【作者】 王静；

【导师】 吴兴龙；

【作者基本信息】 南京大学 ， 微电子与固体电子学， 2012， 博士

【摘要】 硅基半导体材料具有很多特殊的物理和化学性质,是一类很有潜力的材料,在光电子和生物医学领域都有望得到广泛的应用。近来,随着纳米科技和微电子技术的发展,硅基半导体纳米材料成为科学界的研究热点,人们尝试各种途径制备多种形貌的硅基半导体纳米材料并研究它们的发光性质,希望实现高效率、高稳定,尤其是具有宽光谱可调谐发光的固体薄膜。然而,由于硅基半导体纳米材料结构的复杂性,文献中报导的发光一般都仅限于很窄的光谱范围,因而很难将硅基半导体纳米发光材料应用到技术领域。本论文研究用化学腐蚀加超声振荡的方法制备在紫-蓝-绿光区域具有可调谐发光的3C-SiC和Si的量子点,用丙三醇钝化量子点制备了固体薄膜,首次发现一种在整个可见光波段有全色可调谐发光特性的全硅纳米结构固体薄膜。本文的主要研究结果如下：1、制备了丙三醇键合的3C-SiC纳米颗粒固体薄膜,可以被不同波长的光子激发,呈现出全色、可调谐的发光特性。3C-SiC纳米颗粒/丙三醇复合薄膜的发光在360-450nm区域随着激发波长的改变可调谐,分别发出紫-蓝-绿色荧光,发光十分强烈而且稳定以至于肉眼可见。分析发现3C-SiC纳米颗粒/丙三醇复合薄膜的发光主要来源于3C-SiC量子点的限制效应。X射线光电子能谱和X射线吸收近带边结构测量表明,丙三醇分子完全地键合在Si原子终端的表面上。基于密度泛函理论计算丙三醇钝化的3C-SiC纳米颗粒的表面结构和电子态,发现丙三醇分子键合在纳米颗粒上导致了电子结构的改变,以至于导带内的分立能级被准连续能带所取代。准连续能带使得3C-SiC纳米颗粒产生了随着激发波长改变导致的连续可调的光发射现象。另外,我们使用丙三醇钝化的3C-SiC纳米颗粒与多孔硅结合制备多色发光的固体薄膜,说明这种固体薄膜有潜在的应用价值。2、以颗粒直径在微米量级的Si粉末为原料,在氢氟酸与硝酸的混合溶液中进行化学腐蚀和超声振荡,制备出了悬浮在水中的大量Si量子点。这些量子点的直径在1到4nm之间,接近中心对称分布,最可几直径为2nm。Si量子点的形成过程如下：化学腐蚀粉末使得其表面形成一些多孔网状结构,纳米尺度的晶粒交织在其中,超声振荡粉碎这些网状结构,从而形成量子点并进入水中。在Xe灯照射下,Si量子点的水溶液在紫-蓝-绿光区域表现出强的、稳定的光致发光现象,当激发波长从320nm增加到420nm时,发光峰位从400nm红移到520nm。分析与计算结果表明,Si量子点的发光起源于量子限制效应导致的Si量子点中载流子的带带复合。3、测量了pH值为1、4、7、11的Si量子点水溶液的PL和PLE谱。发现,在各种不同的pH值下,Si量子点水溶液都有强烈的光致发光,并且都伴随着发光峰位随激发波长的增加而红移的现象,这说明量子限制效应的存在。在不同的pH值下Si量子点的发光峰形是不同的：酸性环境下,发光强度减弱,以致出现了水的Raman峰；在碱性环境中,发光强度较强,谱线370nm左右出现了一个固定位置的凸起,PLE的峰形有较大变化；在中性溶液中,PL不仅信号很强,而且其特征完全与量子限制效应对应。经过分析认为,强烈的酸性使得大量的氢离子易吸附在Si量子点的表面,使Si量子点的发光强度减弱；而碱性环境下,导致了Si量子点产生表面态或缺陷态；在中性环境下,Si量子点发光较为强烈,并且没有观察到与表面态、缺陷态有关的发光峰,说明尽管Si量子点的可调发光来源于量子限制效应,但表面态、缺陷态也会影响Si量子点的发光。考虑到Si量子点经由化学腐蚀方法制备,其表面化学性质仍然很活泼,氢离子和羟基都极易和颗粒表面键合,这为表面态、缺陷态的产生提供了条件,从而使其发光特性受到影响。因此,Si量子点强烈的光致发光现象来自量子限制效应和表面钝化的双重作用。4、通过用丙三醇钝化Si量子点的表面,我们制备了在紫-蓝-绿光范围内有可调发光的Si量子点／丙三醇复合薄膜；另外将用丙三醇钝化制得的Si量子点组装到多孔硅薄膜上后制得了全硅的发光纳米结构,即在全波段连续可调、发光的Si量子点／丙三醇／多孔硅复合薄膜,其对应不同激发波长下的荧光量子效率主要在20%-30%之间波动,高于同领域中别的样品的通常数值。这是首次在全硅纳米结构中发现全色、可调的发光薄膜。分析表明,基于Si量子点制备的固体薄膜其可调谐的发光是由于丙三醇分子键合和量子限制效应的共同作用。更多还原

【Abstract】 Silicon based semiconductor nanostructures have a variety of special properties which make them useful in the area of optoelectronic, and biomedical applications. In recent years, Si-based semiconductor nanomaterials have attracted enough attention, especially going with the development of nanoscience and microelectronic technique. People have been trying various methods to fabricate different morphologic Si based nanostructures, expecting to achieve effective and stable light emission. However, the complexity of Si based nanostructures makes it difficult to obtain broad range light emitting. In this thesis, we study3C-SiC and Si nanocrystals with tunable light emis-sion in violet to blue-green range, which are fabricated via a chemical etching meth-od with ultrasonic treatment. Moreover, we fabricate solid light emitting films with3C-SiC and Si nanocrystals. In addition, we are the first comers who fabricate a sili-con nanostructures film, with tunable light emission in visible range. The obtained main results are described as follows:1. We have produced glycerol-bonded3C-SiC nanocrystal (NC) films, which when excited by photons of different wavelengths, produce strong and tunable violet to blue-green (360-540nm) emission as a result of the quantum confinement effects rendered by the3C-SiC NCs. The emission is so intense that the emission spots are visible to the naked eyes. The light emission is very stable and even after storing in air for more than six months, and no intensity degradation can be observed. X-ray photo-electron spectroscopy and absorption fine structure measurements indicate that the Si-terminated NC surfaces are completely bonded to glycerol molecules. Calculations of geometry optimization and electron structures based on the density functional the-ory for3C-SiC NCs with attached glycerol molecules show that these molecules are bonded on the NCs causing strong surface structural change, while the isolated levels in the conduction band of the bare3C-SiC NCs are replaced with quasi-continuous bands that provide continuous tunability of the emitted light by changing the frequen-cies of exciting laser. As an application, we demonstrate the potential of using3C-SiC NCs to fabricate full-color emitting solid films by incorporating porous silicon.2. By chemical etching of Si powder in a mixture of nitric acid and hydrofluoric acid, followed with ultrasonic vibration, a large quantity of Si nanocrystals is fabri-cated in water. The diameter of Si nanocrystals varies from1to4nm, with a maximal probability diameter of2nm. Chemical etching results in the formation of intercon-nected nanocrystal network on the surface of Si grains. Consiquent ultrasonic treat-ment separates Si nanocrystals from the network into water. Excited by the Xe lamp, the suspension of Si nanocrystals performances intensive, stable light emitting, wich the PL peak varies from400to520nm, corresponding to the increasing excitation wavelength from320to420nm, respectively.According to the results of a series of measurements, it implies that the tunable PL emissions originates from the band-to-band recombination in the quantum confined Si nanocrystals.3. We obtain the PL and PLE spectra of Si quantum dots solution with different pH values of1,4,7and11. It is found that whatever the pH value is, the photolumi-nescence of Si quantum dots solution is intensive, which the PL peak redshifts when the excitation wavelength increases. All above demonstrates that the tunable photo-luminescence of Si quantum dots mainly originates from quantum confined effect. However, the pattern of PL peak is slightly different from each other, of which the pH value is different:in an acidic environment, the intensity of light emitting decreases that the Raman peak of water comes out; when the solution is alkalescent, although the PL is intensive enough, a fixed shoulder appears at around370nm, with a great change of PLE spectra; the PL in neutral solution is bright as well as responsible to quantum confined effect. According to the results as above, we infer that high acidity will make a large quantity of ionized hydrogen atoms absorbed to the surface of Si quantum dots, which will result in a decreacing intensity of light emitting, while sur-face/defect states of Si quantum dots appear in an environment full of hydroxyl. In a neutral solution, the light emitting of Si quantum dots is intensive and no peaks rela-tive to surface/defect states can be observed. Therefore, it means that although the tunable PL of Si quantum dots mainly comes from quantum confined effect, the sur-face/defect states are still able to influence the light emitting of Si quantum dots. Con-siderting that the Si quantum dots are made from chemical etching, it is unrealistic to expect the Si dots are ideally smooth without hanging bonds or any defects. The chemical properties of Si atoms on the surface of dots are still so active that can be easily bonded to hydrogen atom and hydroxyl group, which helps the generation of surface/defect states. Thus the PL characters of Si quantum dots are influenced. Hence, the intensive light emitting of Si quantum dots comes from both quantum confined effect and surface passivation.4. By passivating the surface of Si quantum dots with glycerin, we fabricate a Si quantum dots/glycerin solid film, which emits photons tunably in the violet to blue-green range. We also fabricate a tunably photoluminescent Si composite nano film, by glycerol passivating the Si quantum dots and subsequently embed the pas-sivated quantum dots into the nano pores of porous silicon. The Si composite nano film shows stable, tunable photoluminescence in all visible range. In add, the quantum efficiency value of this Si composite film mostly varies during20%-30%, corre-sponding to different excitation wavelength, which is far more intensive than usual. This is the first time that we obseved full colored tunable photoluminescence in com-posite nanostructure composed of Si completely. During the study we found that the tunable photoluminescence in such a broad range originates from both quantum con-fined effect and glycerol passivation of Si quantum dots.更多还原