Engineered Surface Structures Research Articles

Modulating the steric effect over high-index facet of MnOx catalysts to enhance toluene oxidation

Engineering surface structures of metal-oxide catalysts are of utmost significance for boosting their catalytic performances. In this work, we reported the high-index (310) facets catalysts (MnOx-AAUS) with oxygen vacancies for VOCs degradation, which was synthesized via an ultrasonic-assisted redox precipitation process. Interestingly, the excellent catalytic performance of MnOx-AAUS catalysts was due to the steric effect between high-index facet with reactants and the simultaneous adsorption-activation of toluene and gaseous oxygen on the high-index (310) facets with oxygen vacancies. The T90% value of the (310) facets catalysts (600 ppm toluene, GHSV = 60,000 mL/g·h, 21 % O2/N2) was significantly lower than that of the previous (001) facets catalysts. Density functional theory (DFT) calculations, along with in-situ FT-IR spectra, revealed that the tilted adsorption configuration of toluene was conducive to simultaneous reaction with the surrounding activated oxygen species. Such the adsorption configuration of toluene/oxygen contributed to the substantially enhanced catalytic activity of the MnOx-AAUS catalyst for VOCs oxidation. This work provides new insights into the roles of high-index facets with oxygen vacancies of MnOx catalysts in the toluene oxidation and paves new avenues for the rational design of highly efficient catalysts for oxidation reactions.

Facet selectively exposed α-MnO2 for complete photocatalytic oxidation of carcinogenic HCHO at ambient temperature

• The {1 0 0}, {1 1 0} and {3 1 0} facets in α-MnO 2 were selectively exposed. • α-MnO 2 with exposed {3 1 0} facets can complete photocatalytic oxidation of HCHO. • Photothermal activity of {3 1 0} facet is consistent with photocatalysis mechanism. • This is the first report on facets control of α-MnO 2 as efficient photocatalysts. Formaldehyde (HCHO) causes increasing concerns due to its ubiquitously found in the indoor environment and being irritative and carcinogenic to humans. Therefore, the complete removal of HCHO at room temperature is meaningful. Crystal facet engineering has appeared as a significant strategy for designing efficient catalysts. It is an effective way to improve the catalytic activity by selectively exposing the highly reactive crystal facets. Herein, the {1 0 0}, {1 1 0}, and {3 1 0} facets in α-MnO 2 were selectively exposed, and the differences in the properties and photocatalytic activity of crystal facets have been carefully compared. Specifically, α-MnO 2 with exposed {3 1 0} facets exhibited superior photocatalytic activity, achieving 100% conversion of carcinogenic airborne HCHO under the solar-light irradiation and even 78% removal efficiency under visible light. Interestingly, it is found that the high activity of {3 1 0} facet with solar-light irradiation is consistent with the photocatalysis mechanism, rather than solar-light-driven thermocatalysis mechanism. Furthermore, it is confirmed that the {3 1 0} facet can not only promote the effective separation of electron and hole, but also benefit the activation of O 2 , which leads to substantially improved photocatalytic activity. This is the first report on engineering surface structures and facets control in the preparation of α-MnO 2 as highly efficient photocatalysts.

Pathogen-Repellent Plastic Warp with Built-In Hierarchical Structuring Prevents the Contamination of Surfaces with Coronaviruses.

Amidst the COVID-19 pandemic, it is evident that viral spread is mediated through several different transmission pathways. Reduction of these transmission pathways is urgently needed to control the spread of viruses between infected and susceptible individuals. Herein, we report the use of pathogen-repellent plastic wraps (RepelWrap) with engineered surface structures at multiple length scales (nanoscale to microscale) as a means of reducing the indirect contact transmission of viruses through fomites. To quantify viral repellency, we developed a touch-based viral quantification assay to mimic the interaction of a contaminated human touch with a surface through the modification of traditional viral quantification methods (viral plaque and TCID50 assays). These studies demonstrate that RepelWrap reduced contamination with an enveloped DNA virus as well as the human coronavirus 229E (HuCoV-229E) by more than 4 log 10 (>99.99%) compared to a standard commercially available polyethylene plastic wrap. In addition, RepelWrap maintained its repellent properties after repeated 300 touches and did not show an accumulation in viral titer after multiple contacts with contaminated surfaces, while increases were seen on other commonly used surfaces. These findings show the potential use of repellent surfaces in reducing viral contamination on surfaces, which could, in turn, reduce the surface-based spread and transmission.

Engineering Single Atom Catalysts to Tune Properties for Electrochemical Reduction and Evolution Reactions

AbstractElectrocatalysis is important to the conversion and storage of renewable energy resources, including fuel cells, water electrolysers, and batteries. Engineering metal‐based nano‐architectures and their atomic‐scale surfaces is a promising approach for designing electrocatalysts. Single metal atom interactions with substrates and reaction environments crucially modulate the surface electronic properties of active metal centers, yielding controllable scaling relationships and transitions between different reaction mechanisms that improve catalytic activity. Single‐atom catalysts (SACs) allow activity and selectivity tuning while maintaining relatively consistent morphologies. SACs have well‐defined configurations and active centers within homogeneous single‐atom dispersions, producing exceptional selectivities, activities, and stabilities. Furthermore, SACs with high per‐atom utilization efficiencies, well‐controlled substrate compositions, and engineered surface structures develop single atom active sites for molecular reactions, enhancing mass activities. Recent developments in different metal‐based SAC nanostructures are discussed to explain their remarkable bi‐functional electrocatalytic activities and high mechanical flexibility, especially in the oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, hydrogen evolution reaction, and in battery applications. Existing barriers to and future insights into improving SAC performance are addressed. This study develops practical and fundamental insights on single atom electrocatalysts directed towards tuning their electrocatalytic activities and enhancing their stabilities.

Surface/Near‐Surface Structure of Highly Active and Durable Pt‐Based Catalysts for Oxygen Reduction Reaction: A Review

Proton exchange membrane fuel cells (PEMFCs) are highly promising energy‐conversion devices because of their zero‐emission and high efficiency. A great deal of Pt is of significant necessity on the cathode to accelerate the rate of kinetically sluggish oxygen reduction reaction (ORR) and maintain the long‐term operation, leading to the prohibitive cost of PEMFCs and limiting their widespread deployment. In the past decades, numerous efforts including manipulation of composition, morphology, and structure have been devoted to improving their higher activity and stability, but still lag behind the actual requirement. ORR is a typical surface‐sensitive electrochemical reaction and its process is mainly determined by surface/near‐surface structure. Herein, the recent advances in the manipulation of surface structure are summarized. The ORR mechanism and evaluation method for activity and stability are introduced. Then, solutions toward the engineering of surface structure and its effect on activity and stability are presented. Finally, comments on the future direction of nanocatalysts for ORR are presented in terms of engineered surface structure.

Influence of Antimycin A, a bacterial toxin, on human dermal fibroblast cell adhesion to tungsten-silicon oxide nanocomposites

Nano- and micro-scale engineered surface structures are often used to control cell morphology and mimic the extracellular matrix in tissue engineering. However, there is little understanding of how toxins produced by common bacteria might affect cell adhesion to these structures. In this study, human dermal fibroblast (GM5565) cells were incubated on patterned tungsten/silicon oxide nanocomposite in media in the presence or absence of Antimycin A. This composite consists of parallel tungsten and silicon oxide lines with identical widths in the range of 0.18 and 50 μm. The morphology of the cells and of their mitochondria was characterized by using high-resolution scanning electron microscopy and fluorescence confocal microscopy. Results show that cells preferentially align along the line axes in a pattern-dependent manner, with a maximum population of cells oriented within 10° of the line axes on the structures containing 10 μm wide lines. Cells treated with Antimycin A, however, show a smaller proportion of cells oriented in this direction as compared to cells cultured in Antimycin A-free media (34.4% vs 53.0%). The majority of mitochondria in cells growing in Antimycin A-free media are tubular in shape and are preferentially positioned on the tungsten lines, whereas these organelles exhibit a circular geometry and are less attracted to the metal lines in the presence of Antimycin A.

First beam test of Laser Engineered Surface Structures (LESS) at cryogenic temperature in CERN SPS accelerator

Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the electron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression.

Improving Purge Air Cooling Effectiveness by Engineered End-Wall Surface Structures—Part II: Turbine Cascade

Motivated by the recent advances in additive manufacturing, a novel turbine end-wall aerothermal management method is presented in this two-part paper. The feasibility of enhancing purge air cooling effectiveness through engineered surface structure was experimentally and numerically investigated. The fundamental working mechanism and improved cooling performance for a 90 deg turning duct are presented in Part I. The second part of this paper demonstrates this novel concept in a low-speed linear cascade environment. The performance in three purge air blowing ratios is presented and enhanced cooling effectiveness and net heat flux reduction (NHFR) were observed from experimental data, especially for higher blow ratios. The Computational fluid dynamics (CFD) analysis indicates that the additional surface features are effective in reducing the passage vortex and providing a larger area of coolant coverage without introducing additional aerodynamic loss.

Improving Purge Air Cooling Effectiveness by Engineered End-Wall Surface Structures—Part I: Duct Flow

Motivated by the recent advances in additive manufacturing, this study investigated a new turbine end-wall aerothermal management method by engineered surface structures. The feasibility of enhancing purge air cooling effectiveness through a series of small-scale ribs added onto the turbine end-wall was explored experimentally and numerically in this two-part paper. Part I presents the fundamental working mechanism and cooling performance in a 90 deg turning duct (part I), and part II of this paper validates the concept in a more realistic turbine cascade case. In part I, the turning duct is employed as a simplified model for the turbine passage without introducing the horseshoe vortex. End-wall heat transfer and temperature were measured by the infrared thermography. Computational fluid dynamics (CFD) simulation was also performed using ANSYS fluent to compliment the experimental findings. With the added end-wall rib structures, purge air flow was observed to be more attached to the end-wall and cover a larger wall surface area. Both experimental and numerical results reveal a consistent trend on improved film cooling effectiveness. The practical design optimization strategy is also discussed in this paper.

Performance Improvement of V-Fe-Cr-Ti Solid State Hydrogen Storage Materials in Impure Hydrogen Gas.

Two approaches of engineering surface structures of V-Ti-based solid solution hydrogen storage alloys are presented, which enable improved tolerance toward gaseous oxygen (O2) impurities in hydrogen (H2) gas. Surface modification is achieved through engineering lanthanum (La)- or nickel (Ni)-rich surface layers with enhanced cyclic stability in an H2/O2 mixture. The formation of a Ni-rich surface layer does not improve the cycling stability in H2/O2 mixtures. Mischmetal (Mm, a mixture of La and Ce) agglomerates are observed within the bulk and surface of the alloy when small amounts of this material are added during arc melting synthesis. These agglomerates provide hydrogen-transparent diffusion pathways into the bulk of the V-Ti-Cr-Fe hydrogen storage alloy when the remaining oxidized surface is already nontransparent for hydrogen. Thus, the cycling stability of the alloy is improved in an O2-containing hydrogen environment as compared to the same alloy without addition of Mm. The obtained surface-engineered storage material still absorbs hydrogen after 20 cycles in a hydrogen-oxygen mixture, while the original material is already deactivated after 4 cycles.

First accelerator test of vacuum components with laser-engineered surfaces for electron-cloud mitigation

Electron cloud mitigation is an essential requirement for high-intensity proton circular accelerators. Among other solutions, laser engineered surface structures (LESS) present the advantages of having potentially a very low secondary electron yield (SEY) and allowing simple scalability for mass production. Two copper liners with LESS have been manufactured and successfully tested by monitoring the electron cloud current in a dipole magnet in the SPS accelerator at CERN during the 2016 run. In this paper we report on these results as well as the detailed experiments carried out on samples—such as the SEYand topography studies—which led to an optimized treatment in view of the SPS test and future possible use in the HL-LHC.

(Invited) Engineering Surface Structures and Energetics of α-Fe2O3 and p-Si for Efficient Solar Water Splitting

Solar hydrogen conversion via photoelectrochemical water splitting is an important technology for energy and environment sustainability. Since the pioneering work of Fujishima and Honda in 1972, tremendous research on semiconductor-based photoelectrochemical water splitting has yielded better understanding of the processes as well as encouraging development of high efficiency photoelectrodes for solar hydrogen generation. In this talk, some recent progresses in heterostructures of α-Fe2O3and p-Si for photoelectrochemical solar water splitting in our group will be introduced. Given the narrow band gap enabling excellent optical absorption, increased charge carrier density and accelerated surface oxidation reaction kinetics become the key points for improved photoelectrochemical performances for water splitting over α-Fe2O3 photoanodes. By engineering the surface structures of α-Fe2O3 nanorods with AgxFe2-xO3, TiO2 and HfO2overlayers, the surface charge recombination was greatly inhibited and the surface water oxidation kinetics were efficiently accelerated, resulting in remarkable enhancement in PEC water splitting performances. p-Si has captured intensive attentions for solar hydrogen conversion due to its high natural abundance and narrow band gap (~1.1 eV). However, the slow charge-transfer kinetics at the p-Si/electrolyte interface lead to large overpotentials for hydrogen evolution and electrocatalysts are always necessary. Recently, we successfully engineered the surface energetics of p-Si with n-WO3 overlayer and Ni molecular complexes, which gave rise to a great anodic shift of up to 300 mV in onset potential for photocathodic water reduction.

Surface feature engineering through nanosphere lithography

How surface geometries can be selectively manipulated through nanosphere lithography (NSL) is discussed. Self-assembled monolayers and multilayers of nanospheres have been studied for decades and have been applied to lithography for almost as long. When compared to the most modern, state-of-the-art techniques, NSL offers comparable feature resolution with many advantages over competing technologies. Several high-resolution alternatives require scan-based implementation (i.e., focused ion beams and e-beam lithography) while NSL is much more of a batch operation, allowing for full wafer or possibly even multiple wafer processing, potentially saving time and increasing throughput in a manufacturing environment. Additionally, NSL has continued to be of interest because it does not require expensive, complex equipment to be researched and realized, which continues to fuel interest in this approach. In spite of these advantages, applying NSL to specific, realizable devices is limited in the literature. The reason for this lack of application is not only unreliability in the self-assembly process, but also control of these patterned nanospheres within larger, multistep processes often required to fabricate most devices. Both of these items are addressed in this paper. The first issue was addressed through the development of a series of custom-designed nanosphere application vessels. These were designed based on the best published results from the literature, utilizing an alternate method of dip-coating but performed through draining the carrier fluid over the substrate rather than moving the substrate across the liquid–air boundary layer. This method is in the easier to perform, but arguably less-reliable spin-coating method also commonly employed. The key enabler in this effort lies in commercially available three-dimensional (3-D) printing technology, and how it was applied to rapidly prototype-improved deposition vessels. This was accomplished primarily with a single day turn-around between each 3-D printed design iteration. Each vessel design was incrementally improved, built, and tested to optimize the best performance in achieving the most reliable, repeatable self-aligned nanosphere layer formation. With an optimized design of this vessel in hand, the second challenge was addressed by using this vessel and the patterned nanosphere layers it produced with a patterned photoresist design to capture single layers of nanospheres in specifically designed locations and orientations. The hybrid mask produced from this approach can be integrated within virtually any multistep fabrication process. Additionally, other processing steps will be discussed, such as reactive ion etching (RIE), plasma ashing, and photoresist reflowing, and how they might be combined with these hybrid masks. Various results from combinations of these steps are presented. Finally, two potential applications which could benefit greatly from the resulting, engineered surface structures are discussed. These include a small-scale device application (engineering the contacting surfaces in a microswitch), as well as a much larger scale surface study application (surface engineering for controlling secondary electron emissions). The final results from this method allow for patterning groups of 500-nm polystyrene nanospheres formed in four to eight distinct rows each. These are positioned within patterned wells created in a 650-nm thick photoresist. The size and location of these wells are as precise as the photolithography process used to form them, in this case, ∼40-nm position error in the location of the edge of the laser using a Heidelberg laser lithography system. By combining multiple wells in close proximity, virtually any combination of nanosphere clusters become possible. Once patterned, postprocessing though RIE and deposition method selection together determine the final shape of the nanoscale features which result.

Using GIS Software for Identification and Zoning of the Areas Prone to Liquefaction in the Bed Soil of the Dams

One of the processing seismic geotechnical problems of the researchers and the expert engineers is the liquefaction in the uncompressed saturation soil seed which could highly harm the engineering surface and underground structures. The main goal in this research is to use GIS software for identification and zoning of the areas prone to liquefaction in the bed soil of the dams. In this research the data of Nazlou dam in Urmia are used. When the liquefaction potential (PL) is evaluated via different methods, the zoning plan of risk intensity of the liquefaction of the soils was produced using GIS software. The results show that the use of GIS software for zoning of the areas prone to liquefaction in the bed soil of the dams is appropriate. Geotechnical engineers are able to preparation the zoning GIS map with desired method and to optimize the bed soil of that part in any depth and bore using the different existing methods in this field with more accuracy which finally leads to the increase of the security of the dam and decrease of the construction costs.

Femtosecond laser surface structuring technique for making human enamel and dentin surfaces superwetting

It is known that good wettability of enamel and dentin surfaces is a key factor in enhancing adhesion of restorative materials in dentistry. Here, we report on a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this new approach produces engineered surface structures. The surface structure engineered and tested here is an array of femtosecond laser-produced parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

Making human enamel and dentin surfaces superwetting for enhanced adhesion

Good wettability of enamel and dentin surfaces is an important factor in enhancing adhesion of restorative materials in dentistry. In this study, we developed a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this approach produces engineered surface structures. The surface structure engineered and tested here is an array of parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

The effect of E-beam engineered surface structures on attachment, proliferation and differentiation of human mesenchymal stem cells

Electron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants. The effect of two newly designed highly porous E-beam engineered surface structures (cubic and star) on attachment, proliferation and differentiation of human mesenchymal stem cells (hMSCs) was investigated and compared to a solid sandblasted control. SEM analysis showed that the E-beam structures allowed cells to attach and spread. Proliferation on the new surface structures was comparable to the solid control. Furthermore, differentiation on the 3D structures was comparable to the control specimen. When culturing 300,000 cells for 10 days, the cubic structure showed a significantly higher differentiation rate compared to the sandblasted specimen. We conclude that the results for attachment, proliferation and differentiation of mesenchymal stem cells on the newly engineered 3-dimensional E-beam surface topographies are promising. In vivo experiments are necessary to assess the bone ingrowth potential of the new surface structures.

Molecular electronics

Current work in molecular electronics usually addresses molecular junction electronic transport properties, where the molecule can be viewed as a barrier for incoming electrons. This is the fundamental Landauer idea of “conduction as scattering” generalized to metal/single molecule/metal molecular nanojunction structures. The experimental contributions from the Gourdon and Hersam groups focus on the tunneling process in molecular transport junctions, using powerful and elegant techniques involving both demanding single-molecule junction synthesis and scanning tunneling microscopy and spectroscopy. The paper by Ho's group extends these experimental methods to examine vibronic components in the STM-geometry conductance, using precisely engineered surface structures. The contribution by Fisher and Ness addresses those inelastic effects in junction transport from a theoretical point of view. The papers from the Mayor and Kushmerick groups address such transport issues as fluctuation and vibronic features of molecular electronic wires by using break-junction and monolayer test beds.