2018 New's Items

Intrinsic Anion Diffusivity in Lead Halide Perovskites is Facilitated by a Soft Lattice

M. Lai
A. Obliger
D. Lu
C.S. Kley
C.G. Bischak
Q. Kong
T. Lei
L. Dou
N.S. Ginsberg
D.T. Limmer
P. Yang
2018

Facile ionic transport in lead halide perovskites plays a critical role in device performance. Understanding the microscopic origins of high ionic conductivities has been complicated by indirect measurements and sample microstructural heterogeneities. Here, we report the direct visualization of halide anion interdiffusion in CsPbCl3–CsPbBr3 single crystalline perovskite nanowire heterojunctions using wide-field and confocal photoluminescence measurements. The combination of nanoscale imaging techniques with these single crystalline...

Microscopy of hydrogen and hydrogen-vacancy defect structures on graphene devices

D. Wong
Y. Wang
W. Jin
H-Z. Tsai
A. Bostwick
E. Rotenberg
R. K. Kawakami
A. Zettl
A. A. Mostofi
J. Lischner
M. F. Crommie
2018

We have used scanning tunneling microscopy (STM) to investigate two types of hydrogen defect structures on monolayer graphene supported by hexagonal boron nitride (hBN) in a gated field-effect transistor configuration. The first H-defect type is created by bombarding graphene with 1-keV ionized hydrogen and is identified as two hydrogen atoms bonded to a graphene vacancy via...

Conceptual Advances from Werner Complexes to Metal–Organic Frameworks

C. S. Diercks
M. J. Kalmutzki
N. J. Diercks
O. M. Yaghi
2018

Alfred Werner’s work on the geometric aspects of how ligands bind to metal ions at the end of the 19th century has given rise, in the molecular realm, to organometallic, bioinorganic, and cluster chemistries. By stitching together organic and inorganic units into crystalline porous metal–organic frameworks (MOFs), the connectivity, spatial arrangement, and geometry of those molecular complexes can now be fixed in space and become directly addressable. The fact that MOFs are porous provides additional space within which molecules can further be transformed and their chemistry...

Observation of Room Temperature Photoluminescence Blinking in Armchair-Edge Graphene Nanoribbons

Pfeiffer, M.
Senkovsky, B. V.
Haberer, D.
Fischer, F. R.
Yang, F.
Meerholtz, K.
Ando, Y.
Grüneis, A.
Lindfors, K.
2018

By enhancing the photoluminescence from aligned seven-atom wide armchair-edge graphene nanoribbons using plasmonic nanoantennas, we are able to observe blinking of the emission. The on- and off-times of the blinking follow power law statistics. In time-resolved spectra, we observe spectral diffusion. These findings together are a strong indication of the emission originating from a single quantum emitter. The room temperature photoluminescence displays a narrow spectral width of less than 50 meV, which is significantly smaller than the previously observed ensemble line width of 0.8 eV....

Anisotropic Dirac Fermions in BaMnBi2 and BaZnBi2

H. Ryu
S. Y. Park
L. Li
W. Ren
J. B. Neaton
C. Petrovic
C. Hwang
S.-K. Mo
2018

We investigate the electronic structure of BaMnBi2 and BaZnBi2 using angle-resolved photoemission spectroscopy and first-principles calculations. Although they share similar structural properties, we show that their electronic structure exhibit dramatic differences. A strong anisotropic Dirac dispersion is revealed in BaMnBi2 with a decreased asymmetry factor compared with other members of AMnBi2 (A = alkali earth or rare earth elements) family. In addition to the Dirac cones, multiple bands crossing the Fermi energy give rise to a...

Trap Passivation in Indium-Based Quantum Dots through Surface Fluorination: Mechanism and Applications

Tae-Gon Kim
Danylo Zherebetskyy
Yehonadav Bekenstein
Myoung Hwan Oh
Lin-Wang Wang
Eunjoo Jang
A. Paul Alivisatos
2018

Treatment of InP colloidal quantum dots (QDs) with hydrofluoric acid (HF) has been an effective method to improve their photoluminescence quantum yield (PLQY) without growing a shell. Previous work has shown that this can occur through the dissolution of the fluorinated phosphorus and subsequent passivation of indium on the reconstructed surface by excess ligands. In this article, we demonstrate that very significant luminescence enhancements occur at lower HF exposure though a different mechanism. At lower exposure to HF, the main role of the fluoride ions is to directly passivate...

Defect Induced Modification of Low-Lying Excitons and Valley Selectivity in Monolayer Transition Metal Dichalcogenides

S. Refaely-Abramson
D. Y. Qiu
S. G. Louie
J. B. Neaton
2018

We study the effect of point-defect chalcogen vacancies on the optical properties of monolayer transition metal dichalcogenides using ab initioGW and Bethe-Salpeter equation calculations. We find that chalcogen vacancies introduce unoccupied in-gap states and occupied resonant defect states within the quasiparticle continuum of the valence band. These defect states give rise to a number of strongly bound defect excitons and hybridize with excitons of the...

Bi-containing n-FeWO4 Thin Films Provide the Largest Photovoltage and Highest Stability for a Sub-2 eV Band Gap Photoanode

L. Zhou
A. Shinde
S. Suram
H. Stein
S. Bauers
A. Zakutayev
J. S. DuChene
G. Liu
E. A. Peterson
J. B. Neaton
J. M. Gregoire
2018

Photoelectrocatalysis of the oxygen evolution reaction remains a primary challenge for development of tandem-absorber solar fuel generators due to the lack of a photoanode with broad solar spectrum utilization, a large photovoltage, and stable operation. Bismuth vanadate with a 2.4–2.5 eV band gap has shown the most promise becauses its photoactivity down to 0.4 V vs RHE is sufficiently low to couple to a lower-gap photocathode for fuel synthesis. Through development of photoanodes based on the FeWO4structure, in particular, Fe-rich variants with addition of...

Coronene-Based Graphene NanoribbonsInsulated by Boron Nitride Nanotubes: Eletronic Properties of the Hybrid Structure

E. Gracia-Espino
H. R. Barzegar
A. Zettl
2018

We present a theoretical study on the formation of graphene nanoribbons—via polymerization of coronene molecules—inside the inner cavity of boron nitride nanotubes. We examine the electronic property of the hybrid system, and we show that the boron nitride nanotube does not significantly alter the electronic properties of the encapsulated graphene nanoribbon. Motivated by previous experimental works, we examine graphene nanoribbons with two different widths and investigate probable scenarios for defect formation and/or twisting of the resulting graphene nanoribbons and their effect...

Linking Molybdenum-Sulfur Clusters for Electrocatalytic Hydrogen Evolution

Z. Ji
C. A. Trickett
X. Pei
O. M. Yaghi
2018

Controlling the spatial arrangement of molecular catalysts on electrodes is critical to developing an optimal electrocatalyst. Mo–S clusters have shown great promise in catalyzing hydrogen evolution for the generation of carbon-free fuel from water. Here we report a synthetic approach to organize these molecular clusters into ordered dimers, cages, and chains through the use of organic linkers, as solved by single-crystal X-ray diffraction. We find that the linkage through the coordination bond between thiolate and Mo3S7 leads to (1...