Tunnelling currents in Langmuir-Blodgett monolayers of stearic acid

Abstract

Tunnelling currents in stearic acid monolayers stored at 15°C in dry He have been monitored over an 8 week period. Measurements were made as a function of both temperature and also applied voltage. It is deduced that the observed currents are associated with defects which are gradually annealed out.

Current Rectification, Switching, Polarons, and Defects in Molecular Electronic Devices

“…This behavior is not really sensitive to a particular molecular structure, since this type of bistability is observed in complex rotaxane-like molecules as well as in very simple alkane chains (CH 2 ) n assembled into LB films [38], and is not even exclusive to the organic films. The data strongly indicates that the switching has an extrinsic origin, and is related either to bistability of molecule-electrode orientation [22,23,34], or transport assisted by defects in the film [54,55].…”

“…It was concluded some decades ago that the conduction through absorbed [54] and Langmuir-Blodgett [55] monolayers of fatty acids (CH 2 ) n , which we denote as Cn, is associated with defects. In particular, Polymeropoulos and Sagiv studied a variety of absorbed monolayers from C7 to C23 on Al/Al 2 O 3 substrates and found that the exponential dependence on the length of the molecular chains is only observed below the liquid nitrogen temperature of 77K, and no discernible length dependence was observed at higher temperatures [54].…”

“…Single defect states result in steps on the associated I-V curve, whereas molecules in the presence of two defects generally exhibit a negative differential resistance (NDR). Both types of behavior are generic and may be relevant to some observed unusual transport characteristics of SAMs and LB films [54,55,58,90,97,98]. We have used an ab-initio approach that combines the Keldysh non-equilibrium Green's function (NEGF) method with selfconsistent pseudopotential-based real space density functional theory (DFT) for systems with open boundary conditions provided by semi-infinite electrodes under external bias voltage [51,49].…”

Transport properties of water and pentane in Langmuir–Blodgett films

“…The measurement of the electrical properties of LB films, such as conductance (Roberts, 1990) and capacitance (Srinivasan et al, 1988), are important because of the possible use of the films in electronic devices. It has been found, for example, that conductivity depends on the humidity of the ambient environment (Tredgold and Winter, 1981;Barraud et al, 19771, a result that is probably due to the presence of moisture in the films.…”

Effect of impurities on transport through organic self-assembled molecular films from first principles

“…In particular, Polymeropoulos and Sagiv have studied a variety of absorbed monolayers from C7 to C23 on Al/Al 2 O 3 substrates and found that the exponential dependence on the length of the molecular chains is only observed below the liquid nitrogen temperature of 77K, and no discernible length dependence was observed at higher temperatures [2]. The current varied strongly with the temperature for LB films on Al/Al 2 O 3 substrates in He atmosphere (believed to hinder the Al 2 O 3 growth) [3], which is not compatible with elastic tunneling. The 100-fold increase of resistance of the annealed films was attributed to the "annealing" of "defects" with time.…”