Seeing single atoms.

New discoveries and ideas often occur at the confluence of events and technologies that allow them to happen. So it was with the first electron microscopic observations of individual atoms at the University of Chicago laboratory of Albert Crewe forty years ago. This paper will describe the technologies developed then, present some of the historical instrumental details and describe the rationale for the designs that came about in that laboratory over a period of about a decade.

Chicago exploration days.

Single heavy atoms supported on thin carbon film were first imaged by Crewe, Wall and Langmore with their dark-field STEM. This glimpse into a hitherto invisible world we owe undeniably to Crewe's vision and determination, and to his gift to electrify, engage and encourage talented students. Since this successful event happened during my sabbatical stay in Crewe's group, the editors of this memorial volume asked me to write an account of its early history, which I gladly composed mostly from memory. The circumstances that led to my collaboration with Albert Crew in Chicago are reviewed, and the main project that we jointly embarked on the Chicago 1MeV STEM is described. It is shown that the project was nearing completion and would have likely been successful, had funding been continued. The paper concludes with a tribute to Albert I wrote many years ago.

Chicago aberration correction work.

The author describes from his personal involvement the many improvements to electron microscopy Albert Crewe and his group brought by minimizing the effects of aberrations. The Butler gun was developed to minimize aperture aberrations in a field emission electron gun. In the 1960s, Crewe anticipated using a spherical aberration corrector based on Scherzer's design. Since the tolerances could not be met mechanically, a method of moving the center of the octopoles electrically was developed by adding lower order multipole fields. Because the corrector was located about 15 cm ahead of the objective lens, combination aberrations would arise with the objective lens. This fifth order aberration would then limit the aperture of the microscope. The transformation of the off axis aberration coefficients of a round lens was developed and a means to cancel anisotropic coma was developed. A new method of generating negative spherical aberration was invented using the combination aberrations of hexapoles. Extensions of this technique to higher order aberrations were developed. An electrostatic electron mirror was invented, which allows the cancellation of primary spherical aberration and first order chromatic aberration. A reduction of chromatic aberration by two orders of magnitude was demonstrated using such a system.

A history of scanning electron microscopy developments: towards "wet-STEM" imaging.

A recently developed imaging mode called "wet-STEM" and new developments in environmental scanning electron microscopy (ESEM) allows the observation of nano-objects suspended in a liquid phase, with a few manometers resolution and a good signal to noise ratio. The idea behind this technique is simply to perform STEM-in-SEM, that is SEM in transmission mode, in an environmental SEM. The purpose of the present contribution is to highlight the main advances that contributed to development of the wet-STEM technique. Although simple in principle, the wet-STEM imaging mode would have been limited before high brightness electron sources became available, and needed some progresses and improvements in ESEM. This new technique extends the scope of SEM as a high-resolution microscope, relatively cheap and widely available imaging tool, for a wider variety of samples.

Emprego da microscopia na análise dos materiais odontológicos / The microscopy use in the dental materials analysis

A microscopia eletrônica de ponta vem revolucionando as pesquisas sobre materiais dentais, trazendo ao cirurgiäo-dentista mais segurança na aplicabilidade de determinados produtos. A partir das análises laboratoriais, é possível identificar, dentre outros, a qualidade de acabamento superficial e a resistência mecânica dos materiais odontológicos. Saiba um pouco mais, neste artigo, a respeito dos três tipos de microscópicos modernos (óptico, de varredura e de transmissäo) utilizados para estes fins