Professor Robert Dorey

Professor of Nanomaterials
PhD, CSci, CEng, FIMMM
+44 (0)1483 689608
30A AB 03


University roles and responsibilities

  • Director of Post Graduate Researchers: Mechanical Engineering Sciences
  • Director of EPSRC Centre for Doctoral Training in Micro and Nanomaterials and Technology
  • Research director of Centre for Engineering Materials
  • Head of Centre for Sustainable Additive Print Manufacturing


    Research interests

    Research projects


    Postgraduate research supervision

    Courses I teach on


    Postgraduate taught

    My publications


    Wang D, Rocks SA, Dorey RA (2010) Formation of PZT micro-scale structures using electrohydrodynamic atomization filling of metallic moulds, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 30 (8) pp. 1821-1826 ELSEVIER SCI LTD
    Sun D, Rocks SA, Edirisinghe MJ, Dorey RA, Wang Y (2005) Electrohydrodynamic deposition of nanostructured lead zirconate titanate, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 5 (11) pp. 1846-1851 AMER SCIENTIFIC PUBLISHERS
    Pickwell AJ, Dorey RA, Mba D (2010) Thick film, Acoustic Emission sensors for embedded structural health monitoring systems, COMADEM 2010 - Advances in Maintenance and Condition Diagnosis Technologies Towards Sustainable Society, Proc. 23rd Int. Congr. Condition Monitoring and Diagnostic Engineering Management pp. 677-684
    Structural heath monitoring of engineering structures is of growing interest due to increased complexity of such structures and the ability to schedule maintenance when it is needed thus preventing unnecessary work or preventing failure. One such method for monitoring the structural health of large scale structures is through the detection of Acoustic Emissions (AE). A novel thick film Acoustic Emission sensor is presented. Piezoelectric thick film AE sensors were fabricated by creating and pattering lead zirconate titanate (PZT) thick films using a powder/sol composite ink deposition technique in conjunction with mechanical patterning of the subsequent films. The resultant AE sensors exhibit a response comparable to commercially available AE sensors. Comparative results between the thick film and commercial sensors will be reviewed and discussed.
    Moldovan C, Nedelcu O, Johander P, Goenaga I, Gomez D, Petkov P, Kaufmann U, Ritzhaupt-Kleissl HJ, Dorey R, Persson K (2007) Ceramic micro heater technology for gas sensors, Proceedings of the International Semiconductor Conference, CAS 1 pp. 197-200
    The paper presents the design and manufacturing steps of micro heaters, built on ceramic suspended membranes for gas sensor applications. The micro heaters are designed and fabricated by combining laser milling techniques, and conductive ceramic technology. Trenches are created in the ceramic substrate in order to define the geometry of the heater using laser processing of the substrate. The heater is completed by filling the trenches with conductive ceramic paste and then baking to remove the solvent from the paste. The final step involves releasing the membrane by laser milling, enabling it to be suspended on four bridges, to minimise the dissipation of the heat in the substrate. The temperature of the heater element was measured with a heat camera from FLIR 40 system comparing the case of the heater positioned on top of a released membrane and that of the non-released membrane. The simulation of the heater build on top of a released membrane was compared with the heater measurements. © 2006 IEEE.
    Whatmore RW, Zhang Q, Huang Z, Dorey RA (2002) Ferroelectric thin and thick films for microsystems, MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING 5 (2-3) pp. 65-76 ELSEVIER SCI LTD
    Dorey RA (2011) Ceramic Thick Films for MEMS and Microdevices, Elsevier
    The MEMS (Micro Electro-Mechanical Systems) market returned to growth in 2010. The total MEMS market is worth about $6.5 billion, up more than 11 percent from last year and nearly as high as its historic peak in 2007. MEMS devices are used across sectors as diverse as automotive, aerospace, medical, industrial process control, instrumentation and telecommunications – forming the nerve center of products including airbag crash sensors, pressure sensors, biosensors and ink jet printer heads. Part of the MEMS cluster within the Micro & Nano Technologies Series, this book covers the fabrication techniques and applications of thick film piezoelectric micro electromechanical systems (MEMS). It includes examples of applications where the piezoelectric thick films have been used, illustrating how the fabrication process relates to the properties and performance of the resulting device. Other topics include: top-down and bottom-up fabrication of thick film MEMS, integration of thick films with other materials, effect of microstructure on properties, device performance, etc.
    Farnsworth M, Tiwari A, Dorey R (2014) Modelling, simulation and optimisation of a piezoelectric energy harvester, PROCEEDINGS OF THE 3RD INTERNATIONAL CONFERENCE IN THROUGH-LIFE ENGINEERING SERVICES 22 pp. 142-147 ELSEVIER SCIENCE BV
    Sansom CL, Jones P, Dorey RA, Beck C, Stanhope-Bosumpim A, Peterson J (2013) Synthesis and characterization of Mn0.5Zn0.5Fe2O4 and Fe3O4 nanoparticle ferrofluids for thermo-electric conversion, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 335 pp. 159-162 ELSEVIER SCIENCE BV
    Dorey R, Roy S, Sharma A, Ghanty C, Majumder SB (2014) Composite film processing, In: Schneller T, Waser R, Kosec M, Payne D (eds.), Chemical Solution Deposition of Functional Oxide Thin Films 9783211993118 19 pp. 445-482 Springer
    Under the broad umbrella of chemical solution depositions (CSD), synthesis of thick films (>1 ¼m) using a combination of sol and particles (consisting of particles >100 nm size) has first been reviewed. Here the sol is used to both enhance the sintering and performance of conventional powder films as well as being integral to the formation of true powder-sol composite films where the sol forms in integral part of the deposited ink. Advantages and limitation of these composite sol-gel processing techniques are considered and deposition routes explored. The subsequent sections are devoted to outline the novel concept of composite thin film synthesis using molecular precursors. Based on the authors' own experience and existing literature, the perspective, potential and possibilities of the electro-ceramic thin films synthesized using sub 100 nm particulate precursor sols has been outlined.
    Bortolani F, Dorey RA (2009) Synthesis of spherical lead zirconate titanate (PZT) nanoparticles by electrohydrodynamic atomisation, ADVANCES IN APPLIED CERAMICS 108 (6) pp. 332-337 MANEY PUBLISHING
    James C, Chakraborty T, Brown A, Comyn T, Dorey R, Harrington J, Laister AJ, Miles RE, Puchmark C, Xu B, Xiong W, Zhang Q, Milne SJ (2009) Laser transfer processing for the integration of thin and thick film ferroelectrics, JOURNAL OF MATERIALS SCIENCE 44 (19) pp. 5325-5331 SPRINGER
    Wang D, Li X, Shi P, Zhao X, Liang J, Ren T, Dong W, Yang R, Wang Y, Dorey RA (2016) Electrohydrodynamic atomization deposition and mechanical polishing of PZT thick films,CERAMICS INTERNATIONAL 42 (11) pp. 12623-12629 ELSEVIER SCI LTD
    Dorey RA, Yeomans JA, Smith PA (2002) Effect of pore clustering on the mechanical properties of ceramics, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 22 (4) pp. 403-409 ELSEVIER SCI LTD
    Dorey RA, Haigh RD, Stringfellow SB, Whatmore RW (2002) Effect of sol infiltrations on the electrical properties of PZT, Ferroelectrics UK 2001 pp. 29-35 MANEY PUBLISHING
    Pickwell AJ, Smith A, Jones PM, Mba D, Dorey RA (2013) ZnO surface modified PZT for enhanced ceramic composite thick film sensors, ADVANCES IN APPLIED CERAMICS 112 (5) pp. 283-287 MANEY PUBLISHING
    Pawlett M, Ritz K, Dorey RA, Rocks S, Ramsden J, Harris JA (2013) The impact of zero-valent iron nanoparticles upon soil microbial communities is context dependent., Environ Sci Pollut Res Int 20 (2) pp. 1041-1049
    Nanosized zero-valent iron (nZVI) is an effective land remediation tool, but there remains little information regarding its impact upon and interactions with the soil microbial community. nZVI stabilised with sodium carboxymethyl cellulose was applied to soils of three contrasting textures and organic matter contents to determine impacts on soil microbial biomass, phenotypic (phospholipid fatty acid (PLFA)), and functional (multiple substrate-induced respiration (MSIR)) profiles. The nZVI significantly reduced microbial biomass by 29 % but only where soil was amended with 5 % straw. Effects of nZVI on MSIR profiles were only evident in the clay soils and were independent of organic matter content. PLFA profiling indicated that the soil microbial community structure in sandy soils were apparently the most, and clay soils the least, vulnerable to nZVI suggesting a protective effect imparted by clays. Evidence of nZVI bactericidal effects on Gram-negative bacteria and a potential reduction of arbuscular mycorrhizal fungi are presented. Data imply that the impact of nZVI on soil microbial communities is dependent on organic matter content and soil mineral type. Thereby, evaluations of nZVI toxicity on soil microbial communities should consider context. The reduction of AM fungi following nZVI application may have implications for land remediation.
    Duval FFC, Dorey RA, Haigh RH, Whatmore RW (2003) Stable TiO2/Pt electrode structure for lead containing ferroelectric thick films on silicon MEMS structures, THIN SOLID FILMS 444 (1-2) pp. 235-240 ELSEVIER SCIENCE SA
    Dorey RA, Dauchy F, Wang D, Berriet R (2007) Fabrication and characterization of annular thickness mode piezoelectric micro ultrasonic transducers., IEEE Trans Ultrason Ferroelectr Freq Control 54 (12) pp. 2462-2468
    Micromachining techniques, in combination with low temperature ceramic composite sol-gel processing, have been used to fabricate annular array thickness-mode piezoelectric micro ultrasonic transducers (Tm-pMUTs). The processing techniques of low temperature (710 degrees C) composite sol-gel ceramic (sol + ceramic powder) deposition and wet etching were used to deposit and structure 27-microm thick lead zirconate titanate (PZT) films on silicon substrates to produce annular array Tm-pMUTs. Using these techniques, high quality PZT materials with near bulk permittivity have been obtained. The Tm-pMUT devices were shown to resonate at approximately 60 MHz in air and 50 MHz in water. From resonance measurements k(t) values ranging between 0.2 and 0.47 have been calculated and shown to depend on the level of porosity within the film. Lower values of kt were observed for films with higher levels of porosity, which was attributed to the relative decrease in the effective piezoelectric coefficient epsilon(33) with respect to stiffness and permittivity as a function of increasing porosity. This paper presents the successful micro-fabrication of a Tm-pMUT device and discusses the optimization of the poling conditions and effect of PZT microstructure on the coupling coefficient k(t). Pulse echo measurements in water, showing a -6 dB center frequency of 53 MHz and 47% -6 dB bandwidth, using a target 15 mm away from the transducer, have been included to demonstrate successful operation of the device. Full analysis of these results will be conducted in later publications.
    Dorey RA, Dauchy F, Wang D, Berriet R (2007) Fabrication and characterisation of annular thickness mode piezoelectric micro ultrasonic transducers,IEEE International Symposium on Applications of Ferroelectrics pp. 732-733
    Micromachining techniques, in combination with low temperature ceramic composite sol gel processing, have been used to fabricate annular array thickness-mode piezoelectric micro ultrasonic transducers (Tm-pMUT). The processing techniques of low temperature (720°C) composite sol gel ceramic (sol + ceramic powder) deposition and wet etching will be described and device architectures demonstrated. Using these techniques, high quality PZT materials with near bulk permittivity have been obtained. The Tm-pMUT device resonated in the range of 50-100MHz with a kt of between 0.3 and 0.4 depending on processing conditions. Examples of devices will be presented along with results of electrical and resonance measurements.
    Stoyanov S, Bailey C, Leach R, Hughes B, Wilson A, O'Neill W, Dorey RA, Shaw C, Underhill D, Almond HJ (2008) Modelling and prototyping the conceptual design of 3D CMM micro-probe, Proceedings - 2008 2nd Electronics Systemintegration Technology Conference, ESTC pp. 193-198
    This paper details the prototyping of a novel three axial micro probe based on utilisation of piezoelectric sensors and actuators for true three dimensional metrology and measurements at micro- and nanometre scale. Computational mechanics is used first to model and simulate the performance of the conceptual design of the micro-probe. Piezoelectric analysis is conducted to understand performance of three different materials silicon, glassy carbon, and nickel - and the effect of load parameters (amplitude, frequency, phase angle) on the magnitude of vibrations. Simulations are also used to compare several design options for layout of the lead zirconium titanate (PZT) sensors and to identify the most feasible from fabrication point of view design. The material options for the realisation of the device have been also tested. Direct laser machining was selected as the primary means of production. It is found that a Yb MaPA based fiber laser was capable of providing the necessary precision on glassy carbon (GC), although machining trials on Si and Ni were less successful due to residual thermal effects.To provide the active and sensing elements on the flexures of the probe, PZT thick films are developed and deposited at low temperatures (
    Dorey RA (2009) Challenges in integration of piezoelectric ceramics in micro electromechanical systems, Materials Science Forum 606 pp. 43-50
    Lead zirconate titanate (PZT) thick films, a few tens of micrometres thick, are of technological interest for integration with microsystems to create micro electromechanical systems (MEMS) with high sensitivity and power output. This paper examines the challenges faced in integrating thick film PZT with other materials to create functional micro devices. Thermal, chemical and mechanical challenges associated with integration will be examined and potential solutions explored. © (2009) Trans Tech Publications, Switzerland.
    Dauchy F, Dorey RA (2007) Patterned crack-free PZT thick films for micro-electromechanical system applications, INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY 33 (1-2) pp. 86-94 SPRINGER LONDON LTD
    Lusiola T, Chelwani N, Bortolani F, Zhang Q, Dorey RA (2011) Low Temperature Production of Lead-Free Piezoelectric Thick Films, FERROELECTRICS 422 pp. 50-54 TAYLOR & FRANCIS LTD
    Dorey RA, Rocks SA, Dauchy F, Wang D, Bortolani F, Hugo E (2008) Integrating functional ceramics into microsystems, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 28 (7) pp. 1397-1403 ELSEVIER SCI LTD
    Sansom C, Tonnellier X, Read R, Nicholls J, Dorey R (2014) Design and fabrication of a coating research machine to explore the nanometer scale coating of glass tubes for Concentrating Solar Power (CSP) systems,Conference Proceedings - 14th International Conference of the European Society for Precision Engineering and Nanotechnology, EUSPEN 2014 1 pp. 59-62
    This paper presents the design and fabrication of a precision designed CSP receiver tube coating machine for research purposes, designed to deposit and examine the properties of novel anti-reflection (AR) coatings possessing a thickness in the nanometre range. The manufacturing process chain and in line thickness control technique are also described.
    Dunn S, Dorey R (2011) Untitled, FERROELECTRICS 421 pp. V-V TAYLOR & FRANCIS LTD
    Duval FFC, Dorey RA, Wright RW, Huang Z, Whatmore RW (2004) Fabrication of PZT composite thick films for high frequency membrane resonators, JOURNAL OF ELECTROCERAMICS 13 (1-3) pp. 267-270 SPRINGER
    Rocks SA, Tredez Q, Almond HJ, Shaw CP, Dorey RA (2009) Bottom up fabrication of a nickel-lead zirconate titanate piezoelectric microcantilevers, MATERIALS LETTERS 63 (1) pp. 88-90 ELSEVIER SCIENCE BV
    Wang D, Edirisinghe MJ, Dorey RA (2008) Formation of PZT crack-free thick films by electrohydrodynamic atomization deposition, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 28 (14) pp. 2739-2745 ELSEVIER SCI LTD
    Dunn S, Dorey R (2011) Untitled, FERROELECTRICS 419 pp. V-V TAYLOR & FRANCIS LTD
    Chakraborty T, Xu B, Harrington J, Chakraborty S, Zhang Q, Miles RE, Dorey R, Milne SJ (2006) Focussed ion beam etching of the interfacial region of lead zirconate titanate thin film after laser-release from sapphire fabrication substrate, 2006 NSTI Nanotechnology Conference and Trade Show - NSTI Nanotech 2006 Technical Proceedings 3 pp. 162-165
    Although many lead zirconate titanate (PZT) based MEMS have been demonstrated, the thermal incompatibility problems associated with in-situ fabrication of PZT films on the device substrate remain a major challenge. Process temperatures of 600-700 °C are common for PZT on silicon, however these temperatures can degrade silicon microelectronics and metal interconnects. By depositing the film on a separate fabrication substrate, such as sapphire, and then using a pulsed UV laser to aid its transfer to the device substrate the problems of thermal incompatibility are avoided [1]. In order to gain a better understanding of the effects of the laser radiation on the interfacial region of the film originally adjacent to the sapphire substrate, we are examining the merits of dual-beam SEM focussed-ion- beam etching (FIBSEM, Nova 200 Nanolab, FEI UK Ltd). Microstructural information from SEM, together with preliminary results using FIBSEM are presented.
    Moldovan C, Nedelcu O, Johander P, Goenaga I, Gomez D, Petkov P, Kaufmann U, Ritzhaupt-Kleissl H-J, Dorey R, Persson K (2007) Ceramic micro heater technology for gas sensors, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY 10 (1) pp. 43-52 EDITURA ACAD ROMANE
    Woolliams PD, Weaver PM, Correia TM, Cain MG, Pickwell A, Dorey RA (2013) Lead zirconate titanate coating of tungsten carbide-cobalt to enable smart coatings, SENSORS AND ACTUATORS A-PHYSICAL 194 pp. 47-51 ELSEVIER SCIENCE SA
    Dorey R, Buchacher T, Allam J, Gregory A, Rokosz M Electrocaloric induced retarded ferroelectric switching, University of Surrey
    Dorey RA, Whatmore RW (2005) Pyroelectric PZT/PMNZTU composite thick films, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 25 (12) pp. 2379-2382 ELSEVIER SCI LTD
    Tillman M, Dorey RA (2013) Enhanced sintering and functional properties of PZT thick films processed using local infrared irradiation, JOURNAL OF MATERIALS SCIENCE 48 (2) pp. 884-890 SPRINGER
    Dorey RA, Leighton GJT (2012) Printed actuators, pp. 410-428
    An actuator can be defined as a mechanical device that creates a physical movement within a system. While this definition can encompass many different devices, the focus of this chapter is on printed films that are able to impart an actuation action by virtue of being composed of an active material (piezoelectric, magnetostrictive and shape memory alloy) that deforms mechanically when subjected to an external stimulus. For film-based actuators, actuation is most commonly achieved by coupling the active material with an inactive support structure that induces a bending moment when the active material is made to contract or expand parallel to the film plane. The approaches used to integrate thick active films with a variety of substrates are examined, along with the limitations and microstructural effects that arise as a consequence of co-processing materials. © 2012 Woodhead Publishing Limited. All rights reserved.
    Dunn S, Dorey R (2011) Guest Editorial: Ferroelectrics,FERROELECTRICS 420 pp. V-V TAYLOR & FRANCIS LTD
    Wilson SA, Jourdain RPJ, Zhang Q, Dorey RA, Bowen CR, Willander M, Wahab QU, Willander M, Safaa MA-H, Nur O, Quandt E, Johansson C, Pagounis E, Kohl M, Matovic J, Samel B, van der Wijngaart W, Jager EWH, Carlsson D, Djinovic Z, Wegener M, Moldovan C, Iosub R, Abad E, Wendlandt M, Rusu C, Persson K (2007) New materials for micro-scale sensors and actuators An engineering review, MATERIALS SCIENCE & ENGINEERING R-REPORTS 56 (1-6) pp. 1-129 ELSEVIER SCIENCE SA
    Dorey RA, Whatmore RW, Beeby SP, Torah RN, White NM (2004) Screen printed PZT composite thick films, INTEGRATED FERROELECTRICS 63 pp. 89-92 TAYLOR & FRANCIS LTD
    Townsend RL, Dorey RA, Rocks SA, Tearle S (2014) The use of interdigitated microelectrode structures for the detection of exposure to simulated airborne environmental dust, Technical Proceedings of the 2014 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2014 2 pp. 57-60
    Particulate matter is ubiquitous in the environment, however industrial processes have increased the amount released into the air. Here, the authors demonstrate the initial development of a novel sensor capable of detecting airborne particulate matter in real time. Interdigitated microelectrodes (IDT) were printed on a silicon wafer substrate and exposed to Arizona Road Dust in a wind tunnel for periods of 2, 5, and 10 minutes with an air sample mass loading of 9.07mg/m3 at a velocity of 1.7m/s. Impedance measurements were taken every 30 seconds during exposure. The average loading efficiency was calculated to be 31%. Impedance measurements were recorded from the IDT samples showing that the impedance decreased in real time over the 10 minute exposure. The observed capturing coefficient was possibly due to surface-particle interaction phenomena, such as particle bounce, impaction and re-entrainment. IDTs have previously been used to detect nanoparticles within aqueous environments however this is the first report of such electrodes being used to successfully detect airborne particles.
    Bortolani F, Dorey RA (2010) Molten salt synthesis of PZT powder for direct write inks, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 30 (10) pp. 2073-2079 ELSEVIER SCI LTD
    Bell C, Farnsworth M, Tiwari A, Dorey R (2013) Theoretical design of a self-rectifying 4-bar linkage mechanism, Procedia CIRP 11 pp. 385-389
    Mechanical systems will almost inevitably fail at some point during operation. This can either be due to a preexisting design flaw or some unexpected damage during usage. No matter how much planning and fault analysis is performed it is impossible to create a perfectly reliable machine. Existing approaches to improving reliability normally involve advances in modeling and detection to include specific mechanisms to overcome a particular failure or mitigate its effect. Whilst this has gone a long way to increasing the operational life of a machine, the overall complexity of systems has improved sharply and it is becoming more and more difficult to predict and account for all possible failure modes. Rather than focusing on mitigating or reducing the probability of failure, a new design philosophy is proposed that allows systems to reconfigure themselves to overcome failure - thus yielding a self-healing design. This approach is demonstrated in the design of a selfrectifying 4-bar linkage mechanism. © 2013 The Authors. Published by Elsevier B.V.
    Whatmore RW, Zhang Q, Shaw CP, Dorey RA, Alcock JR (2007) Pyroelectric ceramics and thin films for applications in uncooled infra-red sensor arrays, PHYSICA SCRIPTA T129 pp. 6-11 IOP PUBLISHING LTD
    James CW, Comyn T, Dorey RA, Underhill D, Milne SJ (2010) Laser-transfer processing of functional ceramic films, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 30 (2) pp. 419-422 ELSEVIER SCI LTD
    Rocks SA, Pollard SJ, Dorey RA, Harrison PTC, Levy LS, Handy RD, Garrod JF, Owen R (2009) Risk Assessment of Manufactured Nanomaterials, pp. 389-421
    Huang Z, Zhang Q, Corkovic S, Dorey RA, Duval F, Leighton G, Wright R, Kirby P, Whatmore RW (2006) Piezoelectric PZT films for MEMS and their characterization by interferometry, JOURNAL OF ELECTROCERAMICS 17 (2-4) pp. 549-556 SPRINGER
    Dorey R (2010) Bottoms up, MATERIALS WORLD 18 (12) pp. 26-28 I O M COMMUNICATIONS LTD INST MATERIALS
    Dorey RA, Haigh RD, Stringfellow SB, Whatmore RW (2002) Effect of sol infiltrations on electrical properties of PZT, BRITISH CERAMIC TRANSACTIONS 101 (4) pp. 146-148 MANEY PUBLISHING
    Duval F, Dorey R, Stringfellow S, Zhang Q, Whatmore R (2002) Comparison of piezoelectric properties of a MOD and a sol-gel doped PZT thin film, Ferroelectrics UK 2001 pp. 37-44 MANEY PUBLISHING
    Wang D, Rocks SA, Dorey RA (2012) Electrohydrodynamic atomization deposition of PZT sol-gel slurry and sol infiltration on the films, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 32 (8) pp. 1651-1658 ELSEVIER SCI LTD
    Dorey R (2013) Piezoelectrics: pressing the point home, ADVANCES IN APPLIED CERAMICS 112 (2) pp. 67-68 MANEY PUBLISHING
    Pickwell AJ, Dorey RA, Mba D (2011) Thick-film acoustic emission sensors for use in structurally integrated condition-monitoring applications., IEEE Trans Ultrason Ferroelectr Freq Control 58 (9) pp. 1994-2000
    Monitoring the condition of complex engineering structures is an important aspect of modern engineering, eliminating unnecessary work and enabling planned maintenance, preventing failure. Acoustic emissions (AE) testing is one method of implementing continuous nondestructive structural health monitoring. A novel thick-film (17.6 ¼m) AE sensor is presented. Lead zirconate titanate thick films were fabricated using a powder/sol composite ink deposition technique and mechanically patterned to form a discrete thick-film piezoelectric AE sensor. The thick-film sensor was benchmarked against a commercial AE device and was found to exhibit comparable responses to simulated acoustic emissions.
    Wang D, Filoux E, Levassort F, Lethiecq M, Rocks SA, Dorey RA (2014) Fabrication and characterization of annular-array, high-frequency, ultrasonic transducers based on PZT thick film, Sensors and Actuators, A: Physical 216 pp. 207-213
    In this work, low temperature deposition of ceramics, in combination with micromachining techniques have been used to fabricate a kerfed, annular-array, high-frequency, micro ultrasonic transducer (with seven elements). This transducer was based on PZT thick film and operated in thickness mode. The 27 ¼m thick PZT film was fabricated using a low temperature (720 °C) composite sol-gel ceramic (sol + ceramic powder) deposition technique. Chemical wet etching was used to pattern the PZT thick film to produce the annular array ultrasonic transducer with a kerf of 90 ¼m between rings. A 67 MHz parallel resonant frequency in air was obtained. Pulse-echo responses were measured in water, showing that this device was able to operate in water medium. The resonance frequency and pulse-echo response have shown the frequency response presented additional resonance mode, which were due to the lateral modes induced by the small width-to-height ratios, especially for peripheral rings. A hybrid finite-difference (FD) and pseudospectral time-domain (PSTD) method (FD-PSTD) was used to simulate the acoustic field characteristics of two types of annular devices. One has no physical separation of the rings while the other has 90 ¼m kerf between each ring. The results show that the kerfed annular-array device has higher sensitivity than the kerfless one. © 2014 Elsevier B.V.
    Pickwell AJ, Dorey RA, Mba D (2013) Development of a thick film PZT foil sensor for use in structural health monitoring applications., IEEE Trans Ultrason Ferroelectr Freq Control 60 (2) pp. 373-379
    Acoustic emission (AE) monitoring is a technique of growing interest in the field of nondestructive testing (NDT). The use of AE devices to monitor the health of structural components is currently limited by the cost of AE equipment, which prohibits the permanent placement of AE devices on structures for the purposes of continuous monitoring and the monitoring of areas with limited access. Micro electromechanical systems (MEMS) can provide solutions to these problems. We present the manufacture of a 4.4-¼m-thick lead zirconate titanate (PZT) film on a 110-¼m-thick titanium foil substrate for use as an AE sensor. The thick-film sensor is benchmarked against commercially available AE sensors in static and dynamic monitoring applications. The thick-film AE device is found to perform well in the detection of AE in static applications. A low signal-to-noise ratio is found to prohibit the detection of AE in a dynamic application.
    Moldovan C, Sosin S, Nedelcu O, Kaufmann U, Ritzhaupt-Kleissl HJ, Dimov S, Petkov P, Dorey R, Persson K, Gomez D, Johander P (2005) Chemoresistive gas sensor manufacturing using mixed technologies, Proceedings of the International Semiconductor Conference, CAS 1 pp. 201-204
    The paper presents the development of a novel suspended membrane resistive gas sensor on a ceramic substrate. The sensor is designed and simulated to be fabricated by combining laser milling techniques, conductive ceramic technology, thin film technology, and semiconductor metal oxides. Trenches are created in the alumina substrate in order to define the geometry of the heater using laser processing of the substrate. The heater is completed by filling the trenches with conductive ceramic paste and then baking to remove the solvent from the paste. The next step consists of polishing the surface to obtain a surface roughness small enough for thin film technology. A dielectric (SiO 2 or ceramic) material is then deposited, acting as hot plate and also as electrical isolation between the heater and sensing electrode. The sensing electrode consists of an interdigitated resistor made of Au or Pt with thickness in the range of 2000 -3000 Å. The gas sensitive layer (SnO 2) is deposited by screen printing or spinning. When heated it react with gas molecules and changes its resistivity, thereby acting as a sensor. The final step involves releasing the sensor, enabling it to be suspended on four bridges, to minimise the dissipation of the heat in the substrate. © 2005 IEEE.
    Duval FFC, Dorey RA, Zhang Q, Whatmore RW (2003) Lead germanium oxide sinter-assisted PZT composite thick films, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 23 (11) PII S0955-2219(02)00417-X pp. 1935-1941 ELSEVIER SCI LTD
    Dorey RA, Whatmore RW, Beeby SP, Torah RN, White NM (2003) Screen printed PZT thick films using composite film technology, INTEGRATED FERROELECTRICS 54 pp. 651-658 TAYLOR & FRANCIS LTD
    Wang D, Zhu X, Liang J, Ren T, Zha W, Dong W, Rocks SA, Dorey RA, Xu Z, Wang X (2015) Electrohydrodynamic jet printing of PZT thick film micro-scale structures, Journal of the European Ceramic Society 35 (13) pp. 3475-3483
    © 2015 Elsevier Ltd.This paper reports the use of a printing technique, called electrohydrodynamic jet printing, for producing PZT thick film micro-scale structures without additional material removing processes. The PZT powder was ball-milled and the effect of milling time on the particle size was examined. This ball-milling process can significantly reduce the PZT particle size and help to prepare stable composite slurry suitable for the E-Jet printing. The PZT micro-scale structures with different features were produced. The PZT lines with different widths and separations were fabricated through the control of the E-Jet printing parameters. The widths of the PZT lines were varied from 80¼m to 200¼m and the separations were changed from 5¼m to 200¼m. In addition, PZT walled structures were obtained by multi-layer E-Jet printing. The E-Jet printed PZT thick films exhibited a relative permittivity (er) of ~233 and a piezoelectric constant (d33, f) of ~66pCN-1.
    Xiao P, Dorey R (2008) Nanostructured Thin Films and Coatings, JOURNAL OF NANOMATERIALS ARTN 931380 HINDAWI PUBLISHING CORPORATION
    Marson S, Dorey RA, Zhang Q, Whatmore RW (2003) Thick PZT micro-features obtained by direct patterning of photosensitive precursor solution, INTEGRATED FERROELECTRICS 54 pp. 585-593 TAYLOR & FRANCIS LTD
    Dauchy F, Dorey RA (2007) Thickness mode high frequency MEMS piezoelectric micro ultrasound transducers, JOURNAL OF ELECTROCERAMICS 19 (4) pp. 383-386 SPRINGER
    Munasinghe C, Heikenfeld J, Dorey R, Whatmore R, Bender JP, Wager JF, Steckl AJ (2005) High brightness ZnS and GaN electroluminescent devices using PZT thick dielectric layers, IEEE TRANSACTIONS ON ELECTRON DEVICES 52 (2) pp. 194-203 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
    Rocks SA, Wang D, Sun D, Jayasinghe SN, Edirisinghe MJ, Dorey RA (2007) Direct writing of lead zirconate titanate piezoelectric structures by electrohydrodynamic atomisation, JOURNAL OF ELECTROCERAMICS 19 (4) pp. 287-293 SPRINGER
    Dorey RA, Stringfellow SB, Whatmore RW (2002) Effect of sintering aid and repeated sot infiltrations on the dielectric and piezoelectric properties of a PZT composite thick film, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 22 (16) PII S0955-2219(02)00062-6 pp. 2921-2926 ELSEVIER SCI LTD
    Dorey RA (2010) Piezo2009: Piezoelectric for end users V, ADVANCES IN APPLIED CERAMICS 109 (3) pp. 129-129 MANEY PUBLISHING
    Dauchy FM, Dorey RA (2007) Patterned high frequency thick film MEMS transducer, INTEGRATED FERROELECTRICS 90 pp. 42-52 TAYLOR & FRANCIS LTD
    Marson S, Dorey RA, Zhang Q, Whatmore RW, Hardy A, Mullens J (2004) Direct patterning of photosensitive chemical solution deposition PZT layers, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 24 (6) pp. 1925-1928 ELSEVIER SCI LTD
    Sun D, Rocks SA, Wang D, Edirisinghe MJ, Dorey RA (2008) Novel forming of columnar lead zirconate titanate structures, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 28 (16) pp. 3131-3139 ELSEVIER SCI LTD
    Dorey RA, Dauchy F, Wang D, Berriet R (2007) Fabrication and characterisation of annular thickness mode piezoelectric micro ultrasonic transducers,2007 SIXTEENTH IEEE INTERNATIONAL SYMPOSIUM ON THE APPLICATIONS OF FERROELECTRICS, VOLS 1 AND 2 pp. 729-730 IEEE
    Dorey RA, Rocks SA (2007) Piezoelectrics for End Users II: From electroactive materials to multifunctional integrated devices, JOURNAL OF ELECTROCERAMICS 19 (4) pp. 241-241 SPRINGER
    Wang D, Rocks SA, Dorey RA (2009) Micromoulding of PZT film structures using electrohydrodynamic atomization mould filling, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 29 (6) pp. 1147-1155 ELSEVIER SCI LTD
    Huang Z, Zhang Q, Corkovic S, Dorey R, Whatmore RW (2006) Comparative measurements of piezoelectric coefficient of PZT films by Berlincourt, interferometer, and vibrometer methods., IEEE Trans Ultrason Ferroelectr Freq Control 53 (12) pp. 2287-2293
    Chemical solution deposition (CSD) techniques were used to prepare lead zirconate (Zr) titanate (Ti) (PZT) thin films with Zr/Ti ratios of 30/70 and 52/48. Usually CSD processing is restricted to making crack-free, single-layer films of 70-nm thick, but modifications to the sol-gel process have permitted the fabrication of dense, crack-free, single layers up to 200 to 300 nm thick, which can be built-up into layers up to 3-microm thick. Thicker PZT films (> 2-microm single layer) can be produced by using a composite sol-gel/ceramic process. Knowledge of the electroactive properties of these materials is essential for modeling and design of novel micro-electromechanical systems (MEMS) devices, but accurate measurement of these properties is by no means straightforward. A novel, double-beam, common-path laser interferometer has been developed to measure the longitudinal (d33) piezoelectric coefficient in films; the results were compared with the values obtained by Berlin-court and laser scanning vibrometer methods. It was found that, for thin-film samples, the d(33,f) values obtained from the Berlincourt method are usually larger: than those obtained from the interferometer and the vibrometer methods; the reasons for this are discussed.
    Dorey RA, Whatmore RW (2004) Electroceramic thick film fabrication for MEMS, JOURNAL OF ELECTROCERAMICS 12 (1-2) pp. 19-32 KLUWER ACADEMIC PUBL
    Duval F, Hladky-Hennion AC, Cattan E, Zhang Q, Dorey R (2006) Design, fabrication and characterisation of high frequency piezoelectric micromachined ultrasonic transducers, Proceedings - IEEE Ultrasonics Symposium 1 pp. 1959-1962
    High frequency bending mode membranes are fabricated using a 1¼m PZT thick film deposited by sol-gel. Finite Element Analysis (FEA) is used to tailor the membrane radius to a resonant frequency in the 5-10MHz frequency range. Using a radius of 16 and 24¼m, devices are produced as individual cells as well as 3x3 and 5x5 arrays. The arrays are designed so that the bottom electrode is common to all cells whereas the top electrode is only common to a column of 5 or 3 cells depending on the type of arrays. Within a column each cell was separated by a wall of silicon (having the length of the substrate of silicon) in order to sustain the array, reduce parasitic vibrations, hence cross-talk. A 16¼m radius membrane shows a resonant frequency of 9MHz and a coupling coefficient of 11%. Suspended cells are also investigated to increase frequency further. Two arms-suspended cells resonate at 8.1MHz for a 24¼m radius membrane. © 2006 IEEE.
    Dorey RA, Whatmore RW (2004) Pyroelectric properties of PZT/PMNZTU composite thick films, JOURNAL OF ELECTROCERAMICS 12 (3) pp. 191-196 KLUWER ACADEMIC PUBL
    Dorey RA, Whatmore RW (2002) Apparent reduction in the value of the d(33) piezoelectric coefficient in PZT thick films, INTEGRATED FERROELECTRICS 50 pp. 111-119 TAYLOR & FRANCIS LTD
    Buchacher T, Dorey R, Allam J, Lepadatu S, Cain M Low field depoling phenomena in soft lead zirconate titanate ferroelectrics, University of Surrey
    Dorey RA, Whatmore RW (2002) Apparent reduction in the value of the d33 piezoelectric coefficient in PZT thick films, Integrated Ferroelectrics 50 pp. 111-119
    Thick PZT films (1 - 20 m) have been prepared using a composite sol gel technique whereby PZT powder and a PZT producing sol are formed into a slurry and spin coated onto silicon wafers. The maximum relative permittivity obtained was approximately 80% of that exhibited by bulk PZT of comparable composition. However, the d33, f and e31, f[1] piezoelectric coefficients were shown to be significantly lower than that of bulk PZT. It has been proposed that the measured value of d33, f is affected appreciably by particle-particle rotation and substrate clamping leading to reduced poling efficiency which may also greatly reduce the value of e 31, f observed. Samples with high levels of porosity have been shown to exhibit a reduced value of d33. This was attributed to 31 and 51 mode piezoelectrically generated charges caused by the bending and shearing of particle-particle bridges. The effect of substrate clamping, on d 33, f and poling, has been studied by monitoring the changes in position and intensity of the (200)/(002) X-ray diffraction (XRD) peaks of composite films. The presence of the substrate was found to introduce tensile stresses parallel to the film plane which distorted the unit cell. Subsequent permanent polarisation following poling was found to be reduced due to the presence of these stresses. The discrepancies between the values of d 33 measured on thick films and bulk ceramics were highlighted as being of particular importance if thick film materials are to be modelled for device applications. Thick film piezoelectric coefficients (i.e. those of the combined film-substrate structure) should not be used in place of material piezoelectric coefficients when attempting to model the behaviour of devices. Such actions would inevitably lead to erroneous results. © 2002 Taylor & Francis.
    Jayasinghe SN, Dorey RA, Edirisinghe MJ, Luklinska ZB (2005) Preparation of lead zirconate titanate nano-powder by electrohydrodynamic atomization, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING 80 (4) pp. 723-725 SPRINGER
    Tillman M, Yeomans JA, Dorey RA (2014) The effect of a constraint on the sintering and stress development in alumina thick films, Ceramics International 40 (7 PART A) pp. 9715-9721
    The microstructural and stress evolution of thick (25 ¼m) alumina films on dense alumina substrates sintered at temperatures from 1300 °C to 1600 °C has been investigated. In this study the constraint on sintering was monitored in the absence of significant differences in thermal expansion between the film and the substrate. For comparison purposes unconstrained alumina pellets sintered at 1300 °C-1600 °C were also examined. Overall, the constrained alumina densified less than the free alumina, as expected, although at intermediate temperatures densification rates were comparable. Sintering in the direction perpendicular to the substrate was enhanced with respect to that parallel to the substrate as a means of stress relaxation. Using fluorescence spectroscopy the residual stresses of the films parallel to the substrates were measured; residual tensile stresses as high as 450±40 MPa were exhibited by the films. The considerable stress development resulted in cracking and delamination of the film from the substrate, subsequently film constraint was reduced and densification was not impeded. © 2014 The Authors.
    Dorey RA, Whatmore RW (2004) Electrical properties of high density PZT and PMN-PT/PZT thick films produced using ComFi technology, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 24 (6) pp. 1091-1094 ELSEVIER SCI LTD
    Wang DZ, Dorey RA (2009) Formation of PZT thick film single elements using EHDA deposition, Materials Science Forum 628 629 pp. 405-410
    In this paper, electrohydrodynamic atomization combined with a polymeric micromoulding technique was used to form PZT single element devices using a PZT sol-gel slurry without an etching process. The PZT single element device was initially designed to work as a piezoelectric ultrasonic transducer consisting of a circular or a square of various sizes, which was produced and used to evaluate the process. The resulting PZT device had a homogenous microstructure. It was observed that the relative permittivity of the circular and square single element devices was especially high at small size due to the fringe effect. The results show that the radius and width of the PZT single circular and square element devices with a thickness of 15¼m should be bigger than 400¼m in order to reduce the fringe effect. © (2009) Trans Tech Publications, Switzerland.
    Navarro A, Rocks SA, Dorey RA (2007) Micromoulding of lead zirconate titanate (PZT) structures for MEMS, JOURNAL OF ELECTROCERAMICS 19 (4) pp. 321-326 SPRINGER
    Duval FFC, Dorey RA, Wright RW, Huang Z, Whatmore RW (2004) High frequency PZT composite thick film resonators, INTEGRATED FERROELECTRICS 63 pp. 27-33 TAYLOR & FRANCIS LTD
    Tyholdt F, Dorey RA, Raeder H (2007) Novel patterning of composite thick film PZT, JOURNAL OF ELECTROCERAMICS 19 (4) pp. 315-319 SPRINGER
    Lusiola T, Bortolani F, Zhang Q, Dorey R (2012) Molten hydroxide synthesis as an alternative to molten salt synthesis for producing K0.5Na0.5NbO3 lead free ceramics, JOURNAL OF MATERIALS SCIENCE 47 (4) pp. 1938-1942 SPRINGER
    Dunn S, Dorey R (2011) Untitled, FERROELECTRICS 422 pp. V-V TAYLOR & FRANCIS LTD
    Dorey RA, Duval FFC, Haigh RD, Whatmore RW (2002) The effect of repeated sol infiltrations on the microstructure and electrical properties of PZT composite sol-gel films, FERROELECTRICS 267 pp. 373-378 TAYLOR & FRANCIS LTD
    Dorey RA (2014) Integrated powder-based thick films for thermoelectric, pyroelectric, and piezoelectric energy harvesting devices, IEEE Sensors Journal 14 (7) pp. 2177-2184
    Energy harvesting devices based on piezoelectric, pyroelectric, and thermoelectric materials offer an attractive solution for batteryless and wireless sensor nodes for a range of sensor applications. Current devices are typically fabricated using semimanual approaches leading to higher costs and reduced yields as well as significant material wastage. Powder-based thick film devices have been shown to be capable of harvesting milliwatt levels of power while the associated printing technologies offer commercially attractive fabrication solutions. This paper provides a review of examples of recent piezoelectric, pyroelectric, and thermoelectric powder-based thick film energy harvester devices and outlines potential fabrication techniques, ink compositions, and ways to reduce processing temperatures that can be used to create integrated thick film energy harvesting devices. The key to the creation of such devices is the management of thermal budgets and processing environments to ensure the functional properties of the thick films are maximized. © 2001-2012 IEEE.
    Tillman M, Yeomans JA, Dorey RA (2014) The effect of a constraint on the sintering and stress development in alumina thick films,Ceramics International
    The microstructural and stress evolution of thick (25 ¼m) alumina films on dense alumina substrates sintered at temperatures from 1300 °C to 1600 °C has been investigated. In this study the constraint on sintering was monitored in the absence of significant differences in thermal expansion between the film and the substrate. For comparison purposes unconstrained alumina pellets sintered at 1300 °C-1600 °C were also examined. Overall, the constrained alumina densified less than the free alumina, as expected, although at intermediate temperatures densification rates were comparable. Sintering in the direction perpendicular to the substrate was enhanced with respect to that parallel to the substrate as a means of stress relaxation. Using fluorescence spectroscopy the residual stresses of the films parallel to the substrates were measured; residual tensile stresses as high as 450±40 MPa were exhibited by the films. The considerable stress development resulted in cracking and delamination of the film from the substrate, subsequently film constraint was reduced and densification was not impeded. © 2014 The Authors.
    Dorey RA, Yeomans JA, Smith PA, Pan J (2001) In situ optical dilatometric measurements of the initial stages of sintering of alumina, ACTA MATERIALIA 49 (3) pp. 519-527 PERGAMON-ELSEVIER SCIENCE LTD
    Duval FF, Dorey RA, Wright RW, Huang Z, Whatmore RW (2004) Fabrication and modeling of high-frequency PZT composite thick film membrane resonators., IEEE Trans Ultrason Ferroelectr Freq Control 51 (10) pp. 1255-1261
    High-frequency, thickness mode resonators were fabricated using a 7 microm piezoelectric transducer (PZT) thick film that was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Zirconium oxide (ZrO2) was selected as a diffusion barrier layer and gave good results when used in conjunction with silicon oxide (SiO2) as an etch stop layer. Using these conditions, devices were produced and the acoustic properties measured and modeled. The resonators showed a resonant frequency of about 200 MHz, an effective electromechanical coupling coefficient of 0.34, and a Q factor of 22. Modeling was based on a Mason-type model that gave good agreement between the experimental data and the simulations. The latter showed, for the PZT thick film, an electromechanical coupling coefficient of 0.35, a stiffness of 8.65 x 10(10) N x m(-2) and an e33,f piezoelectric coefficient of 9 C x m(-2).
    Ferroelectric materials have established themselves as indispensable in key applications such as piezoelectric transducers and energy storage devices. While the use of ferroelectrics in these fields dates back more than 50 years, little progress has been made to extend applications of ferroelectrics into new fields. To a large extend the observed slow progress is not caused by a lack of potential applications, but to by the inherent complexity associated with a structural phase transition, combined with strong coupling of polarisation, strain and temperature, and the strong modification of the phenomena by material defects.
    This thesis takes a look at prospective applications in energy storage for pulse power applications, solid state cooling and non-volatile random access memory and identifies key issues that need to be resolved. The thesis delivers time-domain based approaches to determine ferroelectric switching behaviour of bulk materials and thin films down to sub-ns time scales. The approach permitted study of how information written to a ferroelectric memory decays as a result of multiple non-destructive read operations. Furthermore simultaneous direct measurements of temperature and ferroelectric switching established a direct link between the retarded switching phenomenon observed in ferroelectrics and temperature changes brought by the electrocaloric effect. By comparison with analytical models and numerical simulation a large localised temperature change on the scale of individual domains is postulated. It implies a much larger coupling between switching and local temperature than has been previously considered. In extension of the model the frequency dependence of polarisation fatigue under bipolar conditions is explained by the occurrence of large temperature gradients in the material.
    Dharmasena Randunu Devage Ishara Gihan, Jayawardena Imalka, Mills Christopher, Deane Jonathan, Anguita Jose, Dorey Robert, Silva S (2017) Triboelectric Nanogenerators: Providing a Fundamental Framework,Energy & Environmental Science 10 (8) pp. 1801-1811 Royal Society of Chemistry
    A new model which comprehensively explains the working principles of contact-mode Triboelectric Nanogenerators (TENGs) based on Maxwell?s equations is presented. Unlike previous models which are restricted to known simple geometries and derived using the parallel plate capacitor model, this model is generic and can be modified to a wide range of geometries and surface topographies. We introduce the concept of a distance-dependent electric field, a factor not taken in to account in previous models, to calculate the current, voltage, charge, and power output under different experimental conditions. The versatality of the model is demonstrated for non-planar geometry consisting of a covex-conave surface. The theoretical results show excellent agreement with experimental TENGs. Our model provides a complete understanding of the working principles of TENGs, and accurately predicts the output trends, which enables the design of more efficient TENG structures.
    Buchacher Till, Rokosz M, Dorey Robert, Allam Jeremy, Gregory A (2017) Electrocaloric induced retarded ferroelectric switching,Applied Physics Letters 110 (2) AIP Publishing
    Ferroelectric switching in bulk materials, at modest electric fields, is a relatively fast process, occurring on time scales of microseconds and less. A secondary retarded switching phenomenon also occurs on time scales of seconds and has previously been attributed to defect induced elevated energy barriers between polarisation states. As ferroelectric switching is a thermally activated process the barrier heights are also affected by temperature which is not constant in ferroelectric materials due to the electrocaloric effect. Here an additional EC induced retardation mechanism is proposed whereby EC induced temperature changes repeatedly temporarily prevent further FE switching during cooling cycles.
    Leighton G, Jones P, Lonne Q, Dorey Robert, Giuliano F (2018) Innovative method to produce large-area freestanding functional ceramic foils,Journal of the European Ceramic Society 38 (10) pp. 3483-3488 Elsevier
    Using thick and thin films instead of bulk functional materials presents tremendous advantages in the field of flexible electronics and component miniaturization. Here, a low-cost method to grow and release large-area, microscale thickness, freestanding, functional, ceramic foils is reported. It uses evaporation of sodium chloride to silicon wafer substrates as sacrificial layers, upon which functional lead titanate zirconate ceramic films are grown at 710/°C maximum temperature to validate the method. The freestanding, functional foils are then released by dissolution of the sacrificial sodium chloride in water and have the potential to be integrated into low-thermal stability printed circuits and flexible substrates. The optimization of the sodium chloride layer surface quality and bonding strength with the underlying wafer is achieved thanks to pre-annealing treatment.
    Dharmasena R.D.I.G., Jayawardena K.D.G.I., Mills C.A., Dorey R.A., Silva Ravi (2018) A unified theoretical model for Triboelectric Nanogenerators,Nano Energy 48 pp. 391-400 Elsevier
    A unified theoretical model applicable to different types of Triboelectric Nanogenerators (TENGs) is presented based on Maxwell?s equations, which fully explains the working principles of a majority of TENG types. This new model utilizes the distance-dependent electric field (DDEF) concept to derive a universal theoretical platform for all vertical charge polarization TENG types which overcomes the inaccuracies of the classical theoretical models as well as the limitations of the existing electric field-based model. The theoretical results show excellent agreement with experimental TENGs for all working modes, providing an improved capability of predicting the influence of different device parameters on the output behaviour. Finally, the output performances of different TENG types are compared. This work, for the first time, presents a unified framework of analytical equations for different TENG working modes, leading to an in-depth understanding of their working principles, which in turn enables more precise design and construction of efficient energy harvesters.
    Fantanas Dimitrios, Brunton A, Henley Simon, Dorey Robert (2018) Investigation of the mechanism for current induced
    network failure for spray deposited silver nanowires
    Nanotechnology 29 (46) 465705 pp. 1-8 IOP Publishing
    Silver nanowires are one of the prominent candidates for the replacement of the
    incumbent indium tin oxide in thin and flexible electronics applications. Their main
    drawback is their inferior electrical robustness. Here, the mechanism of the short
    duration direct current induced failure in large networks is investigated by current
    stress tests and by examining the morphology of failures. It is found that the failures
    are due to the heating of the film and they initiate at the nanowire junctions,
    indicating that the main failure mechanism is based on the Joule heating of the
    junctions. This failure mechanism is different than what has been seen in literature
    for single nanowires and sparse networks. In addition, finite element heating
    simulations are performed to support the findings. Finally, we suggest ways of
    improving these films, in order to make them more suitable for device applications.
    Wang Dazhi, Shi Peng, Li Xuemu, Zhou Peng, Zhao Kuipeng, Wei Yunlong, Jiang Chongyang, Liang Junsheng, Dorey R.A. (2018) Fabrication and characterisation of substrate-free PZT thick films,Ceramics International 44 (12) pp. 14258-14263 Elsevier
    This paper reports the preparation of dense and substrate-free PZT thick films. Electrohydrodynamic jet deposition and sol infiltration were utilized to produce dense PZT thick film, then wet chemical etching was employed to successfully remove the silicon substrate. Subsequently, a pure PZT thick film having a thickness of 14/µm without substrate was produced. The piezoresponse force microscopy technique was used to examine the piezoelectric constant (d33, f), it was found that the d33 was increased from 71/pm/V?1 to 140/pm/V?1, having a double increase. It was also observed that the remnant polarization (Pr) and relative permittivity (µr) of PZT film were distinctly improved after the removal of silicon substrate. The experimental result shows that the substrate clamping had great effects on the electrical properties of PZT films and its effect value was evaluated. In addition, the systematic theoretical analysis of the substrate clamping on film was deeply studied. The theoretical analysis agrees well with the experiment results, which can be used to estimate the effect value caused by the substrate clamping.
    Jakubczyk E.M., Mapp A., Chung C.C., Sansom C.L., Jones J.L., Dorey R.A. (2019) Enhancing thermoelectric properties of NaCo2O4 ceramics through Na pre-treatment induced nano-decoration,Journal of Alloys and Compounds 788 pp. 91-101 Elsevier
    High quality NaCo2O4 thermoelectrics are challenging to process due to the volatile nature of Na, the slow densification kinetics, and degradation of NaCo2O4 above 900?950/°C leading to the formation of Na-poor second phases. Fine grained sol-gel derived powders have been used to enhance the densification kinetics while pre-treatment of the NaCo2O4 powder with NaOH, to provide a Na rich environment, has been shown to mitigate Na loss at elevated temperatures. While insufficient to compensate for Na loss at processing temperatures of 1000/°C and above, at lower temperatures it is able to enhance densification and facilitate the formation of complex crystal structures yielding low thermal conductivity (0.66 Wm?1K?1) coupled with high electrical conductivity (3.8/×/103 Sm?1) and a Seebeck coefficient of 34.9. The resultant room temperature power factor and ZT were 6.19/×/10?6 Wm?1K?2 and 0.0026, respectively.
    Dharmasena Randunu Devage Ishara Gihan (2019) Triboelectric self-powered energy systems.,
    Next generation electronics are shaping the life of people by digitally connecting humans and everyday objects using smart technologies. A major challenge related to such technologies is powering the electronic devices while maintaining autonomy and mobility. Triboelectric Nanogenerators (TENGs) provide innovative solutions for powering next generation low-power electronics, by converting movement into electricity. However, these devices are still in their infancy with numerous drawbacks including high device impedance, low output power density and efficiency, mainly due to the lack of understanding of their working principles and optimization techniques. This thesis investigates the fundamental working principles of TENGs and some of their applications as energy harvesting devices.
    The electric field behaviour of different TENG architectures is studied using Maxwell?s equations, leading to the derivation of the distance-dependent electric field (DDEF) model. This new model is capable of fully explaining the electric field behaviour and working principle of TENGs, overcoming the drawbacks of previous models. The DDEF model is developed initially for the vertical contact-separation mode TENG and expanded to represent all working modes which utilise contact-separation movement, via the development of unified DDEF model. The models are then used to simulate the output trends of different experimental TENG devices. An experimental setup is developed and TENG devices fabricated to assess the DDEF model predictions, which verifies the higher accuracy of the new model over previous capacitor-based circuit models.
    Using the unified DDEF model as a framework, the effect of different structural and motion parameters of TENGs on their power output is studied. A number of new analysis techniques are introduced, including the TENG power transfer equation and TENG impedance plots, to identify the output trends and optimisation routes to design TENG devices, resulting an increase of power and reduction of TENG internal impedance by more than an order of magnitude. Finally, application of theoretical knowledge gained from the DDEF model is demonstrated by constructing a direct current output TENG device. This new design produces a constant power output subjected to continuous input motion, showing the potential to be used in self-powered electronic applications.
    Turner Piers, Hodnett Mark, Dorey Robert, Carey J. David (2019) Controlled Sonication as a Route to in-situ Graphene Flake Size Control,Scientific Reports 9 8710 pp. 1-8 Nature Research
    Ultrasonication is widely used to exfoliate two dimensional (2D) van der Waals layered materials such as graphene. Its fundamental mechanism, inertial cavitation, is poorly understood and often ignored in ultrasonication strategies resulting in low exfoliation rates, low material yields and wide flake size distributions, making the graphene dispersions produced by ultrasonication less economically viable. Here we report that few-layer graphene yields of up to 18% in three hours can be achieved by optimising inertial cavitation dose during ultrasonication. We demonstrate that inertial cavitation preferentially exfoliates larger flakes and that the graphene exfoliation rate and flake dimensions are strongly correlated with, and therefore can be controlled by, inertial cavitation dose. Furthermore, inertial cavitation is shown to preferentially exfoliate larger graphene flakes which causes the exfoliation rate to decrease as a function of sonication time. This study demonstrates that measurement and control of inertial cavitation is critical in optimising the high yield sonication-assisted aqueous liquid phase exfoliation of size-selected nanomaterials. Future development of this method should lead to the development of high volume flow cell production of 2D van der Waals layered nanomaterials.

    Silver Nanowires (Ag NWs) are a heavily researched material, mostly as a replace-ment for the industry standard Indium Tin Oxide (ITO). Ag NWs are sought after be-cause they can be used on flexible substrates and be solution deposited. One main drawback of silver NWs is the film failure during either electrostatic discharge (ESD) tests or direct Joule heating, at currents significantly lower than ITO can handle. In this work the up scaling of the spray deposition of Ag NWs and the current induced failure that is observed during film use in electronic devices are investigated. Both of these areas are ones of the few stopping Ag NWs from being adopted by the industry. As part of this project, a holistic approach is taken, where a machine for the deposition was designed and tuned to improve the efficiency of the process, then using that tool process devel-opment was undertaken using various dispersions and finally the current induced failure of the deposited films was investigated. This way a complete understanding was achieved of the spray process and of silver nanowires as a material.

    Using a spray deposition tool, built and commissioned during the project, the indus-try requirements of less than 10% uniformity variation, optical transmission over 90% and haze bellow 1% were achieved for 150 mm width at 100 ©/sq. Furthermore, better understanding of the spray pattern and nozzle overlap was achieved using experimental and simulation data. Based on this tool and the knowledge acquired from its design, a series of customer machines were designed for various applications. The original tool was upgraded to an airbrush-based system, in order to facilitate for R&D work such as process development and sample preparation for small scale application tests. Various nanowire dispersions were tested from various suppliers using this upgraded tool with success. Using the fine-tuned process, films were deposited for solar cells, liquid crystal displays, light emitting diodes and heaters, with great preliminary results. Finally, the deposition of nanowires on 3D surfaces was achieved with great success.

    To understand the current induced failures, the failure mechanism and the maximum current density that the nanowires can withstand needs to be identified. To do that, small scale tests were undertaken and then the films were imaged using SEM and AFM. From these measurements it was found that the maximum current density (18-260 MA/cm2), at which the NW films fail, is much lower than what has been observed in lit-erature (18-260 MA/cm2). As part of this work it was found that for a 100 ©/sq film, the failure occurred at a current density of 7 MA/cm2. This is because of the Joule heating of the nanowires, which in the case of dense networks initiates in the junctions. This is be-cause the junction resistance dominates over the resistance of the individual wires, since it is an order of magnitude higher. It was found that denser nanowire networks (lower sheet resistance), fail at lower current densities. This is because the number and the prox-imity of the junctions increase, resulting in quicker heating and failure. Furthermore, when network is consisted of multiple layers of nanowires, the heat dissipates at a slow-er rate, since the top nanowires have just air for the heat to be transferred to, in contrast with the bottom layer wires, which dissipate heat through direct contact with the glass substrates (better heat conductor than air). The failure is always in a line, perpendicular to the current flow. This is happening because the film failure originates from a weak spot of the sample. This weak spot is on an axis perpendicular to the current flow where there is a less dense patch of the film. When one junction fails, more current has to pass through a smaller number of nanowires, resulting in a chain reaction. Various treatments and NW hybrid materials are proposed in order to decrease the succeptability to the cur-rent ind

    As there are many different graphene production methods which vary in terms of quality, cost, production rate, yield, scalability, post-processing requirements, flake size distribution, and batch-to-batch repeatability, it has been challenging to develop commercial applications that exploit the extraordinary properties of graphene rather than purely using it as a marketing tool. This thesis reports on the study of ultrasonication, which is an established method to exfoliate graphene in the liquid phase, as well as a pre/post-processing technique in other graphene production methods. Due to a poor understanding of inertial cavitation, which is the fundamental mechanism driving graphene exfoliation during ultrasonication, this production method is commonly characterised by low exfoliation rates, reduced yields and limited scalability/controllability. By optimising the inertial cavitation dose, graphene yields of up to 19 ± 4 % can be exfoliated over just 3 hours of sonication at room temperature. Furthermore, inertial cavitation preferentially exfoliates larger flakes during ultrasonication and the size of the graphene flakes is correlated with, and therefore can be controlled by, inertial cavitation dose. Alongside small-scale exfoliation studies, a scalable graphene sonoreactor proof-of-concept (patent pending), has been designed and tested to generate high exfoliation rates and allow for in-situ size distribution control. More generally it is shown cavitation metrology is critical in developing efficient, controllable and repeatable ultrasonication strategies for the liquid phase exfoliation of 2D nanomaterials, and the many applications and industries in which ultrasonication is employed.
    Dharmasena R. D. I. G., Cronin H.M, Dorey R., Silva S. R. P. (2020) Direct Current Contact-Mode Triboelectric Nanogenerators via Systematic Phase Shifting,Nano Energy Elsevier
    The intermittency and discontinuous nature of power generation in Triboelectric Nanogenerators (TENGs) are arguably their most significant drawback, despite the promise demonstrated in low-power electronics. Herein, we introduce a novel technology to overcome this issue, in which, built-in systematic phase shifting of multiple poles is used to design a pseudo direct-current TENG. Unlike previous attempts of constructing near direct-current TENGs that base on the segmentation of electrodes of a sliding mode TENG, this technology introduces a new method that depends on planned excitation of constituent TENG units at different time intervals to obtain the necessary phase shifts, achieved by their structural design that contains an asymmetric spatial arrangement. Therefore, the direct current generation for TENG, which was previously limited to the sliding mode TENG units, are expanded to contact-mode TENGs. The technology allows for continuous and smooth operation of the driven loads and paves the way for a new dawn in energy scavenging from mechanical sources. We use the distance-dependent electric field (DDEF) platform to design the systematic phase shifting technology, which is experimentally demonstrated via a free-standing mode TENG (FSTENG) based design, to power a number of prototype devices. The resultant power output of the TENG indicates a crest factor close to 1.1 at relatively low frequencies, the best reported values for TENGs with contact-mode basic units, to date. This work provides a highly awaited solution to overcome the intermittency and sporadic nature of TENG outputs, thus, promoting the field towards powering next generation autonomous and mobile electronics.