Toward On-Demand Polymorphic Transitions of Organic Crystals via Side Chain and Lattice Dynamics Engineering.

Controlling polymorphism, namely, the occurrence of multiple crystal forms for a given compound, is still an open technological challenge that needs to be addressed for the reliable manufacturing of crystalline functional materials. Here, we devised a series of 13 organic crystals engineered to embody molecular fragments undergoing specific nanoscale motion anticipated to drive cooperative order-disorder phase transitions. By combining polarized optical microscopy coupled with a heating/cooling stage, differential scanning calorimetry, X-ray diffraction, low-frequency Raman spectroscopy, and calculations (density functional theory and molecular dynamics), we proved the occurrence of cooperative transitions in all the crystalline systems, and we demonstrated how both the molecular structure and lattice dynamics play crucial roles in these peculiar solid-to-solid transformations.

On the Discrepancy between Local and Average Structure in the Fast Na Ionic Conductor NaSbWS.

Aliovalent substitution is a common strategy to improve the ionic conductivity of solid electrolytes for solid-state batteries. The substitution of SbS by WS in NaSbWS leads to a very high ionic conductivity of 41 mS cm at room temperature. While pristine NaSbS crystallizes in a tetragonal structure, the substituted NaSbWS crystallizes in a cubic phase at room temperature based on its X-ray diffractogram.

Atypical hemolytic uremic syndrome (aHUS) responsive to mycophenolate mofetil: A case report from Nepal.

Introduction: An atypical hemolytic uremic syndrome is an extremely rare and life-threatening thrombotic microangiopathy. This disorder is caused by dysregulation of the alternative pathway of the complement system in association with genetic abnormalities or the development of autoantibodies. However, 30-50% of patients do not have genetic or acquired mutations in the complement system.

Diverging Expressions of Anharmonicity in Halide Perovskites.

Lead-based halide perovskite crystals are shown to have strongly anharmonic structural dynamics. This behavior is important because it may be the origin of their exceptional photovoltaic properties. The double perovskite, Cs AgBiBr , has been recently studied as a lead-free alternative for optoelectronic applications.

Knowledge, attitude and reported practice regarding donning and doffing of personal protective equipment among frontline healthcare workers against COVID-19 in Nepal: A cross-sectional study.

Background: Coronavirus Disease 2019 (COVID-19) is a respiratory infection with a high rate of transmission primarily via airborne route and direct contact. Proper use of personal protective equipment (PPE) is a proven and effective way to prevent COVID-19 spread in healthcare settings. This study was done aiming to assess the knowledge, attitude, and reported practice, and identify the associated factors regarding donning and doffing of PPE among frontline healthcare workers in Nepal.

Testing the efficacy of sea urchin exclusion methods for restoring kelp.

Kelps are ecosystem engineers, which collectively form forests that provide a variety of important ecosystem services for humans and other organisms. Kelp forests are threatened by multiple local and global stressors, one of the most notable is herbivory. Overabundant sea; urchins can consume kelp, leading to a phase shift from productive forests to unproductive; rocky barrens.

Strongly Anharmonic Octahedral Tilting in Two-Dimensional Hybrid Halide Perovskites.

Recent investigations of two-dimensional (2D) hybrid organic-inorganic halide perovskites (HHPs) indicate that their optical and electronic properties are dominated by strong coupling to thermal fluctuations. While the optical properties of 2D-HHPs have been extensively studied, a comprehensive understanding of electron-phonon interactions is limited because little is known about their structural dynamics. This is partially because the unit cells of 2D-HHPs contain many atoms.

Ultrafast and low-power crystallization in GeSbTe and GeSbTe thin films using femtosecond laser pulses.

Rapid and reversible switching between amorphous and crystalline phases of phase-change material promises to revolutionize the field of information processing with a wide range of applications including electronic, optoelectronics, and photonic memory devices. However, achieving faster crystallization is a key challenge. Here, we demonstrate femtosecond-driven transient inspection of ultrafast crystallization of as-deposited amorphous GeSbTe and GeSbTe thin films induced by a series of 120 fs laser pulses.

Femtosecond laser-induced ultrafast transient snapshots and crystallization dynamics in phase change material.

We report here femtosecond laser-driven transient snapshots of ultrafast crystallization of GeSbTe films from its as-deposited amorphous phase, and the local structural change is validated by micro-Raman spectroscopy and x-ray diffraction. The decay time constant of ∼5  ps in transient spectra with a precise temporal resolution using 400 nm (pump) reveals about 68 volumetric percentage crystallization at a remarkably low fluence of 4.78  mJ·cm.

Saturable absorption in one-dimensional SbSe nanowires in the visible to near-infrared region.

One-dimensional (1D) free-standing nanowires are particularly important for carrier confinement in two dimensions, which provides a platform to explore the nonlinear optical phenomena at the nanoscale. In this Letter, we demonstrate saturable absorption in the resonant and above-bandgap excitations of both ns and fs pulses in 1D crystalline SbSe nanowires prepared by the facile hydrothermal method. Impressively, the average length of the nanowires extends to a few micrometers with a high aspect ratio of 300.

Origin of Unusual Excitonic Absorption and Emission from Colloidal Ag2S Nanocrystals: Ultrafast Photophysics and Solar Cell.

Colloidal Ag2S nanocrystals (NCs) typically do not exhibit sharp excitonic absorption and emission. We first elucidate the reason behind this problem by preparing Ag2S NCs from nearly monodisperse CdS NCs employing cation exchange reaction. It was found that the defect-related midgap transitions overlap with excitonic transition, blurring the absorption spectrum.

Engineering the optical response of a-Se thin films by employing morphological disorder.

In this article, we experimentally demonstrate for the first time that photobleaching (PB) can be induced in morphologically disordered a-Se thin film, an observation which is opposite of the previously well-known photodarkening (PD) effects in morphologically ordered films. Further, the optical response of the film shows many fold increase with increase in control beam intensity. To explain the observed extraordinary phenomenon, we have proposed a model based on the morphological disorder of a modified surface and its subsequent photo-annealing.

First observation of the temperature-dependent light-induced response of Ge(25)As(10)Se(65) thin films.

Ge-rich ternary chalcogenide glasses (ChGs) exhibit photobleaching (PB) when illuminated with bandgap light. This effect originates from the combined effects of intrinsic structural changes and photo-oxidation. In a sharp contradiction to previous observations, in this Letter, we demonstrate, for the first time, that Ge-rich Ge(25)As(10)Se(65) ChG thin films exhibit photodarkening (PD) at 20 K and PB at 300 and 420 K after having been continuously illuminated for ∼3 hours.