Markku Heinonen

Core-level XPS spectra of fullerene, highly oriented pyrolitic graphite, and glassy carbon

Abstract The C 1s spectra of fullerene C 60 , highly oriented pyrolitic graphite (HOPG) and amorphous carbon (a-C) have been measured using X-ray photoemission. The assumed background due to the inelastic scattering of electrons of these spectra has been subtracted by the Tougaard’s method. The relative intensities and the energy positions for the core-level satellites have been determined. For C 60 , a comparison of the low energy π type shake-up satellites gives good agreement between theory and experiment. Also, the energies of these features for fullerene and glassy carbon are very similar, whereas the corresponding energies for HOPG are somewhat larger, presumably, because of the higher density of the latter. Moreover, the atomic force microscopy (AFM) study indicates that the C 60 samples consist of a thick layer of large clusters on the Si(111) surface, which is in line with the molecular character of the XPS spectrum. Furthermore, the broad high energy satellite does not consist of a single plasmon but of many components due to collective excitations characteristic of molecules and solids. These features are discussed in the light of theoretical excitation energies.

Amine Modification of Thermally Carbonized Porous Silicon with Silane Coupling Chemistry

Thermally carbonized porous silicon (TCPSi) microparticles were chemically modified with organofunctional alkoxysilane molecules using a silanization process. Before the silane coupling, the TCPSi surface was activated by immersion in hydrofluoric acid (HF). Instead of regeneration of the silicon hydride species, the HF immersion of silicon carbide structure forms a silanol termination (Si-OH) on the surface required for silanization. Subsequent functionalization with 3-aminopropyltriethoxysilane provides the surface with an amine (-NH(2)) termination, while the SiC-type layer significantly stabilizes the functionalized structure both mechanically and chemically. The presence of terminal amine groups was verified with FTIR, XPS, CHN analysis, and electrophoretic mobility measurements. The overall effects of the silanization to the morphological properties of the initial TCPSi were analyzed and they were found to be very limited, making the treatment effects highly predictable. The maximum obtained number of amine groups on the surface was calculated to be 1.6 groups/nm(2), corresponding to 79% surface coverage. The availability of the amine groups for further biofunctionalization was confirmed by successful biotinylation. The isoelectric point (IEP) of amine-terminated TCPSi was measured to be at pH 7.7, as opposed to pH 2.6 for untreated TCPSi. The effects of the surface amine termination on the cell viability of Caco-2 and HT-29 cells and on the in vitro fenofibrate release profiles were also assessed. The results indicated that the surface modification did not alter the loading of the drug inside the pores and also retained the beneficial enhanced dissolution characteristics similar to TCPSi. Cellular viability studies also showed that the surface modification had only a limited effect on the biocompatibility of the PSi.

Meso- and microporous soft templated hydrothermal carbons for dye removal from water

The hydrothermal carbonization (HTC) technique has shown a great ability in the synthesis of carbon materials with special properties for a wide range of different applications. Here, a hypersaline salt mixture (LiCl–ZnCl2) combined with hydrothermal carbonization was applied in order to obtain sulfur containing micro- and mesoporous (0.3–40 nm) monolithic carbons with high surface areas (400–550 m2 g−1) and well developed porosity (0.4–1.2 cm3 g−1). Fructose was used as a carbon source and sulfur was introduced in an aromatic configuration as 2-thiophenecarboxaldehyde. The resulting carbon materials showed a promising removal capacity (qe = 0.3 mmol g−1) towards methylene blue and the adsorption followed the Sips isotherm independent of the pH. Intraparticle diffusion appeared to control the adsorption kinetics. Carbon materials could be easily regenerated with simple ethanol washing. The dye pollutant could be completely desorbed from the adsorbents surface, while the adsorbent still maintained removal efficiency of above 90% during three cycles.

Resin zirconia bonding promotion with some novel coupling agents.

OBJECTIVES To evaluate and compare three novel coupling agents: 2-hydroxyethyl methacrylate, itaconic acid and oleic acid to two silane coupling agents, one commercial silane product and 3-acryloxypropyltrimethoxysilane on the bond durability of resin composite to zirconia. METHODS Zirconia samples were silica-coated by air abrasion and each of the five coupling agents was then applied to give five test groups. Resin composite stubs were bonded onto the conditioned zirconia surfaces. The samples were stored: dry storage, 30 days in water and thermocycled to give a total of fifteen test groups. The shear bond strengths were determined using a universal testing machine and data analyzed by two-way ANOVA and Tukey HSD (p<0.05) with shear bond strength as dependent variable and storage condition and primers as independent variables. The bond formation of the five coupling agents to zirconia was examined by X-ray photoelectron spectroscopy (XPS). RESULTS Two-way ANOVA analysis showed that there was a significant difference for different primers (p<0.05) and different storage conditions (p<0.05) on the shear bond strength values measured. XPS analysis showed a shift in binding energy for O(1s) after priming with the five coupling agents which revealed different bond formations related to the functional groups of the coupling agents. SIGNIFICANCE The shear bond strength values measured for all coupling agents after water storage and thermocycling exceed the minimum shear bond strength value of 5MPa set by ISO. The silane coupling agent, 3-acryloxypropyltrimethoxysilane, showed the highest bond strength of the three storage conditions.

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.

Candida albicans aspects of novel silane system-coated titanium and zirconia implant surfaces.

OBJECTIVES The aim of the present study was to evaluate the effect of novel silane system coatings on zirconia and titanium implant surfaces and the attachment of the fungal pathogen Candida albicans. MATERIALS AND METHODS Titanium and zirconia specimens were silica-coated and silanized either with a commercial silane primer (RelyX Ceramic Primer™, 3M ESPE) or a novel silane system primer. The novel silane system primer was a blend of 1.0 vol% 3-acryloxypropyltrimethoxysilane and 0.3 vol% bis-1,2-(triethoxysilyl)ethane diluted in acidified ethanol-water solvent. The surface roughness (Ra ), the surface free energy and the chemical composition of substrate surfaces after treatments were evaluated. C. albcans biofilms were developed on silica-coated + silanized surfaces during 48 h of incubation time. Colony forming units (CFU) and real-time PCR (RT-PCR) quantified the cells on the material surfaces. Statistical analyses were carried out by 1-way ANOVA, Tukey post hoc and Games Howell post hoc test at 5% significance level (p). RESULTS On zirconia and titanium surfaces, the Ra and the chemical composition of the specimens were equal (P < 0.05). The surface free energy was decreased on titanium specimens and increased on zirconia specimen after silanization. CFU of C. albicans was significantly lower on zirconia coated with RelyX Ceramic Primer™, (P < 0.001) and on titanium coated with both silanes (P = 0.002). RT-PCR revealed no differences between the mean quantities of C. albicans (P ≥ 0.067). CONCLUSION Silica-coating and silanization had modified the titanium and zirconia surfaces significantly. Both the control and experimental silane primers might inhibit the biofilm formation of C. albicans.

Surface segregation and core-level shift of a PdRh alloy studied by XPS

Abstract The surface core-level shift and surface segregation of a Pd93Rh7 alloy have been considered in the light of X-ray photoemission spectroscopy. A core-level shift of the Pd3d line to a lower binding energy as far as the surface atoms are concerned has been observed, which can be expected on the basis of the Z + 1 approximation. Also, surface segregation of Pd atoms has been found by using different take-off angles between the momentum of the escaping photoelectron and the surface of the PdRh alloy. This effect has been discussed in terms of the surface density of electronic states and the d-band occupancy of an alloy.

One-pot synthesis of an Au/Au2S viologen hybrid nanocomposite for efficient catalytic applications

We report a facile one-pot synthesis of Au/Au2S multicomponent nanoparticles supported on viologen (V) as a hybrid nanocomposite. Sodium dithionite was used as the reducing agent for both Au and V precursors and SDS as the stabilizing agent for Au nanoparticles in aqueous reaction medium. Spectroscopy, microscopy and electrochemical measurements confirm the successful composite formation. The as-prepared flower-like composite showed excellent catalytic properties towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The catalytic activity factor of the Au/Au2S–V hybrid was highest in comparison to those reported for polymer supported Au nanoparticle catalysts. The enhanced catalytic performance can be attributed to the strong adsorption of 4-NP molecules onto the cationic V matrix and Au2S nanoparticle surface along with effective donor–acceptor interactions between Au–Au2S nanoparticles and V facilitating the electron transfer at the hybrid interface.

X-ray photoelectron spectra of crystalline LiNbO3:(Er, Yb)

Abstract Core-level XPS spectra of single crystalline LiNbO3:Er,Yb (0.4 at% each) are reported for the first time. They were acquired in the Al Kα monochromatized mode with use of an electron flood gun. In the stable conditions of surface charge neutralization the Nb 3d spectrum indicated a pure +5 valence of Nb without any contribution of lower valences. Despite low concentration of Er and Yb (almost at the XPS detectability limit), their 4d core-level spectra were recorded in a prolonged acquisition time. They were found indicative of the +3 valence state of both dopants.

XPS analysis of surface compositional changes in InSb1−xBix (111) due to low-energy Ar+ ion bombardment

Surface compositional changes induced by multistep 0.2–1.0 keV Ar+ ion bombardment and subsequent annealing of the single crystalline (111) InSb1−xBix (x≅0.005) epitaxial layer have been studied for the first time by X-ray photoelectron spectroscopy (XPS). Application of Ar+ ion beam with energy ≤0.5 keV produced only a slight increase of the Sb/In concentration ratio above 1.0. On the other hand, 1 keV Ar+ bombardment was found as the most efficient preparation step which led to the removal of the surface oxide (identified here as Sb2Ox), severe reduction of surface carbon content, but also to a decrease of Sb/In ratio towards anion deficiency (Sb/In<0.8). Subsequent short time anneal at 310°C became sufficient to reach nearly stoichiometric Sb/In ratio in the surface region. Final XPS measurements of the sputter-cleaned and annealed surface revealed that admixing of Bi into InSb does not shift the binding energies of Sb 3d and In 3d core-levels of the host compound. The binding energy of Bi 4f in InSb1−xBix was found to be the same as in elemental Bi.