Epitaxial Cubic Silicon Carbide Photocathodes for Visible-Light-Driven Water Splitting

Cubic silicon carbide (3C-SiC) material feature a suitable bandgap and high resistance to photocorrosion. Thus, it has been emerged as a promising semiconductor for hydrogen evolution. Here, the relationship between the photoelectrochemical properties and the microstructures of different SiC materials is demonstrated. For visible-light-derived water splitting to hydrogen production, nanocrystalline, microcrystalline and epitaxial (001) 3C-SiC films are applied as the photocathodes. The epitaxial 3C-SiC film presents the highest photoelectrochemical activity for hydrogen evolution, because of its perfect (001) orientation, high phase purity, low resistance, and negative conduction band energy level. This finding offers a strategy to design SiC-based photocathodes with superior photoelectrochemical performances.

High-Q suspended optical resonators in 3C silicon carbide obtained by thermal annealing

We fabricate suspended single-mode optical waveguides and ring resonators in 3C silicon carbide (SiC) that operate at telecommunication wavelength, and leverage post-fabrication thermal annealing to minimize optical propagation losses. Annealed optical resonators yield quality factors of over 41,000, which corresponds to a propagation loss of 7 dB/cm, and is a significant improvement over the 24 dB/cm in the case of the non-annealed chip. This improvement is attributed to the enhancement of SiC crystallinity and a significant reduction of waveguide surface roughness, from 2.4 nm to below 1.7 nm. The latter is attributed to surface layer oxide growth during the annealing step. We confirm that the thermo-optic coefficient, an important parameter governing high-power and temperature-dependent performance of SiC, does not vary with annealing and is comparable to that of bulk SiC. Our annealing-based approach, which is especially suitable for suspended structures, offers a straightforward way to realize high-performance 3C-SiC integrated circuits.

3D 3C-SiC/Graphene Hybrid Nanolaminate Films for High-Performance Supercapacitors

High-performance supercapacitors feature big and stable capacitances and high power and energy densities. To fabricate high-performance supercapacitors, 3D 3C-SiC/graphene hybrid nanolaminate films are grown via a microwave plasma-assisted chemical vapor deposition technique. Such films consist of 3D alternating structures of vertically aligned 3C-SiC and graphene layers, leading to high surface areas and excellent conductivity. They are further applied as the capacitor electrodes to construct electrical double layer capacitors (EDLCs) and pseudocapacitors (PCs) in both aqueous and organic solutions. The capacitance for an EDLC in aqueous solutions is up to 549.9 µF cm^-2 , more than 100 times higher than that of an epitaxial 3C-SiC film. In organic solutions, it is 297.3 µF cm^-2 . The pseudocapacitance in redox-active species (0.05 Fe(CN)₆ ^3-/4- ) contained aqueous solutions is as high as 62.2 mF cm^-2 . The capacitance remains at 98% of the initial value after 2500 charging/discharging cycles, indicating excellent cyclic stability. In redox-active species (0.01 m ferrocene) contained organic solutions, it is 16.6 mF cm^-2 . Energy and power densities of a PC in aqueous solution are 11.6 W h kg^-1 and 5.1 kW kg^-1 , respectively. These vertically aligned 3C-SiC/graphene hybrid nanolaminate films are thus promising electrode materials for energy storage applications.

Piezoresistive effect of p-type single crystalline 3C–SiC on (111) plane

This paper presents for the first time the effect of strain on the electrical conductivity of p-type single crystalline 3C–SiC grown on a Si (111) substrate.

Graphene/3C-SiC Hybrid Nanolaminate

In this work, we demonstrate a one-step approach to create graphene/3C-SiC nanolaminate structure using microwave plasma chemical vapor deposition technique. Layer-by-layer arrangement of thin 3C-SiC layers and graphene sheets is obtained with the thicknesses of the individual 3C-SiC layers and graphene sheets being 5-10 nm and 2-5 nm, respectively. An intimate contact between 3C-SiC and the graphene sheets is achieved and the nanolaminate film shows a high room temperature conductivity of 96.1 S/cm. A dedicated structural analysis of the nanolaminates by means of high-resolution transmission electron microscopy (HRTEM) reveals that the growth of the nanolaminates follows an iterative process: preferential graphene nucleation around the planar defects at the central region of the SiC layer, leading to the "splitting" of the SiC layer; and the thickening of the SiC layer after being "split". A growth mechanism based on both kinetics and thermodynamics is proposed. Following the proposed mechanism, it is possible to control the layer thickness of the graphene/3C-SiC hybrid nanolaminate by manipulating the carbon concentration in the gas phase, which is further experimentally verified. The high electrical conductivity, large surface area porous structure, feasible integration on different substrates (metal, Mo; semiconductor, Si and 2H-SiC; insulator, diamond) of the graphene/3C-SiC hybrid nanolaminate as well as other unprecedented advantages of the nanolaminate structure make it very promising for applications in mechanical, energy, and sensor-related areas.

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/cm(2)) 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.