Silicon hardness test. 3D Raman map of the results of a Berkovich nanoindentation, or hardness, test on a piece of silicon. A nanoindentation test is used for a very small volume of material. The test is carried out by pressing an indenter into the material to a known maximum load. A Berkovich tip is often used to make the indentation as its measurements are known to a high precision. The area of the indent is measured and then divided by the maximum load used to give the materials hardness. Here, Raman spectroscopy has been used to measure the indent. This method uses the change in wavelength in light reflected from the sample to measure the residual stress left by the indenter, rather than the indent itself.