Search query: Etching and narrowing of graphene from the edges

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abstract: Large scale graphene electronics requires lithographic patterning of narrow graphene nanoribbons for device integration. However, conventional lithography can only reliably pattern approximately 20 nm wide GNR arrays limited by lithography resolution, while sub 5 nm GNRs are desirable for high on/off ratio field effect transistors at room temperature. Here, we devised a gas phase chemical approach to etch graphene from the edges without damaging its basal plane. The reaction involved high temperature oxidation of graphene in a slightly reducing environment in the presence of ammonia to afford controlled etch rate (less than or approximately 1 nm min( 1) We fabricated approximately 20 30 nm wide graphene nanoribbon arrays lithographically, and used the gas phase etching chemistry to narrow the ribbons down to <10 nm. For the first time, a high on/off ratio up to approximately 10(4) was achieved at room temperature for field effect transistors built with sub 5 nm wide graphene nanoribbon semiconductors derived from lithographic patterning and narrowing. Our controlled etching method opens up a chemical way to control the size of various graphene nano structures beyond the capability of top down lithography.
author_names: Xinran Wang

H Dai
title: Etching and narrowing of graphene from the edges.
venue: Nature chemistry
year: 2010

abstract: Opening the transport gap in graphene by minimizing its width is highly desirable to achieve outstanding switching performance, i.e. the high on/off ratio, in its field effect transistors (FETs) In this letter, we propose a simple method to open a comparable transport gap in graphene by narrowing down it into graphene nanoribbon (GNR) via the conventional nanofabrication procedure. In the process, GNR capped with a 50 nm wide hydrogen silsesquioxane mask is trimmed down from the edges by lateral plasma etching. The on/off ratio of the FET device is dramatically enhanced by two orders of magnitude as etching duration increases. The large on/off ratios of ~47 and ~105 are achieved at room temperature and 5.4 K, respectively. The electrical measurement reveals a transport gap opening of ~145 meV in GNR, which corresponds to a resulting width of <10 nm.
author_names: Jian Sun

Takuya Iwasaki

Manoharan Muruganathan

Hiroshi Mizuta
title: Lateral plasma etching enhanced on/off ratio in graphene nanoribbon field effect transistor
year: 2015

abstract: We devised a controlled hydrogen plasma reaction at 300 degC to etch graphene and graphene nanoribbons (GNRs) selectively at the edges over the basal plane. Atomic force microscope imaging showed that the etching rates for single layer and few layer =2 layers) graphene are 0.27 0.05 nm/min and 0.10 0.03 nm/min, respectively. Meanwhile, Raman spectroscopic mapping revealed no D band in the planes of single layer or few layer graphene after the plasma reaction, suggesting selective etching at the graphene edges without introducing defects in the basal plane. We found that hydrogen plasma at lower temperature (room temperature) or a higher temperature (500 degC) could hydrogenate the basal plane or introduce defects in the basal plane. Using the hydrogen plasma reaction at the intermediate temperature (300 degC) we obtained narrow, presumably hydrogen terminated GNRs (sub 5 nm) by etching of wide GNRs derived from unzipping of multiwalled carbon nanotubes. Such GNRs exhibited semiconducting characteristics with high on/off ratios ~1000) in GNR field effect transistor devices at room temperature.
author_names: Liming Xie

Liying Jiao

H Dai
title: Selective etching of graphene edges by hydrogen plasma.
venue: Journal of the American Chemical Society
year: 2010

abstract: We report a facile one step in situ synthesis of amino functionalized graphene dots. These quantum dots were employed for the detection of glucose in both standard aqueous solutions and commercially available fruit juice to assess its practicability. The characterization of the quantum dots revealed that they were decorated with amine functionality. Additionally, the interaction between glucose and amine functionalized graphene quantum dots gave enhancement in the UV vis absorption and photoluminescence (PL) due to aggregation of quantum dots via glucose link. Therefore, the quantum dots were able to detect the concentration of glucose in solution exhibiting linearity from 0.1 to 10 mM and 50 500 mM with a sensitivity transition from 10 mM to 50 mM. The limit of detection for the determination of glucose was found to be 10 mM. This determination was agreed from both UV Vis absorption and PL spectroscopy. However, the PL emission method of determination was most suited with its very high accuracy of 98.04 1.96% and 97.33 2.67% for the linear range of glucose concentration within 0.1 10 mM and 50 500 mM, respectively. The PL enhancement was highly selective towards glucose in mixture of other form of sugars making it suitable for determining glucose in food samples.
author_names: Praveen Mishra

Badekai Ramachandra Bhat
title: Aggregative ways of graphene quantum dots with nitrogen rich edges for direct emission spectrophotometric estimation of glucose.
venue: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy
year: 2019

abstract: We investigate the etching of a pure hydrogen plasma on graphite samples and graphene flakes on SiO2 and hexagonal boron nitride substrates. The pressure and distance dependence of the graphite exposure experiments reveals the existence of two distinct plasma regimes: the direct and the remote plasma regime. Graphite surfaces exposed directly to the hydrogen plasma exhibit numerous etch pits of various size and depth, indicating continuous defect creation throughout the etching process. In contrast, anisotropic etching forming regular and symmetric hexagons starting only from preexisting defects and edges is seen in the remote plasma regime, where the sample is located downstream, outside of the glowing plasma. This regime is possible in a narrow window of parameters where essentially all ions have already recombined, yet a flux of H radicals performing anisotropic etching is still present. At the required process pressures, the radicals can recombine only on surfaces, not in the gas itself. Thus, the tube material needs to exhibit a sufficiently low H radical recombination coefficient, such as found for quartz or pyrex. In the remote regime, we investigate the etching of single layer and bilayer graphene on SiO2 and hexagonal boron nitride substrates. We find isotropic etching for single layer graphene on SiO2, whereas we observe highly anisotropic etching for graphene on a hexagonal boron nitride substrate. For bilayer graphene, anisotropic etching is observed on both substrates. Finally, we demonstrate the use of artificial defects to create well defined graphene nanostructures with clean crystallographic edges.Nanofabrication: remote etching of graphene on hBN is highly anisotropicEtching of graphite with hydrogen plasma gives rise to two distinct etching regimes, governed by the degree of direct plasma exposure. A team led by D. M. Zumbuhl at the University of Basel investigated the interplay between graphite exposure to pure hydrogen plasma and the resulting etching features. When the sample surface is in direct contact with the plasma, a defect rich etching regime occurs, resulting in the formation of etch pits with variable size. However, when graphite is away from the plasma source, a remote anisotropic etching takes place, giving rise to regular hexagons originating from localized defects and edges. In the latter regime, the authors found that in the case of graphene, isotropic etching is obtained using SiO2 as substrate, whereas highly anisotropic etching occurs when graphene is placed on hBN.
author_names: Dorothee Hug

Simon Zihlmann

Mirko K Rehmann

Yemliha Bilal Kalyoncu

Timothy N Camenzind

Laurent Marot

K Watanabe

Takashi Taniguchi

Dominik M Zumbuhl
title: Anisotropic etching of graphite and graphene in a remote hydrogen plasma
venue: npj 2D Materials and Applications
year: 2017

abstract: To replace the noble metal Pt catalysts for oxygen reduction reaction (ORR) developing efficient and earth abundant electrocatalysts is of great importance. Both the morphology and composition engineering of graphene could effectively modify the electronic structure to optimize its electrocatalytic performance for ORR. Here, we report an effective method to dope carbon materials with N, by which the N doping concentration and form could be well controlled. We first grow 3D graphene fibers (3DGFs) by thermal chemical vapor deposition, which are then treated with acid or heated in air and heated in NH3 in succession, obtaining N,O codoped 3DGFs. The codoped 3DGFs exhibit outstanding electrocatalytic performance toward ORR with onset potential of 1.01 V, half wave potential of 0.883 V, long term operation stability with 90% current retention after 50 h, and a good methanol tolerance in alkaline solutions, which are superior to 20 wt% Pt/C catalyst and other reported advanced metal free catalysts. The excellent catalytic performance of the 3DGFs probably arises from the synergic effect of the morphology and composition engineering, e.g. the edges and doping, especially the pyridine N. The present work is expected to open up new approach to design outstanding metal free carbon based electrocatalysts for ORR.
author_names: Jie Zeng

Yongbiao Mu

Xixi Ji

Ziji Lin

Yanhong Lin

Yihui Ma

Zhongxing Zhang

Shuguang Wang

Zhonghua Ren

Jie Yu
title: N,O codoped 3D graphene fibers with densely arranged sharp edges as highly efficient electrocatalyst for oxygen reduction reaction
venue: Journal of Materials Science
year: 2019

abstract: Graphene growth and etching are reciprocal processes that can reach a dynamic balance during chemical vapor deposition (CVD) Most commonly, the growth of graphene is the dominate process, while the etching of graphene is a recessive process often neglected during CVD growth of graphene. We show here that through the rational design of low pressure CVD of graphene in hydrogen diluted methane and regulation of the flow rate of H2, the etching effect during the growth process of graphene could be prominent and even shows macroscopic selectivity. On this basis, etching controlled growth and synthesis of graphene with various morphologies from compact to dendritic even to fragmentary have been demonstrated. The morphology selection mechanism is clarified through phase field theory based on simulations. This study not only presents an intriguing case for the fundamental mechanism of CVD growth but also provides a facile method for the synthesis of high quality graphene with trimmed morphologies.
author_names: Birong Luo

Enlai Gao

Dechao Geng

Huaping Wang

Zhi Ping Xu

Gui Yu
title: Etching Controlled Growth of Graphene by Chemical Vapor Deposition
year: 2017

abstract: Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey carbon TEM grids with chemical vapor deposition graphene and then using those graphene coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self assembly processes of nanomaterials in liquid on the single particle level.
author_names: Matthew R Hauwiller

Justin C Ondry

A Paul Alivisatos
title: Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching
venue: Journal of visualized experiments JoVE
year: 2018

abstract: Graphene is a novel two dimensional nanomaterial that holds great potential in electronic and sensor applications. By etching the edges to form nanoribbons or introducing defects on the basal plane, it has been demonstrated that the physical and chemical properties of graphene can be drastically altered. However, the lithographic or chemical techniques required to reliably produce such nanoribbons remain challenging. Here, we report the fabrication of nanosensors based on holey reduced graphene oxide (hRGO) which can be visualized as interconnected graphene nanoribbons. In our method, enzymatic oxidation generated holes within the basal plane of graphene oxide, and after reduction with hydrazine, hRGO was formed. When decorated with Pt nanoparticles, hRGO exhibited a large and selective electronic response toward hydrogen gas. By combining experimental results and theoretical modeling, we propose that the increased edge to plane ratio, oxygen moieties, and Pt nanoparticle decoration were responsible for the observed gas sensing with hRGO nanostructures.
author_names: Harindra Vedala

Dan C Sorescu

Gregg P Kotchey

Alexander Star
title: Chemical sensitivity of graphene edges decorated with metal nanoparticles.
venue: Nano letters
year: 2011

abstract: Graphene is a two dimensional crystal that is stripped from pristine graphite and made of single layer of carbon atoms. Containing numerous functional groups, graphene derivatives (GDs) could be easily modified and have aroused great attention for potential applications in biomedicine. However, pristine graphene and graphene oxide (GO) could arouse cell and animal toxicity. To screen GDs with high biocompatibility applied for biomedicine, general comparison was performed about the toxicities of six GDs with diverse types of surface modification, size, and redox state, including GO, reduced GO (rGO) graphene quantum dot (GQD) aminated GQD (GQD NH2) carboxyl GQD (GQD COOH) and graphene oxide quantum dot (GOQD) In contrast, it was found that large particle size, oxidation state, high concentration, and long exposure time were unfavorable factors affecting the cell viability. We further explored the mechanism of different toxicity, which could be contribute to cell membrane destruction by sharpened edges of GDs (LDH release, hemolysis) ROS production, immuno inflammatory responses, and activation of apoptotic pathways (IKK/IkBa/NF kB and BAX/BCL 2) Overall, our combined data primarily explored the related biochemical and molecular mechanism underlying the biological behaviors and toxicity of GDs, and we also identified GQD, GQD NH2, GQD COOH, and GOQD could be safely used for biomedical application as drug carriers.
author_names: Jian Li

Xizhi Zhang

Jing Jiang

Yanjie Wang

Haiye Jiang

Junhua Zhang

Xinmin Nie

Bin Liu
title: Systematic Assessment of the Toxicity and Potential Mechanism of Graphene Derivatives In Vitro and In Vivo
venue: Toxicological sciences an official journal of the Society of Toxicology
year: 2019