An
anomalous nature of Raman spectral asymmetry has been reported
here from silicon nanowires (SiNWs) prepared from a heavily doped
p-type Si wafer using a metal induced etching technique. Raman spectra
of SiNWs prepared from two p-type Si wafers with different doping
levels show different behaviors in terms of asymmetry as characterized
by the asymmetry ratio. The SiNWs prepared from high doped p-type
wafer show an anomaly in asymmetry in addition to the red shift and
broadening of the Raman line shape due to the presence of the “FAno-quaNTUM”
(FANTUM) effect. The heavy doping in the wafer provides a continuum
of energy states to be available to interact with confined optic phonons
which results in electron–phonon interaction. SiNWs prepared
from low doped p-type wafer show a red shift and asymmetric broadening
due to the quantum confinement effect alone. Careful analysis has
been provided to clearly understand the role of Fano and quantum effects
in p-type SiNWs with high doping and their relative contribution in
Raman line-shape half-widths. A theoretical framework for supporting
the presence of the FANTUM effect has also been proposed to show that
how a system with appropriate Fano and quantum effects’ relative
contribution may result in a near-symmetric Raman line shape.
We studied the dynamics
of transfer of photoexcited electronic
states in a bilayer of the two-dimensional transition metal dichalcogenide
ReS
2
and tetracene, with the aim to produce triplets in
the latter. This material combination was used as the band gap of
ReS
2
(1.5 eV) is slightly larger than the triplet energy
of tetracene (1.25 eV). Using time-resolved optical absorption spectroscopy,
transfer of photoexcited states from ReS
2
to triplet states
in tetracene was found to occur within 5 ps with an efficiency near
38%. This result opens up new possibilities for heterostructure design
of two-dimensional materials with suitable organics to produce long-lived
triplets. Triplets are of interest as sensitizers in a wide variety
of applications including optoelectronics, photovoltaics, photocatalysis,
and photon upconversion.
In conventional solar cell semiconductor materials (predominantly Si) photons with energy higher than the band gap initially generate hot electrons and holes, which subsequently cool down to the band edge by phonon emission. Due to the latter process, the energy of the charge carriers in excess of the band gap is lost as heat and does not contribute to the
Baseline wander (BW) is a low frequency artifact in biomedical electronic recordings. It is usually caused by patient's respiration or movement of equipments. The removal of this artifact is important in ECG recordings for reliable visual interpretation. This paper presents the implementation of Empirical Mode Decomposition (EMD), Ensemble Empirical Mode Decomposition (EEMD) and EMD based method to remove this disturbance. The EMD based technique serves as an efficient method to remove baseline wander with minimum signal distortion. The results highlights the main differences among all different methods and also show that the EMD based technique is able to remove best baseline wander.
Few-layered transition metal dichalcogenides (TMDs) are increasingly popular materials for optoelectronics and catalysis. Amongst the various types of TMDs available today, rheniumchalcogenides (ReX2) stand out due to their remarkable electronic structure, such as the occurrence of anisotropic excitons and potential direct bandgap behavior throughout multilayered stacks. In this letter, we have analyzed the nature and dynamics of charge carriers in highly crystalline liquid-phase exfoliated ReS2, using a unique combination of optical pump-THz probe and broadband transient absorption spectroscopy. Two distinct time regimes are identified, both of which are dominated by unbound charge carriers despite the high exciton binding energy. In the first time regime the unbound charge carriers cause an increase and a broadening of the exciton absorption band. In the second time regime, a peculiar narrowing of the excitonic absorption profile is observed, which we assign to the presence of built-in fields and/or charged defects. Our results pave the way to analyze spectrally complex transient absorption measurements on layered TMD materials and indicate the potential for ReS2 to produce mobile free charge carriers, a feat relevant for photovoltaic applications.
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