The
fabrication of flexible as well as self-powered optoelectronic devices
is a growing and challenging area of research. Some scientists have
reported the fabrication of either flexible or self-powered photodetectors
recently. However, most of the literature studies fail to report the
fabrication of self-powered as well as flexible photodetectors. This
study reports the fabrication of self-powered, carbon dot (CD)-enhanced,
flexible ZnO/graphite heterojunction-based UV detector where cellulose
paper has been used as the substrate. A detailed study on the crystallinity
and the defects of the ZnO nanorods has been done with appropriate
characterizations. The CD-enhanced ZnO/graphite heterojunction showed
Schottky characteristics. The Schottky parameters such as the barrier
height, ideality factor, and the series resistance have also been
calculated using the Cheung–Cheung method. The observed values
of barrier height, ideality factor, and the series resistance are
0.74 eV, 3.74, and 503 kΩ, respectively. The transient response
at self-powered condition has been demonstrated. The response time
and the recovery time at self-powered condition have also been calculated
with the help of the transient response, and those values are ∼2
and ∼3.2 s, respectively. The responsivity and the specific
detectivity of the fabricated UV detector have been calculated as
9.57 mA/W and 4.27×108 Jones, respectively, at 330
nm wavelength, which is quite comparable with literature-reported
values, considering a self-powered photodetector.
It is interesting to explore the connections between the exchange bias effect (EBE) and magnetic anisotropy (MA). It is often found that materials exhibiting a strong EBE also have enhanced MA. Here we explore 40 nm diameter Co2C nanoparticles (NPs) that exhibit ferromagnetism with a blocking temperature exceeding 300 K. We report the first observation of EBE in these Co2C NPs below 50 K. The effect arises from the exchange coupling of frozen ferromagnetic spins with a freely rotatable spin component. The dynamics of the freely rotatable component freezes in a temperature range between 5 K to 20 K resulting in low-temperature coexistence of a glassy behavior along with ferromagnetism. In fact, Co2C displays a unique separation of onset temperatures of spin freezing (∼20 K), vanishing of EBE (∼50 K), and magnetic blocking (⩾450 K). Our calculations show that Co2C NPs have a core–shell structure. Our study suggests that modifying chemical co-ordination in the shell is one of the effective routes to manipulating MA compared to manipulating EBE.
We report the development of a 3G microswimmer, namely, CNT-bot, capable of undergoing acid-, alkali-, magnetoand phototaxis inside acidic or alkaline baths of peroxide fuel and/or water. The use of carboxyl-functionalised multiwalled carbon nanotubes (MWCNTs) facilitated the propulsion of CNT-bots in an alkaline-water solution by ejecting carbon-dioxide bubbles. Furthermore, doping of magnetite nanoparticles (FeONPs), ferrous ions (Fe 2+ ) and titanium dioxide nanoparticles (TiONPs) induces magnetic, chemical and photonic modes of propulsion. While FeONPs stimulated magnetotaxis at a rate of up to~10 body lengths per second under the influence of a bar magnet, chemotaxis of a similar speed in a peroxide fuel was achieved by bubble-propulsion of oxygen gas originating from the Fenton reaction. In addition, the light-stimulated photo-Fenton reaction led to phototaxis of CNT-bots. A thin coating of magnesium imparted a half-faced Janus appearance to the CNT-bots, which facilitated motion in normal or acidic water media through the ejection of hydrogen gas bubbles. This chemotaxis could be transformed into pHstimulated directional motion by establishing an acid or alkali concentration gradient across the peroxide and/or water baths. The capacity of CNT-bots to produce oxygen (hydrogen) bubbles in peroxide (acidic water) fuel was exploited to power a PEM fuel cell to generate electricity. The pure oxygen and hydrogen gases generated by CNT-bots in separate chambers were fed directly into the fuel cell in which the incessant motions of the particle facilitated the creation and release of the pure gases to achieve on-demand electricity generation. The motor could also induce dye degradation through advanced oxidation owing to the production of intermediate hydroxyl radicals during the Fenton reaction.
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