One of the major merits CH3NH3PbI3 perovskite as an efficient absorber material for photovoltaic cell is its long carrier lifetime. We investigate role intrinsic defects on outstanding properties using density-functional studies. Two types are interest, i.e., Schottky and Frenkel defects. defects, such PbI2 CH3NH3I vacancy, do not make a trap state, which can reduce Elemental like Pb, I, CH3NH3 vacancies derived from act dopants, explains unintentional doping methylammonium lead halides...

Metasurface-based microdisplays Organic light-emitting diodes (OLEDs) have found wide application in high-resolution, large-area televisions and the handheld displays of smartphones tablets. With screen located some distance from eye, typical number pixels per inch is region hundreds. For near-eye microdisplays—for example, virtual augmented reality applications—the required pixel density runs to several thousand cannot be met by present display technologies. Joo et al. developed a...

Hybrid perovskites are currently the fastest growing photovoltaic technology, having reached a solar cell efficiency of over 20%. One possible strategy to further improve perovskite cells is tune degree octahedral tilting halide frame, since this in turn affects optical band gap and carrier effective masses. It commonly accepted that ion sizes main control parameter influencing perovskites. Here we re-examine origin tilts from systematic first-principles calculations. We find while steric...

In general, in thermoelectric materials the electrical conductivity σ and thermal κ are related thus cannot be controlled independently. Previously, to maximize figure of merit state-of-the-art materials, differences relative scaling between as dimensions reduced approach nanoscale were utilized. Here we present an using tin disulfide, SnS2, nanosheets that demonstrated a negative correlation κ. other words, thickness SnS2 decreased, increased whereas decreased. This leads increase 0.13 at...

Quantum states of strongly correlated electrons are prime importance to understand exotic properties condensed matter systems and the controllability over those promises unique electronic devices such as a Mott memory. As recent example, ultrafast switching device was demonstrated using transition between insulating state hidden-order metallic layered metal dichalcogenides 1T-TaS2. However, origin hidden not clear only macroscopic by laser pulse carrier injection reported. Here, we...

Using density functional theory calculations, we investigate the origin of insulating phase and metal-insulator transition (MIT) in octahedral tantalum disulfide (1T-TaS_{2}), a layered van der Waals material with prominent two-dimensional (2D) charge wave (CDW) order. We show that MIT is driven not by 2D order itself, but vertical ordering CDWs or 3D CDW identify two exceptionally stable configurations; one other metallic. The competition mixing configurations account for many mysterious...

One of the major challenges toward Si nanowire (SiNW) based photonic devices is controlling electronic band structure to obtain a direct gap. Here, we present new strategy for nanowires. Our method attributed modulation driven by uniaxial strain. We show that with lattice strain strongly dependent on crystal orientation and diameter SiNWs. In case [100] [111] SiNWs, tensile enhances gap characteristic, whereas compressive attenuates it. [110] SiNWs have different dependence in both make...

Mesenchymal stem cell (MSC) is a promising tool for the therapy of immune disorders. However, their efficacy and mechanisms in treating allergic skin disorders are less verified. We sought to investigate therapeutic human umbilical cord blood-derived MSCs (hUCB-MSCs) against murine atopic dermatitis (AD) explore distinct that regulate efficacy. AD was induced mice by topical application Dermatophagoides farinae. Naïve or activated-hUCB-MSCs were administered mice, clinical severity...

Handedness at the edge of a line Topological insulators are characterized by conducting boundary states. For those existing as two-dimensional (2D) materials, boundaries lines, currents 1D, and their two spin components flow in opposite directions. To address whether this handedness also applies to states 1D topological systems, Cheon et al. deposited indium atoms on surface silicon, where formed wires consisting double zigzag chains. The chains underwent distortions that caused called...

Using density-functional theory we identify a new low-energy structure for GaAs(001) in an As-poor environment. The discovered geometry is qualitatively different from the usual surface-dimer based reconstructions of III-V semiconductor (001) surfaces. stability structure, which has c(8x2) periodicity, explained terms bond saturation and favorable electrostatic interactions between surface atoms. Simulated scanning tunneling microscopy images are good agreement with experimental data,...

We investigate using first-principles calculations the atomic structure of orthorhombic phase ${\mathrm{Ta}}_{2}{\mathrm{O}}_{5}$. Although this has been studied for decades, correct structural model is controversial owing to complication disorder. identify a new low-energy high-symmetry model, where all Ta and O atoms have formal oxidation states $+5$ $\ensuremath{-}2$, respectively, experimentally reported triangular lattice symmetry sublattice appears dynamically at finite temperatures....

Carrier density and temperature-dependent resistivity of graphene grown by chemical vapor deposition (CVD) is investigated. We observe in low mobility CVD device a generic insulating behavior at temperatures, eventually metallic high manifesting nonmonotonic temperature dependent resistivity. This feature strongly affected carrier modulation with the low-density samples exhibiting insulating-like dependence up to higher temperatures than corresponding high-density samples. To explain...

Using first-principles calculations of graphene having high-symmetry distortion or defects, we investigate band gap opening by chiral symmetry breaking, intervalley mixing, in and show an intuitive picture understanding the terms local bonding antibonding hybridizations. We identify that breaking honeycomb lattices is ideal two-dimensional (2D) extension Peierls metal−insulator transition 1D linear lattices. spontaneous Kekule distortion, a 2D version takes place biaxially strained graphene,...

Organic–inorganic perovskites are promising materials for improving the efficiency of solar cells, but there still uncovered issues on understanding their electronic band structures. Using first-principles calculations, we investigate features organo-lead iodide and present efficient model to predict gap variation based orbital interaction scheme. The between Pb I atoms can be controlled through structural modification such as change in lattice constant deviation from cubic symmetry sites....

Scanning tunneling microscopy (STM) and density functional theory (DFT) calculations were used to investigate the surface morphology electronic structure of graphene synthesized on Cu by low temperature chemical vapor deposition (CVD). Periodic line patterns originating from arrangements carbon atoms passivate interaction between metal substrate graphene, resulting in flawless inherent band pristine graphene/Cu. The effective elimination states passivation is expected contribute growth...

Vertical charge order shapes the electronic properties in layered density wave (CDW) materials. Various stacking orders inevitably create nanoscale domains with distinct structures inaccessible to bulk probes. Here, characteristics of 1$T$-TaS$2$ are analyzed using scanning tunneling spectroscopy (STS) and functional theory (DFT) calculations. It is observed that Mott-insulating undergo a transition band-insulating restoring vertical dimerization CDWs. Furthermore, STS measurements covering...

We use density-functional theory to describe the initial stages of Fe film growth on GaAs(001), focusing interplay between chemistry and magnetism at interface. Four features appear be generic: (1) At submonolayer coverages, a strong chemical interaction substrate atoms leads substitutional adsorption intermixing. (2) For films several monolayers more, atomically abrupt interfaces are energetically favored. (3) over range thicknesses, both Ga As adlayers dramatically reduce formation...

Abstract Domain walls in interacting electronic systems can have distinct localized states, which often govern physical properties and may lead to unprecedented functionalities novel devices. However, states within domain themselves not been clearly identified understood for strongly correlated electron systems. Here, we resolve the on a Mott-charge-density-wave insulator 1 T -TaS 2 using scanning tunneling spectroscopy. We establish that wall state decomposes into two nonconducting located...

ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape crystallography of any semiconducting nanomaterial key step towards extending their use in applications. Whilst anisotropic wires have been routinely fabricated, precise control over specific surface facets tailoring polar non-polar growth directions still requires significant refinement. Manipulating energy crystal generic approach...

The overall size of an optical system is limited by the volume components and internal path length. To reach limits miniaturization, it possible to reduce both component length combining concepts metasurface flat optics folded optics. In addition their subwavelength thickness, metasurfaces enable bending conventional geometries off axis beyond law reflection. However, designing for highly off-axis illumination with visible light in combination a high numerical aperture non-trivial. this...

Density functional theory calculations are used to study the initial-stage adsorption of ${\mathrm{O}}_{2}$ molecules on $\mathrm{Si}(111)\ensuremath{-}(7\ifmmode\times\else\texttimes\fi{}7)$ surface. Contrary experimental suggestions, we find no evidence metastable molecular states this surface, i.e., dissociate spontaneously without any barrier. Our electronic and vibrational analysis reveals that resulting atomic-oxygen products can explain ``molecular'' features reported in previous experiments.

The adsorption of water on the Si(001) surface is studied by using density-functional total-energy calculations within generalized gradient approximation. We find that can adsorb molecularly down atom Si dimer, but a dissociative wherein OH (H) forms bond to (up) dimer more favored over molecular (by 1.8 eV). decay state occurs via transition with energy barrier only 0.15 eV. While interaction between molecules repulsive, dissociated species attractive hydrogen bonding.

We have studied the energetics and bonding geometry of ammonia adsorbed Si(100) surface by performing density-functional total-energy calculations within generalized gradient approximation. Ammonia molecules are found to adsorb on down atoms buckled Si dimers with an adsorption energy 1.2 eV, but there exists a low-energy (of about 0.6 eV) activation pathway more stable dissociative chemisorption where ${\mathrm{NH}}_{2}$ (H) bonds (up) atom. This diagram implies that molecular physisorption...

This article presents a unified theoretical model for the band gap transition of mixed halide perovskites. It is also presented that control composition variation in thin film level important as much synthesis new composition.