Self-Assembly of Soot Nanoparticles on the Surface of Resistively Heated Carbon Microtubes in Near-Hexagonal Arrays of Micropyramids.

Almost regular hexagonal arrays of microscopic pyramids consisting of soot nanoparticles are formed on the surface of graphitized hollow filaments, which are resistively heated to ∼1800-2400 °C under an Ar atmosphere containing trace amounts of oxygen (∼300 ppm). At higher temperatures (T > 2300 °C, approximately) the soot particles are represented mainly by multishell carbon nano-onions. The height and width of the pyramids are strongly dependent on the temperature of the resistive heating, diminishing from 5 to 10 µm at T ≈ 1800 °C to ∼1 µm at 2300-2400 °C. Quasi-hexagonal arrays of the micropyramids are organized in the convex "craters" on the surface of the microtubes, which grow with the time of the thermal treatment. The pyramids always point normally to the surface of the craters, except at the boundaries between the craters, where the normal direction is not well-defined. The pyramids are soft and can be easily destroyed by touching them but can be hardened by heating them under an oxygen-free atmosphere. The pyramids are observed only on the exterior surface of the microtubes, not on their inner surface. This suggests that the thermophoretic force generated by a strong temperature gradient near the external surface of the tubes may be the cause of the micropyramid formation. Electrostatic charging of the soot nanoparticles due to thermionic emission may also be relevant to this phenomenon. The micropyramids can function as field emission point sources, as demonstrated with the use of a micronanoprobing station, mounted in a scanning electron microscope.

Characterization of carbon surface chemistry by combined temperature programmed desorption with in situ X-ray photoelectron spectrometry and temperature programmed desorption with mass spectrometry analysis.

The analysis of the surface chemistry of carbon materials is of prime importance in numerous applications, but it is still a challenge to identify and quantify the surface functional groups which are present on a given carbon. Temperature programmed desorption with mass spectrometry analysis (TPD-MS) and X-ray photoelectron spectroscopy with an in situ heating device (TPD-XPS) were combined in order to improve the characterization of carbon surface chemistry. TPD-MS analysis allowed the quantitative analysis of the released gases as a function of temperature, while the use of a TPD device inside the XPS setup enabled the determination of the functional groups that remain on the surface at the same temperatures. TPD-MS results were then used to add constraints on the deconvolution of the O1s envelope of the XPS spectra. Furthermore, a better knowledge of the evolution of oxygen functional groups with temperature during a thermal treatment could be obtained. Hence, we show here that the combination of these two methods allows to increase the reliability of the analysis of the surface chemistry of carbon materials.

Influence of surface chemistry on the adsorption of oxygenated hydrocarbons on activated carbons.

The objective of this work was to study the adsorption of different oxygenated hydrocarbons (methanol, ethanol, 1 and 2-butanol, methyl acetate) on activated carbons from organic mixtures with cyclohexane. Three activated carbons prepared by thermal and chemical treatments of a commercial carbon were employed for this purpose. Their textural properties were found to be similar, whereas their surface chemistries were modified, as shown by temperature-programmed desorption coupled to mass spectrometry (TPD-MS) and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms were obtained by depletion method, and the analysis of adsorbed species was evaluated by TPD-MS to obtain new insight into the interactions between the different hydrocarbons and the carbon surface. Ethanol leads to a high-energy interaction between its hydroxyl function and the oxygenated surface groups and also to a lower energy interaction between the aliphatic part of the molecule and the carbon material. The desorption activation energy for this hydrophilic interaction is high (50 to 105 kJ/mol), and it is related to the nature of the carbon surface groups. The relative importance of these two interactions depend on the size of the alcohol/methanol is similar to ethanol, whereas butanols lead to more dispersive interactions. Methyl-acetate cannot undergo this kind of strong interaction and behaves like cyclohexane, having desorption activation energies ranging between 25 and 45 kJ/mol no matter the molecule and the carbon surface chemistry.

Direct Laser Writing of Crystallized TiO2 and TiO2 /Carbon Microstructures with Tunable Conductive Properties.

Metal oxides are an important class of materials for optoelectronic applications. In this context, developing simple and versatile processes for integrating these materials at the microscale and nanoscale has become increasingly important. One of the major remaining challenges is to control the microstructuration and electro-optical properties in a single step. It is shown here that near-infrared femtosecond laser irradiation can be successfully used to prepare amorphous or crystallized TiO2 microstructures in a single step using a direct laser writing (DLW) approach from a TiO2 precursor thin film doped with a suitable dye. When laser writing is conducted under a nitrogen atmosphere, simultaneous to the crosslinking of the Ti-oxide precursor, the graphitization of the organic species embedded in the initial film is observed. In this case, a carbon network is generated within the TiO2 matrix, which significantly increases the conductivity. Moreover, the TiO2 /C nanocomposite exhibits piezoresistive behavior that is used in a pressure sensor device. Using this route, it is possible to use DLW to fabricate microsized pressure sensors.

Influence of hydroxyapatite microstructure on human bone cell response.

Microstructure of calcium phosphate ceramics has been shown to influence long-term in vitro cellular events like proliferation and differentiation, and to favor bone integration in vivo. As long-term cellular events are known to be dependent of early cell adhesion events, we decided to study the in vitro influence of the microstructure of a microporous hydroxyapatite (mHA) and a nonmicroporous hydroxyapatite (pHA) ceramic on serum protein adsorption and SaOs-2 human bone cells attachment after 30 min, 1, 4, and 24 h and cell growth after 96 h. Plastic coverslips were used as controls. Hydroxyapatite composition of mHA and pHA was confirmed by X-ray diffraction and Fourier transform infra-red spectroscopy. The surface energies of ceramics were calculated from contact-angle measurements in di-iodomethane, water or complete culture medium. The total surface energy was 44.8 mJ/m(2) for pHA and 48.7 mJ/m(2) for plastic. The contact-angle measurement was impossible on mHA likely because they displayed 12% of open microporosity, pHA ceramic exhibiting only closed pores (2.5%). Moreover, the roughness amplitude was largely higher on mHA (Sa = 4.35 microm) than on pHA (Sa = 0.065 microm) and plastic (Sa = 0.042 microm). Three different techniques were used to evaluate protein adsorption on the ceramics. SDS-PAGE of desorbed proteins demonstrated that more proteins desorbed from mHA (66.02 microg/m(2)) than from pHA (17.2 microg/m(2)) or plastic (0.08 microg/m(2)). A new method was used to evaluate in situ the quantity of adsorbed total proteins: the temperature-programmed desorption (TPD) analysis coupled with mass spectrometry. The TPD analysis confirmed that 10-fold more proteins adsorbed on mHA compared with those on pHA. A direct immunolabeling on ceramics revealed than more fibronectin and serum albumin adsorbed on microporous ceramic than on dense ceramic. The morphology of SaOs-2 cells was the same on all the substrates after 30 min. At later time points, cell morphology on mHA was radically different than on other surfaces, with the particularity of the cytoplasmic edge that appeared undistinguishable from the surface. Only the extremity of the cells and lamellipodia were visible. Cells seemed like "adsorbed" by the mHA surface, whereas on plastic and pHA surfaces the cells displayed classical aspects of polygonal spreading. The cells displayed on mHA the highest initial attachment potential after 30 min, 1, 4, 24 h but the lower proliferation potential after four days. This study confirms that a microporous ceramic surface can modulate the adsorption of proteins and further the adhesion and proliferation of human bone cells.

Improving of understanding of beta-hexachlorocyclohexane (HCH) adsorption on activated carbons by temperature-programmed desorption studies.

In order to understand the interactions between beta-hexachlorocyclohexane (HCH) and chemical groups at activated carbon (AC) surface, the solid samples were hydrogenated aiming to decrease the amounts of oxygenated groups. Two AC samples designated by BagH2O and BagP1.5 were prepared by water vapor activation and phosphoric acid activation, respectively, of sugarcane bagasse used as an AC precursor. A more simple molecule 1,2,3-trichloropropane (TCP) is used as a model of chlorinated compound. The AC were characterized by infrared, X-ray photoelectron spectroscopy (XPS), Raman resonance spectroscopies, as well as temperature-programmed desorption coupled with mass spectrometry (TPD-MS). BagP1.5 and BagH2O AC surface contained oxygenated groups. Upon hydrogenation, a decrease of most of these group amxounts was observed for both samples, while hydroxyl groups increased. On the basis of temperature-programmed desorption data obtained for AC samples contaminated with TCP or HCH, it was possible to determine the type of hydrogen bond formed between each AC and HCH.

Synthesis of magnesium- and manganese-doped hydroxyapatite structures assisted by the simultaneous incorporation of strontium.

Samples of crystalline hydroxyapatite (HA) with and without the addition of individual Mg(2+), Mn(2+) and Sr(2+) ions and samples with the addition of all three ions simultaneously were prepared using the precipitation method in an aqueous medium. Chemical, structural, spectroscopic and thermophysical analyses of the synthesized samples were conducted. The obtained results indicate that Sr(2+) ions were easily incorporated into the HA crystal structure, whereas it was difficult to incorporate Mg(2+) and Mn(2+) ions into the HA lattice when these ions were individually introduced into the samples. The synthesis of HA with Mg(2+) or Mn(2+) ions is characterized by the formation of HA with a low concentration of doping elements that is outweighed by the amount of these atoms present in less biocompatible phases that formed simultaneously. However, the incorporation of Sr(2+) along with Mg(2+) and Mn(2+) ions into the samples allowed for the synthesis of HA with considerably higher concentrations of Mg(2+) and Mn(2+) in the crystal lattice.

Inorganic-organic thin implant coatings deposited by lasers.

The lifetime of bone implants inside the human body is directly related to their osseointegration. Ideally, future materials should be inspired by human tissues and provide the material structure-function relationship from which synthetic advanced biomimetic materials capable of replacing, repairing, or regenerating human tissues can be produced. This work describes the development of biomimetic thin coatings on titanium implants to improve implant osseointegration. The assembly of an inorganic-organic biomimetic structure by UV laser pulses is reported. The structure consists of a hydroxyapatite (HA) film grown onto a titanium substrate by pulsed-laser deposition (PLD) and activated by a top fibronectin (FN) coating deposited by matrix-assisted pulsed laser evaporation (MAPLE). A pulsed KrF* laser source (λ = 248 nm, τ = 25 ns) was employed at fluences of 7 and 0.7J/cm(2) for HA and FN transfer, respectively. Films approximately 1500 and 450 nm thick were obtained for HA and FN, respectively. A new cryogenic temperature-programmed desorption mass spectrometry analysis method was employed to accurately measure the quantity of immobilized protein. We determined that less than 7 µg FN per cm(2) HA surface is adequate to improve adhesion, spreading, and differentiation of osteoprogenitor cells. We believe that the proposed fabrication method opens the door to combining and immobilizing two or more inorganic and organic materials on a solid substrate in a well-defined manner. The flexibility of this method enables the synthesis of new hybrid materials by simply tailoring the irradiation conditions according to the thermo-physical properties of the starting materials.