Development of hybrid inorganic-organic light-emitting devices with metal oxide charge transport layers

Organic light emitting diodes (OLEDs) are currently being considered as the next generation technology in flat panel displays and solid state lighting applications. Among which, phosphorescent organic light emitting diodes (PhOLEDs) with nearly 100% internal quantum efficiency including other properties such as self emitting, high luminescence efficiency, broad wavelength range, wide viewing angle, high contrast, low power consumption, low weight, and large emitting area are gaining popularity in both academic and industrial research. Although development and commercialization of OLED technology is growing, there are still several key issues that need to be addressed---the external quantum efficiency (EQE) needs to be improved and the biggest technical challenge is to increase the device operational lifetime. Balanced charge injection and transport is vital for improving the device efficiency which demands for selection of better charge injection and transport materials. In addition imbalanced charge injection also degrades the device via joule\u27s heating and charge accumulation thereby limiting the device lifetime. Sensitivity of organic materials to the ambient atmosphere, particularly oxygen and moisture impedes the device performance.;This thesis work attempts to address these issues in the PhOLEDs through selection of proper charge injection and transport material as well as device structure optimization. At first we prepared thin films of thermally evaporated zinc-tin oxide (ZTO) with various ZnO and SnO2 compositions and studied its optical, electrical and morphological properties. After optimization of transparency and conductivity, these ZTO films showed promising materials for alternate transparent conducting oxides and electron transport layer (ETL) functions. Similarly, thin films of thermally evaporated tungsten oxide (WO 3) were prepared and their optical and electrical properties were studied and evaluated as a hole transport layer (HTL) material. We then fabricated and characterized various hybrid light emitting diode (HyLED) structures comprising of---ZTO as an ETL, WO3 as a HTL, and MoO3 as a hole injecting layer (HIL). The device structures were optimized for better performance in terms of efficiency and operational lifetime. Significant enhancement in EQE and operational lifetime were obtained in HyLEDs having WO3 as a HTL than of PhOLEDs with organic HTL. This is because WO3 improved hole injection as well as enabled facile hole transport thereby maintaining the balance of charge injection into the device. Finally, we also prepared inverted HyLEDs using WO3 as HTL and several metals including Ca, Ca/LiF, and Al/LiF as a cathode and their electron injecting capability were studied. Balanced charge injection was observed when a nanometer thick Ca was used as a cathode and WO3 as a HTL. As a result, inverted HyLED with better EQE and operational lifetime were fabricated

Post cholecystectomy hemobilia: transcatheter embolization of pseudoaneurysms with homemade steel coils

Two patients presented with hemobilia, one and two months following cholecystectomy. Angiography demonstrated pseudoaneurysms arising form the gastroduodenal and right hepatic arteries. Percutaneous transcatheter embolization of the pseudoaneurysms was successfully performed in both patients using homemade steel coils

Physico-Chemical Characterisation of Lateritic Nickel Ores of Sukinda, Orissa

The only nickel ore deposit of significance in India occurs in the chrorniferous ultramafic complex ofSukinda, Orissa. It is a lateritic nickel o re deposit with a reserve of about 150 million tonne having cut-off grade of 0.05% Ni. The processing of this ore is difficult due to ultrafine nature ofgeothite, low content of nickel in the ore (max. 1.5% Ni), complex intergrowths of goethite with quartz, talc, kaolinite and magnetite and abrupt variation of nickel content in the ores in horizontal and vertical profiles. In this study the results of detailed investigations to characterise five bulk samples collected from different sectors of Sukinda-Kansa, TISCO and OMC are discussed.The techniques used for characterisation include granulometric study, optical microscopy, X-ray diffraction, thermal analysis, scanning electron microscopic, infrared studies, electron probe microanalysis, leaching experiments and chemical analyses. This study indicates that the nickel is not present as discrete minerals but mostly associated with goethite. Kansa ore has goethite as major mineral (90%) whereas the other samples contain significant amount of free quartz along with variable amount of chromite,hematite,magnetite, talc, serpentine and kaolin. The fine grained goethite is amorphous to quasi-amorphous in nature. Mineralogy and chemistry of the samples indicate that goethite. Fe and Ni are invariably enriched in the finer size fractions. Electron probe microanalyses indicate that nodular goethire and chromite are Ni-poor (<0.2% Ni) whereas lithiophorite and magnetite contain 11% and 0.9% Ni respectively- The results of the sequential leaching studies involving oxalic, sulphuric and hydrochloric acids indicate three types of association of nickel in goethite: a part with amorphous goethite (ferrilivdrite), a part in weak/A- bonded nature and a part as lattice bound state in goethite . The laterite ore is thus proved to be of comple x in nature which creates problem for liberation of the constituent minerals based on the srnface properties. Classification down to silt size fraction increases the Ni content to about 1.0% in the material. These ores have been succes.sful/v tested on pilot plant scale for extraction of nickel metal by reduction roasting followed by arnnrotriut)r - atnmonicrcal leaching and electrowinnin

Role of Carbon in Enhancing the Performance of MgB2 superconductor

The enhancement of the critical current density (Jc(H)) of carbon and nano-SiC doped MgB2 is presented and compared. The upper critical field (Hc2) being determined from resistivity under magnetic field experiments is though improved for both C substitution and nano-SiC addition the same is more pronounced for the former. In MgB2-xCx carbon is substituted for boron that induces disorder in the boron network and acts as internal pinning centres. The optimal Jc(H) values are obtained for x = 0.1 sample . In case of nano-SiC doped in MgB2, the Jc(H) improves more profoundly and two simultaneous mechanisms seems responsible to this enhancement. Highly reactive nano-SiC releases free carbon atom, which gets easily incorporated into the MgB2 lattice to act as intrinsic pinning centres. Further enhancement is observed for higher nano-SiC concentrations, where the un-reacted components serve as additional extrinsic pinning centres.Comment: 17 Pages text + Fig

Partnerships in mental healthcare service delivery in low-resource settings: developing an innovative network in rural Nepal

Background: Mental illnesses are the largest contributors to the global burden of non-communicable diseases. However, there is extremely limited access to high quality, culturally-sensitive, and contextually-appropriate mental healthcare services. This situation persists despite the availability of interventions with proven efficacy to improve patient outcomes. A partnerships network is necessary for successful program adaptation and implementation. Partnerships network We describe our partnerships network as a case example that addresses challenges in delivering mental healthcare and which can serve as a model for similar settings. Our perspectives are informed from integrating mental healthcare services within a rural public hospital in Nepal. Our approach includes training and supervising generalist health workers by off-site psychiatrists. This is made possible by complementing the strengths and weaknesses of the various groups involved: the public sector, a non-profit organization that provides general healthcare services and one that specializes in mental health, a community advisory board, academic centers in high- and low-income countries, and bicultural professionals from the diaspora community. Conclusions: We propose a partnerships model to assist implementation of promising programs to expand access to mental healthcare in low- resource settings. We describe the success and limitations of our current partners in a mental health program in rural Nepal

Readout of a quantum processor with high dynamic range Josephson parametric amplifiers

We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 $\Omega$ environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250-300 MHz, with input saturation powers up to -95 dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimate of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Lastly, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs.Comment: 9 pages, 8 figure

Measurement-Induced State Transitions in a Superconducting Qubit: Within the Rotating Wave Approximation

Superconducting qubits typically use a dispersive readout scheme, where a resonator is coupled to a qubit such that its frequency is qubit-state dependent. Measurement is performed by driving the resonator, where the transmitted resonator field yields information about the resonator frequency and thus the qubit state. Ideally, we could use arbitrarily strong resonator drives to achieve a target signal-to-noise ratio in the shortest possible time. However, experiments have shown that when the average resonator photon number exceeds a certain threshold, the qubit is excited out of its computational subspace, which we refer to as a measurement-induced state transition. These transitions degrade readout fidelity, and constitute leakage which precludes further operation of the qubit in, for example, error correction. Here we study these transitions using a transmon qubit by experimentally measuring their dependence on qubit frequency, average photon number, and qubit state, in the regime where the resonator frequency is lower than the qubit frequency. We observe signatures of resonant transitions between levels in the coupled qubit-resonator system that exhibit noisy behavior when measured repeatedly in time. We provide a semi-classical model of these transitions based on the rotating wave approximation and use it to predict the onset of state transitions in our experiments. Our results suggest the transmon is excited to levels near the top of its cosine potential following a state transition, where the charge dispersion of higher transmon levels explains the observed noisy behavior of state transitions. Moreover, occupation in these higher energy levels poses a major challenge for fast qubit reset

Overcoming leakage in scalable quantum error correction

Leakage of quantum information out of computational states into higher energy states represents a major challenge in the pursuit of quantum error correction (QEC). In a QEC circuit, leakage builds over time and spreads through multi-qubit interactions. This leads to correlated errors that degrade the exponential suppression of logical error with scale, challenging the feasibility of QEC as a path towards fault-tolerant quantum computation. Here, we demonstrate the execution of a distance-3 surface code and distance-21 bit-flip code on a Sycamore quantum processor where leakage is removed from all qubits in each cycle. This shortens the lifetime of leakage and curtails its ability to spread and induce correlated errors. We report a ten-fold reduction in steady-state leakage population on the data qubits encoding the logical state and an average leakage population of less than $1 \times 10^{-3}$ throughout the entire device. The leakage removal process itself efficiently returns leakage population back to the computational basis, and adding it to a code circuit prevents leakage from inducing correlated error across cycles, restoring a fundamental assumption of QEC. With this demonstration that leakage can be contained, we resolve a key challenge for practical QEC at scale.Comment: Main text: 7 pages, 5 figure