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6895 results in Condensed Matter Physics, Nanoscience and Mesoscopic Physics

Page 56 of 345

  • Foreword

  • Chris Jacobsen, Argonne National Laboratory, Illinois
  • Book:
    X-ray Microscopy
    Published online:
    28 October 2019
    Print publication:
    19 December 2019, pp xiii-xiv

  • Summary

    X-ray microscopy is an interdisciplinary topic, both in terms of its technical details and in terms of the scientific and engineering problems it is applied to. While there are a number of books that provide excellent coverage of certain aspects of x-ray physics, optics, and microscopy, it is my opinion that there has not been a single book that one can hand to someone new in the field of x-ray microscopy to give them an introduction to most of the key aspects they should know about. This book is an attempt to fill that need.

    Are you a new PhD student entering a research group who will use x-ray microscopy for part of your research? If so, you have probably had at least a year or so of university physics during your studies. You are whom I have written the book for! At times I may push you a bit further in mathematics or physics than what you have learned thus far, but if you are in a PhD program you are a serious enough student so this should be OK. Besides, you can always skim over some of the more detailed points.

    Are you an established researcher or engineer who is new to x-ray microscopy? This book is also for you! Your expertise might be with microscopes using other radiation, or on materials you hope to understand better using x-ray microscopy.

    What I hope to do in this book is to give you a feel for the fundamental ideas that come into play in a variety of x-ray microscopy approaches and applications, and to do so with enough detail to allow you to go off and invent new approaches of your own. I look forward to seeing your contributions to x-ray microscopy!

    What do I mean by x-ray microscopy? I have decided to focus on imaging at a spatial resolution of a few micrometers down to nanometers. This is not a book on medical radiology at 0.1 mm resolution as limited by acceptable radiation exposure, and it is not a book on crystallography.

  • 7 - X-Ray Microscope Instrumentation

  • Chris Jacobsen, Argonne National Laboratory, Illinois
  • Book:
    X-ray Microscopy
    Published online:
    28 October 2019
    Print publication:
    19 December 2019, pp 259-320

  • Summary

    Janos Kirz and Michael Feser contributed to this chapter.

    The first x-ray microscopes were one-of-a-kind instruments that were operated by their builders, in a tradition that continues to this day. Although there was a brief phase in the 1950s where commercial point-projection microscopes were available (see Section 6.2, and [Cosslett 1960, Plates IX.B and X]), up until the year 2000 essentially all microscopes were custom-built. These custom-built microscopes are now joined by commercial instruments offering a wide range of capabilities. No matter whether you are using a commercial instrument where you can pop a sample in and push a button to get an image, or a custom instrument, it is useful to understand what “makes it tick.” Hence this chapter. Section 7.1 discusses x-ray sources, while Section 7.2 discusses the optical transport systems and associated equipment needed to bring the x-ray beam to the imaging system. After some brief comments on nanopositioning systems in Section 7.3, the properties of several types of x-ray detectors are covered in Section 7.4. Finally, Section 7.5 provides a short introduction to specimen environments.

    The degree of sophistication in modern x-ray microscopes is worth a moment's pause for thanks. It wasn't always so! What is available today makes the home-built system (Fig. 2.4) that the author first encountered look unbelievably crude, and at that point things had already made significant advances from earlier years [Kirz 1980c, Rarback 1980]. An amusing anecdote was presented by Arne Engström in 1980 [Engström 1980] as he looked back on four decades of work in x-ray microscopy:

    Another trend in x-ray microscopy and x-ray microanalysis, especially in the field of the biomedical sciences, is the increasing sophistication and complexity of systems and equipment for the collection and treatment of experimental absorption data. However, this trend is not unique to this field of research. In fact, over the last 20 to 30 years there has been such a fantastic development of commercially available instrumentation for research and development that, in retrospect, the immediate post-war conditions seems very primitive indeed. For example, I remember the presentation of an automatic recording optical microabsorptiometer applicable to cellular analysis at an AAAS meeting in Boston in 1951.

  • 2 - A Bit of History

  • Chris Jacobsen, Argonne National Laboratory, Illinois
  • Book:
    X-ray Microscopy
    Published online:
    28 October 2019
    Print publication:
    19 December 2019, pp 5-22

  • Summary

    Those who cannot remember the past are condemned to repeat it – George Santayana, Reason in Common Sense (Vol. 1 in The Life of Reason), 1905.

    Janos Kirz contributed to this chapter.

    Röntgen and the discovery of X rays

    The words of discovery are rarely those of Archimedes’ legendary shout of “Eureka!” or “I have found it!” as he supposedly leaped naked from his bathtub (good thing there weren't webcams in those days!). Instead, the words of discovery are more likely to be along the lines of “hmm … that's odd.” Such is the case of the discovery of X rays [Glasser 1933, Mould 1993].

    At the time of their discovery, many investigators were carrying out experiments with various types of cathode ray tubes, but it was only Wilhelm Conrad Röntgen, Professor and Director of the Physical Institute at the University of Würzburg, who noticed some curious phenomena and decided to investigate further. Röntgen was 50 years old at the time, with a reputation for care in experiments even though his research in the physics of gases and fluids was not particularly cutting-edge. Cathode rays (which we would now call electron beams) were all the rage at the time, so Röntgen decided to investigate whether they would exit thin-walled Hittorf–Crookes tubes. To make it easier to use a phosphor to try to observe this, he surrounded a tube with black paper and worked in a darkened room. While setting up the experiment late on a Friday afternoon (November 8, 1895), he noticed that the phosphor was flickering in synchrony with the fluctuations of the glowing filament in the tube – even though the phosphor was some distance away, and with black paper in between! The odd phenomena immediately captured Röntgen's attention to the point that he did not notice an assistant entering the room later on to retrieve some equipment. When Röntgen's wife Bertha finally succeeded in getting a servant to coax him upstairs to their apartment on the top floor of the Institute, Röntgen ate little of his supper and spoke even less before returning that evening to the puzzle in the lab.

  • 8 - X-Ray Tomography

  • Chris Jacobsen, Argonne National Laboratory, Illinois
  • Book:
    X-ray Microscopy
    Published online:
    28 October 2019
    Print publication:
    19 December 2019, pp 321-349

  • Summary

    Doğa Gürsoy contributed to this chapter.

    Up until now we have concentrated on two-dimensional (2D) imaging of thin specimens. However, one of the advantages microscopy with X rays offers is great penetrating power. This means that X rays can image much thicker specimens than is possible in, for example, electron microscopy (as discussed in Section 4.10). For this reason, tomography (where one obtains 3D views of 3D objects) plays an important role in x-ray microscopy. There are entire books written on how tomography works [Herman 1980, Kak 1988], and on its application to x-ray microscopy [Stock 2008], so our treatment here will be limited to the essentials. Examples of transmission tomography images are shown in Figs. 12.1, 12.6, and 12.9, while fluorescence tomography is shown in Fig. 12.3.

    Our discussion of x-ray tomography will be carried out using several simplifying assumptions:

  • • We will assume parallel illumination, even though there are reconstruction algorithms [Tuy 1983, Feldkamp 1984] for cone beam tomography where the beam diverges from a point source.

  • • We will assume that we start with images that provide a linear response to the projected object thickness t(x, y) along each viewing direction. In the case of absorption contrast transmission imaging, this can be done by calculating the optical density D(x, y) = - ln[I(x, y)/I0] = μt(x, y) as given by Eq. 3.83, with μ being the material's linear absorption coefficient (LAC) of Eq. 3.75. In phase contrast imaging, one may have to use phase unwrapping [Goldstein 1988, Volkov 2003] methods to first obtain a projection image which is linear with the projected object thickness since (see Fig. 3.17).

  • • We will assume that there is no spatial-frequency-dependent reduction in the contrast of image features as seen in a projection image. That is, we will assume that the modulation transfer function (MTF) is 1 at all frequencies u (see Section 4.4.7). One can always approach this condition by doing deconvolution (Section 4.4.8) on individual projection images before tomographic reconstruction, or building in an actual MTF estimate into optimization approaches (Section 8.2.1).

  • • We will assume that the first Born approximation applies (Section 3.3.4): we can approximate the wavefield that reaches a downstream plane in a 3D object as being essentially the same as the wavefield reaching an upstream plane.

Page 56 of 345