Geoffrey L. Harding

A study of Love-wave acoustic sensors

Abstract Love-mode acoustic devices are very promising as biosensors in gaseous and liquid environments because of their high sensitivity. An experimental studu of Love-wave devices based on SiO2/ST-cut quartz, over a wide range of SiO2 thickness, is presented in this paper. Devices with up to 7.3 μm thick SiO2 guiding layers have been successully manufactured via an r.f. sputtering technique. Mass sensitivity, velocity, insertion loss, oscillation frequency stability and temperature coefficient of the frequency have been studied as a function of layer thickness. The sensitivity increases with increasing layer thickness and reaches a maximum at around 5.5 μm, for a wavelenght of 40 μm, in accordance with theory. Further increasing the thickness decreases the sensitivity dramatically. High sensitivity (≥ 300 cm2 g−1) can be achieved at thickness between 3.5 and 6.5 μm. The Low-wave dual-channel delay-line oscilltors also demonstrate high frequency stability and low noise levels. The frequencies of the two channels track each other extremely well.

Love wave acoustic immunosensor operating in liquid

Abstract A Love wave acoustic device has been utilized for monitoring antibody-antigen immunoreactions in aqueous solutions in real time. High sensitivity and selectivity are achieved. In this study, sheep IgG is immobilized on the device surface as a receptor layer for detection of antisheep IgG in buffer solution. The kinetics of the antibody-antigen binding are investigated by monitoring the frequency change against reaction time for a wide range of antibody concentrations. A general analytic expression for the frequency against time and antibody concentrations is derived. A response to a concentration of 1 ng ml −1 is unambiguously detected. A dual-channel delay-line configuration. with one channel for sensing and the other as reference, is used to give a comparison of specific and non-specific responses as well as to reduce the temperature effects. The Love wave sensor is robust, reliable and reusable many times.

A multilayer structure for Love-mode acoustic sensors

Abstract A novel multilayer structure, consisting of polymer/SiO 2 /ST-quartz, has been evaluated for Love-mode acoustic sensors. The properties of these new devices have been compared with those of SiO 2 /quartz and polymer/quartz devices. Mass sensitivity, insertion loss, temperature coefficient of the oscillation frequency and frequency stability are studied as a function of the layer thickness. Optimized devices exhibit higher sensitivity than both the SiO 2 /quartz and the polymer/quartz devices produced here. Reduced temperature coefficient of frequency can be obtained in the polymer/SiO 2 /ST-quartz devices due to a compensating effect of the polymer and SiO 2 films. Some of the devices have been operated efficiently in water with good stability, which is promising for biosensing applications.

A comparison of protocols for the optimisation of detection of bacteria using a surface acoustic wave (SAW) biosensor

A dual channel surface acoustic wave (SAW) device has been used as a biosensor to detect two different microorganisms, Legionella and Escherichia coli, simultaneously. A series of experiments was conducted to optimise the use of the SAW for bacterial detection using a novel protocol of coating bacteria on the sensor surface prior to addition of the antibody. Results were compared with an experiment in which a conventional protocol was utilised, where antibody was coated on the sensor surface prior to exposure to bacteria. The concentration of bacteria that attached to the surface of the SAW device was related to the antibody that specifically bound to it and therefore to frequency in a dose dependent fashion. Unlike conventional microbiological techniques quantitative results can be obtained for Legionella and E. coli down to 10(6) cells per ml within 3 h. In addition E. coli was detected down to 10(5) cells per ml in a modified protocol using sheep IgG as a blocking agent.

Design and properties of quartz-based Love wave acoustic sensors incorporating silicon dioxide and PMMA guiding layers

Love wave surface acoustic wave devices are very promising as sensors in gaseous and liquid environments because of their high sensitivity. In this work, two methods of producing the Love wave guiding layer were utilized to fabricate devices based on ST-cut quartz. The methods involved sputter deposition of silicon dioxide films and spin coating of polymethylmethacrylate (PMMA) films. -cut quartz devices with thicknesses up to and PMMA/ST-cut quartz devices with PMMA thicknesses up to have been manufactured and compared. Mass sensitivity, insertion loss, temperature coefficient of oscillation frequency and frequency noise have been studied as a function of layer thickness. A number of hybrid devices consisting of PMMA film/ film/ST-cut quartz have also been assembled and evaluated. These devices exhibit higher sensitivity than the devices and the PMMA devices produced here.

An experimental study of Love-wave acoustic sensors operating in liquids

Abstract It has been shown that properly designed Love-wave acoustic sensors are very promising for sensing in gaseous and liquid environments because of their high sensitivity. Since Love-wave devices do not incur a radiative loss when used in a liquid, they have many potential applications in biosensing. We have successfully manufactured a range of 40 μm wavelength Love-wave devices based on SiO2/ST-quartz, with the SiO2 thickness ranging from 0 to 7.3 μm. The relationship of the mass-loading sensitivity to the thickness of the SiO2 layer has been obtained experimentally. High sensitivity (≥ 300 cm−2 g−1) is achieved at an SiO2 thickness between 3.5 and 6.5 μm. The Love-wave oscillators have operated efficiently in various liquids with excellent stability and low noise. In this paper, we report the experimental results for the devices operating in various liquids. The mass sensitivity, insertion loss, oscillation frequency stability, noise level, liquid viscous loading and acoustoelectric coupling have been studied. The influence of the thickness of the SiO2 layer on some of these properties has also been investigated.

MULTIPLE SCATTERING EFFECTS IN DEPTH RESOLUTION OF ELASTIC RECOIL DETECTION

Multiple scattering strongly affects the depth resolution of Elastic Recoil Detection (ERD) experiments in contrast to its small effects in typical Rutherford Backscattering Spectrometry (RBS) measurements. A comparison of experimental ERD and RBS results shows substantial differences in the depth resolution of these two techniques. The effect of multiple scattering is estimated by computer simulations and is compared to experimental results. The effect of sample material is also discussed and it is shown that in high Z materials multiple scattering is dominant and the depth resolution of ERD is often comparable to the measured structure thickness. The effects reported in this paper are of a general nature and are applicable to all ERD type analysis including He and heavy ion ERD and all kind of detection systems.

Simultaneous Hydrogen Detection with an ERD Gas Ionization Detector

Abstract A large solid-angle gas ionization detector is shown to be capable of simultaneous hydrogen detection during heavy-ion elastic recoil detection of heavier elements. Different modes of detection are possible depending on the specific application. These include a transmission-mode in which the primary ion energy and gas-pressure in the detector are optimized for heavy-ion detection and energy loss signals are recorded for each hydrogen recoil. Alternatively, the primary ion energy can be reduced and the gas pressure in the detector increased so that the recoiled protons are fully stopped in the detector. In this case, a conventional total energy signal can be recorded. The transmission mode is shown to be particularly suited to determining the total hydrogen content of thin films, where the emphasis is on optimum mass and depth resolution for the heavy elements, whilst the stopped mode allows simultaneous hydrogen profiling with reasonable depth resolution.

Cylindrical magnetron co‐sputter etching of copper with applications for solar selective absorbing surfaces

Solar selective absorbing surfaces have been produced on large areas of copper plate seeded by a flux of titanium in a cylindical magnetron co‐sputter etching system. Surface oxide on the copper and the introduction of reactive gas during the etching were necessary for production of reproducible textured surfaces. The variation of optical properties and surface morphology as a function of sputter etching conditions has been studied. Optimum selective surfaces have absorptance α∠0.92 and emittance e∠0.18 at 300 K. Both absorptance and emittance decrease slightly after annealing for thousands of hours at 500 °C in vacuum.