Transparent conductive reduced graphene oxide thin films produced by spray coating

Reduced graphene oxide thin films were fabricated on quartz by spray coating method using a stable dispersion of reduced graphene oxide in N,N-Dimethylformamide.The dispersion was produced by chemical reduction of graphene oxide,and the film thickness was controlled with the amount of spray volume.AFM measurements revealed that the thin films have near-atomically flat surface.The chemical and structural parameters of the samples were analyzed by Raman and XPS studies.It was found that the thin films show electrical conductivity with good optical transparency in the visible to near infrared region.The sheet resistance of the films can be significantly reduced by annealing in vacuum and reach 58 k?with a light transmittance of 68.69%at 550 nm.The conductive transparent properties of the reduced graphene oxide thin films would be useful to develop flexible electronics.     

高温还原氧化石墨烯膜及其导热性能

采用氧化还原法制备了结构致密且具有较高柔韧性的石墨烯薄膜,探究了薄膜经过较高退火温度还原后结构变化,并通过T型稳态法测量了其热导率,研究了还原温度对薄膜热导率和力学性能的影响。结果表明,高温还原有助于氧化石墨烯中含氧官能团的去除和sp2杂化碳晶格的恢复,并且温度越高还原效果越好。当还原温度高达2800℃时,在200~350 K温度范围内石墨烯膜的热导率在336.9~436 W·m^-1·K^-1之间,伴随着温度的升高,热导率有先增大后减小的趋势。     

还原温度对氧化石墨烯结构及室温下H_2敏感性能的影响

以氧化石墨凝胶制备的氧化石墨烯(GO)溶胶为前驱体,在100—350℃温度下还原获得不同还原程度的还原氧化石墨烯(rGO)样品,并采用旋涂工艺制备还原氧化石墨烯气敏薄膜元件.采用X射线衍射、拉曼光谱、傅里叶变换红外光谱和气敏测试等手段研究还原温度对样品结构、官能团和气敏性能的影响.结果表明:经热还原处理的氧化石墨烯结构向较为有序的类石墨结构转变,还原温度为200℃时,样品处于GO向rGO转变的过渡阶段,还原温度达到250℃时,则表现出还原氧化石墨烯特性;无序程度随还原温度的升高先由0.85增大至1.59,随后减小至1.41,总体呈现增加趋势;氧化石墨烯表面含氧官能团随还原温度的升高逐渐热解失去,不同含氧官能团的失去温度范围不同;热还原氧化石墨烯具有优异的室温H_2敏感性能,随着还原温度的升高,元件灵敏度逐渐减小,响应-恢复时间逐渐增大,最佳灵敏度为88.56%,响应时间为30 s.     

Formation of graphene on amorphous SiC film by surface-confined heating with electron beam irradiation

It is demonstrated experimentally that graphene can form on the surface of an amorphous SiC film by irradiating electron beam (e-beam) at low acceleration voltage. As the electron irradiation fluency increases, the crystallinity and uniformity of graphene improve, which is confirmed by the changes of the measured Raman spectra and secondary electron microscopy images. Due to the shallow penetration depth of e-beam with low acceleration voltage, only the region near the surface of SiC film will be heated by the thermalization of irradiated electrons with multiple scattering processes. The thermalized electrons are expected to weaken the bond strength between Si and C atoms so that the thermal agitation required for triggering the sublimation of Si atoms decreases. With these assistances of irradiated electrons, it is considered that graphene can grow on the surface of SiC film at temperature reduced substantially in comparison with the conventional vacuum annealing process.     

MoS2纳微薄膜激光非线性透射的调控研究

超短飞秒脉冲激光(脉冲时间<40 fs)有独特的热效应机理, 但尚无针对其设计的光限幅保护膜. 本文采用易于产业化的离散-旋涂法制备了MoS₂纳微薄膜(厚度150–200 nm). 光限幅测试结果表明, 针对超短脉冲激光, 此纳微薄膜在低光强下增透, 高光强下减透(光限幅); 且能通过改变入射波长, 调控其光限幅阈值, 可用于聚光太阳能电池的效率增强和损伤保护.利用此方法, 对已商用的砷化镓太阳能电池进行涂膜, 发现转换效率降低<3%, 但损伤阈值提高>50%.     

A comparison of the charring and carbonisation of oxygen-rich precursors with the thermal reduction of graphene oxide

Chars and carbonised chars were produced from two oxygen-rich precursors (Phormium tenax leaf fibres and sucrose crystals) and compared to thermally reduced graphene oxide (TRGO) samples using a range of analytical techniques. A hypothesis that carbonised chars are chemically and nanostructurally more similar to TRGOs than to other proposed structural analogues such as graphites and fullerenes was investigated. The greatest similarities in chemical structural features were observed between the well-carbonised chars and thermally reduced graphene oxide both of which had been prepared using heat treatment temperatures above ≈700 °C. However, thermal analysis and infra-red spectroscopy demonstrated how the char formation process differs from the early stages of the thermal reduction of graphene oxide. Major differences in morphology between TRGOs and various chars were also clearly observable using scanning electron microscopy. Prominent signals indicating the presence of aromatic C–H functional groups were observable in char samples and negligible in the thermally reduced graphene oxide samples when both were analysed by infra-red spectroscopy. The similarities and differences on a nanostructural scale between carbonised chars and thermally reduced graphene oxide are discussed with a focus on clarifying existing models for non-graphitisable carbons produced from oxygen-rich precursors.     

Graphene resistive random memory — the promising memory device in next generation

Graphene-based resistive random access memory(GRRAM) has grasped researchers' attention due to its merits compared with ordinary RRAM. In this paper, we briefly review different types of GRRAMs. These GRRAMs can be divided into two categories: graphene RRAM and graphene oxide(GO)/reduced graphene oxide(r GO) RRAM. Using graphene as the electrode, GRRAM can own many good characteristics, such as low power consumption, higher density, transparency,SET voltage modulation, high uniformity, and so on. Graphene flakes sandwiched between two dielectric layers can lower the SET voltage and achieve multilevel switching. Moreover, the GRRAM with r GO and GO as the dielectric or electrode can be simply fabricated. Flexible and high performance RRAM and GO film can be modified by adding other materials layer or making a composite with polymer, nanoparticle, and 2D materials to further improve the performance. Above all,GRRAM shows huge potential to become the next generation memory.     

Green synthesis of silver-graphene nanocomposite-based transparent conducting film

In the present work, silver nanoparticles (Ag NPs)/graphene nanocomposite has been synthesized successfully by simple solvothermal method via green route. Citric acid is used as green reducing agent for the reduction of graphene oxide (GO) and Ag ions. Silver nitrate is used as a precursor material for Ag NPs. As synthesized Ag NPs/graphene nanocomposite has been characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infra-red spectroscopy, UV–vis spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Experimental results confirm the reduction of GO and the successful formation of Ag NPs decorated graphene nanosheets. In addition, spray coating technique is employed for the fabrication of transparent conducting films. Enhancement in the optoelectrical signatures has been achieved using thermal graphitization of fabricated films. Thermal graphitization at 800 °C for 1 h marks the best performance of fabricated film with sheet resistance of ~3.4 kΩ/□ and transmittance (550 nm) of ~66.40%, respectively.     

Experimental study on the preparation,characterization and conductivity improvement of reduced graphene-oxide papers

In the present study, reduced graphene-oxide (r-GO) papers were prepared by vacuum filtration method using chemically obtained graphene oxide as raw materials. Different reduction methods, chemical, thermal or the combination were designed to investigate the influence of reduction process on the structure and conductivity of r-GO papers. The reducibility of the obtained papers was investigated by XPS and Raman. The structure, morphology and electrical conductivity were examined by XRD, SEM and four point resistivity test system, respectively. Results showed that chemical reduction using hydrazine or annealing in reducing ambinent alone was not sufficient to achieve maximum reduction, the highest C/O ratio and highest conductivity was obtained in paper reduced via a combination of hydrazine and thermal annealing treatment. In order to further improve the conductivity of the paper, Ag nanoparticles have been decorated into the paper.     

Mechanically Robust,Electrically Conductive Biocomposite Films Using Antimicrobial Chitosan‐Functionalized Graphenes

An effective way of covalently functionalizing graphene with a chitosan polymer via a nitrene chemistry is demonstrated. The biofunctionalized graphene is prepared by the chemical reduction of graphene oxide using a nitrene chemistry, and then covalently grafting chitosan to the graphene surface. The effectiveness of the biofunctionalized graphene as a reinforcing filler (4 wt%) in a chitosan polymer matrix is verified by the dramatic enhancement of the mechanical properties (breaking stress = 330%, Young's modulus = 243%) and the electrical conductivity (0.3 S m^?1) without much loss in the elongation‐at‐break. The reinforcing effect can be explained by both the homogeneous dispersion of graphene within the matrix and the strong bond arising from the intrinsically intimate contact between the graphene and the matrix. The high antimicrobial activity of the biofunctionalized graphene compared with graphene oxide and chemically reduced graphene may be because of the presence of chitosan polymer on the edges of the graphene. The strong, antimicrobial graphene‐filled composite film can be used for food packaging and for coating various biomedical devices, where bacterial surface colonization is undesirable.     

六方氮化硼薄膜对石墨烯-碳化硅结构近场热辐射的增强

六方氮化硼(hBN)具有跟石墨烯类似的层状结构和晶格参数,研究发现hBN薄膜具有良好的热传导、电绝缘、光学和力学等性能。本文从理论上研究了hBN薄膜对石墨烯-碳化硅(G/S)结构的近场热辐射的影响。研究发现在红外频段.hBN薄膜在低频率区和高频率区会增强G/S结构的近场热辐射,经计算在G/S结构中加入厚度为10 nm的hBN薄膜时获得的辐射热流是同物理条件下G/S结构的1.5倍;而在中频率区hBN薄膜的厚度阻碍了石墨烯表面等离激元和碳化硅表面声子极化激元的耦合,使得近场热辐射热流随hBN薄膜厚度增加而逐渐减弱。本研究的结果可为下一步实验与应用中对hBN薄膜厚度的选择提供理论基础。     

Carbon nanostructure–aSi:H photovoltaic cells with high open-circuit voltage fabricated without dopants

Recently discovered production techniques allow the synthesis of carbon nanostructured films with large surface areas. The abundance of carbon and the unique properties of these nanostructures, including high transparency and excellent electrical conductivity, make these materials very interesting for photovoltaic applications, in particular in combination with amorphous silicon. We examine the properties of thin carbon nanotube films (buckypaper) and graphene in junctions with undoped amorphous silicon thin films. The observed open-circuit voltages, 390 mV for the carbon nanotube film and 150 mV for graphene, suggest that solar cells with high efficiency can be produced without expensive processing steps like doping, multilayer film deposition in high vacuum, or transparent conducting oxide deposition. The buckypaper cells are stable in ambient conditions for many weeks, at least.     

应力对石墨烯热输运性质影响的分子动力学模拟

本文建立了低维薄膜材料导热模型,运用非平衡分子动力学模拟的方法,利用lanmmps软件对单层石墨烯纳米带的导热特性进行仿真分析,根据Fourier定律计算热导率,再对石墨烯纳米带的原子施加一定耦合应力场,把应力耦合作用下的石墨烯热导率与正常的石墨烯纳米带进行了对比研究,模拟数据结果表明:在石墨烯纳米带上施加耦合应力时,会导致石墨烯纳米带热导率升高,且随应力增加而增大,模拟范围内热导率升高2.61倍,并且应力方向会对热导率变化产生一定影响,这个研究为纳米尺度上石墨烯相关研究和进一步提升热导率提供了新思路.     

石墨烯增强半导体态二氧化钒近场热辐射

本文基于涨落耗散定理和并矢格林函数求解麦克斯韦方程来研究两个半无限大平板的近场热辐射净热流,提出了两个半无限大块状二氧化钒组成的V/V结构、石墨烯覆盖两个半无限大块状二氧化钒组成的GV/GV结构和石墨烯覆盖VO2薄膜组成的GV0/GV0结构,深入研究了这三种结构中二氧化钒与石墨烯间的近场热辐射,并分析了真空间距、二氧化钒薄膜厚度和石墨烯化学势等物理参量变化对近场热辐射的影响.研究表明:三种结构的近场热辐射均随间距增大而减小;在真空间距为10 nm时,由石墨烯覆盖的GV/GV结构的近场辐射热流比无石墨烯覆盖的V/V结构增强35倍,耦合效果最好的是GV0/GV0结构,该结构的近场辐射热流比GV/GV结构增强8.6倍;在GV0/GV0结构中,当二氧化钒薄膜厚度为30 nm时,石墨烯化学势从0.1 eV增加到0.6 eV辐射热流会减小3.3倍.本文系统研究了二氧化钒与石墨烯间相互耦合的近场热辐射,对相关结构的近场热辐射实验和实际应用具有理论指导意义.     

石墨烯/AZO/SiC复合结构的近场辐射换热特性

由于倏逝波贡献,近场辐射换热可以远超黑体辐射定律给出的极限换热热流,对近场辐射换热的调控在近场热光伏及热管理方面有重要的应用前景。石墨烯是一种有潜力的可用于近场辐射换热调控的功能材料。本文研究了由石墨烯、铝掺杂氧化锌(aluminum-doped zinc-oxide,AZO)及SiC构成的多层复合薄膜的近场辐射换热特性。研究发现:"AZO薄膜+SiC基底"结构的频谱辐射热流在SiC的SPhP频域出现谷值,而"SiC薄膜+AZO基底"结构同时在两种表面极化激元的共振频率处出现峰值;覆盖单层石墨烯薄膜对"AZO薄膜+SiC基底"结构的近场辐射换热基本没有影响;而"石墨烯/SiC薄膜/AZO基底"结构却可以同时支持三种表面极化激元,并在调控石墨烯化学势到适当值时,可以有效增强近场换热。本研究有助于理解石墨烯对近场辐射换热的调控特性。     

Electronic and structural properties of graphene-based transparent and conductive thin film electrodes

We demonstrate that graphene-based transparent and conductive thin films (GTCFs), fabricated by thermal reduction of graphite oxide, have very similar electronic and structural properties as highly oriented pyrolytic graphite (HOPG). Electron spectroscopy results suggest that the GTCFs are also semi-metallic and that the individual graphene sheets of the film are predominantly oriented parallel to the substrate plane. These films may therefore be considered as a technologically relevant analogue to HOPG electrodes, which cannot be easily processed into thin films.     

纳米结构表面形貌成型机理及其对石墨烯拉曼光谱的影响

通过真空热蒸镀和高温退火法制备的金属纳米复结构SERS基底因其具有良好的灵敏度,稳定性和均匀性而广泛应用于各种检测领域。石墨烯具有优良的光学特性,化学惰性以及荧光猝灭效应,自被发现以后一直是光学微纳器件中的一大热门材料。石墨烯还可以有效分离探针分子与基底,优化拉曼光谱质量,因此广泛应用于SERS研究领域。同时石墨烯可以有效隔绝金属纳米结构与空气的直接接触防止金属纳米结构被氧化而失效,也可以催化氧化银的脱氧反应提升SERS基底的稳定性。在石墨烯/金属纳米复合结构SERS基底在制备过程中,受到金属膜的种类、厚度参数、气体种类、退火时间、温度和气压等因素的影响,制备的金属纳米结构形貌存在很大差异。石墨烯的拉曼光谱会因为应力和掺杂导致其拉曼特征峰出现不同程度的增强,移动以及展宽。（1）采用真空热蒸镀法和高温退火法制备石墨烯/银纳米复合结构SERS基底,建立了金属纳米颗粒成型机理的模型,从孔洞形成、孔洞生长、金属纳米岛形成三个阶段分析了金属纳米粒子的成型过程,实验沉积5,10,15以及20 nm的银薄膜,退火后银纳米结构的覆盖率分别为~35.1%,~24.4%,~30%以及~96.0%,在沉积银薄膜样品上使用湿法转移石墨烯,退火处理后发现石墨烯阻止了银纳米岛的形成过程;（2）理论分析了银薄膜厚度、石墨烯覆盖对复合结构的几何形貌、拉曼增强特性的影响,石墨烯由于其具有较高的杨氏模量和表面张力,可以有效抑制退火过程中银薄膜向纳米粒子转变的过程,从而实现对复合结构表面形貌的调控;（3）实验研究了银纳米粒结构形貌对石墨烯拉曼光谱的影响,并理论分析了蒸镀不同银薄膜厚度的样品对石墨烯的拉曼光谱增强,移动以及展宽影响的具体原因。     

Thermoacoustic theory of graphene films considering heat transfer of substrate materials

Based on thermoacoustic theory, a coupled thermal-mechanical model for graphene films is established, and the analytical solutions for thermal-acoustic radiation from a graphene thin film are obtained. The sound pressure of the graphene film generator on different substrates is measured, and the measurement data is compared with the theoretical results. The frequency response from the experimental results is consistent with the theoretical ones, while the measured values are slightly lower than the theoretical ones. Therefore, the accuracy of the proposed theoretical model is verified. It is shown that thermal-acoustic radiation from a graphene thin film reveals a wide frequency response. The sound pressure level increases with the frequency in the low frequency range, while the sound pressure varies smoothly with frequency in the high frequency range. Thus it can be used as excellent thermal generator. When the thermal effusivity of the substrate is smaller, then the sound pressure of grapheme films will be higher.Furthermore, the sound pressure decreases with the increase of heat capacity per unit area of grapheme films. Results will contribute to the mechanism of graphene films generator and its applications in the design of loudspeaker and other related areas.     

考虑基底热传导的石墨烯薄膜热声理论

主要基于热声效应对石墨烯薄膜发声进行理论研究。首先建立了石墨烯薄膜耦合热振动模型,推导出了石墨烯薄膜发声器的声压表达式。在此基础上,进行了不同基底石墨烯薄膜发声器的声压测试,并将测试值与理论计算结果对比,二者随频率变化趋势基本吻合,测试值略低于理论值,验证了推导出的声压表达式的正确性。研究表明石墨烯薄膜发声器有很宽的频域响应,在低频段声压级随频率增大而增大,在高频段响应平稳,具有作为优秀的热致发声器的潜力。基底材料蓄热系数越小,石墨烯薄膜的声压值越大;声压级随薄膜热容量的增大而减小。研究结果对于石墨烯的发声机制探索及其在扬声器设计等方面的应用具有指导意义。      

电化学制备钛网负载聚吡咯/石墨烯复合膜及其在超级电容器中的应用

通过电化学的方法在钛网上制备了聚吡咯与石墨烯的复合物薄膜,其过程是先在钛网上通过自组装干燥膜法附着上石墨烯氧化物膜,而后采用电化学还原的方法原位还原制备得到石墨烯膜,随后加入吡咯单体,再通过电化学聚合的方法在石墨烯的表面生长聚吡咯,得到的聚吡咯开始以颗粒的形式存在,而后随着聚合的进行得到了链状的聚吡咯.得到的复合膜有高的比表面积和导电性,可以作为电极活性材料用于超级电容器中提供赝电容,结果表明,复合膜作为电极材料的超级电容器拥有高的性能,比电容达400 F/g,并且电极的充放电稳定性高,5000次复合膜充放电循环后比电容还能保留82%,说明该材料适合于超级电容器.