Efficient synthesis of graphene nanoribbons sonochemically cut from graphene sheets

We report a facile approach to synthesize narrow and long graphene nanoribbons (GNRs) by sonochemically cutting chemically derived graphene sheets (GSs). The yield of GNRs can reach ∼5 wt% of the starting GSs. The resulting GNRs are several micrometers in length, with ∼75% being single-layer, and ∼40% being narrower than 20 nm in width. A chemical tailoring mechanism involving oxygen-unzipping of GSs under sonochemical conditions is proposed on the basis of experimental observations and previously reported theoretical calculations; it is suggested that the formation and distribution of line faults on graphite oxide and GSs play crucial roles in the formation of GNRs. These results open up the possibilities of the large-scale synthesis and various technological applications of GNRs.      

以氧化石墨烯为氧化介质制备石墨烯/聚苯胺导电复合材料

采用超声辅助Hummers法制得厚度约为1 nm的氧化石墨烯, 以其为氧化介质与苯胺反应合成了石墨烯/聚苯胺(RGO/PANI)导电复合材料。利用AFM、SEM、XRD和FTIR对反应所得产物进行了表征。结果表明: 苯胺在略高于室温的酸性水溶液中可以对氧化石墨烯(GO)进行还原, 而苯胺自身则被氧化石墨烯中大量的含氧基团氧化并发生聚合反应, 最终生成RGO/PANI导电复合材料, 当苯胺用量为1 mL, 氧化石墨烯用量为0.1 g, 在水浴温度为70 ℃下剧烈搅拌24 h时, 获得的RGO/PANI复合材料导电性最佳, 约为10 S/cm。     

Strain effects in graphene and graphene nanoribbons: The underlying mechanism

A tight-binding analytic framework is combined with first-principles calculations to reveal the mechanism underlying the strain effects on electronic structures of graphene and graphene nanoribbons (GNRs). It provides a unified and precise formulation of the strain effects under various circumstances-including the shift of the Fermi (Dirac) points, the change in band gap of armchair GNRs with uniaxial strain in a zigzag pattern and its insensitivity to shear strain, and the variation of the k-range of edge states in zigzag GNRs under uniaxial and shear strains which determine the gap behavior via the spin polarization interaction.      

Carbon nanotube-dependent synthesis of armchair graphene nanoribbons

Sub-nanometer armchair graphene nanoribbons(GNRs)with moderate band gap have great potential towards novel nanodevices.GNRs can be synthesized in the confined t...     

原位反应制备ZnS/还原氧化石墨烯复合材料及其光催化性能

以氧化石墨烯和ZnAc2为反应前驱物,采用二甲基亚砜(DMSO)作为硫源和反应溶剂,通过一步溶剂热法原位制备出负载ZnS的还原氧化石墨烯(RGO)复合材料(ZnS/RGO)。采用SEM、XRD、激光拉曼(Raman)和荧光光谱对样品的微观形貌和化学结构进行表征。结果显示:原位反应制备的ZnS/RGO复合材料是由呈圆球状并均匀负载的纳米ZnS和6~7层RGO层状结构组成;在模拟紫外光照射下,对甲基橙污染物的光催化结果表明,ZnS/RGO复合材料的降解效率明显高于纯ZnS;同时,在多次循环催化过程中,ZnS/RGO复合材料的光催化效率仍基本保持不变,表明原位反应使ZnS与RGO结合增强。荧光光谱结果表明,ZnS/RGO复合材料光催化效率增强的主要原因在于ZnS中光生电子通过RGO得到有效的分离,进而延长了电子-空穴的复合效率。     

ZnS/还原氧化石墨烯复合材料的制备及光催化性能

水热法一步合成ZnS/还原氧化石墨烯（ZnS/RGO）复合材料,通过XRD、FTIR、Raman、SEM分析溶剂（乙醇、水）对ZnS/RGO复合材料形貌和结构的影响。结果表明,以乙醇为溶剂制备的ZnS颗粒尺寸小、均匀分散在石墨烯片层上,在形成ZnS纳米颗粒的同时将氧化石墨烯（GO）还原成石墨烯。对亚甲基蓝（MB）的光催化结果显示,ZnS/RGO复合材料具有优异的光催化性能,其光催化速率是纯ZnS颗粒的3.7倍,石墨烯作为优良光生电子的传输通道和收集体能够降低光生电子-空穴对的重新结合率,极大提高了ZnS/RGO复合材料的光催化性能。      

Transport in nanoribbon interconnects obtained from graphene grown by chemical vapor deposition

We study graphene nanoribbon (GNR) interconnects obtained from graphene grown by chemical vapor deposition (CVD). We report low- and high-field electrical measurements over a wide temperature range, from 1.7 to 900 K. Room temperature mobilities range from 100 to 500 cm(2)·V(-1)·s(-1), comparable to GNRs from exfoliated graphene, suggesting that bulk defects or grain boundaries play little role in devices smaller than the CVD graphene crystallite size. At high-field, peak current densities are limited by Joule heating, but a small amount of thermal engineering allows us to reach ～2 × 10(9) A/cm(2), the highest reported for nanoscale CVD graphene interconnects. At temperatures below ～5 K, short GNRs act as quantum dots with dimensions comparable to their lengths, highlighting the role of metal contacts in limiting transport. Our study illustrates opportunities for CVD-grown GNRs, while revealing variability and contacts as remaining future challenges.     

还原氧化石墨烯/天然橡胶-丁腈橡胶复合材料的制备与性能

采用水合肼还原氧化石墨烯（GO）制备了还原氧化石墨烯（RGO）,以RGO作为分散介质加入到天然橡胶（NR）和丁腈橡胶（NBR）基体中,通过乳液共混法制备了RGO/NR-NBR复合材料。采用FTIR、Raman、XRD及SEM等手段表征了RGO的结构和形貌,测试结果表明,水合肼还原GO效果较好,基本除去含氧官能团,同时RGO还保留了GO的片层结构。RGO/NR-NBR复合材料的SEM测试结果显示,纳米尺寸的RGO均匀分散在橡胶基体中,且复合材料的拉伸断面粗糙程度显著增加。RGO/NR-NBR复合材料的硫化性能测试结果表明,随RGO的含量增加,复合材料的交联密度、最大扭矩及扭矩差均增大。RGO/NR-NBR复合材料的力学性能随RGO含量的增加而提高,当RGO含量为3.0%时,材料的拉伸强度、100%定伸强度和邵氏硬度分别提高了65.7%、90.3%和21.1%,断裂伸长率降低了13.1%。     

Chemically isolated graphene nanoribbons reversibly formed in fluorographene using polymer nanowire masks

We demonstrated the fabrication of graphene nanoribbons (GNRs) as narrow as 35 nm created using scanning probe lithography to deposit a polymer mask(1-3) and then fluorinating the sample to isolate the masked graphene from the surrounding wide band gap fluorographene. The polymer protected the GNR from atmospheric adsorbates while the adjacent fluorographene stably p-doped the GNRs which had electron mobilities of ～2700 cm2/(V·s). Chemical isolation of the GNR enabled resetting the device to nearly pristine graphene.     

Zn还原氧化石墨烯(RGO)和ZnO/RGO自组装复合材料的电磁响应行为

以天然鳞片石墨为原料制备氧化石墨烯（GO）,通过Zn将其还原为石墨烯（RGO）,且生成的ZnO附着在RGO表面。采用XRD、SEM、FTIR、Raman、TEM和矢量网络分析仪（VNA）研究了不同还原温度对ZnO/RGO复合材料形貌、结构、氧化程度、电磁损耗特性、德拜弛豫模型及电磁响应行为的影响。结果表明:还原温度为50℃时RGO还原后结构更加完整,层间距为0.89 nm时ZnO/RGO复合材料的介电常数和磁导率均较高,在17.15 GHz时反射率达到-41.2 dB,反射损耗小于-10 dB的带宽为3.67 GHz。      

A green approach to the synthesis of reduced graphene oxide nanosheets under UV irradiation

We present a totally green approach towards the synthesis and stabilization of aqueous graphene dispersions through UV-irradiated reduction of exfoliated graphene oxide (GO). Polyvinyl pyrrolidone (PVP) is used to enhance the dispersibility of reduced graphene oxide (RGO) by one-step functionalization. The proposed method is low cost and easy without using any photocatalysts or reducing agents, which can open up a new possibility for green preparation of stable RGO dispersions in large-scale production.     

Sulfur-doped graphene nanoribbons with a sequence of distinct band gaps

Unlike graphene sheets,graphene nanoribbons (GNRs) can exhibit semiconducting band gap characteristics that can be tuned by controlling impurity doping and the GNR widths and edge structures.However,achieving such control is a major challenge in the fabrication of GNRs.Chevron-type GNRs were recently synthesized via surface-assisted polymerization of pristine or N-substituted oligophenylene monomers.In principle,GNR heterojunctions can be fabricated by mixing two different monomers.In this paper,we report the fabrication and characterization of chevron-type GNRs using sulfur-substituted oligophenylene monomers to produce GNRs and related heterostructures for the first time.First-principles calculations show that the GNR gaps can be tailored by applying different sulfur configurations from cyclodehydrogenated isomers via debromination and intramolecular cyclodehydrogenation.This feature should enable a new approach for the creation of multiple GNR heterojunctions by engineering their sulfur configurations.These predictions have been confirmed via scanning tunneling microscopy and scanning tunneling spectroscopy.For example,we have found that the S-containing GNRs contain segments with distinct band gaps,i.e.,a sequence of multiple heterojunctions that results in a sequence of quantum dots.This unusual intraribbon heterojunction sequence may be useful in nanoscale optoelectronic applications that use quantum dots.     

Electrical conductive and graphitizable polymer nanofibers grafted on graphene nanosheets: Improving electrical conductivity and flame retardancy of polypropylene

Polyaniline (PANI) nanofibers grafted reduced graphene oxide (PANI–RGO) is prepared using the “grafting-from” strategy and then is incorporated into polypropylene (PP) matrix by way of the master batch-based melt mixing method. Grafted PANI nanofibers can improve the dispersion and electrical conductivity of reduced graphene oxide (RGO). The electrical conductivity of the modified RGO and its composites is not impaired by the grafted polymer, due to the conductive characteristics of PANI. The barrier action of PANI–RGO can greatly inhibit the release of flammable pyrolysis products of PP. PANI–RGO exhibits a marked flame retardancy effect on PP. The smoke release of the composites is slightly retarded. Transmission electron microscopy image and Raman spectrum of the char residue for PANI–RGO based composite indicate the formation of carbon nanofibers during combustion. The in situ formed carbon nanofibers on graphene nanosheets can enhance barrier performance against heat and mass transfer, resulting in enhanced flame retardancy.     

Cu/还原氧化石墨烯光催化复合材料的制备及其光催化性能

以乙酸铜和氧化石墨烯（GO）为原料,抗坏血酸为还原剂,采用液相化学法合成Cu/还原氧化石墨烯（Cu/RGO）复合材料。通过XRD、SEM、TEM、FTIR和Raman对材料结构及形貌进行表征,并考察Cu/RGO复合材料在H₂O₂辅助作用下对亚甲基蓝（MB）的光催化作用。结果表明：Cu颗粒均匀分布在RGO片层上,相比于纯Cu,Cu/RGO复合材料的光催化性能明显提高,Cu/RGO复合材料用量为0.06 g/L时,对MB显示出最佳的催化效果,200 min内脱色率达到了92.5%,经过5次循环后脱色率仍有88.0%以上。     

Ferromagnetism in graphene nanoribbons: split versus oxidative unzipped ribbons

Two types of graphene nanoribbons: (a) potassium-split graphene nanoribbons (GNRs), and (b) oxidative unzipped and chemically converted graphene nanoribbons (CCGNRs) were investigated for their magnetic properties using the combination of static magnetization and electron spin resonance measurements. The two types of ribbons possess remarkably different magnetic properties. While a low-temperature ferromagnet-like feature is observed in both types of ribbons, such room-temperature feature persists only in potassium-split ribbons. The GNRs show negative exchange bias, but the CCGNRs exhibit a "positive exchange bias". Electron spin resonance measurements suggest that the carbon-related defects may be responsible for the observed magnetic behavior in both types of ribbons. Furthermore, information on the proton hyperfine coupling strength has been obtained from hyperfine sublevel correlation experiments performed on the GNRs. Electron spin resonance finds no evidence for the presence of potassium (cluster) related signals, pointing to the intrinsic magnetic nature of the ribbons. Our combined experimental results may indicate the coexistence of ferromagnetic clusters with antiferromagnetic regions leading to disordered magnetic phase. We discuss the possible origin of the observed contrast in the magnetic behaviors of the two types of ribbons studied.     

Graphene/thermoplastic polyurethane nanocomposites: Surface modification of graphene through oxidation,polyvinyl pyrrolidone coating and reduction

Herein, oxidation, polyvinyl pyrrolidone (PVP) coating and reduction are used to modify the surface of graphene in thermoplastic polyurethane (TPU)/graphene nanocomposites. It is demonstrated that graphene could be easily dispersed in TPU with PVP absorbed on reduced graphene oxide (RGO) as stabilizer during reduction. In the stress–strain curves for these composites containing GO, PVP coated GO (GO/PVP) and reduced GO/PVP (RGO/PVP) as filler, PVP coating and reduction can largely enhance the stress in low modulus region. It is thought to largely related with enhanced interfacial interaction between filler and matrix and healing of graphene structure during reduction. Consequently, the modulus of TPU/GO/PVP and TPU/RGO/PVP is significantly increased. Meanwhile, an electrical percolation threshold of 0.35 wt.% is obtained for TPU/RGO/PVP. Comparing with the results in literature, the filler surface modification used in this study has created nanocomposites with a good balance between electrical conductivity and mechanical properties.     

Bandgap engineering of zigzag graphene nanoribbons by manipulating edge states via defective boundaries

One of the most severe limits of graphene nanoribbons (GNRs) in future applications is that zigzag GNRs (ZGNRs) are gapless, so cannot be used in field effect transistors (FETs), and armchair GNR (AGNR) based FETs require atomically precise control of edges and width. Using the tight-binding approach and first principles method, we derived and proved a general boundary condition for the opening of a significant bandgap in ZGNRs with defective edge structures. The proposed semiconducting ZGNRs have some interesting properties one of which is that they can be embedded and integrated in a large piece of graphene without the need to completely cut them out. We also demonstrated a new type of high-performance all-ZGNR FET. Previous proposals of graphene FETs are all based on AGNRs.     

Electrochemically metal-doped reduced graphene oxide films:Properties and applications

The fine control of doping levels in graphene materials such as reduced graphene oxide(RGO) is important to properly manipulate their ambipolar transport characteristics for various device applications. However, conventional doping methods involve complex chemical reactions, large-scale doping processes,and poor stability. Herein, a simple and controllable electrochemical doping treatment(EDT), performed via the conductive channels created at the RGO surface by the application of an electric field, is introduced to tailor the electrical properties of RGO films. X-ray photoelectron spectroscopy and Raman spectroscopy measurements are performed to detect the presence of Ni atoms in RGO films after the EDT(EDT-RGO).Then, EDT-RGO field-effect transistors(FETs) are fabricated with different doping areas(0 to 100% fractional area) on the RGO active channel to investigate the effect and selective-area doping capability of the EDT. Owing to p-type doping compensation by the intercalated Ni atoms, the electron mobility of the EDT-RGO FET decreases from 1.40 to 0.12 cm~2 V~(-1)s~(-1) compared with that of the undoped RGO-FET,leading to the conversion from ambipolar to unipolar p-type transfer characteristics.     

Characteristics of CVD graphene nanoribbon formed by a ZnO nanowire hardmask

A graphene nanoribbon (GNR) is an important basic structure to open a bandgap in graphene. The GNR processes reported in the literature are complex, time-consuming, and expensive; moreover, the device yield is relatively low. In this paper, a simple new process to fabricate a long and straight graphene nanoribbon with a high yield has been proposed. This process utilizes CVD graphene substrate and a ZnO nanowire as the hardmask for patterning. 8 μm long and 50-100 nm wide GNRs were successfully demonstrated in high density without any trimming, and ～ 10% device yield was realized with a top-down patterning process. After passivating the surfaces of the GNRs using a low temperature atomic layer deposition (ALD) of Al(2)O(3), high performance GNR MOSFETs with symmetric drain-current-gate-voltage (I(d)-V(g)) curves were demonstrated and a field effect mobility up to ～ 1200 cm(2) V(-1) s(-1) was achieved at V(d) = 10 mV.     

Electrochemical actuator based on polypyrrole/sulfonated graphene/graphene tri-layer film

A tri-layer electrochemical actuator was fabricated by the electrodeposition of polypyrrole (PPy) onto a sulfonated graphene (SG)/reduced graphene oxide (RGO) bi-layer film. In this actuator, PPy and RGO were acted as actuation and conductive inert layers, respectively. The SG layer was used to enhance the interfacial interactions. The tri-layer actuator exhibited high and stable actuating performance for over 1000 actuation cycles, and the lifetime of the actuator was tested to be about 5000 cycles. The bending angle of the actuator is larger than 360° and its movement rate was higher than 150° s^− 1 under a driving potential of 1.0 V versus saturated calomel electrode. Furthermore, the low weight density of graphene based supporting layer greatly lowered the energy or charge consuming of the actuator during electrochemical actuation.