Non-metallic Surfaces Research Articles

Comparable electrocatalytic performances of carbon- and Rh-loaded SrTiO3 nanoparticles

Carbon- and Rh-loaded strontium titanate (SrTiO3) nanoparticles (NPs) were synthesized respectively by the wet impregnation method and the aerobic and anaerobic ethanol oxidation methods, and characterized by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction crystallography, UV–vis absorption, Raman spectroscopy, and X-ray photoelectron spectroscopy. Carbon was shown to be uniformly coated on SrTiO3 NPs by the aerobic and anaerobic ethanol oxidation methods Electrocatalytic activities of unmodified and modified SrTiO3 NPs were tested for water splitting and CO2 reduction. The aerobic C-coated and Rh-loaded SrTiO3 catalysts showed comparable activity that was increased by >10-fold of that of unmodified SrTiO3 catalyst. These results demonstrate that both metallic and nonmetallic surface modifications can highly improve the electrocatalytic activity of SrTiO3 NPs and point to highlight a more important role of the modifier in the electrocatalytic reactions than of the SrTiO3 structure.

Homocoupling of terminal alkynes on calcite (10.4)

On-surface synthesis has been identified as highly versatile strategy to prepare molecular structures on surfaces with single-atom precision. Inspired by the classical Glaser coupling, homocoupling of terminal alkynes has attracted great attention for on-surface synthesis. This coupling is known for providing a rigid and linear linkage, which is highly interesting for the synthesis of molecular wires. For molecular wire formation, non-conductive substrates are needed for electronic decoupling. So far, however, coupling of terminal alkynes has not been performed on a bulk insulator surface. Here, we present an atomic force microscopy study, indicating that 4,4″-diethynyl-[1,1′:4′,1″-terphenyl]-2′,5′-dicarboxylic acid undergoes dimerization by homocoupling of the terminal alkyne moiety on the (10.4) surface of the bulk insulator calcite. Our results suggest that upon low-temperature deposition monomers are found on the surface, which can be dimerized by annealing the sample. When following a high-temperature deposition protocol, the dimerization appears to happen already in the crucible and dimers are deposited directly. Our work, thus, indicates that homocoupling of terminal alkynes can also be performed on a non-metallic surface, in line with a recent theoretical study that suggest the role of the surface being the constrain of the chemical motion rather than contributing in terms of electron transfer.

Challenges for lowly-doped phosphorus emitters in silicon solar cells with screen-printed silver contacts

This work points out that the application of phosphorus emitters with low surface concentration Nsurf of a few 1019 cm-3 in combination with state-of-the-art screen-printed and fired silver contacts is no more limited by the specific contact resistance ρC but by the dark saturation current densities underneath the metal contacts j0,met. Eight emitter doping profiles have been designed with different Nsurf ranging between 3.3·1019 cm-3 and 1.2·1020 cm-3 which feature very similar junction depths of about 350 nm. The measured ρC values for these emitters are determined to be between 2 mΩcm2 and 5 mΩcm2 for about 50 µm-wide contact fingers. Their emitter dark saturation current density (alkaline textured and passivated surface) range from 40 fA/cm² to 90 fA/cm². From these parameters and the current-voltage data of large-area Czochralski-grown silicon solar cells featuring an aluminum back surface field, we estimate j0,met to be between 1200 fA/cm² and 3900 fA/cm². Our results show that for decreasing Nsurf, the recombination underneath the metal contacts increases significantly which mainly limits the cell’s open-circuit voltage. We thus conclude that the major challenge for emitters with low Nsurf consists in achieving reasonable low j0,met values in order to benefit on the cell level from the lower recombination activity in the passivated, non-metallized surface area.

In situ nano- to microscopic imaging and growth mechanism of electrochemical dissolution (e.g., corrosion) of a confined metal surface

Reactivity in confinement is central to a wide range of applications and systems, yet it is notoriously difficult to probe reactions in confined spaces in real time. Using a modified electrochemical surface forces apparatus (EC-SFA) on confined metallic surfaces, we observe in situ nano- to microscale dissolution and pit formation (qualitatively similar to previous observation on nonmetallic surfaces, e.g., silica) in well-defined geometries in environments relevant to corrosion processes. We follow "crevice corrosion" processes in real time in different pH-neutral NaCl solutions and applied surface potentials of nickel (vs. Ag|AgCl electrode in solution) for the mica-nickel confined interface of total area ∼0.03 mm2 The initial corrosion proceeds as self-catalyzed pitting, visualized by the sudden appearance of circular pits with uniform diameters of 6-7 μm and depth ∼2-3 nm. At concentrations above 10 mM NaCl, pitting is initiated at the outer rim of the confined zone, while below 10 mM NaCl, pitting is initiated inside the confined zone. We compare statistical analysis of growth kinetics and shape evolution of individual nanoscale deep pits with estimates from macroscopic experiments to study initial pit growth and propagation. Our data and experimental techniques reveal a mechanism that suggests initial corrosion results in formation of an aggressive interfacial electrolyte that rapidly accelerates pitting, similar to crack initiation and propagation within the confined area. These results support a general mechanism for nanoscale material degradation and dissolution (e.g., crevice corrosion) of polycrystalline nonnoble metals, alloys, and inorganic materials within confined interfaces.

Excitation of surface plasmon polaritons on silicon with an intense femtosecond laser pulse

We report the experimental observation of anomalies appearing in the reflection of intense $p$-polarized 100-femtosecond (fs) laser pulses at a nonmetallic material surface with a grating structure. The reflectivity was measured in air as a function of the angle of incidence at a Si grating. The results have exhibited an abrupt decrease to create a sharp dip at a specific incident angle of $\ensuremath{\sim}{24}^{\ensuremath{\circ}}$, where the grating surface was deeply ablated along the edge of the grooves. Similar to the so-called Wood's anomalies, the observed angle-dependent reflectivity provides direct evidence that surface plasmon polaritons (SPPs) can resonantly be excited at the interface between air and the nonmetallic material surface, as the intense fs laser pulse produces a high density of free electrons to form a metal-like layer on the Si grating surface. Calculation for a model target reproduces well the experimental results to confirm the excitation of SPPs on the Si grating, demonstrating the generation of enhanced near fields for the periodic ablation of a target surface.

Research on Lessening of Bonding Effects Between the Metallic and Non-Metallic Surfaces Through the Graphite Films Deposited with Pulsed Electrical Discharges Process

The paper presents the results of experimental research on the physics of natural graphite film formation, the establishment of chemical composition and functional properties of the graphite films, formed on metal surfaces, as a result of the action of plasma in the air environment, at a normal pressure, under the electrical discharge in impulse conditions (EDI). The researchings were performed in the frame of doctoral thesis “Research on lessening of the bonding effects between the metallic and nonmetallic surfaces through the graphite films” and aimed to identify the phenomena that occur at the interface metal/ film of graphite, and to identify also the technological applications that it may have the surface treatment for submitting the films of graphite on metallic surfaces achieved through an innovative process of electrical pulsed discharges. After the research works from the PhD theme above mentioned, a number of interesting properties of graphite pellicle have been identified ie reducing of metal surface polarity. This led to drastic decreases for the values of adhesion when bonding of metal surfaces was performed using a structural polyurethane adhesive designed by ICECHIM. Following the thermo-gravimetric analysis, performed of the graphite film obtained by process of electrical pulsed discharges, have been also discovered other interesting properties for this, ie reversible mass additions at specific values of the working temperature Chemical and scanning electron microscopy analysis have revealed that on the metallic surface subjected to electrical pulsed discharges process, outside the graphite film, it is also obtained a series of spatial formation composed of carbon atoms fullerenes type which are responsible for the phenomenon of addition of mass.

Nanotoxicity in Systemic Circulation and Wound Healing.

Nanotoxicity of nanomaterials is an important issue in view of their potential applications in systemic circulation and wound healing dressing. This account specifically deals with several characteristic features of different nanomaterials which induce hemolysis and how to make them hemocompatible. The shape, size, and surface functionalities of naked metallic as well as nonmetallic nanoparticles surfaces are responsible for the hemolysis. An appropriate coating of biocompatible molecules dramatically reduces hemolysis and promotes their ability as safe drug delivery vehicles. The use of coated nanomaterials in wound healing dressing opens several new strategies for rapid wound healing processes. Properly designed nanomaterials should be selected to minimize the nanotoxicity in the wound healing process. Future directions need new synthetic methods for engineered nanomaterials for their best use in nanomedicine and nanobiotechnology.

Generation of excited electronic states at the nonmetal surface by the hydrogen atoms beam

The low energy excitation electronic states by the hydrogen atoms at the nonmetal surface are described using several possible mechanisms. The study results of the luminescence excited surface of the phosphor ZnS-Tm during interaction with H atoms are reported. Nonstationary with time the light intensity from ZnS-Tm is detected. This phenomenon interpreted on basis of the exchange-associative mechanism taking into account the acceleration of the surface recombination of hydrogen atoms in the adsorbed layer of the vibrationally excited hydrogen molecules. The rates of the absorption and recombination of hydrogen atoms and the desorption rate of the hydrogen molecules are defined. The possible mechanisms of excitation of the surface electronic states during interaction with the hydrogen low-energy atoms are discussed.

Two-Dimensional Heterostructure as a Platform for Surface-Enhanced Raman Scattering

Raman enhancement on a flat nonmetallic surface has attracted increasing attention, ever since the discovery of graphene enhanced Raman scattering. Recently, diverse two-dimensional layered materials have been applied as a flat surface for the Raman enhancement, attributed to different mechanisms. Looking beyond these isolated materials, atomic layers can be reassembled to design a heterostructure stacked layer by layer with an arbitrary chosen sequence, which allows the flow of charge carriers between neighboring layers and offers novel functionalities. Here, we demonstrate the heterostructure as a novel Raman enhancement platform. The WSe2 (W) monolayer and graphene (G) were stacked together to form a heterostructure with an area of 10 mm × 10 mm. Heterostructures with different stacked structuress are used as platforms for the enhanced Raman scattering, including G/W, W/G, G/W/G/W, and W/G/G/W. On the surface of the heterostructure, the intensity of the Raman scattering is much stronger compared with isolated layers, using the copper phthalocyanine (CuPc) molecule as a probe. It is found that the Raman enhancement effect on heterostructures depends on stacked methods. Phonon modes of CuPc have the strongest enhancement on G/W. W/G and W/G/G/W have a stronger enhancement than that on the isolated WSe2 monolayer, while lower than the graphene monolayer. The G/W/G/W/substrate demonstrated a comparable Raman enhancement effect than the G/W/substrate. These differences are due to the different interlayer couplings in heterostructures related to electron transition probability rates, which are further proved by first-principle calculations and probe-pump measurements.

Bicomponent Supramolecular Architectures at the Vacuum-Solid Interface.

This review aims at giving the readers the basic concepts needed to understand two-dimensional bimolecular organizations at the vacuum-solid interface. The first part describes and analyzes molecules-molecules and molecules-substrates interactions. The current limitations and needs in the understanding of these forces are also detailed. Then, a critical analysis of the past and recent advances in the field is presented by discussing most of the key papers describing bicomponents self-assembly on solid surface in an ultrahigh vacuum environment. These sections are organized by considering decreasing molecule-molecule interaction strengths (i.e. starting from strong directional multiple H bonds up to weaker nondirectional bonds taking into account the increasing fundamental role played by the surface). Finally, we conclude with some research directions (predicting self-assembly, multi-components systems, and nonmetallic surfaces) and potential applications (porous networks and organic surfaces).

Electrochemical characterization of micro-cracks in polyurethane resin films deposited on metallic surfaces

Resin films based on polyurethane dispersions (PUDs) have recently gained substantial interest as surface protective coatings. However, defects in the resin films such as micro-cracks may induce high permeability to moisture, thereby compromising the coatings’ performance. In this contribution, we report on a simple electrochemical method for characterization of the micro-cracks in a resin film deposited on a copper surface. Electrochemical measurements are facilitated in a two-electrode cell where the resin-coated copper electrode serves as the anode. The ionic current flow due to electrolyte penetration within the micro-cracks of the resin film is measured and quantified. The ionic current (I) exhibits an inverse exponential dependence on the film thickness (x): I ∝ e−x . The physical basis for this dependence is discussed using a mathematical model that incorporates the surface fraction of micro-cracks in a layered resin film. While the analysis presented herein is for the specific case of PUD resins, the overall methodology is applicable to the characterization of many metallic and non-metallic surface coatings used in corrosion protection and surface functionalization applications.

First Studies for the Development of Computational Tools for the Design of Liquid Metal Electromagnetic Pumps

Abstract Liquid alloy systems have a high degree of thermal conductivity, far superior to ordinary nonmetallic liquids and inherent high densities and electrical conductivities. This results in the use of these materials for specific heat conducting and dissipation applications for the nuclear and space sectors. Uniquely, they can be used to conduct heat and electricity between nonmetallic and metallic surfaces. The motion of liquid metals in strong magnetic fields generally induces electric currents, which, while interacting with the magnetic field, produce electromagnetic forces. Electromagnetic pumps exploit the fact that liquid metals are conducting fluids capable of carrying currents, which is a source of electromagnetic fields useful for pumping and diagnostics. The coupling between the electromagnetics and thermo-fluid mechanical phenomena and the determination of its geometry and electrical configuration, gives rise to complex engineering magnetohydrodynamics problems. The development of tools to model, characterize, design, and build liquid metal thermo-magnetic systems for space, nuclear, and industrial applications are of primordial importance and represent a cross-cutting technology that can provide unique design and development capabilities as well as a better understanding of the physics behind the magneto-hydrodynamics of liquid metals. First studies for the development of computational tools for the design of liquid metal electromagnetic pumps are discussed.

Ultrathin Metal Films with Defined Topographical Structures as In Vitro Cell Culture Platforms for Unveiling Vascular Cell Behaviors.

Implanted material surfaces make direct contact with body tissues to work on its own purpose. Therefore, studies of the surface properties of implantable materials that determine cell fate are very important for successful implantation. Although numerous studies have addressed the relationship between cells and material surfaces, nonmetallic surfaces and metallic surfaces likely produce different cellular responses because of their intrinsic differences in surface energy, roughness, and chemical composition. Moreover, given the nontransparent property of metal materials, which hampers the real-time imaging of cellular behavior, a detailed cellular-level analysis at the metal-tissue interface has not been performed. In this study, metal-based cell culture platforms (MCPs) with defined microscale topographical patterns are developed using a combination of photolithography and direct current magnetron sputtering techniques. The MCPs allow to observe vascular cells on metals in real time and identify the selective regulation of human aortic smooth muscle cells and Human umbilical vein endothelial cells (HUVECs) by metallic surface topography. Additionally, atomic force microscopy, contact angles, and energy-dispersive X-ray spectroscopy analyses show that the MCPs exhibit nearly identical chemical properties with their bulk counterparts, demonstrating that MCPs can be utilized as an in vitro cell culture platform system for understanding the cellular behavior on metal substrates.

Thermal evolution study of nonmetallic impurities and surface passivation of Cu nanopowders produced via a DC thermal plasma synthesis

A range of copper nanopowders (BET particle size 20–70nm) has been prepared through a DC thermal plasma synthesis under varying operating conditions. A thermal evolution analysis was performed on these materials to quantify the nonmetallic impurities (O, C, N, H) which originated from the working and ambient environments. A temperature-programmed oxidation-infrared detection (TPO) was used for carbon and hydrogen determinations, an inert gas fusion-infrared/conductometric detection (GFA) for oxygen and nitrogen determinations. The TPO and GFA evolution patterns provided an insight into impurity speciation in terms of the free and chemically bound carbon, oxidic and adsorbed oxygen, as well as the possible types of organic functionalities. The impurity uptake and speciation were found to be a strong function of the operating conditions, including the choice of the plasma gas and the Cu feedstock. The operating conditions were identified under which the oxidation of the product nanopowder was minimized upon exposure to ambient laboratory environment. The product passivation during the synthesis was attributed to the presence in the working environment of the gaseous species (CO, CN), which are capable of strong chemisorption on the freshly prepared copper surface.

Non-contact gap sensor system completely made of conductive polymer composite

Both of the coil and the object of the traditional eddy current non-contact gap sensor system are made of metal. However, the rigidness of metal makes it difficult to develop a stretchable coil with low cost, and the system cannot work if the object is non-metallic. To overcome the limitations, an eddy current non-contact gap sensor system, in which both the coil and the object are made of stretchable conductive polymer composite, is designed. The current in the composite coil causes an induced current in the composite object covered on the non-metallic surface, leading to the occurrence of the eddy current effect. The experimental data show that the impedance of the composite coil changes regularly with the lift-off. The results verify the feasibility of using the system completely made of the composite to measure the non-contact gap between the non-metallic surfaces.

On the Use of Ultrasound-Based Technology for Cargo Inspection

A new guided wave imaging application for fast, low-cost ultrasound-based cargo scanning system is proposed. The ultimate goal is the detection of high-atomic-number, shielding containers used to diminish the radiological signature of nuclear threats. This ultrasonic technology has the potential to complement currently deployed X-ray-based radiographic systems, thus enhancing the probability of detecting nuclear threats. An array of ultrasonic transceivers can be attached to the metallic structure of the cargo to create a guided Lamb wave. Guided medium thickness and composition variation creates reflections whose placement can be revealed by means of an imaging algorithm. The knowledge of the reflection position provides information about the shielding metallic container location inside the cargo. Moreover, due to the low coupling between metallic and nonmetallic surfaces, only the footprint of metallic containers shows up in the imaging results, thus avoiding false positives from plastic or wooden assets. As imaging capabilities are degraded if working with dispersive Lamb wave modes, the operating frequency is tuned to provide a tradeoff between low dispersion and real-time image resolution. Reflected waves in the guided domain bounds may limit the performance of imaging methods for guided media. This contribution proposes a solution based on real-time Fourier domain analysis, where plane wave components can be filtered out, thus removing nondesired contributions from bounds. Several realistic examples, scaled due to limited calculation capabilities of the available computational resources, are presented in this work, showing the feasibility of the proposed method.

Controlled hydrophilic/hydrophobic property of silica films by manipulating the hydrolysis and condensation of tetraethoxysilane

Controlling surface wettability is an important road to afford the materials with anticipated functional properties, such as anti-fogging, anti-icing and self-cleaning. Manipulating the surface topography and chemical composition is a promising strategy to achieve the expected functional properties. Herein, we concurrently realized the control of surface topography and chemical composition of the film materials via exploiting a simply one step method through the hydrolysis and condensation of tetraethoxysilane (TEOS) to form silica sol-gel films. By adjusting the amount of water, TEOS and basic catalyst, the hydrophilic or hydrophobic chemical groups on the silica particles surface were well controlled. As a result, the sol-gel silica films exhibiting a controllable and wide range contact angles from 7.7±1.5° to 121.6±1.8° were obtained by this simple one-step method. The inorganic nonmetallic, metallic and polymer materials surface could maintain different wettability by the modification of controlled wettability silica films. Furthermore the wettability of silica film could be easily changed from hydrophobicity to superhydrophilicity through a heat-treatment due to the decrease of hydrophobic chemical groups conforming to the time-temperature equivalence principle. Raising temperature and extending holding time were equivalent to chemical bond breaking which result in the wettability change of silica films.

Rhodococcus erythropolis cells adapt their fatty acid composition during biofilm formation on metallic and non-metallic surfaces.

Several parameters are involved in bacterial adhesion and biofilm formation including surface type, medium composition and cellular surface hydrophobicty. When the cells are placed inside tubes, parameters such as oxygen availability should also influence cell adhesion. To understand which cellular lipids are involved in the molecular events of biofilm formation in Rhodococcus erythropolis, cell adhesion was promoted on different metallic and non-metallic surfaces immersed in culture media. These cells were able to modulate the fatty acid composition of the cell membrane in response to both the surface to which they adhered and the growth medium used. To assess the response of the cells to both surfaces and operational conditions, biofilms were also promoted inside a reactor built with five different types of tubes and with medium recirculation. The biofilm biomass could be directly related not to the hydrophobicity of the tubes used but to the oxygen permeability of the tubes. Besides this, cell age influenced the adhesion of the R. erythropolis cells to the tubes. Principal component analysis showed that the lipid composition of the cells could separate cells attached to metallic from those on non-metallic surfaces in the plane formed by PC1 and PC2, and influence biofilm biomass.

Determination of Coating Thickness Using Impulse Excitation and Laser Measurements

Coating is an application of a surface finish to another material and it provides the surfaces of manufactured parts with a number of desirable physical, chemical, and appearance qualities. Nearly all manufactured or fabricated products made of metal or having metal components have some types of surface coating. The coating increases sturdiness, prevents corrosion, provides hardness, or gives an attractive finish to an object. The amount of coating applied to a material, that is, the coating thickness, is crucial to the product’s final use and cost. On the other hand, in the case of surfaces subjected to wear, the same thickness is very important in the life of the product. There are several non-destructive methods of measuring coating thickness. The aim of this paper is the development and validation of an impulse excitation technique and laser measurements to determine coating thickness of metallic or nonmetallic surface.

Predicting Promoter-Induced Bond Activation on Solid Catalysts Using Elementary Bond Orders.

In this Letter, we examine bond activation induced by nonmetal surface promoters in the context of dehydrogenation reactions. We use C-H bond activation in methane dehydrogenation on transition metals as an example to understand the origin of the promoting or poisoning effect of nonmetals. The electronic structure of the surface and the bond order of the promoter are found to establish all trends in bond activation. On the basis of these results, we develop a predictive model that successfully describes the energetics of C-H, O-H, and N-H bond activation across a range of reactions. For a given reaction step, a single data point determines whether a nonmetal will promote bond activation or poison the surface and by how much. We show how our model leads to general insights that can be directly used to predict bond activation energetics on transition metal sulfides and oxides, which can be perceived as promoted surfaces. These results can then be directly used in studies on full catalytic pathways.