Fuyun Zhu

Frequency-Multiplication High-Output Triboelectric Nanogenerator for Sustainably Powering Biomedical Microsystems

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.

Self-Cleaning Poly(dimethylsiloxane) Film with Functional Micro/Nano Hierarchical Structures

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.

3D nanostructure reconstruction based on the SEM imaging principle, and applications

This paper addresses a novel 3D reconstruction method for nanostructures based on the scanning electron microscopy (SEM) imaging principle. In this method, the shape from shading (SFS) technique is employed, to analyze the gray-scale information of a single top-view SEM image which contains all the visible surface information, and finally to reconstruct the 3D surface morphology. It offers not only unobstructed observation from various angles but also the exact physical dimensions of nanostructures. A convenient and commercially available tool (NanoViewer) is developed based on this method for nanostructure analysis and characterization of properties. The reconstruction result coincides well with the SEM nanostructure image and is verified in different ways. With the extracted structure information, subsequent research of the nanostructure can be carried out, such as roughness analysis, optimizing properties by structure improvement and performance simulation with a reconstruction model. Efficient, practical and non-destructive, the method will become a powerful tool for nanostructure surface observation and characterization.

Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

Controllable formation and optical characterization of silicon nanocone-forest using SF 6 /C 4 F 8 in cyclic etching-passivation process

This paper reports a nanocone-forest silicon surface fabricated by an improved DRIE process using SF6/C4F8 in cyclic etching-passivation process, which is maskless, controllable, effective and large-size. As well known, optical property of textured silicon surface is determined mainly by its surface structure, and surface structure is determined by process conditions. In this work, process conditions during the experiment, like etching process parameters, pretreatment, uniformity control and patterned silicon etching, are tested and discussed. Based on these controllable process conditions, nanocone-forest with an average height of 0.4~5μm, aspect ratio of 1~8 and density of 3~30 per 4μm2 formed. By analyzing the influences of nanostructure parameters on optical property, its concluded that high aspect ratio, high density and small height of nanostructure could result in ultra-low reflectance. The optical reflectance of two samples has been reduced to below 0.22% and 0.16% of the solar spectrum, respectively.

Single-step fabrication of superhydrophobic micro/nano dual-scale PDMS film replicated from ultra-low-surface-energy mold

This paper reports a single-step process to fabricate superhydrophobic micro/nano dual-scale (MNDS) poly(dimethylsiloxane) (PDMS) membrane replicated directly from ultra-low-surface-energy MNDS silicon substrate at high temperature without surfactant coating. MNDS silicon surface with ultra-low surface energy was simply fabricated by an improved deep reactive ion etching (DRIE) process. The huge reduction of surface energy and the formation of high-density nanostructures (i.e. nanotips) on well-designed microstructures (i.e. inverted pyramids and V-shape grooves) were realized simultaneously due to the enhancement of passivation step of DRIE process. Therefore, the high-temperature thermal cross-linking process, even higher than 180°C, can be directly utilized on the pattern replication of PDMS without surfactant coating to strengthen the precision. After studying of heating temperature and time, the MNDS PDMS membrane with the static contact angle (CA) of ~151° was realized at the optimized temperature of 85°C after 1-hour heating. The plasma treatment of the same improved DRIE process was utilized to enhance the hydrophobicity. The CA achieved up to more than 160°, while the CA hysteresis was reduced to below 10°.

Triboelectrification based active sensor for polymer distinguishing

We present a novel sensor for polymer distinguishing among a group of known polymers based on the effects of triboelectrification and electrostatic induction. Multiple polymer-electrode cells are integrated on a flexible substrate, each cell produces an independent signal. The manufacture procedure of flexible printed circuit is employed to implement a low-cost and efficient fabrication of the device. According to the triboelectric serials, for different polymer groups, the friction layers can be well-selected. As an example, the distinguishing of polydimethylsiloxane, polyethylene and polyethylene terephthalate has been well demonstrated by employing polyimide and polystyrene as friction layers, showing potential applications in robotics and industrial fields.

A three-step model of black silicon formation in Deep Reactive Ion Etching process

A three-step model used for modeling and simulation of black silicon formation in DRIE (Deep Reactive Ion Etching) process is presented. It divides the plasma etching system into plasma layer, sheath layer and sample surface layer. At the same time, it combines quantum mechanics, sheath dynamics and diffusion theory together based on plasma environment to predict the probability distribution of etching particles so as to simulate the final etching results. The simulation results show very good coincidence with experimental images, proving the applicability of this theory and its promising to make black silicon formation in DRIE process to be controllable and repeatable.

The fabrication of PDMS-based functional surface mimicking the namib desert beetle back for collecting water vapor in the air

This paper presents novel functional surface designed for collecting water vapor, which is combined of PDMS and the micro level hydrophilic metal alloy ball. To imitate biological structure, the metallic balls are designed as hydrophilic part and PDMS substrate as hydrophobic structure. The ball is used as nucleation centers to absorb water vapor in the air to form droplet. Then, with the drop gradually growing up, it will fall off from the ball by gravity. The hydrophobic property of PDMS could promote tumbling of drop more smoothly without adhesion. This device is fabricated by micromachining process, where using PMMA as reverse mold and depositing fluorocarbon films on the PDMS to further enhance the hydrophobic property. The test results prove that this idea and water collection can be achieved obviously.

Surface analysis and process optimization of black silicon

This paper puts forward a description method for surface topography of black silicon using SF6/C4F8 in a cyclic etching-passivation DRIE process. Three main parameters, i.e. density, height and width, are defined and used to describe black silicon and can be extended to several other parameters, such as aspect ratio, duty ratio and so on. By means of these parameters we can also establish a standard modal to provide the very basic data for other kind of research. So a program is developed to achieve these parameters expediently and accurately. Then we discuss the influence of the process parameters to surface topography and finally obtain a group of optimum parameters to fabricate black silicon. Through these results we are expecting to get better cognition of black silicon and form more controllable surface structures for mass production of black silicon.