Investigating Atomic Scale Phenomena at Materials Interfaces with Correlated Techniques in STEM/TEM
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information (albeit in a manner that is not as straightforward to interpret). Again, with the large range of problems that exist, there will be times when one of the techniques will provide the most straightforward means to get the desired information, and ideally we would like to be in a position to choose which one to use during the experiment. For complete analysis there are also diffraction techniques that can provide significant information on interfaces [8,13]. To study materials interfaces, we therefore need to be able to employ a wide variety of techniques and ideally, switch between TEM and STEM mode depending on the information we require. The recent development of the JEOL 2010F 200kV Schottky field emission STEM/TEM has now made it possible to accomplish precisely this [14,15]. Depending on the materials system being investigated it is possible to perform all of the functions of a state-of-theart TEM and all of the functions of the highest resolution dedicated STEM during the same experiment. In this paper, we discuss the practical aspects of tuning the instrument for this wide range of experimental techniques. As most of the recent developments have been concerned with the STEM mode of operation, we shall focus primarily on a description of those techniques and only briefly mention the TEM techniques where relevant (i.e. to demonstrate that
the microscope is still a functioning TEM). Having defined the techniques, we go on to discuss two examples of where multiple TEM and STEM techniques were used to investigate materials interfaces; the analysis of grain boundaries in (Ba,Sr)TiO 3 thin films and the analysis of the effect of As at the film-substrate interface on the quality of CdTe (111) on Si (111) substrates. STEM TECHNIQUES The key to high-resolution STEM is the formation of an electron probe of atomic dimensions. Figure 1 shows the lens arrangement in the JEOL 2010F. Essentially, the electron optics of the microscope above the specimen are aligned in such a way as to make the probe as small as possible on the surface of the specimen. For a given acceleration voltage and emission type (e.g. Schottky field emission or cold field emission) the size of the probe is dependent only on the spherical aberration coefficient of the probe forming lens (0.14nm for the 2010F). Filament
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For a given spherical aberration coefficient and acceleration voltage, the probe size is optimized most readily with the electron "Ronchigram", or "shadow image". This is because the intensity, formed at the microscop
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