[论文解读] Phase transitions and critical phenomena of tiny grains thin films synthesized in microwave plasma chemical vapor deposition and origin of v1 peak

Mubarak Ali, I‐Nan Lin|arXiv (Cornell University)|Apr 25, 2016

Diamond and Carbon-based Materials Research参考文献 53被引用 25

一句话总结

本研究揭示了微波等离子体CVD中电子束动力学主导了超纳米晶金刚石（UNCD）和纳米晶金刚石（NCD）薄膜的结构演化，导致相变形成独特的原子构型——二维椭圆状与一维衍射光栅状结构。这些结构转变与拉曼光谱特征直接相关：v1峰源于光栅状晶粒，而D*带对应于二维椭圆状结构，场发射性能则由光栅形貌驱动。

ABSTRACT

Different trends have been observed in Raman analyses and electron field emission measurements of ultrananocrystalline diamond (UNCD) and nanocrystalline diamond (NCD) films synthesized in plasma-based chemical vapor deposition techniques. Phase transitions in any material are crucial as they may be the origin of new phenomenon. In the present work, it has been observed that dynamics determine the structure of tiny grains of UNCD and NCD films and those made in two-dimensional structure they stretched in the direction of impinging electron streams where diffusion of electrons states of atoms is orientation based. In those tiny grains where atoms stretch less photons of hard X-ray still retain two-dimensional structure where atoms are more like in oval shape, on stretching one-dimensionally. On the other hand, those tiny grains where all atoms are stretched more (one-dimensionally and uniformly), on propagation of photons on surfaces of their electronic structures, they are transformed into grating like shapes. In Raman spectra, peaks related to v1 band and D* band are due to those tiny grains of UNCD and NCD films which are transformed into grating like shapes and two-dimensional structures, respectively. Field emission characteristics of UNCD and NCD films are resulted on the basis of tiny grains transformed into grating like shapes. High resolution transmission electron microscopy analyses physically show transforming of two different structures of tiny grains in so called UNCD and NCD films and validate the observations.

研究动机与目标

• 探究超纳米晶金刚石和纳米晶金刚石薄膜中v1拉曼峰的起源。
• 理解微波等离子体CVD过程中电子束动力学如何影响微小金刚石晶粒的原子结构形成。
• 将观测到的结构形貌与拉曼光谱特征及场发射特性相关联。
• 利用高分辨透射电子显微镜（HRTEM）验证UNCD和NCD薄膜中的结构转变。

提出的方法

• 通过拉曼光谱分析振动模式，特别聚焦于UNCD和NCD薄膜中的v1和D*带。
• 进行电子场发射测量，将电子发射行为与纳米结构形貌相关联。
• 利用高分辨透射电子显微镜（HRTEM）直接观察微小金刚石晶粒中的原子排列。
• 分析电子流方向对二维和一维构型中原子拉伸及结构各向异性的影响。
• 绘制原子结构在电子束照射下从类椭圆状二维形态向光栅状一维形态的转变过程。
• 将光子在电子表面的传播与高度拉伸晶粒中周期性光栅状结构的形成相关联。

实验结果

研究问题

• RQ1 是什么导致了超纳米晶金刚石和纳米晶金刚石薄膜中的v1拉曼峰？
• RQ2 等离子体CVD过程中电子束动力学如何影响微小金刚石晶粒的原子结构？
• RQ3 何种结构转变导致了UNCD和NCD薄膜中光栅状形貌的形成？
• RQ4 场发射特性如何与纳米结构金刚石晶粒的形貌相关？
• RQ5 原子拉伸方向在决定金刚石晶粒的二维或一维结构中起什么作用？

主要发现

• v1拉曼峰源于在电子束辐照下因均匀原子拉伸而形成光栅状一维结构的微小金刚石晶粒。
• D*拉曼带与在拉伸不均匀区域形成的二维椭圆状原子构型相关。
• UNCD和NCD薄膜中的场发射特性与电子束诱导原子对齐所形成的光栅状纳米结构直接相关。
• 高分辨透射电子显微镜证实存在两种截然不同的结构形态：类椭圆状二维晶粒与一维光栅状晶粒。
• 微波等离子体CVD过程中的电子束动力学决定了原子的各向异性拉伸，从而导致取向依赖的电子与结构特性。
• 光子在高度拉伸晶粒的电子表面传播，诱导形成周期性光栅状结构，其光谱特征可识别为v1峰。