A nanoring is a cyclic
nanostructure
A nanostructure is a structure of intermediate size between microscopic and molecular structures. Nanostructural detail is microstructure at nanoscale.
In describing nanostructures, it is necessary to differentiate between the number of dimens ...
with a thickness small enough to be on the
nanoscale
The nanoscopic scale (or nanoscale) usually refers to structures with a length scale applicable to nanotechnology, usually cited as 1–100 nanometers (nm). A nanometer is a billionth of a meter. The nanoscopic scale is (roughly speaking) a lo ...
(10
−9 meters). Note that this definition allows the diameter of the ring to be larger than the nanoscale. Nanorings are a relatively recent development within the realm of nanoscience; the first peer-reviewed journal article mentioning these nanostructures came from researchers at the Institute of Physics and Center for Condensed Matter Physics in
Beijing
}
Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...
who synthesized nanorings made of
gallium nitride
Gallium nitride () is a binary III/ V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords it ...
in 2001.
Zinc oxide
Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cemen ...
, a compound very commonly used in nanostructures, was first synthesized into nanorings by researchers at
Georgia Institute of Technology
The Georgia Institute of Technology, commonly referred to as Georgia Tech or, in the state of Georgia, as Tech or The Institute, is a public research university and institute of technology in Atlanta, Georgia. Established in 1885, it is part of ...
in 2004 and several other common nanostructure compounds have been synthesized into nanorings since. More recently, carbon-based nanorings have been synthesized from cyclo-para-phenylenes as well as porphyrins.
Overview
Although nanorings may have a diameter on the nanoscale, many of these materials have diameters which are larger than 100 nm, with many nanorings having a diameter on the
microscale
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Un ...
(10
−6 meters). As such, nanorings are considered to be members of a sub-class of
nanomaterials
*
Nanomaterials describe, in principle, materials of which a single unit is sized (in at least one dimension) between 1 and 100 nm (the usual definition of nanoscale).
Nanomaterials research takes a materials science-based approach to nan ...
called one-dimensional (1-D) nanomaterials. These are nanomaterials in which one of the three physical dimensions in a
single unit of the material is on a length scale greater than the nanoscale. Other examples of one-dimensional nanomaterials are
nanowire
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...
s, nanobelts,
nanotubes
file:Chiraltube.png, A scanning tunneling microscopy image of a single-walled carbon nanotube
file:Kohlenstoffnanoroehre Animation.gif, Rotating single-walled zigzag carbon nanotube
A carbon nanotube (CNT) is a tube made of carbon with diameters ...
, and
nanosheet A nanosheet is a two-dimensional nanostructure with thickness in a scale ranging from 1 to 100 nm.
A typical example of a nanosheet is graphene, the thinnest two-dimensional material (0.34 nm) in the world. It consists of a single layer o ...
s.
Mechanical Uniqueness
As with other nanomaterials, much of the practical interest in nanorings arises from the fact that in nanorings, one can often observe quantized phenomena which are ordinarily unobservable in bulk matter. Nanorings, in particular, have a few additional properties which are of particular research interest. One-dimensional nanostructures have a variety of potential uses and applications but due to the dimensions of their extended
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...
s, they cannot be grown on discrete crystal growth sites and thus, cannot be synthesized on a
substrate with any crystallographic predictability. Therefore, nanorings are most commonly synthesized aqueously by creating
entropically
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
unique conditions which induce spontaneous nanoring self-assembly. These materials are much more useful if they can be easily manipulated by mechanical or
magnetic forces as many one-dimensional nanostructures are extremely fragile and, thus, difficult to manipulate into useful environments. It has now been demonstrated that
ZnO nanorings made from the spontaneous folding of a single nanobelt crystal can be extensively mechanically manipulated without breaking or fracturing, giving them a unique mechanical advantage over other classes of ZnO nanostructures.
Synthesis
Generally, nanorings are synthesized using a bottom-up approach, as top-down syntheses are limited by the
entropic
Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...
barriers presented by these materials. Currently, the number of different synthetic techniques used to make these particles is almost as diverse as the number of different types of nanorings themselves. One common method for synthesizing nanorings involves first synthesizing nanobelts or nanowires with an uneven
charge distribution
In electromagnetism, charge density is the amount of electric charge per unit length, surface area, or volume. Volume charge density (symbolized by the Greek letter ρ) is the quantity of charge per unit volume, measured in the SI system in co ...
focused on the edges of the material. These particles will naturally
self-assemble
Self-assembly is a process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction. When the ...
into ring structures such that
Coulomb repulsion
Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is conventiona ...
forces are minimized within the resulting
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
. Other approaches for nanoring synthesis include the assembly of a nanoring around a small
seed
A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
particle which is later removed or the expansion and twisting of
porphyrin
Porphyrins ( ) are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). The parent of porphyrin is porphine, a rare chemical com ...
-like structures into a hollow nanoring structure.
References
{{reflist
External links
Nanorings: Seamless Circular Structures Could be Sensors, Resonators and Transducers for Nanoelectronics & Biotechnologyalternative link
Nanoparticles by morphology