Nanostructures

Nanostructures are objects that have at least one dimension in the nanoscale, typically 1 to 100 nanometers. At these dimensions materials often exhibit properties that differ from their bulk counterparts due to quantum effects, electron confinement, and an increased surface-area-to-volume ratio. Common forms include nanoparticles (spherical or irregular particles), nanowires (one dimension much longer than the others), nanotubes (cylindrical structures), nanosheets (two-dimensional layers), and quantum dots (zero-dimensional particles with discrete energy levels).

Nanostructures can be produced by top-down approaches, which start from larger materials and remove material to reach the nanoscale, through methods such as lithography, etching, or milling; or by bottom-up approaches, which assemble structures from atoms or molecules via chemical synthesis, self-assembly, or templating. Materials used range from metals and semiconductors to metal oxides and carbon-based systems, including gold, silver, silicon, titanium dioxide, silica, carbon nanotubes, graphene, and various quantum-dot formulations.

Properties of nanostructures are often size- and shape-dependent, affecting optical, electronic, catalytic, and mechanical behavior. For example, metal nanoparticles can exhibit surface plasmon resonances that depend on size and shape, while semiconductor quantum dots show tunable emission due to quantum confinement. Carbon-based nanostructures offer high strength and conductivity, and oxide nanomaterials can enhance catalytic activity.

Applications span electronics, photonics, catalysis, energy storage and conversion, biomedicine (drug delivery and imaging), sensing, and protective coatings. Characterization typically employs TEM, SEM, AFM, DLS, XRD, and spectroscopy. Challenges include reproducibility, scalable manufacturing, integration with macroscale systems, and safety and environmental considerations.