To
date, several portable, wearable, and even implantable electronics
have been incorporated into ultracompact devices as miniaturized energy-autonomous
systems (MEASs). Electrostatic supercapacitors could be a promising
energy storage component for MEASs due to their high power density
and ultrashort charging time. Several dielectric materials, including
ceramics, polymers, and glass, have been studied for energy storage
applications. However, due to their large thickness (in micrometers
or larger), these materials are inappropriate for use as nanocapacitors.
Recently, ferroelectric and antiferroelectric fluorite-structured
dielectrics (e.g., zirconia and hafnia) have been studied intensively
for data storage and energy-related applications. Their nanoscale
(nm) thickness makes these materials suitable for use as nanocapacitors
in MEASs. This work reviews the energy storage properties of fluorite-structured
antiferroelectric oxides (HfO2 and ZrO2), along
with 3-D device structures, the effect of negative capacitance on
the energy storage characteristics of fluorites, and the future prospects
of this research field.
In ZnTe, longitudinal optical (LO) phonons are strongly coupled with free exciton via long-range order Froehlich interactions. In this study, we ex situ and in situ monitored the effect of annealing temperature on exciton-phonon (e-ph) coupling in vacuum evaporated ZnTe thin films by resonance Raman scattering experiment. The 350 C air-annealed thin film exhibited strong e-ph coupling and nLO phonons up to sixth order were observed in the Raman spectrum. Moreover, a series of (n À 1)LO + TO and (n + 1)LO-TO combination phonon modes appeared at low and high wavenumber shoulders of the nLO phonon modes, respectively. The phenomenon of e-ph coupling was in situ monitored by temperature-dependent Raman scattering experiment for 350 C air-annealed thin film. During the in situ measurements, the energy of free exciton was decreased and the condition of outgoing resonance was achieved with nLO phonon. The observation of strong overtones phonon scattering and combination phonon modes allowed us to study anharmonic phonon decay of the zone center nLO phonons. The decay of the fundamental 1LO and its overtone 2LO phonon was mainly dominated by three-phonon process. For higher order LO phonons with n ≥ 3, the four-phonon process contribution was increased in the decay process with increasing order.
Low‐energy optical phonons with energy in the order of that of acoustic phonons are readily populated at room temperature, and therefore, they play a key role in thermal, electronic, and thermo‐electric fundamental processes in a solid material. High‐quality crystalline cadmium sulfide (CdS) nanowires with a diameter of several tens of nanometer and a length up to several micrometers (3–5 μm) demonstrate strong exciton–phonon coupling. This strong coupling interaction allows us to observe low‐energy optical phonons and their anharmonic couplings to high‐energy phonon modes. In this study, second and higher order multiphonons related to the
E2low phonon were observed in near resonance Raman scattering condition (excitation wavelength of 532 nm). The clear observation of the multiphonon modes makes it possible to study composite phonon anharmonic decay. The experimental results show that low‐energy phonons (both optical and acoustical) dominate anharmonic phonon decay in CdS.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.