Metallic scattering

In transmission electron microscopy, the beam of electrons is passed through a thin section of the specimen that has been stained with heavy metals. The electron-dense metals scatter the incident electrons, thereby producing an image of the specimen. 

X-rays are mainly diffracted by the electrons on each atom. The scattering of the X-ray beam increases as the number of electrons, or equally, the atomic number (proton number), of the atom, Z, increases. Thus heavy metals scatter X-rays far more strongly than light atoms while the scattering from neighbouring atoms is similar in magnitude. 

The small oxygen and/or chlorine contribution to the signal is thus covered by the heavy metal scatterers. The PtOO catalyst after reductive activation exhibits a dispersion almost at monoatomic level (CN(Pt)=1.6) and, after catalytic run, a moderate increase in particle size (CN(Pt) = 4.6) and the presence of chlorine (CN(Cl) = 0.9) on the metallic phase. These results cannot be rationalized on the basis of the structure insensitivity of the hydrodechlorination reaction, since the most active catalyst, Pt09, shows a much higher size of Pt particles. Catalytic activity seems, therefore, to be related to the stability of metal phases under reaction conditions. 

Habashi, E, ed. 1997. Handbook of Extractive Metallurgy. (4 vols.) Weinheim, Germany/New York Wiley-VCH. A comprehensive compilation of data on metals, their extraction, their alloys, and their most important inorganic compounds. The four volumes are organized by families of metals according to their industrial importance vol. 1, The Metal Industry Ferrous Metals vol. 2, Primary Metals, Secondary Metals, Light Metals vol. 3, Precious Metals, Refractory Metals, Scattered Metals, Rare Earth Metals vol. 4, Ferroalloy Metals, Alkali Metals, Alkaline Earth Metals. 

Aside from the attributes of SERS for studies of biological systems in general, significant additional advantages arise for the detection and identification of bacterial pathogens via SERS, particularly when Raman microscopy observations may be exploited. The metal-scattering distance dependence (< 10 nm) of the SERS enhancement mechanisms 29, 34, 55) and the inherent size scale of bacteria (1 pm - 5 pm) account for these additional effects as described in further detail below. 

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