Contrast transfer function

About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.

Atomic studies on ferroelectric oxides by aberration corrected transmission electron microscopy

Abstract: The advent of aberration-corrected transmission electron microscopy in 1998 [1] has provided materials science with entirely new tools for quantitative investigations. Four key innovations have to be mentioned: (1) The possibility to operate the electron microscope as a variable-sphericalaberration instrument allows to derive a new phase contrast theory optimizing both resolution and point spread [2]. In classical Scherzer phase contrast theory the radius of the point spread disc amounts to three times the Scherzer resolution limit. Besides the fact that information is lost by placing an aperture in the diffraction plane to keep the contrast oscillations in the contrast transfer function from affecting the images this point spread is a second disadvantage of the classical Scherzer approach to phase contrast. Both limitations can be substantially reduced in a new theory in which by both the objective lens defocus Z as well as C S the spherical aberration parameter adopt specific values. As a result the resolution limit coincides with the information limit and the point spread gets reduced to about one half of the latter making it an uncritical parameter in practice. (2) The negative spherical aberration imaging (NCSI) technique leads to enhanced contrast of atoms with low nuclear charge number [3]. It relies on two advantages compared to the classical Zernike technique. The shift of the phase of the diffracted waves is, in contrast to the classical Scherzer technique, in clockwise direction leading to white atom contrast. Furthermore the contrast is enhanced by a dynamic non-linear effect. Oxygen, nitrogen and even boron can be imaged directly even when these atomic species occur in close distance to heavy cations. (3) Essentially point-spread-free atomic images allow to measure occupancies of atomic columns, i.e. local concentrations, with lateral atomic resolution evaluating atomically resolved intensity measurements [4]. This means that high-resolution is not only a structural technique. From now on also local composition maps can be derived which are forming an excellent starting point for ab-initio calculations of interface-, boundary- and defect structures. (4) Measurements of atomic distances can be carried out at an accuracy of a few picometers

Aberration Analysis From Diffraction Patterns Produced By Annular Apertures

Abstract: For points on and near the optical axis, asymptotic solutions to the Rayleigh-Sommerfeld diffraction integral are possible for annular apertures illuminated by plane waves of uniform intensity distribution containing rotationally symmetric Seidel aberrations (defocus and spherical aberration). Computer studies of these cases show excellent agreement with experiment. The amount of defocus and spherical aberration can be determined from shifts in positions of on-axis intensity extrema. An empirical study of the non-rotationally symmetric Seidel aberration astigmatism reveals a predictable change in the diffraction pattern allowing for the verification of the aberration to within .05 wavelengths.

Pixelless image deformation characteristics due to optoelectronic integration between quantum well infrared phototransistor and light emitting diode

Abstract: This manuscript focused on image processing due to optoelectronic integration instruments between quantum well infrared phototransistor and light emitting diode (QWIPT-LED). Thus, characteristics analysis of pixelless images deformation due to QWIPT-LED optoelectronic integration instruments are the aim of this manuscript. Pixelless images reabsorption and reemission challenges during radiative conversion from far infrared (FIR) to near infrared (NIR) are addressed. Overcoming the photons recycling process that deteriorate the output image is the main objective. Therefore, curves for the image characteristics are presented with special emphasis on the carrier’s concentration within the QWIPT-LED optoelectronic devices. These characteristics include contrast transfer function and image resolution. Besides providing a complete analysis of image characteristics, this paper extends the analysis to the image conversion efficiency that figure-of-merit characteristic of QWIP-LED. Additionally, the performance of the underlined characteristics is conducted through closed form expressions. The spatial distribution of the electrons concentration that injected from quantum well infrared phototransistor (QWIPT) into light emitting diode (LED) active layer is considered. Also, the effects of image uniformity and nonuniformity on the image contrast and image resolution are presented. Also, the investigation and description of carrier’s movement within optoelectronic QWIPT-LED is perceived. Moreover, optimization of this optoelectronic integrated device is of concern. The obtained result confirms that contrast transfer function of the image depends on the lithography process during integration between QWIPT and LED as well as structural parameters. These parameters represent the LED thickness of the device portion, radiative recombination, non-radiative recombination, number of quantum well (QW) and period length of the QW. As a final conclusion, the reabsorption process can be minimized by optimal design of the structure parameters with number of QW of 14, thicknesses of QWIPT 120 μm and life time ratio of 0.999. These obtained results confirm the potential applicability of the proposed work of QWIPT-LED pixelless image instrument for image conversion under various parameters conditions. Hence, better performance of QWIPT-LED pixelless image instrument can be achieved.