An attractive method to response the current energy crisis and produce sustainable nonpolluting power source is harvesting energy from our living environment. However, the energy in our living environment always exists in low-frequency form, which is very difficult to be utilized directly. Here, we demonstrated a novel sandwich-shape triboelectric nanogenerator to convert low-frequency mechanical energy to electric energy with double frequency. An aluminum film was placed between two polydimethylsiloxane (PDMS) membranes to realize frequency multiplication by twice contact electrifications within one cycle of external force. The working mechanism was studied by finite element simulation. Additionally, the well-designed micro/nano dual-scale structures (i.e., pyramids and V-shape grooves) fabricated atop PDMS surface was employed to enhance the device performance. The output peak voltage, current density, and energy volume density achieved 465 V, 13.4 μA/cm(2), and 53.4 mW/cm(3), respectively. This novel nanogenerator was systematically investigated and also demonstrated as a reliable power source, which can be directly used to not only lighten five commercial light-emitting diodes (LEDs) but also drive an implantable 3-D microelectrode array for neural prosthesis without any energy storage unit or rectification circuit. This is the first demonstration of the nanogenerator for directly driving biomedical microsystems, which extends the application fields of the nanogenerator and drives it closer to practical applications.

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This paper reports a novel single-step wafer-level fabrication of superhydrophobic micro/nano dual-scale (MNDS) poly(dimethylsiloxane) (PDMS) films. The MNDS PDMS films were replicated directly from an ultralow-surface-energy silicon substrate at high temperature without any surfactant coating, achieving high precision. An improved deep reactive ion etching (DRIE) process with enhanced passivation steps was proposed to easily realize the ultralow-surface-energy MNDS silicon substrate and also utilized as a post-treatment process to strengthen the hydrophobicity of the MNDS PDMS film. The chemical modification of this enhanced passivation step to the surface energy has been studied by density functional theory, which is also the first investigation of C4F8 plasma treatment at molecular level by using first-principle calculations. From the results of a systematic study on the effect of key process parameters (i.e., baking temperature and time) on PDMS replication, insight into the interaction of hierarchical multiscale structures of polymeric materials during the micro/nano integrated fabrication process is experimentally obtained for the first time. Finite element simulation has been employed to illustrate this new phenomenon. Additionally, hierarchical PDMS pyramid arrays and V-shaped grooves have been developed and are intended for applications as functional structures for a light-absorption coating layer and directional transport of liquid droplets, respectively. This stable, self-cleaning PDMS film with functional micro/nano hierarchical structures, which is fabricated through a wafer-level single-step fabrication process using a reusable silicon mold, shows attractive potential for future applications in micro/nanodevices, especially in micro/nanofluidics.

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