As electronic devices throughout the world continue to get smaller, there is going to be a limit on how small, or thin, a device can be made using conventional electronics. The same is true for those in the consumer world looking to make transparent and flexible electronics, as many conventional electronics networks are not designed to work in this way. So, what’s the answer? Well, there are different answers depending on the part of the device that needs to be miniaturized. Flexible and transparent screens, batteries, capacitors, and circuit boards can be made efficient and smaller/more flexible by nanotechnology; and more aspects of electronics are continually being impacted by nanomaterials. However, we’re focusing here on one specific type of nanomaterial that shows a lot of promise in electronics, and nanoelectronics, and this is nanowires.
What Are Nanowires?
Nanowires are very long and very thin nanomaterials. In technical terms, this means that they have a high aspect ratio. Given that this is a similar geometry to conventional wires, they possess a lot of potential in electronic and nanoelectronic devices. Nanowires are highly conductive materials, but given their size, they don’t conduct as much electricity as bulkier electronics, but their small size is what makes them useful. Nanowires are also one-dimensional (1D) nanomaterials. This means that the electrons within the nanowires are confined to one dimension and are blocked from moving in the other two—this is a type of quantum confinement that you find with many nanomaterials, as their small size brings about interesting quantum phenomena. Because electrons can only move in one dimension, the electrons in nanowires will only move along the long axis—much like conventional electronic wires.
The electronic states in nanowires do vary compared to bulk materials. Because of the nanowire’s quantum effects, the nanowire’s electrons will occupy discrete bands, rather than a continuum of states. Even though each electron is quantumly confined—because the potential wells within nanowires lie close to each other—they can be connected by the electrons tunneling between the wells. This enables the electrons to flow between the wells with minimal impedance. This is the governing factor of their high conductivity. Nanowires can also be bundled together to increase the degree of conductivity possible within a small localized space, and they can easily be integrated into the matrices of other materials to make them conductive.
Unlike conventional wires, which solely rely on copper because of their conduction properties, there are many different types of nanowires in existence today. Nanowires can be made up of superconducting materials—such as yttrium barium copper oxide (YCBO)—or metals—including platinum, silver, gold, and nickel—or semiconductors—such as gallium arsenide, silicon, and indium phosphide—or insulating materials—such as silicon dioxide and titanium dioxide. These are just a few of the most common examples, as nanowires with novel compositions are coming out all the time. In many cases, from a chemical perspective, many nanowires are inorganic in nature.
The Electronic Applications Where Nanowires Could See Widespread Use
The biggest potential for nanowires is in transistors. Because of their high aspect ratio, it is easy to fabricate dielectric gates around the nanowires, which enables them to be switched off and on with relative ease. Additionally, due to their size, nanowire transistors do not suffer ill-effect from impurities to the same degree as their bulk counterparts, which makes the fabrication cheaper and easier as impurity-free materials are not necessarily required. While many nanowire transistors need a semiconducting junction to help control the flow of electrons, some devices produced contain no junction and the flow of electrons is controlled by a circular structure that squeezes the nanowire—which increases or decreases the flow of electrons depending on whether the ring is in a ‘relaxed’ or ‘squeezing’ state.
There are some other application areas that could be benefitted in the future. These include flexible electronics and sensors. There is a buzz about flexible electronics at the moment, especially as there is something very sci-fi about it. People started getting excited about flexible electronics when they realized that 2D materials could be used in the batteries and touch screens of electronic devices. But these components still need to be connected, and this is where nanowires could come in. Nanowires can be incorporated into various thin-layered material composites and can act as flexible electrical conducting mediums. They can then flex with any other flexible materials in the device without compromising the conductivity of the device. Additionally, because they are so small, they are practically invisible and will not comprise the optical transparency of a screen. Areas of flexible electronics could include consumer electronics such as phones and laptops and wearable devices for medical and fitness applications.
As for sensors, many people know that nanomaterials have advanced the sensing capabilities of various types of sensors. So far, sensors that nanowires have been trialed for measuring various chemicals, gases, and biomolecules, as well as pH. Nanowire-based sensors possess a sensing mechanism that is very similar to how a field-effect transistor (FET) works. In nanowire-based sensors, the nanowire is typically made of semiconducting material. When an interaction occurs between the receptors on the sensor’s surface and the target molecule, it induces a change in the surface potential which changes the localized density of holes and/or electrons in the semiconductor—which then produces a detectable and measurable change.
Nanowires present a way of miniaturizing electronics and creating more flexible electronics by acting as the conducting medium between components in a device. Much like conventional wires, the electrons in nanowires will flow along the long axis of the material, and nanowires can be bundled together to create a higher conductivity in a smaller region of space. There are various applications where nanowires could be widely used in the electronics world, the most common being transistors, but also in flexible and wearable electronics, transparent electronics, and sensors.
Authored Article by: Liam Critchley, Mouser