Gaining insight into molecular tunnel junctions with a pocket calculator without - data fitting. Five-thirds protocol.

The protocol put forward in the present paper is an attempt to meet the experimentalists' legitimate desire of reliably and easily extracting microscopic parameters from current-voltage measurements on molecular junctions. It applies to junctions wherein charge transport dominated by a single level (molecular orbital, MO) occurs off-resonant tunneling. The recipe is simple. The measured current-voltage curve = () should be recast as a curve of /. This curve exhibits two maxima: one at positive bias ( = ), another at negative bias ( = ). The values > 0 and < 0 at the two peaks of the curve for / at positive and negative bias and the corresponding values = () > 0 and = () < 0 of the current is all information needed as input. The arithmetic average of and || in volt provides the value in electronvolt of the MO energy offset = - relative to the electrode Fermi level (|| = ( + ||)/2). The value of the (Stark) strength of the bias-driven MO shift is obtained as = (4/5)( - ||)/( + ||) sign (). Even the low-bias conductance estimate, = (3/8)(/ + /), can be a preferable alternative to that deduced from fitting the - slope in situations of noisy curves at low bias. To demonstrate the reliability and the generality of this "five-thirds" protocol, I illustrate its wide applicability for molecular tunnel junctions fabricated using metallic and nonmetallic electrodes, molecular species possessing localized σ and delocalized π electrons, and various techniques (mechanically controlled break junctions, STM break junctions, conducting probe AFM junctions, and large area junctions).