There is a file in the on-line resources called stm. txt, which contains a grid of values from scanning tunneling microscope (STM) measurements of the (111) surface of silicon. An STM is a device that measures the shape of a surface at the atomic level by tracking a sharp tip over the surface and measuring quantum tunneling current as a function of position. The end result is a grid of values that represent the height of the surface and the file stm. txt contains just such a grid of values. Write a program that reads the data contained in the file and makes a density plot of the values. Use the various options and variants you have learned about to make a picture that shows the structure of the silicon surface clearly.