Researchers recently developed a new approach to measure atomic bonds and nature, revealing that a sound's speed depends on the structure it travels through.
Mirage News specified that scientists from the University of Nottingham and Loughborough University used a measurement approach known as "picosecond ultrasonics," the same as medical ultrasound, to gauge an atom bonding's strength within the material.
Force is essential to all things in everyday life. From as comprehensive as a gravitational force that underscores the whole universe's operation, to as small-scale as an interaction between electrons that can be hair-raising.
Furthermore, force is quite difficult to gauge, particularly when the forces are very big or very small, this is particularly the scenario when one enters the nanoworld, for instance, in what's called the "two-dimensional van der Waals" or 2D-vdW materials where objects comprise length scales in a 10-9-meter-range.
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2D Materials
A similar Phys.org report said such materials are named 2D materials since their properties-physical, chemical, and geometrical, are confined to two dimensions within a thin sheet of material.
Within that said sheet, atoms are tightly attached to each other through strong covalent or ionic bonds, while the layers themselves are held together by weak vdW force.
The totally different nature and co-occurrence of these immensely different strength forces enable researchers to peel the material from huge mined crystals to perfect single layers of atoms and find astonishing phenomena which include room temperature superconductivity, as explained in a study published in Nature.
Using pencils, for instance, drawing on a piece of paper is actually a scientific experiment to produce single atomic layers of graphene or carbon atoms, something that has been commonly done for hundreds of years without realizing it.
Despite intensive examination of vdW materials by various research groups all over the world, there are hardly any experimental approaches to gauge the atomic bonds' strength, as well as the vdW forces, minus destroying the materials.
Picosecond Ultrasonics Used
According to one of the leas researchers from the School of Physics and Astronomy at the University of Nottingham, they used picosecond ultrasonics to gauge both the "strong covalent bonds and weak vdW forces" minus impairing the material.
This approach is akin to the medical ultrasound although with a much higher frequency and therefore, non-invasive. As specified in this report, the research shines 120 femtoseconds "pump: laser pulses on 2D materials' flakes, producing phonons which are "quantized sound waves."
In addition, as phonons are traveling through the material, they are feeling and interacting with the atoms and the bonds within the material.
These phonons' properties, reflecting the atomic bonds' strength, are then gauged by a second probe laser pulse.
The scientists discovered that sound is traveling at very different speeds in various structures of the same substance.
Traveling Through vdW Material
Loughborough University's Alexander Balanov and Mark Greenaway elaborated, while traveling through the vdW material, the ultrasonic acoustic wave is not damaging or destroying the crystal, only deforms it a bit. Meaning, this particular structure can be thought of as a system of springs.
They added, by known the sound's speed from measurements, and the manner these springs are responding to the deformation, the relative strength of covalent forces can be extracted between the atoms and the vdW forces between layers.
If the so-called density functional theory is applied, they continued, with the help of a high-performance computer, such forces of different stacking configurations can be numerically estimated.
These forces can also suggest how to tune the electric, elastic, and even chemical properties of vdW materials' different polymorphs.
Related information about ultrasonics is shown on Jackie Komutatsu's YouTube video below:
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