Electrochemical Properties and Applications of Nanocrystalline, Microcrystalline, and Epitaxial Cubic Silicon Carbide Films

Microstructures of the materials (e.g., crystallinitiy, defects, and composition, etc.) determine their properties, which eventually lead to their diverse applications. In this contribution, the properties, especially the electrochemical properties, of cubic silicon carbide (3C-SiC) films have been engineered by controlling their microstructures. By manipulating the deposition conditions, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are obtained with varied properties. The epitaxial 3C-SiC film presents the lowest double-layer capacitance and the highest reversibility of redox probes, because of its perfect (001) orientation and high phase purity. The highest double-layer capacitance and the lowest reversibility of redox probes have been realized on the nanocrystalline 3C-SiC film. Those are ascribed to its high amount of grain boundaries, amorphous phases and large diversity in its crystal size. Based on their diverse properties, the electrochemical performances of 3C-SiC films are evaluated in two kinds of potential applications, namely an electrochemical capacitor using a nanocrystalline film and an electrochemical dopamine sensor using the epitaxial 3C-SiC film. The nanocrystalline 3C-SiC film shows not only a high double layer capacitance (43–70 μF/cm²) but also a long-term stability of its capacitance. The epitaxial 3C-SiC film shows a low detection limit toward dopamine, which is one to 2 orders of magnitude lower than its normal concentration in tissue. Therefore, 3C-SiC film is a novel but designable material for different emerging electrochemical applications such as energy storage, biomedical/chemical sensors, environmental pollutant detectors, and so on

Breaking Nano-Spaghetti: Bending and Fracture Tests of Nanofibers

Nanofibers composed of silica nanoparticles, used as structural building blocks, and polystyrene nanoparticles introduced as sacrificial material are fabricated by bicolloidal electrospinning. During fiber calcination, sacrificial particles are combusted leaving voids with controlled average sizes. The mechanical properties of the sintered silica fibers with voids are investigated by suspending the nanofiber over a gap and performing three-point bending experiments with atomic force microscopy. We investigate three different cases: fibers without voids and with 60 or 260 nm voids. For each case, we study how the introduction of the voids can be used to control the mechanical stiffness and fracture properties of the fibers. Fibers with no voids break in their majority at a single fracture point (70% of cases), segmenting the fiber into two pieces, while the remaining cases (30%) fracture at multiple points, leaving a gap in the suspended fiber. On the other hand, fibers with 60 nm voids fracture in only 25% of the cases at a single point, breaking predominantly at multiple points (75%). Finally, fibers with 260 nm voids fracture roughly in equal proportions leaving two and multiple pieces (46% vs 54%, respectively). The present study is a prerequisite for processes involving the controlled sectioning of nanofibers to yield anisometric particles

Controlling the Structure of Supraballs by pH-Responsive Particle Assembly

Supraballs of various sizes and compositions can be fabricated via drying of drops of aqueous colloidal dispersions on super-liquid-repellent surfaces with no chemical waste and energy consumption. A “supraball” is a particle composed of colloids. Many properties, such as mechanical strength and porosity, are determined by the ordering of a colloidal assembly. To tune such properties, a colloidal assembly needs to be controlled when supraballs are formed during drying. Here, we introduce a method to control a colloidal assembly of supraballs by adjusting the dispersity of the colloids. Supraballs are fabricated on superamphiphobic surfaces from colloidal aqueous dispersions of polystyrene microparticles carrying pH-responsive poly­[2-(diethylamino)­ethyl methacrylate]. Drying of dispersion drops at pH 3 on superamphiphobic surfaces leads to the formation of spherical supraballs with densely packed colloids. The pH 10 supraballs are more oblate and consist of more disordered colloids than the pH 3 supraballs, caused by particle aggregates with random sizes and shapes in the pH 10 dispersion. Thus, the shape, crystallinity, porosity, and mechanical properties could be controlled by pH, which allows broader uses of supraballs

Controlling the Structure of Supraballs by pH-Responsive Particle Assembly

Supraballs of various sizes and compositions can be fabricated via drying of drops of aqueous colloidal dispersions on super-liquid-repellent surfaces with no chemical waste and energy consumption. A “supraball” is a particle composed of colloids. Many properties, such as mechanical strength and porosity, are determined by the ordering of a colloidal assembly. To tune such properties, a colloidal assembly needs to be controlled when supraballs are formed during drying. Here, we introduce a method to control a colloidal assembly of supraballs by adjusting the dispersity of the colloids. Supraballs are fabricated on superamphiphobic surfaces from colloidal aqueous dispersions of polystyrene microparticles carrying pH-responsive poly­[2-(diethylamino)­ethyl methacrylate]. Drying of dispersion drops at pH 3 on superamphiphobic surfaces leads to the formation of spherical supraballs with densely packed colloids. The pH 10 supraballs are more oblate and consist of more disordered colloids than the pH 3 supraballs, caused by particle aggregates with random sizes and shapes in the pH 10 dispersion. Thus, the shape, crystallinity, porosity, and mechanical properties could be controlled by pH, which allows broader uses of supraballs