Jon Travis

THE EFFECT OF NO2 ON OPTICAL ABSORPTION IN LANGMUIR-BLODGETT FILMS OF OCTA-SUBSTITUTED AMPHIPHILIC COPPER PHTHALOCYANINE MOLECULES

Thin films consisting of 20 layers of 1,4-bis(4-hydroxybutyl)-8,11,15,18,22,25-hexakisdecyl phthalocyaninato copper (CuAmPc) molecules have been deposited onto pre-cleaned glass slides by the Langmuir-Blodgett (LB) technique. The optical absorption of these films were studied in the range 1.4-4.0 eV in air and also in the presence of NO2 gas at 100 ppm level. Prolonged exposures have resulted in dramatic changes in the visible absorption band with the consequence of disappearance of Davydov splitting. Such effects are caused by the domination of local interaction between the central metal atoms and NO2 molecules resulting in a distorted herring-bone structure. This leads to the broadening of the energy levels a(2u) and e(g). Gas adsorption and desorption processes have been described by exponential functions, both characterised by a single time constant

Vision-based closed-loop control of mobile microrobots for microhandling tasks

As part of a European Union ESPRIT funded research project a flexible microrobot system has been developed which can operate under an optical microscope as well as in the chamber of a scanning electron microscope. The system is highly flexible and configurable and uses a wide range of sensors in a closed-loop control strategy. This paper presents an overview of the vision system and its architecture for vision-controlled micro-manipulation. The range of different applications, e.g. assembly of hybrid microsystems, handling of biological cells and manipulation tasks inside an SEM, imposes great demands on the vision system. Fast and reliable object recognition algorithms have been developed and implemented to provide for two modes of operation: automated and semi-automated robot control. The vision system has a modular design, comprising modules for object recognition, tracking and depth estimation. Communication between the vision modules and the control system takes place via a shared memory system embedding an object database. This database holds information about the appearance and the location of all known objects. A depth estimation method based on a modified sheet-of-light triangulation method is also described. Furthermore, the novel approach of electron beam triangulation in the SEM is described.

Computer vision methods for optical microscopes

As the fields of micro- and nano-technology mature, there will be an increased need to build tools that are able to work in these areas. Industry will require solutions for assembling and manipulating components, much as it has done in the macro range. With this need in mind, a new set of challenges requiring novel solutions have to be met. One of them is the ability to provide closed-loop feedback control for manipulators. We foresee that machine vision will play a leading role in this area. This paper introduces a technique for integrating machine vision into the field of micro-technology including two methods, one for tracking and one for depth reconstruction under an optical microscope.

Further optical studies on Langmuir-Blodgett films of octa-substituted metal-free phthalocyanines

Abstract Ellipsometry and optical spectroscopy in the ultraviolet-visible (UV-vis.) and infra-red ranges were used to study the correlation between structure and optical properties of Langmuir-Blodgett (LB) films of octa-substituted metal-free phthalocyanines containing different alkyl chains. The thickness and refractive index of LB films and the orientation of phthalocyanine moieties in the monolayer were obtained from ellipsometric measurements and then data were compared with those from Π A isotherms of the floating layer. UV-vis. absorption spectra of LB films of the molecules show Davydov splitting of the Q band. Small changes in alkyl length lead to significant changes in the Q-band shape. The optical characteristics of monolayers are found to be different from those of multilayer films.

Machine vision methods for autonomous micro‐robotic systems

Purpose – To develop customised machine vision methods for closed‐loop micro‐robotic control systems. The micro‐robots have applications in areas that require micro‐manipulation and micro‐assembly in the micron and sub‐micron range.Design/methodology/approach – Several novel techniques have been developed to perform calibration, object recognition and object tracking in real‐time under a customised high‐magnification camera system. These new methods combine statistical, neural and morphological approaches.Findings – An in‐depth view of the machine vision sub‐system that was designed for the European MiCRoN project (project no. IST‐2001‐33567) is provided. The issue of cooperation arises when several robots with a variety of on‐board tools are placed in the working environment. By combining multiple vision methods, the information obtained can be used effectively to guide the robots in achieving the pre‐planned tasks.Research limitations/implications – Some of these techniques were developed for micro‐visi...

Langmuir-Blodgett films of copper tetra-4-tert-butyl phthalocyanine molecules as NO2 gas sensors

The NO2 gas-sensing characteristics of chemiresistors in the form of multilayered Langmuir-Blodgett (LB) films of copper tetra-4-tert-butyl phthalocyanine (CUTTBPC) molecules deposited on quartz substrates with pre-deposited platinum interdigitated electrodes have been investigated. Response and recovery times, tau res and tau rec, respectively are estimated for different gas concentrations from a model based upon kinematics of adsorption and desorption of NO2 gas molecules by CUTTBPC films. It is found that recovery times are longer than response times irrespective of gas concentration. For a given film thickness, the adsorption probabilities increase while the desorption probabilities decrease, with increasing concentrations. On the basis of the analysis of the results obtained, LB films of CUTTBPC molecules are believed to be a suitable material for disposable NO2 gas sensors.

MODELING OF AN ALL-OPTICAL TIME-DIVISION DEMULTIPLEXER

The communication Networks of the future will require signal switching in the optical domain to avoid the inherent speed bottleneck of optical-electronic-optical conversions. This has resulted in an intense research effort in this area. Of particular interest are wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). The latter offers the advantage that it operates over a single wavelength, removing the problems associated with dispersion in fibre systems whilst the former operates over a number of wavelengths. This thesis concentrates on the modelling and simulation of one particular system: the asymmetric semiconductor laser amplifier loop mirror (ASLALOM) for OTDM.Initially, a literature review looks at the theory of laser operation which complements the following chapter on laser amplifiers. A review of current optical switching devices will be examined next with regard to switching speeds, crosstalk and the possibility of integration. Also wavelength division multiplexing and time division multiplexing are reviewed, comparing the different systems in current use.At the present time, no complete models of an asymmetric semiconductor laser amplifier loop mirror have been developed. The intention of this work is to determine the equations necessary for a model to be developed and thus enable the system to be simulated. Computer modelling of a system prior to implementation is advantageous in all aspects of engineering. As this system is still confined to the laboratory a model would complement any practical work and identify critical design parameters.In this work the Travelling Wave Semiconductor Laser Amplifier (TWSLA) is first modelled in a form which is appropriate for the asymmetric semiconductor laser amplifier loop mirror architecture. The simulations are then used to demonstrate the switching speeds for different configurations and identify any areas needing further work, such as crosstalk, birefringence and polarisation, a method for multi-channel output is also presented. A further aim is to lay a foundation for future work to enable the system to be fully characterised with regard to noise, dispersion and integration.

A Dissimilarity Visualisation System for CT: Pilot Study

One of the capabilities of the human vision process when visualising images is the ability to visualise them at different levels of details. A segmentation procedure has been developed to mimic this capability of human vision process. The developed hierarchical clustering based segmentation (HCS) procedure automatically generates a hierarchy of segmented images. The hierarchy represents the continuous merging of similar, spatially adjacent or disjoint, regions as the allowable threshold value of dissimilarity between regions, for merging, is gradually increased. By the very nature of the HCS procedure a large amount of visual information is produced. A graphical user interface (GUI) was designed to present the segmentation output in an informative way for the user to view and interpret. In addition the GUI displays the original image data by optimally mapping the range of data values to the available 256 gray level values. The purpose of this paper is to describe the development of the designed image visualisation system and to demonstrate some of its functionalities

A voltage-controlled oscillator for use within a pulse frequency modulation system

A fully integrated voltage-controlled oscillator (VCO) for use within a pulse frequency modulation (PFM) system is described, that achieves a linear voltage to frequency transfer characteristic over 17 MHz. The output of the VCO is a pulse waveform with a duty cycle below 20%. The VCO is based on two grounded capacitors and is implemented in a 2.4 µm CMOS technology. Owing to positive feedback, no start-up conditions for the oscillator are required.