Diagenesis of a light, tight-oil chert reservoir at the Ediacaran/Cambrian boundary, Sultanate of Oman

The Al Shomou Silicilyte Member (Athel Formation) in the South Oman Salt Basin shares many of the characteristics of a light, tight-oil (LTO) reservoir: it is a prolifi c source rock mature for light oil, it produces light oil from a very tight matrix and reservoir, and hydraulic fracking technology is required to produce the oil. What is intriguing about the Al Shomou Silicilyte, and different from other LTO reservoirs, is its position related to the Precambrian/Cambrian Boundary (PCB) and the fact that it is a ‘laminated chert‘ rather than a shale. In an integrated diagenetic study we applied microstructural analyses (SEM, BSE) combined with state-of-the-art stable isotope and trace element analysis of the silicilyte matrix and fractures. Fluid inclusion microthermometry was applied to record the salinity and minimum trapping temperatures. The microstructural investigations reveal a fi ne lamination of the silicilyte matrix with a mean lamina thickness of ca. 20 μm consisting of predominantly organic matter-rich and fi nely crystalline quartz-rich layers, respectively. Authigenic, micron-sized idiomorphic quartz crystals are the main matrix components of the silicilyte. Other diagenetic phases are pyrite, apatite, dolomite, magnesite and barite cements. Porosity values based on neutron density logs and core plug data indicate porosity in the silicilyte ranges from less than 2% to almost to 40%. The majority of the pore space in the silicilyte is related to (primary) inter-crystalline pores, with locally important oversized secondary pores. Pore casts of the silica matrix show that pores are extremely irregular in three dimensions, and are generally interconnected by a complex web or meshwork of fi ne elongate pore throats. Mercury injection capillary data are in line with the microstructural observations suggesting two populations of pore throats, with an effective average modal diameter of 0.4 μm. The acquired geochemical data support the interpretation that the primary source of the silica is the ambient seawater rather than hydrothermal or biogenic. A maximum temperature of ca. 45°C for the formation of microcrystalline quartz in the silicilyte is good evidence that the lithifi cation and crystallization of quartz occurred in the fi rst 5 Ma after deposition. Several phases of brittle fracturing and mineralization occurred in response to salt tectonics during burial. The sequences of fracture-fi lling mineral phases (dolomite - layered chalcedony – quartz – apatite - magnesite I+II - barite – halite) indicates a complex fl uid evolution after silicilyte lithifi cation. Primary, all-liquid fl uid inclusions in the fracturefi lling quartz are good evidence of growth beginning at low temperatures, i.e. ≤ 50ºC. Continuous precipitation during increasing temperature and burial is documented by primary two-phase fl uid inclusions in quartz cements that show brines at 50°C and fi rst hydrocarbons at ca. 70°C. The absolute timing of each mineral phase can be constrained based on U-Pb geochronometry, and basin modelling. Secondary fl uid inclusions in quartz, magnesite and barite indicate reactivation of the fracture system after peak burial temperature during the major cooling event, i.e. uplift, between 450 and 310 Ma. A number of fi rst-order trends in porosity and reservoir-quality distribution are observed which are strongly related to the diagenetic and fl uid history of the reservoir: the early in-situ generation of hydrocarbons and overpressure development arrests diagenesis and preserves matrix porosity. Chemical compaction by pressure dissolution in the fl ank areas could be a valid hypothesis to explain the porosity variations in the silicilitye slabs resulting in lower porosity and poorer connectivity on the fl anks of the reservoir. Most of the hydrocarbon storage and production comes from intervals characterized by Amthor et al. 114488 preserved micropores, not hydrocarbon storage in a fracture system. The absence of oil expulsion results in present-day high oil saturations. The main diagenetic modifi cations of the silicilyte occurred and were completed relatively early in its history, i.e. before 300 Ma. An instrumental factor for preserving matrix porosity is the diffi culty for a given slab to evacuate all the fl uids (water and hydrocarbons), or in other words, the very good sealing capacity of the salt embedding the slab.

Fluorescence and photobleaching dynamics of single light-harvesting complexes

Single light-harvesting complexes LH-2 from Rhodopseudomonas acidophila were immobilized on various charged surfaces under physiological conditions. Polarized light experiments showed that the complexes were situated on the surface as nearly upright cylinders. Their fluorescence lifetimes and photobleaching properties were obtained by using a confocal fluorescence microscope with picosecond time resolution. Initially all molecules fluoresced with a lifetime of 1 ± 0.2 ns, similar to the bulk value. The photobleaching of one bacteriochlorophyll molecule from the 18-member assembly caused the fluorescence to switch off completely, because of trapping of the mobile excitations by energy transfer. This process was linear in light intensity. On continued irradiation the fluorescence often reappeared, but all molecules did not show the same behavior. Some LH-2 complexes displayed a variation of their quantum yields that was attributed to photoinduced confinement of the excited states and thereby a diminution of the superradiance. Others showed much shorter lifetimes caused by excitation energy traps that are only ≈3% efficient. On repeated excitation some molecules entered a noisy state where the fluorescence switched on and off with a correlation time of ≈0.1 s. About 490 molecules were examined.

Optical trapping of a cube

The successful development and optimisation of optically-driven micromachines will be greatly enhanced by the ability to computationally model the optical forces and torques applied to such devices. In principle, this can be done by calculating the light-scattering properties of such devices. However, while fast methods exist for scattering calculations for spheres and axisymmetric particles, optically-driven micromachines will almost always be more geometrically complex. Fortunately, such micromachines will typically possess a high degree of symmetry, typically discrete rotational symmetry. Many current designs for optically-driven micromachines are also mirror-symmetric about a plane. We show how such symmetries can be used to reduce the computational time required by orders of magnitude. Similar improvements are also possible for other highly-symmetric objects such as crystals. We demonstrate the efficacy of such methods by modelling the optical trapping of a cube, and show that even simple shapes can function as optically-driven micromachines.

Bessel beams from semiconductor light sources

We report on recent progress in the generation of non-diffracting (Bessel) beams from semiconductor light sources including both edge-emitting and surface-emitting semiconductor lasers as well as light-emitting diodes (LEDs). Bessel beams at the power level of Watts with central lobe diameters of a few to tens of micrometers were achieved from compact and highly efficient lasers. The practicality of reducing the central lobe size of the Bessel beam generated with high-power broad-stripe semiconductor lasers and LEDs to a level unachievable by means of traditional focusing has been demonstrated. We also discuss an approach to exceed the limit of power density for the focusing of radiation with high beam propagation parameter M2. Finally, we consider the potential of the semiconductor lasers for applications in optical trapping/tweezing and the perspectives to replace their gas and solid-state laser counterparts for a range of implementations in optical manipulation towards lab-on-chip configurations. © 2014 Elsevier Ltd.

Impact of high microwave power on hydrogen impurity trapping in nanocrystalline diamond films grown with simultaneous nitrogen and oxygen addition into methane/hydrogen plasma

In this work, we study for the first time the influence of microwave power higher than 2.0 kW on bonded hydrogen impurity incorporation (form and content) in nanocrystalline diamond (NCD) films grown in a 5 kW MPCVD reactor. The NCD samples of different thickness ranging from 25 to 205 μm were obtained through a small amount of simultaneous nitrogen and oxygen addition into conventional about 4% methane in hydrogen reactants by keeping the other operating parameters in the same range as that typically used for the growth of large-grained polycrystalline diamond films. Specific hydrogen point defect in the NCD films is analyzed by using Fourier-transform infrared (FTIR) spectroscopy. When the other operating parameters are kept constant (mainly the input gases), with increasing of microwave power from 2.0 to 3.2 kW (the pressure was increased slightly in order to stabilize the plasma ball of the same size), which simultaneously resulting in the rise of substrate temperature more than 100 °C, the growth rate of the NCD films increases one order of magnitude from 0.3 to 3.0 μm/h, while the content of hydrogen impurity trapped in the NCD films during the growth process decreases with power. It has also been found that a new H related infrared absorption peak appears at 2834 cm-1 in the NCD films grown with a small amount of nitrogen and oxygen addition at power higher than 2.0 kW and increases with power higher than 3.0 kW. According to these new experimental results, the role of high microwave power on diamond growth and hydrogen impurity incorporation is discussed based on the standard growth mechanism of CVD diamonds using CH4/H2 gas mixtures. Our current experimental findings shed light into the incorporation mechanism of hydrogen impurity in NCD films grown with a small amount of nitrogen and oxygen addition into methane/hydrogen plasma.

Synthesis of highly efficient and recyclable visible-light responsive mesoporous g-C3N4 photocatalyst via facile template-free sonochemical route

Herein we demonstrate a facile template-free sonochemical strategy to synthesize mesoporous g-C3N4 with a high surface area and enhanced photocatalytic activity. The TEM and nitrogen adsorption–desorption studies confirm mesoporous structure in g-C3N4 body. The photocatalytic activity of mesoporous g-C3N4 is almost 5.5 times higher than that of bulk g-C3N4 under visible-light irradiation. The high photocatalytic performance of the mesoporous g-C3N4 was attributed to the much higher specific surface area, efficient adsorption ability and the unique interfacial mesoporous structure which can favour the absorption of light and separation of photoinduced electron–hole pairs more effectively. A possible photocatalytic mechanism was discussed by the radicals and holes trapping experiments. Interestingly, the synthesized mesoporous g-C3N4 possesses high reusability. Hence the mesoporous g-C3N4 can be a promising photocatalytic material for practical applications in water splitting as well as environmental remediation.

g-C3N4/NaTaO3 organic–inorganic hybrid nanocomposite:high-performance and recyclable visible light driven photocatalyst

Novel g-C3N4/NaTaO3 hybrid nanocomposites have been prepared by a facile ultrasonic dispersion method. Our results clearly show the formation of interface between NaTaO3 and g-C3N4 and further loading of g-C3N4 did not affect the crystal structure and morphology of NaTaO3. The g-C3N4/NaTaO3 nanocomposites exhibited enhanced photocatalytic performance for the degradation of Rhodamine B under UV–visible and visible light irradiation compared to pure NaTaO3 and Degussa P25. Interestingly, the visible light photocatalytic activity is generated due to the loading of g-C3N4. A mechanism is proposed to discuss the enhanced photocatalytic activity based on trapping experiments of photoinduced radicals and holes. Under visible light irradiation, electron excited from the valance band (VB) to conduction band (CB) of g-C3N4 could directly inject into the CB of NaTaO3, making g-C3N4/NaTaO3 visible light driven photocatalyst. Since the as-prepared hybrid nanocomposites possess high reusability therefore it can be promising photocatalyst for environmental applications.

Light-driven transport of plasmonic nanoparticles on demand

Laser traps provide contactless manipulation of plasmonic nanoparticles (NPs) boosting the development of numerous applications in science and technology. The known trapping configurations allow immobilizing and moving single NPs or assembling them, but they are not suitable for massive optical transport of NPs along arbitrary trajectories. Here, we address this challenging problem and demonstrate that it can be handled by exploiting phase gradients forces to both confine and propel the NPs. The developed optical manipulation tool allows for programmable transport routing of NPs to around, surround or impact on objects in the host environment. An additional advantage is that the proposed confinement mechanism works for off-resonant but also resonant NPs paving the way for transport with simultaneous heating, which is of interest for targeted drug delivery and nanolithography. These findings are highly relevant to many technological applications including micro/nano-fabrication, micro-robotics and biomedicine.

Efficient photo-induced dielectrophoretic particle trapping on Fe:LiNbO3 for arbitrary two dimensional patterning

1D and 2D patterning of uncharged micro- and nanoparticles via dielectrophoretic forces on photovoltaic z-cut Fe:LiNbO3 have been investigated for the first time. The technique has been successfully applied with dielectric micro-particles of CaCO3 (diameter d = 1-3 ?m) and metal nanoparticles of Al (d = 70 nm). At difference with previous experiments in x- and y-cut, the obtained patterns locally reproduce the light distribution with high fidelity. A simple model is provided to analyse the trapping process. The results show the remarkably good capabilities of this geometry for high quality 2D light-induced dielectrophoretic patterning overcoming the important limitations presented by previous configurations.