Focus series

One such approach to counter the effects of spherical aberration is to record a through-focus series, which allows reconstruction of the electron exit-wave function and thereby removal of the spherical aberration. The basic idea of this reconstruction approach, as implemented in the Truelmage software package, will be described after a simplified introduction to HRTEM imaging theory (for more details see Williams and Carter 1996, Reimer 1984, Spence 1988). Furthermore, two application examples are shown to discuss the benefits of focal-series reconstruction and illustrate the information that can be obtained. 

Neidle, S. DNA Structure and Recognition. Focus Series. Oxford IRL Press, 1994. 

For many years efforts have been made to collect more detailed information about the 3rd dimension in TEM. For thin samples (< 50 nm) through-focus series [6] and electron holography [7,8] have been applied successfully. In this paper we mainly restrict the discussion to electron tomography (ET) that can be applied to thicker samples (50-500 nm). For an overview of the several modes of 3D-TEM that elaborates on the microscopy aspects we refer to an earlier review [4], Here we will summarize the principle and practical aspects of ET for the study of molecular sieves. 

Therefore, this simple calculation allows us to approximate the operation in the microscope to the ideal conditions, but this does not eliminate the need for taking through focus series of micrographs, including the amorphous edge detail that will help in the determination of the optical diffractogram power spectrum transferred by the lens, as the more practical and direct method for obtaining HREM information [7, 8]. 

The Scherzer function is determined experimentally by performing the FT of the images of an amorphous filna. At first, focus series images of the amorphous film are made, and then the Fourier transform of each image is recorded (Figures 1.13a, 1.13b, and 1.13c). To determine the information limit [29], it is of interest to have... 

FIGURE 1.13 Through-focus series on a thin carbon film associated with optical diffraction patterns (a) overfocus, (b) optimum focus, and (c) underfocus. 

When the film is heat-treated at 1000°C, coherent scattering domains appear also as bright dots (Figure 1.23a, curve B). They scatter the incident beam at a fixed location. As the aperture size increases resolution improves, so that the domains decrease in size but stay in the same place. At optimum resolution, their size is constant. During a through-focus series (Figure 1.23d), sharpness... 

The starting point of a medicinal chemistry program is the identification of an interesting hit. The definition of such a hit series varies and will be influenced by the TPP or TCP focus. Series potency is an important parameter (against wild-type and resistant strains) as such an EC50 of less than 1 pM is a typical cutoff so as to balance having sufficient numbers of... 

Miller, E. (1996) Changing the way we think about kids with disabilities a conversation with Tom Hehir , in E. Miller and R. Tovey, Inclusion and Special Education, HEL Focus Series No. 1, Cambridge, MA Harvard Educational Publishing. 

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