Sub-bandgap photoluminescence properties of multilayer h-BN-on-sapphire.

Two-dimensional hexagonal boron nitride (h-BN) materials have garnered increasing attention due to its ability of hosting intrinsic quantum point defects. This paper presents a photoluminescence (PL) mapping study related to sub-bandgap-level emission in bulk-like multilayer h-BN films. Spatial PL intensity distributions were carefully analyzed with 500 nm spatial resolution in terms of zero phonon line (ZPL) and phonon sideband (PSB) emission-peaks and their linewidths, thereby identifying the potential quantum point defects within the films. Two types of ZPL and PSB emissions were confirmed from the point defects located at the non-edge and edge of the films. Our statistical PL data from the non-edge- and edge-areas of the sample consistently reveal broad and narrow emissions, respectively. The measured optical properties of these defects and the associated ZPL peak shift and line broadening as a function of temperature between 77° and 300° K are qualitatively and quantitatively explained. Moreover, an enhancement of the photostable PL emission by at least a factor of ×3 is observed when our pristine h-BN was irradiated with a 532 nm laser.

Trace element contamination in water and sediment in an estuarine ecosystem connected to the Bay of Bengal: A preliminary assessment of ecological and human health risks.

The research, focusing on the analysis of nine trace elements, namely As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn, completely analyzed their quantities in both water and sediment inside the Rabnabad Channel. Samples were collected during the post-monsoon and analyzed by ICP-OES following acid digestion. The mean concentrations of elements in water and sediments are as follows: Fe > Mn > Pb > Cu > Ni > Zn > Cr > As>Cd, and Zn > Fe > Pb > Mn > As>Cu > Cr > Ni > Cd. To understand the state of ecological and human health risk, several indices were incorporated. Health risk assessment revealed that children posed higher risk than adults. PERI, TRI, and Igeo indices for water sediment indicate a significant ecological risk. Moreover, Mn and Pb exhibit elevated HPI values and contribute substantially to contamination factors. Correlation and PCA implicate both anthropogenic and geogenic sources, such as agricultural practices, coal-based power plants, and the Payra seaport, in the elevated concentrations of Cd, Cr, Mn, and Fe in both water and sediment samples.

First assessment of trace metals in the intertidal zone of the world's longest continuous beach, Cox's Bazar, Bangladesh.

This study aimed to assess the concentrations of eight trace metals - Cr, As, Pb, Mn, Ni, Zn, Hg, and Co - in the intertidal zone of Cox's Bazar of Bangladesh, the world's longest continuous beach. Most metal concentrations were below sediment quality guidelines and other comparative studies. The mean metal concentrations (mg kg-1) were as follows: Mn (471.67) > Zn (256.35) > Cr (89.96) > Pb (39.66) > Ni (36.44) > As (18.79) > Co (11.08) > Hg (0.0036). Statistical analyses revealed that only samples collected from stations 5 and 7 presented any cause for concern. Risk assessment indices, i.e., Geo-accumulation Index (Igeo), Contamination Factor (CF), Pollution Load Index (PLI), Potential Ecological Risk Index (PERI), and Toxic Risk Index (TRI), all indicated a low to moderate risk of pollution for all sites, suggesting that the study area is currently free from any significant negative impacts resulting from human activities. The calculated Hazard Index (HI) was <1, indicating no significant non-carcinogenic impact on adults or children. The Total Carcinogenic Risk was also well below the threshold value.

Generation of higher-order topological insulators using periodic driving.

Topological insulators (TIs) are a new class of materials that resemble ordinary band insulators in terms of a bulk band gap but exhibit protected metallic states on their boundaries. In this modern direction, higher-order TIs (HOTIs) are a new class of TIs in dimensionsd > 1. These HOTIs possess(d-1)-dimensional boundaries that, unlike those of conventional TIs, do not conduct via gapless states but are themselves TIs. Precisely, annth orderd-dimensional higher-order TI is characterized by the presence of boundary modes that reside on itsdc=(d-n)-dimensional boundary. For instance, a three-dimensional second (third) order TI hosts gapless (localized) modes on the hinges (corners), characterized bydc=1(0). Similarly, a second-order TI (SOTI) in two dimensions only has localized corner states (dc=0). These higher-order phases are protected by various crystalline as well as discrete symmetries. The non-equilibrium tunability of the topological phase has been a major academic challenge where periodic Floquet drive provides us golden opportunity to overcome that barrier. Here, we discuss different periodic driving protocols to generate Floquet HOTIs while starting from a non-topological or first-order topological phase. Furthermore, we emphasize that one can generate the dynamical anomalousπ-modes along with the concomitant 0-modes. The former can be realized only in a dynamical setup. We exemplify the Floquet higher-order topological modes in two and three dimensions in a systematic way. Especially, in two dimensions, we demonstrate a Floquet SOTI (FSOTI) hosting 0- andπcorner modes. Whereas a three-dimensional FSOTI and Floquet third-order TI manifest one- and zero-dimensional hinge and corner modes, respectively.