Winkler H, Gross H
Institut für Zellbiologie, ETH-Hönggerberg, Zürich, Switzerland.
Scanning Microsc Suppl. 1988;2:379-86.
Rotary shadowing is investigated by means of an adapted shadowing model, which has been used for relief reconstruction of unidirectionally shadowed specimens. The metal layer geometry is calculated for a simple geometric object. In order to elucidate the metal accumulation process on the surface, a Monte Carlo simulation of shadowing is applied to synthetic reliefs and to experimental relief reconstruction data of a paracrystalline membrane. For rotary shadowed specimens, no linear relationship between local metal thickness and surface height can be established as in the unidirectional case. Low spatial frequencies of the surface relief contribute very little to the information content of the observed metal film. Contrast produced by rotary shadowed films is lower compared to unidirectionally shadowed ones. The main effects are due to the steep slopes which give rise to the considerable amount of metal viewed in the normal projection, and due to the shadow casts. A further contrast enhancing effect is self-shadowing, an artifact introduced primarily by rotating the specimen during evaporation. The Monte Carlo simulation shows that low elevation angles favor self-shadowing effects. This results in a pronounced granularity that is caused by the random incidence of the atoms and the accumulation at previously deposited atoms or grown clusters. On real surfaces, small decorating clusters can be enlarged by self-shadowing. This explains the increased decoration tendency of rotary shadowed specimens. The Monte Carlo method can be used as a means to differentiate shadowing information from these effects.
通过一种改进的阴影模型对旋转阴影进行了研究，该模型已用于单向阴影标本的浮雕重建。针对一个简单的几何物体计算金属层几何形状。为了阐明表面上的金属积累过程，将阴影的蒙特卡罗模拟应用于合成浮雕和准晶膜的实验浮雕重建数据。对于旋转阴影标本，与单向情况不同，无法建立局部金属厚度与表面高度之间的线性关系。表面浮雕的低空间频率对观察到的金属膜的信息含量贡献很小。与单向阴影膜相比，旋转阴影膜产生的对比度较低。主要影响因素是陡峭的斜坡，这导致在正投影中看到大量的金属，以及阴影投射。另一个对比度增强效应是自阴影，这是在蒸发过程中主要通过旋转标本引入的一种伪像。蒙特卡罗模拟表明，低仰角有利于自阴影效应。这导致了明显的粒度，这是由原子的随机入射以及在先前沉积的原子或生长的团簇处的积累引起的。在实际表面上，小的装饰团簇可以通过自阴影放大。这解释了旋转阴影标本装饰倾向增加的原因。蒙特卡罗方法可作为一种手段，将阴影信息与这些效应区分开来。
