Bangdao Chen

Reversible Bending Behaviors of Photomechanical Soft Actuators Based on Graphene Nanocomposites.

Photomechanical nanocomposites embedded with light-absorbing nanoparticles show promising applications in photoresponsive actuations. Near infrared (nIR)-responsive nanocomposites based photomechanical soft actuators can offer lightweight functional and underexploited entry into soft robotics, active optics, drug delivery, etc. A novel graphene-based photomechanical soft actuators, constituted by Polydimethylsiloxane (PDMS)/graphene-nanoplatelets (GNPs) layer (PDMS/GNPs) and pristine PDMS layer, have been constructed. Due to the mismatch of coefficient of thermal expansion of two layers induced by dispersion of GNPs, controllable and reversible bendings response to nIR light irradiation are observed. Interestingly, two different bending behaviors are observed when the nIR light comes from different sides, i.e., a gradual single-step photomechanical bending towards PDMS/GNPs layer when irradiation from PDMS side, while a dual-step bending (finally bending to the PDMS/GNPs side but with an strong and fast backlash at the time of light is on/off) when irradiation from PDMS/GNPs side. The two distinctive photomechanical bending behaviors are investigated in terms of heat transfer and thermal expansion, which reveals that the distinctive bending behaviors can be attributed to the differences in temperature gradients along the thickness when irradiation from different sides. In addition, the versatile photomechanical bending properties will provide alternative way for drug-delivery, soft robotics and microswitches, etc.

A metal/insulator/metal field-emission cannon.

A barrel-shaped metal/insulator/metal (MIM) field-emission cathode, also referred to as a field-emission cannon, is constructed using conventional SU-8 UV lithography combined with sputtering and lift-off processes. An array of these field-emission cannons has demonstrated uniform field emission in a luminescent pixel array. The field-emission test proves that the unique geometry of the field-emission cannon significantly improves field-emission efficiency and electron beam focus. Detailed data analysis has revealed that both conventional sharp edge field emission and MIM field emission contribute to the total emission current. The field emission starts from an edge emission at gate voltages (Vg) below 8 V. When Vg increases above 8 V, electrons tunnel into the cannon through the thin SiO2 layer and inner metal layer (i.e., the gate electrode). Thus, the MIM field emission starts to dominate.

Bio-inspired directional high-aspect-ratio nanopillars: fabrication and actuation

The Dynamic nature and responsive behaviour are the most attractive features of biological structures, and comprise the goals for next-generation smart materials. The nanostructured arrays provide unique topographic patterns that confer wetting, optical, and many other functions, but their actuation at the sub-micrometer scale is still a challenging goal. In this paper, we provide a simple route to fabricate ordered arrays of slender nanopillars with submicron diameters (400–500 nm) and high aspect ratios (20–40), with controllable slanted angles (60–90°). Experiments reveal that the fabricated slender nanopillars are flexible so that their orientation can be dynamically manipulated in response to an external electric field, while the stiffness can prevent ground or lateral collapse. The high aspect ratio nanopillars with orientation tunability can find applications in the development of smart materials, gecko-inspired reversible adhesion, etc.

Ultrasound-assisted recovery of free-standing high-aspect-ratio micropillars

High-aspect-ratio polymer micropillar arrays are widely employed in microfluidics and microdevices. The collapse of polymer micropillars, however, would induce device degradation, which calls for a recovery method for the collapsed micropillars to restore their performances. In this communication, we propose a cost-effective and robust approach for recovery of free-standing high-aspect-ratio micropillars by ultrasonic-assisted technology. The collapsed micropillar array immersed in a low-surface-energy solution will recover its upright state by ultrasonic stimulation and keep standing steadily due to the low-surface-energy treatment. The collapsed micropillars treated by the proposed approach are entirely able to spring back to their original upright position.

Enhanced photovoltaic performance of dye-sensitized solar cells with TiO2 micro/nano-structures as light scattering layer

Double layered TiO2 micro/nano-structured photo-anodes have been constructed for dye-sensitized solar cells (DSSCs). Mesoporous TiO2 nanoparticles serve as under layer to improve the dye absorption and TiO2 microflowers or nanorod aggregates serve as cover layer to provide prominent light scattering effect as well as electron pathways. The as-prepared architecture was characterized with field emission scanning electron microscopy. The TiO2 microflower scattering layer enhanced the photocurrent of DSSCs due to the increased light absorption by the strong light scattering effect, and reduced electron transfer resistance via the direct electron pathways. Enhanced light scattering effect was observed from TiO2 microflower based cell in the whole visible light range through the UV–Vis and IPCE measurements. Reduced electron transfer resistance was validated by electrochemical impedance test. The contrast experiments between the TiO2 microflowers and TiO2 nanorod aggregates further demonstrated that such open structured TiO2 microflowers are more effective to improve the performance of DSSCs. It is expected that the photo-anode design with TiO2 microflowers as scattering layer will be an alternative approach to improve the performance of DSSCs.

Bio-inspired eyes with eyeball-shaped lenses actuated by electro-hydrodynamic forces

Inspired by vertebrate eyes, electro-hydrodynamic forces functioning as the ciliary muscle of bio-inspired eyes are extremely appealing in micro-optical devices. Eyeball-shaped lenses, composed of a liquid-core-cladding microlens array (LCC-MLA) is firstly utilized to fabricate a bio-inspired eye array through electro-hydrodynamic actuation. In this work, when the applied voltage increases, the microlens shape evolves from spherical crown to LCC-MLA shape (prolate egg). When the applied voltage is removed, the microlens shape changes from prolate egg to sphere. At a result, the electro-hydrodynamic force difference upon the lens interface leads to the adjustment of lens curvature. In addition, bio-inspired eyes manifest reversible 6-fold zoom and a fast responding time (∼50 ms). In contrast with a traditional tunable lens, the LCC-MLA is closer to a biological shape with wide vari-focal ability by electro-hydrodynamic actuation. Herein, these excellent properties make LCC-MLA promising for optics-based imaging sensors.

Improve the transconductance of a graphene field-effect transistor by folding graphene into a wedge

The transport property of a graphene wedge channel is studied theoretically and its leakage current through field emission is estimated when considering the effect of the internal electric field. The transconductance of the graphene transistor is improved from 0.016 to 0.321 μS μm−1 when the graphene is folded into a wedge (with angle of wedge π/6 and radius curvature 2.7 nm at the tip), while the wedge height is much smaller than the space between the top-gate and the channel. The improved transconductance is due to the locally enhanced electric field, which results in a potential well and causes electron accumulation at the wedge tip. The leakage current through field emission J FE shows a super-linear increase with the channel conductive current J DS, where overall the electron supply for the field emission at the wedge tip is improved by the channel bias voltage V DS.

Multiple harmonics suppression for optical encoders based on generalized grating imaging

Abstract In this work, we perform an investigation on the multiple harmonics suppression for optical encoders based on generalized grating imaging. We firstly analyse the formation of the harmonic distortion of the encoder signals and evaluate the interpolation errors caused by the higher harmonic signals. The result shows that the harmonic distortion of the encoder signals depends mainly on the higher harmonic components in the interference fringe. In addition, it shows that the higher harmonic signals influence the Lissajous figure of the encoder signals significantly and introduce a relatively large interpolation error. Then, conditions for eliminating the higher harmonic signals are studied, and optical filtering methods using specially designed index grating are proposed. We explain the filtering principle in detail and present three forms of index grating for multiple harmonics suppression. In particular, we show the patterns of the index grating for eliminating the dominant third and fifth harmonics, corroborating the results with numerical simulations. The results show that the amplitudes of the third and fifth harmonics are equal to zero theoretically, such that approximately ideal sinusoidal signals are obtained. Since the harmonic signals are considerably suppressed, the proposed methods will be useful for high-accuracy interpolation of encoder signals.

Calibration of non-contact incremental linear encoders using a macro–micro dual-drive high-precision comparator

The accuracy of a linear encoder is determined by encoder-specific errors, which consist of both long-range and cyclic errors. Generally, it is difficult to measure the two errors of a non-contact incremental linear encoder with a large measuring range and small signal period in one measurement because of the contradiction between long travel range and high resolution. To resolve this issue, a prototype high-precision interferometric comparator with a macro–micro dual-drive system is presented. The measurement and motion resolution of the comparator are 1 nm and 3 nm, respectively. A measuring range of 320 mm is realized and the theoretical maximum range of the comparator is 2 m. The comparator mainly includes a high-accuracy aerostatic linear-motion stage, a constant displacement ratio piezoelectric-driven stage, two laser interferometers, a 6-DOF grating pair position adjustment devices and a PC-based data processor. The measurable linear movement is afforded, respectively, by the long-stroke stage and the piezoelectric-driven stage for the long-range error and cyclic error measurement. The movement can be measured by the encoder and then be calibrated by the corresponding laser interferometer. In the experiment, the accuracy of a non-contact incremental linear encoder with a 20 μm-long signal period and 320 mm measuring range proposed by our team was calibrated after proper mounting. The long-range error is measured to be 3.123 μm, and the cyclic error is within ±0.159 μm, which matches well with the theoretical estimation given by ±0.145 μm. The measurement uncertainties are estimated and the results confirm the effectiveness and feasibility of the proposed scheme and instruments.

Transverse sensitivity suppression using multi-axis surface encoder with parasitic error compensation

Transverse sensitivity that is mainly resulted from parasitic error motions can introduce undesired motion components and remarkably lower the manipulation qualities of most inertial sensors. This problem becomes even more apparent for multi-axial sensors as additional demands for multi-degree-of-freedom detection become higher. In this letter, a method to minify the transverse sensitivity of an inertial sensor by multi-degree-of-freedom optical sensing and measurement has been reported and tested. A multi-axis-surface-encoder-based biaxial optical accelerometer is fabricated for scheme validation. The surface encoder adopts multi-reading-unit arrangement, and it can not only detect small changes in displacement to calculate the applied acceleration along X- and Y-axes but also quantify the parasitic error motion caused by Z-twist. A suitable compensation strategy is also developed to reveal the concerned outputs without parasitic errors. Experimental results show that the configuration combined with the ...