Laser diodes are efficient light sources. However, state-of-the-art laser diode-based lighting systems rely on light-converting inorganic phosphor materials, which strongly limit the efficiency and lifetime, as well as achievable light output due to energy losses, saturation, thermal degradation, and low irradiance levels. Here, we demonstrate a macroscopically expanded, three-dimensional diffuser composed of interconnected hollow hexagonal boron nitride microtubes with nanoscopic wall-thickness, acting as an artificial solid fog, capable of withstanding~10 times the irradiance level of remote phosphors. In contrast to phosphors, no light conversion is required as the diffuser relies solely on strong broadband (full visible range) lossless multiple light scattering events, enabled by a highly porous (>99.99%) nonabsorbing nanoarchitecture, resulting in efficiencies of~98%. This can unleash the potential of lasers for high-brightness lighting applications, such as automotive headlights, projection technology or lighting for large spaces.
Carbon-based
fibrous scaffolds are highly attractive for all biomaterial
applications that require electrical conductivity. It is additionally
advantageous if such materials resembled the structural and biochemical
features of the natural extracellular environment. Here, we show a
novel modular design strategy to engineer biomimetic carbon fiber-based
scaffolds. Highly porous ceramic zinc oxide (ZnO) microstructures
serve as three-dimensional (3D) sacrificial templates and are infiltrated
with carbon nanotubes (CNTs) or graphene dispersions. Once the CNTs
and graphene coat the ZnO template, the ZnO is either removed by hydrolysis
or converted into carbon by chemical vapor deposition. The resulting
3D carbon scaffolds are both hierarchically ordered and free-standing.
The properties of the microfibrous scaffolds were tailored with a
high porosity (up to 93%), a high Young’s modulus (ca. 0.027–22
MPa), and an electrical conductivity of ca. 0.1–330 S/m, as
well as different surface compositions. Cell viability, fibroblast
proliferation rate and protein adsorption rate assays have shown that
the generated scaffolds are biocompatible and have a high protein
adsorption capacity (up to 77.32 ± 6.95 mg/cm3) so
that they are able to resemble the extracellular matrix not only structurally
but also biochemically. The scaffolds also allow for the successful
growth and adhesion of fibroblast cells, showing that we provide a
novel, highly scalable modular design strategy to generate biocompatible
carbon fiber systems that mimic the extracellular matrix with the
additional feature of conductivity.
In this work, individual hollow and mesoporous graphitic microtubes were integrated into electronic devices using a FIB/SEM system and were investigated as gas and vapor sensors by applying different bias voltages (in the range of 10 mV–1 V). By increasing the bias voltage, a slight current enhancement is observed, which is mainly attributed to the self-heating effect. A different behavior of ammonia NH3 vapor sensing by increasing the applied bias voltage for hollow and mesoporous microtubes with diameters down to 300 nm is reported. In the case of the hollow microtube, an increase in the response was observed, while a reverse effect has been noticed for the mesoporous microtube. It might be explained on the basis of the higher specific surface area (SSA) of the mesoporous microtube compared to the hollow one. Thus, at room temperature when the surface chemical reaction rate (k) prevails on the gas diffusion rate (DK) the structures with a larger SSA possess a higher response. By increasing the bias voltage, i.e., the overall temperature of the structure, DK becomes a limiting step in the gas response. Therefore, at higher bias voltages the larger pores will facilitate an enhanced gas diffusion, i.e., a higher gas response. The present study demonstrates the importance of the material porosity towards gas sensing applications.
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