BN (hBN) holder. The input microwave power was 1400 W, and the pressure was kept at about 2 10 ±3 torr. Argon and helium were used as plasma-processing gases at flow rates of 10 and 140 sccm (standard cubic centimeters), respectively. Nitrogen, boron trifluoride, and hydrogen were used as reactant gases at gas flow rates of 50, 1.5, and 3 sccm, respectively. A bias voltage ranging from ±10 to ±40 V was applied to the substrate during deposition. The substrate temperature was maintained at about 950 C as measured by an optical pyrometer. The cBN film thickness ranged from 200 nm to 2 lm.The films were characterized by Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM)Ðwith its associated techniques selected area electron diffraction (SAED) and electron energy-loss spectroscopy (EELS)Ðand X-ray diffraction (XRD). The XRD measurements were performed using a Rigaku X-ray diffractometer, the SEM using a Philips FEG XL30, the HRTEM using a Philips FEG CM200 with a point resolution of 0.19 nm. A Gatan GIF 200 spectrometer attached to the HR transmission electron microscope was employed for EELS and elemental scanning measurements. The formation of two-dimensional (2D) arrays of metal nanoparticles on substrates [1±4] is of increasing interest to nanoscale-materials scientists and engineers, and is being continuously investigated for practical applications in optical, electrical, and biological technologies. The phenomenon of single-electron tunneling (SET) [5] with gold (Au) nanoparticles covered with an insulation layer is promising for application in nanoscale memory units working at room temperature, where the 2D nanoparticle array forms the surface of an ultrahigh-density memory disk. In bio-optical science, a 2D monolayer of Au nanoparticles has been applied in an enzyme-based sensor for glucose. [6] With the help of near-field enhancement of the nanoscale roughness of metal surfaces, optical sensors for organic polymers or molecules with high sensitivity have also been developed. [7,8] Furthermore, the near-field effects of the surface of metal nanoparticles is made use of in phosphorescent composites embedded with rareearth ions and Au nanoparticles. [9] Several methods for preparing such 2D arrays are knownÐLangmuir±Blodgett techniques, [10] sputtering, [11] electrochemical deposition, [12] self-assembly, [3,8,13] and so on. Our approach is based on using a self-assembly technique to deposit nanometer-sized Au particles on a chemically modified glass substrate, which can then be stabilized by the application of a layer of silica. This communication reports second harmonic generation (SHG) from monolayers of Au nanoparticles fabricated with a variety of immersion times. It will be shown by optical absorption measurements and atomic force microscopy (AFM) that detectable second harmonic (SH) signals are caused by nonlinear polarization of the longitudinal ªin-phaseº modes of coupled COMMUNICATIONS

Probing electrochemical processes by mass spectrometry (EC/MS) is a developing field that benefits from the unmatched identification power of mass spectrometry and from the rapid transfer of electrochemical cell products to the mass spectrometer. Most of the current EC/MS efforts are directed towards the development of differential electrochemical mass spectrometry (DEMS) using the electro‐ionization source for identification of volatile compounds, and towards the application of electrospray mass spectrometers for determination of semivolatile and nonvolatile products. The challenges in coupling mass spectrometry and electrochemistry are described, and different approaches to using the coupled system for diverse applications are reviewed, with emphasis on electrospray mass spectrometry. Reaction mechanism studies, diagnostic applications, and activity imaging of electrodes are demonstrated based on approaches that were devised in our laboratory.

Highly stable FAU-type zeolite membrane for the separation of isopropanol (IPA)-water mixture by pervaporation is described. FAU membrane showed high water permselectivity and permeance. Comparison of FAU membrane with a conventional LTA-type zeolite membrane revealed superior stability of FAU zeolite membrane in a mixture containing a large water content.

A new type of inorganic biosensor is introduced. The sensor comprises glucose oxidase enzymes encapsulated in a sol-gel-derived Prussian blue-silicate hybrid network. Glucose is detected by the biocatalytic reduction of oxygen followed by catalytic reduction of hydrogen peroxide by the Prussian blue catalyst. The sol-gel silicate entails a rigid encapsulating matrix, the Prussian blue provides chemical catalysis and charge mediation from the reduction site to the supporting electrode, and the enzyme is responsible for the biocatalysis. The feasibility of a dual optical/electrochemical mode of analysis is also demonstrated.

Anodic deposition of thin films (up to 0.5 µm thick) of gold nanodispersion from aminosilicate stabilized gold sols is demonstrated for indium-tin oxide and platinum substrates. The films are conductive, semitransparent, and comprised of 4-6 nm gold particles each coated by a thin aminosilicate shell. Anodic deposition of stabilized gold nanoparticles is a new way to produce modified electrodes comprised of silicate-noble metal composite coatings with a high degree of interconnectivity between the gold grains. © 1999 The Electrochemical Society. S1099-0062(98)10-072-X. All rights reserved.Manuscript submitted October 21, 1998; revised manuscript received January 19, 1999. Available electronically March 23, 1999 Chemically functionalized metal nanoparticles exhibit desirable optical and catalytic properties that make them ideal building blocks for two and three-dimensional molecular/nanoarchitectures. Along this line, a rapid progress is taking place in the deposition of monolayers of conductive nanocrystals on solid supports. Natan and coworkers 1-3 laid the basis for a general methodology 4-8 for the preparation of conductive electron-percolating monolayers of stabilized metal nanoparticles on solid supports. The methodology is based on pretreatment of the solid surface (such as metal, glass, and alumina) with organofunctional trialkoxysilane compounds containing amine, cyanide, thiol, or other functional anchors. Stabilized gold or silver nanoparticles are then bound to these coatings. Variants of this methodology include the use of poly(ethyleneimine) or other coated surfaces that can anchor a monolayer of stabilized metal nanoparticles. [4][5][6][7]9 Despite the electronic and electrochemical significance of conductive 3-D nanometallic structures, little research work has been devoted to employing the fast growing technology of stabilized nanoparticle sols for construction of 3-D structures. Notable exceptions are Murray's 10 and Natan's 11 recent reports on conductive nanocrystalline 3-D structures. Murray and co-workers deposited alkanethiol stabilized gold clusters on interdigitated array electrodes and examined their electrochemistry. Natan and coworkers deposited gold colloids layer by layer utilizing bifunctional molecular bridges (e.g., alkyldithiol) between the stabilized nanocrystalline layers. Natan reported that this step by step process is time consuming. 3 This report demonstrates an electrochemical method of polymerizing 3-D gold aminosilane films containing interconnected gold network. This study was influenced by the research of Murray 12 and others (see Ref. 13 for a recent review) that deposited aminosilicate monolayers on ITO and on noble metal electrodes by anodic formation of oxide layers (e.g., PtO or AuO) and subsequent bonding of aminoalkylalkoxysilane moieties on these surfaces. We have recently demonstrated 14 that it is possible to stabilize gold sols in aqueous solutions by aminosilicate shells in which the amine groups are oriented toward the gold surface. These two advances pave...