Synthesis of Berried Nanocrystals by Heavy-Ion Implantation and Stabilized High-Efficient Luminescence

本工作的目的是通过重离子注入和随后的热退火制备直径为1-10 nm的纳米晶体，揭示基本的合成机制，建立晶体界面的发光相关量子态，并将纳米晶体激活为具有稳定发光性能的量子点。这些将有助于作为照相装置的应用和对固体中辐射诱发的基本过程的理解。研究了在SiO_2中制备锗纳米晶的工艺，并对其进行了注入和热退火。通过对比实验和模拟结果，得到了Ge原子在SiO_2基体中溶解度和扩散系数的有效值。根据离子剂量和退火时间的不同，用这些值计算出的析出相的平均直径为10-15 nm。氢在SiO_2包埋的硅纳米晶的发光中起着非常重要的作用。采用离子注入-热退火法制备的含硅SiO_2样品是具有高密度缺陷、局部硅偏析和硅纳米晶的复杂体系。采用适当的退火工艺对系统进行控制，并将氢气注入系统中，利用弹性反冲探测技术揭示了氢气的捕集-脱集过程。在可控的注入和热退火条件下，发现氢可以成功终止Si纳米晶/SiO_2界面上的Si悬空键。SiO_2中注入Si和Ge后，在N_2气氛中热退火后，分别在720 nm和550 nm波长处观察到宽光致发光。

The purpose of this work is to produce nanocrystals of 1-10 nm in diameter by heavy ion implantation and subsequent thermal annealing, to reveal the basic synthesis mechanism, to establish luminescence-related quantum states of crystalline interface and to activate the nanocrystals as quantum dots with stable luminescence property. These will contribute to the application as photo devises and to understanding of radiation-induced fundamental processes in solids1. Fabrication of Ge nanocrystals in SiO_2 was studied for a procedure of implantation and subsequent thermal annealing. A comparison between experimental and simulated changes of the depth profile of implanted Ge atoms led to effective values of solubility and diffusion coefficient of Ge atoms in the SiO_2 matrix. The mean diameter of precipitates calculated using those values are 10-15 nm, depending on ion dose and annealing duration.2. Hydrogen plays very important role in luminescence of Si nanocrystals embedded in SiO_2. Si-containing SiO_2 samples produced by ion implantation followed by thermal annealing are very complex systems having high density defects, locally concentrated Si segregates and Si nanocrystals. Hydrogen was implanted into the system which was controlled by applying an appropriate annealing procedure, and the trapping-detrapping process of hydrogen has been revealed by applying the elastic recoil detection technique. It was found for hydrogen to successfully terminate Si dangling bonds on the interface of Si nanocrystal/SiO_2 under a controlled implantation and thermal annealing condition.3. Broad photoluminescence was observed around wave lengths of 720 nm and 550 nm, respectively, for Si and Ge implanted samples of SiO_2 followed by thermal annealing in N_2 atmosphere.