Nanoscopy

The Nobel Prize in Chemistry for 2014 has been awarded to Eric Betzig, Stefan W. Hell and William E. Moerner for the development of super-resolved fluorescence microscopy. This technique allows scientists to view objects at the nanometre scale and is therefore referred to as nanoscopy.

Since the 17^th century, we have been able to peer into the world of very small things using optical microscopes. In 1873, microscopist Ernst Abbe published an equation to show that optical microscopes could not be used to investigate things that were less than half the wavelength of light, that is, to be seen in an optical microscope the object must be greater than 0.2µm. An optical microscope can therefore be used to see some surface structure of a human hair, but you couldn't use it to see the actual protein building blocks making up the hair.

Stefan Hell was working on fluorescence microscopy, using fluorescent molecules to image parts of a cell. A brief pulse of light makes the fluorescent molecules glow temporarily, following the glow allows scientists to map where the molecules are in the cell. The technique can be used to tell where DNA is located for instance, but it could not be used to determined its structure. Stefan Hall proposed a new method, Stimulated Emission Depletion (STED) in which one pulse of light excites all the fluorescent molecules while another pulse quenches the fluorescence from all the molecules except those in a nanometre-sized volume in the middle. Only this volume is registered. An image is built up be sweeping along the sample and continually measuring light levels. In 2000 Stefan Hall was able to demonstrate the effectiveness of the STED microscope by imaging an E.coli bacterium at a resolution that could never be achieved using an optical microscope.

The nanoscopy method proposed independently by Eric Betzig and W E. Moerner, Single-Molecule Microscopy differs in that it relies on the the superposition of several images.

In 1989, W E. Moerner measured the light absorption of a single molecule for the first time.
W E. Moerner had found that one variant of green fluorescent protein (extracted from fluorescent jellyfish) could be made to fluoresce with light of 488nm wavelength, but that after awhile, the fluorescence faded and would not fluoresce again using 488nm light. The same protein, when hit by light of wavelength 405nm could be brought back to life, and then would fluoresce again when hit with light of 488nm.

In 2006 Eric Betzig demonstrated the usefulness of Single-Molecule Microscopy using a glowing protein coupled to a cell's lysosome. Using a weak light pulse, only some of the molecules were caused to fluoresce, and these were at distances greater than 0.2µm. This image was registered. When the fluorescence of these molecules died out, a new weak light pulse was used to initiate the fluorescence of a few more molecules.This new image was registered. This process was continued many times. When Betzig superimposed all the images, a super-resolution image of the cell's lysosome membrane was the result.

Hard Metal

Hard metal is a mixture of a hard carbide phase, tungsten carbide, and a tougher metal phase, cobalt. It is produced by sintering, a process in which fine powders of tungsten carbide and cobalt are heated up so that the cobalt melts and the material is pulled together by capillary force. This results in a solid material consisting of hard tungsten carbide grains surrounded by the tougher cobalt-rich cement phase.

The size of the tungsten carbide grains determines the hardness of the hard metal.
Scientists know that by doping the material, that is, by adding another substance in tiny amounts, they can limit the size of the grains. For example, adding a tiny amount of vanadium can limit the growth of the grains, instead of growing grains 1/1000 mm in diameter, the addition of vanadium results in grain sizes about 1/10,000 mm. Scientists at the Chalmers University of Technology in Sweden have just used high-resolution electron microscopy to observe an extremely thin layer, only 2 atom layers thick, of a cubical structure on the tungsten carbide grains which they believe is affecting the growth of the grains.

Reference:
Expertanswer (2010, June 14). Materials researchers micromanage atoms in hard metal. ScienceDaily. Retrieved June 16, 2010, from http://www.sciencedaily.com­ /releases/2010/06/100614093343.htm

Study Questions:

1. Write the symbol for each of the following elements: tungsten, carbon, cobalt, vanadium.
2. To which group of the Periodic Table do tungsten, cobalt and vanadium belong?
3. Give possible oxidation states (numbers) for tungsten, cobalt, vanadium and carbon.
   
4. Suggest a formula for tungsten carbide.
5. Would you expect larger or smaller grains of tungsten carbide to grow at higher temperatures?
   

Heavy Fermions

Scientists are interested in studying heavy fermion behaviour because it could lead to the design of new materials for high temperature super-conductors.

Cornell University Scientists imaging the electronic properties of a material composed of uranium, ruthenium and silicon, have found that the effects of heavy fermions begin to appear as the material is cooled below 55K, and, an even more unusual electronic phase transition occurs below 17.5K.

This phase transition was studied using spectroscopic imaging scanning tunneling microscopy (SI-STM) which measures the wavelength of electrons on the surface of the material in relation to their energy. From the wavelength and energy measurements scientists calculated the effective electron mass and found that these electrons were either very heavy, or, that they were acting like very heavy electrons because they were being slowed down. This suggests that these electrons are interacting with the uranium atoms, that is, acting as particles rather than acting as a wave.

Reference:
A. R. Schmidt, M. H. Hamidian, P. Wahl, F. Meier, A. V. Balatsky, J. D. Garrett, T. J. Williams, G. M. Luke & J. C. Davis. Imaging the Fano lattice to 'hidden order' transition in URu₂Si₂. Nature, 2010; DOI: 10.1038/nature09073

Study Questions

1/ What is a fermion?

2/ What is a super-conductor?

3/ What could high temperature superconductors be used for?

4/ What is the atomic symbol for:

• uranium
• ruthenium
• silicon

5/ To which group of the Periodic Table do each of the following elements belong?

• uranium
• ruthenium
• silicon

6/ Convert the following temperatures in Kelvin to ^oC.

• 55K
• 17.5K

7/ What is the relationship between mass, energy and wavelength that would allow Scientists to calculate the effective mass of an electron?

8/ Why would electrons appear to be heavier if they are slowed down?