Under the Microscope

The following sections are included:

• Foreword

• Table of Contents

In this small volume I will attempt to describe the history of microscopy as well as introduce you to the functions of microscopes from early times to the ultra sophisticated techniques of the most modern laboratory. In order to do this I will describe some history of the earliest observations of effects of light and how magnification of small objects developed. In doing this you will be introduced to many new terms which I will try to explain as well as show how they were observed. Since this is a history of microscopy I will get ahead of the story to explain that the term “microscope” was coined in 1624 in Italy by members of the first Accademia Dei Lincei a group which included Galileo who is credited with being one of the early scientific users of the microscope. The word itself is derived from two Greek words small and to view…

In the first century A.D. Seneca described actual magnification by a globe of water. He wrote that letters could be enlarged and made clear by viewing through a globe of glass filled with water. A thousand years later the Arabian scholar Alhazan wrote a major work on optical principles and described the anatomy of the eye and how the lens focuses images…

One of the earliest books on microscopy was by Robert Hooke (1635–1703). He was curator of experiments at the Royal Society of London. In 1663 he was asked to deliver a weekly series of lectures on his work with microscopes. His earliest work involved looking at the structure of a piece of cork. He cut thin sections with a razor blade and was able to see in his microscope the tiny compartments of which it is made. He names these “cells”. In a single experiment he had invented a basic technique of the microscopist and named the fundamental unit of life. In 1665 he published his results in a book “Micrographia”. He examined natural and man made objects from the point of a sewing needle to the eyes of insects. He also reported on the construction of the microscopes he used…

Up to this point we have considered light as a wave motion which vibrates in space in all directions. Looking at a beam of light the vibration directions are in all radial directions perpendicular to the direction of propagation.

The polarizing microscope, also known as the petrographic microscope because of its use in studying rocks, is more than just an image magnifier. With this instrument can be determined optical properties of both crystalline and non crystalline materials that transmit light. Using various accessories one can determine such properties as refractive index, phase transformation temperature and melting point. Looking at thin sections of rocks one can identify the mineral constituents and determine all kinds of information about their relationship to one another…

Early in the history of microscopy scientists looked at metals and other opaque materials as eagerly as they examined the transparent objects that came under their view. Biological materials had a greater impact than the inorganics because parts of living structures were more clearly visible without treatment and because the resulting knowledge had such a tremendous impact on biological science…

In 1801 a British Scientist Thomas Young conducted an experiment in which he let filtered sunlight pass through a pin hole and then on to a surface with two more pinholes. The light then fell on to a screen where he observed alternating strips of brightness and darkness. These are interference fringes. The bright strips are where both waves from the pair of pinholes are at a peak or trough and the dark strips the result of one trough overlapping the other peak. This kind of interference can be seen whenever two waves overlap in space and time. It doesn't matter if the waves are light, water or any other observable form. This experiment as well as the experiments of Fresnel would have convinced most scientists of the wave nature of light except for the problem that the great Isaac Newton in 1704 described his corpuscular theory of light. The politics of that day being what it was kept Young's work from being accepted for a long time. Eventually his work was realized to be right until the issue was confounded again in 1900 by Albert Einstein. He explained the photoelectric effect; where light landing on certain metal surfaces causes electrons to be released. This makes sense if light is considered to be traveling as discrete particles. Einstein called these light quanta and are now known as photons. Instead of a continuing argument this has led scientists to the concept of wave-particle duality. It turns out that the duality also applies to such “particles” as electrons and neutrons. At the same time as Einstein was explaining photoelectric effect Max Planck was developing the quantum theory which also helped to turn the physicist's world upside down…

The following sections are included:

• Interactions with Matter

• Biology

• Resolution

• Electron Diffraction

• Endnote

The scanning electron microscope is probably the most widely used electron beam instrument. At the low end of its operating range its images can be compared to those of optical microscopes while at the high end it is comparable to such instruments as the scanning tunneling microscope. Its resolution now approaches 0.5 nm, close to a transmission electron microscope and many models can handle very large specimens such as industrial gears and silicon wafers. In recent years pictures made with the SEM have been widely published in large circulation magazines as well as scholarly journals. These photographs are notable for their remarkable three-dimensional quality. They convey a sense of reality usually lacking in micrographs made by other means. One example is shown in Figure IX-1. A micrograph made with an ordinary light microscope or a TEM is a two dimensional image. You see a pattern of light and dark areas produced by the transmission of light or electrons through a thin specimen. The light microscope image is two dimensional because of its limited depth of field. It can only be focused sharply in one limited plane. It works best with very thin samples viewed by transmitted light or flat opaque samples by reflected light. The TEM requires even thinner samples for reasons to be discussed…

The following sections are included:

• Optical Microscopy

• Electrons, Atoms and X-Rays

• EPMA

• X-Ray Detection

• Qualitative Analysis

• Quantitative Analysis

• Elemental Mapping

• Materials

The following sections are included:

• Scanning Probe Microscopes (SPM)

• Scanning Near Field Optical Microscopy (SNOM)

• Confocal Microscopy

The following sections are included:

• Imaging

• Microscopy

The grains in most materials range from microns to millimeters in diameter and may contain billions of atoms. Newly created versions of well known materials called nano phase materials or nano materials are less than 100 nm in diameter and contain only tens of thousand of atoms. A three-nanometer diameter cluster contains about 900 atoms and is about a million times smaller than the period at the end of this sentence. These tiny grains respond to light, electricity and stress very differently than micron or millimeter size grains, displaying an array of novel attributes. Nanophase materials because of many unique properties such as an increase in strength of a metal such as copper or an increase in breaking strength of a nanophase ceramic are now of great technologic interest. The control of the structure of these materials is dependent on observations by the most up to date kinds of microscopy using electrons and scanning probe techniques…

The following sections are included:

• Further Reading

• Index