Ultra-pure material

We already reported on the development of two-dimensional nano-sheet transistors and other two-dimensional materials.  One of the challenges that has been previously mentioned is the fact that we do not know the material properties of “pure” materials.  Current technology provides the ability to achieve purities within a range of parts per million.  In the percentage parlance that is 99.9999% pure material.  It is expensive and needed.  Doping silicon wafers with specific impurities can change the bandgap (conductivity increase or decrease) of the resultant material to enable the desired structure flow of electrons.  While the percentage of material purity Sound excellent, there is another way of looking at the analysis. 

Reference 1 refers to an analysis by Flavio Matsumoto on the number of osmium atoms in a cubic centimeter.  He performs the calculation tow different ways and the answers are close.  Both result in 7 x 1022 atoms, with a fractional difference.  Depending on the specific element, the number will vary.  If the material (osmium in this example) is 99.9999999% pure, there will be 7 x 1013 non osmium atoms in the cubic centimeter.  If one then reduces the size in question to one micron cubed, there will be 7 non osmium atoms present.  What happens when materials get near being without impurities?   

Princeton researchers [Ref. 2] have created a sample of gallium arsenide with impurities of one atom in ten billion.  The size of the material was 5 or 6 millimeters cubed.  To test the material, the cooled it to temperatures equivalent to space and inserted the material in a strong magnetic field.  They were interested in observing the changes in the electron flow.  They were surprised in that they found that many of the advanced physics phenomena were able to be observed at weaker magnetic fields.  From the data, it appears that the resultant effects could be observed at two orders of magnitude less than fields required to observe the phenomena in less pure materials. 

Our current technology permits us to make changes in the electrical conductivity of materials by adding a small amount of specific impurities (doping).  It is also known that adding impurities changes the structural lattice to advance or retard the ability of electrons to move within the lattice.  Since the lattice structure is changed, the question that remains is what happens to various other properties of the material.  In order to address that question, various quantities of absolutely pure material need to be created.  The raises the challenge on developing the processes for removing the impurities for the current methods of obtaining the current “high purity” materials.

This is a non-trivial problem.  Graphene has been manufactured for 20 plus years.  There is still a challenge to obtain a large area of graphene without structural defects.  Impurities can create those structural defects.  The work being done on two-dimensions transistors, which can accommodate some defects, has not developed a process that can be employed to create the billions of transistors required for one microprocessor chip.

The new year, 2022, should provide some interesting developments that further our understanding of pure materials.

References:

  1. https://www.quora.com/How-many-atoms-of-osmium-are-there-in-one-cubic-centimeter-I-honestly-cant-find-any-internet-help-whatsoever
  2. https://phys.org/news/2021-11-ultra-pure-semiconductor-frontier-electrons.html

About Walt

I have been involved in various aspects of nanotechnology since the late 1970s. My interest in promoting nano-safety began in 2006 and produced a white paper in 2007 explaining the four pillars of nano-safety. I am a technology futurist and is currently focused on nanoelectronics, single digit nanomaterials, and 3D printing at the nanoscale. My experience includes three startups, two of which I founded, 13 years at SEMATECH, where I was a Senior Fellow of the technical staff when I left, and 12 years at General Electric with nine of them on corporate staff. I have a Ph.D. from the University of Texas at Austin, an MBA from James Madison University, and a B.S. in Physics from the Illinois Institute of Technology.

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