N A N O M AT E R I A L S
1. Introduction
down the physical properties of macroscopic pieces of the same material. The lack of scalability in the physical properties of nanometer-sized structures opens new opportunities and methods for the fabrication of nanoscopic structures with custom-desgined physical properties and, therefore, for the Science of Materials hosting nanometer-scale structural motifs.
A great deal of the expectations raised in the last decade in the fields of Science and Technology at the atomic scale arise from the lack of scalability in the physical properties of matter when its size falls in the nanometer range (the millionth part of a millimeter). Nanoscopic pieces of material can be made out of hundreds of atoms (at least in the dimension in which the size of the material is in the nanometer range) instead of the mind-boggling amount of 1023, characteristic of macroscopic materials. It is thus not surprising that many of the commonly used approximations to understand the physical properties of large-scale materials cannot be applied to nanometer-scale structures.
In the following we will focus on recently developed methods to provide macroscopic materials with nanometer-scale structural motifs able to modify their physical and chemical properties and endorse them with new functionalities. We will however not discuss the synthesis and properties of individual nanostructures, which also a burgeoning field with great potential for applications, but which will most likely be covered in other sections of this report.
Among these properties we find for example electrical conductivity, that becomes quantized in the limit of nanometer-thick wires; the chemical reactivity of nanoparticles, which is dramatically affected by the larger number of surface atoms in these nanostructures as compared to macroscopic materials; the magnetization of nanoscale magnets, that can be severely reduced by the non-negligible effect of thermal fluctuations, etc.
We will however make an exception for the explosive development of the research in graphene, i.e. an atom-thick graphite layer. The discovery of methods to isolate and handle individual graphene sheets has raised many expectations in the field of Nanoelectronics, due to its promising transport properties, which ultimately arise from a peculiar electronic band structure leading to very high Fermi velocity (of the order of 106 m/s), giant electronic mobility (in excess of 104 cm2/V⋅s) and zero effective
These effects exemplify that fact that the physical properties of nanostructures can therefore not be obtained simply by scaling-
37