We have measured the NC-AFM frequency shift dependence on the X-ray energy around the AuL3 absorption edge energy. We found a peak in the frequency shift just above the An region at the AuL3 absorption edge energy while we could not detect any peak in the frequency shift when the NC-AFM tip was placed above the Si regions. This novel phenomenon indicated that the combination of energy-variable X-rays and NC-AFM provides us a new way to nano level chemical mapping at surface. We briefly discussed some possible mechanisms. (C) 2006 Elsevier B.V. All rights reserved.