Nucleation, aggregative growth and detachment of metal nanoparticles during electrodeposition at electrode surfaces

The nucleation and growth of metal nanoparticles (NPs) on surfaces is of considerable interest with regard to creating functional interfaces with myriad applications. Yet, key features of these processes remain elusive and are undergoing revision. Here, the mechanism of the electrodeposition of silver on basal plane highly oriented pyrolytic graphite (HOPG) is investigated as a model system at a wide range of length scales, spanning electrochemical measurements from the macroscale to the nanoscale using scanning electrochemical cell microscopy (SECCM), a pipette-based approach. The macroscale measurements show that the nucleation process cannot be modelled as either truly instantaneous or progressive, and that step edge sites of HOPG do not play a dominant role in nucleation events compared to the HOPG basal plane, as has been widely proposed. Moreover, nucleation numbers extracted from electrochemical analysis do not match those determined by atomic force microscopy (AFM). The high time and spatial resolution of the nanoscale pipette set-up reveals individual nucleation and growth events at the graphite basal surface that are resolved and analysed in detail. Based on these results, corroborated with complementary microscopy measurements, we propose that a nucleation-aggregative growth-detachment mechanism is an important feature of the electrodeposition of silver NPs on HOPG. These findings have major implications for NP electrodeposition and for understanding electrochemical processes at graphitic materials generally

Processes of change in the East Midland footwear industry

SIGLELD:8318.172(SSRC-HR--5819). / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Developments in nanowire scanning electrochemical - atomic force microscopy (SECM-AFM) probes

Since its introduction, SECM-AFM has gained recognition as an extremely useful tool for a wide variety of analytical and imaging applications. We have developed a probe fabrication method that uses single-walled carbon nanotube bundles as a structural template for the formation of a nanowire at the apex of an AFM tip. Subsequent insulation of the probe and cutting across the nanowire yields a disc electrode of well-defined geometry. The probe apex geometry results in topographic information being obtained without causing damage to the electrode by contacting the substrate. Also, by placing the electrode at the apex, electric force imaging can also be realized. The probes are demonstrated to accurately identify active sites and locally generated species by combined topographic and electrochemical measurements on the sub-micron scale. The influence of the probe geometry on the diffusion of species from micrometer scale active sites will also be considered

Surface Charge Visualization at Viable Living Cells

Scanning ion conductance microscopy (SICM) is demonstrated to be a powerful technique for quantitative nanoscale surface charge mapping of living cells. Utilizing a bias modulated (BM) scheme, in which the potential between a quasi-reference counter electrode (QRCE) in an electrolyte-filled nanopipette and a QRCE in bulk solution is modulated, it is shown that both the cell topography and the surface charge present at cellular interfaces can be measured simultaneously at high spatial resolution with dynamic potential measurements. Surface charge is elucidated by probing the properties of the diffuse double layer (DDL) at the cellular interface, and the technique is sensitive at both low-ionic strength and under typical physiological (high-ionic strength) conditions. The combination of experiments that incorporate pixel-level self-referencing (calibration) with a robust theoretical model allows for the analysis of local surface charge variations across cellular interfaces, as demonstrated on two important living systems. First, charge mapping at Zea mays root hairs shows that there is a high negative surface charge at the tip of the cell. Second, it is shown that there are distinct surface charge distributions across the surface of human adipocyte cells, whose role is the storage and regulation of lipids in mammalian systems. These are new features, not previously recognized, and their implications for the functioning of these cells are highlighted