The considerable activity in the area of organic thin films, involving very thin polymeric films and molecular monolayers and multilayers, led to the formation of a panel, sponsored by the Materials Sciences Division of the Department of Energy, to review this field. Its purpose was to better understand the relevant scientific topics and to suggest suitable areas of research. In particular, a number of potential applications were identified, which require further scientific advances for them to see fruition. These include nonlinear and active optical devices, chemical, biochemical, and physical sensors, protective layers (e.g., for passivation), patternable materials both for resists and for mass information storage, surface modification (e.g., wetting and electrochemical electrode properties), and synthetic biomacromolecules. Studies of these films have the added advantage that they could lead to a better scientific understanding of such subjects as the relationships between the microstructure of ordered molecular arrays and their collective properties, the tailoring of interfaces and surfaces, especially when used to model multibody interactions, and the physical and chemical reactions of films involving phase transitions and intraand interfilm transport. The areas that appear to require the most attention include the application of new characterization techniques, such as the scanning tunneling microscope, the improvement of mechanical and thermal stability, the identification and characterization of physical and chemical defects, and the effects of internal ordering on macroscopic properties. It is further recommended that strong interdisciplinary efforts be mounted to address and solve these problems.

To examine DNA-modified surfaces, we have developed a simple, convenient, and reliable procedure based on the voltammetric response of multiply charged transition metal cations (such as [Ru(NH3)6]3+) bound electrostatically to the DNA probes. At micromolar concentrations of the redox molecules in the electrolyte, the reduction and oxidation waves resulting from the immobilized cations on DNA-modified electrodes are well defined, stable, and reproducible. The surface densities of both single- and double-stranded oligonucleotides were accurately determined by integration of the peak for reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+. In addition, the binding constant and electron-transfer rate constant of [Ru(NH3)6]3+ on DNA-modified electrodes were evaluated with the help of classical models. The present research provides not only an applicable and simple protocol for the quantitation of DNA probes on chips but also a versatile and powerful tool for the investigation of the binding activity and electron-transfer kinetics of cationic analytes on DNA-modified surfaces.

Redox-labeled self-assembled monolayers (SAMs) on gold are excellent model systems for the study of long-range electron transfer processes at electrolyte–electrode interfaces, particularly the distance and reorganization energy dependences. In this work, we have shown that the intermolecular interaction among redox centers is in fact a crucial factor in the overall, nonideal electrochemical response of ferrocenylalkanethiolate SAMs on gold. In both single-component and high-ratio binary monolayers of 11-ferrocenyl-1-undecanethiol (FcC11SH), the two distinct pairs of redox peaks are corresponding to rather moderate differences in the packing densities of the two structural domains. We have discovered that the redox peak at lower potential becomes narrower and higher when organic solvents (nitrobenzene or octanol) are added to the aqueous electrolyte, while the peak at the higher potentials is barely influenced. On the basis of the Frumkin isotherm, we have obtained the intermolecular interaction parameters in the different structural domains of the monolayers by fitting the experimental data. The results showed that the intermolecular interaction in the FcC11S–Au SAMs can change from repulsion to attraction upon adding organic solvent in the aqueous electrolyte. It is suggested that the solvent perturbation to the SAM structure at monolayer/electrolyte interface induces remarkable change in the intermolecular interactions and therefore modulates the observed electrochemical responses from nonideal to nearly ideal.

Robust and uniform n-alkyl monolayers were formed on silicon from the reaction of Grignard regents (n-C n H2 n +1MgBr, n = 2, 6, 10, and 15) with hydrogen-terminated Si(111). The capacitive properties of these organic thin films on silicon in contact with aqueous electrolytes were evaluated by electrochemical impedance measurements. In particular, the reciprocal capacitance of the organic thin film modified silicon/aqueous electrolyte interfaces is proportional to the film thickness, which is tunable by simply varying the alkyl chain length. The derived dielectric constant of these organic thin films from the best fit of the reciprocal capacitance vs ellipsometric film thickness plot is ε = 3.3 ± 0.6.

To evaluate the electrical performance of molecularly modified metal-semiconductor diode junctions, organic monolayers were grafted on both hydrogen-terminated and oxidized silicon (p-type) surfaces. Three model systems, i.e., Hg|C 12 H 25 -Si, Hg|SiO 2 -Si, and Hg|C 12 H 25 SiO 3 -SiO 2 -Si, were prepared and systematically characterized based on their current-voltage and capacitance-voltage properties. The experimental results showed that mercury-silicon junctions modified with n-dodecyl monolayer display better rectifying behavior, i.e., larger rectifying ratio and smaller empirical ideality factor (i.e., close to unity), than those passivated with SiO 2 thin films and n-dodecylsiloxane monolayers (formed on oxidized silicon). The differential capacitance measurements revealed that organic modified junctions (both alkylated and alkylsilated samples) have substantially lower densities of interface states in comparison with that of Hg|SiO 2 -Si. This work provides a clear assessment of the varied device performance among differently prepared metal-moleculesemiconductor junctions, which is complementary to the topic studies on the electron transport across these molecular interfaces. More importantly, the present research augments the potential applications of molecular modification and surface engineering in the fabrication of silicon-based microelectronic devices.