低温条件下单晶氮化铝纳米线生长机理的研究

在25mL的不锈钢反应釜中，利用无水三氯化铝与叠氮化钠在无溶剂的条件下直接反应，成功地合成出了单晶氮化铝纳米线，反应温度为450℃，有效反应时间为24h.高分辨率透射电子显微镜测试结果显示，纳米线多为长直线状外貌特征，直径在40—60nm范围内，最大长度可达几个微米.高分辨率电子衍射和X射线衍射结果都表明，多数纳米线为六方结构，也有少量呈现面心立方结构.同时，提出了长直线状六方和面心立方单晶氮化铝纳米线的生长机理的假设，并对六方单晶氮化铝纳米线生长方向的人工控制也进行了讨论. 关键词： 六方单晶氮化铝 纳米线 X射线衍射 透射电子显微镜     

空心微球/网络复合型碳泡沫材料制备与机理分析

在Klett等人于2000年制备的韧带网络型碳泡沫和Bruneten等人在2002年制备了一种空心微球碳泡沫材料结构的基础上,分别经过微观结构优化、碳化、石墨化处理,制备出了一种空心微球/网络复合型碳泡沫材料.扫描电镜和体视显微镜测试结果显示网络韧带和球形空腔呈现明显的空间周期性.X射线衍射(X-ray diffraction,XRD)图谱中,26°处的衍射峰表明该试样具有较高的石墨化特征.同时,对该材料的形成机理进行了分析. 关键词： 碳泡沫 微观结构优化 扫描电镜 X射线衍射     

电极形状与紫外探测器灵敏度关系的研究

在传统工艺的基础上，改变电极的形状可以提高氮化镓(GaN)基材料光导型紫外探测器的灵敏度.经过计算可知，虽然三棱形电极可以使探测器有效受光率提高100％，但工艺复杂，难以实现；而半圆柱形电极虽然使氮化镓薄膜有效受光率仅提高20％左右，但工艺简单，便于加工.     

First principle study of nitrogen vacancy in aluminium nitride

In the framework of density functional theory, using the plane-wave pseudopotential method, the nitrogen vacancy （VN） in both wurtzite and zinc-blende AlN is studied by the supercell approach. The atom configuration, density of states, and formation energies of various charge states are calculated. Two defect states are introduced by the defect, which are a doubly occupied single state above the valance band maximum （VBM） and a singly occupied triple state below the conduction band minimum （CBM） for wurtzite AlN and above the CBM for zinc-blende AlN. So VN acts as a deep donor in wurtzite AlN and a shallow donor in zinc-blende AlN. A thermodynamic transition level E（3＋/＋） with very low formation energy appears at 0.7 and 0,6eV above the VBM in wurtzite and zinc-blende structure respectively, which may have a wide shift to the low energy side if atoms surrounding the defect are not fully relaxed. Several other transition levels appear in the upper part of the bandgap. The number of these levels decreases with the structure relaxation. However, these levels are unimportant to AlN properties because of their high formation energy.     

六方单晶氮化铝薄膜的合成与紫光发光机理

利用无水三氯化铝与叠氮化钠在无溶剂的条件下直接反应,成功地合成出六方单晶氮化铝(h-AlN)薄膜.反应温度为450℃,有效反应时间为20 h.高分辨率透射电镜发现为薄膜形态；电子衍射和X射线衍射结果都表明,氮化铝薄膜为六方结构.光致发光实验显示,在可见光范围内有一较强的辐射峰,中心位于413 nm处,半高宽约为5 nm.同时,本文对六方单晶氮化铝薄膜的生长机理和光致发光机理也进行了讨论.     

First principle study of nitrogen vacancy in aluminium nitride

In the framework of density functional theory, using the plane-wave pseudopotential method, the nitrogen vacancy ($V_{\rm N})$ in both wurtzite and zinc-blende AlN is studied by the supercell approach. The atom configuration, density of states, and formation energies of various charge states are calculated. Two defect states are introduced by the defect, which are a doubly occupied single state above the valance band maximum (VBM) and a singly occupied triple state below the conduction band minimum (CBM) for wurtzite AlN and above the CBM for zinc-blende AlN. So $V_{\rm N}$ acts as a deep donor in wurtzite AlN and a shallow donor in zinc-blende AlN. A thermodynamic transition level $E({3 + } \mathord{\left/ {\vphantom {{3 + } + }} \right. \kern-\nulldelimiterspace} + )$ with very low formation energy appears at 0.7 and 0.6eV above the VBM in wurtzite and zinc-blende structure respectively, which may have a wide shift to the low energy side if atoms surrounding the defect are not fully relaxed. Several other transition levels appear in the upper part of the bandgap. The number of these levels decreases with the structure relaxation. However, these levels are unimportant to AlN properties because of their high formation energy.