The first stretchable energy-harvesting electronic-skin device capable of differentiating and generating energy from various mechanical stimuli, such as normal pressure, lateral strain, bending, and vibration, is presented. A pressure sensitivity of 0.7 kPa(-1) is achieved in the pressure region <1 kPa with power generation of tens of μW cm(-2) from a gentle finger touch.
van
der Waals heterostructures composed of two different monolayer
crystals have recently attracted attention as a powerful and versatile
platform for studying fundamental physics, as well as having great
potential in future functional devices because of the diversity in
the band alignments and the unique interlayer coupling that occurs
at the heterojunction interface. However, despite these attractive
features, a fundamental understanding of the underlying physics accounting
for the effect of interlayer coupling on the interactions between
electrons, photons, and phonons in the stacked heterobilayer is still
lacking. Here, we demonstrate a detailed analysis of the strain-dependent
excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive
strain that enables the interlayer interactions to be modulated along
with the electronic band structure. We find that the strain-modulated
interlayer coupling directly affects the characteristic combined vibrational
and excitonic properties of each monolayer in the heterobilayer. It
is further revealed that the relative photoluminescence intensity
ratio of WS2 to MoS2 in our heterobilayer increases
monotonically with tensile strain and decreases with compressive strain.
We attribute the strain-dependent emission behavior of the heterobilayer
to the modulation of the band structure for each monolayer, which
is dictated by the alterations in the band gap transitions. These
findings present an important pathway toward designing heterostructures
and flexible devices.
Recent supercapacitors show a high power density with long‐term cycle life time in energy‐powering applications. A supercapacitor based on a single metal electrode accompanying multivalent cations, multiple charging/discharging kinetics, and high electrical conductivity is a promising energy‐storing system that replaces conventionally used oxide and sulfide materials. Here, a hierarchically nanostructured 2D‐Zn metal electrode‐ion supercapacitor (ZIC) is reported which significantly enhances the ion diffusion ability and overall energy storage performance. Those nanostructures can also be successfully plated on various flat‐type and fiber‐type current collectors by a controlled electroplating method. The ZIC exhibits excellent pseudocapacitive performance with a high energy density of 208 W h kg−1 and a power density from 500 W kg−1, which are significantly higher than those of previously reported supercapacitors with oxide and sulfide materials. Furthermore, the fiber‐type ZIC also shows high energy‐storing performance, outstanding mechanical flexibility, and waterproof characteristics, without any significant capacitance degradation during bending tests. These results highlight the promising possibility of nanostructured 2D Zn metal electrodes with the controlled electroplating method for future energy storage applications.
The energy harvesting efficiency is of tremendous importance for the realization of a high output-power nanogenerator serving as the basis for self-powered electronics. Here we report that the device performance of a sound-driven piezoelectric energy nanogenerator (SPENG) is remarkably improved by controlling both the carrier density and the interfacial energy in a semiconducting ZnO nanowire (NW), thereby achieving its intrinsic efficiency limits. A SPENG with carrier-controlled ZnO NWs exhibits excellent energy harvesting characteristics with an average power density of 0.9 mW cm À3 , as well as a near 50 fold increase in both output voltage and current compared to those of a conventional ZnO NW. In addition, we demonstrate for the first time that an optimized SPENG is large enough and very suitable to drive electrophoretic ink displays based on voltage-drive systems. This fundamental progress makes it possible to fabricate high performance nanogenerators for viable industrial applications in portable/wearable personal electronics such as electronic papers and smart identity cards.Recent developments in piezoelectric power generators harvesting energy steadily from ambient mechanical vibrations without regard to time, place, or any external conditions, present innovative and emerging research topics in the area of a green energy technology. 6,10,11,13 In particular, a ZnO nanowire (NW) has been intensively studied as one of the most attractive piezoelectric materials for widespread use as a clean and inexhaustible power source in future self-powered nanosystems, including implantable chips, exible/ portable electronics, and environmental and heath monitoring sensors, because of its unique dimensionality and superior transparent and piezoelectric semiconducting properties coupled with biocompatibility, environmental friendliness, and geometrical versatility. 6,10,11 To date various approaches have been reported demonstrating and enhancing unique capabilities for a ZnO NW-based piezoelectric energy generator by introducing various NW arrays and device congurations, exible/textile electrodes and substrates, and diverse types of ambient mechanical energy sources. 6,11,[13][14][15][16][17] However, despite the demonstrated ability and fascinating piezoelectric
Phototransistors
that are based on a hybrid vertical heterojunction
structure of two-dimensional (2D)/quantum dots (QDs) have
recently attracted attention as a promising device architecture for
enhancing the quantum efficiency of photodetectors. However, to optimize
the device structure to allow for more efficient charge separation
and transfer to the electrodes, a better understanding of the photophysical
mechanisms that take place in these architectures is required. Here,
we employ a novel concept involving the modulation of the built-in
potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The
effects of the built-in potential across the depletion region near
the type II junction interface in the QD layers are found to improve
the photoresponse as well as decrease the response times to 950 μs,
which is the faster response time (by orders of magnitude) than that
recorded for previously reported 2D/QD phototransistors. Also, by
implementing an electric-field modulation of the MoS2 channel,
our experimental results reveal that the detectivity can be as large
as 1 × 1011 jones. This work demonstrates an important
pathway toward designing hybrid phototransistors and mixed-dimensional
van der Waals heterostructures.
Two-dimensional
(2D) heterostructured or alloyed monolayers composed
of transition metal dichalcogenides (TMDCs) have recently emerged
as promising materials with great potential for atomically thin electronic
applications. However, fabrication of such artificial TMDC heterostructures
with a sharp interface and a large crystal size still remains a challenge
because of the difficulty in controlling various growth parameters
simultaneously during the growth process. Here, a facile synthetic
protocol designed for the production of the lateral TMDC heterostructured
and alloyed monolayers is presented. A chemical vapor deposition approach
combined with solution-processed precursor deposition makes it possible
to accurately control the sequential introduction time and the supersaturation
levels of the vaporized precursors and thus reliably and exclusively
produces selective and heterogeneous epitaxial growth of TMDC monolayer
crystals. In addition, TMDC core/shell heterostructured (MoS2/alloy, alloy/WS2) or alloyed (Mo1–x
W
x
S2) monolayers
are also easily obtained with precisely controlled growth parameters,
such as sulfur introduction timing and growth temperature. These results
represent a significant step toward the development of various 2D
materials with interesting properties.
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