We report on the structure of ring deposits formed following the free evaporation of a sessile droplet containing nanoparticles. The nanostructure of the evaporatively formed deposits was revealed using atomic force microscopy (AFM). The structures were found to form a peak about 5 microns wide and one micron high and to exhibit a gentle slope gradually increasing in height in the direction of the three phase contact line motion. A theory is proposed to explain the formation and shape of these deposits. A comparison between the theory and the experiments shows a very good qualitative and quantitative agreement.