Shapeshifting: Quantum Dots & Programmable Matter

Throughout history alchemists have tried to transform matter into different forms, most notably, ordinary metals like tin and copper into gold. They’ve never succeeded because atoms don’t change identities very easily. Now, a form of nanotechnology sidesteps that problem with the Quantum Dot, an artificial atom. Quantum Dots probably won’t fulfill the alchemists’ dream of golden riches, but they may someday lead to programmable, shape-shifting matter.[break]

QDs are already being used for their optical properties in televisions and photovoltaic cells, and it’s possible that someday QDs could be used to mimic the properties of elementary atoms.[break]

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An atom of any element consists of a cluster of protons and neutrons, the “nucleus,” surrounded by a cloud of one or more electrons. Physicists visualize the arrangement of electrons into lobes of various shapes, called “orbitals,” which are nothing like circular planetary orbits. Each orbital can hold two electrons. Orbitals, in turn, organize themselves into “shells.” The innermost shell has just one orbital, with a maximum capacity of 2 electrons, while the outermost shell holds 36 orbitals, with room for 72 electrons.[break]

[textwrap_image align=”right”]http://scottjarol.com/wp-content/uploads/2015/02/Orbitals_Captioned1-e1424325369325.jpeg[/textwrap_image]The ability of an atom to combine, or “bind,” with other atoms depends on how many empty slots remain in its outermost shell. Certain elements are non-reactive because their shells are filled, and therefore offer no “slots” with which to share electrons with other atoms. Some common non-reactive elements we encounter in everyday life are neon and gold. Gold doesn’t tarnish because it can’t bind with oxygen. In contrast, carbon has four openings in its outer shell, and therefore binds easily with as many as four other atoms at one time. With it’s four connection points carbon can form complex molecules, such as DNA, as well as the rigid crystalline structure of diamond.[break]

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Which brings us back to Quantum Dots. A QD is a manmade structure that impersonates an atom by arranging electrons to behave like an atom’s outer shell. A QD has no atomic nucleus to attract electrons with the charge of its protons. Instead, a QD forms an electronic barrier, like a fence, which traps electrons in a confined space. Once captured and squeezed together, the electrons form orbital-like structures. From outside, the QD looks something like an atom.[break]
This is a bit of an exaggeration. The atomic nucleus has a distinct advantage over a QD because it’s positive charge holds its electrons together from the inside, and can roam around looking for other atoms with which to combine and form molecules. A QD, on the other hand, at least the QDs that exist today, are constructed on a “substrate” such as a silicon wafer, just like digital electronics, so they’re locked into position on two dimensional surfaces. What makes these QDs particularly interesting is that the control mechanisms that are used to contain electrons can also be used to alter their number and energy levels, simulating various types of atoms on demand. With more flexible substrates, it may  be possible to assemble QDs into fully programmable matter. Imagine what could happen if QDs were assembled into shapeshifting machines capable of reorganizing themselves for any purpose.[break]

For exciting speculations on future applications of programmable materials based on QDs, read Wil McCarthy’s novel, The Wellstone, along with his non-fiction exploration, Hacking Matter: Levitating Chairs, Quantum Mirages, And The Infinite Weirdness Of Programmable Atoms.