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High-resolution characterization of hexagonal boron nitride coatings exposed to aqueous and air oxidative environments

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Nano Research 2017年第6期10卷 2046-2055页

作者： Lanlan Jiang Na Xiao Bingru Wang Enric Grustan-Gutierrez Xu Jing Petr Babor Miroslav Kogbal Guangyuan Lu Tianru Wu Haomin Wang Fei Hui Yuanyuan Shi Bo Song Xiaoming Xie Mario Lanza Institute of Functional Nano & Soft Materials (FUNSOM) Soochow University Suzhou 215123 China CEITEC BUT Brno University of Technology Brno 61669 Czech Republic State Key Laboratory of Functional Materials for In formatics Shanghai Institute of Microsystems and Information Technology Chinese Academy of Sciences Shanghai 200050 China School of Physical Science and Technology Shanghai Tech University Shanghai 201210 China

Hexagonal boron nitride （h-BN） is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature, which facilitates blocking the flow of electrons, thereby preventing the occurrence of galvanic reactions. Nevertheless, this may not be the case when an h-BN-protected material is exposed to aqueous environments. In this work, we analyzed the stability of mono and multilayer h-BN stacks exposed to H202 and atmospheric conditions. Our experiments revealed that monolayer h-BN is as inefficient as graphene as a protective coating when exposed to H202. Multilayer h-BN offered a good degree of protection. Monolayer h-BN was found to be ineffective in an air atmosphere as well. Even a 10-15 layers-thick h-BN stack could not completely protect the surface of the metal under consideration. By combining Auger electron spectroscopy and secondary ion mass spectrometry techniques, we observed that oxygen could diffuse through the grain boundaries of the h-BN stack to reach the metallic substrate. Fortunately, because of the diffusive nature of the process, the oxidized area did not increase with time once a saturated state was reached. This makes multflayer （not monolayer） h-BN a suitable long-term oxidation barrier. Oxygen infiltration could not be observed by X-ray photoelectron spectroscopy. This technique cannot assess the chemical composition of the deeper layers of a material. Hence, the previous reports, which relied on XPS to analyze the passivating properties of h-BN and graphene, may have ignored some important subsurface phenomena. The results obtained in this study provide new insights into the passivating properties of mono and multilayer h-BN in aqueous media and the degradation kinetics of h-BN-coated metals exposed to an air environment.

关键词： hexagonal boron nitride protective coating local oxidation nanoscale two-dimensional (2D)materials

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Ageing mechanisms and reliability of graphene-based electrodes

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Nano Research 2014年第12期7卷 1820-1831页

作者： Yuanyuan Shi Yanfeng Ji Fei Hui Hai-Hua Wu Mario Lanza Institute of Functional Nano & Soft Materials Soochow University 199 Ren-Ai Road Suzhou Industrial Park Suzhou Jiangsu 215123China

The development of flexible transparent electrodes for next generation devices has been appointed as the major topic in carbon electronics research for the next five years. Among all candidate materials tested to date, graphene and graphene based nanocomposites have shown the highest performance. Although some incipient anti-oxidation tests have been reported, in-deep ageing studies to assess the reliability of carbon-based electrodes have never been performed before. In this work, we present a disruptive methodology to assess the ageing mechanisms of graphene electrodes, which is also extensible to other carbon- based and two-dimensional materials. After performing accelerated oxidative tests, we exhaustively analyze the yield of the electrodes combining nanoscale and device level experiments with Weibull probabilistic analyses and tunneling current simulation, based on the Fowler-Nordheim/Direct-Tunneling models. Our experiments and calculations reveal that an ultra-thin oxide layer can be formed on the pristine surface of graphene. We quantitatively analyze the consequences of this layer on the properties of the electrodes, and observed a change in the conduction mode at the interface （from Ohmic to Schottky）, an effect that should be considered in the design of future graphene-based devices. Future mass production of carbon-based devices should include similar reliability studies, and the methodologies presented here （including the accelerated tests, characterization and modeling） may help other scientists to move from lab prototypes towards industrial device production.

关键词： electrode local oxidation conductive atomic force microscopy (CAFM) tunneling

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Electrical and mechanical performance of graphene sheets exposed to oxidative environments

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Nano Research 2013年第7期6卷 485-495页

作者： Mario Lanza Yan Wang Teng Gao Albin Bayerl Marc Porti Montserrat Nafria Yangbo Zhou Guangyin Jing Yanfeng Zhang Zhongfan Liu Dapeng Yu Huiling Duan State Key Laboratory for Turbulence and Complex System Department of Mechanics and Aerospace Engineering CAPT College of Engineering Peking University Beijing 100871 China Beijing Aeronautical Science and Technology Research Institute Beijing 10221 I China Center for Nanochemistry (CNC) Beijing National Laboratory for Molecular Sciences State Key Laboratory for Structural Chemistry of Unstable and Stable Species College of Chemistry and Molecular Engineering Academy for Advanced Interdisciplinary Studies Peking University Beijing 100871 China Electronic Engineering Department Universitat Autonoma de Barcelona Cerdanyola del Valles 08193 Spain Department of Physics State Key Laboratory for Mesoscopic Physics Peking University Beijing 100871 China Physics Department Northwest University Xi'an 710069 China

Graphene coatings have been shown to protect the underlying material from oxidation when exposed to different media. However, the passivating properties of graphene in air at room temperature, which corresponds to the operating conditions of many electronic devices, still remain undear. In this work, we analyze the oxidation kinetics of graphene/Cu samples in air at room temperature for long periods of time （from I day to 113 days） using scanning electron microscopy, conductive atomic force microscopy and Auger electron microscop3~ and we compare the results with those obtained for similar samples treated in H202. We observe that unlike the graphene sheets exposed to H202, in which the accumulation of oxygen at the graphene domain boundaries evolves in a very controlled and progressive way, the local oxidation of graphene in air happens in a disordered manner. In both cases the oxide hillocks formed at the graphene domain boundaries can propagate to the domains until reaching a limiting width and height. Our results demonstrate that the local oxidation of the underlying material along the domain boundaries can dramatically decrease the roughness, conductivity, mechanical resistance and frictional characteristics of the graphene sheet, which reduces the performance of the whole device.

关键词： graphene local oxidation domain boundary passivating layer

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