Shell, electron growth

Enormous developments in the area of soluble noble metal clusters protected with monolayers are discussed. Mass spectrometry has been the principal tool with which cluster growth has been examined. The composition and chemistry of clusters have been examined extensively by mass spectrometry. Besides gold, silver, platinum, copper and iron clusters have been examined. Clusters have also been examined by tandem mass spectrometry and the importance of ligands in understanding closed shell electronic structure is understood from such studies. Protein protected noble metal clusters belong to a new group in this family of materials. Naked metal clusters bearing the same core composition as that of monolayer protected clusters is another class in this area, which have been discovered by laser desorption ionization from protein templates. 

Figure 3.30 Scanning electron micrograph of tubercles in Fig. 3.28. Note the clam-shell growth steps formed by successive fractures at the tubercle base. Tubercle is about 200 pm in diameter. (Courtesy of National Association of Corrosion Engineers, Corrosion 91 Paper No. 84 by H. M. Herro.)...

A. V. and Alivisatos, A. P. (1997) Epitaxial growth of highly luminescent CdSe/CdS core/shell nanocrystals with photostability and electronic accessibility. J. Am. Chem. Soc., 119, 7019-7029. 

It is noteworthy that the HRTEM cannot distinguish core and shell even by combining X-ray or electron diffraction techniques for some small nanoparticles. If the shell epitaxially grows on the core in the case of two kinds of metals with same crystal type and little difference of lattice constant, the precise structure of the bimetallic nanoparticles cannot be well characterized by the present technique. Hodak et al. [153] investigated Au-core/Ag-shell or Ag-core/Au-shell bimetallic nanoparticles. They confirmed that Au shell forms on Ag core by the epitaxial growth. In the TEM observations, the core/shell structures of Ag/Au nanoparticles are not clear even in the HRTEM images in this case (Figure 7). 

As seen in Table //, the outer shell, which in copper has one electron, now proceeds to develop in the subsequent elements until, with krypton, it again has eight electrons and the properties of a noble gas. The completion of the M shell, and the growth of the N... 

In the nuclei of atoms neutrons are concentrated, in addition to protons the presence of neutrons in the nucleus does not change the ordinal number of the element, but it contributes to the growth of its atomic weight. Elements having the same number of protons, but differing in the number of neutrons, are called isotopes. Electrons, being practically particles almost without any mass, move in eliptical paths in one or several shells round the nucleus approximately in the same manner as the planets move round the sun. 

---