2020 New's Items

Subwavelength pixelated CMOS color sensors based on anti-Hermitian metasurface

J. S. T. Smalley
X. Ren
J. Y. Lee
W. Ko
W.-J. Joo
H. Park
S. Yang
Y. Wang
C. S. Lee
H. Choo
S. Hwang
X. Zhang
2020

The demand for essential pixel components with ever-decreasing size and enhanced performance is central to current optoelectronic applications, including imaging, sensing, photovoltaics and communications. The size of the pixels, however, are severely limited by the fundamental constraints of lightwave diffraction. Current development using transmissive filters and planar absorbing layers can shrink the pixel size, yet there are two major issues, optical and electrical crosstalk, that need to be addressed when the pixel dimension approaches wavelength scale. All these fundamental...

Direct observation of Klein tunneling in phononic crystals

X. Jiang
C. Shi
S. Wang
Y. Wang
S. Yang
S. G. Louie
X. Zhang
Z. Li
2020

Tunneling plays an essential role in many branches of physics and has found important applications. It is theoretically proposed that Klein tunneling occurs when, under normal incidence, quasiparticles exhibit unimpeded penetration through potential barriers independent of their height and width. We created a phononic heterojunction by sandwiching two types of artificial phononic crystals with different Dirac point energies. The direct observation of Klein tunneling as shown by the key feature of unity transmission is demonstrated. Our experiment reveals that Klein tunneling occurs...

Design and synthesis of multigrain nanocrystals via geometric misfit strain

Myoung Hwan Oh
Min Gee Cho
Dong Young Chung
Inchul Park
Youngwook Paul Kwon
Colin Ophus
Dokyoon Kim
Min Gyu Kim
Beomgyun Jeong
X. Wendy Gu
Jinwoung Jo
Ji Mun Yoo
Jaeyoung Hong
Sara McMains
Kisuk Kang
Yung-Eun Sung
A. Paul Alivisatos
Taeghwan Hyeon
2020

The impact of topological defects associated with grain boundaries (GB defects) on the electrical, optical, magnetic, mechanical and chemical properties of nanocrystalline materials1,2 is...

Critical differences in 3D atomic structure of individual ligand-protected nanocrystals in solution

Byung Hyo Kim
Junyoung Heo
Sungin Kim
Cyril F. Reboul
Hoje Chun
Dohun Kang
Hyeonhu Bae
Hyejeong Hyun
Jongwoo Lim
Hoonkyung Lee
Byungchan Han
Taeghwan Hyeon
A. Paul Alivisatos
Peter Ercius
Hans Elmlund
Jungwon Park
2020

Precise three-dimensional (3D) atomic structure determination of individual nanocrystals is a prerequisite for understanding and predicting their physical properties. Nanocrystals from the same synthesis batch display what are often presumed to be small but possibly important differences in size, lattice distortions, and defects, which can only be understood by structural characterization with high spatial 3D resolution. We solved the structures of individual colloidal platinum nanocrystals by developing atomic-resolution 3D liquid-cell electron microscopy to reveal critical...

Scaling Laws of Exciton Recombination Kinetics in Low Dimensional Halide Perovskite Nanostructures

Mengyu Gao
Hao Liu
Sunmoon Yu
Sheena Louisia
Ye Zhang
David P. Nenon
A. Paul Alivisatos
Peidong Yang
2020

Carrier recombination is a crucial process governing the optical properties of a semiconductor. Although various theoretical approaches have been utilized to describe carrier behaviors, a quantitative understanding of the impact of defects and interfaces in low dimensional semiconductor systems is still elusive. Here, we develop a model system consisting of chemically tunable, highly luminescent halide perovskite nanocrystals to illustrate the role of carrier diffusion and material dimensionality on the carrier recombination kinetics and luminescence efficiency. Our advanced...

Self-Limiting Shell Formation in Cu@Ag Core–Shell Nanocrystals during Galvanic Replacement

Gaurav A. Kamat
Chang Yan
Wojciech T. Osowiecki
Ivan A. Moreno-Hernandez
Marc Ledendecker
A. Paul Alivisatos
2020

The understanding of synthetic pathways of bimetallic nanocrystals remains limited due to the complex energy landscapes and dynamics involved. In this work, we investigate the formation of self-limiting Cu@Ag core–shell nanoparticles starting from Cu nanocrystals followed by galvanic replacement with Ag ions. Bulk quantification with atomic emission spectroscopy and spatially resolved elemental mapping with electron microscopy reveal distinct nucleation regimes that produce nanoparticles with a tunable Ag shell thickness, but only up to a certain limiting...

Perovskite-Carbon Nanotube Light-Emitting Fibers

Vida Jamali
Farnaz Niroui
Lauren W. Taylor
Oliver S. Dewey
Brent A. Koscher
Matteo Pasquali
A. Paul Alivisato
2020

Active fibers with electro-optic functionalities are promising building blocks for the emerging and rapidly growing field of fiber and textile electronics. Yet, there remains significant challenges that require improved understanding of the principles of active fiber assembly to enable the development of fiber-shaped devices characterized by having a small diameter, being lightweight, and having high mechanical strength. To this end, the current frameworks are insufficient, and new designs and fabrication approaches are essential to accommodate this unconventional form factor. Here,...

Real-time observation of dynamic structure of liquid-vapor interface at nanometer resolution in electron irradiated sodium chloride crystals

Amy Ren
David Lu
Edward Wong
Matthew R. Hauwiller
A. Paul Alivisatos
Gang Ren
2020

The dynamics and structure of the liquid and vapor interface has remained elusive for decades due to the lack of an effective tool for directly visualization beyond micrometer resolution. Here, we designed a simple liquid-cell for encapsulating the liquid state of sodium for transmission electron microscopic (TEM) observation. The real-time dynamic structure of the liquid-vapor interface was imaged and videoed by TEM on the sample of electron irradiated sodium chloride (NaCl) crystals, a well-studied sample with low melting temperature and quantum super-shells of clusters. The...

Elucidating the Weakly Reversible Cs–Pb–Br Perovskite Nanocrystal Reaction Network with High-Throughput Maps and Transformations

Jakob C. Dahl
Xingzhi Wang
Xiao Huang
Emory M. Chan
A. Paul Alivisatos
2020

Advances in automation and data analytics can aid exploration of the complex chemistry of nanoparticles. Lead halide perovskite colloidal nanocrystals provide an interesting proving ground: there are reports of many different phases and transformations, which has made it hard to form a coherent conceptual framework for their controlled formation through traditional methods. In this work, we systematically explore the portion of Cs–Pb–Br synthesis space in which many optically distinguishable species are formed using high-throughput robotic synthesis to understand their formation...

Sub-Bandgap Photoinduced Transient Absorption Features in CdSe Nanostructures: The Role of Trapped Holes

Dipti Jasrasaria
John P. Philbin
Chang Yan
Daniel Weinberg
A. Paul Alivisatos
Eran Rabani
2020

Transient absorption (TA) is widely used to study the dynamics of various processes, such as trapping, nonradiative decay, or transferring of photoexcited carriers in semiconductor nanocrystals. TA spectra of these systems show photoinduced absorption (PA) features that appear lower in energy than those of the band edge, which have been attributed to sub-bandgap absorptions of photoexcited electrons and holes. Here, we perform atomistic, semiempirical pseudopotential calculations in CdSe nanostructures to compute oscillator strengths for sub-bandgap transitions of conduction band...