Mercury Drop Junctions

The groups of Majda [74] and Whitesides [47, 48, 75] have both developed metal-SAM/SAM-metal junctions using Hg drops as one or both electrodes (Fig. 10.12). In a mercury drop experiment, both electrodes are covered with a SAM and immersed in a solution. The contact area between the two SAMs is fairly large - up to 1 mm in diameter, which corresponds to ca. 1011-1013 molecules. Yet, despite producing nowhere near single molecular junctions, the ease of fabrication and versatility of this method make it an excellent candidate as a standard laboratory test-bed and /3-values for several n-conjugated molecules have been determined in this way. 

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Weiss, E.A., Chiechi, R.C., Kaufman, G.K., Kriebel, J.K., Li, Z., Duati, M., Rampi, M.A., and Whitesides, G.M. (2007) Influence of defects on the electrical characteristics of mercury-drop junctions self-assembled monolayers of n-alkanethiolates on rough and... 

Faraday s law (p. 496) galvanostat (p. 464) glass electrode (p. 477) hanging mercury drop electrode (p. 509) hydrodynamic voltammetry (p. 513) indicator electrode (p. 462) ionophore (p. 482) ion-selective electrode (p. 475) liquid-based ion-selective electrode (p. 482) liquid junction potential (p. 470) mass transport (p. 511) mediator (p. 500) membrane potential (p. 475) migration (p. 512) nonfaradaic current (p. 512)... 

Other important experimental techniques utilized in the molecular transport studies include the mercury-drop junctions52,53 which have been used to study the transport through alkanethiols, and nanorods (a metallic nanowire-S AM-metallic nanowire junction)54 which have been used to measure 16-mercaptohexadecanoic acid. 

The abihty to measure and to control charge transport across nanometer-scale metal-molecule-metal junctions represents a key step toward the realization of molecular-based electronics [190-192]. Various experimental approaches have been employed to study molecular junctions in two- and three-terminal configurations. These include scanning probe microscopies (STM, STS, CP-AFM) [193-208], crossed-wire junctions [209], mechanical [210-215] and electromigration [216,217] break junctions, nanopores [218] and mercury drop electrodes [219]. Approaches in condensed media, and in par-... 

Fig. 6 Schematic representation cf double-SAM junctions between a metal surface and a mercury drop (adapted fiom Ref 35)...

In 1890 Ostwald introduced the normal calomel electrode ( ) as a reference electrode of fixed potential in equilibrium with aqueous potassium chloride solution. Ostwald calibrated a normal calomel electrode against a dropping mercury electrode and obtained a mean value of 0.560 volt. He referred to this value as the absolute value of the electrode potential of the normal calomel electrode. Ostwald recommended the use of the normal calomel electrode as the null electrode, or the standard electrode, in the measurement of the potential difference at a metal-solution junction. He suggested that the electromotive potential measurement with the normal calomel... 

The polarographic cell assembly comprising cell base and cover with a dropping mercury electrode as the cathode, a platinum wire auxiliary electrode as the anode and a saturated calomel reference electrode making solution contact via a liquid junction bridge. The mercury column is kept at a constant height, to have a natural drop time of about 4 s. The instrumental conditions for the differential pulse technique were 0.5 s drop time, -10 mV/S scan rate, 50 mV modulation amplitude. 

Linear sweep voltammetry (LSV) was carried out using a two-electrode Kalousek cell in conjunction with a slowly dropping mercury electrode with m = 0.67 mg and natural drop-time ti = 11.4 s (in 1.0 M KCl at 0.0 V) at h = 25 cm as the working electrode and a saturated calomel electrode, separated by liquid junction, as the reference electrode. In sulfuric acid solutions of pH less than 0 an Hg/HgS04 reference electrode was used, as was previously described. The voltage scans were started 6 s after the previous drop was dislodged. 

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