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The immobilization of gold nanoparticles (AuNPs) on functionalized electrodes has been shown to be an effective way for switching on the electrochemistry at an otherwise passivated surface. Herein, the attachment of AuNPs onto the industrially available p+- Si(100) electrodes was studied by means of cyclic voltammetry and X-ray photoelectron spectroscopy. The hydrosilylation of p+-Si(100) with 1,8-nonadiyne followed by the "click" of azido propylamine onto the alkyne end formed a self-assembled monolayer (SAM), which protected the p+-Si(100) against oxidation and prevented the electron transfer from dissolved Ru(NH3)63 +. Upon the attachment of AuNPs, however, electron transfer was initially restored. The performance of the p+-Si-SAM-AuNP electrode was found to decay with repeated voltammetric cycling due to the formation of SiOx underneath the SAM. These results suggest that p+-Si-SAM-AuNP electrodes can be used in electrochemical devices for single use applications but are not suitable for long-term use.

We seek to understand how the thermodynamics and kinetics of anthraquinone-containing self-assembled monolayer on silicon electrodes are affected by two key experimental variables: the intensity of the light assisting the anthraquinone/anthrahydroquinone redox process and the local solution environment. The substrates are chemically passivated poorly doped p-type silicon electrodes. The study presents a strategy for the selective modulation of either the anodic or the cathodic process occurring at the interface. Cyclic voltammetry studies showed that unlike for a proton-coupled electron transfer process performed at metallic electrodes, for the redox reaction of the anthraquinone unit on a silicon electrode it becomes possible to (i) selectively facilitate only the oxidation process by increasing the electrolyte pH or (ii) at a given pH value to increase the illumination intensity to anodically shift the onset of the reduction step only but leave the oxidation process thermodynamic unchanged. A model concerning the proton coupled electron transfer mechanism was proposed, where the electron transfer is the rate-determining step for the anthraquinone reduction while a deprotonation step is the rate-determining event for the anthrahydroquinone oxidation on poorly doped illuminated p-type silicon.

Two different interfaces prepared via UV-hydrosilylation of undecylenic acid and 1,8-nonadiyne on silicon(111) have been explored to develop a robust electrochemical DNA sensor. Electrodes modified with undecylenic acid were found to stably immobilise DNA but could not resist the growth of insulating oxides, whereas 1,8-nonadiyne modified electrodes satisfy both requirements.

In this paper we explore a multi-step synthetic strategy toward fabrication of monolayer-modified Si(100) electrodes that can be electrochemically switched. The synthetic scheme is modular and benefits from an established intramolecular lactonization scheme of benzoquinone analogs. A redox-tagged pendant group can be released from the surface such as to allow for in situ monitoring of the switch process. We show that this model system can be used to elucidate chemical and structural events for a surface dynamic system that is rapidly gaining popularity. The influence of polarization times, overpotentials and semiconductor doping type on the kinetic of the switch event is also investigated. In both basic and acidic aqueous electrolytes the release of suitable redox-active markers is found to require unexpectedly large cathodic overpotentials. The release event is accompanied by minor oxidation of the electrode surface and the switched constructs can be regenerated by chemical means with no appreciable deterioration of surface quality. 2013 the Owner Societies.

EMF behind transient reactance (EBTR) model of a synchronous generator has widely been used in the studies of power system stability. The damping in the quadrature axis of a synchronous machine is normally represented by a single time constant equivalent circuit. However, the presence of field in addition to the damper circuit in the direct axis of the machine makes modelling difficult in the direct axis based on the emf behind transient reactance. As a result approximate representations are normally employed. The models based on appropriate representations do not produce accurate results. In this paper, an accurate comprehensive model for the direct axis is presented. The development emerges from the detailed representation of the machine with fluxes as the state variable. The emfs behind field and d-axis damper transient reactances are considered in the model. The validity of the model is tested by comparison with the responses obtained from a detailed model