基于等离子体诊断的MPCVD单晶金刚石生长优化设计

微波等离子体化学气相沉积(Microwave plasma chemical vapor deposition,MPCVD)技术是制备大尺寸、高品质单晶金刚石的理想途径,然而MPCVD单晶金刚石生长过程的复杂性与晶体生长需求的多样性难以对生长过程进行优化设计。针对此问题,本研究提出了一种基于等离子体诊断技术的MPCVD单晶金刚石生长的系统性设计方法,采用等离子体成像和光谱分析对微波等离子体进行量化诊断。并利用自主研发的MPCVD设备,研究了腔室压力-微波功率-等离子体性状-衬底温度间的物理耦合特性和量化关系,得到了不同参数下的等离子体有效长轴尺寸、基团浓度和分布、能量密度等数据,以实验观测数据为基础拟合得到了单晶金刚石生长工艺图谱。根据此工艺图谱,可以通过选择生长温度和所需生长面积来选取工艺参数,且通过实验验证,表明此图谱具有较强的指导意义,预测参数误差小于5%。同时根据该图谱的预测,研究了不同等离子体能量密度下的单晶金刚石生长情况,在较低功率下(2600 W)也得到了较高的能量密度(148.5 W/cm3),含碳前驱体的浓度也高于其他工艺条件,因而获得了较高的生长速率(8.9μm/h)。此套方法体系可以针对不同单晶金刚石生长需求进行有效的等离子体调控和工艺优化。

Growth Parameters of DK8031 Maize Variety as Affected by Varying Irrigation and Nitrogen Fertilizer Rates in Embu County, Kenya

Determination of crop growth parameters of maize helps assess the performance of the crop for food security. A study was conducted in two seasons covering 2012 and 2013 to establish optimal irrigation and nitrogen fertilizer rates for drought tolerant hybrid maize （Zea mays L.）, DK8031 variety, in sandy loam soils using furrow irrigation. Four additive irrigation levels （119.05 mm, 238.10 mm, 357.15 mm and 476.2 mm） were allocated the main plots while five nitrogen fertilizer rates （0 kg/ha, 60, 75 kg/ha, 90 kg/ha and 100 kg/ha） were allocated the sub-plots. Both irrigation and nitrogen fertilizer treatments significantly enhanced crop growth parameters under consideration. Stand count per treatment plot, plant height and number of leaves per ranged from 45-59 plants/plot, 215-238 cm and 14-16 leaves respectively. It was concluded that use of supplementary irrigation and phased nitrogen fertilizer rates for maize growing in areas such as Embu can greatly promote crop growth.