Puckering Effect (2 of 2) (image) University of Pennsylvania Caption Interatomic forces cause attraction between the atomic sheet and the nano-scale tip of the atomic force microscope. Thin sheets deflect toward the tip, therefore increasing friction. When the tip starts to slide, the sheet deforms further as the deformed area is partially pulled along with the tip. The color scale of the atoms indicates how far the atoms have moved upward (red) or downward (blue) from their original positions. Thicker sheets cannot deflect as easily because they are much stiffer, so the increase in friction is less pronounced, consistent with study measurements. Credit University of Pennsylvania and Science Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.