Beyond optical microscopy  (Page 8/5)

Introduction

Light microscopes are used in a number of areas such as medicine, science, and engineering. However, light microscopes cannot give us the high magnifications needed to see the tiniest objects like atoms. As the study of both microstructures and macrostructures of materials have come to the forefront of materials research and development new methods and equipment have been developed. Both the usage of electrons and atomic force rather than light permits advanced degrees of observations than would allow an optical microscope. As the interest in new materials in general and nanomaterials in particular is growing alternatives to optical microscopy are proving fundamental to the advancement of nanoscale science and technology.

Scanning electron microscope

SEM: A Brief History

The scanning electron microscope is an incredible tool for seeing the unseen worlds of microspace. The scanning electron microscope reveals new levels of detail and complexity in the world of micro-organisms and miniature structures. While conventional light microscopes use a series of glass lenses to bend light waves and create a magnified image, the scanning electron microscope creates magnified images by using electrons instead of light waves.

The earliest known work describing the conceptualization of the scanning electron microscope was in 1935 by M. Knoll who, along with other pioneers in the field of electron optics, was working in Germany. Although it was Manfred von Ardenne who laid the foundations of both transmission and surface scanning electron microscopy just before World War II, it is Charles Oatley who is recognized as the great innovator of scanning electron microscopy. Oatley’s involvement with the SEM began immediately after World War II when, his recent wartime experience in the development of radar, allowed him to develop new techniques that could be brought to overcome some of the fundamental problems encountered by von Ardenne in his pre-war research.

Von Ardenne (1938) constructed a scanning transmission electron microscope (STEM) by adding scan coils to a transmission electron microscope. [1] In the late 1940s Oatley, then a lecturer in the Engineering Department of Cambridge University, England, showed interest in conducting research in the field of electron optics and decided to re-investigate the SEM as an accompaniment to the work being done on the TEM (by V. E. Cosslett, also being developed in Cambridge at the Physics Department). One of Oatley's students, Ken Sander, began working on a column for a transmission electron microscope using electrostatic lenses, but after a long period of illness was forced to suspend his research. His work then was taken up by Dennis McMullan in 1948, when he and Oatley built their first SEM by 1951. By 1952 this instrument had achieved a resolution of 50 nm.