Using 2.5-D particle-in-cell (PIC) simulations, the formation of a double layer (DL) and its stability are studied. The ion beam accelerated by the DL generates fluctuations above the ion cyclotron frequency, triggering its fragmentation into substructures (DLSSs) like U- and V-shaped electrostatic shocks. The DL and DLSSs are seen to continually emit electron holes of varied shapes and sizes into the high-potential plasma above them, while below ions are transversely heated.