Surface diffusion study of single crystal and bicrystal ceramics by AFM

本研究中使用的一组样品是双晶MgO，其具有（100）表面和晶界在[010]方向上倾斜24^0。在原子力显微镜（AFM）检测后，将样品加热到1100-1400 ℃，用AFM重新检测，发现晶界宽度（w）与退火时间t^<1/4>成正比，这意味着表面扩散控制了这一过程。结果发现，原子力显微镜可以在较低的温度和较短的退火时间研究晶界开槽。用此方法测定的表面扩散系数与文献中用干涉显微镜测得的数据符合得很好.用光刻技术和随后的退火，在MgO单晶的（100）平面上形成了正弦形的轮廓.然后在这些试样上研究正弦曲线衰减。计算的扩散系数比晶界开槽法快几个数量级。本文还研究了与双晶MgO取向相同的双晶SrTiO_3。与MgO相反，SrTiO_3在沟槽形成后的表面横截面与Mullins的预测完全一致。在测量中还观察到SrTiO_3中的晶界开槽是由表面扩散控制的。这得到了槽高h测量值的支持。由于干涉显微镜不能测量h，因此AFM测量h是独特的。晶界开槽法测定SrTiO_3中的表面扩散与SrTiO_3中的氧晶格扩散几乎在同一范围内，但比Sr晶格扩散快。虽然Ti在SrTiO_3中的扩散系数尚不清楚，但本文的结果是运动较慢的阳离子的表面扩散。

One group of the samples used in this study was bicrystal MgO which was made with (100) surface and grain boundary tilted 24^0 in [010] direction. After examining by AFM,the samples were heated at 1100-1400ﾟC and reexamined by AFM.The grain boundary width (w) is proportional to t^<1/4>, where t is the annealing time, implying that surface diffusion controls the process. It was found that AFM made it possible to study grain boundary grooving at lower temperatures and short annealing time. The surface diffusion coefficient determined in this way was in good agreement with the data in the literature determined by interference microscope.Using photoetching technique and subsequent annealing, sinusoidal profile was formed on (100) plane surface of MgO single crystals. The sinusoidal profile decay was then studied on these specimens. The diffusion coefficients calculated from the results were several orders of magnitude faster than the results obtained by grain boundary grooving. This suggests that mechanism is different in these two processes.Bicrystal SrTiO_3 with the same orientation as bicrystal MgO was also studied. Contrary to MgO the cross section of the surface of SrTiO_3 after the formation of groove was exactly the same as that predicted by Mullins. It was also observed in the measurement that grain boundary grooving in SrTiO_3 was controlled surface diffusion. This was supported by the measurement of groove height, h. Since h can not be measured by interference microscope, the measurement of his unique to AFM.The surface diffusion in SrTiO_3 determined by grain boundary grooving is almost in the same range as the oxygen lattice diffusion in SrTiO_3 but is faster than Sr lattice diffusion. Although the diffusion coeffcient of Ti in SrTiO_3 is not known, the present result is the surface diffusion of slower moving cation.