12CaO.7Al2O3 ceramic: A review of the electronic and optoelectronic applications in display devices

The alumina-based compound, 12CaO.7Al2O3, is a ceramic material with a unique cage-like lattice. Such a structure has enabled scientists to extract various new characteristics from this compound, most of which were unknown until quite recently. This compound has the ability to incorporate different anionic species and even electrons to the empty space inside its cages, thereby changing from an insulator into a conductive oxide. The cage walls can also incorporate different rare earth phosphor elements producing an oxide-based phosphor. All these characteristics are obtained without a significant change in the structure of the lattice. It is, therefore, reasonable to expect that this compound will receive attention as a potential material for display applications. This review article presents recent investigations into the application of 12CaO.7Al2O3 ceramic in various display devices, the challenges, opportunities and possible areas of future investigation into the development of this naturally abundant and environmental friendly material in the field of display.LP Displays Ltd, Blackburn, UK for partial funding of the studentship at Queen Mary, University of London. Dr Lesley Hanna of Wolfson Centre for Materials Processing, Brunel University Londo

Vibrational spectroscopic studies on crystallisation of sol-gel derived thin films of calcia-alumina binary compound

An optimized sol-gel process has been developed to produce homogeneous thin films of calcium aluminate binary (12CaO·7Al2O3) compound, on magnesium oxide substrates via spin coating. Fourier transform infrared and Raman spectroscopies have been employed to investigate the effect of annealing temperature and duration on the phase transformations in the films. Heat treatment at 1,300 °C under air atmosphere for 2 h produced single-phase 12CaO·7Al2O3 films. However, annealing at a lower temperature of 1,100 °C in air for a period of 4 h in total resulted in the crystallization of 5CaO·3Al2O3 rather than 12CaO·7Al2O3. The X-ray photoelectron spectrum of the thin film annealed at 1,300 °C corresponds to the binding energies of C12A7 compound. The annealing temperature of 1,300 °C for 2 h is found to be sufficient for formulating single phase calcia-alumina binary films in correct stoichiometric ratio of 12:7. © 2014 Springer Science+Business Media New York

Kinetic study of crystallisation of sol-gel derived calcia-alumina binary compounds

In-situ High Temperature X-ray Diffraction (HTXRD) and Differential Scanning Calorimetric (DSC) studies were performed on a sol-gel derived binary compound of a calcia-alumina (C12A7) system consisting of calcium oxide (CaO) and aluminium oxide (Al2O3) in a ratio of 12:7 for in situ investigation into the phase transformations under progressively increasing thermal activation from roomerature to 1200 °C. The crystallisation of amorphous samples formulated at roomerature on magnesium oxide (MgO) single crystal (100) substrates was found to be complete on heat treatment at 1100 °C for 3 h. This observation was further supported by independent Fourier Transform Infrared (FTIR) and Raman Spectroscopies. Values of 348 kJ/mol and 375 kJ/mol were estimated from Kissinger plots for activation energies of crystallisation of CaO and Al2O3 constituents, respectively

In situ chemichromic studies of interactions between a lutetium bis-octaalkyl-substituted phthalocyanine and selected biological cofactors

This article is available open access through the publisher’s website at the link below. Copyright @ 2011 The Royal Society.Spin-coated films, approximately 100 nm thick, of a newly synthesized bis[octakis(octyl)phthalocyaninato] lutetium(III) complex on ultrasonically cleaned glass substrates exhibit pronounced chemichromic behaviour with potential application in healthcare. In situ kinetic optical absorption spectroscopic measurements show that the phthalocyanine Q-band is red shifted by 60 nm upon oxidation arising from exposure to bromine vapour. Recovery to the original state is achieved by the treatment of the oxidized films with nicotinamide adenine dinucleotide and l-ascorbic acid (vitamin C) in an aqueous solution containing 1.5 M lithium perchlorate. The neutralization process is found to be governed by first-order kinetics. The linear increase of the reduction rate with increasing concentration of cofactors provides a basis for calibration of analyte concentrations ranging from 3.5 mM down to 0.03 mM.Air Force Office of Scientific Research, Air Force Material Command, USAF and the Leverhulme Trust

AC impedance studies on metal/nanoporous silicon/p-silicon structures

Alternating current (AC) impedance measurements have been performed on 10−15 thick porous silicon layers on a (100) p-type silicon (p(+)Si) substrate with the aluminium (Al) top electrode in a sandwich configuration in the range of 20 Hz to 1 Hz and in the temperature ranging between 152 K−292 K. The ac conductivity sac was found to increase with frequency f according to the universal power low: sAf=acs where the exponent s is a frequency and temperature dependent quantity. Hopping process is found to be dominant at low temperatures and high frequencies while a thermally activated free band process is responsible for conduction at higher temperatures. Capacitance is found to decrease with frequency but increase with temperature. Frequency dependence of loss tangent is observed with a temperature dependent minimum value

A tetrabenzotriazaporphyrin based organic thin film transistor: Comparison with a device of the phthalocyanine analogue

The characteristics of bottom-gate bottom-contact organic thin film field-effect transistors (OTFTs) with 70 nm thick films of solution processed non-peripherally octahexyl-substituted nickel tetrabenzo triazaporphyrin (6NiTBTAP) molecules as active layers on silicon substrates are experimentally studied and the results are compared with the similary configured transistors using the corresponding nickel phthalocyanine (6NiPc) compound. 6NiTBTAP transistors are found to exhibit improved performance over 6NiPc transistors in terms of greater saturation hole mobility, two orders of magnitude higher on/off ratio and lower threshold voltage. This enhanced performance of 6NiTBTAP OTFTs over 6NiPc devices is attributed to improved surface morphology and large grain size of the active 6NiTBTAP film

Printed graphene films with positive temperature coefficient of resistivity

0.5μm thick graphene films printed on plastic substrates exhibit metallic type conduction with a positive value of 1.5×〖10〗^(-3) K^(-1) for the temperature coefficient of resistance over the temperature range from 260K to 330K . The crystallites of approximately 6.5 nm in their average size in the film are found from the X-Ray diffraction pattern to be oriented preferentially along [002] plane.Dr. Indrani Banerjee is grateful to Commonwealth Association, UK for funding the present research work under the fellowship placement scheme (grant reference INCF-2014-66). The studentship of Ms Faris is partially sponsored by the Air Force Office of Scientific Research, Air Force Material Command, USAF, under Grant No. FA8655-08-1-3056

High-mobility solution-processed copper phthalocyanine-based organic field-effect transistors

© 2011 National Institute for Materials ScienceSolution-processed films of 1,4,8,11,15,18,22,25-octakis(hexyl) copper phthalocyanine (CuPc6) were utilized as an active semiconducting layer in the fabrication of organic field-effect transistors (OFETs) in the bottom-gate configurations using chemical vapour deposited silicon dioxide (SiO2) as gate dielectrics. The surface treatment of the gate dielectric with a self-assembled monolayer of octadecyltrichlorosilane (OTS) resulted in values of 4×10−2 cm2 V−1 s−1 and 106 for saturation mobility and on/off current ratio, respectively. This improvement was accompanied by a shift in the threshold voltage from 3V for untreated devices to −2V for OTS treated devices. The trap density at the interface between the gate dielectric and semiconductor decreased by about one order of magnitude after the surface treatment. The transistors with the OTS treated gate dielectrics were more stable over a 30-day period in air than untreated ones.Technology Strategy Board, UK (Project No: TP/6/EPH/6/S/K2536J)

Graphene films printable on flexible substrates for sensor applications

Fifteen-layered graphene films have been successfully deposited onto flexible substrates using a commercial ink consisting of graphene particles dispersed in an acrylic polymer binder. A value of 74.9 × 105cm−2 was obtained for the density of defects, primarily located at the flake edges, from the ratio of the D and G Raman peaks located at 1345cm1 and 1575cm1 respectively. 0.5μm thick drop-cast films on interdigitated silver electrodes exhibited Ohmic conduction with a small activation energy of 12meV over the temperature range from 260K to 330K . The photo-thermoelectric effect is believed to be responsible for photoconduction through graphene films under illumination intensity of 10mWm-2 at 270 nm, corresponding to the UV absorption peak. The photo-transient decay at the bias of 1V involves two relaxation processes when the illumination is switched off and values of 8.9 × 103 and 4.3 × 104 are found for the relaxation time constant using the Kohlrauch stretched exponential function analysis.Dr. Indrani Banerjee is grateful to Commonwealth Association, UK for funding the present research work under the fellowship placement scheme (Grant reference INCF-2014-66). The studentship of Ms Faris is partially sponsored by the Air Force Office of Scientific Research, Air Force Material Command, USAF, under Grant No. FA9550-15-1-0123. We are also thankful to Miss V. M. Torrejon of Brunel University for support in computer graphics

Effect of Progressive Muscle Relaxation in Female Health Care Professionals

Background: Increasing population, fast paced industrialization, increased, competitiveness, unanticipated problems in the work place have increased the stress among the females working in health care in recent times.Aim: The aim of the following study is to detect the stress levels among female health care professionals in the age group of 25-35 years and its impact on health. Subjects and Methods: A prospective cross-sectional pilot project was conducted in a tertiary care hospital in Eastern part of India, after receiving approval from the Institutional Ethics Committee and informed consent form was taken from the subjects. Stress level in the subjects was  assessed according to the presumptive life event stress scale. Females withscores above 200 were selected. For these, initial assessment of  anthropometric measurement, electrocardiogram and lipid profile analysis, resting pulse rate, blood pressure, physical fitness index (PFI), breath holding time (BHT), isometric hand grip (IHG) test results were evaluatedand recorded. All subjects were given training of progressive muscle  relaxation (PMR) for 3 months. After 3 months, the lipid profile and vital parameters, Perceived Stress Scale values were re-evaluated and subjects were asked to repeat the same exercises and data thus recorded were analyzed using Statistical Package for the Social Sciences (SPSS) version 16 (SPSS Inc. Released 2007. SPSS for Windows, Version 16.0. Chicago, SPSS Inc.).Results: Significant decrease in resting heart rate, blood pressure and Perceived Stress Scale levels was seen after PMR training in the subjects. Results of BHT, IHG tests and PFI were significantly increased after PMR training. There was a significant decrease in total cholesterol, triglyceride and low-density lipoprotein cholesterol in subjects after practicing PMR for 3 months. Conclusions: Increasing stress among female health care professionals is a cause for concern and there is a need to adopt early life-style  modification by practicing relaxation exercises to ameliorate stress and to improve not only their quality-of-life in general, but patient care in  particular.Keywords: Female stress, relaxation techniques, health care professional