Clifford L. Renschler

Metal-dispersed porous carbon films as electrocatalytic sensors

The attractive features of ultrathin porous carbon films have been coupled with the efficient catalytic action of dispersed metal particles. In particular, loading of these submicrometer foams with ruthenium or platinum centers offers a dramatic increase in the electron transfer rates of important redox systems, such as NADH, uric acid, ascorbic acid, acetaminophen, hydrazine or hydrogen peroxide. Characterization of the electrocatalytic behavior (with respect to the pH, scan rate or metal loading) and the attractive low-potential analytical (sensing) performance are reported. Scanning electron microscopy sheds useful insights into the distribution of the metals within the porous electrode matrix.

Nanoband electrodes for electrochemical stripping measurements down to the attomole range

Abstract Small-volume measurements of lead and cadmium have been accomplished using a mercury-coated nanoband electrode. The band electrodes are fabricated from ultrathin carbonized polyacrylonitrile films. The coupling of the inherent sensitivity of stripping analysis, with submicroliter sample volumes and enhanced plating efficiency (due to enhanced diffusional flux) results in remarkably low detection limits of 100 femtograms (5 × 10−16 mole) lead. To our knowledge, this detection limit is significantly lower than previously reported values for electrochemical stripping work. Air-saturated quiescent sample droplets can thus be assayed by the square-wave or potentiometric stripping modes. Variables influencing the stripping response are explored and the stripping performance is characterized. Applicability to direct measurement of lead in microliter blood samples is illustrated.

Enzyme Nanoband Electrodes

Abstract Enzyme nanoelectrodes have been constructed by immobilizing glucose oxidase, alcohol oxidase or tyrosinase onto ultrathin carbon films (of 35–50 nm thickness). The enzyme immobilization is accomplished via entrapment within electropolymerized poly(o-phenylenediamine) coatings. Cyclic voltammetry and controlled-potential amperometry are used to characterize the performance of the new nanoscopic biosensors under different preparation and operation conditions. The resulting electrodes offer convenient and rapid measurements of millimolar substrate concentrations, and (to the best of our knowledge) are the smallest enzyme probes reported to date.

Curcumin as a positive resist dye optimized for g- and h-line exposure

It has now been firmly established, both theoretically and experimentally, that the addition of a non-bleachable absorber (or dye) to photoresist can reduce notching and other linewidth control variations associated with the patterning of reflective surfaces. Such variations are due to two separate, but closely related, effects. The first of these effects is reflection of light off scattering centers on the substrate at angles other than surface-normal.

Demonstration of completely organic, optically clear radioluminescent light

A new type of radioluminescent light source has been demonstrated. This all‐organic system consists of covalently bound tritium within a solid, optically clear polymeric matrix. The matrix contains a set of organic luminophores that capture excitation energy from beta decay and red shift the energy in a stepwise fashion, after which a chosen wavelength is emitted as fluorescence. Both blue and orange lights have been fabricated. Unlike currently available tritium gas tube lights or radioluminescent paints, the brightness of these new systems is, in principle, scalable because self‐attenuation and absorption effects are minimized.

Microelectrode ensembles based on overlaying ultrathin porous polyacrylonitrile on dense carbon films

A new procedure for preparing microelectrode ensembles, based on casting an ultrathin microcellular polyacrylonitrile (PAN) insulating foam onto a dense carbonized PAN film, is described. The resulting partially blocked surfaces display the behavioral characteristics of ensembles of recessed microelectrodes (of small depth), with steady-state currents at moderate and long timescales. Cyclic voltammetry and chronoamperometry were used to elucidate the electrochemical behavior, while scanning electron microscopy sheds useful light on the surface microstructure. Square-wave stripping voltammetry is demonstrated for the quantification of nanomolar concentrations of lead using short deposition periods and unstirred solutions. These and other PAN-derived composite electrodes present new opportunities for various electrochemical and analytical applications.

Solid State Radioluminescent Sources Using Tritium-Loaded Zeolites, and Their Proposed Use as Process Monitors

Zeolite-based tritium lamps are a possible alternative to traditional tritium gas tube light sources. Rare earth luminescing centers may be ion-exchanged into zeolite matrices. Close proximity of tritium atoms to the rate earths can be provided by highly tritiated water sorbed within the pore structure of the zeolite aluminosilicate matrix. Zeolites are optically clear and radiation stable. Light outputs up to 2 W/cm{sup 2}, with good stability, are shown her for tritiated water-loaded zeolites. In this paper, procedures for obtaining light sources are presented and result are discussed. The possible use of these luminescent materials as process monitors for the tritium content of zeolite absorption columns is also proposed.

Effect Of Diffuse Reflectivity On Photoresist Linewidth Control

Recent studies in our laboratory have shown that the diffuse reflectivity of sputtered A1/1% Si films plays a significant role in the lot to lot control of photoresist linewidth for 2.0 m features on our 16K SRAM device. The exposure energy required to produce 2.0 m resist lines on product wafers at this level was monitored and correlated with both the total and diffuse reflectivity as measured on control wafers included with the product wafers during Al/Si deposition. Fourteen product lots were monitored over a period of several months. The results show a strong correlation between changes in the diffuse reflectivity and the exposure energy. An increase of 64% in the diffuse reflectivity of the Al/Si film is accompanied by an increase of 80% in the exposure energy required to produce 2.0 m lines in positive resist. For these same lots, the total reflectivity varies by less than ±3%, usually taken as an indication of good process control at metal deposition, with no apparent correlation to the exposure energy. Several different resist processes were investigated to control the effects of changes in the diffuse reflectivity. The most promising of these has been a new dyed photoresist developed at Sandia. The unbleachable dye has been selected for optimal performance at the exposure and alignment wavelengths used in the Ultratech stepper. The diffuse reflectivity of Al/Si films coated with dyed resist is diminished by a factor of eight over the reflectivity of films coated with our standard resist. The total reflectivity is diminished by a factor of five.

Photodegradation in ballistic laminates: Spectroscopy and lifetime extension

Polycarbonate (PC), a critical component in ballistic laminates (BLs), is known to degrade upon exposure to ultraviolet (UV) light. For the purpose of reducing the photodegradation, a UV blocking chemical has been added to the adhesives used to join the layers of the BL. This report describes the development of a spectroscopic method for monitoring surface photodegradation of PC and the methods use in demonstrating the effectiveness of the UV blocker. Reports in the literature demonstrate that photodegradation in thin PC films may be detected by transmission infrared (IR) spectroscopy. The present work extends this approach to thick films, where small surface changes are detected by reflectance IR spectroscopy. We show that UV photodegradation of the PC surface produces a characteristic shift in the carbonyl absorption band at about 1775 cm−1. This shift is consistently observed in PC samples that have been subjected to direct artificial exposure and in PC samples that have been subjected through the outboard layers of the BL to both natural and artificial exposure. When a UV blocker is incorporated into the adhesive layers of the laminate, no peak shift is observed in the carbonyl band after the equivalent of 10 years of exposure.