23 research outputs found
Low-Temperature Photochemically Activated Amorphous Indium-Gallium-Zinc Oxide for Highly Stable Room-Temperature Gas Sensors
We
report on highly stable amorphous indium-gallium-zinc oxide
(IGZO) gas sensors for ultraviolet (UV)-activated room-temperature
detection of volatile organic compounds (VOCs). The IGZO sensors fabricated
by a low-temperature photochemical activation process and exhibiting
two orders higher photocurrent compared to conventional zinc oxide
sensors, allowed high gas sensitivity against various VOCs even at
room temperature. From a systematic analysis, it was found that by
increasing the UV intensity, the gas sensitivity, response time, and
recovery behavior of an IGZO sensor were strongly enhanced. In particular,
under an UV intensity of 30 mW cm<sup>–2</sup>, the IGZO sensor
exhibited gas sensitivity, response time and recovery time of 37%,
37 and 53 s, respectively, against 750 ppm concentration of acetone
gas. Moreover, the IGZO gas sensor had an excellent long-term stability
showing around 6% variation in gas sensitivity over 70 days. These
results strongly support a conclusion that a low-temperature solution-processed
amorphous IGZO film can serve as a good candidate for room-temperature
VOCs sensors for emerging wearable electronics
High-Mobility and Hysteresis-Free Flexible Oxide Thin-Film Transistors and Circuits by Using Bilayer Sol–Gel Gate Dielectrics
In
this paper, we demonstrate high-performance and hysteresis-free solution-processed
indium–gallium–zinc oxide (IGZO) thin-film transistors
(TFTs) and high-frequency-operating seven-stage ring oscillators using
a low-temperature photochemically activated Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> bilayer gate dielectric. It was found that the IGZO
TFTs with single-layer gate dielectrics such as Al<sub>2</sub>O<sub>3</sub>, ZrO<sub>2</sub>, or sodium-doped Al<sub>2</sub>O<sub>3</sub> exhibited large hysteresis, low field-effect mobility, or unstable
device operation owing to the interfacial/bulk trap states, insufficient
band offset, or a substantial number of mobile ions present in the
gate dielectric layer, respectively. To resolve these issues and to
explain the underlying physical mechanisms, a series of electrical
analyses for various single- and bilayer gate dielectrics was carried
out. It is shown that compared to single-layer gate dielectrics, the
Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> gate dielectric exhibited
a high dielectric constant of 8.53, low leakage current density (∼10<sup>–9</sup> A cm<sup>–2</sup> at 1 MV cm<sup>–1</sup>), and stable operation at high frequencies. Using the photochemically
activated Al<sub>2</sub>O<sub>3</sub>/ZrO<sub>2</sub> gate dielectric,
the seven-stage ring oscillators operating at an oscillation frequency
of ∼334 kHz with a propagation delay of <216 ns per stage
were successfully demonstrated on a polymeric substrate
Static and Dynamic Water Motion-Induced Instability in Oxide Thin-Film Transistors and Its Suppression by Using Low‑<i>k</i> Fluoropolymer Passivation
Here,
we report static and dynamic water motion-induced instability in indium–gallium–zinc-oxide
(IGZO) thin-film transistors (TFTs) and its effective suppression
with the use of a simple, solution-processed low-<i>k</i> (ε ∼ 1.9) fluoroplastic resin (FPR) passivation layer.
The liquid-contact electrification effect, in which an undesirable
drain current modulation is induced by a dynamic motion of a charged
liquid such as water, can cause a significant instability in IGZO
TFTs. It was found that by adopting a thin (∼44 nm) FPR passivation
layer for IGZO TFTs, the current modulation induced by the water-contact
electrification was greatly reduced in both off- and on-states of
the device. In addition, the FPR-passivated IGZO TFTs exhibited an
excellent stability to static water exposure (a threshold voltage
shift of +0.8 V upon 3600 s of water soaking), which is attributed
to the hydrophobicity of the FPR passivation layer. Here, we discuss
the origin of the current instability caused by the liquid-contact
electrification as well as various static and dynamic stability tests
for IGZO TFTs. On the basis of our findings, we believe that the use
of a thin, solution-processed FPR passivation layer is effective in
suppressing the static and dynamic water motion-induced instabilities,
which may enable the realization of high-performance and environment-stable
oxide TFTs for emerging wearable and skin-like electronics
Synthesis of Vertical MoO<sub>2</sub>/MoS<sub>2</sub> Core–Shell Structures on an Amorphous Substrate via Chemical Vapor Deposition
Vertical
MoO<sub>2</sub>/MoS<sub>2</sub> core–shell structures
were synthesized on an amorphous surface (SiO<sub>2</sub>) by chemical
vapor deposition at a high heating rate using a configuration in which
the vapor phase was confined. The confined reaction configuration
was achieved by partially covering the MoO<sub>3</sub>-containing
boat with a substrate, which allowed rapid buildup of the partially
reduced MoO<sub>3–<i>x</i></sub> crystals in an early
stage (below 680 °C). Rapid temperature ramping to 780 °C
enabled spontaneous transition of the reaction environment from sulfur-poor
to sulfur-rich, which induced a sequential phase transition from MoO<sub>3–<i>x</i></sub> to intermediate MoO<sub>2</sub> and finally to MoO<sub>2</sub>/MoS<sub>2</sub> core–shell
structures. The orthorhombic crystal structure of MoO<sub>3–<i>x</i></sub> contributed to the formation of vertical crystals
on the amorphous substrate, whereas the nonvolatility of the subsequently
formed MoO<sub>2</sub> enabled layer-by-layer sulfurization to form
MoS<sub>2</sub> on the oxide surface with minimal resublimation loss
of MoO<sub>2</sub>. By adjustment of the sulfurization temperature
and time, excellent control over the thickness of the MoS<sub>2</sub> shell was achieved through the proposed synthesis method
Ultrasensitive Room-Temperature Operable Gas Sensors Using p‑Type Na:ZnO Nanoflowers for Diabetes Detection
Ultrasensitive room-temperature
operable gas sensors utilizing the photocatalytic activity of Na-doped
p-type ZnO (Na:ZnO) nanoflowers (NFs) are demonstrated as a promising
candidate for diabetes detection. The flowerlike Na:ZnO nanoparticles
possessing ultrathin hierarchical nanosheets were synthesized by a
facile solution route at a low processing temperature of 40 °C.
It was found that the Na element acting as a p-type dopant was successfully
incorporated in the ZnO lattice. On the basis of the synthesized p-type
Na:ZnO NFs, room-temperature operable chemiresistive-type gas sensors
were realized, activated by ultraviolet (UV) illumination. The Na:ZnO
NF gas sensors exhibited high gas response (<i>S</i> of
3.35) and fast response time (∼18 s) and recovery time (∼63
s) to acetone gas (100 ppm, UV intensity of 5 mW cm<sup>–2</sup>), and furthermore, subppm level (0.2 ppm) detection was achieved
at room temperature, which enables the diagnosis of various diseases
including diabetes from exhaled breath
Monolithic Metal Oxide Transistors
We devised a simple transparent metal oxide thin film transistor architecture composed of only two component materials, an amorphous metal oxide and ion gel gate dielectric, which could be entirely assembled using room-temperature processes on a plastic substrate. The geometry cleverly takes advantage of the unique characteristics of the two components. An oxide layer is metallized upon exposure to plasma, leading to the formation of a monolithic source–channel–drain oxide layer, and the ion gel gate dielectric is used to gate the transistor channel effectively at low voltages through a coplanar gate. We confirmed that the method is generally applicable to a variety of sol–gel-processed amorphous metal oxides, including indium oxide, indium zinc oxide, and indium gallium zinc oxide. An inverter NOT logic device was assembled using the resulting devices as a proof of concept demonstration of the applicability of the devices to logic circuits. The favorable characteristics of these devices, including (i) the simplicity of the device structure with only two components, (ii) the benign fabrication processes at room temperature, (iii) the low-voltage operation under 2 V, and (iv) the excellent and stable electrical performances, together support the application of these devices to low-cost portable gadgets, <i>i.e</i>., cheap electronics
Insight into the Microenvironments of the Metal–Ionic Liquid Interface during Electrochemical CO<sub>2</sub> Reduction
Recently, many experimental
and theoretical efforts are being intensified
to develop high-performance catalysts for electrochemical CO<sub>2</sub> conversion. Beyond the catalyst material screening, it is also critical
to optimize the surrounding reaction medium. From vast experiments,
inclusion of room-temperature ionic liquid (RTIL) in the electrolyte
is found to be beneficial for CO<sub>2</sub> conversion; however,
there is no unified picture of the role of RTIL, prohibiting further
optimization of the reaction medium. Using a state-of-the-art multiscale
simulation, we here unveil the atomic origin of the catalytic promotion
effect of RTIL during CO<sub>2</sub> conversion. Unlike the conventional
belief, which assumes a specific intermolecular coordination by the
RTIL component, we find that the promotion effect is collectively
manifested by tuning the reaction microenvironment. This mechanism
suggests the critical importance of the bulk properties (e.g., resistance,
gas solubility and diffusivity, viscosity, etc.) over the detailed
chemical variations of the RTIL components in designing the optimal
electrolyte components, which is further supported by our experiments.
This fundamental understanding of complex electrochemical interfaces
will help in the development of more advanced electrochemical CO<sub>2</sub> conversion catalytic systems in the future
Low-Temperature Postfunctionalization of Highly Conductive Oxide Thin-Films toward Solution-Based Large-Scale Electronics
Although
transparent conducting
oxides (TCOs) have played a key role in a wide range of solid-state
electronics from conventional optoelectronics to emerging electronic
systems, the processing temperature and conductivity of solution-processed
materials seem to be far exceeding the thermal limitations of soft
materials and insufficient for high-perfomance large-area systems,
respectively. Here, we report a strategy to form highly conductive
and scalable solution-processed oxide materials and their successful
translation into large-area electronic applications, which is enabled
by photoassisted postfunctionalization at low temperature. The low-temperature
fabrication of indium–tin-oxide (ITO) thin films was achieved
by using photoignited combustion synthesis combined with photoassisted
reduction process under hydrogen atmosphere. It was noteworthy that
the photochemically activated hydrogens on ITO surface could be triggered
to facilitate highly crystalline oxygen deficient structure allowing
significant increase of carrier concentration and mobility through
film microstructure modifications. The low-temperature postfunctionalized
ITO films demonstrated conductivity of >1607 S/cm and sheet resistance
of <104 Ω/□ under the process temperature of less
than 300 °C, which are comparable to those of vacuum-deposited
and high-temperature annealed ITO films. Based on the photoassisted
postfunctionalization route, all-solution-processed transparent metal-oxide
thin-film-transistors and large-area integrated circuits with the
ITO bus lines were demonstrated, showing field-effect mobilities of
>6.5 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> with relatively good operational stability and oscillation frequency
of more than 1 MHz in 7-stage ring oscillators, respectively
Highly Sensitive Textile Strain Sensors and Wireless User-Interface Devices Using All-Polymeric Conducting Fibers
Emulation of diverse electronic devices
on textile platform is considered as a promising approach for implementing
wearable smart electronics. Of particular, the development of multifunctional
polymeric fibers and their integration in common fabrics have been
extensively researched for human friendly wearable platforms. Here
we report a successful emulation of multifunctional body-motion sensors
and user-interface (UI) devices in textile platform by using in situ
polymerized polyÂ(3,4-ethylenedioxythiophene) (PEDOT)-coated fibers.
With the integration of PEDOT fibers in a fabric, via an optimization
of the fiber pattern design, multifunctional textile sensors such
as highly sensitive and reliable strain sensors (with maximum gauge
factor of ∼1), body-motion monitoring sensors, touch sensors,
and multilevel strain recognition UI devices were successfully emulated.
We demonstrate the facile utilization of the textile-based multifunctional
sensors and UI devices by implementing in a wireless system that is
capable of expressing American Sign Language through predefined hand
gestures
Transcriptional regulation of bile acid enzyme genes by <i>Crebh.</i>
<p>(<b>A</b>) Mice (n = 5) or primary human hepatocytes (n = 3) were infected with indicated adenoviruses for 96 hrs. Liver tissues were obtained and protein and total RNA was extracted for western blot and qPCR analyses, respectively. *<i>p</i><0.05 vs. Ad-GFP group. (<b>B</b>) HepG2 cells were co-transfected with CREBH-N and different CYP7A1-Luc and CYP27A1-Luc promoter constructs, and luciferase assay was performed. (<b>C–D</b>) HepG2 cells were transfected with wild type (wt) or CREBH-mutant (mut) constructs of CYP7A1-Luc or CYP27A1-Luc followed by 2-AG-ether treatment for 12 hrs and luciferase assay was performed (D) or immunoprecipitation of HepG2 chromatin from cells exposed to DMSO (control) or 2-AG-ether was performed with IgG or Crebh antibody (E). Promoter regions were amplified by PCR, as depicted. Percentage of DNA immunoprecipitated with Crebh antibody relative to input chromatin was quantified by qPCR. *<i>p</i><0.05 vs. control. Data represents mean ± SE.</p