2018 New's Items

Inversion symmetry and bulk Rashba effect in methylammonium lead iodide perovskite single crystals

K. Frohna
T. Deshpande
J. Harter
W. Peng
B. A. Barke
J. B. Neaton
2018

Methylammonium lead iodide perovskite (MAPbI3) exhibits long charge carrier lifetimes that are linked to its high efficiency in solar cells. Yet, the mechanisms governing these unusual carrier dynamics are not completely understood. A leading hypothesis—disproved in this work—is that a large, static bulk Rashba effect slows down carrier recombination. Here, using second harmonic generation rotational anisotropy measurements on MAPbI3 crystals, we demonstrate that the bulk structure of tetragonal MAPbI3 is...

Molecular Switch-like Regulation in Motor Proteins

S. Tafoya
C. Bustamante
2018

Motor proteins are powered by nucleotide hydrolysis and exert mechanical work to carry out many fundamental biological tasks. To ensure their correct and efficient performance, the motors' activities are allosterically regulated by additional factors that enhance or suppress their NTPase activity. Here, we review two highly conserved mechanisms of ATP hydrolysis activation and repression operating in motor proteins—the glutamate switch and the arginine finger—and their associated regulatory factors. We examine the implications of these regulatory mechanisms in proteins that are...

Electroluminescent Refrigeration by Ultra-efficient GaAs Light-emitting Diodes

T.P. Xiao
K. Chen
P. Santhanam
S. Fan
E. Yablonovitch
2018

Electroluminescence—the conversion of electrons to photons in a light-emitting diode (LED)—can be used as a mechanism for refrigeration, provided that the LED has an exceptionally high quantum efficiency. We investigate the practical limits of present optoelectronic technology for cooling applications by optimizing a GaAs/GaInP double heterostructure LED. We develop a model of the design based on the physics of detailed balance and the methods of statistical ray optics, and predict an external luminescence efficiency of ηext = 97.7% at 263 K. To enhance the...

Quantitative Prediction of Optical Absorption in Molecular Solids from an Optimally Tuned Screened Range-Separated Hybrid Functional

A. K. Manna
S. Refaely-Abramson
A. M. Reilly
A. Tkatchenko
J. B. Neaton
L. Kronik
2018

We show that fundamental gaps and optical spectra of molecular solids can be predicted quantitatively and nonempirically within the framework of time-dependent density functional theory (TDDFT) using the recently developed optimally tuned screened range-separated hybrid (OT-SRSH) functional approach. In this scheme, the electronic structure of the gas-phase molecule is determined by optimal tuning of the range-separation parameter in a range-separated hybrid functional. Screening and polarization in the solid state are taken into account by adding long-range dielectric screening to...

The Geometry of Periodic Knots, Polycatenanes and Weaving from a Chemical Perspective: A library for Reticular Chemistry

Y. Liu
M. O'Keeffe
M. Treacy
O. Yaghi
2018

The geometry of simple knots and catenanes is described using the concept of linear line segments (sticks) joined at corners. This is extended to include woven linear threads as members of the extended family of knots. The concept of transitivity that can be used as a measure of regularity is explained. Then a review is given of the simplest, most ‘regular’ 2- and 3-periodic patterns of polycatenanes and weavings. Occurrences in crystal structures are noted but most structures are believed to be new and ripe targets for designed synthesis.

Specific Metal-Support Interactions between Nanoparticle Layers for Catalysts with Enhanced Methanol Oxidation Activity

Sinmyung Yoon
Kyunghwan Oh
Fudong Liu
Ji Hui Seo
Gabor A. Somorjai
Jun Hee Lee
Kwangjin An
2018

Oxide supports often play a critical role in metal-supported catalysts owing to their charge transfer phenomena that can alter catalytic performance. Herein, in place of conventional bulk oxide supports, monodisperse oxide nanoparticles (NPs) were exploited as supports for Pt catalysts. Depending on the type of oxide NP, Pt/oxide layered catalysts exhibited dramatic changes in the catalytic activity and selectivity for methanol oxidation. While Pt NPs deposited on MnO, Fe3O4, Co3O4...

The Making and Breaking of Lead-Free Double Perovskite Nanocrystals of Cesium Silver–Bismuth Halide Compositions

Y. Bekenstein
J. C. Dahl
J. Huang
W. Osowiecki
J. K. Swabeck
E. Chan
P. Yang
A. P. Alivisatos
2018

Replacing lead in halide perovskites is of great interest due to concerns about stability and toxicity. Recently, lead free double perovskites in which the unit cell is doubled and two divalent lead cations are substituted by a combination of mono- and trivalent cations have been synthesized as bulk single crystals and as thin films. Here, we study stability and optical properties of all-inorganic cesium silver(I) bismuth(III) chloride and bromide nanocrystals with the double perovskite crystal structure. The cube-shaped nanocrystals are monodisperse in size with typical side lengths...

Chemical Diversity in a Metal-Organic Framework Revealed by Fluorescence Lifetime Imaging

W. Schrimpf
J. Jiang
Z. Ji
P. Hirschle
D. Lamb
O. Yaghi
S. Wuttke
2018

The presence and variation of chemical functionality and defects in crystalline materials, such as metal–organic frameworks (MOFs), have tremendous impact on their properties. Finding a means of identifying and characterizing this chemical diversity is an important ongoing challenge. This task is complicated by the characteristic problem of bulk measurements only giving a statistical average over an entire sample, leaving uncharacterized any diversity that might exist between crystallites or even within individual crystals. Here, we show that by using fluorescence imaging and...

Review on in situ Sum Frequency Generation Vibrational Spectroscopy Studies of Liquid-Solid Interfaces in Electrochemical Systems

Hui-Ling Han
Yonatan Horowitz
Gabor A. Somorjai
2018

The demand for safe, sustainable, and cheap energy production technologies and storage devices has grown at an overwhelming rate since the birth of the commercial lithium ion battery in the 1990s. As our research in electrochemical systems advances, we face fundamental questions arising from the electrified electrode–electrolyte interface that requires optical methods that can characterize the underlying structure and composition of intermediate species under reaction conditions. Sum frequency generation vibrational spectroscopy (SFGVS) emerges as a prominent optical characterization...

Enrichment of molecular antenna triplets amplifies upconverting nanoparticle emission

D. J. Garfield
N. J. Borys
S. M. Hamed
J. B. Neaton
et. al
2018

Efficient photon upconversion at low light intensities promises major advances in technologies spanning solar energy harvesting to deep-tissue biophotonics. Here, we discover the critical mechanisms that enable near-infrared dye antennas to significantly enhance performance in lanthanide-doped upconverting nanoparticle (UCNP) systems, and leverage these findings to design dye–UCNP hybrids with a 33,000-fold increase in brightness and a 100-fold increase in efficiency over bare UCNPs. We show that increasing the lanthanide content in the UCNPs shifts the primary energy donor from the...