The world of nanotechnology is an interesting space, and one that is filled with so much variety. Many people hear about how nanotechnology can be used in quantum computing and other similar electronic technologies, but how many people understand the quantum world of nanotechnology? This article aims to shed some light on the basic principles of quantum nanotechnology.

There are two fundamental principles at the core of nanotechnology – The first is that the smaller you make the material, the greater the relative surface area of the material; and the second is the loss of bulk properties in lieu of quantum phenomena when you get to such a small scale.

It all starts with a box…

And by a box, I mean a particle in a box. Quantum nanotechnology is based around the principle of electron tunnelling. The basic theory is that a particle confined to a one-dimensional box cannot escape unless the electron tunnels its way out of the confinement. This is a phenomenon only exhibited by quantum materials and is not seen with any bulk materials. This principle can be extended to incorporate all 3-dimensions – the so-called particle in a three-dimensional box. The amount of electron confinement introduced to a material will determine its dimension – as quantum dimensions are more relative the electron confinement (and in how many dimensions the electrons act in) than the atomic spatial arrangement.

Quantum dots

Quantum dots are likely to be the most known quantum structure in this article. The interesting thing about quantum dots, is that electronically, they are confined in all 3-dimensions, so they are classed as zero-dimensional materials.

Quantum dots are an interesting class of materials, and many of them luminesce (which is usually tuneable). They are semiconducting in nature and are often referred to artificial atoms because they possess discrete electronic states – i.e. the states can only take certain values of energy (unlike bulk materials). Quantum dots are now gaining a lot of interest across many applications, and some research now focuses on the phenomena of double quantum dots.

Quantum wires

Otherwise known as nanowires, quantum nanowires are an electrically conductive one-dimensional structure with electrons confined in two dimensions. They are referred to as ‘wires’ because the electron movements are confined to one transverse direction, i.e. along the wire, making their mode of operation similar to conventional wires. They are used to pass electrons in electronic devices, or sensing devices, but can only be used a certain energy levels, because their bands are also discrete. One major benefit of quantum wires is their high aspect ratio, where the length of the wire can be up to 1000 times greater than their width.

Quantum wells

Quantum wells are only confined in one direction, so electrons can tunnel in two directions. This enables quantum wells (also known as potential wells) to be connected to each other under the right conditions.

Quantum wells are usually seen in semiconducting materials and the geometry of the well forces the particles into a planar axis. Quantum wells are a phenomenon created by the discrete energy bands of holes and electrons in semiconducting materials. These discrete energy levels lead to sub-bands with the material, where each well is not connected to each other and the electrons cannot tunnel out.

However, there are cases where the distance between potential wells is not sufficient to block all electrical contact between wells. The electrons can then tunnel and link the potential wells together, creating a ‘superlattice’. These superlattices contain minibands which run the length of the connected potential wells, meaning that electrons can easily travel between wells and enables the superlattice to exhibit excellent charge carrier properties, and in some cases, superconductivity.