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

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Self-organization in many solution-processed, semiconducting conjugated polymers results in complex microstructures, in which ordered microcrystalline domains are embedded in an amorphous matrix1. This has important consequences for electrical properties of these materials: charge transport is usually limited by the most difficult hopping processes and is therefore dominated by the disordered matrix, resulting in low charge-carrier mobilities2 (⩽10-5 cm2 V-1 s-1). Here we use thin-film, field-effect transistor structures to probe the transport properties of the ordered microcrystalline domains in the conjugated polymer poly(3-hexylthiophene), P3HT. Self-organization in P3HT results in a lamella structure with two-dimensional conjugated sheets formed by interchain stacking. We find that, depending on processing conditions, the lamellae can adopt two different orientations—parallel and normal to the substrate—the mobilities of which differ by more than a factor of 100, and can reach values as high as 0.1 cm2 V-1 s-1 (refs 3, 4). Optical spectroscopy of the field-induced charge, combined with the mobility anisotropy, reveals the two-dimensional interchain character of the polaronic charge carriers, which exhibit lower relaxation energies than the corresponding radical cations on isolated one-dimensional chains. The possibility of achieving high mobilities via two-dimensional transport in self-organized conjugated lamellae is important for applications of polymer transistors in logic circuits5 and active-matrix displays4,6.

Two-dimensional charge transport in self-organized, high-mobility conjugated polymers

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software

/pdf/advanced-capabilities-for-materials-modelling-with-quantum-40poaosrve.pdf

Advanced capabilities for materials modelling with Quantum ESPRESSO.

Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudo-potential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement theirs ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software.

/pdf/advanced-capabilities-for-materials-modelling-with-quantum-1mm65lmkt8.pdf

Advanced capabilities for materials modelling with Quantum ESPRESSO

We describe information which has been obtained on point defects detected in various types of GaAs materials using electron paramagnetic resonance as well as electrical and optical techniques. From a comparison of their characteristics and those of simple intrinsic defects (As and Ga interstitials, vacancies and antisites) it is concluded that native defects are not simple intrinsic defects, with the exception of the antisites, but complexes formed by the interaction of such defects between themselves or with impurities. Particular emphasis is given to the As antisite complexed with an As interstitial, the so‐called EL2 defect which plays a major role in the electrical properties of bulk materials. Differential thermal analysis, positron annihilation, and x‐ray diffraction demonstrate that bulk materials contain a large concentration of vacancy‐related defects and As precipitates located along dislocations which play the role of gettering centers. Presumably, bulk materials also contain other As clusters of various sizes although only the smallest ones (EL2) have been detected. All these As clusters are sources of As interstitials which play an important role in thermal treatments. As to semi‐insulating materials, their electrical properties result mainly from the compensation between the double donor, called EL2, associated with the As antisite and the double acceptor ascribed to the Ga antisite.

Native defects in gallium arsenide

Gallium nitride (GaN) light emitting diodes (LEDs) were irradiated at room temperature with electrons in the range 300-1400 keV A threshold energy of 440 keV was observed, corresponding to a gallium atom displacement energy of 19/spl plusmn/2 eV This value of the displacement energy compares with that of silicon carbide but is smaller than that of diamond and larger than that of gallium arsenide (GaAs) No threshold energy for the nitrogen atom was observed It is concluded that the nitrogen sublattice repairs itself through annealing The measured displacement energy is used to determine the Rutherford cross section, which permits a theoretical comparison of electron and proton irradiation damage in GaN The effects of 25 MeV electrons on gallium nitride films have been studied by photoluminescence (PL), and according to the literature, they introduce transitions in the near infrared part of the spectrum Experiments on gallium nitride films using 2 MeV protons are reported in this work The same transitions in the near infrared part of the spectrum are observed by PL It is deduced that 2 MeV protons are about 1000 times more damaging than 25 MeV electrons The Rutherford cross section predicts a value of 214 The difference is attributed to the defect recombination rate which depends on the particle type The nature of the transitions in the near infrared part of the spectrum is reviewed The GaN films were annealed at 400/spl deg/C for 30 min As a result of annealing, another transition appears in the green part of the spectrum Transitions involving the gallium vacancy in irradiated GaN are discussed

Radiation hardness of gallium nitride

We present here a complete set of experimental results, obtained by electron paramagnetic resonance (EPR) and deep-level transient spectroscopy (DLTS), on the so-called EL2 defect in GaAs. It is obtained on semi-insulating materials and specially doped materials grown as semi-insulating ones, which have been submitted to electron irradiation, thermal treatments, and annealing followed by a quench. First, we show that there are two types of defects which give rise to the same EPR spectrum associated with the antisite ${\mathrm{As}}_{\mathrm{Ga}}$: the one associated with EL2, since it presents its well-characterized metastable property, and another one associated with the isolated ${\mathrm{As}}_{\mathrm{Ga}}$, which is not metastable. Second, we demonstrate that an EL2 defect can be transformed into an isolated ${\mathrm{As}}_{\mathrm{Ga}}$ by a thermal treatment. Third, we describe how EL2 defects can be regenerated by a low-temperature treatment in materials which have been annealed and quenched. These results, together with considerations on self-diffusion in GaAs, allow us to conclude that EL2 is a complex formed by an isolated ${\mathrm{As}}_{\mathrm{Ga}}$ and an intrinsic interstitial defect, namely ${\mathrm{As}}_{\mathrm{i}}$ or ${\mathrm{Ga}}_{\mathrm{i}}$. Finally, we studied the kinetics of EL2 regeneration by DLTS in quenched material; since this regeneration occurs through the interstitial mobility and since the associated activation energy is similar to the one found for ${\mathrm{As}}_{\mathrm{i}}$ mobility in electron irradiated p-type material, we deduce that EL2 is the complex ${\mathrm{As}}_{\mathrm{Ga}+{\mathrm{As}}_{\mathrm{i}}}$. All these results, as well as the ones provided by the literature, can be understood if the stable state of EL2 corresponds to ${\mathrm{As}}_{\mathrm{i}}$ in second-neighbor position of ${\mathrm{As}}_{\mathrm{Ga}}$ while the metastable state corresponds to ${\mathrm{As}}_{\mathrm{i}}$ in first-neighbor position.

Identification of a defect in a semiconductor: EL2 in GaAs.

The magnetic properties of ${\mathrm{Co}}^{2+}$ ions in epitaxial (Zn,Co)O layers with 10% Co concentration have been studied by electron paramagnetic resonance spectroscopy. The Co-related EPR spectrum is characterized by a 200-G broad anisotropic single line with g factors close to those of the isolated ${\mathrm{Co}}^{2+}$ ion. The temperature dependence of the EPR signal follows a Curie-Weiss law with a critical temperature of +12 K. We find no evidence for a high-temperature ferromagnetic state. Magnetocrystalline anisotropy is observed and a canted spin arrangement is suggested.

H. J. von Bardeleben

Papers

Native defects in gallium arsenide

Radiation hardness of gallium nitride

Identification of a defect in a semiconductor: EL2 in GaAs.

Electron paramagnetic resonance study of Zn 1-x Co x O: A predicted high-temperature ferromagnetic semiconductor

Behavior of electron-irradiation-induced defects in GaAs.