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Nano Letters

Dima Bolmatov, Mikhail Zhernenkov, Lewis Sharpnack, Dena M Agra-Kooijman, Satyendra Kumar, Alexey Suvorov, Ronald Pindak, Yong Q Cai, Alessandro Cunsolo
The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in Inelastic X-ray Scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems...
May 26, 2017: Nano Letters
Jinhua Hong, Yuhao Pan, Zhixin Hu, Danhui Lv, Chuanhong Jin, Wei Ji, Jun Yuan, Ze Zhang
Direct observation of atomic migration both on and below surfaces is a long-standing but important challenge in materials science as diffusion is one of the most elementary processes essential to many vital material behaviors. Probing the kinetic pathways, including metastable or even transition states involved down to atomic scale, holds the key to the underlying physical mechanisms. Here, we applied aberration-corrected transmission electron microscopy (TEM) to demon-strate direct atomic-scale imaging and quasi-real-time tracking of diffusion of Mo adatoms and vacancies in monolayer MoS2, an important 2D transition metal dichalcogenide (TMD) system...
May 26, 2017: Nano Letters
Ayan Kumar Biswas, Hasnain Ahmad, Jayasimha Atulasimha, Supriyo Bandyopadhyay
Rotating the magnetization of a shape anisotropic magnetostrictive nanomagnet with voltage-generated stress/strain dissipates much less energy than most other magnetization rotation schemes, but its application to writing bits in non-volatile magnetic memory has been hindered by the fundamental inability of stress/strain to rotate magnetization by full 180(o). Normally, stress/strain can rotate the magnetization of a shape anisotropic elliptical nanomagnet by only up to 90(o), resulting in incomplete magnetization reversal...
May 26, 2017: Nano Letters
Hannu-Pekka Komsa, Ryosuke Senga, Kazutomo Suenaga, Arkady V Krasheninnikov
Atomic chains are perfect systems for getting fundamental insights into the electron dynamics and coupling between the electronic and ionic degrees of freedom in one dimensional metals. Depending on the band filling, they can exhibit Peierls instabilities (or charge density waves), where equally spaced chain of atoms with partially filled band is inherently unstable, exhibiting spontaneous distortion of the lattice that further leads to metal-insulator transition in the system. Here, using high-resolution scanning transmission electron microscopy, we directly image the atomic structures of a chain of iodine atoms confined inside carbon nanotubes...
May 26, 2017: Nano Letters
Hao Liu, Mark Wolf, Khim Karki, Young-Sang Yu, Eric A Stach, Jordi Cabana, Karena W Chapman, Peter J Chupas
Capacity fading has limited commercial layered Li-ion battery electrodes to <70% of their theoretical capacity. Higher capacities can be achieved initially by charging to higher voltages, however, these gains are eroded by a faster fade in capacity. Increasing lifetimes and reversible capacity are contingent on identifying the origin of this capacity fade to inform electrode design and synthesis. We used operando X-ray diffraction, to observe how the lithiation-delithiation reactions within a LiNi0.8Co0...
May 26, 2017: Nano Letters
Toru Hirahara, Sergey V Eremeev, Tetsuroh Shirasawa, Yuma Okuyama, Takayuki Kubo, Ryosuke Nakanishi, Ryota Akiyama, Akari Takayama, Tetsuya Hajiri, Shinichiro Ideta, Masaharu Matsunami, Kazuki Sumida, Koji Miyamoto, Yasumasa Takagi, Kiyohisa Tanaka, Taichi Okuda, Toshihiko Yokoyama, Shin-Ichi Kimura, Shuji Hasegawa, Evgueni V Chulkov
Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) for technological applications. While most studies have focused on doping magnetic impurities to open a gap at the surface-state Dirac point, many undesirable effects have been reported to appear in some cases that makes it difficult to determine whether the gap opening is due to the time-reversal symmetry breaking or not. Furthermore, the realization of the QAHE has been limited to low temperatures...
May 26, 2017: Nano Letters
Mikhail Dunaevskiy, Pavel Geydt, Erkki Lähderanta, Prokhor Alekseev, Tuomas Haggrén, Joona-Pekko Kakko, Hua Jiang, Harri Lipsanen
The Young's modulus of thin conical InP nanowires with either wurtzite or mixed "zinc blende/wurtzite" structures was measured. It has been shown that the value of Young's modulus obtained for wurtzite InP nanowires (E[0001] = 130 ± 30 GPa) was similar to the theoretically predicted value for the wurtzite InP material (E[0001] = 120 ± 10 GPa). The Young's modulus of mixed "zinc blende/wurtzite" InP nanowires (E[111] = 65 ± 10 GPa) appeared to be 40% less than the theoretically predicted value for the zinc blende InP material (E[111] = 110 GPa)...
May 26, 2017: Nano Letters
Dahong Chen, Lele Peng, Yifei Yuan, Yue Zhu, Zhiwei Fang, Chunshuang Yan, Gang Chen, Reza Shahbazian-Yassar, Jun Lu, Khalil Amine, Guihua Yu
A general template-directed strategy is developed for the controlled synthesis of two-dimensional (2D) Co3O4 nanosheets with unique holey architecture and tunable hole sizes that enable greatly improved alkali-ion storage properties (demonstrated for both Li and Na ion storage). The as-synthesized holey Co3O4 nanosheets with 10 nm holes exhibit excellent reversible capacities of 1324 mAh/g at 0.4 A/g and 566 mAh/g at 0.1 A/g, for Li and Na ion storage, respectively. The improved alkali-ion storage properties are attributed to the unique interconnected holey framework that enables efficient charge/mass transport as well as accommodates volume expansion...
May 25, 2017: Nano Letters
Ying Liu, Yinlian Zhu, Yunlong Tang, Yujia Wang, Yixiao Jiang, Yaobin Xu, Bin Zhang, Xiuliang Ma
Ferroelectrics hold promise for sensors, transducers, and telecommunications. With the demand of electronic devices scaling down, they take the form of nanoscale films. However, the polarizations in ultrathin ferroelectric films are usually reduced dramatically due to the depolarization field caused by incomplete charge screening at interfaces, hampering the integrations of ferroelectrics into electric devices. Here, we design and fabricate a ferroelectric/multiferroic BiFeO3/PbTiO3 system, which exhibits discontinuities in both chemical valence and ferroelectric polarization across the interface...
May 25, 2017: Nano Letters
Taekhee Ryu, Yves Lansac, Yun Hee Jang
A fullerene derivative with five hydroxyphenyl groups attached around a pentagon, (4-HOC6H4)5HC60 (1), has shown an asymmetric current-voltage (I-V) curve in a conducting atomic force microscopy experiment on gold. Such molecular rectification has been ascribed to the asymmetric distribution of frontier molecular orbitals over its shuttlecock-shaped structure. Our non-equilibrium Green's function (NEGF) calculations based on density functional theory (DFT) indeed exhibit an asymmetric I-V curve for 1 standing up between two Au (111) electrodes, but the resulted rectification ratio (RR ~ 3) is insufficient to explain the wide range of RR observed in experiments performed under a high bias voltage...
May 25, 2017: Nano Letters
Tomer Lewi, Hayden A Evans, Nikita A Butakov, Jon A Schuller
Subwavelength Mie resonators have enabled new classes of optical antenna and nanophotonic devices and can act as the basic meta-atoms constituents of low-loss dielectric metasurfaces. In any application, tunable Mie resonances are key to achieving dynamic and reconfigurable operation. However, active tuning of these nanoantennas is still limited and usually results in sub-linewidth resonance tuning. Here, we demonstrate ultra-wide dynamic tuning of PbTe Mie resonators fabricated via both laser ablation and a novel solution-processing approach...
May 25, 2017: Nano Letters
Rui Su, Carole Diederichs, Jun Wang, Timothy C H Liew, Jiaxin Zhao, Sheng Liu, Weigao Xu, Zhanghai Chen, Qihua Xiong
Polariton lasing is the coherent emission arising from a macroscopic polariton condensate first proposed in 1996. Over the past two decades, polariton lasing has been demonstrated in a few inorganic and organic semiconductors in both low and room temperatures. Polariton lasing in inorganic materials significantly relies on sophisticated epitaxial growth of crystalline gain medium layers sandwiched by two distributed Bragg reflectors in which combating the built-in strain and mismatched thermal properties is nontrivial...
May 25, 2017: Nano Letters
Lucas Lafetá, Alisson Ronieri Cadore, Thiago Grasiano Mendes-de-Sa, Kenji Watanabe, Takashi Taniguchi, Leonardo Cristiano Campos, Ado Jorio, Leandro M Malard
In this work we probe the third-order non-linear optical property of graphene, hexagonal boron nitride and their heterostructure by the use of coherent anti-Stokes Raman Spectroscopy. When the energy difference of the two input fields match the phonon energy, the anti-Stokes emission intensity is enhanced in h-BN, as usually expected while for graphene an anomalous decrease is observed. This behaviour can be understood in terms of a coupling between the electronic continuum and a discrete phonon state. We have also measured a graphene/h-BN heterostructure and demonstrate that the anomalous effect in graphene dominates the heterostructure non-linear optical response...
May 25, 2017: Nano Letters
Thang Pham, Ashley L Gibb, Zhenglu Li, S Matt Gilbert, Chengyu Song, Steven G Louie, Alex Zettl
No abstract text is available yet for this article.
May 25, 2017: Nano Letters
Hengming Huang, Baoying Dai, Wei Wang, Chunhua Lu, Jiahui Kou, Yaru Ni, Lianzhou Wang, Zhongzi Xu
Element doping has been extensively attempted to develop visible-light-driven photocatalysts, which introduces impurity levels and enhances light absorption. However, the dopants can also become recombination centers for photogenerated electrons and holes. To address the recombination challenge, we report a gradient phosphorus-doped CdS (CdS-P) homojunction nanostructure, creating an oriented built-in electric-field for efficient extraction of carriers from inside to surface of the photocatalyst. The apparent quantum efficiency (AQY) based on the cocatalyst-free photocatalyst is up to 8...
May 25, 2017: Nano Letters
Dingchang Lin, Yayuan Liu, Wei Chen, Guangmin Zhou, Kai Liu, Bruce Dunn, Yi Cui
Research on lithium (Li) metal chemistry has been rapidly gaining momentum nowadays not only because of the appealing high theoretical capacity, but also its indispensable role in the next-generation Li-S and Li-air batteries. However, two root problems of Li metal, namely high reactivity and infinite relative volume change during cycling, bring about numerous other challenges that impede its practical applications. In the past, extensive studies have targeted these two root causes by either improving interfacial stability or constructing a stable host...
May 25, 2017: Nano Letters
Yixuan Yu, Dian Yu, Christine A Orme
Nanocrystal superlattices are typically fabricated by either solvent evaporation or destabilization methods that require long time periods to generate highly ordered structures. In this paper, we report for the first time the use of electric fields to reversibly drive nanocrystal assembly into superlattices without changing solvent volume or composition, and show that this method only takes 20 min to produce polyhedral colloidal crystals, which would otherwise need days or weeks. This method offers a way to control the lattice constants and degree of preferential orientation for superlattices and can suppress the uniaxial superlattice contraction associated with solvent evaporation...
May 25, 2017: Nano Letters
Tianyi Ma, Xiangnan Yu, Huiyu Li, Wenguang Zhang, Xiaolu Cheng, Wentao Zhu, Xinping Qiu
A novel design of hollow structured SnO2@Si nanospheres was presented, which not only demonstrates high volumetric capacity as anode of LIBs, but also prevents aggregation of Sn and confines solid electrolyte interphase thickening. An impressive volumetric specific capacity of 1030 mAh cm-3 was maintained after 500 cycles. The electrochemical impedance spectroscopy and differential scanning calorimetry indicated that solid electrolyte interphase can be confined in pores of as-prepared hollow structured SnO2@Si...
May 24, 2017: Nano Letters
Yifei Jiang, Muskendol Novoa, Teeranan Nongnual, Rhonda Powell, Terri F Bruce, Jason D McNeill
Small semiconductor structures often exhibit "telegraph noise". If the number of charge carriers is small, then spontaneous changes in the number of carriers can lead to abrupt switching between two or more discrete levels, leading to burst noise or popcorn noise in transistors. We have observed similar behavior in the fluorescence of organic semiconductor nanoparticles, where typical carrier populations are often less than ~10 carriers per nanoparticle. Spontaneous changes in the number of charges results in abrupt switching between 2 or more fluorescence intensity levels, since the charges act as highly efficient fluorescence quenchers...
May 24, 2017: Nano Letters
Martin Hjort, Peter Kratzer, Sebastian Lehmann, Sahil J Patel, Kimberly A Dick, Chris J Palmstrom, Rainer Timm, Anders Mikkelsen
We study the surface diffusion and alloying of Sb into GaAs nanowires (NWs) with controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal phases. Using atomically resolved scanning tunneling microscopy, we find that Sb preferentially incorporates into the surface layer of the {110}-terminated Zb segments rather than the {112 ̅0}-terminated Wz segments. Density functional theory calculations verify the higher surface incorporation rate into the Zb phase and find that it is related to differences in the energy barrier of the Sb-for-As exchange reaction on the two surfaces...
May 24, 2017: Nano Letters
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