Surface Atomic Composition Research Articles

Si(111) Surface Engineered with Ordered Nanostructures by an Atom Transfer Radical Polymerization

Si(111) substrates were functionalized with a covalent 4-ClCH2C6H4SiCl3 monolayer that binds to the surface using the −SiCl3 group and leaves an unreacted −CH2Cl group. The remaining benzyl chloride functionality at the top of the Si(111) substrate allowed additional functionalization by an atom transfer radical polymerization process, mediated by copper complexes. Ordered, surface-confined polystyrene assemblies, covalently bound to the silicon, have been obtained. Atomic force microscopy measurements show a long-range order of these nanostructures. X-ray photoelectron spectroscopy provided quantitative results on the surface atomic composition as well as on the nanostructure thickness. The polystyrene structures on the silicon surface were also investigated by attenuated total reflectance infrared spectroscopy.

Time-dependent mussel-inspired functionalization of poly(l-lactide-co-ɛ-caprolactone) substrates for tunable cell behaviors

Surface properties of biomaterials, such as hydrophobic/hydrophilic balance, chemical group distribution, and topography play important roles in regulation of many cellular behaviors. In this study, we present a bio-inspired coating of synthetic biodegradable poly(L-lactide-co-ɛ-caprolactone) (PLCL) films by using polydopamine for tunable cell behaviors such as adhesion and proliferation. Polydopamine coating decreased the water contact angles of the PLCL film from 75° to 40°, while the amount of coated polydopamine increased from 0.6 μg/cm(2) to 177.9 μg/cm(2). During the process, dopamine could be directly polymerized on the surface of the PLCL film to form a thin layer or nanosized particles of self-aggregates, which resulted in increase of overall roughness in a time-dependent manner. Characterization of surface atomic composition revealed an increase in signals from nitrogen and the C-N bond, both suggesting homogeneous polydopamine coating with prolonged coating time. The mechanical properties were similar following reaction with polydopamine for a time shorter than 30 min, while alterations in elongation and Young's modulus were observed when the coating time exceeded 240 min. Cell adhesion and proliferation on the polydopamine-coated films were significantly greater than those on the non-coated films. Interestingly, these cell behaviors were significantly improved even under the minimal coating time (5 min). In summary, the bio-inspired coating is of use to generate modular surface of biomaterial based on synthetic poly(α-hydroxy ester)s for tunable cell behaviors with optimization of coating time within the range in which their mechanical properties are not compromised.

Surface Modification of Cobalt Chromium Alloy via Phosphonic Acid Organic Nanosized Thin Films

To address critical challenges with the use of Co-Cr alloy, a common metal alloy used in biomedical applications we demonstrated the formation of phosphonic acid organic nanosized thins films on Co-Cr alloy. X-ray photoelectron spectroscopy (XPS) determined the surface atomic composition before and after film deposition. The presence of phosphorous 'P' after deposition indicated presence of organic film formation. Similarly, changes in surface hydrophobicity as indicated by contact angle measurements suggested organic thin film formation.

In-Vitro Corrosion Inhibition of Magnesium Alloy via Organic Nanocoatings

Magnesium alloy has been gaining interest for its potential biomedical applications as a biodegradable / bioabsorbable metallic implant. However its major disadvantage for biomedical applications is its low corrosion resistance especially in physiological environments. We demonstrate the formation of organic nano-coatings to control the bio-corrosion of Mg alloy. X-ray photoelectron spectroscopy (XPS) determined the surface atomic composition before and after film deposition. The presence of phosphorous "P" after deposition indicated the presence of organic film formation. Similarly, changes in surface hydrophobicity as indicated by contact angle measurements suggested organic thin film formation. Preliminary, In-Vitro corrosion behavior in PBS solutions indicated the effectiveness of these coatings to control the in vitro corrosion of Mg alloy

Specific and non-specific interactions of procaine with activated carbon surfaces

The adsorption of procaine on eight activated carbon surfaces from simulated intestinal fluid (SIF) was evaluated using a rotating bottle method and isoperibol calorimetry. The adsorption data were fit using the modified Langmuir-like equation to calculate the non-specific and specific adsorption capacities. The surface atomic compositions were determined by X-ray photoelectron spectroscopy (XPS). A linear relationship was found between the relative non-specific adsorption capacity and the unoxidized hydrocarbon content of the activated carbon surfaces, which indicated that the non-specific adsorption site for procaine is the bare carbon surface. The apparent area occupied per procaine molecule, calculated from the specific capacity, was linearly correlated to the sum of the relative percentages of the C O and O C O functional states on the surfaces. This suggested that the primary adsorption sites for procaine on the activated carbon surfaces were the oxygen-containing functional states of C O and O C O, where procaine was adsorbed via hydrogen bonding. The differential heats of displacement for procaine on the four activated carbon surfaces are approximately equal to each other, which indicated that the interactions between procaine and the functional states on all surfaces are energetically equivalent.

Influence of water/O2 plasma treatment on cellular responses of PCL and PET surfaces

In this study, low pressure water/O₂ plasma treatment was performed in order to obtain COOH functionalities on the surface of poly-ε-caprolactone (PCL) membranes as well as non-woven polyester fabric (NWPF) discs. The plasma treatments were performed in a cylindrical, capacitively coupled RF-plasma-reactor and then following steps were performed: in situ (oxalyl chloride vapors) gas/solid reaction to convert -OH functionalities into -COCl groups; and hydrolysis under open laboratory conditions using air moisture for final-COOH functionalities. COOH and OH functionalities on modified surfaces were detected quantitatively by using fluorescent labeling technique and an UVX 300G sensor. Electron spectroscopy for chemical analysis (ESCA) was used to evaluate the relative surface atomic compositions and the carbon and oxygen linkages located in non-equivalent atomic positions of untreated and modified surfaces. Atomic force microscope (AFM) analysis showed that nanoscale features of the PCL surfaces are dramatically changed during the surface treatments. Scanning electron microscopy (SEM) results indicated the changes in the relatively smooth appearance of the untreated NWPF discs after the plasma treatment. Periodontal ligament (PDL) fibroblasts were used in cell culture studies. Cell culture results showed that plasma treated PCL membranes and NWPF discs were favorable for the PDL cell spreading, growth and viability due to the presence of functional groups and/or nanotopographies on their surfaces.

Electrodeposition법으로 제조한 Ni-Fe 나노박막 및 나노선의 특성에 미치는 용액 조성의 영향

The micro Vickers hardness and internal stress of Ni-Fe metal thin film synthesized by electrodeposition method at <TEX>$25^{\circ}C$</TEX> were studied as a function of bath composition, and surface microstructure and atomic compositions of thin films were investigated by SEM and EDS. And the shape change of <TEX>$200\;{\AA}$</TEX> Ni-Fe nanowires made using anodic aluminum oxide(AAO) templates by electrodeposition method were observed by SEM as a function of ultrasonic treatment time and bath composition. The Fe deposition contents on the substrate non-linearly increased with Fe ion concentration over total metal ion concentration. In case of low Fe contents film, the grain size is smaller and denser than high Fe contents deposited films, and the micro Vickers hardness increased with Fe contents of electrodeposited films. These results affected the shape change of nanowire after ultrasonic treatments.

Preliminary Investigations into the Purification and Functionalization of Multiwall Carbon Nanotubes

about 50 h at 120 ‐ C in order to purify and oxidize the raw material. The oxidized multiwall carbon nanotubes were rinsed with deionized water until stabilization of the filtrate pH. Measurement techniques included elemental analysis (CHN), scanning electron microscopy with energy dispersive X-ray spectrometer, inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy and thermal analysis. With the measurement techniques used the following information was obtained: CHN analysis provided information about the quantitative composition of the following elements carbon, hydrogen, nitrogen, scanning electron microscopy imaging provided information on shape, thickness and length of the nanotubes, energy dispersive X-ray spectrometry analysis of information about surface atomic composition of the quantitative analysis, inductively coupled plasma mass spectrometry quantitative analysis of the atomic composition (metals, especially Fe, Al), the Fourier transform infrared studies provided information about qualitative analysis of surface functional groups CxOyHz (COOH, OH, COO) and thermal gravimetric‐dier ential thermal analysis — quantitative analysis of thermal decomposition products. It was found that oxidation leads to the removal of amorphous carbon and forms mainly carboxylic functional groups linked to the nanotubes. The Fourier transform infrared spectra indicate the presence of some other structures, like ketone (quinone), acid anhydride, ether and epoxy groups. Nitric acid treatment also eectively removes aluminum oxide catalyst and iron catalyst from commercial multiwall carbon nanotubes.

Optimization of Pt–Ir on carbon fiber paper for the electro-oxidation of ammonia in alkaline media

Abstract Plating bath concentrations of Pt(IV) and Ir(III) have been optimized as well as the total catalytic loading of bimetallic Pt–Ir alloy for the electro-oxidation of ammonia in alkaline media at standard conditions. This was accomplished using cyclic voltammetry, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and statistical optimization tools. Concentrations of Pt(IV) and Ir(III) of the plating bath strongly influence electrode surface atomic compositions of the Pt–Ir alloy directly affecting the electro-oxidation behavior of ammonia. Several anode materials were studied using cyclic voltammetry, which demonstrated that Pt–Ir was the most active catalyst for the electro-oxidation of ammonia. Criteria for optimization were minimizing the climatic oxidation overpotential for ammonia and maximizing the exchange current density. Optimized bath composition was found to be 8.844 ± 0.001 g L−1 Pt(IV) and 4.112 ± 0.001 g L−1 Ir(III) based on electrochemical techniques. Physical characterization of the electrodes by SEM indicates that the plating bath concentrations of Pt and Ir influence the growth and deposition behavior of the alloy.

Segregation Study of the [formula omitted] phase on the Al–Li Alloy Surface using Auger Electron Spectroscopy

Auger Electron spectroscopy (AES) has been used to study lithium segregation on Al-3.49wt%-Li alloy surface. In this work, the surface atomic composition as a function of temperature was followed. In our previous works, the activation energy of Li segregation has been determined experimentally being in agreement with the resulted theoretical value. In this paper, one showed that the segregation energy of Li on the surface depends of the crystalline structure and of the Li content in the Al-Li alloy matrix. β-AlLi phase on the alloy surface, used in the power sources for the propulsion of electrical vehicles and for stocking energy, is obtained by progressive heating. We showed that the segregated lithium on the alloy surface is reversible as a function of decreasing temperature and consequently β-AlLi phase is converted in α-AlLi phase. On the other hand, the brutal heating of the sample drives to the conversion of the α-AlLi phase to β-AlLi phase and stabilizes the surface towards other segregation; therefore the conversion of β-AlLi phase to α-AlLi phase is irreversible.

Synthesis of silver nanoclusters on zeolite substrates

Silver nanoclusters were synthesized by reducing silver nitrate with ethylene glycol at 160 °C in the presence of zeolite. A one-pot procedure has rendered uniform size distributions of quasispherical silver clusters of average sizes of 100–200 nm synthesized on the surfaces of cubiclike zeolite substrates of ∼1 μm side. Bulk material microanalysis measurements showed samples with silver mass percentages of 20%–38%. Surface atomic composition analysis found silver concentrations of 3.1%–5.7%, zeolite compounds and nontraces of nitrogen were measured. The binding energy for the Ag 3d5/2 core electrons was shifted to higher energies at 368.6 eV compared to that of metallic silver. Herein, is presented a cost-effective technique for producing a narrow size distribution of silver nanocomposites with great potential for optoelectronics, catalysis, and nanobiotechnological applications.

Physical and chemical characterizations of corn stover and poplar solids resulting from leading pretreatment technologies

In order to investigate changes in substrate chemical and physical features after pretreatment, several characterizations were performed on untreated (UT) corn stover and poplar and their solids resulting pretreatments by ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), controlled pH, dilute acid, flowthrough, lime, and SO 2 technologies. In addition to measuring the chemical compositions including acetyl content, physical attributes determined were biomass crystallinity, cellulose degree of polymerization, cellulase adsorption capacity of pretreated solids and enzymatically extracted lignin, copper number, FT-IR responses, scanning electron microscopy (SEM) visualizations, and surface atomic composition by electron spectroscopy of chemical analysis (ESCA). Lime pretreatment removed the most acetyl groups from both corn stover and poplar, while AFEX removed the least. Low pH pretreatments depolymerized cellulose and enhanced biomass crystallinity much more than higher pH approaches. Lime pretreated corn stover solids and flowthrough pretreated poplar solids had the highest cellulase adsorption capacity, while dilute acid pretreated corn stover solids and controlled pH pretreated poplar solids had the least. Furthermore, enzymatically extracted AFEX lignin preparations for both corn stover and poplar had the lowest cellulase adsorption capacity. ESCA results showed that SO 2 pretreated solids had the highest surface O/C ratio for poplar, but for corn stover, the highest value was observed for dilute acid pretreatment with a Parr reactor. Although dependent on pretreatment and substrate, FT-IR data showed that along with changes in cross linking and chemical changes, pretreatments may also decrystallize cellulose and change the ratio of crystalline cellulose polymorphs (Iα/Iβ).

Simulation of a ceramic isolator sputtering process in the stationary plasma thruster

The results of simulation experiments on studying variation in the atomic composition of the ceramic isolator surface layer in the stationary plasma thruster in its operation on xenon and xenon-nitrogen mixture are presented. The data of the detailed analysis of the ceramic isolator surface atomic composition before and after a plasma impact are given. The experimental results showed that nitrogen presence in the working fluid insignificantly influences the variation in the ceramics surface layer composition.

Origin of Oxygen Reduction Reaction Activity on “Pt3Co” Nanoparticles: Atomically Resolved Chemical Compositions and Structures

Rotating disk electrode measurements of acid-treated “Pt3Co” nanoparticles showed specific oxygen reduction reaction (ORR) activity (∼0.7 mA/cmPt2 at 0.9 V vs RHE in 0.1 M HClO4 at room temperature), twice that of Pt nanoparticles. Upon annealing at 1000 K in vacuum, the ORR activity at 0.9 V was increased to ∼1.4 mA/cmPt2 (four times that of Pt nanoparticles). High-resolution transmission electron microscopy and aberration-corrected high-angle annular dark-field in the scanning transmission electron microscope was used to reveal surface atomic structure and chemical composition variations of “Pt3Co” nanoparticles on the atomic scale. Such information was then correlated to averaged Pt−Pt distance obtained from synchrotron X-ray powder diffraction data, surface coverage of oxygenated species from cyclic voltammograms, and synchrotron X-ray absorption spectroscopy. It is proposed that ORR activity enhancement of acid-leached “Pt3Co” relative to Pt nanoparticles is attributed to the formation of a percolate...

The use of XPS spectra for the study of reaction mechanisms: the atom inventory method

AbstractX‐ray photoelectron spectroscopy (XPS) allows the analysis of the surface atomic composition of a solid and can be used for mechanistic studies of solid–gas and solid–liquid reactions. The change of atomic composition of a surface after a reaction can be calculated considering hypothetical mechanisms based on the known reactivity of the organic moieties bound to the solid surface. Atom inventory of the elements involved in the reactions was used to quantify the components of the XPS spectrum after the reaction and consequently the change of concentration in at%. The method was used to study the basic hydrolysis and photolysis of the intermediates bound to the carbon matrix after the reduction of SO2 on activated carbon. Consistent mechanisms were postulated for these reactions. Basic hydrolysis hydrolyzed the sultine intermediate, and the attack of hydroxide ion on the episulfide formed a sulfide anion, eliminating S2− in a consecutive step. Laser photolysis of modified activated carbon in t‐butanol showed the insertion of the organic moiety in the carbon matrix with expulsion of an SO2 radical anion that oxidized to ${\rm SO}_4^{2 - } $. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Morphology, surface roughness, electron inelastic and quasielastic scattering in elastic peak electron spectroscopy of polymers

AbstractIn elastic peak electron spectroscopy (EPES), the nearest vicinity of elastic peak in the low kinetic energy region reflects electron inelastic and quasielastic processes. Incident electrons produce surface excitations, inducing surface plasmons, with the corresponding loss peaks separated by 1–20 eV energy from the elastic peak.In this work, X‐ray photoelectron spectroscopy (XPS) and helium pycnometry are applied for determining surface atomic composition and bulk density, whereas atomic force microscopy (AFM) is applied for determining surface morphology and roughness. The component due to electron recoil on hydrogen atoms can be observed in EPES spectra for selected primary electron energies. Simulations of EPES predict a larger contribution of the hydrogen component than observed experimentally, where hydrogen deficiency is observed. Elastic peak intensity is influenced more strongly by surface morphology (roughness and porosity) than by surface excitations and quasielastic scattering of electrons by hydrogen atoms. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Structure–property relations and cytotoxicity of isosorbide‐based biodegradable polyurethane scaffolds for tissue repair and regeneration

Microporous scaffolds with potential applications for tissue engineering were produced from the biodegradable aliphatic isosorbide-based polyurethane using a combined salt leaching-solvent evaporation-coagulation process. Alkaline sodium phosphate heptahydrate crystals were used as a solid porogene, and acetone-water mixture was used as a nonsolvent-coagulant. The scaffolds used in this study had interconnected pores with sizes in the range of 70-120 microm and a pore-to-volume ratio of 87%. The XPS measurements showed that the residence of the scaffold in an aqueous solution of the alkaline porogene changed its surface atomic composition, that is increased the surface concentration of oxygen and nitrogen and reduced the surface concentration of hydrocarbons relative to the control material. This also enhanced the hydrophilicity of the scaffold's surfaces as assessed from contact angle measurements. The alkaline porogene did not affect the polymer's molecular weight. The MTT cytotoxicity assay showed that the isosorbide-based polyurethane scaffold is noncytotoxic. The amounts of interleukin-6 and interleukin-8 proinflammatory cytokines released from human blood leukocytes exposed to the polyurethane scaffolds in vitro were comparable and/or lower than the amount of the cytokines released by leukocytes exposed to the culture-grade polystyrene control.

Investigations on surface composition and microstructure of sintered barium titanate

The paper describes studies on surface atomic composition, microstructure and microarea elemental distribution in sintered undoped as well as donor or acceptor doped polycrystalline barium titanate ceramics. The specimens examined are derived from barium titanate powders synthesized by two different wet chemical procedures namely oxalate precursor route and gel-to-crystallite conversion. The compositional analysis is carried out by backscattering spectrometry (BS) involving 3.05 MeV $^{16}O(\alpha,\alpha)^{16}O$ resonant scattering while investigations on microstructure and microarea elemental distribution are performed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), respectively. The specimens prepared by either method are monophasic; however, their surface atomic composition, microstructural features as well as electrical characteristics are significantly different. The specimens obtained by oxalate precursor route generally have Ti rich surfaces and exhibit coarse to fine grained microstructure depending on the nature and extent of doping. The Mn-doped specimens exhibit appreciable O deficiency. The specimens prepared by gel to crystallite conversion, in contrast, usually have Ba enriched surfaces and exhibit fine-grained microstructure EDS measurements show the segregation of acceptors such as Mn, Cu and Zn in the grain boundaries of oxalate precursor derived ceramics. Further, the relative atomic ratio of Ti to Ba at the sites of segregations is higher compared to other locations.

Surface modification of thick SiC gradient coatings on doped graphite under long pulse plasma irradiation

Selection of candidate plasma facing materials (PFM) in experimental fusion device is very important due to its direct influence on the plasma performance. To meet the requirements of high power and steady state operation, one kind of multi-element doped graphite GBST1308 (1%B4C, 2.5%Si, 7.5%Ti) with thick SiC gradient coatings was chosen as the main limiter materials for the HT-7 device. Surface modification of the SiC coatings on doped graphite under long pulse plasma irradiation was carefully investigated by examining the surface morphology, structure, and atomic composition. The obtained results showed the crystal structure of SiC was replaced by lamellar matter or film with plentiful oxygen and some other elements existed in the surface of graphite tiles after the plasma irradiation.

First-principles kinetic Monte Carlo simulations for heterogeneous catalysis: Application to the CO oxidation atRuO2(110)

We describe a first-principles statistical mechanics approach enabling us to simulate the steady-state situation of heterogeneous catalysis. In a first step, density-functional theory together with transition-state theory is employed to obtain the energetics of the relevant elementary processes. Subsequently the statistical mechanics problem is solved by the kinetic Monte Carlo method, which accounts for the correlations, fluctuations, and spatial distributions of the chemicals at the surface of the catalyst under steady-state conditions. Applying this approach to the catalytic oxidation of CO at $\mathrm{Ru}{\mathrm{O}}_{2}(110)$, we determine the surface atomic structure and composition in reactive environments ranging from ultra-high vacuum (UHV) to technologically relevant conditions, i.e., up to pressures of several atmospheres and elevated temperatures. We also compute the $\mathrm{C}{\mathrm{O}}_{2}$ formation rates (turnover frequencies). The results are in quantitative agreement with all existing experimental data. We find that the high catalytic activity of this system is intimately connected with a disordered, dynamic surface ``phase'' with significant compositional fluctuations. In this active state the catalytic function results from a self-regulating interplay of several elementary processes.