Size-Dependent Properties of Nanomaterials

As the size of a nanoparticle decreases, the energy needed to excite an electron across the band gap increases, leading to a higher energy (shorter wavelength) of light absorbed or emitted.

The way a nanoparticle interacts with light depends on its size. Smaller nanoparticles (less than 20nm) primarily absorb light, while larger ones (over 100nm) mainly scatter it.

When light hits a metal nanoparticle, the oscillating electric field causes the free electrons to vibrate in unison, creating a plasmon resonance. This resonance can dramatically affect the nanoparticle's optical properties.

The intentional addition of impurities into a semiconductor material to change its electrical, optical, or structural properties.

The size, shape, and surface coating of a nanoparticle can significantly influence its interaction with light, leading to different absorption and scattering patterns.

Nanoparticles can interact with each other to form larger structures. This aggregation can change the way they interact with light, often leading to increased scattering.

Surface modifications, like adding functional groups, can change the way a nanoparticle interacts with light by affecting its electronic structure and how it interacts with its surroundings.

The wavelength at which electrons in a nanoparticle (NP) resonate, primarily due to the size of the NP.

A type of plasmon resonance where half of the electron cloud moves parallel to the applied field and the other half moves antiparallel.

The electrical properties of nanomaterials are based on the movement of electrons & the spaces they leave behind, known as 'holes', and on the arrangement of atoms in their structure.

Nanomaterials, particularly carbon nanotubes, have unique electrical properties that can be modified based on their diameter, twist, and number of layers.

Carbon nanotubes can be either conducting or semi-conducting, depending on how the atoms are arranged.

Nanoparticles, when smaller than 100 nanometers, can have a lower melting point compared to their bulk counterparts.

The change in melting point (Δθ) of a nanoparticle is inversely proportional to its radius (r).

The relationship between the change in melting point (Δθ) and nanoparticle radius (r) can be calculated using the formula Δθ = 2Toσ/ρLr.

The change in melting point (Δθ) can be very significant, even reaching hundreds of degrees when particle size drops below 10 nanometers.

The surface tension coefficient (𝝈) is often unknown. We can estimate it by measuring the melting point of a material as the radius of its particles changes.

Many phase transitions, like ferroelectric-paraelectric or Curie transitions, show size dependence similar to melting point. This means the temperature at which these changes happen can vary with particle size.

The Curie temperature, the point where a ferromagnetic material loses its magnetism, is significantly affected by particle size. Smaller particles exhibit lower Curie temperatures.

Lattice constants, which describe the spacing between atoms in a crystal, can change with particle size. For example, in CdS nanoparticles, the lattice constants decrease as the particle size decreases.

Even at room temperature, amorphous (non-crystalline) Cu thin films can crystallize into a more stable crystalline structure. This process, called self-annealing, is due to the size effect and doesn't require the high temperatures used for bulk materials.

In contrast to bulk materials, nano materials exhibit different magnetic properties. Paramagnetic materials, which don't retain magnetism after removing an external field, show different behavior at the nanoscale.

Ferromagnetic materials are composed of domains where many atomic moments align, creating a strong magnetic field. In the unmagnetized state, these domains are randomly organized. When a magnetic field is applied, the domains align, resulting in magnetization even after the field is removed.

The magnetic properties of nanoscale materials are significantly different from those of bulk materials. This is due to the increased surface area and quantum effects.

Nanoparticles exhibit unique optical properties due to their size, shape, and surface coating. These factors influence how they interact with light, affecting their absorption and scattering patterns.