Fig. 4

Multi-nanodiamond (ND) mapping of deformation induced by a single indentation. a Schematic of the gelatin deformation by an atomic force microscopy (AFM) indentation. The NDs were dispersed on the surface of the gelatin. b The AFM image, and c, the fluorescence confocal image of the gelatin sample. Scale bars in b and c are 5 μm. d Fluorescence confocal image showing the NDs in Group I. The green dots mark the NDs indicated by the highest fluorescence intensity. The directions and the sizes of the arrows represent the rotation axes and the rotation angles of the NDs, respectively. The red triangle marks the position of the AFM tip indentation. e The rotation angle χ and f the reconstructed deformation taken from all eight groups of NDs (around eight different AFM indentation positions), plotted as functions of the distance between the NDs and the AFM tip indentation positions. The data from the NDs in the same group are presented in the same color. The solid gray lines are the simulation results using the surface tension model (with the gray shadow showing a ±300 nm uncertainty of distance given by the optical resolution). The dashed lines are simulation results from the Hertz–Sneddon model. The inset zooms in the simulation results of the gelatin surface near the AFM tip. The horizontal error bars in e are the optical resolution