Several silylated coumarin dyes with different linkages and degrees of functionality have been synthesized and incorporated in both SiO 2 xerogels and various solvent hosts. The absorption and fluorescence spectra were examined to explore selected structural and environmental effects on the optical properties of these dyes. Silylated dyes (also referred to as grafted or functionalized dyes) are dye molecules that have been chemically altered to provide alkoxysilane functionality allowing the active molecule to be covalently bonded to the host. Silylation of dye molecules had little effect on the absorption and fluorescence spectra in neutral solvent environments. The optical spectra of silylated dyes compared to those of their conventional counterpart were less influenced by the local chemical environment (e.g., pH) and thus allow for greater control and stability of the fluorescent properties of the dyes in different host environments. Spectroscopy during the drying/gelling of a derCoum xerogel film containing a silylated coumarin dye illustrate changes in the chemical forms of the dye molecules associated with changes in the local chemical environment of the dye.

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The photostability characteristics of numerous silylated coumarin dyes within SiO 2 xerogels and SiO 2 :PDMS Polyceram films, and of neat silylated coumarin dye films have been determined and related to the sol-gel processing conditions and host composition. FTIR spectroscopy was used to monitor the hydrolysis reaction rates of the silylated dyes and other Si-alkoxide precursors. The silylated dyes had varying reaction rates depending on the degree of functionality and the linkage between the alkoxide and the dye. Matching the reaction rates between TMOS and the silylated dye was accomplished by prehydrolysis of the silylated dye. The photostability of the dyes in the xerogels was measured by monitoring the drop in fluorescence intensity upon pumping with a N 2 laser and also by monitoring the drop in dye absorption upon irradiating the films with a UV lamp. At optimized prehydrolysis times, a silylated coumarin dye (derCoum) within a SiO 2 xerogel host demonstrated a 3-fold improvement in long-term photostability compared to its unsilylated counterpart. The use of a silylated dye results in covalently bonding the dye to the host matrix, increasing the probability that the dye will be caged and inhibiting dynamic processes which can lead to photodegradation. CP-MAS 29 Si NMR data for a derCoum xerogel confirmed that a large degree of dye bonding occurred. The addition of PDMS to the basic SiO 2 xerogel host composition had little effect on the photostability of the dye. The neat dye films showed improved fluorescence photostability with increase in hydrolysis time. These films showed poor photostability upon exposure to UV lamp degradation due to lower thermal degradation resistance and/or thermal conductivity compared to the SiO 2 xerogel films.

Abstract. Numerous silylated coumarin dyes have been incorporated within silica: polydimethylsiloxane Polyceram hosts using the sol-gel process to form crack-free, polishable monoliths. The use of silylated laser dyes allows for covalently bonding the laser dyes to their hosts. Photostability of the samples was evaluated by measuring the decrease in the dye absorption in the Polyceram upon ultraviolet lamp exposure and by monitoring the fluorescence intensity as function of pump pulses from a N2 laser at 337 nm. Both methods showed a significant improvement in photo-and thermal-stability of the silylated dye Polyceram compared to that of the unsilylated dye Polyceram at a dye : Si mole ratio of 10 -4 : 1. The improved stability is attributed to the immobilization and higher degree of caging of the silylated dye Polyceram with respect to the unsilylated dye Polyceram.

Abstract. Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica: polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with a Q-switched, frequency doubled Nd : YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm 2. UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.

The use of a solid-state dye laser for commercial applications has been limited largely by the poor photostability of the gain medium. Techniques are examined to improve the photostability of Coumarin and Pyrromethene-BF2 567 (PM-567) laser dyes within xerogel and Polyceram hosts synthesized by sol-gel processing. The photochemical mechanisms by which laser dyes degrade are discussed and determined specifically for PM-567. PM-567 was determined to degrade both by photooxidation and acid degradation. Techniques for improving photostability are described from a molecular engineering perspective. These techniques include: covalently attaching the laser dye to the host; controlling the chemical environment of the dye; increasing dye caging by increasing the Si02 content; removing porosity from the host; and incorporating additives such as hindered amine light stabilizers to minimize photodegradation.

The advances on IC technology have made defect localization extremely challenging. “Soft” failures (resistive vias and contacts) are typically difficult to localize using commonly available failure analysis (FA) techniques such as emission microscopy (EMMI) and scanning optical microscopy (SOM), and often cannot be observed by two-dimensional inspections using layer by layer removal. The article describes the Resistive Contrast Imaging (RCI) defect localization technique (also known as Electron Beam Absorbed Current (EBAC), instrumentations, and case studies on test structures or process control monitors especially designed to detect “soft” open failures on advanced (28nm and below) technology devices. It also lists the key SEM parameters critical for effective FA using the RCI nano-probing system.

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