【作者】 朱江；

【导师】 孟长功；

【作者基本信息】 大连理工大学 ， 物理化学， 2011， 博士

【摘要】 二十一世纪是信息技术的时代,以晶体硅芯片技术和光电子材料为代表的半导体材料是信息技术的基础。随着信息技术的发展,对信息的传递速度,储存能力,处理功能等提出了更高要求。上世纪90年代初发现多孔硅室温高效率光致发光后,引起了人们对多孔硅研究的热潮。多孔硅基发光二极管和多孔硅基全硅光电集成的初步实现,打破了硅作为间接带隙(1.12 eV)半导体材料难于实现高效发光的难题。在硅芯片中引进光电子技术,以光子代替电子作为信息载体,可以大大提高信息传输速度和处理能力。当然目前多孔硅发光还存在诸多缺点,如发光寿命短,重复性较差,性能不稳定等等。制备具有稳定性质的多孔硅结构,确定多孔硅发光机理,提高发光稳定性,从而增强多孔硅基发光二极管的效率和寿命,是目前多孔硅研究的重要课题。为避免通常使用的腐蚀法对生成的多孔硅结构的限制,近年来出现了利用氧化还原反应制备多孔硅的新方法。本论文以微孔和介孔全硅分子筛为原材料,通过真空镁热还原法,制备了几种具有不同结构形态的多孔硅材料,并对其晶相,形貌,微观形态,孔结构进行了多角度的分析和研究。基于多孔硅材料的发光特性,研究了所制备多孔硅材料的光致发光性质,初步探讨了多孔硅材料静态吸附小分子或负载氧化锌后发光性质变化的机理。主要研究结果如下：1.通过实验探索,采用化学试剂,添加结构导向剂或螯合剂调节晶体的结晶方式,利用水热法成功、稳定地制备了棒状立方体全硅方钠石和silicalite-I单晶体。采用旋液法分别稳定地制备了MCM-48型介孔分子筛球以及二氧化硅实心球。通过扫描电镜、透射电镜、光学显微镜、红外光谱、荧光光谱和氮气吸附等方法对所得产物进行全面系统的表征,为后面工作中分析研究热还原反应后晶相及孔结构的变化奠定了基础。2.通过实验探索,优化实验条件,采用高真空镁热还原法,在630-650℃温度范围内,‘将合成的几种全硅分子筛以及二氧化硅实心球还原为具有较高比表面积的多孔硅材料。分别对制备的多孔硅材料的形貌、成分、晶相、孔结构和荧光性质进行了测试和表征,结合反应物的性质,分析了可能的反应机理。产物多孔硅宏观上保持了原来全硅分子筛的形貌,而内部结构各异。所有制备的多孔硅都具有光致发光性质,但发光频率及强度则各不相同。3.横向比较发现所制备的多孔硅材料具有一些共性：(i)产物多孔硅基本保持了分子筛原有的形貌,粒径大小不变。(ii)所制备的多孔硅材料基本为晶态。由分子筛单晶体得到的多孔硅颗粒表面呈单晶态,内部为多晶；由MCM-48型分子筛球和二氧化硅实心球得到的球形多孔硅,基本呈多晶态,但存在少量无定形硅。(iii)产物多孔硅材料的氮气吸附脱附研究表面,其等温线类型相似,且都有吸附滞后环出现,孔径在介孔范围内。(iv)产物多孔硅形态各异,但均具有光致发光现象,空气中自然氧化一个月后,均出现发光蓝移现象。不同的产物多孔硅各有特性：(i)由全硅方钠石单晶得到的立方体多孔硅表面为单晶态,内部为15-20 nm的岛状多晶结构。(ii)由silicalite-I单晶得到的棒状多孔硅表面为单晶硅,内部为带有不规则孔的类层状多晶结构,类层状结构层层相叠互连,构成三维结构。(iii)由MCM-48型分子筛球得到的多孔硅球,与原来MCM-48型分子筛相比,其内部孔结构更为疏松,其微结构是由大量硅纳米微晶聚集而成。(iv)二氧化硅实心球则完全转化为疏松形态的球形多孔硅,其中还分布着弯曲的管道状的结构。4.对所合成的多孔硅材料进行初步的应用探讨。由于多孔硅材料的光学特性,适合应用于光学传感领域,因此在静态吸附气体小分子或负载氧化锌后,对处理后的样品的荧光性质进行研究,探讨该材料应用于传感领域的可能性。并对荧光光谱的变化机理进行了分析,得到引起荧光光谱变化的原因,为该材料的后续应用研究提供原始的实验和理论依据。更多还原

【Abstract】 The 21th century is the age of information technology, based on the semiconductor materials such as crystal silicon chip technology and photoelectric materials. The development of information technology needs more advantages for the transfer speed, memory ability and process function of information. It was in the year of 1990 that the photoluminescence from porous silicon was discovered in ambient, which evoked people’s passion for the research for porous silicon.Porous silicon based light emission diode and photoelectric integration have been synthesized in the 1990s, which broke the bottleneck that silicon is the indirect band gap semiconductor material and is difficult to realize effective light emission. When the photoelectric technology is brought into the silicon chip, photons, instead of electrons, become the information carrier, which could dramatically enlarge the transfer speed, memory ability and process function of information. Nowadays there still exist many disadvantages of the emission from porous silicon, such as the short life time, low repetition, instability and etc.It is necessary to synthesize different porous silicon structures with stable optical property. At present the important topics about porous silicon is to confirm the emission mechanism, improve the emission stability and increase the efficiency and life time of silicon-based light emission diode. However, the similarly traditional etching process resulted in similar structures in porous silicon, which limited the abundance of porous silicon structures, thus the study of synthesis and properties of new structure silicon materials becomes one of the most important subjects in the research of material field. In recent years, displacement reaction began to be used in porous silicon preparation.In this dissertation, porous silicon granules with different structures have been synthesized from several representative types of pure silica zeolites by the magnesiothermal process in vacuum under a modest temperature. A series of methods have been introduced to characterize the so-obtained materials from several points of view, such as the crystal phase, images and microcosmic structures. Based on the features of the materials, the photoluminescence (PL) properties have been investigated. Furthermore, after small molecules adsorbed or zinc oxide loaded in the materials, the mechanisms of changes in the PL spectra have also been deduced. The main results are as follows. 1. Silicalite-I and pure silica sodalite single crystals have been synthesized successfully and stably with pure chemical reagents in hydrothermal processes, by adding EDTA-Na4 and pyrocatechol as mineraliser respectively. Pure silica MCM-48 and amorphous SiO2 spheres have been synthesized by rotating-liquid method. The products have been characterized intensively by different ways, such as scanning electron microscopy (SEM), optical microscopy, N2-adsorption analysis, infrared spectra (IR), photoluminescence spectra (PL) and etc. Generally, these products possess outstanding properties to be applied as a raw material for the thermal reduction reaction and pave the way for the following works.2. Porous silicons with different structures have been synthesized from the so-obtained zeolites and SiO2 spheres by magnesiothermal process in vacuum under a temperature range of 630-650℃. The crystal phase, images, microcosmic structures and photoluminescence property of the as-synthesized porous silicons have been characterized. The possible reaction mechanism has been speculated with the properties of products.3. Generally compared and taken from a global view of these materials, some commonness have been found and stated as follows. (a) The as-synthesized porous silicon granules maintain the former shape from zeolites, with the size unchanged. The modest temperature and appropriate reaction time prevent the shape from distorting and collapsing. Meanwhile, the formation of the magnesia phase penetrating into the crystal silicon granule also solidifies the framework of the granule. (b) All porous silicons are mainly composed of crystal silicon. There exists some single crystal silicon piece in those from zeolites single crystals. A small amount of amorphous silicon has been found in the products from both MCM-48 and amorphous SiO2 spheres. (c) From the N2 adsorption-desorption isotherms we found that the porous silicons have similar adsorption properties and the pore diameter are all belong to mesoporous range. (d) Each specimen displays a fine photoluminescence by an ultraviolet excitation. The photoluminescence center shifts blue after long time oxidation.Of course, different porous silicon has its own characteristics. (a) The porous silicon granule from sodalite single crystal is composed of single crystal surface and island-like structure in the inside. (b) The porous silicon from silicalite-I single crystal is composed of single crystal surface and layered inside with irregular pores. (c) The MCM-48 spheres have been entirely changed to spherical porous silicon, consisting of silicon nanocrystals. (d) The structure of spherical porous silicon from amorphous SiO2 spheres is very loosen and there distribute many curved pipe-like channels.4. The synthesized porous silicons have been applied for adsorbing small molecule gases including NH3 and H2S. The photoluminescence spectra have been collected after the gas adsorption. Zinc oxide has also been successfully loaded in the porous silicon from silicalite-I and the photoluminescence spectrum of the loaded specimen has been obtained. The mechanisms of the variation in the emission spectra are investigated and speculated, which supplies the follow-up researches with the original data and theoretical foundation.更多还原