Jinguang Cai

High-performance all-solid-state flexible carbon/TiO2 micro-supercapacitors with photo-rechargeable capability

A high-performance all-solid-state flexible interdigitated carbon/TiO2 micro-supercapacitor (MSC) with photo-rechargeable capability was prepared by combining a laser direct writing technique with electrophoretic deposition of TiO2 nanoparticles. The carbon/TiO2 MSC shows the same excellent capacitive performance as the pure carbon MSC, such as high specific capacitance up to 27.3 mF cm−2 at a typical current density of 0.05 mA cm−2, excellent cycling stability, long-time stability, and mechanical stability. Under UV light irradiation, the carbon/TiO2 MSC can be charged to above 100 mV, and still maintain 60 mV after 10 photo-charging cycles, demonstrating its photo-rechargeable capability. Whats more, after 10 photo-charging cycles, the carbon/TiO2 MSC shows no capacitive performance degradation, which can be attributed to the high structural stability of the carbon/TiO2 MSC under UV light irradiation.

Facile Preparation of Hierarchical Structures Using Crystallization-Kinetics Driven Self-Assembly

Hierarchical structures (HSs) constructed by nanoparticle-based building blocks possess not only the properties of the primary building blocks but also collective properties of the assemblies. Here we report the facile preparation of hierarchical Ag nanoparticles/polyhedral oligomeric silsequioxane molecule (POSS) hybrid branched structures within tens of seconds by using spin-coating and doctor-blade methods. An assembly mechanism mainly controlled by POSS-crystallization kinetics and space resistance of Ag nanoparticles toward the diffusion of POSS molecules was tentatively proposed. It was demonstrated as a universal method for the preparation of hierarchical hybrid branched structures on arbitrary substrates, as well as by using other different POSS and inorganic nanoparticles. As a demonstration, Ag hierarchical structures obtained by heat treatment exhibit excellent SERS performance with enhancement factors as high as on the order of 10(7), making them promising sensors for the detection of trace amount of analyte adsorbed on the surface. Two-dimensional SERS mapping was also demonstrated by using a direct imaging system with high mapping speed and high resolution. Moreover, the substrates with Ag hierarchical structures were used as a SERS sensor for in situ detection due to the excellent SERS performance and stability of the structures.

A versatile platform of catechol-functionalized polysiloxanes for hybrid nanoassembly and in situ surface enhanced Raman scattering applications

Inspired by the marine mussel strategy of adhesion in aqueous environments, catechol-functionalized polysiloxane (CFPS) was synthesized. Facile dip-coating showed good film forming ability on various organic and inorganic substrates with a surface roughness of 4.6 nm (50 μm × 50 μm). Silver nanoparticles (AgNPs) are anchored onto CFPS-modified substrates using a dip coating process. The scanning electron microscopy images revealed that AgNPs were distributed homogeneously on numerous substrates. Moreover, the surface number density and average interspace of the AgNPs were tuned easily by controlling the concentration of AgNP dispersions. A substrate with high-density AgNPs exhibited excellent surface enhanced Raman scattering (SERS) performance with an enhancement factor as high as 7.89 × 107 and an ultra-low detection limitation of 10−10 M, which can be ascribed to the “hotspots” formed between the adjacent AgNPs controlled by CFPS-induced self-assembly. The AgNP structures prepared on different substrates modified using CFPS show a similar high intensity, suggesting a versatile platform of the CFPS film for AgNP assemblies. In addition, AgNPs were anchored to be extremely stable on substrates because of strong hydrogen bonding interactions provided by the high surface-density catechol units of CFPS, which made the substrate a promising SERS sensor for practical applications. In situ SERS detection was also demonstrated on apple peel with no damage to AgNP structures.

Laser direct writing of conductive micropatterns using copper nanoparticle ink toward 3D interconnection

The formation of conductive micropatterns via laser direct writing using metal nanoparticle ink was studied toward 3D interconnection. Copper (Cu) micropatterns were fabricated by laser irradiation on a precursor film prepared via spin-coating of a Cu nanoparticle ink on a substrate. A focused laser beam was scanned on the copper nanoparticle film using a xyz motion control stage. The solution etching of the film after laser scanning gave a Cu micropattern via removing unirradiated area. A copper wiring with a hollow structure was fabricated by layer-by-layer 3D printing, where the spin-coating of Cu nanoparticle ink and the laser direct writing were repeated alternatively.

Formation of copper micropatterns by laser direct writing using copper nanoparticle ink

The 2D and 3D laser direct writing using Cu nanoparticle ink were studied using a compact blue-violet semiconductor laser. The laser direct writing based on a motion controller and G-code language program on PC enabled to prepare various kinds of shaped Cu grids which can be easily designed on-demand. A Cu grid pattern was prepared on a flexible and transparent polymer substrate and applied to a stress sensor. A star-shaped grid was fabricated a polymer substrate and the performance as a stress sensor for detecting the motion of human hand devises was demonstrated toward wearable electronics. In the preliminary 3D study, we have employed the layer-by-layer formation of a 3D structure, where cycle of the spin-coating of a metal nanoparticle ink and the laser direct writing were repeated. The 3D microstructures prepared by the 3D laser direct writing using Ag and Cu nanoparticle inks suggested the possibility of a 3D interconnection.

Flexible carbon micro-supercapacitors prepared by direct cw-laser writing

Micro-/nano-scale power supply units with high energy and high power densities are critical components for the development of compact miniaturized portable electronic devices. Supercapacitors have attracted many research attentions due to their high power density, robust cycle performance, pollution-free operation, and maintenance-free features. Besides, the properties of small size, light weight, and flexibility are also required. On-chip microsupercapacitors (MSCs) have the potential acting as power supply units in portable devices, due to their simplified packaging processes and compatibility to the integrated circuits. However, the fabrication methods and materials should be cost-effective, scalable, and compatible to current electronic industry. Carbon materials own high specific surface areas, electrochemical stability, and high electrical conductivity, which are critical parameters for high-power supercapacitors. Moreover, the high mechanical tolerance makes them good candidates for flexible wearable devices. Therefore, MSCs based on carbon materials would satisfy the requirements of portable electronics. In this work, we demonstrated the fabrication of carbon MSCs by laser direct writing on commercial polyimide sheets in Ar with lowcost semiconductor cw-laser with a wavelength of 405nm. The obtained structures are macro-nanostructures comprising graphitized and amorphous carbon with relatively smooth surfaces and low resistance, in compared with the structures obtained by laser writing in air. As-prepared micro-supercapacitors show a high capacitance of about 14.9 mF/cm2 at a scanning rate of 10 mV/s, which is comparable to the reported highest capacitance of carbon-based supercapacitors fabricated by pulse-laser writing.

Laser direct writing of reduced graphene oxide micropatterns and sensor applications

Micropatterns consisting of reduced graphene oxide (rGO) and graphene oxide (GO) were fabricated via laser direct writing where an insulating GO was converted to a conductive rGO by laser-induced reduction. The rGO/GO microinterdigitated electrode showed humidity sensing behaviors. The influence of the shape and size of the rGO/GO microinterdigitated electrode was studied to discuss the sensing mechanism and to improve the sensitivity. Three kinds of rGO(w)/GO(g) micropatterns were prepared by laser direct writing on a GO-coated PET (polyethylene terephthalate) substrate using a CW 405 nm semiconductor laser, where w and g are the rGO electrode width and the GO gap width between rGO electrodes in micrometer unit, respectively. The humidity sensing properties of rGO(400)/GO(100), rGO(160)/GO(40), and rGO(80)/GO(20) were studied by monitoring the output voltage waveform from an electronic circuit consisting an rGO/GO interdigitated electrode and resistors in AC mode operation. The sensitivity enhancement induced by charging property of an rGO/GO interdigitated electrodes was observed accompanying transient decay of the output voltage. The shape and size of an rGO/GO interdigitated electrode remarkably influenced the humidity sensing behaviors depending on the contribution ratio of C and R parameters.

Laser Direct Writing and Selective Metallization of Metallic Circuits for Integrated Wireless Devices

Portable and wearable devices have attracted wide research attention due to their intimate relations with human daily life. As basic structures in the devices, the preparation of high-conductive metallic circuits or micro-circuits on flexible substrates should be facile, cost-effective, and easily integrated with other electronic units. In this work, high-conductive carbon/Ni composite structures were prepared by using a facile laser direct writing method, followed by an electroless Ni plating process, which exhibit a 3-order lower sheet resistance of less than 0.1 ohm/sq compared to original structures before plating, showing the potential for practical use. The carbon/Ni composite structures exhibited a certain flexibility and excellent anti-scratch property due to the tight deposition of Ni layers on carbon surfaces. On the basis of this approach, a wireless charging and storage device on a polyimide film was demonstrated by integrating an outer rectangle carbon/Ni composite coil for harvesting electromagnetic waves and an inner carbon micro-supercapacitor for energy storage, which can be fast charged wirelessly by a commercial wireless charger. Furthermore, a near-field communication (NFC) tag was prepared by combining a carbon/Ni composite coil for harvesting signals and a commercial IC chip for data storage, which can be used as an NFC tag for practical application.

Selective metallization based on laser direct writing and additive metallization process

The selective metallization on a flexible polymer film via laser direct writing and the following additive metallization process was studied as an alternate to conventional semi-additive process in the fabrication of printed circuit board. A Cu micropattern was fabricated on a polyimide film via CW blue-violet laser direct writing using a Cu nanoparticle ink and applied to a seed layer for the Cu electroplating. The on-demand processing of a Cu micropattern whose line width and thickness are ca. 5 and 2 μm, respectively, was achieved by combination of a laser-written seed micropattern and the following electro-plating. The homogeneity of the Cu micropatterns prepared from Cu nanoparticles was easily improved by combination with the following Cu plating.

Laser direct writing micro-supercapacitors from graphene oxide films

This study reports the laser direct writing of graphene oxide (GO) to form reduced graphene oxide (RGO)-GO-RGO interdigitated on-chip micro-supercapacitors (MSCs) by reducing GO to RGO. The resolution of the laser writing lines can be lowered to 10 μm, which is much lower than that formed by the CO2 pulse laser, suggesting the potential to fabricate much smaller MSCs in 10 μm scale. The micro-supercapacitor employed GO itself as the humidity-sensitive electrolyte with no need of other electrolytes. The typical device shows a high capacitance of 12.5 mF/cm2 at the scan rate of 10 mV/s at the humidity of 90%, which is much higher than the reported value obtained by the pulsed CO2 laser, even the micro-supercapacitors with electrolytes.