2018 New's Items

Biexcitonic Optical Stark Effects in Monolayer Molybdenum Diselenide

C-K. Yong
J. Horng
Y. Shen
H. Cai
A. Wang
CK. Lin
S. Zhao
K. Taniguchi
S. Tongay
F. Wang
2018

Floquet states, where a periodic optical field coherently drives electrons in solids1,2,...

Correlation of Electron Tunneling and Plasmon Propagation in a Luttinger Liquid

S. Zhao
S. Wang
F. Wu
W. Shi
I. B. Utama
T. Lyu
L. Jiang
Y. Su
S. Wang
K. Watanabe
T. Taniguchi
A. Zettl
X. Zhang
C. Zhou
F. Wang
2018

uantum-confined electrons in one dimension behave as a Luttinger liquid. However, unambiguous demonstration of Luttinger liquid phenomena in single-walled carbon nanotubes (SWNTs) has been challenging. Here we investigate well-defined SWNT cross junctions with a point contact between two Luttinger liquids and combine electrical transport and optical nanoscopy measurements to correlate completely different physical properties (i.e., the electron tunneling and the plasmon propagation) in the same Luttinger liquid system. The suppressed electron tunneling at SWNT junctions exhibits a...

Pause Sequences Facilitate Entry Into Long-lived Paused States by Reducing RNA Polymerase Transcription Rates

R. Gabizon
A. Lee
H. V-Movahed
R. Ebright
C. Bustamante
2018

Transcription by RNA polymerase (RNAP) is interspersed with sequence-dependent pausing. The processes through which paused states are accessed and stabilized occur at spatiotemporal scales beyond the resolution of previous methods, and are poorly understood. Here, we combine high-resolution optical trapping with improved data analysis methods to investigate the formation of paused states at enhanced temporal resolution. We find that pause sites reduce the forward transcription rate of nearly all RNAP molecules, rather than just affecting the subset of molecules that enter long-lived...

Conversion of Imine to Oxazole and Thiazole Linkages in Covalent Organic Frameworks

P. J. Waller
Y. S. AlFaraj
C. S. Diercks
N. N. Jarenwattananon
O. M. Yaghi
2018

Imine-linked ILCOF-1 based on 1,4-phenylenediamine and 1,3,6,8-tetrakis(4-formylphenyl)pyrene was converted through consecutive linker substitution and oxidative cyclization to two isostructural covalent organic frameworks (COFs), having thiazole and oxazole linkages. The completeness of the conversion was assessed by infrared and solid-state NMR spectroscopies, and the crystallinity of the COFs was confirmed by powder X-ray diffraction. Furthermore, the azole-linked COFs remain porous, as shown by nitrogen sorption experiments. The materials derived in this way demonstrate increased...

Visualization and Control of Single-Electron Charging in Bilayer Graphene Quantum Dot

J. Velasco, Jr.
J. Lee
D. Wong
S. Kahn
H-Z. Tsai
J. Costello
T. Umeda
T. Taniguchi
K. Watanabe
A. Zettl
F. Wang
M. F. Crommie
2018

Graphene p–n junctions provide an ideal platform for investigating novel behavior at the boundary between electronics and optics that arise from massless Dirac Fermions, such as whispering gallery modes and Veselago lensing. Bilayer graphene also hosts Dirac Fermions, but they differ from single-layer graphene charge carriers because they are massive, can be gapped by an applied perpendicular electric field, and have very different pseudospin selection rules across a p–n junction. Novel phenomena predicted for these massive Dirac Fermions at p–n junctions...

Facilitating Laboratory Research Experience Using Reticular Chemistry

S. J. Lyle
R. W. Flaig
K. E. Cordova
O. M. Yaghi
2018

Rapid development in the field of reticular chemistry has allowed scientists ever-increasing control over the design and synthesis of crystalline porous materials. The promise that this field has in the development of next-generation materials for numerous applications (gas storage and separation, catalysis, chemical sensing, electronics) relies on the effective training of new scientists in the diverse array of computational, synthetic, and analytical techniques that reticular chemistry requires. Herein, we describe a laboratory-research experience designed to equip a class of upper...

Torsional Instability in the Single-Chain Limit of a Transition Metal Triachalcogenide

Pham
Oh
Stetz
2018

The scientific bounty resulting from the successful isolation of few to single layers of two-dimensional materials suggests that related new physics resides in the few- to single-chain limit of one-dimensional materials. We report the synthesis of the quasi–one-dimensional transition metal trichalcogenide NbSe3 (niobium triselenide) in the few-chain limit, including the realization of isolated single chains. The chains are encapsulated in protective boron nitride or carbon nanotube sheaths to prevent oxidation and to facilitate characterization. Transmission...

Push it to the Limit: Comparing Periodic and Local Approaches to Density Functional Theory for Intermolecular Interactions

J. Witte
J. B. Neaton
M. Head-Gordon
2018

With the aim of systematically comparing two popular approaches to density functional theory – all-electron calculations with local basis sets, and periodic calculations employing plane wave basis sets and norm-conserving pseudopotentials – we have computed complete-basis binding energies across the S22 set of intermolecular interactions, a dataset consisting of noncovalent interactions of small- and medium-sized molecules containing first- and second-row atoms, using the Troullier-Martins norm-conserving pseudopotentials with SPW92, a local spin-density approximation; and PBE, a...

Molecular Switch-like Regulation Enables Global Subunit Coordination in a Viral ring ATPase

S. Tafoya
S. Liu
J. Castillo
R. Atz
M. Morais
S. Grimes
P. Jardine
C. Bustamante
2018

Subunits in multimeric ring-shaped motors must coordinate their activities to ensure correct and efficient performance of their mechanical tasks. Here, we study WT and arginine finger mutants of the pentameric bacteriophage φ29 DNA packaging motor. Our results reveal the molecular interactions necessary for the coordination of ADP–ATP exchange and ATP hydrolysis of the motor’s biphasic mechanochemical cycle. We show that two distinct regulatory mechanisms determine this coordination. In the first mechanism, the DNA up-regulates a single subunit’s catalytic activity, transforming it...

Single-Crystalline Layered Metal-Halide Perovskite Nanowires for Ultrasensitive Photodetectors

J. Feng
C. Gong
H. Gao
W. Wen
Y. Gong
X. Jiang
B. Zhang
Y. Wu
Y. Wu
H. Fu
L. Jiang
X. Zhang
2018

Metal-halide perovskites have long carrier diffusion lengths, low trap densities and high carrier mobilities, and are therefore of value in the development of photovoltaics and light-emitting diodes. However, the presence of thermally activated carriers in the materials leads to high noise levels, which limits their photodetection capabilities. Here, we show that ultrasensitive photodetectors can be created from single-crystalline nanowire arrays of layered metal-halide perovskites. A series of nanowires was fabricated in which layer-by-layer self-organization of insulating organic...