A theoretical analysis of HREM imaging for 〈110〉 tetrahedral semiconductors

Structure analysis of defects in nanometer space inside a crystal: creation and agglomeration of point defects in Si and Ge revealed by high-resolution electron microscopy

Recent structural studies of point-defect-agglomerates in Si and Ge by high-resolution transmission electron microscopy (HRTEM) are compiled along with some new results. After examining the wave nature of incident electrons on defect formation during HRTEM observation and the correlated recombination of point defects under electron irradiation, we show that HRTEM is the unique means to analyze the atomic structure of small agglomerates of point defects, nanometer in size, inside a crystal. Emphasis is placed on the extension of studies made possible only by the elaborate and crucial structure determination by HRTEM: the mechanism of agglomeration at the atomic level, the extraction of novel unit structures of point defects, and the electronic structure of the agglomerate. Some examples on the subjects are demonstrated in cases of the [113] and [001] defects. The effect of specimen surfaces on structure determination is also discussed. Finally, a development of TEM technique with in-situ optical spectroscopy is described, which is utilized to pursue interaction of point defects under electron irradiation and thus may reinforce HRTEM experiments.

(110) HREM of interfacial structures in semiconductor hetero-structures

We have established a (110) cross-sectional high-resolution transmission electron microscopy (HREM) method to observe atomic structures of semiconductor hetero-interfaces. We show theoretically that the semiconductors in a hetero-structure exhibit strong contrast for an EM specimen thickness near their extinction distances, allowing atomic-scale observations of the interfacial structures between them. Furthermore, to obtain a clear HREM image, an EM specimen preparation technique is developed in which chemical etching is used to remove ion milling artifacts. This HREM method allows edge-on imaging of interfaces formed along the (110) direction; observations of atomic steps at AlAs/GaAs interfaces and a chemically ordered structure at Si/Ge interfaces are demonstrated.

Compositional variations in apatites with respect to preferential ionic extraction

Detection of ionic losses from the apatitic structure (Ca10(PO4)6(OH)2) by high-resolution electron microscopy was investigated theoretically. Linear image analysis showed the need for an objective aperture of at least 3.7 nm-1 to visualize four different coordinates (CaII, OH-, P and mid-point between CaII-P bond). High-resolution image analysis and plotting of OH- column intensity against specimen thickness showed an inverse proportionality between composition and OH- image intensities for very thin specimens (less than 2 nm). Image intensity variation would be detectable experimentally, but the preparation of such thin specimens by ultramicrotomy is impossible.