Uranyl and tungstate compounds have found favor as negative stains because of their high scattering power relative to biological molecules. However, other properties, such as specimen preservation, resistance to alterations or crystallization in the electron beam, and signal to noise (S/N) ratio, are also important. It may be that lower density materials may have advantages in these areas. A new negative stain, methylamine vanadate, CH3 NH2.VO3 ("NanoVan"), offers a near physiological pH of 8, similar to phosphotungstate (pH 7) with much smoother background. It is also very stable in the electron beam with minimal granulation at a dose of l04 el / nm2 . The resolution obtainable with vanadate appears to be comparable to uranyl at low dose, but superior at higher dose where uranyl forms coarse grains (see Fig. 1). Problems with uranyl such as unwanted positive staining and need for pH below 4 can be avoided. The lower contrast permits use of thicker stain embedment for better preservation and less flattening without excessive beam attenuation.
Effects of High-Density Pulse Currents on the Solidification Structures of Cu-SiCp/AZ91D Composites