CuInS2 nanocrystals with the wurtzite structure show promise for applications requiring efficient energy transport due to their anisotropic crystal structure. We investigate the source of photoluminescence in the near-infrared spectral region recently observed from these nanocrystals. Spectroscopic studies of both wurtzite CuInS2 itself and samples alloyed with Cd or Zn allow the assignment of this emission to a radiative point defect within the nanocrystal structure. Further, by varying the organic passivation layer on the material, we are able to determine that the atomic species responsible for nonradiative decay paths on the nanocrystal surface are Cu- or S-based. Density functional theory calculations of defect states within the material allow identification of the likely radiative species. Understanding both the electronic structure and optical properties of wurtzite CuInS2 nanocrystals is necessary for their efficient integration into potential biological, photovoltaic, and photocatalytic applications.

Herein, we report the unprecedented direct synthesis of a recently discovered metastable wurtzite phase of Cu2–x Se. Nanocrystals of Cu2–x Se were synthesized employing dodecyl diselenide as the selenium source and ligand. Optical characterization performed with UV–vis–NIR spectroscopy in solution showed a broad plasmonic band in the NIR. Structural characterization was performed with X-ray diffraction (XRD) and transmission electron microscopy. Variable-temperature XRD analysis revealed that the wurtzite nanocrystals irreversibly transform into the thermodynamic cubic phase at 151 °C. Replacement of dodecyl diselenide with dodecyl selenol yielded cubic phase Cu2–x Se, allowing for polymorphic phase control. An aliquot study was performed to gain insight into the mechanism of phase selectivity. The direct synthesis of this novel wurtzite phase could enable the discovery of new phenomena and expand the vast application space of Cu x Se y compounds.

The thickness and lateral distribution of sand and mud beds and bedsets on channel bars from the tidally influenced Fraser River, British Columbia, Canada, are quantitatively assessed. Fifty-six vibracores totalling ca 114 m of vertical section are used to tabulate bed thicknesses. Statistical calculations are undertaken for nine channel bars ranging from the freshwater and tidal zone, to the sustained brackish water and tidal zone. The data reveal that thickness trends can be organized into three groups that broadly correspond to time-averaged hydrodynamic and salinity conditions in the various distributary channels. Thick sand beds (up to 30 cm) and thin mud beds (up to 5 cm) characterize the freshwater tidal zone. The tidal and freshwater to brackish-water transition zone comprises thin sands (up to 10 cm) and thicker muds (up to 19 cm), and the sustained brackish water tidal zone consists of thin muds (up to 6 cm) with relatively thicker sands (up to 25 cm). The results suggest that the locus of mud deposition occurs in the tidal freshwater to brackish-water zone, probably reflecting mud flocculation and deposition at the turbidity maximum. Landward of the turbidity maximum, mud deposition is linked to tidal influence (tidal backwater effect and reverse eddy currents on channel margins) as mud beds thin in the landward direction. These results support the hypothesis that mud deposition is greatest at the turbidity maximum and decreases in both the seaward and landward direction. This study also showcases that mud-bed thicknesses are greatest towards the turbidity maximum and thin in both the landward and seaward direction. In the rock record, the apex of mud deposition probably marks the position of the palaeo-turbidity maximum.

The Fraser River is the largest undammed river on the west coast of North America. In its lower reaches, a saltwater wedge intrudes up to 30 km inland during mixed semi-diurnal tidal cycles that range up to 5.3 m in height. Sediments deposited in the lower reaches of the Fraser River show distinctive characteristics that reflect the relative control of river versus tidal processes, as well as the persistence of saline water at each point along the channel. Grain-size trends along the river are controlled by the hydrodynamics in each distributary. Mud deposition is concentrated in the zone of saltwater-freshwater mixing. Coarse-grained sand and mud/fine-grained sand deposition is largely seasonally controlled, wherein bed material (diameter > 0.177 mm) is deposited during the waning freshet, and washload transported mud and fine-grained sand (< 0.177 mm) is deposited during the late-stage waning freshet flow and during base flow. The diversity and density of bioturbation changes according to the volume and residence time of brackish water at the bed. Higher salinity water and greater durations that saline water is sustained at any locale, supports a more diverse and uniformly distributed trace assemblage. With decreasing salinity, the trace assemblage decreases in diversity and bioturbation becomes more sporadically distributed. This results in a reduction of infaunal diversity from 100% on the nearly fully marine tidal flats in the abandoned part of the lower delta plain, to 14% in intertidal sediments of the brackish-water reach. The character of the sediments deposited across the tidal-fluvial transition provide criteria for differentiating sediments deposited within freshwater-tidal reaches, brackish-water-tidal reaches, and mixed tidal-fluvial distributaries. These data are presented as a process-based analog for tidal-fluvial sediments preserved in the rock record. The results can be used to predict changes in facies character across the tidal-fluvial transition of similar tide-influenced, river-dominated systems or their rock-record equivalents.

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