纳米材料的溶剂加压热合成、结构及性能

论文题目：纳米材料的溶剂加压热合成、结构及性能

作者简介：谢　毅，1967年7月生，1994年9月-1996年5月在中国科学技术大学凝聚态物理专业攻读博士学位, 导师钱逸泰教授。1996年5月获中国科学技术大学理学博士学位。攻博期间在《Science》等国内外重要期刊上发表论文九篇。

摘 要

建立了在有机溶剂中实现直接反应的技术, 将有机溶剂加压热合成发展到制备在水溶液中无法形成的或易氧化、易水解的纳米非氧化物。在国际上首次用此技术在280℃下于苯体系中制备出30nm GaN, XPS给出其化学式为Ga0.95N。所得 GaN在370nm处发光,与块材相同, 未表现出量子尺寸效应; 与理论计算得GaN的激子玻尔半径为11nm是一致的。 XRD表明所得的纳米GaN大部分为六方纤锌矿相, 还含有少量岩盐型亚稳相, 文献报道仅利用金刚石砧和同步X射线衍射技术在至少37GPa下仅证实岩盐型GaN的存在, 但一旦压力释放, 该相重新转化回六方相。本工作国际上首次在低于5MPa下制得岩盐型GaN, 并用高分辨电镜直接观察到其存在。在HRTEM照片上根据已知的六方相的晶胞参数验证了由XRD给出的常压下岩盐型GaN的晶胞参数: a=4.100。在300℃下制备的样品为纤锌矿型、闪锌矿型和岩盐型三相共存的纳米GaN, 给出了闪锌矿型GaN的晶胞参数为a=4.420。
在聚醚体系中160℃下制备出10nm InP和纳米InAlP固溶体。所得纳米InP在450nm处有一弱的宽发光带, 与块材相比发生了很大兰移, 表现出量子尺寸效应; 与量子理论计算得InP的激子玻尔半径为29nm是一致的。 通过对聚醚体系中InP团簇的紫外-可见吸收光谱和光致发光光谱的研究, 发现溶剂加压热合成法制备纳米
材料时经历了团簇→(胶体)→非晶→纳米晶的过程; 发现不同的有机溶剂对产物成相和颗粒生长是至关重要的因素; 初步认为聚醚类溶剂能够限制纳米InP颗粒的生长是由于其不仅能打开InCl3的二聚体结构, 而且具有和中心金属元素形成离子配合物的能力.
利用水热还原反应制备出160×80nm短棒状和80nm板状Fe3O4, 用化学法测定其Fe(III)/Fe(II)比为2.13:1。用类似的反应制备出30nm球状的ZnFe2O4和NiFe2O4纳米粉末。利用水热晶化反应制备出6nm ZnS, 红外光谱表明所得纳米ZnS在400-5000cm-1范围内基本无吸收, 比较对ZnS凝胶的水热晶化和普通热处理发现水热晶化过程不仅能提高产物的晶化程度, 而且有效地防止了纳米硫化物的氧化。

ABSTRACT

The thesis established a new technique to prepare nanocrystalline phosphides and nitrides in nonaqueous system under pressure, which is named solvothermal process. Benzene-thermal reaction of Li3N and GaCl3 under pressure was carried out for preparation of 30nm GaN at 280℃, which is much lower than that of traditional methods. X-ray Photoelectron Spectrum analyses of the sample gave the average composition of Ga0.95N. The Photoluminecence spectrum of as-prepared GaN was similar to that of bulk GaN, exhibiting no quantum size effects, which
is consistent with the Bohr exciton radius of 11nm. The X-ray Powder Diffraction pattern indicated that the sample was mainly hexagonal phase GaN with small amount of rocksalt phase GaN with a=4.100. It is the first time that the existence of GaN in rocksalt structure, which
previously appeared under pressure at least 37GPa, was observed directly with High Resolution Transmission Electron Microscopy. HRTEM verified the cell parameter of rocksalt GaN and showed that there was a transitional region between the two cubic phases of GaN with zincblende and rocksalt. The sample prepared at 300℃ was the wurtzite GaN coexisted with zincblende and rocksalt structure. The cell parameter of zincblende　GaN was measured to be a=4.420.
10nm InP and nanocrystalline InAlP solid solutions were obtained in1,2-dimethoxyethane system at 160℃. The PL spectrum of as-prepared InP showed a large blue-shift, exhibiting the quantum size effects, which is consistent with the Bohr exciton radius of 29nm. In the preparation of nanocrystalline InP, InP clusters were observed through UV-Vis absorption spectrum and PL spectrum. A possible mechanism is that the clusters act as the intermediate and combines to form amorphous and finally nanocrystalline InP particles during the solvothermal process. The ability of 1,2-dimethoxyethane that dissociation and the formation of ionic complexes may play an important role in the mechanism to limit the growth of particles.
160×80nm Fe3O4 in short-rod shape and 80nm Fe3O4 in plate shape were synthesized through hydrothermal reductive reaction. Chemical analyses indicated that the ratio of Fe(III) to Fe(II) was 2.13：1. 30nm NiFe2O4 and ZnFe2O4 powders in spherical shape were prepared through a similar　process. Hydrothermal crystallization process was used to prepare 6nm ZnS. IR spectrum of as-prepared ZnS showed no absorption in the range from 400 to 5000cm-1. Compared to the normal thermal process,the　hydrothermal crystallization process can not only enhance the　crystallinity of the products, but also effectively avoid
the oxidazation of nanocrystalline sulphide.