Contents: (Small 11/2012)

The cover image illustrates distributions of surface temperature in an interconnected array of effi cient, ultrathin, microscale light-emitting diodes based on GaN. The devices exploit high-quality epitaxial material released from sapphire substrates by laser lift off, and then deterministically assembled onto surfaces of interest by transfer printing. Devices can be achieved with thicknesses of a few micrometers and lateral dimensions from 1 mm 1 mm to as small as 25 m 25 m, limited only by lithography. Theoretical and experimental studies of heat dissipation in these unusual devices indicate their thermal compatibility with hydrogels and other 'soft' substrate materials, as models for their potential use embedded in or mounted on organs of the human body, for optogenetics, drug delivery, thermal therapy, or other purposes. For further information, please read the Communication "High-Effi ciency, Microscale GaN Light-Emitting Diodes and Their Thermal Properties on Unusual Substrates" by J. A. Rogers and co-workers beginning on page 1643.