Browsing by Author "Salaoru, Iulia"
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Item Open Access 3-D Printing of Flexible Two Terminal Electronic Memory Devices(Materials Research Society, 2018-01-10) Salaoru, Iulia; Paul, Shashi; Maswoud , S.Recent strategy in the electronics sector is to ascertain the ways to make cheap, flexible and environmentally friendly electronic devices. The 3D inkjet printing technology is based on the Additive Manufacturing concept and it is with no doubt capable of revolutionising the whole system of manufacturing electronic devices including: material selection; design and fabrication steps and device configuration and architecture. Thus, 3D inkjet printing technology (IJP) is not only one of the most promising technologies to reduce the harmful radiation/ heat generation but also achieve reductions in manufacturing cost. Here, we explore the potential of 3D – inkjet printing technology to provide an innovative approach for electronic devices in especially information storage elements by seeking to manufacture and characterise state-of-art fully inkjet printed two terminal electronic memory devices. In this work, ink-jettable materials (Ag and PEDOT:PSS) were printed by a piezoelectric Epson Stylus P50 inkjet printing machine on a flexible substrate. All components of the memory cells of a simple metal/active layer/metal structure were deposited via inkjet printing. The quality of the printed layers was first assessed by Nikon LABOPHOT-2 optical microscope, fitted with Nikon Camera DS-Fi1. Furthermore, an in-depth electrical characterisation of the fabricated memory cells was carried out using HP4140B picoammeter.Item Metadata only 3D Printing of Flexible Two Terminal Electronic Memory Devices(2017-12) Salaoru, Iulia; Maswoud, Salah; Paul, Shashi; Manjunatha, Krishna NamaRecent strategy in the electronics sector is to ascertain the ways to make cheap, flexible and environmentally friendly electronic devices. The 3D Inkjet printing technology is based on the Additive Manufacturing concept [1] and it is with no doubt capable of revolutionizing the whole system of manufacturing electronic devices including: material selection; design and fabrication steps and device configuration and architecture. 3D Inkjet printing technology (IJP) is one of the most promising technologies to reduce the harmful radiation/ heat generation and also achieve reduction in manufacturing cost. Here, we explore the potential of 3D – inkjet printing technology to provide an innovative approach for electronic devices in especially information storage elements by seeking to manufacture and characterize state-of-art fully inkjet printed two terminal electronic memory devices. In this work, an ink-jettable material was formulated, characterized and printed by a a piezoelectric Epson Sylus P50 Inkjet printing machine on a flexible substrate. The active printed layers were deposited into a functioning simple metal/insulator/metal structure. Firstly, from ink perspective, the main physical properties such as rheological behaviour; surface tension and wettability were investigated. Furthermore, an in-depth electrical characterization of the fabricated memory cells was carried out using HP4140B picoammeter and an HP4192A impedance analyser. [1] N.Hopkinson, R.Hague, P.Dickens, Rapid manufacturing; an industrial revolution for the digital age. West Sussex, UK, John Wiley and Sons; 2006 [2] Iulia Salaoru, Zuoxin Zhou, Peter Morris, Gregory Gibbons, Inkjet printing of polyvinyl alcohol multilayers for addiive manufacturing applications, J.Appl.Polym.Sci., 133(25), 43572 (2016) [3] Ruth Cherrington, B.M.Wood, Iulia Salaoru, Vannessa Goodship, Digital printing of titanium dioxide for dye sensitized solar cells, JoVE, e53963, (2016) [4] Iulia Salaoru, Zuoxin Zhou, Peter Morris, Gregory J. Gibbons, Inkjet-printed Polyvinyl Alcohol Multilayers, JoVE,123, e55093-e55093, (2017).Item Open Access Additive manufacturing of heat-sensitive polymer melt using a pallet-fed material extrusion(Elsevier, 2018-10-28) Zhou, Zuoxin; Salaoru, Iulia; Morris, Peter; Gibbons, GregoryItem Metadata only Bistability in electrically writable non-volatile polymer memory devices.(Mater. Res. Soc. Symp. Proc, 2009) Salaoru, Iulia; Paul, ShashiIn recent years, interest in applications of organic materials in electronic devices (light emitting diodes, field effect transistors, solar cells), has increased rapidly. The advantages of organic materials are the ease of processing, lower production costs and structural flexibility allowing achievement of the desired electrical and mechanical characteristics. Very recently, there have been demonstrations of blends of polymer and metal nanoparticles and/or small organic molecules in memory devices; such memory devices are called polymer memory devices (PMDs). These devices show two electrical conductance states (“high” and “low”) when voltage is applied, thus rendering the structures suitable for data retention. These two states can be viewed as the realisation of non-volatile electrical memory. There is always growing need to look for inexpensive, fast, high-density memory devices with longer retention times and PMDs do possess some of these aforesaid criteria. Albeit, there is a rapid development in this area, the memory mechanism is still unclear. This work attempts to analyse the memory effect in PMDs and proposes a theory based on experimental data. The thin film polymer blends (polyvinyl acetate, polyvinyl alcohol and polystyrene) and small organic molecules were deposited by spin coating onto a glass substrate marked with thin metal tracks. A top contact was evaporated onto the blend after drying - this resulted in a metal-organic-metal (MOM) structure. MOM devices with different metal electrodes (a series of metals with different work functions Al, In,Cu,Cr, Ag and Au) were used to understand the exact electrical transport mechanism through the blend and the individual polymers. An in-depth electrical analysis of these MOM devices was carried out using an HP4140B picoammeter (current-voltage) and an LCR HP4192 bridge. FTIR and UV-VIS spectroscopy were also conducted in order to understand blend properties and the effect of the same, if any, on the electrical charging mechanism in the PMDs.Item Open Access Coexistence of memory resistance and memory capacitance in TiO2 solid state devices(Springer, 2014-09-23) Salaoru, Iulia; Li, Qingjiang; Khiat, Ali; Prodromakis, ThemistoklisThis work exploits the coexistence of both resistance and capacitance memory effects in TiO2-based two-terminal cells. Our Pt/TiO2/TiOx/Pt devices exhibit an interesting combination of hysteresis and non-zero crossing in their current-voltage (I-V) characteristic that indicates the presence of capacitive states. Our experimental results demonstrate that both resistance and capacitance states can be simultaneously set via either voltage cycling and/or voltage pulses. We argue that these state modulations occur due to bias-induced reduction of the TiOx active layer via the displacement of ionic species.Item Open Access Comparative Study of Silicon Nanowires Grown From Ga, In, Sn, and Bi for Energy Harvesting(IEEE, 2020-08-14) Manjunatha, Krishna Nama; Salaoru, Iulia; Milne, W.I; Paul, ShashiA high density of silicon nanowires for solar cell applications was fabricated on a single crystalline silicon wafer, using low eutectic temperature metal catalysts, namely, gallium, indium, tin, and bismuth. The use of silicon nanowires is exploited for light trapping with an aim to enhance the efficiency of solar cells. Additionally, we have optimized the deposition parameters so that there is merely deposition of amorphous silicon along with the growth of silicon nanowires. Thus, it may improve the stability of silicon-based solar cells. The different catalysts used are extensively discussed with experimental results indicating stable growth and highly efficient silicon nanowires for photovoltaic applications. To test the stability, we measured the open-circuit voltage for four hours and the change in voltage was ±0.05 V. The fabrication of all-crystalline silicon solar cells was demonstrated using the conventional mature industrial manufacturing process that is presently used for the amorphous silicon solar cells. To summarize, this research compares various post-transition metals as a catalyst for the growth of nanowires discussing their properties, and such silicon nanowires can be utilized in several other applications not only limited to photovoltaic research.Item Open Access Correlated Resistive/Capacitive State Variability in Solid TiO2 based Memory Devices(Springer, 2017-04-25) Li., Qingjiang; Salaoru, Iulia; Ali, Khiat; Prodromakis, Themistoklis; Hui, XuIn this work, we experimentally demonstrated the correlated resistive/capacitive switching and state variability in practical TiO2 based memory devices. Based on filamentary functional mechanism, we argue that the impedance state variability stems from the randomly distributed defects inside the oxide bulk. Finally, our assumption was verified via a current percolation circuit model, by taking into account of random defects distribution and coexistence of memristor and memcapacitor.Item Open Access Creating Electrical Bistability Using Nano-bits – Application in 2-Terminal Memory Devices(Cambridge University Press, 2017-01-12) Salaoru, Iulia; Alotaibi, Sattam; Al Halafi, Zahara; Paul, ShashiIntensive research is currently underway to exploit the highly interesting properties of nano-bits (“nano-sized particles and molecules”) for optical, electronic and other applications. The basis of these unique properties is the small-size of these structures which result in quantum mechanical phenomena and interesting surface properties. The small molecules and/or nano-particles are selected in such a way so that it can create an internal electric in the nano-composite. We define a nanocomposite is an admixture of small molecules and/or nano-particles and a polymer. We have demonstrated the internal electric field in our devices, made from nano-bits (nano-particles and/or molecules) and insulating materials, can contribute to the electrical bistability i.e. two conductive states.Item Embargo Development of a direct feed fused deposition modelling technology for multi-material manufacturing(AIP publishing (American Institute of Physics), 2016) Zhou, Zuoxin; Salaoru, Iulia; Morris, Peter; Gibbons, GregoryFused Deposition Modelling (FDM) is one of the most widely used Additive Manufacturing (AM) technologies to fabricate a three-dimensional (3D) object via melt processing of a thermoplastic filament. However, it is limited in the variety of materials that can be fed and mixed during the process. In this study, a concept of direct feed FDM technology was presented, which allowed co-feeding of multiple materials in any available form. Different materials were mixed at predetermined ratios and deposited together to form a 3D object with variable properties and functionalities that meet specific requirements. To demonstrate the capability of this AM system, heat-sensitive polyvinyl alcohol (PVOH) and its additives were processed. A geometry with various features was successfully manufactured with dimensions closely matching those of the design specification. The FDM processed PVOH showed insignificant thermal decomposition as it retained its original colour, flexibility, and water solubility. During the process, a fluorescent whitening agent was successfully incorporated into the polymer melt. Therefore, the printed sample exhibited a strong fluorescence effect from the UV-visible and fluorimeter results.Item Metadata only Digital printing of functional materials: a step forward to green electronics - invited talk(2019-08) Salaoru, IuliaHow can we fabricate more ecological friendly functional materials and electronic devices? Nowadays, the environmental issues of electronics from both the perspectives of used materials and manufacturing process is a major concern. The usage, storage, disposal protocol and the volume of waste material continues to increase the environmental footprint of our increasingly “throw away society”. Almost ironically, that society is increasingly involved in pollution prevention, resources consumption issues and post-consumer waste management. Clearly, there exists a dichotomy between environmentally aware usage and consumerism. The current technology to manufacture functional materials and electronic devices requires heat generation in a deposition process and hence generation of harmful chemicals/radiation. Additionally, there are environmental limitations, for example, high vacuum equipment requires enormous amounts of electricity to run, thus creating a larger carbon footprint. With this background, it is imperative to explore new electronic functional materials but as well as new manufacturing pathways. This talk will encompass the potential of inkjet printing technology as an innovative manufacturing pathway for functional materials, and electronic devices as an reliable alternative to traditional manufacturing protocols.Item Open Access Digital Printing of Titanium Dioxide for Dye Sensitized Solar Cells(Journal of Visualized Experiments, 2016-04-05) Salaoru, Iulia; Cherrington, Ruth; Wood, B. M.; Goddship, VannessaSilicon solar cell manufacturing is an expensive and high energy consuming process. In contrast, dye sensitized solar cell production is less environmentally damaging with lower processing temperatures presenting a viable and low cost alternative to conventional production. This paper further enhances these environmental credentials by evaluating the digital printing and therefore additive production route for these cells. This is achieved here by investigating the formation and performance of a metal oxide photoelectrode using nanoparticle sized titanium dioxide. An ink-jettable material was formulated, characterized and printed with a piezoelectric inkjet head to produce a 2.6 μm thick layer. The resultant printed layer was fabricated into a functioning cell with an active area of 0.25 cm2 and a power conversion efficiency of 3.5%. The binder-free formulation resulted in a reduced processing temperature of 250 °C, compatible with flexible polyamide substrates which are stable up to temperatures of 350 ˚C. The authors are continuing to develop this process route by investigating inkjet printing of other layers within dye sensitized solar cells.Item Metadata only Electrical bistability in a composite of polymer and barium titanate nanoparticles.(Royal Society, 2009) Salaoru, Iulia; Paul, ShashiGrowth in the use of organic materials in the fabrication of electronic devices is on the rise. Recently, some attempts have been undertaken to manufacture polymer memory devices. Such devices are fabricated by depositing a blend (an admixture of organic polymer, small organic molecules and nanoparticles) between two metal electrodes. These devices show two electrical conductivity states (“high” and “low”) when a voltage is applied, thus rendering the structures suitable for data retention. In this paper, we describe an attempt to fabricate memory devices using ferroelectric nanoparticles embedded in an organic polymer. This paper also discusses issues related to the observed memory effectItem Metadata only Electrical Conductivity Bistability in Nano-Composite(The society for solid-state and electrochemical science and technology, 2013-05-12) Prime, Dominic Charles; Salaoru, Iulia; Paul, Shashi; Al Halafi, Zahara; Green, MarkNano-composite polymer memory devices are fabricated by depositing a blend (an admixture of organic polymer, small organic molecules and nanoparticles) between two metal electrodes. These devices show two electrical conductance states (“1” and “0”) when voltage is applied, thus rendering the structures suitable for data retention. These two states can be viewed as the realisation of non-volatile memory. Nano-composite polymer memory devices comprising of a blend of a polymer and small molecules and/or nanoparticles are investigated. This study is aimed at further understanding the electrical bistability observed in such devices. This work also investigates if an electrical charge can be transferred to gold nano-particles and, between small molecule complexes.Item Open Access Electrical Re-Writable Non-Volatile Memory Device based on PEDOT:PSS Thin Film(MDPI, 2020-02-10) Salaoru, Iulia; Pantelidis, Christos ChristodoulosIn this research, we investigate the memory behavior of poly(3,4 ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) cross bar structure memory cells. We demonstrate that Al/PEDOT:PSS/Al cells fabricated elements exhibit a bipolar switching and reproducible behavior via current–voltage, endurance, and retention time tests. We ascribe the physical origin of the bipolar switching to the change of the electrical conductivity of PEDOT:PSS due to electrical field induced dipolar reorientation.Item Metadata only Electrically re-writable non-volatile memory device - using a blend of sea salt and polymer.(2008) Salaoru, Iulia; Paul, ShashiIntensive research is currently underway to exploit the highly interesting properties of nano-sized particles and organic molecules for optical, electronic and other applications. Recently, it has been shown that nano-sized particles and small organic molecules embedded in polymer matrices can be used to realise memory devices. Such memory devices are simple to fabricate via the spin-on technique. This work presents an attempt to use sea salt, embedded in polyvinyl acetate, in the making of the memory devices. A polymer blend of polyvinyl acetate and sodium chloride (NaCl) was prepared in methanol and spin coated onto a glass substrate marked with thin Al tracks and a top contact was evaporated onto the blend after drying - this resulted in a metal-organic-metal (MOM) structure. The current-voltage (I-V) behaviour of MOM devices shows that the devices can be switched from a high conductivity state to a low conductivity state, by applying an external electric field - this property can be exploited to store data bits. The possible charging mechanism, based on the electric dipole formation, is presented in this work. Polymer blends of polyvinyl acetate with nano-particles of BaTiO3 are also investigated to further our understanding of charging mechanism(s).Item Metadata only Electronic polymer memory devices—Easy to fabricate, difficult to understand.(Elsevier, 2010) Paul, Shashi; Salaoru, IuliaItem Open Access Emulating long-term synaptic dynamics with memristive devices(arXiv, 2016-04-22) Wei, Shari Lim; Vasilaki, Eleni; Khiat, Ali; Salaoru, Iulia; Berdan, Radu; Prodromakis, ThemistoklisThe potential of memristive devices is often seeing in implementing neuromorphic architectures for achieving brain-like computation. However, the designing procedures do not allow for extended manipulation of the material, unlike CMOS technology, the properties of the memristive material should be harnessed in the context of such computation, under the view that biological synapses are memristors. Here we demonstrate that single solid-state TiO2 memristors can exhibit associative plasticity phenomena observed in biological cortical synapses, and are captured by a phenomenological plasticity model called “triplet rule”. This rule comprises of a spike-timing dependent plasticity regime and a “classical” hebbian associative regime, and is compatible with a large amount of electrophysiology data. Via a set of experiments with our artificial, memristive, synapses we show that, contrary to conventional uses of solid-state memory, the co-existence of field- and thermally-driven switching mechanisms that could render bipolar and/or unipolar programming modes is a salient feature for capturing long-term potentiation and depression synaptic dynamics. We further demonstrate that the non-linear accumulating nature of memristors promotes long-term potentiating or depressing memory transitions.Item Embargo The evanescent waves in metallic strip gratings and complex structures in subwavelength regime(Elsevier, 2015-09-19) Iftimie, Nicoleta; Tascu, Sorin; Salaoru, Iulia; Steigmann, Rozina; Savin, Adriana; Irimia, Mihaela; Iacomi, F.The paper investigates the formation of evanescent waves in metallic strip gratings on the Ag/ZnO/SiO2/Si structure with silver strips when TEz incident wave in the radiofrequency range was used. The Ag/ZnO/SiO2/Si structure was fabricated by vacuum thermal evaporation technique and Scanning Electron Microscopy was used to evidence its high quality structure with parallel silver strips of same width and thickness. Simulation of the evanescent wave formation at the edge of Ag strips, with thicknesses in the range of micrometers, was performed, before performing the test in the subwavelength regime by the mean of a new transducer improved with metamaterials lens. The generation in slits, in air, of the electric evanescent mode, when metallic strip grating was excited with a TEz polarized wave at a frequency of 474 MHz, was successfully demonstrated.Item Metadata only Fabrication of photovoltaic devices using novel organic polymer/nanostructure blends.(Cambridge University Press, 2011) Black, Dave; Salaoru, Iulia; Paul, ShashiItem Metadata only Ferro-electric nanoparticles in polyvinyl acetate (PVAc) matrix – A method to enhance the dielectric constrant of polymers.(American Scientific Publishers, 2010) Black, Dave; Paul, Shashi; Salaoru, IuliaIn order to take advantage of the possibilities for constructing electronic devices, offered by organic materials, it is essential to be able to control their electrical characteristics. By incorporating tetragonal barium titanate nanoparticles with a phosphonic acid ligand into a matrix of poly-vinyl acetate it has been shown that it is possible to increase the relative permittivity of the polymer. The upper limit of this effect has not yet been found, although carrying out the same work using barium titanate filler without the ligands exhibits behaviour consistent with conduction effects that occur at the percolation limit of the polymer. The devices produced using the ligand exhibit even distribution of nanoparticles within the polymer matrix and good and reproducible electrical characteristics.