Silicon is the second most abundant element on the Earth and one of the more abundant elements in our Solar System. Variations in the relative abundance of the stable isotopes of Si (Si isotope fractionation) in different natural reservoirs, both terrestrial (surface and deep Earth) as well as extra-terrestrial (e.g. meteorites, lunar samples), are a powerful tracer of present and past processes involving abiotic as well as biotic systems. The versatility of the Si isotope tracer is reflected in its wide-ranging applications from understanding the origin of early Solar System objects, planetary differentiation, Moon formation, mantle melting and magma differentiation on the Earth, ancient sea-water composition, to modern-day weathering, clay formation and biological fractionation on land as well as in the oceans. The application of Si isotopes as tracers of natural processes started over six decades ago and its usage has seen a sudden increase over the last decade due to improvements in mass spectrometry, particularly the advent of multicollector inductively coupled plasma mass spectrometers, which has made Si isotope measurements safe and relatively easy while simultaneously improving the accuracy and precision of measurements.

A better understanding of the electronic structure of perovskite materials used in photovoltaic devices is essential for their development and optimization. In this investigation, synchrotron-based photoelectron spectroscopy (PES) was used to experimentally delineate the character and energy position of the valence band structures of a mixed perovskite. The valence band was measured using PES with photon energies ranging from ultraviolet photoelectron spectroscopy (21.2 eV) to hard X-rays (up to 4000 eV), and by taking the variation of the photoionization cross sections into account, we could experimentally determine the inorganic and organic contributions. The experiments were compared to theoretical calculations to further distinguish the role of the different anions in the electronic structure. This work also includes a thorough study of the valence band maximum and its position in relation to the Fermi level, which is crucial for the design and optimization of complete solar cells and their functional properties.

Borophene, single atomic-layer sheet of boron ( Science 2015 , 350 , 1513 ), is a rather new entrant into the burgeoning class of 2D materials. Borophene exhibits anisotropic metallic properties whereas its hydrogenated counterpart borophane is reported to be a gapless Dirac material lying on the same bench with the celebrated graphene. Interestingly, this transition of borophane also rendered stability to it considering the fact that borophene was synthesized under ultrahigh vacuum conditions on a metallic (Ag) substrate. On the basis of first-principles density functional theory computations, we have investigated the possibilities of borophane as a potential Li/Na-ion battery anode material. We obtained a binding energy of -2.58 (-1.08 eV) eV for Li (Na)-adatom on borophane and Bader charge analysis revealed that Li(Na) atom exists in Li(Na) state. Further, on binding with Li/Na, borophane exhibited metallic properties as evidenced by the electronic band structure. We found that diffusion pathways for Li/Na on the borophane surface are anisotropic with x direction being the favorable one with a barrier of 0.27 and 0.09 eV, respectively. While assessing the Li-ion anode performance, we estimated that the maximum Li content is LiBH, which gives rises to a material with a maximum theoretical specific capacity of 504 mAh/g together with an average voltage of 0.43 V versus Li/Li. Likewise, for Na-ion the maximum theoretical capacity and average voltage were estimated to be 504 mAh/g and 0.03 V versus Na/Na, respectively. These findings unambiguously suggest that borophane can be a potential addition to the map of Li and Na-ion anode materials and can rival some of the recently reported 2D materials including graphene.

To the league of rapidly expanding 2D materials, borophene is a recent addition. Herein, a combination of ab initio density functional theory (DFT) and nonequilibrium Green’s function (NEGF) based methods is used to estimate the prospects of this promising elemental 2D material for gas sensing applications. We note that the binding of target gas molecules such as CO, NO, NO2, NH3, and CO2 is quite strong on the borophene surface. Interestingly, our computed binding energies are far stronger than several other reported 2D materials like graphene, MoS2, and phosphorene. Further rationalization of stronger binding is made with the help of charge transfer analysis. The sensitivity of the borophene for these gases is also interpreted in terms of computing the vibrational spectra of the adsorbed gases on top of borophene, which show dramatic shift from their gas phase reference values. The metallic nature of borophene enables us to devise a setup considering the same substrate as electrodes. From the computation of the transmission function of system (gas + borophene), appreciable changes in the transmission functions are noted compared to pristine borophene surface. The measurements of current–voltage (I–V) characteristics unambiguously demonstrate the presence and absence of gas molecules (acting as ON and OFF states), strengthening the plausibility of a borophene based gas sensing device. As we extol the extraordinary sensitivity of borophene, we assert that this elemental 2D material is likely to attract subsequent interest.

No abstract

Aqueous nitrate, NO3-(aq), was studied by 2D-IR, UV-IR, and UV-UV time-resolved spectroscopies in combination with molecular dynamics (MD) simulations with the purpose of determining the hydration dynamics around the anion. In water, the D3h symmetry of NO3-is broken, and the degeneracy of the asymmetric-stretch modes is lifted. This provides a very sensitive probe of the ionwater interactions. The 2D-IR measurements reveal excitation exchange between the two nondegenerate asymmetric-stretch vibrations on a 300-fs time scale concomitant with fast anisotropy decay of the diagonal-peak signals. The MD simulations show that this is caused by jumps of the transition dipole orientations related to fluctuations of the hydrogen bonds connecting the nitrate ion to the nearest water molecules. Reorientation of the ion, which is associated with the hydrogen-bond breaking, was monitored by time-resolved UV-IR and UV-UV spectroscopy, revealing a 2-ps time constant. These time scales are very similar to those reported for isotope-labeled water, suggesting that NO3-(aq) has a labile hydration shell. connecting the nitrate ion to the nearest water molecules. Reorientation of the ion, which is associated with the hydrogen bond breaking, is monitored by time resolved UV-IR-and UV-UV spectroscopy, revealing a 2 ps time constant. These time scales are very similar to those reported for isotope-labeled water, suggesting that NO 3¯( aq) has a labile hydration shell.

Recent advances in solid-state nano-device-based DNA sequencing are at the helm of the development of a new paradigm, commonly referred to as personalized medicines. Paying heed to a timely need for standardizing robust nanodevices for cheap, fast, and scalable DNA detection, in this article, the nanogap formed by the lateral heterostructure of graphene and hexagonal boron nitride (hBN) is explored as a potential architecture. These heterostructures have been realized experimentally, and our study boasts the idea that the passivation of the edge of the graphene electrode with hBN will solve many of practical problems, such as high reactivity of the graphene edge and difficulty in controlled engineering of the graphene edge structure, while retaining the nanogap setup as a useful nanodevice for sensing applications. Employing first-principle density-functional-theory-based nonequilibrium Green's function methods, we identify that the DNA building blocks, nucleobases, uniquely couple with the states of the nanogap, and the resulting induced states can be attributed as leaving a fingerprint of the DNA sequence in the computed current-voltage (I-V) characteristic. Two bias windows are put forward: lower (1-1.2 V) and higher (2.7-3 V), where unique identification of all four bases is possible from the current traces, although higher sensitivity is obtained at the higher voltage window. Our study can be a practical guide for experimentalists toward development of a nanodevice DNA sensor based on graphene-hBN heterostructures.

No abstract