The common idea of “thin” involves familiar items like a sheet of paper or plastic film. Scientific exploration has moved far beyond this macroscopic scale, focusing on materials that are only a single atom thick. When thickness is reduced to the atomic level, materials exhibit entirely new and extraordinary properties. These ultrathin structures, formally classified as two-dimensional (2D) materials, represent the current frontier in materials science and nanotechnology.
Measuring Thinness: Entering the Atomic Realm
The standard units of measurement for this scale are the nanometer (nm) and the angstrom (Å). A single nanometer is one-billionth of a meter. One angstrom is even smaller, representing one-tenth of a nanometer, which is a convenient size for measuring the diameter of individual atoms.
To illustrate this scale, a single strand of human hair measures between 50,000 and 100,000 nanometers in thickness. A typical human red blood cell is much smaller, with a thickness of about 2,000 to 2,500 nanometers. Even traditional examples of thinness, like gold leaf, are about 100 nanometers thick.
Materials at the atomic scale, by contrast, are measured in single angstroms. A single atom typically has a diameter between 0.1 and 0.5 nanometers, or 1 to 5 angstroms. This difference in scale allows researchers to classify materials that are only one or a few atoms high as truly two-dimensional, exhibiting properties fundamentally distinct from their bulk, three-dimensional counterparts.
The Thinnest Known Materials: Graphene and Beyond
The thinnest known material is Graphene, a two-dimensional crystal composed entirely of carbon atoms. Graphene is defined by its structure: a single layer of carbon atoms arranged in a repeating hexagonal lattice, resembling a honeycomb pattern. This structure gives Graphene an atomic thickness of approximately 0.34 nanometers, which is precisely the thickness of a single carbon atom.
Graphene’s isolation in 2004 launched the field of 2D materials. Graphene remains the archetypal and thinnest example, but other one-atom-thick contenders exist. Borophene, a single layer of boron atoms that can be synthesized on a substrate, is considered a two-dimensional metal with a thickness ranging from 0.27 to 0.42 nanometers.
Not all 2D materials are a single atom thick. Transition Metal Dichalcogenides (TMDs), such as Molybdenum Disulfide (MoS₂), are popular 2D semiconductors. A single layer of a TMD is a three-atom-thick sheet, comprised of one metal atom layer sandwiched between two chalcogen atom layers. This monolayer structure measures around 0.65 nanometers (6.5 Å) thick, making it structurally distinct from the one-atom layer of Graphene.
Why Thinness Matters: Applications in Technology
The thinness of 2D materials like Graphene is directly responsible for their unique and extraordinary properties. One primary application is in flexible electronics, which requires materials that are simultaneously conductive, transparent, and mechanically resilient. Graphene’s flexibility allows it to endure over 10,000 bending cycles without degradation, making it an ideal candidate to replace brittle materials like indium tin oxide in bendable screens and touch sensors.
The large surface area and high conductivity of these ultrathin materials also make them effective for efficient energy storage devices, such as supercapacitors. The atomic layers of materials like Graphene and MXenes offer numerous accessible sites for ion storage. This leads to devices with high power density and a much longer lifespan than traditional batteries. Research focuses on creating three-dimensional structures from these two-dimensional sheets to maximize the surface area accessible to the electrolyte ions.
The precise, angstrom-scale thickness of 2D materials is being leveraged for advanced filtration and desalination technology. Membranes made from nanoporous Graphene and other 2D materials can be fabricated with holes just a few angstroms wide. This allows water molecules to pass through at high speed while effectively rejecting salts and other impurities. This atomic-scale precision offers the potential for water purification systems with increased efficiency and lower energy consumption compared to current reverse osmosis methods.