Many of the fascinating properties of oxides have been intensively studied in bulk crystals. Thin films offer additional degrees of freedom for the development of materials that cannot be grown in bulk form. Nanostructured materials, such as nanoscale composites or nanostructures embedded in a matrix material, are good examples.
Nanostructures have many interesting properties. Some of the terms and concepts that are often referred to when discussing nanostructure properties are:
Depending on the band structure of the materials used in nanostructures, carriers may be confined within or near a nanostructure. This can result in the appearance of steps or discrete energy levels in the density of states spectrum. Discrete energy levels in a nanostructure can be used in optical and tunneling devices.
Nanostructures have a large surface area-to-volume ratio, which is why nanostructures are actively studied as catalysts and as chemical sensors, where absorbed or adsorbed gas can change the conductivity of a device.
Nanoscale composites containing components that give a strong dielectric response and a strong magnetic response in the same spectral range can result in a material that has simultaneously negative dielectric permittivity and negative magnetic susceptibility, resulting in a material where electromagnetic waves can propagate, but where the refractive index is negative.
By tuning the density and size of nanostructures, it is possible to design materials where the magnetic and transport properties are predominantly governed by the shape and density of nanostructures, rather the component materials themselves. Percolative transitions from an insulating state to a metallic state, for example, can in some cases by driven by external fields.