Short Deposition Times Research Articles

The Effect of Marginal Zn2+ Excess Released from Titanium Coating on Differentiation of Human Osteoblastic Cells.

Composite coatings based on chitosan and zinc nanoparticles (ZnNPs) were successfully produced on Ti13Zr13Nb substrates by cathodic electrophoretic deposition (EPD). The unfavorable phenomenon of water electrolysis-induced nonuniformity was reduced by applying a low voltage (20 V) and a short deposition time (1 min). Surface analysis (roughness and hydrophilicity) reveals the potential of these coatings for enhancing cell attachment and bone-implant integration. However, there is a concern about adhesion and strength; therefore, incorporating ZnNPs shows promise for enhancing mechanical properties, suggesting opportunities for further optimization of the process. The aim of this work was to investigate whether Zn2+ released from coating yields overt cellular impairment. hFOB1.19 osteoblastic cells were used as a model in this study. A subtoxic, 0.125 mmol/L, Zn concentration did not cause significant negative changes in cultured osteoblastic cells, as there was no significant change in their viability and their mitochondrial metabolism. Moreover, the alkaline phosphatase and lactate dehydrogenase activities were aggravated. However, a high, over 0.175 mmol/L, Zn2+ concentration caused total cell death. This was caused by the inhibition of mitochondrial enzymes' activities. Our data indicate that composite coatings releasing Zn2+ may be used as the differentiating factor toward osteoblastic cells.

Electrodeposition of Silicon in the Low-Temperature LiCl-KCl-CsCl-K2SiF6 Melt Under Direct and Pulse Current

In this work, the effect of electrolysis modes and their parameters on the morphology of the silicon deposits on glassy carbon were studied. In direct current mode it was found that an increase in current density and deposition time changes the morphology of the silicon from a coating to a deposit with a complex surface. Scanning electron microscopy showed that silicon films produced at low current densities and a short deposition time are represented by spherical particles with a diameter of less than 1 μm. The pulse current mode made it possible to increase the cathode density of the deposition current, and the pulse current density to an average of ≈250 mA cm−2 does not lead to the formation of a large amount of dendritic deposit. It was found that a low frequency makes it possible to obtain higher-quality silicon coatings, because when the frequency increases, the coating most often does not cover the entire electrode. The high value of the duty cycle, even at low pulse current densities, always leads to the formation of dendrites. An increase in the total deposition time also leads to an increase in the amount of deposit and the formation of dendrites.

Thermal shock behavior of novel (Yb0.1Gd0.9)2Zr2O7 thermal barrier coatings with a Cr modified (Ni, Pt)Al bond coat

The durability of thermal barrier coatings (TBCs) is significantly influenced both by the ceramic top coat and the bond coat. In this study, novel YbGdZrO ceramic coats were deposited on the surfaces of three types of Cr-modified (Ni, Pt)Al bond coats via electron beam physical vapor deposition (EB-PVD) technique. These Cr-modified (Ni, Pt)Al bond coats were fabricated by magnetic sputtering Cr onto the (Ni, Pt)Al bond coats with varying sputtering times of 30, 60, and 90 min. The results indicates that the thickness of the Cr-modified layer increases with the extension of sputtering time. A short deposition time of 30 min is adequate for achieving an appropriate Cr content in the (Ni, Pt)Al bond coats, which ensures selective oxidation of Al element within the bond coat and further enhances the metallurgical interfacial bonding strength with the ceramic coat by adapting to the concentration gradient diffusion. However, as the sputtering time is extended to 60 and 90 min, α-Cr begins to form in the Cr-modified (Ni, Pt)Al bond coats, which negatively affects the oxidation resistance of the bond coat. Consequently, the thermal shock life of the TBCs samples is significantly reduced with increasing sputtering time. The longest thermal shock lifetime is obtained on the bond coat with Cr plating time of 30 min owing to a differing thermally grown oxide formation and failure mechanism.

Incremental Feeding of Perovskite Powders: Angstrom‐Precision Growth for Single‐Source Solar Cell Fabrication

Vacuum‐based deposition of halide perovskites receives a lot of attention for its proven scalability and conformal depositions. Co‐evaporation has remarkable success, but efficiencies continue to lag behind their solution‐based counterparts. This is in part attributed to the complex sublimation behavior of some organic ammonium precursor salts and the increased complexity of the absorber materials, requiring the use of four or more sources in a conventional co‐evaporation setup. The latter has driven work into single‐source methods with flash evaporation presented as one such method. However, flash evaporation processes typically evaporate all material in a single batch, leading to short deposition times at high temperatures. Particle sputtering effects seen at these high temperatures drive processes toward low temperatures where prolonged exposure causes degradation. Here, a pulse‐driven incremental powder feeding system is presented. This method is capable of stable flash evaporation rates for >1 h, with controlled rates as low as 1.5 Å per pulse (±0.89). The feasibility of this method is demonstrated for three different perovskite compositions: FAPbBr3, MAPbI3, and FA1−xMAxPbSnI3:SnF2. Furthermore, FAPbBr3 and MAPbI3 are integrated into all vacuum‐processed thin‐film solar cells leading to power conversion efficiencies (PCE) of ~4% and 10%, respectively.

A Novel Thin-Layer Flow Cell Sensor System Based on BDD Electrode for Heavy Metal Ion Detection.

An electrochemical sensor based on a thin-layer flow cell and a boron-doped diamond (BDD) working electrode was fabricated for heavy metal ions determination using anodic stripping voltammetry. Furthermore, a fluidic automatic detection system was developed. With the wide potential window of the BDD electrode, Zn2+ with high negative stripping potential was detected by this system. Due to the thin-layer and fluidic structure of the sensor system, the electrodepositon efficiency for heavy metal ions were improved without using conventional stirring devices. With a short deposition time of 60 s, the system consumed only 0.75 mL reagent per test. A linear relationship for Zn2+ determination was displayed ranging from 10 μg/L to 150 μg/L with a sensitivity of 0.1218 μA·L·μg-1 and a detection limit of 2.1 μg/L. A high repeatability was indicated from the relative standard deviation of 1.60% for 30 repeated current responses of zinc solution. The system was applied to determine Zn2+ in real water samples by using the standard addition method with the recoveries ranging from 92% to 118%. The system was also used for the simultaneous detection of Zn2+, Cd2+, and Pb2+. The detection results indicate its potential application in on-site monitoring for mutiple heavy metal ions.

Thermal cycling effects on the local microstructure and mechanical properties in wire-based directed energy deposition of nickel-based superalloy

In additive manufacturing, intrinsic heat treatments take place during deposition that affect the properties of AM-structures. In this work, the influence of thermal cycling on the local microstructure and mechanical properties of nickel-based superalloy in wire-based electron beam directed energy deposition (EB-DED) was investigated. Structures were fabricated using a continuous deposition strategy (CDS) and discontinuous interpass cooling strategy (ICS) revealing changes in thermal profiles, time-temperature history, and microstructure. An altered morphology along the build-up height and interdendritic zones enriched in Nb are formed. Nb and Mo did not show a clear trend of segregation along the build-up height. Lower fractions of the Laves phase and MCs are found for both configurations. Differences between deposition strategies and locations within AM-structures are found for the γ" and δ phase. The higher Nb content in the interdendritic zone promotes the precipitation of γ" and δ phase by shortening the aging times compared to wrought materials. The longer deposition times of ICS favour the precipitation of fine γ" in the interdendritic zone throughout the deposition height. In contrast, the short deposition time of CDS leads to an increase in temperature and a heterogeneous distribution of γ" along the height, i.e. coarsening of the γ" followed by a dissolution along the built-up height. The microstructural changes correlate with the mechanical properties. Structures fabricated with ICS exhibit homogeneous mechanical properties throughout, while the graded microstructure of CDS results in graded mechanical properties and decreasing strength throughout.

Impact of Texture Height and Ozone-Based Rounding on Silicon Heterojunction Solar Cells Performance

In this study, the effect of ozone-based rounding was investigated for three random-pyramid texture height ranges for Silicon Heterojunction (SHJ) at the cell and module levels. In a first experiment, 5 ozone-based rounding process times (0, 2, 4, 6, 8 and 10 minutes) were applied to two texture-height ranges (Small and Medium) to observe variations in the reflection response of the wafers. In a second experiment, 3 ozone-based rounding treatment times (0, 2 and 6 minutes) were applied to three texture-height ranges (Small, Medium and Large) and to observe the results both on the cell and on the module levels. The first experiment has shown that ozone-based rounding increases reflection and has a more pronounced effect for smaller than larger sized texture-heights. An increase in the minimum wavelength of reflection is seen after the Transparent Conductive Oxide (TCO) deposition, indicating that shorter deposition times can be used. The results of the second experiment show that, even though the Short-Circuit Current (Jsc) decreases for the three textures with rounding time, it is compensated by an increase in the pseudo-Fill-Factor (pFF). A maximum is seen at the cell level for 2 minutes of rounding for the small and large texture sizes, but which is leveled at the module. In conclusion, these results indicate that 2 minutes of ozone-based rounding can be beneficial for the cell’s final efficiency as the improvement in passivation still compensates the optical losses resulting in a lower Jsc.

Friction Coefficient Dynamics of Tribological Coatings from Engine Lubricants: Analysis and Interpretation

Even today, there is no full understanding of the relationship between the physical, chemical, and mechanical properties and the behavior of the lubricating films formed in tribological systems. Most of the published scientific research measures and reports the overall values of friction and wear, but the information given via statistical signals in the tribological tests is, in general, dismissed, leaving a hole in the study of the dynamics of tribological systems. In this work, an experimental study of statistical friction data, coating characteristics, and tribological performance is carried out using a pin-on-disk tribometer to test some metallic samples coated with lubricant films under several experimental conditions. The results indicate that long deposition times at high deposition temperatures of coatings from engine oil develop low-friction intervals, which fall until 20% of the uncoated coefficient friction. However, an unexpected and unfavorable behavior of the coatings was observed for the short deposition times and high temperature. In these conditions, the developed friction profiles reached a maximum level of friction that was 20% more than the uncoated coefficient friction. Moreover, it was found that the proper analysis and interpretation of the statistical data, in combination with the characterization of the coatings, describes the dynamics of the interactions between the bodies in contact and reveals the transitions of the surfaces with non-homogeneous properties throughout their depth.

Area-Selective Atomic Layer Deposition on Metal/Dielectric Patterns: Amphiphobic Coating, Vaporizable Inhibitors, and Regenerative Processing.

Area-selective atomic layer deposition (AS-ALD) has drawn significant attention in the past decade because of the potential applications in bottom-up processing, which enables fabricating nanostructures at the atomic level without multiple patterning and lithographic processing that could easily cause alignment issues. Although AS-ALD has been demonstrated using various self-assembled monolayers (SAMs), it is still challenging to develop wet SAM deposition for AS-ALD that is suitable for industrial and semiconductor processes. In this work, we demonstrate highly effective AS-ALD of Al2O3 on Co/SiO2 patterned wafers using fluorinated thiol in both solution and vapor phase. Compared with conventional SAMs using alky-thiols, the fluorinated-thiol SAMs demonstrate greater blocking ability against ALD precursors owing to excellent hydrophobicity. Furthermore, much shorter deposition times can be achieved in vaporizable fluorinated thiol molecules, improving processing throughput and productivity. Most importantly, the SAM regeneration and redosing processes can further enhance the selectivity of AS-ALD, opening a promising avenue to realize the bottom-up approach in practical semiconductor applications.

Facile fabrication of Sn/SnOx electrode as an efficient electrocatalyst for CO2 reduction to formate

Producing valuable hydrocarbons via electrochemical reduction of CO2 has been a promising active research area. In this study, it was aimed to develop a low-cost and efficient Sn-based electrode reducing CO2 to formate with high selectivity. SnOx thin-film electrode was prepared via potentiostatic electrodeposition at the potentials of −0.5 V, −0.6 V, −0.7 V, and −0.8 V vs. Ag/AgCl on a pure Sn plate for 300 s in an acidic media. The Sn/SnOx electrode which was prepared at −0.6 V was found to have the highest Faradaic efficiency. Electrochemical reduction of CO2 was carried out on this Sn/SnOx electrode in aqueous CO2-saturated 0.1 M KHCO3 solution. The optimum values for the parameters which have significant impacts on Faradaic efficiency for producing formate namely, electrolysis potential and electrolysis time were determined. The maximum Faradaic efficiency of formate on the Sn/SnOx electrode was obtained as 74.7 % at the applied potential of −1.8 V in an H-type cell. The maximum Faradaic efficiency of formate obtained on the Sn/SnOx electrode reached about twice the value obtained on the Sn plate (39.7 %). The results also indicated that the Sn/SnOx electrode has higher catalytic stability and electrochemically active surface area (2.08 cm2) than the bare Sn plate (0.82 cm2). This study showed that an efficient Sn/SnOx electrode can be developed with a simple method that involves only a SnSO4/H2SO4 solution and as short as 300 s plating duration via electrodeposition at a lower overpotential of −0.6 V. The novelty of this study can be attributed to the combination of simple and unique electrocatalyst preparation procedure with less energy consumption and chemical/additive use, short deposition time, and relatively low overpotential for developing an efficient Sn/SnOx electrocatalyst ensuring a high Faradaic efficiency for formate production. Thus, producing formate from the conversion of CO2 which is a waste carbon source, was achieved by a quite simple and economic method.

Joint growth of BiOI and BiSI films in the chemical deposition process

Films of bismuth oxoiodide and thioiodide BiOI and BiSI as a light absorber for solar cells were synthesized and characterized. The influence of the duration of the chemical deposition process on the composition and morphology of the obtained films has been studied. It has been shown that BiOI is formed at a short deposition time, while BiOI and BiSI joint growth with an increase in the deposition time. The synthesized BiOI/BiSI photoelectrodes demonstrate a developed morphology, the invariance of the surface microstructure during stationary polarization measurements, as well as a heightened photocorrosion resistance. The high stability of operation in a photoelectrochemical cell reveals the potential of the new BiOI/BiSI light-absorbing material as a promising semiconductor for solar cells, photoelectrochemical sensors, detector and photocatalysts.

Electrochemical formation and stability of copper selenide thin films in the choline chloride-urea deep eutectic solvent at gold electrode

The electrodeposition of copper-selenium binary compounds on gold electrode was investigated in the choline chloride – urea (ChCl-U) deep eutectic solvent at 110 °C. Cyclic voltammetry and potentiostatic deposition followed by stripping voltammetries were employed to gain thermodynamic insights pointing to the formation of Cu2Se, which is supported by X-Ray Photoelectron Spectroscopy. The electrochemical stability domain of the compound is about 900 mV (from ≈−0.81 V to ≈+0.07 V vs. a silver quasi-reference electrode) and is consistent with the thermodynamics of induced co-deposition. The domain is limited at positive potentials by the oxidation to Se(0) and at negative potentials by the reduction to Cu(0). While copper is readily deposited on the gold electrode, the electrodeposition of selenium requires a significant overpotential. As a consequence, copper is kinetically favoured in the co-deposition and is present in its pure form at short deposition times. This is circumvented by using longer deposition times or more negative potentials. Photoelectrochemical measurements show that the as-deposited compound behaves as a p-type semiconductor.

Solution deposition conditions influence the surface properties of 3-mercaptopropyl(trimethoxysilane) (MPTS) films

The deposition of organosilanes onto semiconducting and metal oxide surfaces is a versatile approach to impart corrosion resistance or provide a site for the subsequent immobilization of a range of molecules. Organosilane deposition is however, quite a complex process, with many factors influencing the film properties. Here, we investigated the deposition of 3-mercaptopropyl(trimethoxysilane) (MPTS) in organic solvents on Si substrates with various post-deposition treatments and subsequently characterize film properties using surface analytical techniques including ellipsometry, X-ray photoelectron spectroscopy (XPS), static water contact angles, and attenuated total reflection Fourier transform infra-red (ATR-FTIR) spectroscopy. Condensation of MPTS onto Si surfaces was most efficient in more anhydrous and hydrophobic solvents such as toluene, with monolayer thickness values (≈0.77 nm) being observed at MPTS concentrations of 0.08–1% (v/v), whereas all thickness values were seen to be below monolayer coverage when deposition was carried out in ethanol, regardless of the concentration used. It was found that the shortcomings of ethanol deposition can be overcome by applying a pre-hydrolysis period at low pH to achieve similar film thicknesses and properties compared to toluene at shorter deposition times - which is important when functionalization needs to be carried out in plastic consumables. Moreover, with minimal post-deposition treatments it was found that controllable film thicknesses can also be achieved with a high-retention of thiol functional groups which is evidenced by a clear S 2p XPS peak at a binding energy of 164.0 eV. However, these films will only be loosely bound to the surface and be lost upon further treatments. Overall, the procedures developed are important for many applications such as biomolecule immobilization, and the functionalization of planar substrates and nanoparticles, where the organosilane thickness, degree of order, reactivity and surface concentration of thiols influence film functionality.

Electrodeposition of Amorphous Molybdenum Oxide on Iron-Group Element Based Plating and its Novel Application as a Corrosion Protective Coating

The corrosion resistance of materials composed of metal is an essential property for preventing material deterioration caused by corrosion. In this study, we demonstrate that corrosion resistance can be significantly improved through the electrodeposition of molybdenum oxide onto a metal plating containing iron-group elements. Mo oxide can be electrodeposited using a simple plating bath, low current density, and short deposition time, exhibiting a fascinating metallic gloss appearance. GI-XRD and XPS analyses revealed that amorphous Mo oxide adhered to the substrate by a seed layer partially reduced to metallic Mo by the iron-group element in the substrate, based on the principle of “induced co-deposition.” A Mo oxide coating with a thickness of approximately 100 nm decreases the corrosion current density of Ni-W plating by approximately 5 times and the passivation current density by approximately 10 times in a 3 mass% NaCl solution. Mo oxide coatings represent an attractive strategy for improving the corrosion resistance of various metal materials containing iron-group elements.

Mechanical property of Pyro-Carbon coated SiC fibers fabricated by continuous chemical vapor deposition method

PurposeA continuous chemical vapor deposition (CVD) method has been used to fabricate pyro-carbon (PyC) coating on continuous silicon carbide (SiC) fibers. The paper aims to evaluate these coated fibers by testing filament tensile and using microstructure characterization.Design/methodology/approachThe continuous SiC fiber-reinforced SiC matrix (SiC/SiC) composite is widely studied in aerospace and nuclear applications. The PyC is the probable option in fusion and fast reactor. However, the conventional fabrication method of PyC coating has some drawbacks influencing performance and efficiency.FindingsThe results showed that PyC-coated SiC fibers with continuous CVD method are more straight than conventional ones and residual deformations could not be observed, and these PyC coatings have complete geometry and uniform thickness. In different process conditions, the thickness of PyC coating could control from ∼100 to ∼1,000 nm.Originality/valueThe coated SiC fibers in a lower gas ratio (1:7 to 1:3), lower pressure (500–1,000 Pa) and appropriate winding speed (3 to 5 rpm) have relative high filament tensile strength (∼3.5 to ∼3.9 GPa). And the strength of coated SiC fibers has a negative correlation with the measured thickness of PyC coating. A distinctive growth process was discovered in the continuous CVD method. In a certain range, the quicker growing rate of PyC is obtained in shorter deposition time which means an efficient and quality method could be applied to fabricate coatings.

Ultrathin GaAs solar cells with a high surface roughness GaP layer for light‐trapping application

AbstractBy reducing the thickness of the absorber layers, ultrathin GaAs solar cells can be fabricated in a more cost‐effective manner using less source material and shorter deposition times. In this work, ultrathin GaAs solar cells are presented with a diffuse scattering layer based on wide bandgap GaP grown directly on the device layers of the cells with MOCVD. The roughness and surface morphology are quantified using atomic force microscopy and the resulting diffuse scattering capability is assessed using wavelength‐dependent reflectance measurements. Ohmic rear contacts are made using contact points etched through the GaP layer, for which an etching procedure using I2:KI was developed and optimized. The performance of the GaP textured ultrathin GaAs cells are compared with equivalent planar cells using current density‐voltage measurements and external quantum efficiency measurements, where the GaP textured cells demonstrate an increase of 6.7% in the short‐circuit current density (JSC), which was found to be as high as 21.9 mA·cm−2 as a result of increased photon absorption by light‐trapping.

Wide range tunability of surface plasmon resonance of nanostructured Ag deposited by off-axis magnetron sputtering

In this work, nanostructured Ag showing size distribution dependent tunable surface plasmon resonance (SPR) are grown on glass substrate using off-axis DC magnetron sputtering at a sputtering power of 74 W. Argon gas pressure is set at 8.0 Pa and the deposition time is varied in the range 5–300 s. The structural, morphological, and optical properties are examined by using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), and UV–Visible spectrophotometer. XRD patterns of all samples reveal characteristic (111) and (200) peaks of fcc Ag. Broad XRD peaks suggest formation of nanosized Ag crystallites with mean crystallite size of 3 nm. FESEM images depict near spherical Ag grains up to 120 s deposition time and elongated grains with greater substrate coverage with extended deposition time of 300 s. SPR features are well distinct in the optical absorption spectra which are highly sensitive to the deposition time. Within a short deposition time of 5–60 s, nanostructured Ag demonstrates wide range SPR tunability from 438 nm to 530 nm. It is observed that the variations in the size distribution as estimated from FESEM images are crucial to observe systematic red shift of SPR with increasing deposition time. Nanosized Ag produced by off-axis magnetron sputtering may be used as a vital component in plasmonic devices and sensors.

Ash Aerosol and Deposit Formation from Combustion of Coal and Its Blend with Woody Biomass at Two Combustion Scales: Part 1─1.5 MWTH Pilot-Scale Combustor Tests

There is great interest worldwide in repurposing electric utility boilers designed to fire pulverized coal to fire, instead woody biomass or blends of woody biomass with coal. In this investigation, two prepared biomass/coal blends and the pure parent coal were fired in a 1500 kW pulverized coal combustor with a primary objective of elucidating the mineral particle behavior. The results reported here, although complete in themselves, comprise the first part of a two-part systematic study to investigate the effects of combustion scale on ash deposition rates at scales of 1500 kW (this study), and 1.2 × 106 kW (471 MWe) using identical coal and coal/biomass fuels and similar analytical techniques. The woody biomass of interest was composed of materials collected in a Utah National Forest and was prepared using a torrefaction technique (for both combustion scales) and a separate steam explosion technique (for the 1500 kW pilot scale only, described here). Biomass samples were blended in 15 wt % biomass with a Utah bituminous coal and were pulverized along with samples of pure coal at a specification of 70 wt % passing through 200 mesh. To sample entrained and deposited mineral matter, a water-cooled extractive probe for ash aerosol and an air-cooled ash deposit probe were designed, constructed, and implemented. The probes were inserted into sample ports at gas temperatures in the range of 1200–1370 K with a deposit coupon surface temperature of 811 K, conditions representative of a utility boiler vertical reheater and of a fouling deposit mechanism. Aerosol size distributions were determined using a scanning mobility particle sizer (SMPS) and an aerodynamics particle sizer (APS), and a Berner low-pressure Impactor (BLPI) collected size-segregated aerosol samples for subsequent elemental analysis. A laser diffraction particle size analyzer (Beckman Coulter LS230) was used to determine the size distributions of ash deposit samples. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS) was used to determine the morphology and composition of ash deposit samples. For the pilot-scale tests reported here, the experimental results suggested little difference in mineral matter behavior between pure coal and biomass blends. The measured aerosol PSDs showed nearly identical behaviors, with modes at approximately 20 nm and 3 μm. The size-segregated aerosol particles were slightly enriched in Na, K, and Ca and deficient in Si and Al for biomass blends compared to the pure coal. The deposition rates were 60% greater in port 7 than in port 10 at 106 vs 65 g/(m2 h). Deposit samples collected for 90 min showed essentially the same deposition rate for coal and the two biomass blends, while short deposition times (30 min) suggested higher initial deposition rates for the biomass blends. The deposit composition and morphology were nearly identical for all three fuels.

Enhancing Photovoltage of Metal-Insulator-Semiconductor (MIS) Photoanode By Coordination Polymer Via Facile Chemical Deposition

Photoelectrochemical (PEC) water splitting is a promising route to convert intermittent sunlight into chemical fuels, which can be stored and used on-demand to produce electricity. One of the remaining challenges for the development of efficient PEC water splitting systems is related to the photoanode, which requires a high-performance light absorber with an excellent catalyst to drive the OER that needs high potential [1]. The metal-insulator-semiconductor (MIS) architecture employing Si as the photoanode is an attractive system due to the wide light absorption range of Si (Eg 1.1 eV) and high OER catalytic activity of metal [2-3]. For the latter, metal nanoparticles including Co and Ni can be dispersed on the semiconductor surface via electrodeposition in high-performance Si MIS photoanodes [2]. Furthermore, surrounding the metal nanoparticles and the uncoated Si with a higher-work-function material leads to significant improvement of photovoltage due to the pinch-off effect [4]. Up to this point, the surrounding layer is generally the oxidized phase of the base metal, such as its oxide or oxyhydroxide, and the fabrication techniques used to introduce the surrounding layer are limited to a few choices, i.e., electrodeposition, photodeposition, or annealing methods [4]. Copper(I) thiocyanate (CuSCN) is a coordination polymer which can be prepared by a simple chemical deposition through conversion of Cu [6]. Because Cu and CuSCN have work functions of 4.5-4.9 [7] and 5.4 eV [8], respectively, the Cu/CuSCN junction on n-Si is expected to develop the pinch-off region and increase the performance of Si/SiOx/Cu photoanode. In this presentation, we aim to highlight two key developments of Cu-based MIS Si photoanodes prepared by facile methods. Firstly, we employed electrodeposition to coat 30-nm Cu nanoparticles on n-Si, resulting in a photoanode with a low OER onset potential of 1.37 V vs reversible hydrogen electrode (RHE). Secondly, we added CuSCN on the n-Si/SiOx/Cu photoanode via a simple chemical deposition in an aqueous bath containing ammonium thiocyanate (NH4SCN) and ethylenediaminetetraacetic (EDTA). The presence of CuSCN on n-Si/SiOx/Cu was confirmed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectroscopy. The optimal n-Si/SiOx/Cu/CuSCN with a short CuSCN deposition time showed a 100-mV improvement in the onset potential relative to the unmodified n-Si/SiOx/Cu. Based on open-circuit-potential (OCP) measurements, the CuSCN-modified photoanode exhibited a high photovoltage of 460 mV. We believe that the findings can provide a new strategy for further surface modification of PEC devices to achieve efficient and low-cost solar harvesting technology.[1] Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev. 2010, 110 (11), 6446–6473.[2] Loget, G. Water Oxidation with Inhomogeneous Metal-Silicon Interfaces. Curr. Opin. Colloid Interface Sci. 2019, 39 (l), 40–50.[3] Aroonratsameruang, P.; Pattanasattayavong, P.; Dorcet, V.; Mériadec, C.; Ababou-Girard, S.; Fryars, S.; Loget, G. Structure–Property Relationships in Redox-Derivatized Metal–Insulator–Semiconductor (MIS) Photoanodes. J. Phys. Chem. C 2020, 124 (47), 25907–25916.[4] Laskowski, F. A. L.; Oener, S. Z.; Nellist, M. R.; Gordon, A. M.; Bain, D. C.; Fehrs, J. L.; Boettcher, S. W. Nanoscale Semiconductor/Catalyst Interfaces in Photoelectrochemistry. Nat. Mater. 2020, 19 (1), 69–76.[5] Lee, S. A.; Choi, S.; Kim, C.; Yang, J. W.; Kim, S. Y.; Jang, H. W. Si-Based Water Oxidation Photoanodes Conjugated with Earth-Abundant Transition Metal-Based Catalysts. ACS Mater. Lett. 2020, 2 (1), 107–126.[6] Xu, J.; Xue, D. Fabrication of Upended Taper-Shaped Cuprous Thiocyanate Arrays on a Copper Surface at Room Temperature. J. Phys. Chem. B 2006, 110 (23), 11232–11236.[7] Gartland, P. O.; Berge, S.; Slagsvold, B. J. Photoelectric Work Function of a Copper Single Crystal for the (100), (110), (111), and (112) Faces. Phys. Rev. Lett. 1972, 28 (12), 738–739.[8] Worakajit, P.; Hamada, F.; Sahu, D.; Kidkhunthod, P.; Sudyoadsuk, T.; Promarak, V.; Harding, D. J.; Packwood, D. M.; Saeki, A.; Pattanasattayavong, P. Elucidating the Coordination of Diethyl Sulfide Molecules in Copper(I) Thiocyanate (CuSCN) Thin Films and Improving Hole Transport by Antisolvent Treatment. Adv. Funct. Mater. 2020, 30 (36), 2002355.

Mass Transport in Nanoporous Gold and Correlation with Surface Pores for EC1 Mechanism: Case of Ascorbic Acid

AbstractThe present work correlates the mass transport of ascorbic acid (AA), which undergoes an electrochemical reaction accompanied by a first‐order chemical reaction (EC1 mechanism), with the size of surface pores of nanoporous gold (NPG) films. NPG films were electrodeposited on gold microelectrodes, generating polycrystalline, and highly porous surfaces. Studies of AA electrooxidation reveal mainly diffusional mass transport driven by EC1 pathways on the NPG electrodes prepared by changing the deposition potential. Similar studies on the NPGs prepared by changing the deposition time exhibit mainly diffusional transport at shorter deposition times, and largely an adsorption process driven by EC1 at longer deposition times. Such transition in the reaction pathways from diffusion EC1 to adsorption EC1 is correlated with the evolution of micrometer large surface pores in NPG films prepared at longer deposition times, allowing the diffusion of AA from the bulk solution to the volume of NPG, which enhances the adsorption probability.