A surface-enhanced infrared absorption spectroscopic chalcogenide waveguide sensor based on the silver island film was proposed for the first time to enhance the sensing performance in both liquid and gas phases. The chalcogenide waveguide sensor was fabricated by the lift-off and oblique angle deposition methods. The surface morphology of the silver island film with different thicknesses was characterized. The absorption of ethanol (liquid) at a wavelength of 1654 nm and that of methane (gas) at 3291 nm were measured using the fabricated chalcogenide waveguide sensor. The chalcogenide waveguide sensor integrated with the 1.8 nm-thick silver island film revealed the best sensing performance. With an acceptable increased waveguide loss resulting from the fabrication of the film, the absorbance enhancement factors for ethanol and methane were experimentally obtained to be >1.5 and >2.3, respectively. The 1σ limit of detection of methane for the sensor integrated with the 1.8 nm-thick silver island film was ∼4.11% for an averaging time of 0.2 s. The mathematic relation between the absorbance enhancement factor and the waveguide loss was derived for sensing performance improvement. Also, the proposed rectangular waveguide sensor provides an idea for the design of a sensor-on-a-chip instead of other waveguide sensors with a high requirement of fabrication accuracy, for example, a slot waveguide or a photonic crystal waveguide.
We
demonstrate the use of functional-unit-based material design
for thermoelectrics. This is an efficient approach for identifying
high-performance thermoelectric materials, based on the use of combinations
of functional fragments relevant to desired properties. Here, we reveal
that linear triatomic resonant bonds (LTRBs) found in some Zintl compounds
provide strong anisotropy both structurally and electronically, along
with strong anharmonic phonon scattering. An LTRB is thus introduced
as a functional unit, and compounds are then screened as potential
thermoelectric materials. We identify 17 semiconducting candidates
from the MatHub-3d database that contain LTRBs. Detailed transport
calculations demonstrate that the LTRB-containing compounds not only
have considerably lower lattice thermal conductivities than other
compounds with similar average atomic masses, but also exhibit remarkable
band anisotropy near the valence band maximums due to the LTRB. K5CuSb2 is adopted as an example to elucidate the
fundamental correlation between the LTRB and thermoelectric properties.
The [Sb–Cu–Sb]5– resonant structures
demonstrate the delocalized Sb–Sb interaction within each LTRB,
resulting in the softening of TA phonons and leading to large anharmonicity.
The low lattice thermal conductivity (0.39 W/m·K at 300 K) combined
with the band anisotropy results in a high thermoelectric figure of
merit (ZT) for K5CuSb2 of 1.3 at 800 K. This
work is a case study of the functional-unit-based material design
for the development of novel thermoelectric materials.
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