Suppose an STM tip is scanned (at fixed z height) across a single ad-atom sitting atop a perfectly flat crystalline surface of the same element. Determine the factor by which the current will increase when scanning the tip over the ad-atom, assuming an atomic radius of 1A. Use the expression below for tunneling current I as a function of tip-sample distance z given below, assuming c= 1010(eVm) and a work function of 5eV. I=TSUecz Problem 2 Sketch the general current-voltage (I-V) curves expected for tunneling spectroscopy of three different sample types: metal, insulator, and a semiconductor ( n-type, 3eV bandgap). Problem 3 The Si(001)-(2x1) reconstructed surface exhibits rows of surface dimers. At right are STM images obtained at (A) negative and (B) positive bias. Explain the observations in terms of molecular orbitals, illustrated with a sketch. Draw the expected I-V scans expected when the tip is positioned atop a Si atom, and additionally when the tip is placed above the space directly between dimer atoms