P.W. Haycock

Response behaviour of tin oxide thin film gas sensors grown by MOCVD

Abstract Tin oxide is the most widely studied semiconducting oxide for use in gas sensor applications. However, the majority of previous study has been centred around porous media produced as thick films or thin sputtered films. This paper concerns the behaviour of relatively non-porous thin films grown by metal-organic chemical vapour deposition (MOCVD) and presents their response behaviour to the hazardous gases H2S, CH4 and NO2. The films were produced from tetratertiarybutoxytin at 350°C. They were found to act as selective H2S sensors at room temperature and show sensitive responses to all three gases above 200°C. The response to all gases is a reduction in resistance and the effect of water vapour on the response is small.

Reservoir computing and extreme learning machines for non-linear time-series data analysis

Random projection architectures such as Echo state networks (ESNs) and Extreme Learning Machines (ELMs) use a network containing a randomly connected hidden layer and train only the output weights, overcoming the problems associated with the complex and computationally demanding training algorithms traditionally used to train neural networks, particularly recurrent neural networks. In this study an ESN is shown to contain an antagonistic trade-off between the amount of non-linear mapping and short-term memory it can exhibit when applied to time-series data which are highly non-linear. To overcome this trade-off a new architecture, Reservoir with Random Static Projections (R(2)SP) is investigated, that is shown to offer a significant improvement in performance. A similar approach using an ELM whose input is presented through a time delay (TD-ELM) is shown to further enhance performance where it significantly outperformed the ESN and R(2)SP as well other architectures when applied to a novel task which allows the short-term memory and non-linearity to be varied. The hard-limiting memory of the TD-ELM appears to be best suited for the data investigated in this study, although ESN-based approaches may offer improved performance when processing data which require a longer fading memory.

A method of poling LiNbO3 and LiTaO3 below Tc

A method of poling LiNbO3 and LiTaO3 significantly below their Curie temperatures is proposed and results are presented. The technique involves excitation of the crystal lattice by an energetic beam of electrons while applying an electron field along the c axis. The lowest temperatures and fields successfully used so far are 600 °C with 10 V cm−1 for LiNbO3 and 400 °C with 900 V cm−1 for LiTaO3. These do not necessarily define lower limits for the process.

Phase diagram and single crystal growth of (La, Sr)2CuO4 from CuO solution

The system (La,Sr)2CuO4-CuO has been investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA) and slow-cooling flux growth experiments. The phase diagram is given and was used in the crystal growth experiments. The crystal products have been characterised by EPMA and by X-ray powder pattern and single crystal techniques. Large single crystals have been grown from CuO as flux by spontaneous nucleation and top seeding.

Defect Detection in Reinforced Concrete Using Random Neural Architectures

This article discusses how detecting defects within reinforced concrete is vital to the safety and durability of infrastructure. A non-invasive technique, ElectroMagnetic Anomaly Detection (EMAD) is used in this article to provide information into the electromagnetic properties of reinforcing steel for which data analysis is currently performed visually. The first use of two neural network approaches to automate the analysis of this data is investigated in this article. These approaches are called Echo State Networks (ESNs) and Extreme Learning Machines (ELMs) where fast and efficient training procedures allow networks to be trained and evaluated in less time than traditional neural network approaches. Data collected from real-world concrete structures are analyzed in this article using these two approaches as well as using a simple threshold measure and a standard recurrent neural network. Two ESN architectures provided the best performance for a mesh-reinforced concrete structure, while the ELM approach offers a large improvement in the performance of a single tendon-reinforced structure.

The Gas‐Sensing Properties of Tin Oxide Thin Films Deposited by Metallorganic Chemical Vapor Deposition

A series of undoped SnO 2 films was grown by metallorganic chemical vapor deposition (MOCVD) from an Sn(O t Bu) 4 precursor. The characterization of their CO- and H 2 O-gas sensing properties is reported. The films were very sensitive to low levels of CO at elevated temperatures (200 to 400°C), although a significant cross-sensitivity to relative humidity was found. Response and recovery times were very short in comparison with a Pt-doped thick film SnO 2 pellet. The optimum working temperature was found to be 300 to 350°C, where linear responses to CO concentration and to relative humidity were seen once drift had been taken into account. All MOCVD films tested showed superior responses to a sputtered film.

FMR studies of cobalt thin films deposited by MOCVD

Abstract Ferromagnetic resonance has been used to investigate the magnetic anisotropy in thin films of cobalt and Co/ZnO multilayers deposited by MOCVD. In general, the samples exhibited an overall in-plane magnetic anisotropy, the strength of which decreased with decreasing cobalt layer thickness. A buffer layer of ZnO was found to decrease the strength of the anisotropy with respect to a film of the same thickness deposited onto glass. In some relatively thin single films, two resonance modes were observed. This was also the case in multilayers deposited onto a ZnO buffer layer. The origins of these modes are discussed.

Time dependence and mechanisms of magnetization reversal in Tb–Fe–Co films

Measurements have been made of the time dependence of magnetization, under constant applied field conditions, of thin films of Tb–Fe–Co alloy. The results have been analyzed using a model in which it is assumed that magnetization proceeds by thermal activation of irreversible switching of the magnetic moments of identical elementary volumes. It is assumed that the activation energy for switching, intrinsically the same for all elementary volumes, varies according to local interactions. Values of the fluctuation field Λ are derived and it is found that for the films examined, Λ is independent of magnetization M and the applied field. It is shown that information about the magnetic interactions between the elementary volumes, due to exchange and demagnetizing fields, may be derived from graphs of dM/dt vs M.

Magnetic X-ray and neutron scattering from holmium and terbium

Abstract We report complementary magnetic X-ray and neutron diffraction measurements on the rare earth metals, holmium and terbium, using the 9.4 diffractometer at the Synchrotron Radiation Source (Daresbury Laboratory) and the white-beam SXD diffractometer at the ISIS pulsed neutron source (Rutherford Appleton Laboratory). Holmium, which has been studied extensively in previous X-ray and neutron investigations, was employed in preliminary measurements to develop the necessary experimental techniques. New X-ray results on terbium are described, of the temperature variation of the modulation wavevector and of the resonant enhancement at the L III absorption edge. The neutron and X-ray results are compared for the two samples studied.

Atmospheric Pressure CVD of Antimony Oxides

Communication: Thin films of Sb2O3 (senarmonite) have been deposited from antimony(III) n-butoxide at atmospheric pressure from 500 to 550 degreesC without the addition of a separate oxygen source. Films are analyzed using SEM (see Figure), EDX, and XRD, which indicates a strong (111) texture. On the other hand, the decomposition of antimony(iii) ethoxide in the same temperature range produces only antimony metal. However, when the deposition temperature is increased to 600 degreesC Sb6O13, is deposited.