Surface Preparation Procedures Research Articles

(Invited) (Photo-)Electrochemical Reactions on Semiconductor Surfaces:Si and III-V Surfaces – Atomic and Electronic Structure

Semiconductor/electrolyte interfaces are used in many application areas where strong non linear variations in the electric performance depending on applied potential or due to illumination play a decisive role. Often a simplified explanation on charge redistribution across the semiconductor/electrolyte junctions is applied considering only the charge redistribution involving the bulk and the electrolyte following an idealized semiconductor /metal Schottky barrier model. But as will be addressed in our contribution strong deviations are usually observed in real devices which are due to Fermi level pinning effects and adsorbate related double layer potential shifts of the band edges. This is especially true for photoelectrochemical cells used in water splitting devices. For this reason we will present detailed surface science studies on the properties of Si and III-V surfaces espcially by applying photoelectron spectroscopy.In so-called model experiments the effect of surface states found on differently doped Si(111) and (100) surfaces is investigated in relation to the resulting surface electronic structure after appying different surface preparation and processing procedures. Additionally the reactivity and the changes in electronic structure following a „frozen electrolyte“ junction formation will be presented after water exposure at low sample temperature. The results are compared to photoelectrochemical cells based on Si single crystals as well as thin film multiabsorber cells used as photocathodes.For III-V semiconductors at first the surface properties of etched InP, GaP and GaInP (100) surfaces will be compared and further modified by subsequent vacuum based processing steps as heating and sputtering. The best surfaces are in their surface composition very close to samples prepared by MOCVD. Also for the III-V materials the interaction with H2O was investigated. In all cases Fermi level pinning close to the valence band maximum was observed and compared to the resulting band diagrams of photoelectrochemical devices used for HER.In combining photoelectrochemical studies with surface science investigations on the electrode properties using directly contacted but also buried junction photoelectrodes it can be shown that defect levels related to remaining dangling bond states play a dominant role for the performance of the devices. The concentration of the remaining defect states influence the obtained performance in dependence of the interfacial contact composition preferring the formation of buried junctions. In conclusion we suggest that surface science studies of photoelectrodes before and after electrochemical studies are essential and need to be further developed for in operando experiments with special emphasis also in the valence band regime to obtain improved insights into semiconductor/electrolyte junction properties.

Disposable electrochemical sensor for tryptamine detection using a graphite sheet electrode modified with poly(toluidine blue)

Tryptamine (TRYP) is a biogenic amine present in several foods and beverages, and despite some beneficial effects on human health, high intakes of TRYP can be harmful. Therefore, accurate analytical methods for TRYP quantification in food samples are necessary. This study describes a cost-effective electrochemical sensor for TRYP determination in cheese samples based on a poly(toluidine blue) (PTB) film electropolymerized onto graphite sheets (GS). Electrode preparation involved two simple steps: (1) electropolymerization of toluidine blue by potential cycling in phosphate buffer solution, and (2) PTB overoxidation by potential cycling in a 0.1 mol L–1 KOH solution. The overoxidation of PTB led to a remarkable increase in sensitivity and detectability towards TRYP, due to the introduction of negatively charged groups that electrostatically preconcentrate TRYP at electrode surface. Using square wave voltammetry, a linear range for TRYP from 0.05 to 0.9 μmol L−1 (0.008 – 0.144 ppm) was achieved with a detection limit of 12 nmol L−1 (0.002 ppm). Also, the electrodes exhibited a remarkable antifouling ability leading to highly reproducible voltammetric responses for TRYP. In addition to being inexpensive (disposable), GS substrates enabled PTB electropolymerization with no need for cleaning or surface preparation procedures. Therefore, the approach described here proved to be promising for the simple, inexpensive, and accurate determination of TRYP in cheese samples.

Dangling Bond Defects on Si Surfaces and Their Consequences on Energy Band Diagrams: From a Photoelectrochemical Perspective

Using silicon in multijunction photocells leads to promising device structures for direct photoelectrochemical water splitting. In this regard, photoelectron spectra of silicon surfaces are used to investigate the energetic condition of contact formation. It is shown that the Fermi‐level position at the surface differs from the values expected from their bulk doping concentrations, indicating significant surface band bending which may limit the overall device efficiency. In this study, the influence of different surface preparation procedures for p‐ and n‐doped Si wafers on surface band bending is investigated. With the help of photoemission and X‐ray absorption spectroscopy, Si dangling bonds are identified as dominating defect centers at Si surfaces. These defects lead to an occupied defect band in the lower half and an unoccupied defect band in the upper half of the Si bandgap. However, partial oxidation of the defect centers causes a shift of defect bands, with only donor states remaining in the Si bandgap. Source‐induced photovoltages at cryogenic temperatures indicate that partial surface oxidation also decreases the recombination activity of these defect centers. It is shown that defect distribution, defect concentration, and source‐induced photovoltages need to be considered when analyzing Fermi‐level pinning at Si surfaces.

Surface Preparation for Single-Molecule Fluorescence Imaging in Organic Solvents.

The development of single-molecule techniques provides opportunities to investigate the properties and heterogeneities of individual molecules, which are almost impossible to be obtained in ensemble measurements. Recently, single-molecule fluorescence microscopy is being applied more and more to study chemical reactions in organic solvents. However, little has been done to optimize the surface preparation procedures for single-molecule fluorescence imaging in organic solvents. In this work, we developed a method to prepare the surface for single-molecule fluorescence imaging in organic solvents with a well-controlled surface density of chemically immobilized dye molecules and a low density of nonspecifically adsorbed impurities. We also compared the surfaces prepared by two different procedures and studied the impacts of the polarities of the solvent and the surface functionality on the quality of prepared surface. We found that higher polarities of both the solvent and the surface functionality provided better control of the surface density of chemically immobilized dyes and helped reduce the nonspecific adsorption of both dyes and fluorescent impurities in organic solvents. We further performed single-molecule fluorescence imaging in DMF and investigated the photophysical properties of dyes and fluorescent impurities, which could be used to filter out false counts in single-molecule fluorescence measurements.

Effect of surface preparation on PtSe2 crystal surface morphology

Transition metal dichalcogenides, a new class of layered materials, have recently been deemed as an excellent material platform for the further development of microelectronics. Contrary to the general trend, which is geared toward layers, we focus our attention on basic research regarding bulk PtSe2. The justification for this approach is based on the fact that some research (e.g., on the impact of the doping process on the material’s properties) can be performed on the bulk crystal. We believe that the conclusions drawn from our approximation can be extrapolated to thin films and monolayers. In this paper, we present a morphological study of the influence of the surface preparation procedure on the PtSe2 substrate. We show that mechanical exfoliation is one possible way to achieve a clean PtSe2 surface. However, STM measurements revealed that this process is insufficient to achieve an atomically clean surface. Subsequent additional annealing under UHV conditions led to an improved surface morphology by reducing the number of mobile PtSe2 flakes as well as the density of small surface clusters. Finally, STM measurements show other interesting surface structures, such as cracks, bulges, and flakes with heights lower than the apparent height typical of a PtSe2 monolayer.

Nanoindentation mapping defects filtration for heterogeneous materials using generative adversarial networks

Advanced composite materials with multiple phases and heterogeneous microstructure necessitate spatial mapping characterization of elastic modulus to develop constitutive relations and overall mechanical response. Such modulus mapping can be obtained using the nanoindentation technique, where the indenter tip raster over the selected microstructure region. Typically, a surface preparation procedure is done in the specimens to ensure proper contact between the indenter tip and sample surface. However, a near-perfect surface finish is unachievable in heterogeneous materials, primarily with ceramic reinforcements, due to the differential material removal rate during polishing. Thus, the nanoindenter records localized erroneous measurements due to differences in surface roughness and corresponding force response. This study establishes a novel deep learning-based strategy to rectify incorrect experimental spatial measurements acquire during nanoindentation modulus mapping. The integrated bicubic interpolation and generative adversarial networks (GANs) model was trained using 14 ceramic and 18 metallic data sets, each comprising 65,536 measurements. The developed algorithm was validated against experimental measurements on four unknown specimens. The standard deviation in measured elastic modulus reduces by ~50% in ceramics and ~ 72% in metallic samples. This computational framework proposes a novel approach to reducing uncertainty in materials' properties using state-of-the-art computer vision techniques.

Optimization of delamination resistance of vacuum infused glass laminate aluminum reinforced epoxy (GLARE) using various surface preparation techniques

GLARE (glass-reinforced fibre–metal laminate ) is aluminum based material of fiber metal laminate (henceforth FML) that is often fabricated by expensive autoclave procedure. In this study, the process of Injected Molding or (also known as VARTM was employed as a cost-effective alternative to produce GLARE. Several aluminum surface preparation procedures are applied to improve the interlaminar shear strength. A T3 temper 2024 aluminum alloy with 1*1 plain fabricated glass fabrics were used to make GLARE composites. GLARE consists of two aluminum sheet as external layer and glass fabric as internal layers. Four sets of aluminum sheets were prepared, one unanodized and three other anodized. Three different anodizing procedures (constant voltage mode, increasing voltage mode and decreasing voltage mode) have been adopted in this research. Two types of curing treatments were applied on VARTM fabricated specimens. According to ASTM D1876 T-peel test standard, the sets of prepared specimens have been tested to examine the adhesive bonding strength and fracture toughness of mode-I. The obtained results which include force-displacement curves, peak loads and fracture toughness were showed that a significant improvement for anodized specimens with all voltage modes. The first curing treatment offered better results than second curing treatment. The best improvement was obtained from anodized specimen with decreasing voltage mode cured by the first treatment which reaches to six times the results obtained from unanodized specimen. The delamination behavior for this specimen was verified numerically.

Comparison of Electrical Contacting Techniques to Carbon Fiber Reinforced Plastics for Self-Strain-Sensing Applications

The electrical conductivity of carbon fibers can be used to enable the design of intrinsically smart carbon fiber reinforced plastics (CFRPs). Resistance and impedance measurements of the structural material itself can then be used to measure physical stimuli such as strain or damage without requiring a dedicated sensor to be installed. Measuring the resistance with high precision requires good electrical contact between the measurement equipment and the conductive carbon fibers. In the literature, many different combinations of surface contacting material and surface preparation procedures are used, but only seldomly compared to one another. This article aims to compare frequently used electrical contact methods by analyzing their contact resistance to a pultruded CFRP rod. Furthermore, this study explores the change of contact resistance with increasing mechanical strain. The results show that contact resistance is highly dependent on both the material used for contacting the fibers as well as the surface preparation technique. From the combinations analyzed in this article, the electrodeposition in combination with a surface treatment using concentrated sulphuric acid shows the most promising results.

Surface structure and quenching effects in BiFeO3‐BaTiO3 ceramics

AbstractThe structure and properties of Mn‐doped 0.67BiFeO3‐0.33BaTiO3 ceramics are systematically investigated with respect to the effects of annealing prior to rapid cooling by quenching in air. Air‐quenching induces a change in crystal structure from pseudo‐cubic to rhombohedral, with higher quenching temperatures leading to an increased rhombohedral distortion. These structural changes are correlated with the appearance of more well‐defined ferroelectric domain configurations. It is shown that the surface preparation procedures for XRD measurements can induce significant changes in the peak profiles, indicating differences in crystal structure between the surface and bulk regions. Frequency dispersion in the temperature‐dependent relative permittivity for the as‐sintered sample is significantly reduced after quenching, accompanied by enhancement of the Curie point and improved temperature‐stability of piezoelectric properties. It is proposed that the formation of defect clusters by A‐site cation diffusion during cooling is circumvented by quenching, leading to the observed modification of structural distortion and ferroelectric properties.

Adhesion of AlCrN coating deposited on TiB2/Ti composites sintered by SPS dedicated for high temperature tribological applications

The aim of the work was to investigate the adhesion of AlCrN coating deposited by PVD method on TiB2/Ti composites manufactured by Spark Plasma Sintering (SPS). The composites were produced from three kinds of mixtures of powders: (1) Ti and TiB2, (2) Ti6Al4V and TiB2 and (3) Ti and B. Each of the mixtures was prepared at 50/50 wt. % ratio of components. Before the coating deposition the specimens were polished to obtain the surface roughness typically required for machine parts. For each set of specimens an individual surface preparation procedure was developed. The coating adhesion was measured using a scratch tester. The process of scratching was carried out to observe the characteristic moments of adhesive and cohesive failures. The highest critical loads were obtained for the coating deposited on composites produced from the mixture of two powders containing pure Ti and TiB2.

Turkey Berries Leaves Extract as Corrosion Inhibitor Embedded Steel in Concrete

Different approaches such as surface preparation and cathodic protective procedures traditionally used have been used for corrosion reduction. Corrosion inhibitors have proved to be the most cost-effective and simple method for protecting and corrosion protection of the concrete embedded steel. The inhibitors reduce the rate of corrosion, preventing monetary damages incurred by metallic corrosion on steels. The toxicity of conventional bio-toxic organic compounds is a significant concern. Eco-friendly, non-toxic green inhibitors are the focus of intensive research. This research focuses on acidic solutions to imitate manufacturing processes on methods of corrosion preventive use of turkey-leaves extract-based corrosion inhibitors for steel. The dosage percentage will be raised by 0.5%, 1.0%, 1.5%, 2.0% and 2.5%. The present work provides an overview of corrosion forms, the corrosion mechanism and, in particular, a current application research is turkey leaves extracts as corrosion inhibitors in steel production.

The effect of different surface preparation methods and various aging periods on microtensile bond strength for composite resin repair.

To evaluate the effect of various aging periods and different surface preparation methods on microtensile bond strength (μTBS) for composite repair. One hundred twelve composite resin blocks were formed using a nanohybrid composite resin. The samples were distributed into four groups according to surface preparation methods (n = 28): control (sound composite blocks); Er, Cr: YSGG laser; air abrasion; silicone carbide. All samples were then divided into four subgroups according to various aging periods: (i) No aging, (ii) 10,000 thermocycling, (iii) 30,000 thermocycling, and (iv) 50,000 thermocycling. Following surface preparation and aging procedures, surface topography of one sample from each group was evaluated under scanning electron microscope (SEM). The repair composites were bonded to the sample surfaces, using a three-step etch&rinse adhesive. Finally, thirty beams of size 1 × 1 × 8 mm from each group were subjected to μTBS test and failure modes were determined. The data were analyzed using two-way ANOVA, Post-hoc Bonferroni, and Chi-square tests (P = 0.05). When different surface preparation methods were evaluated together, no aging and 10,000 thermocycling groups displayed higher μTBS values (P < 0.05). When all aging periods were evaluated together, the surface preparation with air abrasion provided higher μTBS (P < 0.05). The interactions of various aging periods with different surface preparation methods revealed significant variations in repair μTBS (P < 0.05). There were statistically significant differences on failure mode distributions among surface preparation methods (P < 0.001). SEM evaluations provided valuable outcomes that help to comment on the μTBS findings. Different surface preparation methods, various aging periods, and the interaction of both affected the repair μTBS of the tested nanohybrid composite resin.

Surface Treatments Effect on Carbon Fiber Composite-Different Alloy Adhesion Performance

Carbon fiber reinforced composites have a wide range of uses, especially in aviation and aerospace, marine and automotive. The adhesion properties of these high-tech materials with other materials are critical. Adhesive selection, surface treatment type and surface preparation procedures control adhesion performance. In this study, the effect of surface treatments that increase adhesion strength in carbon fiber composite (CFRP) structures was investigated. In order to improve the adhesion properties of carbon fiber composite materials with different metals, mechanical and physical surface treatment techniques have been used. 7075 aluminum alloy (Al) and 304 stainless steel alloy (SS) were subjected to sandblasting and plasma activation processes after surface cleaning in experimental studies. After surface activation processes, the surface wetting angle was measured and adhesion tests were carried out. In experimental results, it has been observed that plasma and sandblasting processes increase adhesion strength by 30-50%.

Fractographic analysis of the hygrothermal effect in co-bonded and secondary bonded joints under mode II delamination loading

Adhesive bonding technologies exhibit several advantages over conventional mechanical fasteners which include lower weight, reduced stress concentration in the adherents and excellent fatigue properties allowing the design of smooth surface contour and damage tolerant aerostructures. The overall structural performance of the composite joint depends on several factors related to the manufacturing process, such as surface preparation procedure, adhesive type, aging effects, and deficiency of inspection procedures. For this reason, there is a clear need to understand better how the joints behavior can be affected by them and the causes of their failure in order to improve the design and performance. In this context, this work presents the application of Scanning Electron Microscopy (SEM) technique to perform the fractographic analysis in two different types of joints namely co-bonded (CB) and secondary bonding (SB) that were submitted to a interlaminar fracture toughness tests under Mode II loading at Room Temperature Ambient (RTA) and Environmental Temperature Wet (ETW) conditions. The fracture surface of each sample submitted Mode II was prepared and analyzed regarding its failure aspects, enabling their association with the mechanical behavior of the samples during the fracture toughness tests and the values obtained. A detailed study on the fracture aspects of the composite joints was carried out correlating the fracture aspects with the mechanical behavior, type of processing and environmental conditioning in which each type of joint was tested, thus validating the use of these joints for operating conditions similar to those experienced in-service concerning aeronautical applications.

VOx molecular level grafted g-C3N4 for highly selective oxidation of methanol to dimethoxymethane

A composite material VOx/g-C3N4 was prepared and its composition and structure was characterized by FT-IR, XRD, SEM, TEM and XPS. The results showed that VOx was grafted on g-C3N4 surface with molecularlevel dispersion via V or O atoms interacting with the characteristic groups on g-C3N4 surface. The highly dispersed VOx/g-C3N4 exhibited effectively catalytic activity and high selectivity for oxidation of methanol into methoxymethane (DMM), giving 44.9 mol/(molV·h) TOF and 95.2% selectivity of DMM. The dependence of catalytic activity on the surface properties and preparation procedure of the catalyst, reaction conditions and kinetics, and the stability of the catalyst were explored. Also, the in situ DRIFTS spectra of methanol adsorption on the VOx/g-C3N4 surface and effect of O2 on the adsorption, as well as the reaction mechanism were discussed.

Surface Preparation for Single-Molecule Chemistry

Immobilization procedures, intended to enable prolonged observation of single molecules by fluorescence microscopy, may generate heterogeneous microenvironments, thus inducing heterogeneity in the molecular behavior. On that account, we propose a straightforward surface preparation procedure for studying chemical reactions on the single-molecule level. Sensor fluorophores were developed, which exhibit dual-emissive characteristics in a homogeneously catalyzed showcase reaction. These molecules undergo a shift of fluorescence wavelength of about 100 nm upon Pd(0)-induced deallylation in the Tsuji-Trost reaction, allowing for separate visualization of the starting material and product. Whereas a simultaneous immobilization of dye and inert silane leads to strongly polydisperse reaction kinetics, a consecutive immobilization routine with deposition of dye molecules as the last step provides substrates underlying the kinetics of ensemble experiments. Also, the found kinetics are unaffected by the chemical variation of inert silanes, nearly uniform, and therefore well reproducible. Additional parameters like photostability, signal-to-noise ratio, dye-molecule density, and spatial distribution of dye molecules are, as well, hardly affected by surface modification in the successive immobilization scheme.

Si-Ge Heterostructures Fabricated by Room Temperature Wafer Bonding

A newly developed technology was used for in situ surface activation and wafer bonding of silicon and germanium substrates in order to achieve high quality, full strength, room temperature covalent wafer bonding. An ion beam was employed for the surface preparation procedure, resulting in contamination-free substrates with low bulk damage.After surface preparation the substrates were handled and placed into contact under high vacuum environment. Cross section HR-TEM analysis revealed the presence of a thin amorphous interfacial layer after room temperature bonding.Thermal annealing was performed in order to prepare the samples for electrical characterization. Current-voltage measurements showed near-ideal diode characteristics with an ideality factor of 1.1 obtained after correcting for the series resistance which consists of a contact and an interface resistance.

Comparative Analysis and Adhesion Testing of Hot-Applied Rubberized Asphalt Membrane Products

Abstract Hot liquid-applied rubberized-asphalt membranes (referred to in this paper as HRA membranes) have over a 40-year track record of use in roofing and waterproofing applications. In the authors' experience, this use has been generally consistent with respect to surface preparation and membrane application procedures. However, the physical and material properties of HRA membranes are not well known and not consistently reported by all manufacturers, leaving designers with limited basis for comparing products. Further, the industry has not reached a consensus on defining adequate adhesion of HRA membranes in the field, or standard field testing procedures for quantifying membrane adhesion. The testing procedures and minimum performance requirements historically used for evaluating HRA membranes are found in a Canadian General Standards Board (CGSB) standard withdrawn in January 2005. However, this archaic standard is still considered the only material standard for HRA membranes in the industry. ASTM International committees are currently developing new standards for the testing and application of HRA membranes based on CGSB Standards recognized in the industry, but consensus has not yet been reached. The laboratory testing program summarized in this paper was performed in two phases, and with five commonly used HRA membrane products. The authors designed the Phase 1 program to compare physical properties of HRA membranes to better understand membrane durability and expected performance across the different products. Phase 1 testing also included material analysis of each HRA membrane, focusing on percentages and types of fillers used with the rubberized-asphalt products. Phase 2 was primarily an adhesion testing program developed to evaluate the bond of HRA membranes to concrete with various surface profiles and preparations, but also included low-temperature flexibility membrane testing and tensile strength testing of reinforcing fabrics used in fabric-reinforced HRA membrane assemblies.

Microstructure of as atomized and annealed U-Mo7 particles: A SEM/EBSD study of grain growth

Significant progresses in the performances under in-pile irradiation of particular U-Mo based fuels have been observed over the last fifteen years. One of the remaining issues has still to be tackled for use as a LEU fuel in the high power research reactors: the U-Mo recrystallization and its associated swelling have to be controlled or delayed. One way to mitigate this problem would be to optimize the initial microstructure of U-Mo atomized particle, by homogenizing Mo concentration and increasing grain size. This paper mainly focuses on U-Mo grain growth.Based on samples prepared in the framework of KOMO-5 and EMPIrE tests, a methodological work based on the use of EBSD is presented. In particular, surface preparation procedures are proposed for powders and rods, this last one being most likely readily applicable for plate analysis.As-atomized microstructures are analyzed in detail and subsequently compared to those obtained on particles annealed at 1000 °C under various conditions. It is found that 1 h annealing under vacuum is a good compromise of temperature and time to meet the development goals, provided that few impurity precipitates are present within U-Mo particles, since these can impact grain growth.

Textured Sb2Te3 films and GeTe/Sb2Te3 superlattices grown on amorphous substrates by molecular beam epitaxy

The realization of textured films of 2-dimensionally (2D) bonded materials on amorphous substrates is important for the integration of this material class with silicon based technology. Here, we demonstrate the successful growth by molecular beam epitaxy of textured Sb2Te3 films and GeTe/Sb2Te3 superlattices on two types of amorphous substrates: carbon and SiO2. X-ray diffraction measurements reveal that the out-of-plane alignment of grains in the layers has a mosaic spread with a full width half maximum of 2.8°. We show that a good texture on SiO2 is only obtained for an appropriate surface preparation, which can be performed by ex situ exposure to Ar+ ions or by in situ exposure to an electron beam. X-ray photoelectron spectroscopy reveals that this surface preparation procedure results in reduced oxygen content. Finally, it is observed that film delamination can occur when a capping layer is deposited on top of a superlattice with a good texture. This is attributed to the stress in the capping layer and can be prevented by using optimized deposition conditions of the capping layer. The obtained results are also relevant to the growth of other 2D materials on amorphous substrates.