a Entries marked "typ" may vary significantly with sample or preparation procedures. b Number refers to heat treatment temperatures, for example, GC-20 was treated at 2000 °C. c Depends on technique used to measure density. d Depends strongly on doping level. See ref 30. e See ref 35.

No abstract

Various well-established and novel surface modification procedures were used on glassy carbon (GC) electrodes to yield surfaces with low oxide content or which lack specific oxide functional groups. In addition, monolayers of several different adsorbates were formed on GC surfaces before electrochemical evaluation. Both the nonspecific monolayer adsorbates and reagents which chemisorb to specific functional groups were observed on the surface with Raman and photoelectron spectroscopy. The various GC surfaces were then evaluated for their electron transfer reactivity with nine redox systems in aqueous electrolyte, including Ru(NH 3 ) 6 2+/3+ , Fe(CN 6 ) 3-/4-, ascorbic acid, and Fe aq 3+/2+ . The nine systems were categorized according to their kinetic sensitivity to surface modification. Several, including Ru(NH 3 ) 6 2+/3+ , are insensitive to surface modifications and are considered outer sphere. Fe aq 3+/2+ , V aq 2+/3+ , and Eu aq 2+/3+ are catalyzed by surface carbonyl groups and are very sensitive to the removal of surface oxides or derivatization of CdO groups. Ascorbic acid and Fe(CN) 6 3-/4constitute a third group which are not catalyzed by oxides but which do require a specific surface interaction. A procedure for classifying redox systems by their kinetics on modified carbon surfaces is proposed.

CHAPTER 2 MAGNITUDE OF RAMAN SCATTERING 15 2.1. Theoretical Overview 15 2.2. Definition of Raman Cross Section 20 2.3. Magnitude of Raman Cross Sections 24 2.4. Raman Scattering Intensity 30 CHAPTER 3 COLLECTION AND DETECTION OF RAMAN SCATTERING 35 3.1. Signal Magnitude and Collection Function 35 3.2. Instrumental Variables Comprising the Collection Function 37 3.3. Spectrometer Response Function 41 3.4. Multiplex and Multichannel Spectrometers 43 CHAPTER 4 SIGNAL-TO-NOISE IN RAMAN SPECTROSCOPY 49 4.1. Definition and Measurement of SNR 49 4.2. Noise Sources 52 v

A review with 228 references on experimental investigation of conductor/molecule/metal molecular electronic junctions is presented. Devices based on covalent and LangmuirBlodgett bonding of single molecules or molecular monolayers to conducting substrates are reviewed, as characterized by scanning probe microscopy and microelectronic techniques. Phenomena observed to date include molecular rectification, conductance switching, and nonlinear current/voltage behavior. Prospects and problems for the application of molecular junctions to the more general area of molecular electronics are discussed.

Many scientists have a passing familiarity with Raman spectroscopy and those of us who have tried using it, say 15 years ago, to identify chemical groups were probably disappointed. At the time, a long recording time and poor signal/noise ratios did not inspire strong recommendations for chemical analysis. This was disappointing because there was always a deep-seated feeling that here was a technique that could be capable of detailed chemical analysis, indeed chemical imaging. How things have changed! The more widespread use of infrared lasers, CCD detectors and signal processing using powerful PCs have all reduced the recording times from around one hour to about 30 seconds. The general convenience of the technique is bringing it to the attention of a wider audience of chemists and materials scientists. This volume by McCreery is another in the excellent Wiley series of monographs on Analytical Chemistry. These have provided a very high standard, indeed a `flagship' of authority and quality in this broad area. The treatment given here will capture the attention of both the novice who wants to find out how Raman spectroscopy works, and the expert practitioner who requires some original sources of information. It will be very useful to all researchers who use, or wish to use, the Raman technique. The introductory sections really do highlight the differences to be expected between modern Raman techniques and the `rival' techniques of near infrared (NIR) and Fourier transform infrared (FTIR) spectroscopies. The treatment is a no-nonsense, pragmatic approach, with comparable spectra for the techniques, warts and all! Later sections then go on to give a rigorous analysis of signal levels, signal/noise ratios and practical details of the lasers, detectors and software that are best suited to specific needs and applications. There are several extensions of Raman spectroscopy that have been made possible by improved software and instrumentation in recent years, but probably the ability to form images is the one that will capture a large share of devotees. In conclusion, McCreery gives a very well balanced and authoritative account of Raman microscopy in all its different variants. He repeats this very effectively for its application via fibre-optic probes, and the examples that he has selected are clear, simple and useful. The section on surface enhanced Raman spectroscopy (SERS) is a model of clarity and one that I will use in future lectures. I can recommend this volume without hesitation. P J Dobson

Contact mode atomic force microscopy (AFM) was used to intentionally scratch a monolayer deposited on a pyrolyzed photoresist film (PPF). The force was set to completely remove the monolayer but not to damage the underlying PPF surface. A line profile determined across the scratch with tapping mode AFM permitted determination of the monolayer thickness from the depth of the scratch. A statistical process was devised to avoid user bias in determining the monolayer thickness and was used to determine the thickness as a function of derivatization parameters. PPF surfaces modified by reduction of diazonium ions of stilbene, biphenyl, nitrobiphenyl, terphenyl, and nitroazobenzene (NAB) were scratched and their modification layer thicknesses determined. For single-scan derivatizations of 1 mM diazonium ions to -0.6 V versus Ag+/Ag, the biphenyl and stilbene monolayers exhibited thicknesses close to those expected for true monolayers. However, more extensive derivatization resulted in multilayers up to 6.3 nm thick for the case of NAB. Such multilayers imply that electrons are transmitted through the growing film during diazonium reduction, despite the fact that electron tunneling would not be expected to be operative over such long distances. The results are consistent with a conductance increase in the growing film, which yields a partially conductive layer that can support further diazonium ion reduction and additional layer growth.

The electron transfer (ET) kinetics of Ru(NH3)e34"/2+, IrCle1 2"73", Fe(CN)63-/4-, Feaq2+/3+, and Vaq2+/3+ were examined on several modified glassy carbon surfaces. The kinetics of the equated ions were very sensitive to the density of surface oxides, while those of the other redox systems were not In particular, chemical derivatization of surface carbonyl groups decreased the rate of electron transfer with Fe3+/2+ by 2-3 orders of magnitude but had little effect on Ru(NH3)e3+/2+ or IrCl62_/3_. The electron tranfer rates for Fe3+/2+ correlated with surface C=0 density determined by resonance Raman spectroscopy. Neutral, cationic, and anionic nonspecific adsorbers decreased the rates of ET with the equated ions approximately equally but had little effect on Ru-(NH3)e2-/3+. The redox systems studied were classified into two groups: those which are catalyzed by surface carbonyl groups and those which are not Possible catalytic mechanisms are considered.rate enhancement depends on specific interactions with surface carbonyl groups. The strong effect of this specific interaction underlies the extreme sensitivity of Feaq2+/3+, Euaq2+/3+, and Vaq2+/3+ electron transfer kinetics to surface chemistry on carbon electrodes.