The Champagne Artifact in Negative Staining TEM

Negative staining is a simple yet extremely useful procedure for examining nanometer-sized specimens such as intact microorganisms (viruses and some bacteria), subcellular components, and even nonbidogical particulates. It is a well established procedure, with extensive literature in many disciplines (Hayat and Miller, 1990). Although numerous variations exist, the basic procedure involves placing the specimen and stain onto a grid containing a substrate - usually plastic with or without a carbon backing. The stains consist of salts of heavy metals such as tungsten, uranium, or molybdenum which surround and often penetrate the specimen. Afier drying into an amorphous, glass-like background, the stains provide contrast based upon differential thickness.

Using a TEM Electron Energy Loss Spectrometer to Eliminate Offensive Carbon “halos” from Platinum Replicas of Quick-Frozen, Deep-Etched Biological Samples

A significant improvement in image quality can be achieved, when imaging deepetch replicas via TEM, by using an electron energy loss spectrometer in a rather unorthodox manner. Microscopes equipped with true imaging spectrometers, such as the Zeiss EM 902, permit the viewer to subtract the offensive carbon “background halo” which is characteristic of all deep-etch replicas. Heretofore, this “halo” has been an unavoidable consequence of the need to “back” or physically support the otherwise extremely delicate platinum replica. In fact, much thicker carbon supports would be desirable, since fragmentation of platinum replicas during their cleaning represents the single greatest impediment to successful use of the deep-etch technique. Until now, such thick carbon has created hopeless “halos” and excessive blurring of replicas in the TEM. Amazingly, such imaging problems can be circumvented, regardless of the thickness of the carbon “backing”, by “dialing out” the carbon signal from the TEM image!

Ultrathin Platinum Crystal Surface Structures

The importance of atom layer terraces or steps on platinum surfaces used for catalysis as discussed by Somorjai justifies an extensive investigation of the structure of platinum surfaces through electron microscopy at the atomic resolution level. Experimental and theoretical difficulties complicate the quantitative determination of platinum surface structures but qualitative observation of surface structures on platinum crystals is now possible with good experimental facilities.Ultrathin platinum crystals with nominal 111 orientation are prepared using the procedure reported by Hines without the application of a carbon backing layer. Platinum films with thicknesses of about ten atom layers are strong enough so that they can be mounted on grids to provide ultrathin platinum crystals for examination of surface structure. Crystals as thin as possible are desired to minimize the theoretical difficulties in analyzing image contrast to determine structure. With the current preparation procedures the crystals frequently cover complete openings on a 400 mesh grid.