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In this paper,large-sized sapphire (230×210 mm,27.5 kg) was grown by SAPMAC method (sapphire growth technique with micro-pulling and shoulder-expanding at the cooled center). Dislocation peculiarity in large sapphire boule (0001) basal plane was investigated by chemical etching,scanning electron microscopy and X-ray topography method. The triangular dislocation etch pit measured is 7.6×101~8.0×102 cm-2,in which relative high-density dislocations were generated at both initial and final stages of crystal growth. The analysis of single-crystal X-ray topography shows that there are no apparent sub-grain boundaries; the dislocation lines are isolated and straight. Finally,the origins of low-density dislocation in sapphire crystal are discussed by numerical analysis method. 相似文献
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Theoretical and experimental investigations of coherent phonon dynamics in sapphire crystal using femto- second time-resolved coherent anti-Stokes Raman scattering 下载免费PDF全文
We report on the theoretical and the experimental investigations of the coherent phonon dynamics in sapphire crystal using the femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) technique. The temporal chirped white-light continuum (WLC) is used for the Stokes pulse, therefore we can perform the selective excitation of the phonon modes without using a complicated laser system. The expected quantum beat phenomenon is clearly observed. The theoretical formulas consist very well with the experimental results. The dephasing times of the excited phonon modes, the wavenumber difference, and the phase shift between the simultaneously excited modes are obtained and discussed. This work opens up a way to study directly high-frequency coherent phonon dynamics in bulk crystals on a femtosecond time scale and is especially helpful for understanding the nature of coherent phonons. 相似文献
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冷心放肩微量提拉法大尺寸蓝宝石单晶生长过程的模拟分析 总被引:3,自引:1,他引:3
利用数值模拟方法计算了冷心放肩微量提拉法(SAPMAC)蓝宝石晶体生长过程。结合晶体直径变化、裂纹出现位置与延续方向、晶体透明性等实验现象,通过与提拉法、温梯法、坩埚移动法等相对比,分析了冷心放肩微量提拉法晶体生长各阶段的工艺特点,并根据模拟计算结果对晶体生长系统和晶体生长控制工艺进行了改进。分别利用增大热交换器的散热参数、降低加热温度、改进降温曲线、调节外加轴向和径向温度梯度的方式来实现对晶体生长的引晶、放肩、等径和收尾控制。通过实验比较证明了改进后的晶体生长系统和晶体生长控制工艺能够生长出性能较好的大尺寸蓝宝石晶体。 相似文献
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采用有限元法对冷心放肩微量提拉法蓝宝石晶体生长过程中晶体内的温度、应力分布进行了模拟计算,结合实验结果讨论了蓝宝石晶体热性能的各向异性对晶体生长的影响。研究结果表明,对于冷心放肩微量提拉蓝宝石晶体生长系统,较大的轴向热导率有利于提高晶体的生长速率和界面稳定性,而稍大的径向热导率则有利于保持微凸的生长界面。晶体内的热应力受径向热膨胀系数的影响显著,随着径向热膨胀系数的增大而增大,最大热应力总是出现在籽晶与新生晶体的界面区域。在实验中选a轴为结晶取向,成功生长出了直径达230mm、高质量蓝宝石晶体。 相似文献
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长脉冲激光切割蓝宝石的断口分析 总被引:1,自引:0,他引:1
采用长脉冲激光对蓝宝石晶体在不同的保护气体作用下切割获得的断口进行了研究。Nd∶YAG脉冲激光分别在N2、Ar、O2保护气氛下对蓝宝石晶体的(0001)面上以相同的工艺参数进行切割。蓝宝石切割断口的物相和形貌分别采用XRD和SEM进行表征。结果表明:在保护气体作用下,Ar保护气氛下的切割深度最大,断口平整,有金属光泽,检测断口处以多晶α-Al2O3相为主相,并有少量的Al相;N2保护下断口无金属光泽,有粉化现象,存在多晶α-Al2O3相为主相,并有少量的AlN相;O2保护气下切割深度最浅,而且断口表面粉化严重,检测出以多晶α-Al2O3相为主相,三种切痕条纹均与激光的切削方向相反。 相似文献
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处理了无链转移时脉冲激光引发自由基聚合中的动力学问题:推导出聚合产物数均和重均分子量的严格数学表达式,给出了链自由基、死聚物及总的聚合产物的归一化的分子量分布函数.计算结果表明:随着单体转化率的上升,各种分子参数,例如数均和重均分子量,以及多分散指数的数值周期性地振荡,且振幅逐渐下降.分子量分布曲线则包含一些特征峰,且随着每次脉冲激光产生的初级自由基浓度的降低,分布曲线峰的数目增加.另外,与歧化终止相比,偶合终止使产物的分子量分布略为变窄. 相似文献
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