131 research outputs found
A new reactive sputtering technique for the low temperature deposition of transparent light emitting ZnS:Mn thin films
No full textThe temperature sensitive nature of the substrates used in the flexible displays market necessitates a low temperature deposition technique for processing them. ZnS:Mn exhibiting high intensity photoluminescence and good crystallinity has been deposited onto Si wafers, glass microscope slides and polymeric substrates using a new reactive sputtering technology referred to as HiTUS. This technique enables very high deposition rates and requires no substrate heating. When incorporated as part of a complete EL device, as-deposited ZnS:Mn films are seen to exhibit stable electroluminescence on Si, glass and planarised PET substrate materials. Post annealing of the devices on Si and glass at temperatures of up to 600 °C show that the HiTUS films perform better than equivalent ZnS:Mn films deposited using RF magnetron sputtering
Enhanced electrical and optical properties of room temperature deposited Aluminium doped Zinc Oxide (AZO) thin films by excimer laser annealing
No full textHigh quality transparent conductive oxides (TCOs) often require a high thermal budget fabrication process. In this study, Excimer Laser Annealing (ELA) at a wavelength of 248 nm has been explored as a processing mechanism to facilitate low thermal budget fabrication of high quality aluminium doped zinc oxide (AZO) thin films. 180 nm thick AZO films were prepared by radio frequency magnetron sputtering at room temperature on fused silica substrates. The effects of the applied RF power and the sputtering pressure on the outcome of ELA at different laser energy densities and number of pulses have been investigated. AZO films deposited with no intentional heating at 180 W, and at 2 mTorr of 0.2% oxygen in argon were selected as the optimum as-deposited films in this work, with a resistivity of 1×10−3 Ω.cm, and an average visible transmission of 85%. ELA was found to result in noticeably reduced resistivity of 5×10−4 Ω.cm, and enhancing the average visible transmission to 90% when AZO is processed with 5 pulses at 125 mJ/cm2. Therefore, the combination of RF magnetron sputtering and ELA, both low thermal budget and scalable techniques, can provide a viable fabrication route of high quality AZO films for use as transparent electrodes
Lattice misfit versus performance of thin film electroluminescent structures
No full textThin polycrystalline electroluminescent thin films (TFEL) of ZnS:Mn (phosphor) and Y2O3 (insulator) were deposited individually or as multilayers onto Si (100) substrates. Their crystallinity and the luminescent efficiency of the phosphor films were investigated at varying thermal annealing temperatures. It is shown that the luminescent quality of the phosphor layer increases up to 700 °C, whereas the electroluminescence operating intensity of TFEL devices saturates at 500 °C. The structural analysis of the insulating and phosphor layers shows that they recrystallize at annealing temperatures of, respectively, 500 and 600 °C, and that their lattice misfit doubles at processing temperatures >=500 °C. Since TFEL devices should benefit from enhanced luminescence efficiency and crystallinity at high annealing temperatures, we suggest that the lack of improvement in device performance beyond 500 °C is due to interface alterations. According to previous works, we propose that the lattice misfit increase between the phosphor and dielectric thin films modifies the morphology of the phosphor–insulator boundary inducing a modification of the interface states density, and hence, modifying high field electron transport properties of TFEL devices
Electrical and structural characteristics of yttrium oxide films deposited by rf-magnetron sputtering on n-Si
No full textYttrium oxide dielectric films were grown by rf-magnetron sputtering on n-Si(100) substrates and annealed in vacuum at temperatures ranging from 400 to 600 °C. The main aim of this work was the investigation of the interface between the dielectric film and silicon. Both structural (x-ray diffraction and transmission electron microscopy) and electrical characterization were used for this purpose. No structural change was observed on the interfacial native oxide layer after annealing at 600 °C for 1 h. Metal–oxide–semiconductor structures defined by the evaporation of Al electrodes show low leakage currents, moderate dielectric constant (around 14), and high densities of positive charges trapped in the oxide. Hysteresis effects in capacitance–voltage (C–V) curves reduce with the annealing temperature. Another interesting observation is the parallel shift of the C–V curves along the voltage axis with frequency. An insulator trap model is proposed to explain this behavior
Assessment matters
No full textThis guide is intended as an introduction to current debates and issues in good assessment practice in higher education. It does not claim in any sense to be comprehensive - which would require several volumes, given the rapid expansion of research into assessment issues over recent years - but rather attempts to introduce some of the key debates around both the purposes of assessment and aspects of good practice in assessment, as identified and explored in recent research. It raises questions as much as it supplies answers, with the intention of encouraging tutors to think more carefully and deeply about the purpose and nature of their assessment activities
Transparent and Flexible Thin Film Electroluminescent Devices Using HiTUS Deposition and Laser Processing Fabrication
No full textHighly transparent thin film electroluminescent structures offering excellent switch on characteristics, high luminance and large break-down voltages have been deposited onto glass and flexible polymeric materials with no substrate heating using high target utilization sputtering. Deposition of ZnS:Mn as the active light emitting layer and Y2O3,Al2O3,Ta2O5, and HfO2 as dielectric materials arranged in single and multiple layer configurations were investigated. Devices incorporating Al2O3,HfO2 quadruple layers demonstrate the highest attainable luminance at low threshold voltage. Single pulse excimer laser irradiation of the phosphor layer prior to deposition of the top dielectric layer enhanced the luminance of the devices. The devices fabricated on glass and polymeric substrates exhibited a maximum luminance of 500 and 450 cdm−2 when driven at 270 VRMS and 220 VRMS, respectively, with a 1.0 kHz sine wave
Temperature dependent characteristics of La2O2S: Ln [Ln = Eu,Tb] with various Ln concentrations over 5-60 ºC
No full textThis research is aimed at developing an optical sensor for remotely measuring human skin temperature in electromagnetically hostile environments, such as within a magnetic resonance imaging (MRI) scanner. In this feasibility study, various concentrations of europium doped lanthanum oxysulphide (La2O2S: Eu- 0.1-15 mol % (m/o)) and terbium doped lanthanum oxysulphide (La2O2S: Tb - 0.005-50 m/o) have been investigated in terms of crystallinity, photoluminescent (PL) spectral and decay time characteristics. For both phosphors, X-ray diffraction (XRD) has shown that as dopancy increases, the (100) and (002) reflections merge and there is a reduction in the c-axis parameter as well as the crystallite size. Photoluminescent characterisation (337 nm excitation) has also shown a dependency to dopant concentration through variance of peak intensity. Temperature dependent decay time measurements were carried out over a low temperature range of 5 to 60 °C. Optimum brightness of these temperature dependent lines is achieved at concentrations of 1 and 10 m/o for La2O2S: Eu and La2O2S: Tb respectively. However, optimum temperature dependency is achieved at lower concentration for La2O2S: Eu, specifically at 0.1 m/o. In comparison to conventional phosphor temperature dependent characteristic, La2O2S: Tb showed an increase in decay time with respect to temperature for concentrations above 2 m/o
Excimer laser processing of inkjet-printed and sputter-deposited transparent conducting SnO2:Sb for flexible electronics
No full textThe feasibility of low-temperature fabrication of transparent electrode elements from thin films of antimony-doped tin oxide (SnO2:Sb, ATO) has been investigated via inkjet printing, rf magnetron sputtering and post-deposition excimer laser processing. Laser processing of thin films on both glass and plastic substrates was performed using a Lambda Physik 305i excimer laser, with fluences in the range 20–100 mJ cm− 2 reducing sheet resistance from as-deposited values by up to 3 orders of magnitude. This is consistent with TEM analysis of the films that shows a densification of the upper 200 nm of laser-processed regions
The optimality of being efficient : designing auctions
No full textA cornerstone of the auction literature is the theory of"optimal auctions."'This theory uses mechanism design techniques to characterize, in general settings, the auction that maximizes the seller's expected revenues. One feature of the solution is that typically there is a conflict between the goals of revenue maximization and efficiency. The revenue-optimizing seller often either places goods in hands other than those who value them the most or withholds goods entirely from the market. However, the conclusion that the seller gains by assigning goods inefficiently depends critically on two strong assumptions: (1) the seller can prevent resale among bidders from occurring after the auction; and (2) the seller can commit to not sell the withheld goods after the auction. In this paper, the authors examine how the optimal auction problem changes when one or both of these assumptions are relaxed. This paper is organized as follows. In section 2, the authors establish the seller's general incentive to misassign goods and they identify settings where the optimal auction is efficient. In section 3, they solve two variations on the optimal auction, which recognize the possibility of resale. Section 4 proves that perfect resale destroys the seller's incentive to misassign goods. Section 5 establishes that with perfect resale, any misassignment of goods results in strictly lower seller revenues than the best efficient assignment. In section 6, the paper shows that the Vickrey auction is not distorted by the possibility of resale.International Terrorism&Counterterrorism,Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Markets and Market Access,Economic Theory&Research,Banks&Banking Reform,Access to Markets,International Terrorism&Counterterrorism,Environmental Economics&Policies
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