A systematic study of thiophene Langmuir-Blodgett films including new conjugated donor-acceptor molecules

Hemicyanine dyes are an extensively investigated group of materials which show promise for second-order non-linear optical properties; they have also proved to be good materials for deposition by the Langmuir-Blodgett technique. This work concerns a closely related group of materials which contain a thiophene moiety in place of the nitrogen heterocycle of the hemicyanine material. The synthesis of several groups of novel amphiphiles containing the thiophene moiety, and their subsequent screening as materials for deposition by the Langmuir Blodgett technique is described. General trends in the behaviour of the simplest materials are noted, whilst the report of the characterization of the more complex D--A thiophenes is extended to include data relating to the production of heterogeneous monolayer and alternate layer structures.     

A technique for microwave ranging and remote phase synchronization

A very precise electrical-distance measurement system that is also capable of supplying a phase-synchronous signal to a remote location is required for a new type of radio telescope, the large adaptive reflector (LAR). The system is based on a round-trip phase synchronization method, and is designed to work over a free-space path of length up to 1 km, the focal distance of the telescope. The electrical length of this path is to be measured with an accuracy of 70 μm and a phase-stable signal is to be provided at the remote end as the basis for a local-oscillator signal of stability equivalent to 5° at 22 GHz. Phase synchronization and distance measurement are accomplished with the same microwave ranging circuit. The distance measurement is derived from phase comparison of high-frequency signals, including a novel use of the Chinese Remainder Theorem (CRT) to resolve the unavoidable wavelength ambiguity. The design of the system is described, and limitations imposed by phase-measurement and frequency-setting accuracy are explored. Errors due to atmospheric dispersion are negligible under most circumstances. Accurate phase synchronization has been demonstrated over a free-space path of ~300 m. The complete system has been simulated under noisy conditions, and its ability to meet the specifications demonstrated     

Synthesis,chemical stability and application of a thiohydroxamic acid linker (THA) for solid-phase organic synthesis

The synthesis and chemical compatibility of a ‘traceless’ thiohydroxamic acid (THA) linker is reported. The linker is shown to be stable to visible light and heat. This paper also describes preliminary work in the application of the THA linker to act as a polymer-supported source of radicals.     

Recent developments in precision radial grating manufacture

It was approximately two years ago that the Cranfield Unit for Precision Engineering (CUPE) established its own in-house facility for the manufacture of master radial gratings¹. This has been strengthened following the recent purchase of master radial and linear grating generating equipment from the National Engineering Laboratory, East Kilbride, and the transfer of technical knowledge to make the system operable. As a result CUPE is now is possession of two operable grating manufacturing facilities - a resist system (CUPE) and photographic emulsion system (ex-NEL).     

Diagonal horn integrated with micromachined waveguide forsubmillimetre applications

The feasibility of coupling silicon micromachines rectangular waveguide to a modified diagonal horn antenna using a model at 110 GHz is demonstrated. The antenna patterns obtained are similar to those obtained with a standard diagonal horn. A method of reducing the on-axis cross polarization response of diagonal horns is also presented     

Microwave noise measurement errors caused by frequencydiscrepancies and nonzero bandwidth

We develop analytical expressions for two frequency-related errors encountered in noise parameter measurements of devices with high-reflection coefficients such as GaAs FET's and HEMT's. The first error is caused by a discrepancy between the measurement frequency of the noise-measuring receiver and the frequency of the reflection coefficient-measuring apparatus. The second is caused by variation of the noise power spectral density across the bandwidth of the noise-measuring receiver. A noise power measurement on a cooled GaAs FET is presented as a demonstration, in which the noise power level exhibits narrow peaks which rise about 10 dB above the general level at regular frequency intervals. It is shown that the severity of both of the frequency-related errors is related to the shape of these peaks. Simple expressions are derived which allow the severity of these two types of errors to be estimated when values are available for the reflection coefficient magnitudes and transmission line lengths in a system. Expressions are also derived which give the variation with frequency of the measured noise power and also of the two error terms, if the noise parameters of the device under test are also available. This analysis accounts successfully for the main features of the experimental noise power observation     

Photoetching of narrow deep slots for stylus wear standards

The performance of surface texture instruments needs to be assessed periodically. Although a step height standard checks vertical magnification and an R_a standard checks mathematical integration, no stylus wear standard was available for checking resolution.Such a standard has now been produced with vertical-walled slots of widths 2.5, 5, 10 and 20μm, and a minimum depth of 42.4μm, made by anisotropic photoetching of polished silicon slices.During exposure of photoresist the slots were aligned with a crystal cleavage plane to control line width and this was achieved using a circular table to orientate the slice with a chrome-on-glass mask.These stylus wear standards are now commercially available     

A mass spectrometric investigation into microenvironmental effects in solid-supported radical chemistry

Deuterated N-ethylpiperidine hypophosphite (d-EPHP) and tributyltin deuteride (TBTD) have been used to explore potential microenvironmental effects in resin-bound radical propagation. A deuterium labelling mass spectrometric method was used to show that efficiency of radical chain propagation on resin can be influenced by the choice of solid-support when using the slow radical chain carrier, EPHP.