Two new methods of preparing thin porous metallic films, based on controlled co‐crystallization of latex microspheres and gold nanoparticles, have been developed by these authors. The new materials show interesting optical properties and excellent surface‐enhanced Raman spectroscopy (SERS) activity. The Figure shows a square pore array obtained at a specific film thickness.
The ability of a planar array infrared (PA-IR) spectrograph to obtain spatially resolved infrared spectra
(infrared line images) of a monolayer film with reasonable signal-to-noise-ratios is demonstrated, and the
first infrared line images of a monolayer film ever recorded are reported. In this context, octadecyltrichlorosilane (OTS) monolayer films self-assembled on glass substrates were investigated as a function
of three different solvents (hexane, benzene, and toluene). It is shown that the PA-IR line images could
be used to investigate surface coverage and conformational order as a function of spatial location. A frequency
versus absorbance relationship was observed that can be interpreted as a well-defined correlation between
conformational order and surface coverage. The plot of this relationship, which looks similar to a phase
diagram containing a first-order phase transition, is in excellent agreement with that reported recently
(Liu, Y.; Wolf, L. K.; Messmer, M. C. Langmuir
2001, 17, 4329) by sum frequency generation (SFG). On
the basis of the results from this study and the SFG results, it appears that conformational order and
surface coverage of self-assembled OTS monolayer films on glass can be treated as two dependent
thermodynamic state functions. In addition, these results suggest that different solvent systems can be
exploited to tailor self-assembled monolayer films in terms of surface coverage and conformational order.
The gate conductor material affects the threshold voltage of metal-oxidesemiconductor (MOS) transistors through the influence of the electrochemical work function and electric charge. Measurements of the threshold voltage from current voltage characteristics may therefore provide a method to estimate the electronic properties of biomolecules located on the gate electrode. We have deposited DNA from the corn genome onto the gate oxide of Si nMOS transistors and measured the effects on the current-voltage characteristics. We found that the DNA decreased the drain-source current compared to devices with clean gate oxides and pure buffer solutions. The threshold voltage was extracted by current-voltage measurements in the linear operating region and was found to increase by +1.9 volts after application of the DNA specimen, a value consistent with the expected negative charge density. This large change suggests that MOS devices may be useful as sensitive bioelectronic detectors.
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