Flexible NiO–Graphene–Carbon Fiber Mats Containing Multifunctional Graphene for High Stability and High Specific Capacity Lithium-Ion Storage

An electrode’s conductivity, ion diffusion rate, and flexibility are critical factors in determining its performance in a lithium-ion battery. In this study, NiO–carbon fibers were modified with multifunctional graphene sheets, resulting in flexible mats. These mats displayed high conductivities, and the transformation of active NiO to inert Ni⁰ was effectively prevented at relatively low annealing temperatures in the presence of graphene. The mats were also highly flexible and contained large gaps for the rapid diffusion of ions, because of the addition of graphene sheets. The flexible NiO–graphene–carbon fiber mats achieved a reversible capacity of 750 mA h/g after 350 cycles at a current density of 500 mA/g as the binder-free anodes of lithium-ion batteries. The mats’ rate capacities were also higher than those of either the NiO–carbon fibers or the graphene–carbon fibers. This work should provide a new route toward improving the mechanical properties, conductivities, and stabilities of mats using multifunctional graphene

Enhancing Optical Confinement of InGaN Thin-Film Microdisk Lasers with Hybrid Omnidirectional Reflectors

The conventional GaN microdisk laser adopts an undercut structure for the optical confinement, which provides poor overlap between the whispering gallery modes and the multiquantum well gain region. The thin-film microdisk structure was proposed to overcome this shortcoming, but the absorptive nature of the metallic bonding layer with mirror compromises optical confinement. In this work, an SiO2/TiO2 distributed Bragg reflector is integrated with the metallic mirror to form an omnidirectional reflector that provides high optical reflectance across a wide range of incidence angles to promote optical confinement in the microdisk. Optical-pumped lasing with an average lasing threshold power density of 46.5 W/cm2 and Q factors of 18200 (near threshold) is achieved. The narrowest lasing line width of ∼0.02 nm is obtained at the average excitation power density of 48.02 W/cm2, representing a major advancement in the GaN microdisk laser technology