Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Electronics obtained through the bottom-up approach of molecular-level control of material composition and structure may lead to devices and fabrication strategies not possible with top-down methods. This review presents a brief summary of bottom-up and hybrid bottom-up/top-down strategies for nanoelectronics with an emphasis on memories based on the crossbar motif. First, we will discuss representative electromechanical and resistance-change memory devices based on carbon nanotube and core-shell nanowire structures, respectively. These device structures show robust switching, promising performance metrics and the potential for terabit-scale density. Second, we will review architectures being developed for circuit-level integration, hybrid crossbar/CMOS circuits and array-based systems, including experimental demonstrations of key concepts such lithography-independent, chemically coded stochastic demultipluxers. Finally, bottom-up fabrication approaches, including the opportunity for assembly of three-dimensional, vertically integrated multifunctional circuits, will be critically discussed.

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Nanoelectronics from the bottom up

Photocatalytic and photoelectrochemical (PEC) water splitting using semiconductor materials has attracted considerable interest due to its potential to cleanly produce H 2 from water by utilizing abundant solar light. Since Fujishima and Honda used a TiO 2 photoanode in 1972 to split water, researchers have been attempting to develop water-splitting systems that can efficiently use visible light (which accounts for almost half of the solar spectrum on the Earth's surface) in order to realize efficient conversion of solar light. In this report, we review recent progress in this field by focusing on strategies that utilize visible light. Such strategies include two-step photoexcitation systems that were inspired by photosynthesis in nature, band engineering for producing novel photocatalysts that have both a high visible light absorption and suitable energy levels for water splitting, the development of new cocatalysts for efficient H 2 or O 2 production, fabrication of efficient photoelectrodes based on visible-light-responsive semiconductors, and the construction of tandem-type PEC water-splitting systems.

Recent progress on photocatalytic and photoelectrochemical water splitting under visible light irradiation

Harnessing solar energy for the production of clean hydrogen fuels by a photoelectrochemical (PEC) cell represents a very attractive but challenging alternative This review focuses on recent developments of some promising photoelectrode materials, such as BiVO4, a-Fe2O3, TaON, and Ta3N5 for solar hydrogen production Some strategies have been developed to improve PEC performances of the photoelectrode materials, including: (i) doping for enhancing visible light absorption in the wide bandgap semiconductor or promoting charge transport in the narrow bandgap semiconductor, respectively; (ii) surface treatment for removing segregation phase or surface states; (iii) electrocatalysts for decreasing the overpotentials; (iv) morphology control for enhancing the light absorption and shortening transfer distance of minority carriers; (v) other methods, such as sensitization, passivating layer, and band structure engineering using heterojunction structures, and so on Photochemical durability of the photoelectrodes is also discussed, since any potential PEC technology must balance efficiency against cost and photochemical durability Photochemical durability may be amended by optimizing the photoelectrode, electrocatalyst, and electrolyte at the same time In addition, solar seawater splitting is briefly introduced because it has received attention recently Finally, trends in research in PEC cells for solar hydrogen production are detailed

Photoelectrochemical cells for solar hydrogen production: current state of promising photoelectrodes, methods to improve their properties, and outlook

We demonstrate large-scale (1 kb) high-density crossbar arrays using a Si-based memristive system. A two-terminal hysteretic resistive switch (memristive device) is formed at each crosspoint of the array and can be addressed with high yield and ON/OFF ratio. The crossbar array can be implemented as either a resistive random-access-memory (RRAM) or a write-once type memory depending on the device configuration. The demonstration of large-scale crossbar arrays with excellent reproducibility and reliability also facilitates further studies on hybrid nano/CMOS systems.

https://web.eecs.umich.edu/~wluee/Lu_JoSiCrossbar_NL2009.pdf

High-density crossbar arrays based on a Si memristive system.

We present experimental results that show a metal—non-metal (MNM) transition occurring in hydrogenated amorphous Si (a-Si: H) analogue memory devices as a function of temperature. The dc resistance of the devices undergoes a continuous change in the range 65–100 K from semiconductor-like behaviour to metallic behaviour, as the temperature increases. The ac conductivity, measured over the frequency range 1–3·1 × 107 Hz, shows an anomalous change as the temperature is varied over the MNM transition. Ac characteristics were modelled using multicomponent RC and RL equivalent circuits below and above the MNM transition region respectively. It is found that the capacitance increases markedly when the temperature approaches the MNM transition from the semiconductor side. Near the transition temperature this capacitance disappears, and the equivalent circuit now requires an inductive component together with a resistance which has a positive temperature coefficient of resistance equivalent to that of the ...

Capacitance anomaly near the metal—non-metal transition in Cr—hydrogenated amorphous Si—V thin-film devices

Experimental results on the constant current stressing and forming of hydrogenated amorphous silicon (a-Si) Cr/p+-V thin film devices are presented. In the initial stage of electro-forming by constant current stressing, with increasing injection of charge via either increasing bias or time, the current=f(v) properties of devices exhibit an instability, as shown by a decrease in the reverse current. Eventually, with further increase in the current bias, the local current density reaches a critical value IF, and a rapid `runaway' processes occurs, which results in an irreversible change of the initial higher resistance state into a permanent `formed' state of lower resistance.

Constant current forming in Cr/p + a-Si:H/V thin film devices

Experimental results on the constant current stressing in hydrogenated amorphous silicon (a-Si:H) Cr–p+–V thin film devices are presented. With increasing injection of charge via either increasing bias or time, the current-voltage characteristics of devices exhibit instability, as shown by a decrease in the reverse current. This is interpreted in terms of the creation of defects in the a-Si:H. The defect generation rate. as measured by the voltage shift ΔV at a constant reverse current in the J-V curve, is found to follow a square-root time dependent law. In addition, a decrease in device conductance after stressing is also observed, which is described by a mechanism of dopant equilibrium during and after stressing.

Current-induced instability in Cr–p+ a-Si:H–V thin film devices

Switching and filament formation in hot-wire CVD p-type a-Si:H devices

We report on the area dependence of switching in both Cr/ p + a-Si:H/Ag(Al) and Cr/ p + μc-Si/Ag(Al) filament switches. The doped amorphous (a-Si:H) or microcrystalline (μc-Si) thin Si layers are made by hot-wire chemical vapor deposition. The device active region area (A) is varied over 5 orders of magnitude, from 10 -7 to 10 -2 cm 2 , using photolithographically defined Ag and Al top contacts. Before switching, the resistance of 100-μm 2 devices is normally about 100 kΩ for μc-Si and 10 GΩ for a-Si:H. After switching with applied current ramps, the resistance decreases to a few hundred ohms in all a-Si devices and to a few thousands ohms in μc-Si devices. In both μc-Si and a-Si:H devices, the switching voltage (V sw ) decreases with increasing device area according to V sw ~ V 0 -αln(A/A 0 ) with α=0.3V for a-Si:H and α=0.04V for μc-Si. For both materials, the switching current roughly obeys the power law I sw ∞ A β with β~1. A statistical model is proposed to explain the area scaling of the switching voltage and relate the parameters to the material properties.

Jian Hu

Papers

Capacitance anomaly near the metal—non-metal transition in Cr—hydrogenated amorphous Si—V thin-film devices

Constant current forming in Cr/p + a-Si:H/V thin film devices

Current-induced instability in Cr–p+ a-Si:H–V thin film devices

Switching and filament formation in hot-wire CVD p-type a-Si:H devices

Area-Dependent Switching in Thin Film-Silicon Devices