28 Science Research Writing Henze et al., 1987; Orhon et al., 1989; Germirli et al., 1991). However, little has been reported under anaerobic conditions (Germili et al., 1998; Ince et al., 1998). Since medium-high strength industrial wastewaters have been treated effi ciently by anaerobic treatment systems, both the inert COD fraction of wastewaters under anaerobic conditions and the soluble microbial products produced within the anaerobic treatment systems should be investigated. A novel anaerobic reactor system, crossfl ow ultrafi ltration membrane anaerobic reactor (CUMAR) has previously shown great potential for retaining high biomass levels and high biological activity within a fully functioning anaerobic digester (Ince et al., 1993, 1994, 1995a). Since the CUMAR system can be operated at high organic loading rates, the quantifi cation of its effi ciency under varying loading rates would be of considerable interest, particularly with regard to the nature and quantity of soluble COD produced in the reactor effl uent under various operating conditions. In this study, formation of soluble microbial products within a 120:1 [is this correct? Should it be 120:1?] pilot-scale CUMAR system treating brewery wastewater will, therefore, be discussed in relation to reactor operating conditions. Organic vapour phase deposition: a new method for the growth of organic thin fi lms with large optical non-linearities 1. INTRODUCTION Th ere is considerable interest in organic materials with large second-order hyperpolarizabilities for use in non-linear optical (NLO) devices such as modulators and frequency doublers [1]. To achieve a high fi gure of merit for such NLP devices requires a material with a non-centrosymmetric bulk structure and low dielectric constant. To this end, NLP-active chromophores are traditionally incorporated into a polymer matrix and electrically poled to achieve the necessary bulk symmetry. However, such materials
Introduction — Writing Task 29 are limited by their low glass transition temperatures and poor stabilities at elevated temperature. Recently, single crystals of organic and organometallic salts [2–4] have been shown to possess extremely large second-order (x(2)) NLP eff ects leading to a high second harmonic generation (SHG) effi ciency. Th e naturally non-centrosymmetric crystal structures of these compounds obviates the need for external poling. Furthermore, these salts have a high optical damage threshold and suffi cient stability with respect to temperature to withstand many conventional semiconductor fabrication processes. In particular, highly pure single crystals of the salt, 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) [2], have been shown to have a value of x(2) at least 103 times greater than that of urea due to dipole alignment of the cation and anion constituents of the DAST structure. To illustrate this alignment, the DAST bulk crystal structure is shown in the inset of Fig. 1. For many applications such as waveguide devices, it is desirable to grow NLO materials into optical quality thin fi lms. Although thermal evaporation in a high vacuum environment has been used to grow thin fi lms of many organic [5–7] and inorganic materials, the technique is not always applicable to highly polar molecules [8] or organic salts. For example, when heated in vacuum, DAST decomposes before vaporization. Although in situ reactions of multicomponent organic molecules to synthesize polymer fi lms previously has been demonstrated using vacuum techniques as physical vapour deposition or vapour deposition polymerization [9], attempts in our own laboratory at double-source co-evaporation of DAST neutral precursors 4′-dimethylamino-4-stilbazole (DAS) and methyl p-toluenesulfonate (Methyltosylate, MT) to form DAST have been unsuccessful, due in part to the radically diff erent vapour pressures of DAS and MT, which leads to highly non-stoichiometric growth. In contrast, atmospheric or low pressure (eg milliTorr) vapour phase epitaxy (VPE) has been used to grow epitaxial thin fi lms of many III-V compound semiconductors, such as InP and GaAs, where there is a large diff erence in the vapour pressures of the group III and group V atomic constituents [10]. Th is method was recently extended to allow the growth of III-V and II-VI