石墨烯是由sp²杂化单层碳原子组成的二维蜂窝状结构，具有大的比表面积、高的透光率、电子迁移率、激子束缚能和热稳定性，这使得石墨烯(graphene)在透明电极、场效应晶体管、光伏器件、气敏传感器等方面有巨大的应用潜力。但本征石墨烯具有零带隙特性，不会产生荧光，这极大的限制了它在光电器件中的应用，打开石墨烯的带隙是其在半导体光电子器件领域应用的前提。石墨烯的光学性质由其对称性决定，可以通过引入无序结构来改变，途径之一就是通过调控sp²区域的尺寸来调控发光的波长。 超大规模集成电路都是以Si材料作为基础，而且下一代信息技术的一个重要发展方向就是硅基光子学，但作为间接带隙半导体，Si发光效率较低，需要将光子器件或电子器件集成在Si芯片上，实现光电集成，缩短光电互联的长度，提高信息处理速度。构筑graphene／Si器件，不仅可以实现硅掺杂石墨烯提高石墨烯的激子结合能，增强石墨烯室温激子发光，还可以直接将器件集成到Si芯片上。但石墨烯与Si集成时存在晶格失配和热失配，采用纳米技术可以很好解决这个问题。本论文在Si纳米孔柱阵列(Si nanoporous pillar array，Si-NPA)上用化学气相沉积法(chemical vapor deposition，CVD)成功原位制备了石墨烯，实现了与Si-NPA的异质接触，得到一种新型的graphene／Si-NPA纳米异质结构，该结构在室温下展现出较强的激子发光特性、稳定良好的场发射性能、和较弱的光电导性能。本论文主要进行了以下研究工作： (1)采用两种不同的方法制备graphene／Si-NPA异质结：1、以Ni为催化剂，CVD法在Si-NPA上直接沉积生成石墨烯；2、采用氧化还原法制备石墨烯，然后旋涂在Si-NPA上形成异质结。 先采用化学水浴法制备Ni催化剂，研究了不同前驱体、生长时间、溶液PH值对催化剂覆盖度、颗粒均匀度的影响，确定了Ni(CH₃COO)₂·4H₂O为前驱体、生长时间15 min、PH值为8是得到Ni纳米晶催化剂的最佳制备条件。然后采用CVD方法在Ni／Si-NPA上生长石墨烯，通过控制碳沉积时间来调节石墨烯的层数，在此选用5 min、10min沉积时间，制备出厚度分别为3和8个碳原子层的石墨烯。此外，我们通过氧化还原法成功制备了分散均匀，尺寸为5～7nm的石墨烯，并将其旋涂在Si-NPA上，形成graphene／Si-NPA纳米异质结构。 (2)Graphene／Si-NPA纳米异质结的结构、组成、及室温激子发射特性。 利用XRD、FESEM、TEM、HRTEM、Raman等表征了CVD法制备的graphene／Si-NPA的形貌、结构及组成，确定制备的石墨烯尺寸为～17 nm，具有良好的结晶度和分散性。光吸收谱表明石墨烯具有3.3 eV的吸收带边。在光激发下，石墨烯在紫外和可见光区域(2.06-3.6 eV)出现一系列连续分立的激子发射峰。此外，声子谱伴随激子峰也在室温下长期稳定存在。石墨烯的低温光致发光谱表明激子发光来源于自由激子、束缚激子的复合发光和缺陷态发光。通过分析石墨烯的载流子传输特性，基于能带理论构建了石墨烯的激子发光物理模型。我们认为石墨烯发光的机理除了激子能带间的跃迁外，Si原子的掺杂、催化剂Ni纳米晶的等离子增强等因素，对石墨烯的室温激子发光都起到了重要的作用，该研究结果对增强石墨烯的室温激子发光具有重要的参考价值。 为了更好地揭示这一现象，我们测试了graphene／Si-NPA复合体系的量子产率为3.09％，平均荧光寿命为1.08 ns。通过对387 nm、473 nm处发光峰的寿命测试，确定了387 nm的发光是由自由激子到σ能带跃迁造成的，而473 nm处的发光是由两种机理构成：束缚激子复合和石墨烯的边沿缺陷态发光。 为了对比，测试了旋涂法制备的graphene／Si-NPA异质结的激发光谱和光致发光谱。结果表明，该方法中Si原子与石墨烯接触不紧密，相互没有电子和能量交换，在紫外光激发下复合体系没有出现石墨烯的激子发光，异质结的光谱只是两种材料发光的简单叠加。另外实验观察到Si-NPA的发光强度变强，可能是石墨烯作为Si-NPA的光学窗口，在反射折射的过程中增加了Si-NPA的光吸收。 (3)Graphene／Si-NPA和石墨纳米结构(nano-graphite)／Si-NPA的可见光探测特性。 激子运动过程传播动量和能量，但不传播电荷，运动过程中不产生光电导。根据此理论，graphene／SiNPA体系激子发光较强，应该不会产生光电导现象或光电导较弱。为了验证此理论，我们采用Ag丝做电极，采用同面电极法分别制成1.0×1.0 ㎝的Si-NPA、Ni／Si-NPA及graphene／SiNPA光电导探测器。结果表明， Ag电极与Si-NPA、Ni／Si-NPA、graphene／Si-NPA都形成了欧姆接触。与基底SiNPA和Ni／Si-NPA相比，graphene／Si-NPA具有较低的面电阻率和较高的光电导响应度，但光生电流较弱在毫安甚至微安数量级。在后续实验中我们将通过增加碳的沉积时间得到较厚的石墨层，降低石墨烯的激子结合能，进而降低激子光吸收，增加产生光电流的光子数。 将碳膜生长时间延长为15 min后，在Si-NPA上生成一层石墨纳米结构(graphite nanostructure，nano-graphite)，它主要由石墨纳米颗粒和纳米线组成，而纳米颗粒和纳米线又是由更小的石墨晶体聚集而成。光学和电学测量表明nanographite／Si-NPA与graphene／Si-NPA相比，具有更强的宽光谱吸收(11.79-15.9％)、更高的电流开关比(75)和光电响应度(～0.16AW⁻¹)，并且具有超低的工作电压。研究结果表明nano-graphite／Si-NPA较高的电流开关比和响应度主要由厚且致密的石墨纳米膜的强光吸收、低的激子光吸收发射和低的方块电阻等因素形成的。 (4)Graphene／Si-NPA的场发射特性 所制备Graphene／Si-NPA复合体系因存在多界面而形成了高的载流子的浓度(5.45×10²⁴ ㎝⁻³)和低的面电阻率～2.5×10⁻⁸Ω ㎝，提供大量小尺寸的石墨烯(平均尺寸11.1 nm)，具有大量能发射电子的边缘点，而且基底微米量级的硅柱阵列不仅能增加石墨烯的生长面积，还可以减小场发射电子的静电屏蔽，所以极具场发射应用价值。 将CVD法制备的graphene／Si-NPA复合结构作为冷阴极材料，采用二极管测试模型，在高真空下研究其场发射性质。器件的载流子浓度和面电阻率利用霍尔效应获得，测试时使用范德堡循环测试法降低副作用。结果表明：5 min石墨烯生长时间的graphene／Si-NPA场发射F-N曲线呈现线性变化，是典型的量子隧穿效应形成的冷阴极电子发射。其开启场强为2.85 V／μm，在4.2 V／μm的电场下可以获得～53.9μA／㎝²的发射电流密度。根据Fowler-Nordheim理论，计算出场增强因子为～2700。在低工作电压下，graphene／Si-NPA也显示出比垂直基底生长的石墨烯更高的场发射稳定性。 实验结果表明，graphene／Si-NPA的开启场强与石墨烯的生长时间有关，10 min石墨烯生长时间的graphene／Si-NPA开启场强增长至8.5 V／μm，在高低电场范围内，场发射F-N曲线呈现双斜率现象。这是由高低电场范围内电子发射位置不同造成的。在低电场下，石墨烯的电子隧穿石墨烯和真空势垒形成隧穿电子；在高场强下，Ni纳米晶中的电子隧穿Ni和石墨烯及石墨烯和真空间的势垒形成发射电子。实验结果表明5 min石墨烯生长时间的graphene／Si-NPA更适合做冷阴极材料。 关键词：硅纳米孔柱阵列(Si-NPA)；石墨烯；纳米异质结构；激子发射；光响应；场发射

 Single-layer graphene bonded with sp²-hybridized carbon atoms possesses twodimensional honeycomb lattice structure, and thus exhibits excellent physical properties, such as extremely high specific surface area, light transmittance, electronic mobility, exciton binding energy and thermal stability, etc. These make it have great potential application in the field of transparent electrodes, field effect transistors, photovoltaic devices, gas sensors, and so on. However, it had no fluorescence because the band gap of graphene is zero, which greatly limits its application in optoelectronic devices. So it is prerequisite to open the band gap of graphene for the application in the semiconductor device. The optical properties of carbon materials are determined by the symmetry. Therefore, the wavelength of the luminescence could be adjusted by introducing unordered structure that can be induced by changing the size of the sp² region. Si has been used in the super-large-scale integration in the past decades, and the silicon-based photonics have been become an important development direction of the next generation of information technology. However, as an indirect bandgap semiconductor, Si is an inefficient light emitter, so other direct-bandgap materials are usually hired to fabricate optical or photoelectric devices on the Si chip to shorten the length of the photoelectric interconnection, and thereby improve the information processing speed. The integration of graphene with Si not only forms graphene/Si devices, but also makes silicon dope into graphene to improve exciton binding energy of graphene and enhance the temperature of exciton emission. And the devices could also directly integrate onto the Si chip and shorten the distance of signal transmission path. Though lattice mismatch and thermal mismatch is existence in the integration of graphene with Si, growing graphene on the silicon nanostructure could solve this problem. We successfullcy prepared graphene on silicon nanoporous pillar array (Si-NPA) by chemical vapor deposition (CVD) method, realized heterogeneous contact with Si-NPA, and obtained a new type of graphene/Si-NPA nano-heterostructure device. The structure exhibits excitonic emitting characteristics and stable field emission properties at room temperature, though the photoconductivity is poor. The mean researches conducted are list as follows. (1)Prepartion of the graphene/Si-NPA nanoheterostructure through CVD and spin-coating methods. Graphene was grown on Si-NPA via CVD method, using a thin layer of predeposited Ni nanocrystallites as catalyst. The effects of precursors, growth time and solution pH on catalyst coverage and particle uniformity were investigated. The results showed that Ni nanocrystals prepared by Ni(CH₃COO)₂·4H₂O had suitable thickness and uniform particle size distribution. The optimized growth time of the Ni catalyst was 15 min and the pH was 8. Graphene was grown on the Si-NPA using CVD method. The growth times of graphene were 5 and 10 minutes, and got graphene with 3 and 8 carbon atomic layers respectively. Furthermore, in order to compared with the photoelectric properties prepared by CVD, graphene with a size of 5～7 nm was successfully prepared by Redox method, and spin-coated on Si-NPA to form graphene/Si-NPA nanoheterostructure. (2)Room-temperature excitonic emission with phonon replica from graphene deposited on Si-NPA. Based on the graphene/Si-NPA prepared above, XRD, SEM, TEM, HRTEM, Raman, etc. were used to characterize the morphology, structure and composition of graphene/Si-NPA. Graphene were determined to be of high quality and well-dispersed, with a diameter size of smaller than 17 nm. Light absorption measurements showed that graphene had an absorption band edge at 3.3 eV. They also showed regular and sharp excitonic emitting peaks in the ultraviolet and visible region (2.06-3.6 eV) at room temperature. Moreover, phonon replicas with long-term stability appeared with the excitonic peaks at room temperature. Temperature-dependent photoluminescence from the graphene revealed that the excitonic emission derived from free and bound excitonic recombination and defect state emission of graphene. A physical model based on band energy theory was constructed to analyze the carrier transport of the graphene. In addition to the transition between graphene bands, the doping of Si into graphene and Ni nanocrystallites on Si-NPA, which acted as a metal-enhanced fluorescence substrate, were supposed to play important roles in the room temperature exciton luminescence of graphene. Results of this study would be valuable in determining the luminescence mechanism of graphene. The quantum yield of the graphene/Si-NPA nanoheterostructure was tested to be 3.09% and the average fluorescence lifetime was 1.08 ns. The lifetime analysis of the luminescence peaks at 387 and 473 nm showed that the 387 nm luminescence was from the free exciton transition, while the luminescence at 473 nm came from the emission of bound excitons and edge-defect state of graphene. For comparison, the excitation and photoluminescence spectra of graphene/Si-NPA prepared by spin-coating were tested. The results showed that there was no electron and energy transfer between the graphene and Si-NPA under optical excitation. Graphene and Si-NPA emitted their own intrinsic fluorescence respectively and graphene has no room temperature exciton emission phenomenon. In addition, as an optical window of Si-NPA, graphene increases the light absorption of Si-NPA, and thereby enhancing the luminescence intensity of Si-NPA slightly. (3)Visible photodetection realized by graphene/Si-NPA and graphite nanostructure (nano-graphite)/Si-NPA. The exciton motion process propagates momentum and energy, but does not propagate charge, and does not produce photoconductivity during motion. By this theory, the excitonic emission of graphene/SiNPA system was strong and should give birth to poor photocurrent. To verify this theory, Ag wires were used as electrodes to constructure 1.0 × 1.0 ㎝ Si-NPA, Ni/Si-NPA and graphene/Si-NPA photoconductive detectors. The results show that the Ag electrodes were ohmic contact with Si-NPA, Ni/Si-NPA, and graphene/Si-NPA. Because the resistance of graphene/Si-NPA was lower than that of Si-NPA and Ni/Si-NPA, and the photoconductive response was slightly higher than the latters, though the photocurrent is weaker in the order of mA or even μA. Absorption of graphene/Si-NPA was low and was supposed to be due to the fewer layers of graphene and the strong exciton transitions caused by the weak electrostatic shielding of fewer-layer graphene. Therefore, in order to get better optical absorption and lower exciton emission, we obtained thick graphite nanostructures by increasing the deposition time of carbon in the subsequent experiments. Nano-graphite shown as nanoparticles and nanowires, which composed of graphite nanocrystallites (nc-graphite) was grown on Si-NPA by CVD through prolonging growth time to 15 min. The spectral measurements show that nanographite/Si-NPA possesses strong light absorption in the visible region of400-800 nm. Driven by an ultralow bias of 0.1 mV, a switching ratio of 75, a photoresponsivity of ～0.16 AW⁻¹ and a rise/fall time of 12.24/5.66 s were obtained. Nano-graphite/Si-NPA existed no spectral response. The high switching ratio and responsivity were ascribed to the formation of a thick and compact graphite nanofilm, the low excitonic absorption and square resistance. (4)Electron field emission from graphene grown on Si nanoporous pillar array. Graphene/Si-NPA prepared by CVD has high carrier concentration (5.45×10²⁴ ㎝⁻³), lower resistivity (～2.5×10⁻⁸Ω㎝) and smaller size (～11.1 nm), and thus it has a large number of edge points as emitting sites. Moreover, the Si-NPA as substrate not only increases the growth area of graphene, but also reduces the electrostatic shielding of field-emitting electrons. Therefore, we believed that graphene/Si-NPA should have a promising application in the electron field emission. The electron field emission of graphene/Si-NPA prepared by the CVD method was measured in a high vacuum chamber using a diode structure. For the graphene/Si-NPA with 5 min graphene growth time, the J-E curve could keep in a normal emission state when it was applied voltages and the transferred F-N plots (ln(J/E²)-1/E relation) was approximately linear, which indicated it was cold cathode electron emission by typical quantum tunneling effect. The turn-on field was ～2.85 V/μm, and an emission current density of～53.9 μA/㎝² was obtained at an electric field of 4.2 V/μm. The planar resistance and resistivity of graphene/Si-NPA were measured by Hall effect using Van De Pauw method. Based on the experimental data, the enhancement factor was calculated to be ～2700 according to the Fowler-Nordheim theory. The cold cathode also showed higher emission stability than vertically standing graphene at low operating voltages. For graphene/Si-NPA with 10 min graphene growth time, the turn-on field was twice as much as the graphene/Si-NPA with 5 min graphene growth time. The emission current density is also lower than the latter. Moreover, the F-N curves showed a two-slope behavior in the high and low voltage range. This might be due to the mainly emitting sites change in the low and high applied voltage rang. At low applied voltage range, direct F-N tunneling occurred at graphene-vacuum barrier, while F-N tunneling occurred through both Ni-graphene and graphene-vacuum barriers at a high electric field range. The experimental results show that graphene /Si-NPA with 5 min graphene growth time is more suitable for fabricating Si-based low-voltage cold cathodes with high device performances. Keywords: Silicon nanoporous pillar array (Si-NPA); graphene; nanoheterostructure; excitonic emission; photoresponse; field emission