2017 New's Items

Ultrafast Fluorescent Decay Induced by Metal-Mediated Dipole–Dipole Interaction in Two-Dimensional Molecular Aggregates

Q. Hu
D. Jin
J. Xiao
S. H. Nam
X. Liu
Y. Liu
X. Zhang
N. X. Fang
2017

Two-dimensional molecular aggregate (2DMA), a thin sheet of strongly interacting dipole molecules self-assembled at close dis- tance on an ordered lattice, is a fascinating fluorescent material. It is distinctively different from the conventional (single or col- loidal) dye molecules and quantum dots. In this paper, we ver- ify that when a 2DMA is placed at a nanometric distance from a metallic substrate, the strong and coherent interaction between the dipoles inside the 2DMA dominates its fluorescent decay at a picosecond timescale. Our streak-camera lifetime measurement and...

Ruddlesden–Popper Phase in Two-Dimensional Inorganic Halide Perovskites: A Plausible Model and the Supporting Observations

Y. Yu
D. Zhang
P. Yang
2017

A Ruddlesden–Popper (RP) type structure is well-known in oxide perovskites and is related to many interesting properties such as superconductivity and ferroelectricity. However, the RP phase has not yet been discovered in inorganic halide perovskites. Here, we report the direct observation of unusual structure in two-dimensional CsPbBr3 nanosheets which could be interpreted as the RP phase based on model simulations. Structural details of the plausible RP domains and domain boundaries between the RP and conventional perovskite phases have been revealed on...

Control of Architecture in Rhombic Dodecahedral Pt–Ni Nanoframe Electrocatalysts

N. Becknell
Y. Son
D. Kim
D. Li
Y. Yu
Z. Niu
T. Lei
B. T. Sneed
K. L. More
N. M. Markovic
V. R. Stamenkovic
P. Yang
2017

Platinum-based alloys are known to demonstrate advanced properties in electrochemical reactions that are relevant for proton exchange membrane fuel cells and electrolyzers. Further development of Pt alloy electrocatalysts relies on the design of architectures with highly active surfaces and optimized utilization of the expensive element, Pt. Here, we show that the three-dimensional Pt anisotropy of Pt–Ni rhombic dodecahedra can be tuned by controlling the ratio between Pt and Ni precursors such that either a completely hollow nanoframe or a new architecture, the excavated nanoframe,...

Iodine versus Bromine Functionalization for Bottom-Up Graphene Nanoribbon Growth: Role of Diffusion

C. Bronner
T. Marangoni
D. J. Rizzo
R. A. Durr
J. H. Jorgensen
F. R. Fischer
M. Crommie
2017

Deterministic bottom-up approaches for synthesizing atomically well-defined graphene nanoribbons (GNRs) largely rely on the surface-catalyzed activation of selected labile bonds in a molecular precursor followed by step-growth polymerization and cyclodehydrogenation. While the majority of successful GNR precursors rely on the homolytic cleavage of thermally labile C–Br bonds, the introduction of weaker C–I bonds provides access to monomers that can be polymerized at significantly lower temperatures, thus helping to increase the flexibility of the GNR synthesis process. Scanning...

Controlled Isotropic and Anisotropic Shell Growth in β-NaLnF4 Nanocrystals Induced by Precursor Injection Rate

S. Fischer
J. K. Swabeck
A. P. Alivisato
2017

Precise morphology and composition control is vital for designing multifunctional lanthanide-doped core/shell nanocrystals. Herein, we report controlled isotropic and anisotropic shell growth techniques in hexagonal sodium rare-earth tetrafluoride (β-NaLnF4) nanocrystals by exploiting the kinetics of the shell growth. A drastic change of the shell morphology was observed by changing the injection rate of the shell precursors while keeping all other reaction conditions constant. We obtained isotropic shell growth for fast sequential injection and a preferred...

Temperature-Dependent Hole Transfer from Photoexcited Quantum Dots to Molecular Species: Evidence for Trap-Mediated Transfer

J. H. Olshansky
A. D. Balan
T. X. Ding
X. Fu
Y. V. Lee
A. P. Alivisatos
2017

The effect of temperature on the rate of hole transfer from photoexcited quantum dots (QDs) is investigated by measuring the driving force dependence of the charge transfer rate for different sized QDs across a range of temperatures from 78 to 300 K. Spherical CdSe/CdS core/shell QDs were used with a series of ferrocene-derived molecular hole acceptors with an 800 meV range in electrochemical potential. Time-resolved photoluminescence measurements and photoluminescence quantum yield measurements in an integrating sphere were both performed from 78 to 300 K to obtain temperature-...

Ultralow Thermal Conductivity in All-Inorganic Halide Perovskites

W. Lee
H. Li
A. B. Wong
D. Zhang
M. Lai
Y. Yu
Q. Kong
E. Lin
J. J. Urban
J. C. Grossman
P. Yang
2017

Controlling the flow of thermal energy is crucial to numerous applications ranging from microelectronic devices to energy storage and energy conversion devices. Here, we report ultralow lattice thermal conductivities of solution-synthesized, single-crystalline all-inorganic halide perovskite nanowires composed of CsPbI3 (0.45 ± 0.05 W·m−1·K−1), CsPbBr3 (0.42 ± 0.04 W·m−1·K−1), and CsSnI3 (0.38 ± 0.04 W·m...

Atomate: A High-Level Interface to Generate, Execute, and Analyze Computational Materials Science Workflows

K. Mathew
J. Montoya
A. Faghaninia
S. Dwarakanath
M. Aykol
H. Tang
I. Chu
T. Smidt
B. Bocklund
M. Horton
J. Dagdelen
B. Wood
2017

We introduce atomate, an open-source Python framework for computational materials science simulation, analysis, and design with an emphasis on automation and extensibility. Built on top of open source Python packages already in use by the materials community such as pymatgen, FireWorks, and custodian, atomate provides well-tested workflow templates to compute various materials properties such as electronic bandstructure, elastic properties, and piezoelectric, dielectric, and...

Observation of Ultralong Valley Lifetime in WSe2/MoS2 Heterostructures

J. Kim
C. Jin
B. Chen
H. Cai
T. Zhao
P. Lee
S. Kahn
K. Watanabe
T. Taniguchi
S. Tongay
M. F. Crommie
F. Wang
2017

The valley degree of freedom in two-dimensional (2D) crystals recently emerged as a novel information carrier in addition to spin and charge. The intrinsic valley lifetime in 2D transition metal dichalcogenides (TMD) is expected to be markedly long due to the unique spin-valley locking behavior, where the intervalley scattering of the electron simultaneously requires a large momentum transfer to the opposite valley and a flip of the electron spin. However, the experimentally observed valley lifetime in 2D TMDs has been limited to tens of nanoseconds thus far. We report efficient...

The Chemistry of Metal–Organic Frameworks for CO2 Capture, Regeneration and Conversion

C. A. Trickett
A. Helal
B. A. Al-Maythalony
Z. H. Yamani
K. E. Cordova
O. M. Yaghi
2017

The carbon dioxide challenge is one of the most pressing problems facing our planet. Each stage in the carbon cycle — capture, regeneration and conversion — has its own materials requirements. Recent work on metal–organic frameworks (MOFs) demonstrated the potential and effectiveness of these materials in addressing this challenge. In this Review, we identify the specific structural and chemical properties of MOFs that have led to the highest capture capacities, the most efficient separations and regeneration processes, and the most effective catalytic conversions. The interior of...