THIS MONTH IN NPG ASIA MATERIALS

Volume 9, July 2017

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July 28 2017

Original Article

Kinetically controlled formation of uniform FePO4 shells and their potential for use in high-performance sodium ion batteries

Shu-Yi Duan, Jun-Yu Piao, Tian-Qi Zhang, Yong-Gang Sun, Xiao-Chan Liu, An-Min Cao and Li-Jun Wan

NPG Asia Mater 9: e414; doi:10.1038/am.2017.136

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We developed a simple but effective protocol to construct uniform FePO4 coating layer on various substrates. By controlling the precipitation kinetics, we were able to form uniform FePO4 nanoshells with its thickness precisely defined in nanometer accuracy. Specifically, a core-shell structured electrode material of MWCNTs@FePO4 was constructed, which showed promising potential as a cathode material for sodium ion battery as revealed by its high discharge capacity as well as the much improved rate capability.

Original Article

Organic electronic synapses with pinched hystereses based on graphene quantum-dot nanocomposites

Hwan Young Choi, Chaoxing Wu, Chang Han Bok and Tae Whan Kim

NPG Asia Mater 9: e413; doi:10.1038/am.2017.133

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Organic electronic synapses based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/graphene quantum-dot (GQD) nanocomposites were fabricated by using a solution method. Current–voltage (IV) curves for the devices under dual positive bias voltage sweeps and under dual negative bias voltage sweeps showed that the conductance with a pinched hysteresis gradually increased and gradually decreased, respectively, with increasing applied voltage which is a fingerprint of e-synapses. The current in the devices was found to decrease with increasing concentration of GQDs in the active layer, and the devices fabricated utilizing the ratio of PEDOT:PSS to GQDs of 1:0.4 showed the best performance among the e-synapses. The carrier transport and operating mechanisms of the e-synapses are described in this paper on the basis of both the IV results and the trapping and escape of electrons from the GQDs. We believe that our letter contains significant results of interest to a broad spectrum of NPG Asia Materials readers.

Original Article

Colloidal templating of highly ordered gelatin methacryloyl-based hydrogel platforms for three-dimensional tissue analogues

Bae Hoon Lee, Hitomi Shirahama, Myung Hee Kim, Jae Ho Lee, Nam-Joon Cho and Lay Poh Tan

NPG Asia Mater 9: e412; doi:10.1038/am.2017.126

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We demonstrate the fabrication of three-dimensional, highly ordered protein-based hydrogel platforms for tissue engineering applications. The combination of colloidal templating microfabrication strategies and highly substituted, photocrosslinkable gelatin methacryloyl (GelMA) protein allowed us to fabricate inverted colloidal crystal (ICC) scaffolds with uniform pore interconnectivity, high structural stability and tailorable degradation properties. The resulting scaffolds provided cell attachment sites and promoted intercellular interaction among hepatocytes, which resulted in improved cell function compared to a flat, two-dimensional system. The results demonstrate the potential of GelMA ICC scaffolds to become an effective tissue engineering platform for drug screening and regenerative medicine applications.

Original Article

Universal high work function flexible anode for simplified ITO-free organic and perovskite light-emitting diodes with ultra-high efficiency

Su-Hun Jeong, Seong-Hoon Woo, Tae-Hee Han, Min-Ho Park, Himchan Cho, Young-Hoon Kim, Hyunsu Cho, Hobeom Kim, Seunghyup Yoo and Tae-Woo Lee

NPG Asia Mater 9: e411; doi:10.1038/am.2017.108

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We report a new anode material that has multifunction of both an anode and a hole injection layer (HIL) as a single layer. Our anode has easy work function tunability up to 5.8eV and thus makes ohmic contact without any HIL. We applied our anodes to simplified organic light-emitting diodes, resulting in high efficiency (62% phel−1 for single and 88% phel−1 for tandem). Our anode showed a similar tendency in simplified perovskite light-emitting diodes. We also demonstrated large-area flexible lightings using our anodes. Our results provide a significant step toward the next generation of high-performance simplified light-emitting diodes.

Original Article

Transferable single-crystal GaN thin films grown on chemical vapor-deposited hexagonal BN sheets

Kunook Chung, Hongseok Oh, Janghyun Jo, Keundong Lee, Miyoung Kim and Gyu-Chul Yi

NPG Asia Mater 9: e410; doi:10.1038/am.2017.118

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Here, we utilize large-size scalable single-crystal 2D films to grow single crystalline inorganic semiconductors. Centimeter-scale hexagonal boron nitride (h-BN) films were synthesized on a single-crystal Ni(111) using chemical vapor deposition (CVD). Single-crystal GaN layers were directly grown on h-BN using metal–organic vapor phase epitaxy. The CVD-grown h-BN exhibited many atomic cliffs that enabled us to grow high-density GaN islands to be merged as homogeneous and flat GaN films. We also investigated the crystallinity and growth mechanism of the GaN films grown on CVD-grown h-BN using transmission electron microscopy and X-ray diffraction.

Original Article

Homogeneous dewetting on large-scale microdroplet arrays for solution-processed electronics

Xuying Liu, Chuan Liu, Kenji Sakamoto, Takeshi Yasuda, Pan Xiong, Lijuan Liang, Tengzhou Yang, Masayuki Kanehara, Jun Takeya and Takeo Minari

NPG Asia Mater 9: e409; doi:10.1038/am.2017.123

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A Homogeneously unidirectional dewetting on large-area microdroplet arrays was developed, which was induced via the gravity-induced deformation in droplets combined with alternating lyophilic/lyophobic patterns. This process allows the scaling-up deposition of thin films including organic semiconductors and transition metal oxides as the autogenous shrinkage of droplets, which further enables the fabrication of large-area organic thin-film transistor (OTFT) arrays. The resulting field-effect mobility and on/off ratio of fully-printed OTFTs exceed 13cm2 V−1 s−1 and 108, respectively.

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July 14 2017

Original Article

In vivo targeted therapy of gastric tumors via the mechanical rotation of a flower-like Fe3O4@Au nanoprobe under an alternating magnetic field

Ting Yin, Haigang Wu, Qian Zhang, Guo Gao, Joseph G Shapter, Yulan Shen, Qiaozhi He, Peng Huang, Wen Qi, Chunlei Zhang, Yuming Yang and Daxiang Cui

NPG Asia Mater 9: e408; doi:10.1038/am.2017.117

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Despite great efforts that have focused on anticancer adjuvants, drug resistance in cancer therapy is still a challenging problem. Conventional spherical nanoprobes are unable to effectively destroy the cellular structure in therapy which means the gastric tumor has a high risk of drug resistance. Herein we developed a novel flower-like targeting Fe3O4@Au-HPG-Glc nanoprobe that can rotate along the central axis of the core and substantially destroy the tumor cells by damaging the tumor cells under an alternating magnetic field. The successful application of novel shape-dependent therapy strategy would potentially reduce drug resistance problems of gastric tumors.

Original Article

Bimetallic AuRh nanodendrites consisting of Au icosahedron cores and atomically ultrathin Rh nanoplate shells: synthesis and light-enhanced catalytic activity

Yongqiang Kang, Qi Xue, Ruili Peng, Pujun Jin, Jinghui Zeng, Jiaxing Jiang and Yu Chen

NPG Asia Mater 9: e407; doi:10.1038/am.2017.114

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The bimetallic Au@Rh core–shell nanodendrites with ultrathin Rh nanoplate shells show the light-enhanced catalytic activity for the hydrogen generation reaction from aqueous hydrazine solution.

Original Article

Route to achieving perfect B-site ordering in double perovskite thin films

Josée E Kleibeuker, Eun-Mi Choi, Edward D Jones, Tse-Min Yu, Bianca Sala, Belinda A MacLaren, Demie Kepaptsoglou, David Hernandez-Maldonado, Quentin M Ramasse, Lewys Jones, Juri Barthel, Ian MacLaren and Judith L MacManus-Driscoll

NPG Asia Mater 9: e406; doi:10.1038/am.2017.113

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To profit of the breadth of multifunctional properties that double perovskites (A2BB’O6) exhibit, it is required to have high control on cation ordering of the B-site. We show that by growing thin films under minor in-plane strain along the (111) direction, cation ordering can be stimulated as a result of the formation of two differently sized and shaped B-sites. Such an approach enables the study of many new ordered double perovskites which have never been made before.

Original Article

Micron-thick highly conductive PEDOT films synthesized via self-inhibited polymerization: roles of anions

Wei Shi, Qin Yao, Sanyin Qu, Hongyi Chen, Tiansong Zhang and Lidong Chen

NPG Asia Mater 9: e405; doi:10.1038/am.2017.107

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Micron-thick highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) films are fabricated using a novel self-inhibited polymerization (SIP) approach. The newly adopted inhibitor-free heavy oxidative solutions containing weakly basic anions (WBAs) such as dodecylbenzenesulfonate (DBSA) enables the spin-coating of thick and homogeneous oxidant layer, and meanwhile effectively inhibits both the crystallization of the oxidant and the H+ formation throughout the polymerization process.

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July 07 2017

Original Article

On the speed of piezostrain-mediated voltage-driven perpendicular magnetization reversal: a computational elastodynamics-micromagnetic phase-field study

Ren-Ci Peng, Jia-Mian Hu, Long-Qing Chen and Ce-Wen Nan

NPG Asia Mater 9: e404; doi:10.1038/am.2017.97

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Piezostrain-enabled magnetization switching in magnetic/piezoelectric heterostructures consists of multiple coupled kinetic processes that have rarely been considered together, thus an accurate computational analysis on the switching speed has remained outstanding. Here a computational approach is developed to accurately analyze the speed of such piezostrain-enabled magnetization switching by linking local elastodynamics in the piezoelectric to local magnetization dynamics in the magnet. For example, the approach is utilized to analyze the speed of a recently proposed scheme of piezostrain-enabled 180° perpendicular magnetization switching, where the overall switching time is shown to be below 10ns in a model CoFeB/Pb(Zr,Ti)O3 heterostructure.

Original Article

Platinum loaded on dual-doped TiO2 as an active and durable oxygen reduction reaction catalyst

Bing-Jen Hsieh, Meng-Che Tsai, Chun-Jern Pan, Wei-Nien Su, John Rick, Jyh-Fu Lee, Yaw-Wen Yang and Bing-Joe Hwang

NPG Asia Mater 9: e403; doi:10.1038/am.2017.78

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Dual-ion doping: Through theoretical and experimental methods, we determined that dual-doped TiO2 has a much higher electron conductivity than that of single-doped TiO2, and more Pt occupies the defect sites of dual-doped TiO2. Pt on this dual-doped support is almost three times more active than Pt on single-doped TiO2 and is more stable than Pt on carbon.

Original Article

Van der Waals epitaxy between the highly lattice mismatched Cu-doped FeSe and Bi2Te3

Arsham Ghasemi, Demie Kepaptsoglou, Pedro L Galindo, Quentin M Ramasse, Thorsten Hesjedal and Vlado K Lazarov

NPG Asia Mater 9: e402; doi:10.1038/am.2017.111

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One of the main criteria for realising new, interface-related heterostructure behaviours is the ability to control the atomic and electronic properties on an atomic level which typically requires creating epitaxially matched superlattices. Here, we demonstrate that single-crystalline, misfit-dislocation free interfaces between tetragonal Cu-doped FeSe and trigonal Bi2Te3 symmetry lattices with very large lattice mismatch (19%) can be realised due to the van der Waals-like bonding between the FeSe and Bi2Te3. The atomically resolved interface structure analysis and DFT calculations show that the Se and Te atomic columns are relaxed, so the overall strain is less than 10% and the energy cost associated with such displacements is less than 0.01eV, which is significantly lower than the thermal energy at room temperature (0.0257eV).

Original Article

Beyond 8% ultrathin kesterite Cu2ZnSnS4 solar cells by interface reaction route controlling and self-organized nanopattern at the back contact

Fangyang Liu, Jialiang Huang, Kaiwen Sun, Chang Yan, Yansong Shen, Jongsung Park, Aobo Pu, Fangzhou Zhou, Xu Liu, John A Stride, Martin A Green and Xiaojing Hao

NPG Asia Mater 9: e401; doi:10.1038/am.2017.103

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Over 8% efficient ultrathin kesterite Cu2ZnSnS4 (CZTS) solar cells have been developed by interface reaction route controlling and self-organized nanopattern at the back contact. An ultrathin dielectric Al2O3 intermediate layer is inserted into the Mo/CZTS interface to inhibit the detrimental interfacial reaction between CZTS and Mo, and then turns into a self-organized nanopatterning with opening for electrical contact. The typical issues of phase segregation and voids at the back contact region therefore can be addressed, which reduces back contact recombination and improves the device performance. A 7.6% efficiency world record for 1cm2 CZTS solar cells also has been achieved by this interface modification.

Original Article

Three-dimensional buckled honeycomb boron lattice with vacancies as an intermediate phase on the transition pathway from α-B to γ-B

Woo Hyun Han, Young Jun Oh, Duk-Hyun Choe, Sunghyun Kim, In-Ho Lee and Kee Joo Chang

NPG Asia Mater 9: e400; doi:10.1038/am.2017.98

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We report the discovery of novel metastable boron allotropes, called hex-Bν, using the crystal structure search method. First-principles calculations reveal that hex-Bν shows not only dynamical, mechanical stability but also structural flexibility under high pressures and high temperatures. We suggest a new pressure-induced transition pathway from α-B12 to γ-B28 under extreme conditions, in which our discovered allotropes can act as intermediate phases. This work provides a possible solution to the long-standing fundamental question on the phase transition mechanism between boron allotropes.

Original Article

Construction of a photothermal Venus flytrap from conductive polymer bimorphs

Hanwhuy Lim, Teahoon Park, Jongbeom Na, Chihyun Park, Byeonggwan Kim and Eunkyoung Kim

NPG Asia Mater 9: e399; doi:10.1038/am.2017.101

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A photothermally foldable soft bimorph was prepared by dry transfer of poly(3,4-ethylenedioxythiophene)s (PEDOT) onto poly(dimethylsiloxane) film. The reversible folding nature of the soft bimorph was programmable to convert the two-dimensional (2D) array of bimorph into complex three-dimensional (3D) architectures such as Venus flytrap under light. These 3D structures were returned reversibly to the original unfolded 2D structures under dark. The Venus flytrap could perform a task to snap and move an object within few second of near-infrared exposure. A localized heat pocket was generated inside the folding structure due to the large photothermal effect of PEDOT.

Original Article

Full picture discovery for mixed-fluorine anion effects on high-voltage spinel lithium nickel manganese oxide cathodes

Dae-wook Kim, Hiromasa Shiiba, Nobuyuki Zettsu, Tetsuya Yamada, Takeshi Kimijima, Gabriel Sánchez-Santolino, Ryo Ishikawa, Yuichi Ikuhara and Katsuya Teshima

NPG Asia Mater 9: e398; doi:10.1038/am.2017.90

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We demonstrated experimental and theoretical approaches to obtain a full picture of the mixed-anion effects for LiNi0.5Mn1.5O4−xFx cathode materials. The fluorine anion reduced the activation barrier for lithium (Li)-ion hopping along the most energetically preferable 8a-16c-8a route, enhancing the C-rate capability. Simultaneously, the coordination bond of the linear F–Mn3+–F (Mn@2F diagonal) arrangement increased the oxidation potential to 5.1V (vs Li+/Li). This hampered full extraction of Li+ from the spinel lattice, which was triggered by the oxidation of Mn3+ below the cutoff voltage (3.5–4.8V (vs Li+/Li)), leading to a capacity loss.

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