| Silicon nanoporous pillar array (Si-NPA) which is prepared by hydrothermal erosion method is a kind of silicon micro/nanometer composite system. It forms a triple-layer structure on two scales of micrometer and nanometer. The array structure consisting of a plurality of approximately identical micron-sized array of columns perpendicularly to the surface, nanoporous structure consisting of high-density nanopore evenly distributed on each column, and nanoporous pore wall composed of silicon oxide-coated silicon nanocrystals. Studies and tests show that Si-NPA has a large specific surface area and a strong surface activity, reduction, can be directly restore the noble metal (gold, silver, copper, platinum, etc.) from its salt solution without the use of any reducing agent. In addition, Si-NPA also shows outstanding physical characteristics. One is broad-band high light absorption, the overall integral reflectivity is less than 4% in the wavelength range of 200?2400 nm, indicating that Si-NPA is a good light absorption material; the other is a strong and stable photoluminescence , before and after annealing can emission strong red and blue light.The morphological and physical properties of Si-NPA indicate that it can be used as an ideal substrate or template to prepare or assemble a variety of silicon-based nanocomposites to achieve new physical properties. For example, a series of composite nanometer systems such as metal / Si-NPA, wide bandgap compound semiconductor / Si-NPA, carbon nanotube / Si-NPA and so on were prepared based on Si-NPA as the substrate. A new type of nanometer ultra low concentration biomolecule detector, gas / humidity sensor, light emitting diode, solar cell and field emission cold cathode were prepared and device performance was enhanced. Si-NPA mainly plays a dual role of assembly template and functional substrate. This will lay the foundation of the optimization of the physical properties and device performance of Si-NPA and Si-NPA-based composite nanometer systems.In the above study, it was found that the performance of Si-NPA-based composite nanometer system and its device was strongly dependent on the surface morphology and structural characteristics of Si-NPA. The experimental results show that by changing the composition and concentration of the hydrothermal etching solution, corrosion temperature, etching time , the resistivity (doping concentration)of the original monocrystalline silicon wafer and so on, can modulate the surface density, the characteristic size, the height, the porosity and the structural features of the silicon column, as well as the optical and luminescent properties, electrical properties, surface passivation state and the physicochemical properties of Si-NPA.Ion implantation is a widely used technique for surface modification of materials.Ion implantation of sc-Si wafers can not only change the doping concentration of sc-Si wafers, but also may cause localized microcrystation / amorphization of the surface of silicon wafers, resulting in sc-Si lattice structures and surfaces changes in physical and chemical state. Which will provide a new technical approach for the modulation of Si-NPA surface morphology and structure, if followed by hydrothermal corrosion technology.In this paper, Si-NPA was prepared by hydrothermal etching using ion implantation and after ion implantation annealing of sc-Si wafers, and compared with Si-NPA prepared with the original sc-Si wafers. The effects of titanium ion implantation and annealing on the surface composition and structure of sc-Si wafers and the surface morphology and photoluminescence properties of Si-NPA were investigated. Analyze the relevant processes and physical mechanisms, and finally provide guidance for the morphology and structure modulation and the optimization of physical properties of Si-NPA. The main results are as follows:(1) Effect of titanium ion implantation and implantation on the surface structure and chemical composition of sc-Si. In the experiment,the implanted ion energy was 60 keV, and the original sc-Si wafer was ion implanted and annealed at three injection doses of 5 × 1015 cm-2,1 × 1016 cm-2 and 5×1016 cm-2. The experimental results show that: (a) After the implantation of titanium ions, the near-ideal and complete lattice structure on the surface is severely damaged, cause localized microcrystation/amorphization of the sample surface, and the larger the ion implantation dose, the higher the localized microcrystallization or amorphization; (b) The implanted titanium ions are dispersed in the sc-Si without forming an isolated titanium crystal phase or a titanium-silicon alloy phase; (c) After high temperature annealing, sc-Si surface lattice structure get a certain degree of repair, crystallinity has been improved and a titanium-silicon alloy phase was observed in the high-dose implanted silicon wafer. The above results provide a basis for the analysis of the effect of ion implantation on the structure,morphology and physical properties of Si-NPA.(2) Effect of titanium ion implantation and post-implantation annealing on the surface structure and morphology of Si-NPA. The experimental results show that Si-NPA prepared by sc-Si wafers ion implantation and post-implantation annealing: (a)When the ion implantation dose is low, the large area uniformity of the silicon column array is reduced, that is, the density distribution and size distribution of the silicon column are uneven. However, with the increase of the ion implantation dose,the density distribution and the uniformity of the size distribution are obviously improved. (b) Compared with the Si-NPA prepared by the original sc-Si wafer, the ion implantation can not significantly change the surface density of the silicon column, but with the increase of the implantation dose, the diameter and height of the silicon column of Si-NPA are gradually smaller. The above results show that the diameter and height of silicon column of Si-NPA can be effectively controlled by ion implantation combined with annealing.(3) Effect of titanium ion implantation and post-implantation annealing on the photoluminescence properties of Si-NPA. The experimental results show that: (a) the photoluminescence intensity of Si-NPA prepared by ion implantation and post-implantation annealing with the original sc-Si wafer decreases and peak redshift with the increase of ion implantation dose; (b) For the two red light emission peaks that make up the Si-NPA photoluminescence spectrum, the relative intensity ratio decreases with the increase of the ion implantation dose, and the relative strength of the two reversal; (c) The photoluminescence intensity of Si-NPA prepared by post-implantation annealing is much higher than that of Si-NPA prepared by ion implantation but unannealed silicon wafers. The results show that the morphology of Si-NPA is controlled by ion implantation and post-implantation annealing, and also controlled the photoluminescence properties of the Si-NPA.(4) Cooling time and heating time to control the surface morphology and structure of Si-NPA during hydrothermal corrosion. In the experiment, the influence of heating and cooling time on the surface morphology of Si-NPA was studied by the fixed cooling time (heating time) and change the heating time (cooling time). The experimental results show that the thickness of Si-NPA can be controlled by changing the heating time, while increasing the cooling time can reduce the roughness of silicon column in Si-NPA surface.(5) Effect of corrosion time on surface morphology and structure of Si-NPA during constant temperature chemical corrosion. In the experiment, the original sc-Si wafer and the ion implanted silicon wafer were chemically etched at a constant temperature of 50? for 1 ?12 h. The results show that the Si column surface of Si-NPA becomes more uniform with the increase of chemical corrosion time,the surface roughness of silicon column decreases, the column height increases and the diameter of silicon column decreases slightly. Compared two groups of experiments,it was proved that the ion implantation could significantly accelerate the corrosion process of sc-Si. |
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