Carbon Contamination Research Articles

Homoepitaxial growth of device-grade GaAs using low-pressure remote plasma CVD

We have achieved the growth of high-quality, homoepitaxial 100 GaAs thin films at 0.5 mbar and 500 °C using a Remote Plasma Chemical Vapor Deposition (RP-CVD) reactor. With this process, we demonstrate a film growth rate up to 3 μm/h, comparable to the conventional MOCVD technique. The resulting films exhibit structural characteristics close to those of commercial GaAs wafers, with excellent crystalline quality as confirmed by SAED patterns and XRD rocking-curve measurements for the 004 peak with a FWHM of 0.004°. AFM measurements reveal a surface roughness of 0.2 nm, similar to that of a polished wafer. Analysis of the chemical composition – as determined through XPS surface and depth-profiled measurements – indicates that the film is homogeneous, with a constant III/V ratio of 1 throughout the whole layer, and has no detectable carbon or oxygen contamination. Additionally, the films demonstrate a sharp photoluminescence peak (FWHM of 55 meV), a p-type doping concentration of 1.1018 cm−3, and a hole mobility of 172 cm2 V⁻1.s⁻1. This work thus demonstrates a cost-effective growth method for III-V devices, enabled by the reduced gas consumption (only a few sccm, compared to tens of L/min in MOCVD) in RP-CVD operation at low pressure.

Effect of NaOH etching and oxygen plasma treatments on surface characteristics and their potential to activate micro-arc oxidized TiO2 coatings

Activation treatments such as NaOH etching or O2 plasma can play an essential role in surface conjugation of titanium with biomolecules, providing a better interaction at the bone-implant interface. However, their application on complex titanium dioxide (TiO2) surfaces is still not explored. In this contribution, bioactive and porous TiO2 coatings produced by micro-arc oxidation (MAO) were treated with NaOH etching or O2 plasma and then placed in contact with a reactive isocyanate test compound to evaluate the potential of molecule conjugation. Results suggested that O2 plasma treatment has only changed the surface chemistry of the coating through carbon contaminants removal, plasma-driven oxidation and generation of functional OH species, including reactive carboxyl groups. This chemical modification by plasma has made the surface superhydrophilic. After NaOH etching, the coating became rougher and also superhydrophilic, containing titanate structures doped with sodium and calcium on its surface and inside the inner pores. Upon reaction with butyl isocyanate, the O2 plasma-treated surfaces seem to better provide molecule conjugation, introducing characteristic conjugation bonds, and also making MAO coatings more hydrophobic due to the surface-terminated methyl chains from isocyanate. This proof-of-concept study has demonstrated the promising grafting potential given by O2 plasma on complex TiO2 surfaces.

Mobility of trace elements in a coastal contaminated site under groundwater salinization dynamics

Water pollution is a significant issue resulting from past long-term actions. The remediation projects carried out under law constraints for industrial plants, which have been the major contributors to environmental and water pollution, are currently providing a significant amount of data about contaminated soil, surface waters, and groundwater. Most of such plants worldwide are in coastal zones. Based on a significant amount of chemical and environmental data for a coastal contaminated site subject to variable groundwater salinization, this study aimed to understand the mobility of some trace elements because of coastal zone dynamics. Data concerned 688 groundwater samples, including As, Hg, Cd, Crtot, Cu, Ni, Pb, V, Se, Zn, pH, electrical conductivity, chlorides, total organic carbon and organic contaminants as quantitative variables, enhanced by additional qualitative variables such as groundwater salinity, season, water level, precipitation, and industrial activity type to make the dataset as representative as possible of the site under investigation. The study used robust multivariate statistical analyses to analyse the complex dataset and explain the relevant factors influencing contaminant behaviour under different environmental conditions. The Multivariate Statistical Analysis distinguished three clusters of trace elements with diverse reactivity to changes in groundwater salinization. The first includes Se, Cu, Crtot, V, and Ni, showing the highest correlation with electrical conductivity and chlorides because of their high affinity to form chloride or organic chloride complexes and for ion competition. Zn and Pb cluster in the second group: they are less reactive to groundwater salinization and more influenced by cation and anion competition and organic matter. The mobility of Hg and As (third cluster) significantly correlates with Fe and Mn, underlining the dominant role of reductive dissolution of trace elements-bearing minerals (Fe/Mn/Al-oxy-hydroxides) and metal-organic complexes. The correlation between the clustering of variables in groundwater and soils shows the influence of sediment structure, mineral composition, and physical and chemical soil conditions on the distribution in soils of trace elements and their transport to groundwater. The study proposes a valuable approach for assessing the effects of salinization in contaminated coastal aquifers. It supports planning multi-purpose characterization and monitoring campaigns of contaminated coastal sites and provides guidance on the correct associated remediation projects.

2M NaCl by XPS using monochromatic Al K α x rays

Cryo-XPS enables the study of many substances that are unsuitable for standard XPS analysis, such as moderately volatile liquids, biological samples, porous materials, and polymeric materials that may outgas significantly under ultrahigh vacuum conditions. In this article, XPS spectra of a 50 μl frozen droplet of 2M sodium chloride solution (NaCl) in Millipore water purified to 18.2 MΩ cm at 25 °C were obtained using an Al Kα (1486.6 eV) source with a quartz (1010) crystal monochromator through first order diffraction and irradiating the sample at 54.7° to the surface normal. The sample was sputter cleaned using a Gas Cluster Ion Source pre-acquisition to remove the minor layer of adventitious carbon contamination on the surface. Spectra of the principal lines include Na 1s, O 1s, and Cl 2p. Spectra of O KLL, Na KLL, Cl 2s, Na 2s, Na 2p, O 2s, and valence band were also acquired.

Mid-infrared transparent Y2O3-MgO composites with wide transmittance range and weak absorption peaks via the reduction of carbon contamination and agglomerations

Y2O3-MgO composites are promising for mid-infrared windows and domes in harsh environments. However, the insufficient transmittance range (the transmittance >30% only in ∼2-7 μm) and strong absorption peak (the transmittance <32% at 7.0 μm) of Y2O3-MgO composites severely limit their application range because of agglomerations and carbon contamination from organics in the raw materials, currently. In this study, utilizing carbon-free raw materials and high molecular motions, the reduction of carbon contamination and agglomerations within the as-synthesized nanopowers was achieved via the modified co-precipitation synthesis. A highly mid-infrared transparent (the maximum transmittance of 79% at 6.0 μm) Y2O3-MgO composite with wide transmittance range (the transmittance >30% in 2.2-9.7 μm) and weak absorption peaks (the transmittance ≈68.57% at 7.0 μm) was fabricated by the hot-pressing sintering method using the as-obtained nanopowders in the absence of exogenous dopants. And the modified co-precipitation synthesis is a method with great potential for the development of mid-infrared transparent Y2O3-MgO composites with wide transmittance range and weak absorption peaks.

Calcium titanate corrosion inhibitor enabling carbon as inert anode for oxygen evolution in molten chlorides

The corrosion inhibition efficacy of titanate (CaTiO3) for carbon anodes in molten salts was investigated through various analytical techniques, including linear sweep voltammetry, X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The results demonstrate that the addition of CaTiO3 corrosion inhibitor efficiently passivates the carbon anode and leads to the formation of a dense CaTiO3 layer during the electrolysis process in molten CaCl2−CaO. Subsequently, the passivated carbon anode effectively undergoes the oxygen evolution reaction, with an optimal current density for passivation identified at 400 mA/cm2. Comprehensive investigations, including CaTiO3 solubility tests in molten CaCl2−CaO and numerical modeling of the stability of complex ionic structures, provide compelling evidence supporting “complexation−precipitation” passivation mechanism. This mechanism involves the initial formation of a complex containing TiO2·nCaO by CaTiO3 and CaO, which subsequently decomposes to yield CaTiO3, firmly coating the surface of the carbon anode. In practical applications, the integration of CaTiO3 corrosion inhibitor with the carbon anode leads to the successful preparation of the FeCoNiCrMn high-entropy alloy without carbon contamination in the molten CaCl2−CaO.

Unveiling the oxidation stability of 2D gallium-intercalated monolayer epitaxial graphene through correlative microscopy

The oxidation- and air-stability of 2D gallium-intercalated monolayer epitaxial graphene was determined using correlative microscopy. Site-specific studies including AFM, scanning electron microscope, cross section STEM-HAADF, and EELS revealed that the oxygen signal detected by XPS and AES analyses originated from oxidized surface carbon contaminants without the presence of oxygen at the 2D gallium layers. In addition, the air-stability of the 2D gallium was correlated with the presence of intact epitaxial graphene. The absence of graphene leads to oxidation of the 2D gallium in air, consequently losing the crystallinity of the epitaxial gallium layer. This study invokes the importance of correlative microscopy to better understand defects in 2D metals that have been recently recognized through the confinement heteroepitaxy. In addition, this study highlights the advantage of using high spatial resolution STEM techniques in comparison with XPS that has relatively lower resolution.

Specific of mechanical alloying of solid-liquid binary system Fe-Ga and effect of different process control agents

Mechanical alloying allows obtaining nonequilibrium structures in various systems, often possessing unique properties, including magnetic ones. Considering the unusual structural features of the magnetostrictive Fe-Ga alloy, this approach may be promising for this system. In this work, extensive experimental studies were carried out aimed at studying the features of mechanical alloying of Fe-Ga. The object of the study was the system Fe-20 wt% Ga in which disordered solid solution α-Fe(Ga) is formed. It was shown that high-intensity milling is an effective tool for mechanical alloying of solid-liquid binary system Fe-Ga, but a serious problem is a low powder recovery, less than 50 %. To solve this problem, various process control agents were tested. Their influence on powder recovery, process kinetics, particle size, carbon contamination, and magnetic properties was studied using a large set of techniques such as XRD, SEM, EDS, VSM, LIBS, and others. It has been shown that, based on a combination of factors, the optimal process control agent for this system is ethanol in an amount of 1 wt%

Fluidized Bed Chemical Vapor Deposition of Copper on Micronic Alumina Powders

AbstractUniformly coating micronic particles with metals is of main interest for a broad range of applications. This study demonstrates the feasibility of depositing pure copper on the surface of micronic alumina particles by the fluidized bed chemical vapor deposition process from the cheap and nontoxic copper acetylacetonate precursor. Thanks to the development of a preconditioning protocol, a complete fluidization of the particles organized as porous agglomerates was reached. The coating of the individual particles was favored by using conditions involving low deposition rates. The influence of key operating parameters on the process behavior and on the characteristics of the deposit was studied. The deposited copper was of cubic crystal structure without carbon nor oxide contamination.

Patterning damage mechanisms for two-dimensional crystalline polymers and evaluation for a conjugated imine-based polymer

High-quality patterning determines the properties of patterned emerging two-dimensional (2D) conjugated polymers and is essential for potential applications in future electronic nanodevices. However, the most suitable patterning method for 2D polymers has yet to be determined because we still do not have a comprehensive understanding of their damage mechanisms by visualizing the structural modification that occurs during the patterning process. Here, the damage mechanisms during patterning of 2D polymers, induced by various patterning methods, are unveiled based on a systematic study of structural damage and edge morphology in an imine-based 2D polymer (polyimine). Patterning using a focused electron beam, focused ion beam (FIB) and mechanical carving is evaluated. The focused electron beam successively introduces a sputtering effect, knock-on displacement damage and massive radiolysis with increasing electron dose from9.46×107electrons nm-2to1.14×1010electrons nm-2. Successful patterning is enabled by knock-on damage but impeded by carbon contamination beyond a critical sample thickness. A FIB creates current-dependent edge morphologies and extensive damage from ion implantation caused by the tail of the unfocused beam. A precisely controlled tip can tear the polyimine film through grain boundaries and hence create a patterning edge with suitable edge roughness for certain application scenarios when beam damage is avoided. Taking structural damage and the resulting quantitative edge roughness into consideration, this study provides a detailed instruction on the proper patterning techniques for 2D crystalline polymers and paves the way for tailored intrinsic properties and device fabrication using these novel materials.

Copper oxides CuO and Cu2O processed by spark plasma sintering—Electrical characterization and photo-activated conductivity

Commercial powders made of two copper oxides were compacted with spark plasma sintering (SPS). Their dielectric properties were studied in a broad range of frequencies and temperatures. Various relaxation phenomena were documented. DC resistivity was measured as well. Microstructure and phase composition were studied, and phase purity was shown for CuO, whereas Cu2O was more sensitive to carbon contamination during the SPS processing. Influence of the sintering temperature on microstructure and electrical properties was described for both materials. Change of DC resistivity induced by visible light irradiation was monitored for 48h. The overall difference between CuO and Cu2O from the electrical standpoint was finally not so dramatic as the stoichiometry indicated. Both materials exhibited giant permittivity, but extremely dependent on frequency and temperature. Application could find such systems mainly in the branch of sensors.

Insight into the fate of bioplastic and similar plant-based material debris in aquatic environments via continuous monitoring of their leachate composition – Release of carbon, metals, and additives

Currently, the environmental problems associated with plastic production and waste, such as the consequences of worldwide pollution of natural waters with microplastics, have led to the seeking of alternative materials that can at least partially replace conventional petroleum-based plastics. Substitute materials include bioplastics and similar plant-based materials or their composites. However, their fate when disposed of in unintended environments (e.g., water bodies) remains largely unknown, while such information is highly desirable prior to massive expansion of exploiting such materials. This study aims to contribute filling this knowledge gap. Specifically, 19 different types of bioplastic and similar plant-based material debris (corresponding to the size of microplastics) were kept in long-term contact with water to mimic their behaviour as water pollutants, and the leachates were continuously analysed. Eighteen of the 19 investigated materials released significant amounts of dissolved organic carbon—up to 34.0 mg per g of debris after 12 weeks of leaching. Each leachate also contained one or more of the following elements: Al, B, Ba, Ca, Fe, K, Mg, Mn, N, Na, P, Si, Ti, and Zn. Non-targeted analysis aimed at providing more specific insight into the leachate composition tentatively revealed 91 individual chemicals, mostly fatty acids and other carboxylic acids, phthalates, terephthalates, adipates, phenols, amides, alcohols, or organophosphates. Based on the compound characteristics, they might be additives, non-intentionally added substances, as well as their degradation products. In general, the current results imply that bioplastics and similar plant-based materials should be considered complex materials that undergo industrial processing and comprise additives rather than harmless natural matter. Additionally, various compounds can release from the bioplastic and similar plant-based material debris when deposited in water. It might have consequences on the fluxes of carbon, metals and specific organic contaminants, and it resembles some properties of conventional petroleum-based microplastics.

Demystifying the tropics: FTIR characterization of pantropical woods and their α-cellulose extracts for past atmospheric 14C reconstructions

To ensure unbiased tree-ring radiocarbon (14C) results, traditional pretreatments carefully isolate wood cellulose from extractives using organic solvents, among other chemicals. The addition of solvents is laborious, time-consuming, and can increase the risk of carbon contamination. Tropical woods show a high diversity in wood-anatomical and extractive composition, but the necessity of organic-solvent extraction for the 14C dating of these diverse woods remains untested. We applied a chemical treatment that excludes the solvent step on the wood of 8 tropical tree species sampled in South-America and Africa, with different wood-anatomical and extractive properties. We analyzed the success of the extractive removal along with several steps of the α-cellulose extraction procedure using Fourier Transform Infrared (FTIR) spectroscopy and further confirmed the quality of 14C measurements after extraction. The α-cellulose extracts obtained here showed FTIR-spectra free of signals from various extractives and the 14C results on these samples showed reliable results. The chemical method evaluated reduces the technical complexity required to prepare α-cellulose samples for 14C dating, and therefore can bolster global atmospheric 14C applications, especially in the tropics.

Ultraclean Suspended Graphene by Radiolysis of Adsorbed Water.

Access to intrinsic properties of a 2D material is challenging due to the absence of a bulk that would dominate over surface contamination, and this lack of bulk also precludes effective conventional cleaning methods that are almost always sacrificial. Suspended graphene and carbon contaminants represent the most salient challenge. This work has achieved ultraclean graphene, attested by electron energy loss (EEL) spectra unprecedentedly exhibiting fine-structure features expected from bonding and band structure. In the cleaning process in a transmission electron microscope, radicals generated by radiolysis of intentionally adsorbed water remove organic contaminants, which would otherwise be feedstock of the notorious electron irradiation induced carbon deposition. This method can be readily adapted to other experimental settings and other materials to enable previously inhibited undertakings that rely on the intrinsic properties or ultimate thinness of 2D materials. Importantly, the method is surprisingly simple and robust, easily implementable with common lab equipment.

Surface segregation phenomena encountered during solid carbon active screen plasma nitrocarburizing of AISI 316L

Plasma nitrocarburizing of an austenitic stainless steel AISI 316L was performed in an N2-H2 atmosphere (50 % H2 and 50 % N2) with a carbon-fiber reinforced carbon (CFC) active screen. The experimental concept of a plasma-discharged CFC active screen in conjunction with a substrate holder at floating potential ensures that no charged particles are present on the sample surface and no sputtering occurs. As a result, carbon contaminations are formed on the surface which were studied in detail with a combination of scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). The results indicate that a layer of about 25–50 nm of carbon is formed. At the same time, a strong segregation of Mn, Ni and Cr is observed below the coating within the steel substrate. Both effects progress with treatment time and there exists a clear correlation between the formation of the carbon layer and the segregation effect.

Nanoindentation Test of Ion-Irradiated Materials: Issues, Modeling and Challenges.

Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a body-centered cubic (bcc) crystal structure. Ion irradiation is an indispensable tool in the study of the radiation effects of materials for nuclear energy systems. Due to the shallow damage depth in ion-irradiated materials, the nanoindentation test is the most commonly used method for characterizing the changes in mechanical properties after ion irradiation. Issues that affect the analysis of irradiation hardening may arise due to changes in the surface morphology and mechanical properties, as well as the inherent complexities in nanoscale indentation. These issues, including changes in surface roughness, carbon contamination, the pile-up effect, and the indentation size effect, with corresponding measures, were reviewed. Modeling using the crystal plasticity finite element method of the nanoindentation of ion-irradiated materials was also reviewed. The challenges in extending the nanoindentation test to high temperatures and to multiscale simulation were addressed.

Binder System Composition on the Rheological and Magnetic Properties of Nd-Fe-B Feedstocks for Metal Injection Molding

The applications of Nd-Fe-B-based magnets are experiencing significant diversification to achieve efficiency and miniaturization in different technologies. Metal injection molding (MIM) provides new opportunities to manufacture Nd-Fe-B magnets with high geometrical complexity efficiently. In this study, the impacts of the binder system composition and powder loading on the rheological behavior, contamination, and magnetic properties of the Nd-Fe-B MIM parts were investigated. A high-pressure capillary rheometer was used to measure the apparent viscosity and pressure drops for feedstocks with different binder formulations and powder contents. Also, oxygen and carbon contamination, density, and magnetic properties were measured for different feedstock formulations and powder loadings. From the rheological, density, and magnetic properties points of view, the binder system consisting of 45 vol.% LLDPE as backbone was selected as the optimum formulation. The findings indicated that the sample with this binder system and 55 vol.% powder content had a high density (6.83 g/cm3), remanence (0.591 T), and coercivity (744.6 kA/m) compared to other binder compositions. By using 58 vol.% powder loading, the values of density (7.54 g/cm3), remanence (0.618 T), and carbon residue (982 ppm) improved, and a suitable rheological behavior was still observed. Thus, a suitable feedstock formulation was developed.

Enhanced Photoluminescence of Plasma-Treated Recycled Glass Particles.

Recycled soda-lime glass powder is a sustainable material that is also often considered a filler in cement-based composites. The changes in the surface properties of the glass particles due to the treatments were analyzed by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. We have found that there is a relatively high level of carbon contamination on the surface of the glass particles (around 30 at.%), so plasma technology and thermal annealing were tested for surface cleaning. Room temperature plasma treatment was not sufficient to remove the carbon contamination from the surface of the recycled glass particles. Instead, the room temperature plasma treatment of recycled soda-lime glass particles leads to a significant enhancement in their room temperature photoluminescence (PL) by increasing the intensity and accelerating the decay of the photoluminescence. The enhanced blue PL after room-temperature plasma treatment was attributed to the presence of carbon contamination on the glass surface and associated charge surface and interfacial defects and interfacial states. Therefore, we propose blue photoluminescence under UV LED as a fast and inexpensive method to indicate carbon contamination on the surface of glass particles.

Sample preparation using plasma jet treatment for total reflection X-ray fluorescence analysis

Total reflection X-ray fluorescence (TXRF) is widely used for trace element analysis. This method is advantageous because of its simple sample preparation. However, the sample must be placed within the analytical volume (region and height). In this study, the analytical volume was experimentally evaluated and visualized using thin, localized Au layers. The intensity distributions of the Au Lβ lines and background Au Lβ peaks were visualized. Images of the intensity ratio of the Au Lβ line and the background peak were drawn and analyzed to determine the analysis region on the glass substrate depending on the glancing angle. A glancing angle of 0.025° was optimal for TXRF analysis, resulting in a large signal-to-background (SB) ratio. Glancing angles of 0.05° and 0.075° were also effective for obtaining large SB ratios for a relatively large area (>4 mm2). To reduce the thickness of the dried residue and the self-absorption of the XRF emitted from the residue, a glass substrate was subjected to He plasma jet treatment. X-ray photoelectron spectroscopy confirmed that the carbon contamination was reduced from the surface of the glass by the plasma jet treatment, thereby modifying the chemical properties to confer hydrophilicity to the glass surface. The time variation of the C1 s peak intensity suggests that the hydrophilic property was maintained for several hours. The plasma-treated glass was effective in obtaining a thin layer-like residue from a white wine sample. The TXRF results indicated improved recovery and RSD, particularly for low-Z elements, because the absorption effect was reduced in the thin layer-like residue.

Dual-carbon isotope analysis of benzene polycarboxylic acids for tracking black carbon across different environments

Black carbon (BC) is ubiquitous in the environment and is a significant component of the refractory carbon pool. However, its sources, biogeochemical processes, and environmental residence times are poorly understood. One important reason is that the technical protocols for isolating/analyzing BC vary across different matrices, thereby bringing inconsistency among studies on BC in different environment media. Benzene polycarboxylic acids (BPCA), produced by nitric acid oxidation of the condensed aromatic structure that is common in BC and BC-like substances, has been proven to be a useful molecular proxy for tracking BC in the Earth's surface. Here, we introduce a new technical approach for the compound-specific dual-carbon isotope (δ13C and Δ14C) analysis of BPCA. The BPCA compounds are isolated using preparative liquid chromatography, in which trifluoroacetic acid is used in the mobile phase instead of phosphoric acid. This allows complete removal of solvent from the isolated BPCA fraction, so that conversion of BPCA isolates into CO2 can be done by conventional oxidation methods for off-line Δ14C analysis with accelerator mass spectrometry. Liquid chromatography (void column)-stable carbon isotope ratio mass spectrometry is employed to measure δ13C of the isolated BPCA, leaving as much BPCA carbon amount as possible for 14C analysis. Blockage of oxidation chamber due to incomplete oxidation of other organic acids in the samples is avoided thanks to preliminary isolation of BPCA. We tested the approach by applying it to solid and dissolved BC species in a suite of environmental reference materials, including maize char, coal, riverine natural organic matter (NOM 2R101N), marine sediment (SRM 1941b), urban dust (SRM 1649b), and coke-polluted soils. We assessed the offsets of BPCA-δ13C and BPCA-Δ14C values caused by procedural carbon contaminations to correct measured carbon isotopic values. Paired δ13C-Δ14C data of individual BPCA were plotted to validate and demonstrate the ability of this dual carbon isotope technique in tracking BC across different environmental matrices. We observed slightly different δ13C-Δ14C signatures among individual BPCA, indicating that the less condensed BC may have younger apparent radiocarbon ages.