fermi level relative to the appropriate frontier molecular orbital (HOMO or LUMO) and the electrode-molecule coupling strength Γ (level width) are recognized as two main factors that determine the electrical properties of a typical molecular
junction. We show that a compact analytical model derived by Ioan Baldea (Heidelberg) from the Landauer formalism provides a quantitative fit to the I-V data for a broad spectrum of molecular tunnel junctions and yields values of ε h and Γ that vary systematically with molecular structure and choice of electrode materials. Because of its simplicity, the model is readily accessible to the experimentalist and it is far superior to the commonly used Simmons model because it is based on appropriate physics (e.g., the correct electronic structure) and it provides far better fits to the I-V data. Furthermore, the model predicts the self-similarity of non-resonant tunnel junctions: upon appropriate renormalization, the I-V characteristics for a broad swath of molecular junctions collapse onto a universal curve, as could be expected. We will present transport data and theoretical analysis of tunnel junctions based on molecules such as oligophenylene dithiols, alkane dithiols, alkyl ether dithiols, and the corresponding monothiols – all with systematically varying lengths – and electrodes fabricated from Ag, Au and Pt metals. In all cases, we will emphasize that the compact analytical analysis facilitates structure-property
correlations and a powerful physical organic chemistry approach to molecular electronics.