Terahertz instrumentation has improved significantly in recent years such that THz imaging systems have become more affordable and easier to use. THz systems can now be operated by non-THz experts greatly facilitating research into many potential applications. Due to the non-ionising nature of THz light and its high sensitivity to soft tissues, there is an increasing interest in biomedical applications including both in vivo and ex vivo studies. Additionally, research continues into understanding the origin of contrast and how to interpret terahertz biomedical images. This short review highlights some of the recent work in these areas and suggests some future research directions.
The realization of high-performance tunable absorbers for terahertz frequencies is crucial for advancing applications such as single-pixel imaging and spectroscopy. Based on the strong position sensitivity of metamaterials' electromagnetic response, we combine meta-atoms that support strongly localized modes with suspended flat membranes that can be driven electrostatically. This design maximizes the tunability range for small mechanical displacements of the membranes. We employ a micro-electromechanical system technology and successfully fabricate the devices. Our prototype devices are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness (~1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and fast switching speed (~27 μs). The absorption is tuned by an applied voltage, with the most marked results achieved when the structure reaches the snap-down state. In this case, the resonance shifts by 4200% of the linewidth (14% of the initial resonance frequency), and the absolute absorption modulation measured at the initial resonance can reach 65%. The demonstrated approach can be further optimized and extended to benefit numerous applications in THz technology.
Layer-structured
black phosphorus (BP) demonstrating high specific
capacity has been viewed as a very promising anode material for future
high-energy-density Li-ion batteries (LIBs). However, its practical
application is hindered by large volume change of BP and poor mechanical
stability of BP anodes by traditional slurry casting technology. Here,
a free-standing flexible anode composed of BP nanosheets and nanocellulose
(NC) nanowires is fabricated via a facile vacuum-assisted filtration
approach. The constructed free-standing BP@NC composite anode offers
three-dimensional (3D) mixed-conducting network for Li+/e– transports. The substrate of NC film has a
certain flexibility up to 10.2% elongation that can restrain the volume
change of BP and electrode during operation. In addition, molecular
dynamic (MD) simulation and density function theory (DFT) show the
greatly enhanced Li+ diffusion in BP@NC composite where
the Li ions receive less repulsive force at the interface of BP interlayer
and nanocellulose. Benefiting from above multifunction of nanocellulose,
the BP@NC composite exhibits high capacities of 1020.1 mAh g–1 at 0.1 A g–1 after 230 cycles and 994.4 mAh g–1 at 0.2 A g–1 after 400 cycles,
corresponding to high capacity retentions of 87.1% and 84.9%, respectively.
Our results provide a low-cost and effective strategy to develop advanced
electrodes for next-generation rechargeable batteries.
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