Clusters of gold atoms form peculiar pyramidal shape

Posted: January 6, 2020 by oldbrew in News, research

A model of 20 oranges is compared with the theoretical and experimental structure [credit: KU Leuven]


Peculiar? Maybe, but the clusters are just based on the triangular number sequence: 0,1,3,6,10 etc. (add one more than last time).
– – –
Freestanding clusters of twenty gold atoms take the shape of a pyramid, researchers discovered.

This is in contrast with most elements, which organize themselves by forming shells around one central atom, says EurekAlert.

The team of researchers led by KU Leuven published their findings in Science Advances.

Clusters composed of a few atoms tend to be spherical. They are usually organized in shells of atoms around a central atom. This is the case for many elements, but not for gold!

Experiments and advanced computations have shown that freestanding clusters of twenty gold atoms take on a pyramidal shape.

Credit: Wikipedia


They have a triangular ground plane made up of ten neatly arranged atoms, with additional triangles of six and three atoms, topped by a single atom [see figure where a model of twenty oranges is compared with the theoretical and experimental structure].

The remarkable tetrahedral structure has now been imaged for the first time with a scanning tunnelling microscope. This high-tech microscope can visualise single atoms.

It operates at extremely low temperatures (269 degrees below zero) and uses quantum tunnelling of an electrical current from a sharp scanning metallic tip through the cluster and into the support. Quantum tunnelling is a process where electrical current flows between two conductors without any physical contact between them.

Full article here.

Comments
  1. oldbrew says:

    Any two consecutive numbers in the triangular number series will sum to the square of another number:
    1 + 3 = 2²
    3 + 6 = 3²
    6 +10 = 4²
    etc.

  2. oldmanK says:

    A tetrahedron. Atomic arrangements is a wide science with many avenues to explore. Metallurgy and the science of alloys is an important one (with disastrous results for the careless). Also a source of problems in developing fields, particularly electronics. See https://en.wikipedia.org/wiki/Whisker_(metallurgy)

  3. oldbrew says:

    From the report:
    Gold clusters ranging from a few to several dozens of atoms in size are known to possess remarkable properties.

    The new discovery helps scientists evaluate the catalytic and optical performances of these clusters, which is relevant for designing cluster-based catalyst and optical devices. Recent applications of clusters include utilisation in fuel cells and carbon capture.
    – – –
    Sounds expensive.

  4. oldbrew says:

    The remarkable tetrahedral structure has now been imaged for the first time

    As gold, so water?…

    Tetrahedral geometry of water found to account for its remarkable properties
    https://resonance.is/tetrahedral-geometry-water-found-account-remarkable-properties/

  5. oldmanK says:

    The catalytic performance of gold, together with carbon in the cubic structure, is well known. (Ask any woman).

  6. HM says:

    The standard theory of the atomic nucleus is that the protons and neutrons are bound together, (despite the protons repelling each other) by the same force that binds the quarks inside them individually, now called the ‘strong interaction’.

    asfaik, this suggests no particular theory why gold atoms in particular would stack like a pyramid. I will get to this but first a tiny sidetrack.

    My impression is there is an outstanding question: what determines the the stability of various isotopes of all the elements, their half-lives and so on? [Please note the common literature acts like this has been solved]. I have seen two people suggest an answer starting with hypothesis: the nuclei actually do have particular structures.

    One is the lunatic named Miles Mathis (occasionally mentioned in comments here). His nucleus theory is that neutrons stick *between* protons. He also has some aether involved, or something, I have not exactly studied this closely.

    He has diagrams. In his pdf about mercury (his claim why it is liquid)
    http://milesmathis.com/mercliq.pdf
    there is both a diagram of gold and a link to an avi of the AU nucleus rotating
    http://milesmathis.com/gold.avi

    with this comment
    “We see that Gold doesn’t have the balance of Mercury, but it does have 3 or 4 protons in all directions (top, bottom, and all sides), which makes it fairly unreactive like Mercury. ”

    In other words, his structure for gold [au] is a 3d plus sign.

    If not predictive this seems consistent with it stacking like a pyramid. Since Mathis said this *before* the stacking was observed, I considered it worth posting here.

    If one wants to glean another marginal prediction, nuclei protons & neutrons do have a ‘magnetic moment’ and Mathis’ au is not perfectly symmetrical so maybe the bottom of the pyramid has a slightly different one. I have no idea what is, under standard theory, supposed to generated this ‘moment’.

  7. Ian MacCulloch says:

    You might be interested in this 1997 effort –

    EW SERIES OF MASSIVE GOLD CLUSTERS HAS “EXTRAORDINARY” QUANTUM PROPERTIES WITH POTENTIAL USES IN NANOELECTRONICS

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    For Immediate Release
    April 17, 1997
    NEW SERIES OF MASSIVE GOLD CLUSTERS HAS “EXTRAORDINARY” QUANTUM PROPERTIES
    WITH POTENTIAL USES IN NANOELECTRONICS
    Structure of Molecular Clusters | Formation of Molecular Clusters |
    Unique Electronic Properties & Applications | Interdisciplinary Research
    Leads to Results
    An interdisciplinary team of researchers at the Georgia Institute of
    Technology has isolated a new series of highly stable and massive
    gold-cluster molecules that possess a set of “extraordinary” quantum
    properties.
    “With these properties, the molecules are very attractive building blocks
    for testing one type of ultra miniaturized architecture envisioned by some
    for 21st-century nanoelectronics, as well as for other chemical and
    molecular-biological applications,” said Dr. Robert L. Whetten, Professor
    of Physics and Chemistry at Georgia Tech. Photo copyright
    information
    Graduate Students Igor Vezmar and Joseph Khoury use a high-mass
    spectrometer to analyze the new series of gold clusters. (200-dpi
    JPEG version – 241k)
    Supported by the National Science Foundation, the U.S. Office of Naval
    Research, the Packard Foundation, and the Georgia Tech Foundation, the
    work was reported April 16 at the 213th National Meeting of the American
    Chemical Society in San Francisco.
    Structure of Molecular Clusters
    Each molecule in the new series has a compact, crystalline gold core. This
    pure metallic core, just one-to-two billionths of a meter (1-2 nanometers)
    across, is encapsulated within a shell of tightly packed hydrocarbon
    chains linked to the core via sulfur atoms.
    The principal members of the series have core-masses of about 14,000;
    22,000 and 28,000 protons, corresponding to about 75, 110 and 145 gold
    atoms, respectively, and are thus in the same mass range as larger protein
    molecules, as reported by M. M. Alvarez and colleagues in a paper
    published recently in Chemical Physics Letters. These differ, both in size
    and the higher yield with which they are obtained, from their heavier
    analogs described in 1996 by Whetten and colleagues in Advanced Materials.

    The precise structures of the cores are as yet unknown, but theoretical
    and experimental evidence suggests they are faceted with a particular
    gem-stone shape, as reported in a forthcoming paper by Whetten, Dr. Uzi
    Landman, and their co-workers in the Zeitschrift fer Physik.
    “The surrounding chains can be of any length, and can be modified to
    confer particular chemical properties, so that they can be incorporated
    into various solid-state and solution structures,” Whetten noted. “Most
    importantly, each member of the series behaves as a substance composed of
    infinitely replicated molecules, which can be separated from other members
    of the series to yield pure substances with precisely defined properties.”

    Formation of Molecular Clusters
    The gold cluster molecules emerge spontaneously during the decomposition
    of certain gold-thiolate polymers of the type commonly used in decorative
    gold paints and in gold anti-arthritis drugs. With sufficient control of
    the decomposition process, this series can be isolated without concurrent
    production of larger gold crystals. It is then relatively easy to separate
    the principal members of the series from each other to obtain the
    necessary homogeneity. Once purified, the molecules spontaneously assemble
    into crystalline thin films, powders, or macrocrystals, while preserving
    the discrete properties of the individual gold nanocrystal cores.
    Gold is important technically not only for its inertness — once made, the
    clusters are immune to corrosion — but also for its highly stable
    surfaces, which find application as junctions in critical microelectronic
    applications.
    Unique Electronic Properties & Applications
    “The main fascination of very small metal crystals, and the foundation for
    their envisioned use in future electronics, arises from the fact that
    their conduction electrons are quantized both in their number — charge
    quantization — and in the states they can occupy — energy quantization,”
    Whetten added. “In crystals larger than a few nanometers, these effects
    can only be observed and used at very low temperatures, such as that of
    liquid helium, near absolute zero. The new series of nanocrystals are both
    sufficiently small that these effects are prominent even at ordinary
    temperatures and yet are large enough to have the robust crystalline
    properties of the bulk metal.”
    The electromagnetic and conduction properties of the clusters are
    extremely sensitive to charging, and somewhat less so to energy level.
    Whetten believes these states can be used in a proposed electronic
    circuitry known as “single-electronics.”
    The new gold cluster materials are the first to exhibit the
    charge-quantization effect in a macroscopically obtained material, for
    which every cluster behaves identically. The first measurements were
    conducted in the laboratory of Dr. Phil First at Georgia Tech by observing
    the step-like changes in the current passing from a scanning tunneling
    microscope tip to a gold plate through a single gold cluster molecule as
    the voltage was increased.
    The highly regular spacing between these steps, known as the “Coulomb
    staircase,” showed that the molecules’ gold core is charging like a small
    metal sphere in a series of discrete steps by adding or removing single
    electrons.
    An article in Chemical & Engineering News reported that Whetten and
    collaborators at the University of North Carolina-Chapel Hill have
    developed an electrode based on the most massive of the new series. Using
    this charging effect, the researchers have been able to do some
    electrochemistry work that is continuing.
    The quantization of the energy levels of the conduction electrons is
    observed separately in optical spectroscopy experiments — the spectrum of
    transmitted visible or infrared light — that reveals discrete level
    structure, even at room temperature.
    Interdisciplinary Research Leads to Results
    Research in the area of nanometer-scale molecular materials is highly
    interdisciplinary, requiring the skills of many diverse researchers and
    facilities. The molecular gold materials have been developed in Whetten’s
    Georgia Tech laboratory, as guided also by the theoretical predictions and
    modeling of Landman’s Center for Computational Materials Science.
    They were characterized in the Georgia Tech Facility for High Resolution
    Microscopy, directed by Dr. Z. L. Wang, in the X-ray facilities at Georgia
    Tech of Dr. Angus Wilkinson and the National Synchrotron Light Source by
    Dr. Peter W. Stephens of the State University of New York-Stony Brook. The
    research in Whetten’s laboratory has been carried out by a team of
    graduate students including Marcos M. Alvarez, Joseph Khoury, Greg
    Schaaff, Marat Shafigullin, Brian Salisbury, and Igor Vezmar.

    RESEARCH NEWS AND PUBLICATIONS OFFICE
    430 Tenth St. N.W., Suite N-116
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    Atlanta, Georgia 30318

    MEDIA RELATIONS CONTACTS:
    John Toon (404-894-6986);
    Internet: john.toon@edi.gatech.edu; FAX: (404-894-6983)

    TECHNICAL:
    Dr. Robert Whetten (404-894-8255); Internet:
    robert.whetten@physics.gatech.edu.

    PHOTO COPYRIGHT INFORMATION: Photographs are copyrighted by the Georgia
    Tech Research Corporation and may be freely used by the news media with
    credit to the Georgia Institute of Technology. The photographer is Stanley
    Leary, Georgia Tech Communications Division.

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