Photolithographic Patterning and Doping of Silica Xerogel Films

This study shows that conventional photolithography can be applied for patterning native or organic dye-doped silica films (0.5 m thick) obtained via a base-catalyzed sol-gel process. Photoresist was spin-coated onto high optical quality xerogel films, soft-baked, exposed to UV irradiation through a photomask, and developed with a commercial photoresist developing solution. Etching away of the photoresist-unprotected areas of the silica films was carried out with a dilute HF solution, while the remaining unexposed photoresist was removed with acetone. Interdigitated array patterns with features as small as 0.5 mm show a smooth surface and extremely sharp interfaces. Densification of the films at 550°C for 2 h decreases the film thickness by 11%, increases the refractive index from 1.420 to 1.456, and allows for well-defined patterning down to length scales of 10 m. Since the densification conditions are incompatible with organic dopants, it is demonstrated that sol-gel films can be doped after pattering (post-doping) by adsorption of cationic dyes from solution. Scanning electron microscopy reveals that the microstructure of patterned sol-gel films is similar to that of bulk monoliths, indicating that the photolithographic procedure is not harmful to the film quality. All patterned films demonstrate highly regular light diffraction patterns.     

Contribution to the quantitative x-ray analysis of individual submicrometre particles: Asbestos fibres

Summary A procedure for the analysis of individual asbestos fibres in the submicrometre diameter range, based on the ratio method of thin film analysis, is presented. The reliability of this method has been tested in a study of identification of asbestos fibres. The systematic and statistical errors were investigated.

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Beitrag zur quantitativen Röntgenmikroanalyse einzelner Submikrometerteilchen: Asbestfasern

Zusammenfassung Es wurde versucht, eine Quantifizierungsmethode analog der Verhältnismethode zur Analyse dünner Schichten für die Analyse von Asbestfasern mit Durchmessern im Submikrometerbereich zu entwickeln. Die Zuverlässigkeit der Methode wurde mit einem Anwendungsbeispiel überprüft, und alle systematischen und statistischen Fehler wurden dargelegt.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Immobilization of Pd Catalysts on Mesoporous Silica for Amine- and Copper-Free Sonogashira Coupling Reactions

Immobilization of catalysts on solid supports is a promising approach to combine the advantages of heterogeneous and homogeneous catalysts. Pd(PPh₃)₂Cl₂, known as an extremely active homogeneous catalyst for the Sonogashira coupling reaction, has been immobilized on high-surface-area MCF (mesocellular foams)–type mesoporous silica powder modified with 3-aminopropyltriethoxysilane and subsequently with diphenylphosphine. The functionalized MCF-type silica and supported catalysts have been characterized by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), elemental analysis, nitrogen sorption porosimetry, and scanning electron microscopy (SEM). Such supported Pd catalysts have proven to be useful recyclable reagents for copper- and amine-free Sonogashira coupling reactions of haloaromatic compounds with terminal alkynes.     

One-step synthesis and redox properties of dodecahydro-3a,9a-diazaperylene--the most easily oxidized p-phenylenediamine

Dodecahydro-3a,9a-diazaperylene (DHDAP) was prepared in one step from p-phenylenediamine and 1-bromo-3-chloropropane, and its first redox potential is 292 mV more negative than the first redox potential of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), thus becoming the most easily oxidized p-phenylenediamine homologue.     

A facile synthesis of 2,7‐diazapyrene

2,7‐Diazapyrene is synthesized in three high‐yield steps from commercially available 1,4,5,8‐naphthalene tetracarboxylic dianhydride, which first reacts with concentrated ammonium hydroxide solution at room temperature to give 1,4,5,8‐naphthalenetetracarboxylic diimide (96%). The latter compound is subsequently reduced with borane in refluxing tetrahydrofuran to give 1,2,3,6,7,8‐hexahydro‐2,7‐diazapyrene (77%), which in turn is oxidized with manganese dioxide in refluxing benzene giving 2,7‐diazapyrene (71%).     

Synthesis and spectroscopic properties of the elusive 3a,9a-diazaperylenium dication

The 3a,9a-diazaperylenium dication (1) was synthesized for the first time in two steps from p-phenylene diamine. Ab initio calculations show a twisted ground state with a 6.4 degrees tilt between the two quinolizinium building blocks. Dication 1 is photoluminescent in fluid solutions of H(2)O, CH(3)CN, and CH(3)NO(2), but not in rigid matrices of the same solvents. This phenomenon has been attributed to a geometric relaxation of the tilted ground state into an emitting planar lowest singlet excited state. [structure: see text]     

Nanoengineered Silica-Polymer Composite Aerogels with No Need for Supercritical Fluid Drying

Owing to their low density, dielectric constant, thermal conductivity, high porosity and chemical inertness, monolithic aerogels could be useful in a variety of electronic, optical and chemical applications [1]. However, practical implementation has been slow, because aerogels are fragile, environmentally sensitive (hydrophilic) and most importantly, the final stage of their preparation involves supercritical fluid (SCF) extraction [1c]. It is reported herewith that for a nominal 3-fold increase in density, typical polymer crosslinked silica aerogels are not only stronger (> 300×) and less hydrophilic (< 10×) than the underlying silica backbone, but they can also withstand the capillary forces exerted upon their nanostructured framework by the residing meniscus of selected solvents, and thus they can be dried under ambient pressure without need for supercritical fluid (SCF) extraction. The best solvent identified for that purpose is pentane, and the resulting aerogels are both microscopically and macroscopically identical to their SCF-CO₂ dried counterparts. Being able to dry monolithic crosslinked aerogels without SCF extraction is expected to facilitate their commercial application.Employed by the Ohio Aerospace Institute.