【作者】 许士才；

【导师】 满宝元；

【作者基本信息】 山东师范大学 ， 原子与分子物理， 2014， 博士

【摘要】 石墨烯是由碳原子以sp2杂化轨道组成六角型呈蜂巢状的单原子层的二维晶体。石墨烯独特的结构赋予了其超凡的物理性质。石墨烯中电子（载荷子）的性质与相对论性的中微子非常相似，其运动速度达到了光速的1/300，远远超过了电子在一般导体中的运动速度。理论上，石墨烯的电子迁移率可达到2×105cm2/V·s，使其表现出非凡的导电性。石墨烯具有优良的透明度，单层石墨烯的透过率在可见—红外区可以达到97.7%。因此，石墨烯是一种良好的透明导电材料，可以作为电极应用在透明触控屏幕、液晶显示器、甚至是太阳能电池等电子器件上。除了独特的电子学特性，石墨烯还表现出典型的可饱和吸收特性。与传统的半导体材料不同，石墨烯独特的零带隙结构使其对光的吸收没有选择性，适用于工作在各种波长的激光器。近几年，石墨烯超凡的性能吸引了人们广泛的研究。本论文在这些研究的基础上，围绕提高石墨烯的透明导电性、实现石墨烯的应用展开了一系列工作。本文用化学气相沉积（CVD）方法在铜箔上制备了大面积的石墨烯薄膜，设计了双温区结构的CVD系统实现了高品质石墨烯在绝缘石英基片上直接生长。并以石墨烯为基础，制备了石墨烯扬声器、石墨烯生物传感器、石墨烯饱和吸收体等器件。主要工作如下：（1）设计了一个双温区CVD系统，在绝缘的SiO2基片上制备了高品质的石墨烯薄膜。石墨烯薄膜的厚度可通过前驱气体的比例、流量以及生长时间进行控制。拉曼光谱和高分辨透射电子显微镜（HRTEM）分析表明石墨烯的晶粒尺寸可达到~100nm。霍尔测量表明室温下石墨烯的载流子浓度为~1500cm2/V·s，石墨烯薄膜的电导性和光透射率可以媲美转移后金属催化的石墨烯。本工作避免了石墨烯繁杂的转移过程，为石墨烯的制备开辟了一条新的途径。（2）基于石英基片上直接生长的石墨烯，我们设计了场效应管（FET）结构的石墨烯生物传感器，用于检测生命体内的能量分子三磷酸腺苷（ATP）。该传感器显示了毫秒级时间分辨率，为实时监测生命体动态的生命活动提供了可能。此外，此传感器测量的范围非常宽，在0.002–5mM的浓度范围内，其电流的响应与ATP浓度对数呈现了良好的线性关系，灵敏度达到50%。由于0.002–5mM的浓度覆盖了真实生命体内的ATP浓度范围，此项工作对研究生命体中动态的生命过程具有现实的意义。（3）将石墨烯作为电极转移在聚偏氟乙烯（PVDF）压电薄膜的两侧，利用PVDF的逆压电效应，制备了一种透明、可弯曲的薄膜扬声器。测试表明，该扬声器在几赫兹到几万赫兹极宽频率范围内都可获得较好的音频响应，具有高声压级（SPL）、低谐波失真（THD）和低功耗的特点。与传统的商用扬声器相比，石墨烯薄膜扬声器无磁、透明、可弯曲、极有希望成为未来超薄、超轻的可穿戴的电子器件。（4）将二维石墨烯与一维纳米线复合制备了一种复合透明柔性电极。这种复合薄膜的电阻仅为~16/□，而透过率却高达91.1％，展示了优异的化学稳定性和机械柔韧性，这些性质要远远优于商用的ITO和最好的石墨烯电极。本工作展示了一种制备低成本高性能柔性透明电极的方法。（5）将石墨烯转移到单晶C面的石英基片上，制备了石墨烯饱和吸收体。由于生长的为单层石墨烯，可通过转移次数精确控制石墨烯的层数。使用这些饱和吸收体，我们在Nd:YVO4激光器上实现了稳定的Q锁模，在6.0W的泵浦功率下，得到了1.6W的平均输出功率，本工作证实了低成本、宽频带的石墨烯饱和吸收体适合于超快高能的脉冲激光。更多还原

【Abstract】 Graphene is a single atomic layer of sp2bonded carbon atoms arranged in a twodimensional hexagonal lattice. Charge carriers in graphene move at an ultrafast speed, similarto relativistic, massless Dirac particles. Its mobility reaches to~1/300light speed, much higherthan that of ordinary electron in conductor. In theory, the carrier mobility of graphene is morethan2×105cm2/V·s at room temperature, making graphene possesses outstanding conductivity.Graphene has high transparency, the monolayer graphene only absorb2.3%light in visible toinfrared region. Therefore, graphene is a kind of conductive and transparent material, which canbe as the transparent electrode for many devices, such as touch-screen panel, liquid crystaldisplays and solar cells. Besides unique electronic structure，graphene shows typical saturableabsorption behavior. Unlike the tranditional semiconductors, the absorption characteristics ofgraphene are little wavelength dependence due to its zero-bandgap structure. Thus graphene canmodulate many lasers working in different wavelength. Recently, the extraordinary propertiesof graphene have attracted widely investigations. Based on these studies, we did a series ofwork around the improvement of conductivity and transparency and application of graphene.In this study, we fabricated lage-area graphene films on copper foils using chemical vapordeposition (CVD) method and synthesized high-quality graphene on quartz substrates in theabsent of metal catalyst. Based on these grown graphene, we fabricated loudspeakers, biosensor,and graphene saturable absorber, etc. The main works was as follows:(1) We demonstrate that the continuous and uniform graphene films can be directlysynthesized on the substrates using a two-temperature zone assembled chemical vapordeposition system and their layers can be controlled by adjusting the precursor partial pressure.Raman spectroscopy and transmission electron microscopy confirm the formation of themonolayer graphene with a grain size of~100nm. Hall measurement shows a roomtemperature carrier mobility of above1500cm2/V·s. The optical transmittance and conductanceof the graphene films are comparable to those of transferred metal-catalyzed graphene. Themethod avoids the complicated and skilled post growth transfer process, providing a novel wayfor the preparation of graphene.(2) Based on the direct-grown graphene, we fabricated a biosensor in the configuration of field-effect transistor (FET) for the detection of energy molecules (ATP). This graphene-basedbiosensor achieves a high time resolution of a few milliseconds and a high sensitivity to ATPmolecules in a very wide range from0.002to5mM. It is found that current change is roughlylinear increase with logarithm of ATP concentration in a very wide range from0.002to5mM.The sensitivity reached up to50%. This technique provides a novel platform to detect ATPmolecules and could potentially be employed in studying some essential cellular functions inliving cells.(3) We transferred graphene on the two sides of polyvinylidene fluoride (PVDF)piezoelectric film. Based on converse piezoelectric effect, we fabricated a kind of flexible andtransparent loudspeakers. This thin film loudspeaker can generate sound with wide frequencyrange, high sound pressure level (SPL) and low total harmonic distortion (THD), and has muchless power consumption. Compared to the commercial thin film speaker, graphene-basedloudspeakers have many advantages, such as magnet-free, transparent and flexible, which isexpected to be used as an extremely thin, lightweight wearable electronic devices.(4) We report a hybrid structure employing two-dimensional graphene and networks ofone-dimensional silver nanowires as transparent and flexible electrodes. The hybrid films havesheet resistances as low as~16/□with high transmittance of91.1%at550nm, and exhibitimpressive stability against oxidation and mechanical flexibility. These properties are superior tocommercial transparent electrodes such as indium tin oxides and comparable to the best reportedresults in transparent electrodes. Our method could readily provide a route towards low-costapproaches for realizing high performance transparent electrodes.(5) We trasfered graphene on c-plane quartz and maked graphene saturable absorber. Thehigh-quality monolayer graphene film with large area was grown on Cu foils by chemical vapordeposition (CVD) technique. The graphene saturable absorbers (SAs) with the well-defined layernumber were fabricated by controlling of transfer process precisely. Using the graphene SAs, thestable Q-switched mode-locking pulse trains were realized in a diode-pumped Nd: YVO4laser.At the pump power of6.0W, the average output power reached a high value of1.6W. This worksuggests that the low-cost, broadband graphene SA could potentially be employed in thepractical high-power mode-locking laser system.更多还原