Updated: 11/24/2005; 11:39:11 PM.

Nanoscale technology
Interesting tech developments in nanotech, nanostructured materials, etc.


daily link  Monday, January 26, 2004


Quantum Dots and Programmable Matter: Quick intro to an amazing future for materials science.  With reference to Wired article and FAQ:  "A quantum dot is any device capable of confining electrons in three dimensions, in a space small enough that their quantum (wavelike) behavior dominates over their classical (particle-like) behavior.  Under cryogenic conditions, this typically occurs with dimensions of 1000 nm (0.001 mm) or less.  At room temperature, confinement spaces of 20-30 nm or smaller are required.

Once the electrons are confined, they repel one another and also obey the Pauli Exclusion Principle, which forbids any two electrons from having the same quantum state.  Thus, the electrons in a quantum dot will form shells and orbitals highly reminiscent of (though larger than) the ones in an atom, and will in fact exhibit many of the optical, electrical, thermal, and (to some extent) chemical properties of an atom.  This electron cloud is therefore referred to as an artificial atom.  ..

Q13: How is programmable matter made?

A13: Current forms of programmable matter fall into three types: colloidal films, bulk crystals, and quantum dot chips which confine electrons electrostatically.  Quantum dots can be grown chemically as nanoparticles of semiconductor surrounded by an insulating layer.  These particles can then be deposited onto a substrate, such as a semiconductor wafer patterned with metal electrodes, or they can be crystalized into bulk solids by a variety of methods.  Either substance can be stimulated with electricity or light (e.g., lasers) in order to change its properties.

Electrostatic quantum dots are patterns of conductor (usually a metal such as gold) laid down on top of a quantum well, such that varying the electrical voltage on the conductors can drive electrons into and out of a confinement region in the well -- the quantum dot.  This method offers numerous advantages over nanoparticle ("colloidal") films, including a greater control over the artificial atom's size, composition, and shape.  Numerous quantum dots can be placed on the same chip, forming a semiconductor material with a programmable dopant layer near its surface.

Rolling such chips into cylindrical fibers produces "wellstone," a hypothetical woven solid whose bulk properties are broadly programmable.  ..

Q21: What is programmable matter good for?

A21: Almost anything.  It can improve the efficient collection, storage, distribution, and use of energy from environmental sources.  It can be used to create novel sensors and computing devices, probably including quantum computers.  It can create materials which are not available by other means, and which change their apparent composition on demand.  Currently, the design of new materials is a time- and labor-intensive process; with programmable matter, it becomes a real-time issue, similar to the design and debugging of software.  ..

Single-electron transistors, a form of quantum dot, were first proposed by A.A. Likharev in 1984 and constructed by Gerald Dolan and Theodore Fulton at Bell Laboratories in 1987.  The first semiconductor SET, a type of quantum dot sometimes referred to as a designer atom, was invented by Marc Kastner and John Scott-Thomas at MIT in 1989.  The term "artificial atom" was coined by Kastner in 1993.  Wil McCarthy was the first to use the term "programmable matter" in connection with quantum dots, and to propose a mechanism for the precise, 3D control of large numbers of quantum dots inside a bulk material.  The most interesting forms of this device or substance -- known as "quantum dot fiber" or "wellstone" -- are not produceable using circa 2003 technology, although related products may be.  The term "wellstone" was coined by McCarthy's business associate, Gary E. Snyder. "

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Copyright 2005 © Ken Novak.
Last update: 11/24/2005; 11:39:11 PM.