Structure determination at room temperature and phase transition studies aboveT c in ABi4Ti4O15 (A = Ba, Sr or Pb)

The room temperature structure of three compounds belonging to the Aurivillius family (n = 4), ABi₄Ti₄O₁₅ (A = Ba, Sr or Pb) has been analysed. BaBi₄Ti₄O₁₅ crystallizes in a tetragonalI4/mmm space group whereas SrBi₄Ti₄O₁₅ and PbBi₄Ti₄O₁₅ crystallize in the orthorhombic space group A2₁am. The starting model for the Sr and Pb analogues was derived fromab initio methods and refined using the Rietveld method. The cations Ba and Sr are disordered over the Bi sites while the Pb cation is found exclusively in the [Bi₂O₂]²⁺ layers. The TiO₆ octahedra are tilted with the Ti-O bonds forming zigzag chains along the “c” axis. The displacement of Bi atoms along the “a” axis might be responsible for ferroelectricity in these compounds. The high temperature X-ray data aboveT _c indicate no structural transition for A = Ba and Pb while A = Sr transforms to the tetragonal structure.     

A prospective future towards bio/medical technology and bioelectronics based on 2D vdWs heterostructures

Nano Research - Nano-biotechnology research has become extremely important due to the possibilities in manipulation and characterization of biological molecules through nanodevices. Nanomaterials...     

Quantifying Quasi‐Fermi Level Splitting and Mapping its Heterogeneity in Atomically Thin Transition Metal Dichalcogenides

One of the most fundamental parameters of any photovoltaic material is its quasi‐Fermi level splitting (?µ) under illumination. This quantity represents the maximum open‐circuit voltage (V_oc) that a solar cell fabricated from that material can achieve. Herein, a contactless, nondestructive method to quantify this parameter for atomically thin 2D transition metal dichalcogenides (TMDs) is reported. The technique is applied to quantify the upper limits of V_oc that can possibly be achieved from monolayer WS₂, MoS₂, WSe₂, and MoSe₂‐based solar cells, and they are compared with state‐of‐the‐art perovskites. These results show that V_oc values of ≈1.4, ≈1.12, ≈1.06, and ≈0.93 V can be potentially achieved from solar cells fabricated from WS₂, MoS₂, WSe₂, and MoSe₂ monolayers at 1 Sun illumination, respectively. It is also observed that ?µ is inhomogeneous across different regions of these monolayers. Moreover, it is attempted to engineer the observed ?µ heterogeneity by electrically gating the TMD monolayers in a metal‐oxide‐semiconductor structure that effectively changes the doping level of the monolayers electrostatically and improves their ?µ heterogeneity. The values of ?µ determined from this work reveal the potential of atomically thin TMDs for high‐voltage, ultralight, flexible, and eye‐transparent future solar cells.     

Tunneling Photocurrent Assisted by Interlayer Excitons in Staggered van der Waals Hetero‐Bilayers

Vertically stacked van der Waals (vdW) heterostructures have been suggested as a robust platform for studying interfacial phenomena and related electric/optoelectronic devices. While the interlayer Coulomb interaction mediated by the vdW coupling has been extensively studied for carrier recombination processes in a diode transport, its correlation with the interlayer tunneling transport has not been elucidated. Here, a contrast is reported between tunneling and drift photocurrents tailored by the interlayer coupling strength in MoSe₂/MoS₂ hetero‐bilayers (HBs). The interfacial coupling modulated by thermal annealing is identified by the interlayer phonon coupling in Raman spectra and the emerging interlayer exciton peak in photoluminescence spectra. In strongly coupled HBs, positive photocurrents are observed owing to the inelastic band‐to‐band tunneling assisted by interlayer excitons that prevail over exciton recombinations. By contrast, weakly coupled HBs exhibit a negative photovoltaic diode behavior, manifested as a drift current without interlayer excitonic emissions. This study sheds light on tailoring the tunneling transport for numerous optoelectronic HB devices.     

Allelic deletions on chromosome 11q13 in multiple endocrine neoplasia type 1-associated and sporadic gastrinomas and pancreatic endocrine tumors

Endocrine tumors (ETs) of pancreas and duodenum occur sporadically and as a part of multiple endocrine neoplasia type 1 (MEN1). The MEN1 tumor suppressor gene has been localized to chromosome 11q13 by linkage analysis but has not yet isolated. Previous allelic deletion studies in enteropancreatic ETs suggested MEN1 gene involvement in tumorigenesis of familial pancreatic ETs (nongastrinomas) and sporadic gastrinomas. However, only a few MEN1-associated duodenal gastrinomas and sporadic pancreatic nongastrinomas have been investigated. We used tissue microdissection to analyze 95 archival pancreatic and duodenal ETs and metastases from 50 patients for loss of heterozygosity (LOH) on 11q13 with 10 polymorphic markers spanning the area of the putative MEN1 gene. Chromosome 11q13 LOH was detected in 23 of 27 (85%) MEN1-associated pancreatic ETs (nongastrinomas), 14 of 34 (41%) MEN1-associated gastrinomas, 3 of 16 (19%) sporadic insulinomas, and 8 of 18 (44%) sporadic gastrinomas. Analysis of LOH on 11q13 showed different deletion patterns in ETs from different MEN1 patients and in multiple tumors from individual MEN1 patients. The present results suggest that the MEN1 gene plays a role in all four tumor types. The lower rate of 11q13 LOH in MEN1-associated and sporadic gastrinomas and sporadic insulinomas as compared to MEN1 nongastrinomas may reflect alternative genetic pathways for the development of these tumors or mechanisms of the MEN1 gene inactivation that do not involve large deletions. The isolation of the MEN1 gene is necessary to further define its role in pathogenesis of pancreatic and duodenal ETs.     

Experimental Investigations on the Seismic Response of a Base-Isolated Reinforced Concrete Frame Model

The existing knowledge based on the physical characteristics of rubber-based seismic isolators and the validity of assumptions involved in design can be strengthened with shake table tests and field monitoring during earthquakes. Existing structures can be retrofitted with seismic isolators and successful examples are coming up day by day. This paper presents the results of analytical and experimental investigations of a one-third scaled model of a reinforced concrete soft first-storied structure mounted on natural rubber-based isolators and subjected to uniaxial seismic motion. Translational and rocking responses of the scaled model were measured under four different synthetic time histories, covering a wide range of frequencies. Through base isolation, the time period of the horizontal mode is far removed from the peak spectrum but the rocking modes may well be entrapped in the peak region. Hence, a simplified fail-safe system for protection against overturning was also studied.     

STWS approach for Hammerstein system of nonlinear Volterra integral equations of the second kind

In this paper, single-term Walsh series (STWS) method is applied to obtain the numerical solutions of Hammerstein systems of nonlinear Volterra integral equations of second kind (HSNVIES). Using the properties of the STWS method, HSNVIES can be easily converted into solvable recursive system of algebraic equations. Solutions obtained from the recursive system of algebraic equations are the solutions of the HSNVIES. Illustrative examples are provided with numerical solutions and the efficiency of this STWS method is also compared with the existing methods.