Guang Yao

Simultaneously Harvesting Thermal and Mechanical Energies based on Flexible Hybrid Nanogenerator for Self-Powered Cathodic Protection.

Metal corrosion occurs anytime and anywhere in nature and the corrosion prevention has a great significance everywhere in national economic development and daily life. Here, we demonstrate a flexible hybrid nanogenerator (NG) that is capable of simultaneously or individually harvesting ambient thermal and mechanical energies and used for a self-powered cathodic protection (CP) system without using an external power source. Because of its double peculiarities of both pyroelectric and piezoelectric properties, a polarized poly(vinylidene fluoride) (PVDF) film-based NG was constructed to scavenge both thermal and mechanical energies. As a supplementary, a triboelectric NG was constructed below the pyro/piezoelectric NG to grab ambient mechanical energy. The output power of the fabricated hybrid NG can be directly used to protect the metal surface from the chemical corrosion. Our results not only verify the feasibility of self-powered CP-based NGs, but also expand potential self-powered applications.

Reducing dielectric loss in CaCu3Ti4O12 thin films by high-pressure oxygen annealing

The nature of dielectric loss in high dielectric constant CaCu3Ti4O12 (CCTO) thin films was systematically studied by characterizing the films grown in high-pressure oxygen annealing processes. The films were grown on (001) LaAlO3 substrates by a polymer assisted deposition (PAD) technique while the annealing processes were performed in various high oxygen pressure environments. Microstructural characterizations by X-ray diffraction and atomic force microscopy indicated that the phase and morphologies of the films were strongly impacted by the annealing oxygen pressures. It was found that the high oxygen pressure annealing can significantly reduce the dielectric loss, which may be attributed to the TiO2 phase separation in CCTO, good quality of thin films grown by the PAD technique and fewer oxygen vacancies. The optimized room temperature low dielectric loss tangent of 0.002 at 10–100 kHz was achieved in the samples annealed with high pressure O2 of about 5 atm, which is more than one order of magnitude lower than that from the normal pressure annealed samples.

Chemical and mechanical strains tuned dielectric properties in Zr-doped CaCu3Ti4O12 highly epitaxial thin films

The nature of strain tuned dielectric properties in CaCu3Ti4O12 (CCTO) films was systematically studied with chemical strain (various doping rates) and physical strain (different oxygen pressure treatments). Microstructural characterization revealed that the lattice parameters of the highly epitaxial CCTO thin films are strongly dependent upon both Zr doping rates and annealing oxygen pressures. Dielectric property measurements indicate that the dielectric loss can be tuned by optimizing the doping rate and annealing oxygen pressure. These findings indicate that the dielectric properties of CCTO can be manipulated by the in-plane strain achieved from either chemical or physical treatment.

Highly stretchable and shape-controllable three-dimensional antenna fabricated by “Cut-Transfer-Release” method

Recent progresses on the Kirigami-inspired method provide a new idea to assemble three-dimensional (3D) functional structures with conventional materials by releasing the prestrained elastomeric substrates. In this paper, highly stretchable serpentine-like antenna is fabricated by a simple and quick “Cut-Transfer-Release” method for assembling stretchable 3D functional structures on an elastomeric substrate with a controlled shape. The mechanical reliability of the serpentine-like 3D stretchable antenna is evaluated by the finite element method and experiments. The antenna shows consistent radio frequency performance with center frequency at 5.6 GHz during stretching up to 200%. The 3D structure is also able to eliminate the hand effect observed commonly in the conventional antenna. This work is expected to spur the applications of novel 3D structures in the stretchable electronics.

Thermal Release Transfer Printing for Stretchable Conformal Bioelectronics

Abstract Soft neural electrode arrays that are mechanically matched between neural tissues and electrodes offer valuable opportunities for the development of disease diagnose and brain computer interface systems. Here, a thermal release transfer printing method for fabrication of stretchable bioelectronics, such as soft neural electrode arrays, is presented. Due to the large, switchable and irreversible change in adhesion strength of thermal release tape, a low‐cost, easy‐to‐operate, and temperature‐controlled transfer printing process can be achieved. The mechanism of this method is analyzed by experiments and fracture‐mechanics models. Using the thermal release transfer printing method, a stretchable neural electrode array is fabricated by a sacrificial‐layer‐free process. The ability of the as‐fabricated electrode array to conform different curvilinear surfaces is confirmed by experimental and theoretical studies. High‐quality electrocorticography signals of anesthetized rat are collected with the as‐fabricated electrode array, which proves good conformal interface between the electrodes and dura mater. The application of the as‐fabricated electrode array on detecting the steady‐state visual evoked potentials research is also demonstrated by in vivo experiments and the results are compared with those detected by stainless‐steel screw electrodes.

Ultrafast response flexible breath sensor based on vanadium dioxide

Real-time monitoring of breath can provide clinically relevant information about apnea syndrome and other important aspects of human physiology. Here, we introduce a flexible skin-like breath sensor developed by transfer-printing vanadium dioxide (VO2) thin films on PDMS substrates. This flexible breath sensor can conformably laminate on the skin under the nose with different curvatures and operate at different environment temperatures through day and night. Attributed to the high temperature coefficient of resistance of VO2, the enhanced breath sensing performance was demonstrated and the response time and recovery time can be as fast as 0.5 s. The excellent sensing performance and fast response time indicate that the VO2-based breath sensor is feasible in monitoring breath for prevention of apnea syndrome.

A Ferroelectric Ceramic/Polymer Composite‐Based Capacitive Electrode Array for In Vivo Recordings

A new implantable capacitive electrode array for electrocorticography signal recording is developed with ferroelectric ceramic/polymer composite. This ultrathin and electrically safe capacitive electrode array is capable of attaching to the biological tissue conformably. The barium titanate/polyimide (BaTiO3 /PI) nanocomposite with high dielectric constant is successfully synthesized and employed as the ultrathin dielectric layer of the capacitive BaTiO3 /PI electrode array. The performance of the capacitive BaTiO3 /PI electrode array is evaluated by electrical characterization and 3D finite-element modeling. In vivo, neural experiments on the visual cortex of rats show the reliability of the capacitive BaTiO3 /PI electrode array. This work shows the potentials of capacitive BaTiO3 /PI electrode array in the field of brain/computer interfaces.

Surface step terrace tuned microstructures and dielectric properties of highly epitaxial CaCu3Ti4O12 thin films on vicinal LaAlO3 substrates.

Controllable interfacial strain can manipulate the physical properties of epitaxial films and help understand the physical nature of the correlation between the properties and the atomic microstructures. By using a proper design of vicinal single-crystal substrate, the interface strain in epitaxial thin films can be well controlled by adjusting the miscut angle via a surface-step-terrace matching growth mode. Here, we demonstrate that LaAlO3 (LAO) substrates with various miscut angles of 1.0°, 2.75°, and 5.0° were used to tune the dielectric properties of epitaxial CaCu3Ti4O12 (CCTO) thin films. A model of coexistent compressive and tensile strained domains is proposed to understand the epitaxial nature. Our findings on the self-tuning of the compressive and tensile strained domain ratio along the interface depending on the miscut angle and the stress relaxation mechanism under this growth mode will open a new avenue to achieve CCTO films with high dielectric constant and low dielectric loss, which is critical for the design and integration of advanced heterostructures for high performance capacitance device applications.

Ultrasensitive Flexible Temperature-Mechanical Dual-Parameter Sensor Based on Vanadium Dioxide Films

Flexible temperature and mechanical sensing capabilities are of great importance in the artificial intelligence. Here, we report a skin conformable, high sensitive temperature-mechanical dual-parameter sensor based on a PET/vanadium dioxide (VO2)/PDMS multilayer structure fabricated using the transfer printing technique. The ultrahigh mechanical sensitivity to strains in the range of 0%–0.1% with a gauge factor over 400 was attributed to the disconnection-reconnection process of the ziplike nanoscale cracks under strain or vibration. And the enhanced temperature sensing performance with a resolution of 0.1 K was attributed to the high temperature coefficient of resistance of VO2 material. The temperature and the mechanical signals simultaneously recorded in the electrical resistance signal were separated via fast Fourier transform (FFT) and inverse FFT. The flexibility and ultra-sensitivity to temperature and vibration make the sensor a promising application in advanced artificial intelligence.

Tuning the strain and physical properties of highly epitaxial CaCu 3 Ti 4 O 12 thin films on vicinal substrates

Epitaxial thin films of perovskite-like structural CaCu3Ti4O12 (CCTO) were grown on vicinal (001) single-crystal LaAlCb (LAO) substrates to investigate the evolution of micro structure and dielectric properties of the films with the mismatch strain induced by surface step terrace. The different surface terrace width of the substrates produced by various miscut angles of 1.0°, 2.5°, and 5.0° along [110] direction successfully tuned the lattice structure, which were confirmed by X-ray diffraction. A model is proposed that the substrate step terrace dimensions on each vicinal LAO substrate can be tuned by miscutting angles, which introduces compressive and tensile strained domains of the CCTO film and further affect the dielectric properties. Based on this growth mode, we can achieve high dielectric constant and reduce the dielectric loss by a proper design of the miscutting angles.