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Un Jeong Kim, Jun Suk Kim, Noejung Park, Sanghyub Lee, Ukjae Lee, Yeonsang Park, Jinbong Seok, Sungwoo Hwang, Hyungbin Son, Young Hee Lee
Metal/graphene interface has been one of the most important research topics with regard to charge screening, charge transfer, contact resistance, and solar cells. Chemical bond formation of metal/graphene can be deduced from the defect induced D-band and its second-order mode, 2D band, measured by Raman spectroscopy, as a simple and non-destructive method. However, a phonon mode located at ~ 1350 cm-1 , which is normally known as the defect-induced D-band, is intriguing for graphene deposited with noble metals (Ag, Au, and Cu)...
December 5, 2018: ACS Nano
Lin Zhang, Yong Hu, Shuquan Chang, Ying-Shi Guan, Shenqiang Ren
Multicomponent crystalline heterostructures are a powerful approach to integrate different functional materials into the ordered structures. Here we describe three-dimensional spherical assembly of binary organic solids that consist of electron donor and acceptor molecules. A mechanistic study of heterostructure formation reveals that the dewetting and drying-mediated assembly processes are responsible for the spherical crystallite formation. The assembled spherical heterostructures are highly tunable, crystalline and chemically stable, exhibiting phase separation controlled optoelectronic behavior...
December 5, 2018: Nanoscale
Luojiang Zhang, K N Hui, K S Hui, Siu Wing Or
High performance of an electrode relies largely on scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. Here, a 3D heterostructured core-shell architecture was fabricated as a supercapacitor electrode, in which Co3O4 nanowire cores were grown on nickel foam prior to the in situ deposition of layered double hydroxide (LDH) nanosheet shells. Owing to the unique configuration and hybridization, the as-fabricated Co3O4@LDH core-shell electrode exhibited high capacities of 818...
December 5, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
Bin Wang, Cheng Tang, Hao-Fan Wang, Xiao Chen, Rui Cao, Qiang Zhang
A cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalyst will be significant for the future energy scenario. The emergence of the core-shell heterostructure has invoked new feasibilities to inspire the full potential of non-precious-metal candidates. The shells always have a large thickness, affording robust mechanical properties under harsh reaction conditions, which limits the full exposure of active sites with highly intrinsic reactivity and extrinsic physicochemical characters for optimal performance...
December 5, 2018: Advanced Materials
Yuanyuan Wang, Wei Wei, Baibiao Huang, Ying Dai
On the basis of first-principles calculations, we examined the possibility of functionalized transition metal carbides and nitrides (f-MXenes) as ideal electrode materials for two-dimensional (2D) Janus MoSSe through interfacial electronic properties and Schottky barriers within MoSSe/f-MXene van der Waals (vdW) heterostructures. We found that the interactions between MoSSe and f-MXenes are weak, and thus the intrinsic electronic features of MoSSe could be reserved. Based on band structure calculations, the minus n-type (vanishing) Schottky barrier heights could be assigned to MoSSe/Ti2C(OH)2 and MoSSe/Mo2C(OH)2, and the p-type Schottky barrier height assigned to Sc2NO2 turns out to be negligible...
December 5, 2018: Physical Chemistry Chemical Physics: PCCP
Reyhaneh Toufanian, Andrei Piryatinski, Andrew H Mahler, Radhika Iyer, Jennifer A Hollingsworth, Allison M Dennis
The large bulk bandgap (1.35 eV) and Bohr radius (~10 nm) of InP semiconductor nanocrystals provides bandgap tunability over a wide spectral range, providing superior color tuning compared to that of CdSe quantum dots. In this paper, the dependence of the bandgap, photoluminescence emission, and exciton radiative lifetime of core/shell quantum dot heterostructures has been investigated using colloidal InP core nanocrystals with multiple diameters (1.5, 2.5, and 3.7 nm). The shell thickness and composition dependence of the bandgap for type-I and type-II heterostructures was observed by coating the InP core with ZnS, ZnSe, CdS, or CdSe through one to ten iterations of a successive ion layer adsorption and reaction (SILAR)-based shell deposition...
2018: Frontiers in Chemistry
Seunghwan Seo, Seo-Hyeon Jo, Sungho Kim, Jaewoo Shim, Seyong Oh, Jeong-Hoon Kim, Keun Heo, Jae-Woong Choi, Changhwan Choi, Saeroonter Oh, Duygu Kuzum, H-S Philip Wong, Jin-Hong Park
The priority of synaptic device researches has been given to prove the device potential for the emulation of synaptic dynamics and not to functionalize further synaptic devices for more complex learning. Here, we demonstrate an optic-neural synaptic device by implementing synaptic and optical-sensing functions together on h-BN/WSe2 heterostructure. This device mimics the colored and color-mixed pattern recognition capabilities of the human vision system when arranged in an optic-neural network. Our synaptic device demonstrates a close to linear weight update trajectory while providing a large number of stable conduction states with less than 1% variation per state...
November 30, 2018: Nature Communications
Dongdong Gao, Yirui Wang, Yi Liu, Huiping Sun, Minghong Wu, Haijiao Zhang
The interfacial engineering plays an important role in enhancing the electrochemical properties of graphene-based hybrid materials for energy conversion and storage. Herein, we propose a facile interfacial engineering route for achieving a novel type of SnS2 /N-doped graphene (SnS2 /NG) composite with superior lithium storage capability. Interestingly, the SnS2 particles formed show two totally different morphologies including ultrasmall nanoparticles about 5 nm and ultrathin nanosheets, and they are strongly coupled with nitrogen-doped graphene, giving rise to a unique 0D/2D heterostructure...
November 26, 2018: Journal of Colloid and Interface Science
Jonas Lähnemann, David A Browne, Akhil Ajay, Mathieu Jeannin, Angela Vasanelli, Jean-Luc Thomassin, Edith Bellet-Amalric, Eva Monroy
We present a systematic study of top-down processed GaN/AlN heterostructures for intersubband optoelectronic applications. Samples containing quantum well superlattices that display either near- or mid-infrared intersubband absorption were etched into nano- and micro-pillar arrays in an inductively coupled plasma. We investigate the influence of this process on the structure and strain-state, on the interband emission and on the intersubband absorption. Notably, for pillar spacings significantly smaller (≤1/3) than the intersubband wavelength, the magnitude of the intersubband absorption is not reduced even when 90% of the material is etched away and a similar linewidth is obtained...
November 30, 2018: Nanotechnology
Mario Behrens, Andriy Lotnyk, Jürgen W Gerlach, Isom Hilmi, Tobias Abel, Pierre Lorenz, Bernd Rauschenbach
Two-dimensional van-der-Waals-bonded chalcogenide heterostructures have recently received a lot of attention due to promising applications in the fields of photonics, plasmonics and data storage. Of particular interest is the interfacial switching process inherent in these structures, which is assumed to occur locally at the van-der-Waals interfaces and thus represents an intracrystalline transition. However, detailed experimental studies on the underlying mechanism are still lacking. In this work, epitaxially grown thin films consisting of van-der-Waals-bonded Ge-Sb-Te and GeTe/Sb2Te3 based heterostructures are employed as a model system to investigate structural changes induced by a single ns-laser pulse...
November 30, 2018: Nanoscale
Aristi Christofi
In this Letter, we propose a nonreciprocal heterostructure which combines magnetism and chirality in a simple, easy-to-fabricate design and exhibits at least two orders of magnitude larger magnetochiral dichroism, compared to other proposed metamaterials. This effect stems from the simultaneous lack of time-reversal and space-inversion symmetries and is enhanced by collective slow-photon modes originating from the strong bending of the photonic bands at the Brillouin zone boundaries. We investigate the optical properties of this bianisotropic multilayer heterostructure, consisting of consecutive bilayers of chiral and magnetic materials, embedded in air, and discuss the associated photonic band structure and transmission/absorption spectra obtained by means of full electrodynamic calculations...
December 1, 2018: Optics Letters
Hongyuan Li, Zhe Ying, Bosai Lyu, Aolin Deng, Lele Wang, Takashi Taniguchi, Kenji Watanabe, Zhiwen Shi
Scanning probe lithography based on local anodic oxidation (LAO) provides a robust and general nanolithography tool for a wide range of applications. Its practical use, however, has been strongly hampered due to the requirement of a pre-fabricated micro-electrode to conduct the driving electrical current. Here we report a novel electrode-free LAO technique, which enables in-situ patterning of as-prepared low-dimensional materials and heterostructures with great flexibility and high precision. Unlike conventional LAO driven by a DC current, the electrode-free LAO is driven by a high-frequency (>10 kHz) AC current applied through capacitive coupling, which eliminates the need of a contacting electrode and can be used even for tailoring insulating materials...
November 30, 2018: Nano Letters
Weifeng Yang, Hiroyo Kawai, Michel Bosman, Baoshan Tang, Jianwei Chai, Wei Le Tay, Jing Yang, Hwee Leng Seng, Huili Zhu, Hao Gong, Hongfei Liu, Kuan Eng Johnson Goh, Shijie Wang, Dongzhi Chi
The understanding of the interlayer interactions in vertical heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is essential to exploit their advanced functions for next-generation optoelectronics and electronics. Here we demonstrate a monolithic stacking of TMDC heterostructures with 2D MoS2 and WS2 layers via in situ physical vapor deposition. We find that the kinetically sputtered atoms are able to overcome the interlayer van der Waals forces between the vertical layers, leading to a substantial number of randomly oriented stacks with various twist angles...
November 30, 2018: Nanoscale
Luise Rost, Sebastian Gies, Markus Stein, Christian Fuchs, Siegfried Nau, Pirmin Kükelhan, Kerstin Volz, Wolfgang Stolz, Martin Koch, Wolfram Heimbrodt
(Ga,In)As/GaAs/Ga(As,Sb) and (Ga,In)As/GaAs/Ga(N,As) type-II double quantum well heterostructures have been grown by metal-organic vapor phase epitaxy. A growth interruption procedure was used to intentionally modify the morphology of the internal interfaces. The heterostructures were investigated using continuous wave and time-resolved photoluminescence as well as optical pump-optical probe spectroscopy. We find a correlation between the interface morphology and optical and kinetic properties. A growth interruption of about 120 s yielded substantially smoother interfaces both on vertical as well as lateral length scales...
November 30, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Kuang-Hsu Wu, Xing Huang, Hassan Tahini, Peter Kappen, Rui Huang, Xin Tan, Ling-Yun Jang, Yuxiao Ding, Sean C Smith, Wei Qi, Ian R Gentle, Dang Sheng Su, Rose Amal, Da-Wei Wang
The interface at metal oxide-carbon hybrid heterojunction is the source to 'synergistic effect' in catalysis. Understanding the structure-function property is key for designing more advanced catalyst-support systems. Using a model MnIII-Ox single-layer catalyst on carbon, we herein report a full elucidation to the catalytic synergism at hybrid heterojunction in the oxygen reduction reaction (ORR). A successful fabrication of the single-layer catalyst from bottom-up is fully charac-terized by X-ray absorption fine structure (XAFS) and high-resolution transmission electron microscopy (HR-TEM)...
November 30, 2018: ACS Applied Materials & Interfaces
Alexander S Pashchenko, Leonid S Lunin, Eleonora M Danilina, Sergei N Chebotarev
This work reports on an experimental investigation of the influence of vertical stacking of quantum dots, the thickness of GaAs potential barriers, and their isovalent doping with bismuth on the photoluminescence properties of InAs/GaAs heterostructures. The experimental samples were grown by ion-beam deposition. We showed that using three vertically stacked layers of InAs quantum dots separated by thin GaAs barrier layers was accompanied by a red-shift of the photoluminescence peak of InAs/GaAs heterostructures...
2018: Beilstein Journal of Nanotechnology
D Lee, B Chung, Y Shi, G-Y Kim, N Campbell, F Xue, K Song, S-Y Choi, J P Podkaminer, T H Kim, P J Ryan, J-W Kim, T R Paudel, J-H Kang, J W Spinuzzi, D A Tenne, E Y Tsymbal, M S Rzchowski, L Q Chen, J Lee, C B Eom
The metal-insulator transition in correlated materials is usually coupled to a symmetry-lowering structural phase transition. This coupling not only complicates the understanding of the basic mechanism of this phenomenon but also limits the speed and endurance of prospective electronic devices. We demonstrate an isostructural, purely electronically driven metal-insulator transition in epitaxial heterostructures of an archetypal correlated material, vanadium dioxide. A combination of thin-film synthesis, structural and electrical characterizations, and theoretical modeling reveals that an interface interaction suppresses the electronic correlations without changing the crystal structure in this otherwise correlated insulator...
November 30, 2018: Science
Ke Xu, Yuanfeng Xu, Hao Zhang, Bo Peng, Hezhu Shao, Gang Ni, Jing Li, Mingyuan Yao, Hongliang Lu, Heyuan Zhu, Costas M Soukoulis
Two-dimensional (2D) transition metal dichalcogenides (TMDs) MX2 (M = Mo, W; X = S, Se, Te) possess unique properties and novel applications in optoelectronics, valleytronics and quantum computation. In this work, we performed first-principles calculations to investigate the electronic, optical and transport properties of the van der Waals (vdW) stacked MX2 heterostructures formed by two individual MX2 monolayers. We found that the so-called Anderson's rule can effectively classify the band structures of heterostructures into three types: straddling, staggered and broken gap...
November 29, 2018: Physical Chemistry Chemical Physics: PCCP
Hong Wei Qiao, Shuang Yang, Yun Wang, Xiao Chen, Tian Yu Wen, Li Juan Tang, Qilin Cheng, Yu Hou, Huijun Zhao, Hua Gui Yang
A gradient heterosturcture is one of the basic methods to control the charge flow in perovskite solar cells (PSCs). However, a classical route for gradient heterosturctures is based on the diffusion technique, in which the guest ions gradually diffuse into the films from a concentrated source of dopants. The gradient heterosturcture is only accessible to the top side, and may be time consuming and costly. Here, the "intolerant" n-type heteroatoms (Sb3+ , In3+ ) with mismatched cation sizes and charge states can spontaneously enrich two sides of perovskite thin films...
November 28, 2018: Advanced Materials
Shuiyuan Wang, Chunsheng Chen, Zhihao Yu, Yongli He, Xiaoyao Chen, Qing Wan, Yi Shi, David Wei Zhang, Hao Zhou, Xinran Wang, Peng Zhou
Just as biological synapses provide basic functions for the nervous system, artificial synaptic devices serve as the fundamental building blocks of neuromorphic networks; thus, developing novel artificial synapses is essential for neuromorphic computing. By exploiting the band alignment between 2D inorganic and organic semiconductors, the first multi-functional synaptic transistor based on a molybdenum disulfide (MoS2 )/perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) hybrid heterojunction, with remarkable short-term plasticity (STP) and long-term plasticity (LTP), is reported...
November 28, 2018: Advanced Materials
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