Dagobert M. de Leeuw

Formation of high-quality self-assembled monolayers of conjugated dithiols on gold: base matters.

This Article reports a systematic study on the formation of self-assembled monolayers (SAMs) of conjugated molecules for molecular electronic (ME) devices. We monitored the deprotection reaction of acetyl protected dithiols of oligophenylene ethynylenes (OPEs) in solution using two different bases and studied the quality of the resulting SAMs on gold. We found that the optimal conditions to reproducibly form dense, high-quality monolayers are 9-15% triethylamine (Et(3)N) in THF. The deprotection base tetrabutylammonium hydroxide (Bu(4)NOH) leads to less dense SAMs and the incorporation of Bu(4)N into the monolayer. Furthermore, our results show the importance of the equilibrium concentrations of (di)thiolate in solution on the quality of the SAM. To demonstrate the relevance of these results for molecular electronics applications, large-area molecular junctions were fabricated using no base, Et(3)N, and Bu(4)NOH. The magnitude of the current-densities in these devices is highly dependent on the base. A value of β=0.15 Å(-1) for the exponential decay of the current-density of OPEs of varying length formed using Et(3)N was obtained.

Doped polyaniline polymer fuses: Electrically programmable read-only-memory elements

We demonstrate polymeric electrically programmable read-only-memory elements based on camphorsulfonic-acid–doped polyaniline lines. Their working mechanism relies on irreversible reduction of the electrical conductivity by Joule heating like electrical safety fuses. The heating power is supplied electrically. The critical power required to “blow up” the fuse is strongly reduced by notches. The influenc eo f the notch design can be predicted reasonably well using a simple thermal model. The critical power becomes less than 1 mW for fuses with notches narrower than 2 m. This power can be delivered by organic transistors already at modest voltages, opening the way of integration of these memory elements in all-polymer circuits.

Soluble fullerene derivatives : The effect of electronic structure on transistor performance and air stability

The family of soluble fullerene derivatives comprises a widely studied group of electron transporting molecules for use in organic electronic and optoelectronic devices. For electronic applications, electron transporting (n-channel) materials are required for implementation into organic complementary logic circuit architectures. To date, few soluble candidate materials have been studied that fulfill the stringent requirements of high carrier mobility and air stability. Here we present a study of three soluble fullerenes with varying electron affinity to assess the impact of electronic structure on device performance and air stability. Through theoretical and experimental analysis of the electronic structure, characterization of thin-film structure, and characterization of transistor device properties we find that the air stability of the present series of fullerenes not only depends on the absolute electron affinity of the semiconductor but also on the disorder within the thin-film.