In addition to Ampere, Kelvin, Mol and Co., the kilogram also is now defined by a natural constant. In concrete terms, this means that the original kilogram, which has been the measure of all things for 130 years, has now served its purpose in Paris. This is made possible by the single crystals grown from the highly enriched isotopic silicon-28 at the Leibniz-Institut für Kristallzüchtung (IKZ).
The new International System of Units (SI) was adopted at the 26th General Conference on Weights and Measures in Paris on 16 November 2018. Now the system officially came into force on 20 May 2019, the World Metrology Day. From now on, 7 natural constants form the foundation of all measures.
Prototype of a silicon-28 single crystal after growth in a floating zone plant in the context of the KILOGRAM project.
Hereafter, a new definition for the kilogram is valid using the Planck constant and thus this unit is no longer determined through the mass of the „original kilogram". The scientific and high-technology communities mostly benefit from this.
The IKZ played a decisive role in replacing the almost 130-year-old artificial object of the original kilogram, because the structurally perfect crystals of isotopically-pure silicon-28 (Si-28, enrichment up to 99.9995 %) grown at the IKZ were of decisive importance for this project.
In these crystals, almost all the atoms have the same mass and are arranged in a regular three-dimensional lattice, which makes a very exact assignment possible between the mass of the crystal and the number of its atoms.
From this relation, the value of the Avogadro constant could be derived with unprecedented precision and thus used as a fundamental natural constant for the definition of the kilogram, since the Plank constant could be determined more precisely with the help of the Avogadro constant.
In the new SI system, the value of the Avogadro constant is determined and one mole therefore contains exactly 6.02214076×10 to the power of 23 individual particles.
But that is not everything. Now all 7 basic units are defined by natural constants. This has been the case for many years for the second (with the hyperfine structure transition of the ground state in the Cs atom), the metre (via the speed of light) and the candela (via the photometric radiation equivalent of a special radiation).
Now the other units also follow, whereby here the elementary charge (for the ampere), the Boltzmann constant (for the Kelvin), the Avogadro constant (for the mole) and the Planck constant (for the kilogram) play the decisive roles.
Within the framework of the "KILOGRAM" projects led by the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, several very precise spheres with shape deviations of less than 20 nm at a diameter of about 94 mm and with a defect-free polished surface were prepared from the silicon-28 crystals grown at IKZ using the float-zone method (FZ).
Under these preconditions, PTB succeeded in determining the number of silicon-28 atoms in a crystal sphere of 1 kilogram total mass, with the required uncertainty of less than 2 x 10 to the power of -8.
It amounts to: 2.152538397 x 10 to the power of 25 atoms of silicon-28
In order to guarantee the necessary purity of the crystals grown from this material, various material-intensive molten-zone cleaning steps are necessary. The special challenges were therefore the approx. 1000 times higher material price compared to conventional silicon as well as the limited amount of material availability.
Silicon is regarded as a very comprehensively investigated semiconductor material that dominates microelectronics and thus communication technologies worldwide. The IKZ will continue to work on the extreme requirements for the further improvement of material properties in order to enable future applications such as artificial intelligence and quantum technologies.
„IKZ´s expertise on isotope pure Si crystals, developed during this metrology project, will allow us to play in the next round a key role as materials science institute for the development of innovative quantum technologies", states Prof. Dr. Thomas Schröder, Scientific Director at IKZ.
Dr. Nikolay Abrosimov | EurekAlert!
Immortal quantum particles: the cycle of decay and rebirth
14.06.2019 | Technische Universität München
Small currents for big gains in spintronics
13.06.2019 | University of Tokyo
The well-known representation of chemical elements is just one example of how objects can be arranged and classified
The periodic table of elements that most chemistry books depict is only one special case. This tabular overview of the chemical elements, which goes back to...
Light can be used not only to measure materials’ properties, but also to change them. Especially interesting are those cases in which the function of a material can be modified, such as its ability to conduct electricity or to store information in its magnetic state. A team led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg used terahertz frequency light pulses to transform a non-ferroelectric material into a ferroelectric one.
Ferroelectricity is a state in which the constituent lattice “looks” in one specific direction, forming a macroscopic electrical polarisation. The ability to...
Researchers at TU Graz calculate the most accurate gravity field determination of the Earth using 1.16 billion satellite measurements. This yields valuable knowledge for climate research.
The Earth’s gravity fluctuates from place to place. Geodesists use this phenomenon to observe geodynamic and climatological processes. Using...
Discovery by Brazilian and US researchers could change the classification of two species, which appear more akin to jellyfish than was thought.
The tube anemone Isarachnanthus nocturnus is only 15 cm long but has the largest mitochondrial genome of any animal sequenced to date, with 80,923 base pairs....
Researchers at Chalmers University of Technology, Sweden, have discovered a completely new way of capturing, amplifying and linking light to matter at the nanolevel. Using a tiny box, built from stacked atomically thin material, they have succeeded in creating a type of feedback loop in which light and matter become one. The discovery, which was recently published in Nature Nanotechnology, opens up new possibilities in the world of nanophotonics.
Photonics is concerned with various means of using light. Fibre-optic communication is an example of photonics, as is the technology behind photodetectors and...
29.04.2019 | Event News
17.04.2019 | Event News
15.04.2019 | Event News
18.06.2019 | Life Sciences
18.06.2019 | Life Sciences
18.06.2019 | Life Sciences