Nanowire
A "nanowire" is a wire of dimensions of the order of a nanometer ( meters).The nanowires could be used, in a near feature, as components of nanotechnology to create electrical circuits out of compounds that are capable of being formed into extremely small circuits.
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2 Use of nanowires 3 References |
A suspended nanowire is a wire in vacuum chamber held at the extremities.
A suspended nanowire can be produced by chemical etching of a bigger wire, or bombarding a bigger wire with some highly energetic particles (atoms or molecules).
Another way to produce a suspended nanowire is to indent the tip of an STM in the surface, of a metal near the melting point, and retract it. This can form a wire very much like the tip of a fork does with the cheese of a pizza.
A deposited nanowire is a nanowire that lies on a surface of a different material, possibily a metallic wire over an isolating surface.
A deposited nanowire can be built by stacking atoms one by one using the tip of an STM to move them. (To be expanded)
Nanowires show peculiar electrical properties due to their size.
Essentially the motion of electrons can fall under the regime of ballistic transport: the electrons can travel freely from one electrode to the other.
Furtermore the conductivity can undergo a quantization in energy: i.e. the energy of the electrons going through a nanowire can assume only discrete values, multiple of the Landauer constant (where e is the charge of the electron and h is the Planck's constant).
The conductivity is hence described as the sum of the transport by seprate channels of different quantized energy levels. The thinner the wire is, the smaller the number of channles available to the transport of electrons.
This has been proven by measuring the conductivity of a nanowire while pulling it: while it shrinks, its conductivity decreases in a stepwise fashion and the plateaus correspond to multiples of G.
The nanowires can show peculiar shapes. Sometimes they can show noncrystalline order, assuming e.g. a pentagonal symmetry or a helicoidal shape.
The lack of crystalline order is due to the fact that a nanowire is periodic only in one dimension (along its axis). Hence it can assume any order in the other directions (in plane) if this is energetically favorable.
E.g., in some cases nanowires can show a fivefold symmetry, usually not observed in nature, but for clusters of few atoms.
The fivefold symmetry is equivalent to the icosahedral symmetry of (small) atomic clusters: the icosahedron is often an energetically favorable shape for cluster of few atoms, but icosahedral ordering is not observed in cystals since it is not possible to stack togher icosahedra (repeating infinite copies of them in each direction) and tile the whole space (fill it without holes).
Physics of nanowires
Production of nanowires
Nanowire are not observed spontaneously in nature and must be produced in a laboratory.
Nanowires can be either suspended or deposited.Conductivity of nanowires
The conductivity of a nanowire can be studied suspending it between two electrodes.Structure of nanowires
Use of nanowires
Nanowires still belong to the experimental world of laboratories. In a not to far future they could reach production: there are several ideas on how to use them, they could be used to build special electronic devices thank to the electrical properties they show.
References
R. Landauer, J. Phys.: Cond. Matter 1, 8099 (1989)