Polyacrylonitrile (PAN) films have been fabricated by both spin and solvent casting techniques, and pyrolyzed to produce carbon films in the thickness range of 200–50000. These films have higher electrical conductivities than carbon films produced from most other precursors at similar temperatures. The chemical structure of the films at different stages of processing was investigated by UV, IR, Raman, and XPS spectroscopies. An extra degree of control over the final electrical conductivity was obtained by varying the PAN content of copolymer precursors. Oxidation rates and an activation energy were determined. Finally, processing techniques are described which allow both dry and wet film transfer and lithographic patterning.

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.

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 method's 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.

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.

Novel ultrathin (0.4 mu m) porous carbon films are employed as transducers for amperometric biosensors. Such foamlike nanoscopic films couple the advantages of high enzyme loadings (within the micropore hosts) and large microscopic area with a small geometric area. Both electropolymerization and metalization are used to entrap the enzyme within the micropores. Scanning electron microscopy sheds useful insights into the unique morphology of the growing enzyme layer. The greatly enhanced sensitivity is coupled with a fast and stable response. Factors influencing the performance of porous-film-based biosensors are examined and discussed. The improved performance is illustrated in connection with glucose and phenol sensors. The latter offers a remarkably low detection limit of 2.5 x 10(-8) M. The new nanoscopic foams should prove useful for many other electroanalytical applications.

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.

A method is described to produce thin films of carbon by the pyrolysis of spin-cast polyacrylonitrile. UV, IR, and Raman spectroscopies were employed to investigate the chemical structure of the films during pyrolysis. The electrical conductivity of films made in this way can be varied over several decades by changing the final temperature of carbonization. These films can also be photolithographically patterned and manipulated by wet and dry transfer techniques. As such, these films may have utility in microelectronic and hybrid microcircuit applications.

A variety of dyes have been proposed as absorbers for photoresists. The nonbleachable absorbance incorporated in this way can result in a reduction in standing waves and/or reflective notching (nonuniform linewidths due to reflections off the substrate). In addition, it can provide increased visual contrast at the patterned resist inspection stage. A variation on the visual contrast improvement involves the use of a dye which fluoresces, allowing for more precise resist metrology. The deposition and growth processes used here result in large oxide and polycrystalline silicon steps with high aspect ratios. Processes such as LOCOS which allow less severe topography, are inherently radiation soft and cannot be used on our fabrication process. The resulting steep sidewalls make metal coverage and etch significantly more difficult. Thus, the glass layer which isolates metal conductors from oxide steps is smoothed with either a thermal reflow or a plasma etch of a partially planarized coating to reduce the aspect ratio of the step. This results in metal coverage with a 45{degrees} angle at each step, which causes severe notching. This paper reports on an attempt to develop a resist which would eliminate this notching problem. Although the addition of unbleachable dye to photoresist formore » the control of notching is well established, most of the dyes used have one or more serious shortcomings, such as a poor match of the absorption spectrum with the exposure spectrum or low solubility in resist. Severe notching requires the use of a resist dye with optimized physical and spectroscopic properties to allow high optical absorbance to be achieved without the onset of other problems such as particulate formation or changes in thermal properties.« less

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.

The technique of density profiling was used to monitor the diffusion of bishydroxycyclopentylbutadiyne (HCPB) through a silicone rubber. Reaction of HCPB with excess hydrosilane sites, unreacted during the polymer cure process, immobilized part of the diffusant and led to the development of a concentration front, or plateau, in the diffusion profiles. Kinetic modelling was used to reproduce the salient features of the profiles and to provide a means of obtaining a diffusion coefficient. The diffusion coefficient was found to be a decreasing function of concentration, in contrast to the behaviour observed in most systems.

Polyacrylonitrile films have been spin cast and pyrolyzed to produce thin (500–1500 Å) carbon films. These films have higher electrical conductivities than films produced by other methods at similar temperatures. The conductivity can be varied by at least four orders of magnitude by changing the pyrolysis temperature. Ultraviolet, infrared, and Raman spectroscopies were used to investigate the chemical structure of the films during different stages of processing.

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.