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中国物理学会期刊

模板对异构体选择性生长的动力学控制作用与化学气相沉积金刚石的生长机理

CSTR: 32037.14.aps.54.4300

The dynamic control of the templates in selectivity growth from their isomers and the growth mechanism of CVD diamond

CSTR: 32037.14.aps.54.4300
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  • 阐述了模板的动力学控制作用对大尺度有序结构特别是亚稳相的生长,对自由能相差很小的异构体的选择生长所具有的重要作用.汲取现有金刚石生长理论的合理思想,以模板概念为基础给出了对化学气相沉积(CVD)过程的动力学热力学综合描述:1)碳原子在碳氢化合物中的化学势高于固相碳,气相碳氢化合物的碳原子有可能落到化学势较低的固态碳的各种异构体.2)气相碳通过表面反应实现向固相碳的转化.3)表面的模板作用是控制气相碳原子转换方式的主要动力学因素,不同的表面(石墨各种取向的表面及金刚石不同取向的表面)选择了落入其上的碳原子的结构方式及能量状态.4)因此,衬底的不同区域可发生几种不同的独立的表面反应过程,这些反应对应于不同表面的生长.5)而这些表面反应的方向性及速度受表面临域热力学因素的影响,反应的方向性决定了某种晶面是生长或刻蚀,在特定的温度、压强及各种气体分压下可以实现金刚石的生长和石墨的刻蚀.6)衬底局域晶格结构及键价结构和衬底表面气相的温度、压强及各种气体分压等热力学条件共同决定了成核的临界条件.7)与外界有能量和物质交换的等离子体系统,以及气相中发生的一系列化学反应,仅起到了维持某种固相表面生长所需要的非平衡热力学条件和化学条件的作用.金刚石和石墨表面具有的模板动力学控制作用,在特定热力学条件下主导自身外延层的生长方式;异质衬底的某些局域微观结构可以作为新相生长成核的局域模板;不同材料、不同的处理方法、及不同的化学环境下的衬底具有不同的局域微观结构,从而决定了多晶薄膜的取向优势.

     

    The key role of templates in the process of large-scale growth of ordered metastable phase and that of selectivity growth from their isomers with approximately equal free energy have been emphasized. Considering the rational elements in the existing models, the dynamics and thermodynamics theory for the growth process of diamond films have been given: 1) The chemical potential of carbon atoms is higher in the state of hydrocarbon gases than in the solid state. The carbon atoms in hydrocarbon gases may drop down to graphite or diamond surface that has a lower chemical potential. 2) The gas-state carbon atoms may change into the solid state through surface reactions. 3) The effect of surface of the template is a major factor for controlling the way of conversion of the gas-state carbon atoms. The different surfaces (surfaces with different orientations of graphite and diamond) can choose the different structure and energy state of the carbon atoms dropped onto them.4) Therefore, several kinds of different and independent surface reaction processes can occur at different sites of the substrate. These reactions correspond to the growths on different surfaces; 5) The orientation and velocity of these surface reactions are affected by the thermodynamic factors of neighboring surfaces. The direction of interaction determines whether growth or etching occurs for certain crystal surface. Growth of diamond and etching of graphite may be realized in a special range of temperature, of pressu re, of flow ratio of different gases. 6) The critical condition of nucleation wa s determined by the thermodynamic conditions such as local crystal lattice struc ture of the substrate, bonding structure, the gas temperature on the substrate s urface, pressure, the fractional pressure of different kinds of gases, and so on . 7) The plasma system that has energy exchange with the surroundings, and a ser ies of chemical reactions that occur in the gas phase can only provide the requi red non-equilibrium thermodynamic and chemical conditions to keep the growth of certain solid phase surface. The surfaces of diamond and graphite have the chara cter of template, they will dominate the epitaxy pattern of themselves. Heteroge neous substrates have certain local microstructure to play the role of a local t emplate for new phase nucleation. Different local microstructures caused by diff erent substrates, processing method and different chemical conditions will deter mine the orientation character,of the film.

     

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