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18. Transfers thermiques d'énergie

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Pourquoi on a pas froid dans un Igloo par ScienceEtonnante - I Phyz Good #02 - String Theory. YouTube. Expérience de convection. Manipulating atoms to make better superconductors. Spectacle inédit : une liaison entre deux atomes filmée pour la première fois. En 1895, le Français Louis Lumière présentait au public La Sortie de l’usine Lumière à Lyon, 45 secondes d’images tournées au cinématographe et comptant parmi les toutes premières de l’histoire du cinéma. 125 ans plus tard, ce sont là encore quelques secondes d’images en noir et blanc qui viennent marquer, cette fois, le petit monde de la physique.

Spectacle inédit : une liaison entre deux atomes filmée pour la première fois

Des chercheurs de l’Université d’Ulm, en Allemagne, et de l’Université de Nottingham, au Royaume-Uni, sont parvenus à filmer pour la toute première fois les instants précis où deux atomes se lient et se séparent. Une scène palpitante survenue dans l’infiniment petit, à une échelle un demi-million de fois inférieure à l’épaisseur d’un cheveu humain. Chaque atome présent dans l'expérience mesurait en effet entre 0,1 et 0,3 nanomètre. C’est précisément pour cette raison qu’il n’existait jusqu’à présent aucune image filmée de ce processus chimique sur lequel repose la réalité même de la matière. Des électrons comme "pellicule"... Scanning tunneling microscope.

Researchers develop 'MicroMegascope': imaging with a tuning fork. Currently, atomic force microscopes (AFMs) are one of the most widely used tools for imaging, measuring, and manipulating matter at the nanoscale.

Researchers develop 'MicroMegascope': imaging with a tuning fork

One of the key components of an AFM is a microscale oscillator, which scans the topographical features of a sample. Unfortunately, however, the fabrication of microscale oscillators is a complex and expensive process. In a new paper published in Nanotechnology, a team of researchers from the Laboratoire de Physique Statistique at the École Normale Supérieure, CNRS, in Paris, have demonstrated that a 7-centimeter-long aluminum tuning fork can replace the microscale oscillator in an AFM, and still produce images of nanoscale resolution and equal quality.

"By analogy, to feel a roughness of 100 nm with an instrument 7 cm long is like feeling the thickness of a virus under the antenna of the Eiffel tower," coauthor Antoine Niguès at the École Normale Supérieure told More information: L. Transferts thermiques. Le microscope à effet tunnel. La liaison hydrogène observée au microscope à force atomique. Sans les liaisons hydrogène, l'eau et l'ADN perdraient bon nombre de leurs propriétés.

La liaison hydrogène observée au microscope à force atomique

Les chimistes et les biologistes ne peuvent donc qu'être intéressés par la performance d'une équipe de chercheurs chinois travaillant dans le domaine de la nanotechnologie. Terahertz spectroscopy goes nano. Brown University researchers have demonstrated a way to bring a powerful form of spectroscopy—a technique used to study a wide variety of materials—into the nano-world.

Terahertz spectroscopy goes nano

Laser terahertz emission microscopy (LTEM) is a burgeoning means of characterizing the performance of solar cells, integrated circuits and other systems and materials. Laser pulses illuminating a sample material cause the emission of terahertz radiation, which carries important information about the sample's electrical properties. "This is a well-known tool for studying essentially any material that absorbs light, but it's never been possible to use it at the nanoscale," said Daniel Mittleman, a professor in Brown's School of Engineering and corresponding author of a paper describing the work.

"Our work has improved the resolution of the technique so it can be used to characterize individual nanostructures. " That's one example of where this could be useful, Mittleman said, but it's certainly not limited to that. Researchers turn atomic force microscope measurements into color images. A French and Japanese research group has developed a new way of visualizing the atomic world by turning data scanned by an atomic force microscope into clear color images.

Researchers turn atomic force microscope measurements into color images

The newly developed method, which enables observation of materials and substances like alloys, semiconductors, and chemical compounds in a relatively short time, holds promise of becoming widely used in the research and development of surfaces and devices. Individual molecules and atoms are much smaller than the wavelengths of light that we can see. Visualizing such tiny structures requires special instruments that often provide black-and-white representations of the positions of atoms. Atomic force microscopes (AFMs) are among the most powerful tools available for probing surfaces at the atomic scale level.

Hydrogen bonds directly detected for the first time. For the first time, scientists have succeeded in studying the strength of hydrogen bonds in a single molecule using an atomic force microscope.

Hydrogen bonds directly detected for the first time

Researchers from the University of Basel's Swiss Nanoscience Institute network have reported the results in the journal Science Advances. Hydrogen is the most common element in the universe and is an integral part of almost all organic compounds. Molecules and sections of macromolecules are connected to one another via hydrogen atoms, an interaction known as hydrogen bonding. These interactions play an important role in nature, because they are responsible for specific properties of proteins or nucleic acids and, for example, also ensure that water has a high boiling temperature. To date, it has not been possible to conduct a spectroscopic or electron microscopic analysis of hydrogen and the hydrogen bonds in single molecules, and investigations using atomic force microscopy have also not yielded any clear results. Des chercheurs créent une molécule inédite et stable - Au-delà des nuages. Le microscope à effet tunnel. Le microscope à effet tunnel. First-ever videos show how heat moves through materials at the nanoscale and speed of sound.

Using a state-of-the-art ultrafast electron microscope, University of Minnesota researchers have recorded the first-ever videos showing how heat moves through materials at the nanoscale traveling at the speed of sound.

First-ever videos show how heat moves through materials at the nanoscale and speed of sound

The research, published today in Nature Communications, provides unprecedented insight into roles played by individual atomic and nanoscale features that could aid in the design of better, more efficient materials with a wide array of uses, from personal electronics to alternative-energy technologies. Energy in the form of heat impacts all technologies and is a major factor in how electronic devices and public infrastructure are designed and engineered. It is also the largest form of waste energy in critical applications, including power transmission and especially transportation, where, for example, roughly 70 percent of the energy in gasoline is wasted as heat in automobile engines. Icists measure van der Waals forces of individual atoms for the first time. Physicists at the Swiss Nanoscience Institute and the University of Basel have succeeded in measuring the very weak van der Waals forces between individual atoms for the first time.

icists measure van der Waals forces of individual atoms for the first time

To do this, they fixed individual noble gas atoms within a molecular network and determined the interactions with a single xenon atom that they had positioned at the tip of an atomic force microscope. As expected, the forces varied according to the distance between the two atoms; but, in some cases, the forces were several times larger than theoretically calculated. These findings are reported by the international team of researchers in Nature Communications. Van der Waals forces act between non-polar atoms and molecules.

Although they are very weak in comparison to chemical bonds, they are hugely significant in nature. Atomic force microscope reveals molecular ghosts.