Here, we show that the surface wettability of ultrathin (6–16nm) TiO2 films deposited by atomic layer deposition (ALD) can be tuned by an ultraviolet (UV) light treatment. The controllability is also ...shown to be largely dependent on the deposition temperature and thickness. The surface of a 16-nm-thick ALD TiO2 film deposited at 200°C was shown to be super-hydrophilic (water contact angle <1°) by an UV treatment (~3mW/cm2) applied for only 8min due to the photocatalytic activity of the films, while thinner films and films deposited at lower temperatures were not. Microscopic and optical characterizations prove that the difference mainly stems from the crystallinity, the bandgap energy and the defect density of the TiO2 films.
•ALD TiO2 surface shows UV-induced wettability by photocatalytic activity.•The wettability is dependent on the thickness and the deposition temperature.•Bandgap and defect density affect the generation and the recombination of carriers.•16nm-thick ALD TiO2 deposited at 200°C becomes super-hydrophilic by UV treatment.
Determining the optimal thickness range of the interlayed yttria-doped ceria (YDC) films promises to further enhance the performance of solid oxide fuel cells (SOFCs) at low operating temperatures. ...The YDC interlayers are fabricated by the atomic layer deposition (ALD) method with one super cycle of the YDC deposition consisting of 6 ceria deposition cycles and one yttria deposition cycle. YDC films of various numbers of ALD super cycles, ranging from 2 to 35, are interlayered into bulk fuel cells with a 200 um thick yttria-stabilized zirconia (YSZ) electrolyte. Measurements and analysis of the linear sweep voltammetry of these fuel cells reveal that the performance of the given cells is maximized at 10 super cycles. Auger elemental mapping and X-ray photoelectron spectroscopy (XPS) techniques are employed to determine the film completeness, and they verify 10 super cycles of YDC to be the critical thickness point. This optimal YDC interlayer condition (6Ce1Y × 10 super cycles) is applied to the case of micro fuel cells as well, and the average performance enhancement factor is 1.4 at operating temperatures of 400 and 450 °C. A power density of 1.04 W cm−2 at 500 °C is also achieved with the optimal YDC recipe.
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► Yttria-doped ceria interlayers are fabricated by atomic layer deposition. ► The completeness of YDC films with various ALD super cycles is studied through electroanalysis. ► Auger elemental mapping and X-ray photoelectron spectroscopy are used to verify the film coverage. ► The effect of the optimal YDC interlayer in micro fuel cells is presented.
A novel route to fabricate functional interface between highly-dense platinum (Pt) catalysts and 2D MoS2 using atomic layer deposition (ALD) and plasma treatment is proposed. Densely-decorated ALD Pt ...nanoparticles on plasma-functionalized MoS2 is evaluated as H2 sensor, resulting in highly sensitive detection of nonpolar H2 with the lower detection limit down to 2.5 ppm.
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•Atomic layer deposited(ALD) Pt on plasma-treated MoS2 as a sensitive H2 sensor.•Effects of plasma treatment and Pt ALD cycles on sensor performance are elucidated.•ALD Pt-MoS2 H2 sensor shows high sensitivity(greater than400) and low detection limit(2.5 ppm).•ALD Pt-MoS2 sensor shows excellent selectivity and long-term stability for 4 weeks.
Hydrogen gas (H2) has garnered significant attention as an alternative clean energy source, and its sensitive detection is essential to prevent explosions due to leakage in storage systems. Molybdenum disulfide (MoS2), which exhibits a large surface area-to-volume ratio from atomically thin two-dimensional (2D) structure, has attracted attention as a suitable H2 sensing material. However, pristine MoS2 exhibits low sensitivity to nonpolar H2. This paper demonstrates a decoration method for platinum (Pt) catalysts on 2D MoS2 using atomic layer deposition (ALD) and its application to fabricate highly sensitive H2 sensors. Additionally, to induce homogeneous distribution of Pt nanoparticles on chemically inert MoS2 surfaces, oxygen plasma pretreatment is employed as the MoS2 surface functionalization method. Consequently, highly sensitive detection of H2 with the sensitivity over 400 and the lower detection limit set to 2.5 ppm, is achieved using ALD Pt-decorated MoS2, and a sensing mechanism is proposed.
Ru is extensively used in electrical and energy applications because of its high electrical conductivity and catalytic activity. This study reports the H
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plasma-enhanced atomic layer deposition ...(PEALD) of Ru thin films using a novel carbonyl cyclohexadiene ruthenium precursor. The optimized process conditions for depositing Ru thin films by PEALD were established based on the growth per cycle (GPC), chemical formation, crystallinity, conformality, and resistivity, according to process parameters such as precursor pulse time, H
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plasma pulse time, purge time, and deposition temperature. Pure Ru thin films (low carbon and oxygen) were deposited with low resistivity (30.8 μΩ cm) and showed high conformality (> 95%) on the Si trenches. The oxidant-free PEALD Ru process reported in this study may have implications on the fabrication of high-quality interfaces between Ru and easily-oxidized substrates.
The deposition of high‐quality dielectric films on graphene surfaces is crucial in fabricating high‐performance graphene‐based electronics. In this study, the first application of UV‐assisted atomic ...layer deposition (UV‐ALD) to graphene surfaces and the fabrication of graphene field‐effect transistors (GFETs) with UV‐ALD Al2O3 dielectric thin films is demonstrated. Optimal UV irradiation (5 s per cycle) during the ALD process results in denser and smoother Al2O3 dielectric films deposited on the graphene surface with the intimate graphene‐dielectric interface, while excessive UV irradiation in turn prohibits the film nucleation. As a result, the GFETs with a high‐quality dielectric layer deposited by UV‐ALD show improved performance with a Dirac voltage close to 0 V and hole mobility of 1221 cm2 V−1 s−1, i.e., > 200% increase compared to those with thermal ALD. This study demonstrates that UV‐ALD is an effective and simple option to realize a high‐quality interface between 2D materials and ultra‐thin dielectric films.
This work demonstrates the application of UV light‐assisted atomic layer deposition (UV‐ALD) to effectively functionalize graphene surfaces and fabricate high‐performance graphene field effect transistors (GFETs). The GFET with UV‐ALD Al2O3 dielectric layer shows a low Dirac voltage of 8 V and a high hole mobility of 1221 cm2 V−1 s−1 that is a 207% improvement compared to those by thermal ALD.
This study presents atomic scale characterization of grain boundary defect structure in a functional oxide with implications for a wide range of electrochemical and electronic behavior. Indeed, grain ...boundary engineering can alter transport and kinetic properties by several orders of magnitude. Here we report experimental observation and determination of oxide-ion vacancy concentration near the Σ13 (510)/001 symmetric tilt grain-boundary of YSZ bicrystal using aberration-corrected TEM operated under negative spherical aberration coefficient imaging condition. We show significant oxygen deficiency due to segregation of oxide-ion vacancies near the grain-boundary core with half-width < 0.6 nm. Electron energy loss spectroscopy measurements with scanning TEM indicated increased oxide-ion vacancy concentration at the grain boundary core. Oxide-ion density distribution near a grain boundary simulated by molecular dynamics corroborated well with experimental results. Such column-by-column quantification of defect concentration in functional materials can provide new insights that may lead to engineered grain boundaries designed for specific functionalities.
This study investigates the functionality of bi-layered electrolytes in intermediate temperature solid oxide fuel cells. A thin yttria-stabilized zirconia (YSZ) layer is expected to protect the ...underlying gadolinia doped ceria (GDC) electrolyte from being chemically reduced and significantly improve cell stability and durability. Although a thinner YSZ layer is preferable to minimize ohmic loss, there are limitations as to how thin the YSZ film can be and still serves as a valid protection layer. The limitation is partially attributed to the inter-diffusion and significant morphological changes during the high temperature sintering processes. In this study, a stable operation was demonstrated for extended duration (>80 h) with only a 28 nm YSZ layer (corresponding to a YSZ/GDC thickness ratio of 6.5 × 10−5) when limitations in both fabrication (<∼800 °C) and operating conditions (<∼600 °C, dry H2) were imposed. Furthermore, the functionality of a protection layer with a given thickness was found to strongly depend on the method of depositing the protective layer. Protective layers deposited by atomic layer deposition (ALD) can be much thinner than those prepared by physical vapor deposition; the YSZ/GDC thickness ratio for a stable operation approached close to a theoretical value when the ALD was used.
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•Feasibility of ultra-thin protective layer for a stable and high-performing SOFC.•Validates a theoretical guideline for bi-layered electrolytes prepared by ALD.•Chemical and structural stability of bi-layered electrolytes in various environments.•Useful design/operational guidelines for IT-SOFCs using bi-layered electrolyte scheme.
Electrochemical impedance spectroscopy (EIS) measurements in yttria stabilized zirconia (YSZ) with a single Σ13(510)/001 grain boundary in a common SOFC electrolyte showed that oxide ion diffusion is ...blocked when it jumps across the grain boundary at operating temperatures between 300 and 525°C. The EIS results are supported by secondary ion mass spectrometry (SIMS) measurements combined with oxygen isotope annealing on the bicrystal YSZ. The SIMS results showed that the 18O/16O+18O ratio dropped sharply near the grain boundary regions.
► YSZ with a single Σ13(510)/001 grain boundary(GB) was characterized by HRTEM. ► Bulk and GB ionic conductivity was investigated by using employing EIS technique. ► Oxygen isotope annealing was performed to compare 18O/16O concentration. ► Oxide ion diffusion through YSZ GB was spectrometrically characterized by nanoSIMS. ► Results showed the GB ionic conductivity is orders of magnitude lower than the bulk.
Reflection-type photoplethysmography (PPG) pulse sensors used in wearable smart watches, true wireless stereo, etc., have been recently considered a key component for monitoring biological signals ...such as heart rate, SPO
, and blood pressure. Typically, the optical front end (OFE) of these PPG sensors is heterogeneously configured and packaged with light sources and receiver chips. In this paper, a novel quarter-annulus photodetector (NQAPD) with identical inner and outer radii of curvature has been developed using a plasma dicing process to realize a ring-type OFE receiver, which maximizes manufacturing efficiency and increases the detector collection area by 36.7% compared to the rectangular PD. The fabricated NQAPD exhibits a high quantum efficiency of over 90% in the wavelength of 500 nm to 740 nm and the highest quantum efficiency of 95% with a responsivity of 0.41 A/W at the wavelength of 530 nm. Also, the NQAPD is shown to increase the SNR of the PPG signal by 5 to 7.6 dB compared to the eight rectangular PDs. Thus, reflective PPG sensors constructed with NQAPD can be applied to various wearable devices requiring low power consumption, high performance, and cost-effectiveness.
Atomic layer deposition (ALD) has recently attracted attention as a technique to synthesize and engineer high-performance catalysts and electrodes for fuel cells. Unique advantages of the ALD process ...include surface conformality and film uniformity along nano-scale features and the ability to deposit one atom layer or less per deposition cycle, enabling atomic-scale modification of the composition and morphology of the material surface. Many recent reports have demonstrated the effectiveness of the ALD surface modification strategy for the development of novel fuel cell materials. For enhancement of fuel cell performance, development of superior electrocatalytic electrodes is essential as a significant portion of energy loss occurs due to the charge transfer reaction either on the surface of electrodes or at the interfaces between electrodes and electrolytes. Therefore, ALD is considered a key fabrication process to design and engineer high-performance fuel cell systems. This review covers the important recent developments advanced electrode materials for solid oxide fuel cells (SOFCs) provided by the unique abilities of ALD for surface engineering and interface modification. Performance enhancement and related mechanisms are also discussed in depth.
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