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About this book

Helium Ion Microscopy: Principles and Applications describes the theory and discusses the practical details of why scanning microscopes using beams of light ions – such as the Helium Ion Microscope (HIM) – are destined to become the imaging tools of choice for the 21st century. Topics covered include the principles, operation, and performance of the Gaseous Field Ion Source (GFIS), and a comparison of the optics of ion and electron beam microscopes including their operating conditions, resolution, and signal-to-noise performance. The physical principles of Ion-Induced Secondary Electron (iSE) generation by ions are discussed, and an extensive database of iSE yields for many elements and compounds as a function of incident ion species and its energy is included. Beam damage and charging are frequently outcomes of ion beam irradiation, and techniques to minimize such problems are presented. In addition to imaging, ions beams can be used for the controlled deposition, or removal, of selected materials with nanometer precision. The techniques and conditions required for nanofabrication are discussed and demonstrated. Finally, the problem of performing chemical microanalysis with ion beams is considered. Low energy ions cannot generate X-ray emissions, so alternative techniques such as Rutherford Backscatter Imaging (RBI) or Secondary Ion Mass Spectrometry (SIMS) are examined.

Table of Contents

Frontmatter

Chapter 1. Introduction to Helium Ion Microscopy

Abstract
The scanning electron microscope (SEM) has become the most widely used high-performance microscope. However because of the fundamental limitations of electron beams the new technology of ion beam microscopy is being developed
David C. Joy

Chapter 2. Microscopy with Ions: A Brief History

Abstract
Every microscope requires a high brightness, reliable, stable source of illumination in order to function, and both the quality and the quantity of the illumination provided will determine, and ultimately limit, the performance of the instrument. Each type of microscope will have its own type of illuminating source. For a high-performance scanning electron or ion microscope, the most desirable property of the beam source is that the source must have a high brightness.
David C. Joy

Chapter 3. Operating the Helium Ion Microscope

Abstract
As noted in the previous section, the present ALIS helium ion source is a descendant of the original work based on FIM technology (for a historical overview see Muller and Tsong 1993) although important research in this area has also been carried out by several other prominent groups (e.g. Orloff and Swanson 1977). In order to be suitable for application, in a high-performance particle beam microscope, the source should ideally not only be bright, but also be as compact as possible to ensure mechanical stability, provide highly stable emission over time periods of several hours, be capable of operating at energies at least in the 10–50 keV range, and be capable of being re-formed and then reused multiple times without a significant change in performance. An overview of history of the helium ion microscope can be found in the literature (Economou 2011), while other technical details can be found in the published patents listed at the end of the bibliography.
David C. Joy

Chapter 4. Ion–Solid Interactions and Image Formation

Abstract
Both electron and ion beams can be used to provide a number of different modes of imaging and microanalysis In every case, and in order to properly optimize and interpret the data generated by the instrument, it is necessary to know something about what kinds of beam interactions are involved, what information may be obtained from each, and how the signal yields and spatial resolution can be optimized in each case. Images whose origins are neither known nor understood can never be any more than just a pretty picture.
David C. Joy

Chapter 5. Charging and Damage

Abstract
A major concern in both scanning electron and scanning ion microscopy is that of sample charging, but strategies to eliminate this problem are available.
David C. Joy

Chapter 6. Microanalysis with HIM

Abstract
For many users, the most important application of an SEM is its ability to identify the chemical composition of a specimen. Energy dispersive spectroscopy (EDS) of the X-rays fluoresced from samples of interest by the incident electron beam provides chemical microanalysis combining unparalleled sensitivity together with high spatial resolution for elements across the entire periodic table. This technique would therefore also be the automatic first choice for microanalysis when using ion beams if it were a viable option.
David C. Joy

Chapter 7. Ion-Generated Damage

Abstract
It has to be expected that both ions and electrons will damage specimens under examination to a greater or lesser degree. Electrons are low in mass but can travel at velocities which are a significant fraction of the speed of light. In general, electrons do not significantly damage metallic or inorganic specimens, but even relatively low doses of electrons can be expected to chemically alter or destroy organic materials such as polymers and biological samples.
David C. Joy

Chapter 8. Working with Other Ion beams

Abstract
A feature of the GFIS ion source is that every aspect of its operation and behavior—from its imaging resolution, the energy range over which it operates, the efficiency of signal production, and the damage it does to the materials that it examines—is ultimately affected by the choice of imaging gas. Ideally, the same source could rapidly be reconfigured to select and generate any one of a number of different ion beams. Because each type of ion has its own strengths and weaknesses, this feature would add substantially to the utility of the ion microscope.
David C. Joy

Chapter 9. Patterning and Nanofabrication

Abstract
As seen above, ion beams can rapidly remove material from a specimen placed in the HIM. Depending on the proposed application, this could then be considered either as damage—and so be undesirable—or as a unique tool to pattern material. The use of Ga+ beams for thinning or cross sectioning materials prior to examination in a transmission electron microscope is well known and in widespread use. As noted earlier, less known is the fact that light ions such as He+ can also remove material from a surface, although at a much reduced rate, providing a method to shape, mark, and pattern materials on nanoscale.
David C. Joy

Backmatter

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