Physical Background and Quantum Size Effect

The availability of small solids such as transition metal dusters [17-19] offers a field of research that raises basic questions How small must the number of atoms be for the properties of the original metal to be lost. How does an ordered accumulation of atoms behave when it is no longer under the influence of its ambient bulk matter And, perhaps most important in the context of this subchapter What types of applications of these new materials in microelectronic devices can be expected in the future  

To answer these questions, the following scenario should be considered. If a metal particle, initially having bulk properties, is reduced in size down to a few hundreds or dozens of atoms, the density of states in the valence and conduction bands decreases and the electronic properties change dramatically - that is, the conductivity, collective magnetism and optical plasmon resonance vanish such that the quasi-continuous density of states is replaced by quantized levels with a size-dependent spacing. 

This size-quantization effect may be regarded as the onset of the metal-nonmetal transition such that, in another terminology, these quantum-size nanopartides may also labeled as artificial atoms [20-22]. 

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