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by Rowe Alistair - published on , updated on

The reduction in size of otherwise well characterized materials can signficantly modify their optical and electronic properties. This is true for the piezoresistance (the mechanical stress induced variation of the electrical resistivity) in semiconductor materials like silicon.

Traditionally, piezoresistance is directly linked to the electronic structure of materials as the periodic table below shows. The radius of each circle in this image is proportional to the corresponding element’s piezoresistance. It can be seen, for example, that the alkanline metals which are mechanically soft, tend to have large piezoresistance’s while the opposite is true for transition metals. Most elements have positive piezoresistance, meaning that the resistivity is reduced under compressive stresses. Some elements with exceptional electronic properties like Bismuth or Lithium, have a negative piezoresistance.

The radius of the circle around each element is proportional to that element’s piezoresistance (on a log base 10 scale). The trends in the columns and rows are clearly visible, proving that the piezoresistance is an electronic structure phenomenon. The image is adapted from the review article ’Piezoresistance in silicon and its nanostructures’.

In this activity, we explore the effects of changes in size and form on the piezoresistance of solids, and in silicon in particular. Most recently we have been studying the effect of mechanical stress on electrically connected nano-objets in the space charge limit where trapping or localisation at crystal defects becomes important. For more information contact Alistair Rowe.