Figure 3. A piezoelectric nanogenerator fabricated using ZnO nanowire arrays for driving

Research in the near future involves the integration of multi-functional nanodevices into selfcontained nanosystems with capabilities of sensing, controlling, communicating and actuating/responding. A nanosystem is composed not only of nanodevices but also a nanopower-source (or nano-battery). But the small size of the nano-battery significantly limits the battery lifetime. It is highly desirable for wireless devices (and required for implanted biomedical systems) to be selfpowered without using a battery, which not only can enhance the adaptability of the devices but also greatly reduce the size and weight of the system. Therefore, a pressing goal of nanotechnology is to harvest energy from the environment for selfpowering these nanodevices [1] .The goal for nanotechnology is to build self-powered nanosystems with ultrasmall size, supersensitivity, extraordinary multi-functionality and extremely low power consumption. As a result, the energy harvested from the environment may be sufficient to power the system.