Showing papers by "S. Roth published in 1994"

Organic Quantum Wells: Molecular Rectification and Single-Electron Tunnelling

Abstract: We present the first direct observation of molecular rectification as a consequence of asymmetric tunnelling process through molecular quantum wells. In addition, single-electron tunnelling effects were observed which might be attributed to the charging of single molecules or molecular stacks. As molecular systems we used LB-film-based heterostructures consisting of an octasubstituted metallophthalocyanine and a perylene-3,4,9,10-tetracarboxyldiimide derivative sandwiched between two gold electrodes. By using a special thermal evaporation technique to deposit the top gold electrode, we have overcome the problem of short circuits and were able to fabricate highly reproducible devices.

With organtsed metaijorganic filmmetal heterostructures towards molecular electronic devices

Abstract: This paper presents new results on the ordering patterns in organic films of functionalized molecules. The films were prepared with the Langmuir-Blodgett (LB)-technique and show an arrangement of the molecules, which opens applications on the background of molecular electronics.

New LB heterostructures containing electron donating and accepting molecules

Abstract: The structure of new Langmuir-Blodgett films of molecules containing electron donating thiophene moieties and electron accepting viologene moieties is investigated with polarisation dependent Fourier transform infrared spectroscopy. The spectra show strong polarisation dependence allowing determination of the microscopic structure within the films. The molecules are oriented upright on the substrate. Models for the layer structure are established

Nonlinear Excited State Phenomena and Electro-luminescence in Fullerene Crystals

Abstract: The characteristics of photo and electroluminescent emission from C60 crystals are reported. The photoluminescence emission is seen to increase nonlinearly with the third power of the input intensity above a threshold intensity. Associated with this nonlinear increase is the emergence of a long lifetime emission component and a redshifting of the emission spectrum. Furthermore, above an intensity which coincides with the onset of the nonlinear emission, the photoconductive response increases with the cube of the input power. At high excitation densities, the photoconductive response becomes relatively temperature independent compared to the thermally activated behaviour observed at low intensities. The characteristics of the temperature dependence are associated with a high electron mobility phase in the highly excited state and therefore an optically driven insulator to metal transition is proposed as a description of the observed phenomena. Using gold and aluminium electrodes as contacts, a bro...

A time resolved study of electrolummescence in fullerene crystals

Abstract: Summary form only given. Earlier work has shown the ability of fullerene crystals to electroluminesce under DC conditions with a highly nonlinear current-intensity characteristic above a certain threshold voltage [1]. This is similar to the nonlinear phenomena found in the highly excited luminescence and photoconductivity, that are discussed in terms of many body effects [2]. To develop this theoretical model and to investigate the temporal behaviour of electron-hole recombination, measurements of the electroluminescent response of a silver-C60-silver device to triangle and rectangular voltage pulses of different frequencies were performed in the present case. The experiments show the occurence of a phase shift between the voltage pulse and the luminescence signal. This phase shift approaches asymptotically the value of /spl pi//2 with increasing frequency, corresponding to a time delay of about 100 /spl mu/s. In addition an accompanying drop of the luminescence intensity is observable. A theoretical analysis of these processes is proposed, taking into account the dependence of the accumulation and recombination time on the charge carrier concentration.

A New LB Film Forming Molecule Containing Both an Electro- and Photoactive Part

Abstract: LB multilayers of the amphiphilic unsymmetrical disulphide S-(2-azobenzenethio)-11-mercaptoundecanoic acid (AMU) have been prepared and investigated by spectroscopic methods. A reversible photochromic switch can be observed upon film irradiation.