Surface sensitive study to determine the reactivity of soot with the focus on the European emission standards IV and VI

Diesel soot (Euro IV and Euro VI) was investigated with spectroscopic methods such as near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoemission spectroscopy (XPS). C and O K-edge NEXAFS show that structural disorder on the surface is accompanied by a higher amount of oxygen functional groups. O K-edge NEXAFS and O1s XPS results are discussed with the aim to elucidate the nature of the oxygen surface species. The analysis of the data presented here allows the postulation of a hypothetical structure for soot samples emitted by diesel engines.     

Self-assembled carbon nanotubes on gold: polarization-modulated infrared reflection-absorption spectroscopy, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy study

Recently we reported noncovalent functionalization of nanotubes in an aqueous medium with ionic liquid-based surfactants, 1-dodecyl-3-methylimidazolium bromide (1) and 1-(12-mercaptododecyl)-3-methylimidazolium bromide (2), resulting in positively charged single-wall carbon nanotube (SWNT)-1,2 composites. Thiolation of SWNTs with 2 provides their self-assembly on gold as well as templating gold nanoparticles on SWNT sidewalls via a covalent -S-Au bond. In this investigation, we studied the electronic structure, intermolecular interactions, and packing within noncovalently thiolated SWNTs and also nanotube alignment in the bulk of SWNT-2 dried droplets and self-assembled submonolayers (SAMs) on gold by high-resolution X-ray photoemission spectroscopy (HRXPS), C K-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). HRXPS data confirmed the noncovalent nature of interactions within the nanocomposite of thiolated nanotubes. In PM-IRRAS spectra of SWNT SAMs on gold, the IR-active vibrational SWNT modes have been observed and identified. According to PM-IRRAS data, the hydrocarbon chains of 2 are oriented with less tilt angle to the bare gold normal in a SAM deposited from an SWNT-2 dispersion than those of 1 deposited from an SWNT-1 dispersion on the mercaptoethanesulfonic acid-primed gold. For both the dried SWNT-2 bulk and the SWNT-2 SAM on gold, the C K-edge NEXAFS spectra revealed the presence of CH-pi interactions between hydrocarbon chains of 2 and the pi electronic nanotube structure due to the highly resolved vibronic fine structure of carbon 1s --> R*/sigma*C-H series of states in the alkyl chain of 2. For the SWNT-2 bulk, the observed splitting and upshift of the SWNT pi* orbitals in the NEXAFS spectrum indicated the presence of pi-pi interactions. In the NEXAFS spectrum of the SWNT-2 SAM on gold, the upshifted values of the photon energy for R*/sigma*C-H transitions indicated close contact of 2 with nanotubes and with a gold surface. The angle-dependent NEXAFS for the SWNT-2 bulk showed that most of the molecules of 2 are aligned along the nanotubes, which are self-organized with orientation parallel to the substrate plane, whereas the NEXAFS for the SWNT-2 SAM revealed a more normal orientation of functionality 2 on gold compared with that in the SWNT-2 bulk.     

Acetone adsorption on ice investigated by X-ray spectroscopy and density functional theory

Using a combination of X-ray photoemission and near-edge X-ray absorption spectroscopy (NEXAFS) as well as density-functional theory (DFT), we have investigated the adsorption of acetone on ice in the temperature range from 218 to 245 K. The adsorption enthalpy determined from experiment (45 kJ mol(-1)) agrees well with the adsorption energy predicted by theory (41 to 44 kJ mol(-1)). Oxygen K-edge NEXAFS spectra indicate that the presence of acetone at the ice surface does not induce the formation of a pre-melted layer at temperatures up to 243 K. DFT calculations show that the energetically most favored adsorption geometry for acetone on ice is with the molecular plane almost parallel to the surface.     

Adlayers of dimannoside thiols on gold: surface chemical analysis

Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C-O) and acetal moieties (O-C-O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.     

RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS

The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2-6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes.     

Selective adsorption of atomic hydrogen on a h-BN thin film

The adsorption of atomic hydrogen on hexagonal boron nitride (h-BN) is studied using two element-specific spectroscopies, i.e., near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS). B K-edge NEXAFS spectra show a clear change in the energy region of the π* band before and after reaction with atomic deuterium. On the other hand, N K-edge NEXAFS spectra show only a little change. B 1s XPS spectra show a distinct component at the low binding energy side of a main component, while N 1s XPS spectra show peak broadening at the high binding energy side. These experimental results are analyzed by the discrete variational Xα method with a core-hole effect and are explained by a model in which hydrogen atoms are preferentially adsorbed on the B sites of h-BN. Based on the experimental and theoretical results, we propose a site-selective property of BN material on adsorption of atomic hydrogen.     

Influence of oxygen on the crystalline-amorphous transition in gallium nitride films

Oxygen is a common impurity in nitride-based materials that affects the properties of technologically important materials such as gallium nitride semiconductors. In this work, the influence of oxygen on the structural evolution of GaN films is investigated using near-edge X-ray absorption fine structure (NEXAFS). The combined spectra of Ga L3-edge, N K-edge, and O K-edge indicate that the gallium coordination, formed by a mixture of oxide and nitride bonds, is directly dependent on the concentration of oxygen in the films. Below 24 atom % oxygen, gallium atoms are tetrahedrally coordinated within the films, while at higher concentrations the octahedral environment persists.     

NEXAFS光谱分析聚合物修饰的单壁碳纳米管

利用C1s、O1s、N1s近边X射线吸收精细结构(Near Edge X-Ray Absorption Fine Structure,NEXAFS)光谱对聚合物修饰的碳纳米管进行了分析,研究了氧化及偶联聚合物对碳纳米管结构的影响。氧化碳纳米管及十八胺修饰的、聚合物/十八胺双修饰的碳纳米管的NEXAFS光谱均出现了碳/氧K边π*(C=O)和σ*(C-O)共振峰;而十八胺修饰的、聚合物/十八胺双修饰的碳纳米管则出现了氮K边π*(N-C=O)和σ*(N1s)共振峰。分析表明,NEXAFS光谱可有效表征聚合物修饰的碳纳米管。     

Layer-by-layer electrostatic self-assembly of single-wall carbon nanotube polyelectrolytes

We have used anionic and cationic single-wall carbon nanotube polyelectrolytes (SWNT-PEs), prepared by the noncovalent adsorption of ionic naphthalene or pyrene derivatives on nanotube sidewalls, for the layer-by-layer self-assembly to prepare multilayers from carbon nanotubes with polycations, such as poly(diallyldimethylammonium) or poly(allylamine hydrochloride) (PDADMA or PAH, respectively), and polyanions (poly(styrenesulfonate), PSS). This is a general and powerful technique for the fabrication of thin carbon nanotube films of arbitrary composition and architecture and allows also an easy preparation of all-SWNT (SWNT/SWNT) multilayers. The multilayers were characterized with vis-near-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) measurements, atomic force microscopy (AFM), and imaging ellipsometry. The charge compensation in multilayers is mainly intrinsic, which shows the electrostatic nature of the self-assembly process. The multilayer growth is linear after the initial layers, and in SWNT/polyelectrolyte films it can be greatly accelerated by increasing the ionic strength in the SWNT solution. However, SWNT/SWNT multilayers are much more inert to the effect of added electrolyte. In SWNT/SWNT multilayers, the adsorption results in the deposition of 1-3 theoretical nanotube monolayers per adsorbed layer, whereas the nominal SWNT layer thickness is 2-3 times higher in SWNT/polyelectrolyte films prepared with added electrolyte. AFM images show that the multilayers contain a random network of nanotube bundles lying on the surface. Flexible polyelectrolytes (e.g., PDADMA, PSS) probably surround the nanotubes and bind them together. On macroscopic scale, the surface roughness of the multilayers depends on the components and increases with the film thickness.     

Structural study of NO adsorbed on the reconstructed Pt(110)-(1 x 2) surface with X-ray photoelectron diffraction and near-edge X-ray absorption fine structure spectroscopy

The adsorption structure of NO on the reconstructed Pt(110)-(1 x 2) surface was studied with X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD), low-energy scanned-angle photoelectron diffraction (LESA-PD), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The experiments were performed at 180 K, where no surface lifting from (1 x 2) to (1 x 1) takes place after NO adsorption. XPS indicates that the (1 x 2) unit cell of the Pt(110) surface contains 1.5 NO molecules at the saturated coverage. XPD and LESA-PD analyses allow us to propose a structural model for the NO adlayer, where two-thirds of the NO molecules in the (1 x 2) unit cell are adsorbed on the atop site of the close-packed Pt rows (ridges) along the [10] direction with an inclined geometry and one-third of the NO molecules adsorb on the bridge site between the Pt ridges with an upright configuration. This model is supported by the N K-edge NEXAFS experiments and is consistent with the recently reported model based on the density functional theory (Orita, H.; Nakamura, I.; Fujitani, T. J. Phys. Chem. B 2005, 109, 10312).     

Improved blood compatibility of rapamycin-eluting stent by incorporating curcumin

This paper dealt with improving the blood compatibility of the rapamycin-eluting stent by incorporating curcumin. The rapamycin- and rapamycin/curcumin-loaded PLGA (poly(d,l-lactic acid-co-glycolic acid)) coatings were fabricated onto the surface of the stainless steel stents using an ultrasonic atomization spray method. The structure of the coating films was characterized by Fourier transform infrared spectroscopy (FTIR). The optical microscopy and scanning electron microscopy (SEM) images of the drug-eluting stents indicated that the surface of all drug-eluting stents was very smooth and uniform, and there were not webbings and "bridges" between struts. There were not any cracks and delaminations on stent surface after expanded by the angioplasty balloon. The in vitro platelet adhesion and activation were investigated by static platelet adhesion test and GMP140 (P-selection), respectively. The clotting time was examined by activated partially prothromplastin time (APTT) test. The fibrinogen adsorption on the drug-loaded PLGA films was evaluated by enzyme-linked immunosorbent assay (ELISA). All obtained data showed that incorporating curcumin in rapamycin-loaded PLGA coating can significantly decrease platelet adhesion and activation, prolong APTT clotting time as well as decrease the fibrinogen adsorption. All results indicated that incorporating curcumin in rapamycin-eluting coating obviously improve the blood compatibility of rapamycin-eluting stents. It was suggested that it may be possible to develop a drug-eluting stent which had the characteristics of not only good anti-proliferation but also improved anticoagulation.     

Structure, morphology and interface properties of ultrathin SnTTBPP(OH)2-films adsorbed on Ag(100)

The molecular interaction of dihydroxo[5,10,15,20-tetrakis(4-tert-butyl-phenyl)porphyrinato]-tin(IV) (SnTTBPP(OH)(2)), the structural order and growth of ultrathin films on Ag(100) have been studied by means of low-energy electron diffraction (LEED) and synchrotron based photoelectron spectroscopy, i.e., X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS/XANES) spectroscopy. For the first time, monolayer adsorption of a metalloporphyrin with octahedral coordination of the metal center by two additional axial hydroxo ligands is investigated in a multi-technique study. The delicate balance of molecule-substrate interactions and intermolecular interactions leads to the formation of a densely-packed organic monolayer which is commensurate with the Ag(100) substrate. From NEXAFS linear dichroism an almost coplanar orientation of the porphyrin system is derived. XPS and NEXAFS clearly indicate that the axial hydroxo ligands are cleaved in monolayer films, i.e., upon adsorption to the Ag substrate. With increasing film thickness orientational order gets lost and leads to polycrystalline growth for thicker films as confirmed by scanning X-ray transmission microscopy (STXM).     

X-ray absorption spectroscopy to probe surface composition and surface deprotection in photoresist films

Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) is utilized to provide insight into surface chemical effects in model photoresist films. First, NEXAFS was used to examine the resist/air interface including surface segregation of a photoacid generator (PAG) and the extent of surface deprotection in the film. The concentration of PAG at the resist-air interface was higher than the bulk concentration, which led to a faster deprotection rate at that interface. Second, a NEXAFS depth profiling technique was utilized to probe for compositional gradients in model resist line edge regions. In the model line edge region, the surface composition profile for the developed line edge was dependent on the post exposure bake time.     

Molecular orientation and composition at the surface of spin‐coated polyfluorene:Fullerene blend films

The surface composition in spin‐coated films of polyfluorene:fullerene blends was determined quantitatively by near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy. By comparing partial and total electron yield spectra, we found vertical compositional differences in the surface region. Furthermore, the orientation of the polymer chains was investigated by variable‐angle NEXAFS. Blend films of poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole] with [6,6]‐phenyl‐C61‐butyric acid methyl ester in two different blend ratios were studied. Results showed polymer enrichment of the surfaces for films with a polymer:fullerene weight ratio of 20:80 and of 50:50, spin‐coated from both chlorobenzene and chloroform solutions. The angular dependence of the NEXAFS spectra of the pure polymer films showed a preferential plane‐on orientation, which was slightly stronger in the subsurface region than at the surface. In blend films, this orientational preference was less pronounced and the difference between surface and subsurface vanished. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Fabrication and Properties of Conducting Polypyrrole/SWNT‐PABS Composite Films and Nanotubes

We report the electropolymerization and characterization of polypyrrole films doped with poly(m‐aminobenzene sulfonic acid (PABS) functionalized single‐walled nanotubes (SWNT) (PPy/SWNT‐PABS). The negatively charged water‐soluble SWNT‐PABS served as anionic dopant during the electropolymerization to synthesize PPy/SWNT‐PABS composite films. The synthetic, morphological and electrical properties of PPy/SWNT‐PABS films and chloride doped polypyrrole (PPy/Cl) films were compared. Characterization was performed by cyclic voltammetry, atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman spectroscopy. SEM and AFM images revealed that the incorporation of SWNT‐PABS significantly altered the morphology of the PPy. Cyclic voltammetry showed improved electrochemical properties of PPy/SWNT‐PABS films as compared to PPy/Cl films. Raman Spectroscopy confirmed the presence of SWNT‐PABS within composite films. Field effect transistor (FET) and electrical characterization studies show that the incorporation of the SWNT‐PABS increased the electronic performance of PPy/SWNT‐PABS films when compared to PPy/Cl films. Finally, we fabricated PPy/SWNT‐PABS nanotubes which may lead to potential applications to sensors and other electronic devices.     

Geometric and Electronic Structures of Pyrazine Molecule Chemisorbed on Si(100) Surface by XPS and NEXAFS Spectroscopy

The geometric and electronic structures of several possible adsorption configurations of the pyrazine ({C\begin{document}$ _{4} $\end{document}}{H\begin{document}$ _{4} $\end{document}}{N\begin{document}$ _{2} $\end{document}}) molecule covalently attached to Si(100) surface, which is of vital importance in fabricating functional nano-devices, have been investigated using X-ray spectroscopies. The Carbon K-shell (1s) X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy of predicted adsorbed structures have been simulated by density functional theory with cluster model calculations. Both XPS and NEXAFS spectra demonstrate the structural dependence on different adsorption configurations. In contrast to the XPS spectra, it is found that the NEXAFS spectra exhibiting conspicuous dependence on the structures of all the studied pyrazine/Si(100) systems can be well utilized for structural identification. In addition, according to the classification of carbon atoms, the spectral components of carbon atoms in different chemical environments have been investigated in the NEXAFS spectra as well.     

Near-edge X-ray absorption fine structure investigations of order in carbon nanotube-based systems

Probing order in nanotube systems is of fundamental importance in devising applications of these tubes in field emission applications as well as for components of composite materials. We use near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to qualitatively and quantitatively study the degree of order and alignment in a wide range of carbon nanotube-based systems, including single-walled carbon nanotube (SWNT) powder, SWNT films, and aligned multiwalled carbon nanotubes. The results are compared to analogous data obtained from a highly ordered pyrolytic graphite (HOPG) sample.     

The electronic structure and adsorption geometry of L-histidine on Cu(110)

The adsorption of L-histidine on clean and oxygen-covered Cu(110) surfaces has been studied by soft X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The valence band spectra, carbon, nitrogen and oxygen 1 s XPS and N K edge absorption spectra were measured for submonolayer, monolayer, and multilayer films. The spectra provide a detailed picture of the electronic structure and adsorption geometry at each coverage. In the monolayer, the histidine molecules are randomly oriented, in contrast to the submonolayer regime, where the molecules are coordinated to the copper surface with the imidazole functional group nearly parallel to, and strongly interacting with, the surface. The pi*/sigma* intensity ratio in NEXAFS spectra at the nitrogen edge varies strongly with angle, showing the imidazole ring is oriented. Adsorption models are proposed.     

Self-metalation of 2H-tetraphenylporphyrin on Cu(111): an x-ray spectroscopy study

The bonding and the temperature-driven metalation of 2H-tetraphenylporphyrin (2H-TPP) on the Cu(111) surface under ultrahigh vacuum conditions were investigated by a combination of x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy with density functional theory calculations. Thin films were prepared by organic molecular beam epitaxy and subsequent annealing. Our systematic study provides an understanding of the changes of the spectroscopic signature during adsorption and metalation. Specifically, we achieved a detailed peak assignment of the 2H-TPP multilayer data of the C1s and the N1s region. After annealing to 420 K both XPS and NEXAFS show the signatures of a metalloporphyrin, which indicates self-metalation at the porphyrin-substrate interface, resulting in Cu-TPP. Furthermore, for 2H-TPP monolayer samples we show how the strong influence of the copper surface is reflected in the spectroscopic signatures. Adsorption results in a strongly deformed macrocycle and a quenching of the first NEXAFS resonance in the nitrogen edge suggesting electron transfer into the LUMO. For Cu-TPP the spectroscopic data indicate a reduced interaction of first-layer molecules with the substrate as demonstrated by the relaxed macrocycle geometry.     

Does the nanometre scale topography of titanium influence protein adsorption and cell proliferation?

To investigate the influence of titanium films with nanometre scale topography on protein adsorption and cell growth, three different model titanium films were utilized in the present study. The chemical compositions, surface topographies and wettability were investigated by using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurement, respectively. The films share the same surface chemistry but exhibit different topographies on a nanometre scale. Thus, they act as model systems for biological studies regarding surface topography effects. The films were obtained by varying the deposition rate and the film thickness, respectively. These films displayed nanometre scale surface roughness (root mean square roughness, R_rms) from 2 to 21 nm over areas of 50 μm × 50 μm, with different grain sizes at their surfaces. Albumin and fibrinogen adsorption on these model titanium films were performed in this study. Bicinchoninic acid assay was employed to determine the amount of adsorbed protein on titanium film surfaces. No statistically significant differences, however, were observed for either albumin or fibrinogen adsorption between the different groups of titanium films. No statistically significant influence of surface roughness on osteoblast proliferation and cell viability was detected in the present study.