International Journal of Nanoscience

This paper focuses on the use and value of XPS and NEXAFS spectroscopies to unveil the nature of the chemical bond of various bifunctional nitrile molecules adsorbed on Si(001) 2×1 at 300 K. The adsorption modes are also discussed in the light of recent theoretical publications devoted to optimized geometries and reaction paths of these molecules on Si(001).

The mechanism of cycloaddition reaction between ethylene and the Si dimer on Si(100) is discussed from our recent experimental results using high-resolution electron energy loss spectroscopy and valence photoelectron spectroscopy at ~50 K. The weakly adsorbed π-complex state is identified as a precursor for di-σ bond formation and the activation barrier is roughly estimated to be ~0.2 eV. A different reaction route may exist since a di-σ species is also observed at low temperature. Using cycloaddition reaction, unsaturated organic molecules are chemically attached to the dimer on Si(100), and the adsorbed species are relatively stable. Thus, scanning tunneling spectroscopy (STS) measurements of a single adsorbed molecule can be carried out at room temperature. We report the STS results of 2-butyne adsorbed on Si(100).

Trifluoropropyl-trichlorosilane reagents were used to tailor the surface chemistry of porous nano-structured thin films fabricated using glancing angle deposition (GLAD). GLAD produces high surface area films of isolated columnar structures and provides complete control over the film morphology. Here, the chemical tunability of these GLAD films was investigated using solution and vapor-phase surface functionalization methods. All films were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and advancing aqueous contact angle measurements. Our results indicate that the surface chemistry of the GLAD films was effectively changed after functionalization by either approaches. We also note that vapor-phase functionalization provides more consistent results and eliminates the need for organic solvents, making it an ideal method for tailoring the surface properties of GLAD films for specific applications.

Protein microarray or protein chip is an important tool in proteomics. However, duplicating the success of the DNA chip for the protein chip has been difficult. This account discusses a key issue in protein microarray development, i.e., surface chemistry. Ideally, the surface chemistry for protein microarray fabrication should satisfy the following criteria: the surface resists nonspecific adsorption; functional groups for the facile immobilization of protein molecules of interest are readily available; bonding between a protein molecule and a solid surface is balanced to provide sufficient stability but minimal disturbance on the delicate three-dimensional structure of the protein; linking chemistry allows the control of protein orientation; the local chemical environment favors the immobilized protein molecules to retain their native conformation; and finally, the specificity of linking chemistry is so high that no pre-purification of proteins is required. Strategies to achieve such an ideal situation are discussed, with successful examples from our laboratories illustrated. Finally, the need of surface technology for membrane protein microarray fabrication is addressed.

CaSi₂ with a Zintl phase was investigated for the synthesis of nanosheets due to its facile formation of Ca²⁺(Si^-)₂. The anionic Si^- is isoelectronic with V elements and forms anion partial lattices of corrugated layers like As. The Ca²⁺ planar layers are sandwiched between the anion layers. This CaSi₂ precursor was dispersed in a tetrabutylammonium hydroxide (TBA⁺OH^-), and the resulting solid was lamellar Si·TBA composite. Finally, simple heat treatment of the lamellar precursor at 950°C under vacuum leads to Si nanosheets. The Si nanosheets grown along [111] direction has lateral dimensions up to several hundreds of microns, and thickness of 20–70 nm. Photoluminescence measurements reveal that the present Si nanosheets have visible emission bands ranging from green to red.

A study on recombination of neutral oxygen atoms on the surface of different metals is presented. The source of oxygen atoms was a weakly ionized highly dissociated oxygen plasma created in an inductively coupled radio-frequency discharge. Ionized particles as well as excited molecules were effectively recombined and de-excited on the walls of a noncatalytic tube between the discharge and the experimental chamber, so the gas in the latter consisted only of well-thermalized neutral molecules and atoms. The density of oxygen atoms in the experimental chamber was measured with a catalytic probe. Depending on discharge parameters, the O density was between 2×10²⁰ and 5×10²¹ m^-3. Thin foils of different metals were mounted in the experimental chamber and exposed to oxygen atoms. Due to heterogeneous surface recombination of oxygen atoms on the surface of the samples, the metal temperature was increased well above the ambient temperature. The recombination coefficient was calculated from the foil temperature using physical formalism. Among the materials tested the highest recombination coefficient of 0.41 was found for pure polycrystalline iron. The recombination coefficient for flat and well-oxidized nickel, copper, stainless steel, and niobium were found to be 0.27, 0.23, 0.07, and 0.09, respectively, while the recombination coefficient for nanostructured niobium was 0.8. The accuracy of these values was estimated to be about 30%.

We have investigated the electronic structure of the interface formed by depositing Au on Cs-doped and Na-doped tris(8-hydroxyquinoline) aluminum (Alq) film using ultraviolet and X-ray photoemission spectroscopy (UPS and XPS). The initial Au deposition quenches the Alq gap state caused by the alkali metal doping. Further Au depositions shift gradually the energy levels opposite to that induced by Cs doping, especially the highest occupied molecular orbital (HOMO) that shows approximately full recovery to the pristine Alq position. However, the recovery is only partial for other levels, most noticeably the C 1s core level. The results indicate that the gap state and energy level positions can be decoupled in the organic semiconductors, and that it is possible to fine tune the electronic structure by selective doping in the interface region.

Based on a first principles study of the interaction of carbon with Ni(111), a new way is proposed to improve the coking resistance of Ni-based catalysts. Three forms of chemisorbed carbon—on-surface carbon atoms, bulk nickel carbide and graphene — are distinguished and their relative stability is studied. At low coverages, on-surface carbon atoms will diffuse to the Ni bulk until saturation at a C:Ni mole fraction of about 1:2. The formation of the carbide will affect the catalytic properties of Ni and might lead to catalyst deactivation. When the on-surface carbon can accumulate to high coverages, formation of a graphene overlayer becomes preferred, leading to surface blocking and catalyst deactivation. Boron was found to be a potential promoter to prevent coking of Ni-based catalysts by effectively blocking the diffusion of carbon into the Ni bulk.

N-doped anatase TiO₂ has been prepared by thermal decomposition of Ti containing metal complexes. The light absorption onset has been shifted to the visible region by ~ 100 nm when compared to pure TiO₂. The N environment of N-doped TiO₂ has been studied by XPS and the results confirm the presence of N–Ti–O in the N-doped samples. Also, there is a shift in the binding energy values of Ti 2_p3/2, and the additional peak for O 1s in N-doped TiO₂ confirms the increase in the covalent nature of TiO₂ during the N-doping. The photocatalytic activity of N-doped TiO₂ has been studied both in the UV and visible regions and N-doped TiO₂ shows higher activity than the Degussa TiO₂ in the visible region.

In this work, the effect of oxyfluorination on surface characteristics of carbon fibers was investigated in terms of fracture toughness and crack resistance properties of the epoxy matrix composites. The surface properties of the carbon fibers were determined by the acid-base values, X-ray photoelectron spectroscopy (XPS), and FT-IR measurements. And their fracture toughness of the composites was studied in critical stress intensity factor K_IC and critical energy release rate mode II G_IIC. As the experimental XPS results showed, O_1S/C_1S ratio was increased by oxyfluorination, due to the oxygen-containing functional groups and the format in the C–F_x bonds on carbon fiber surfaces. It was found that the fracture toughness and crack resistance of the composites were improved by the oxyfluorination, which could probably be attributed to the increase of the degree of adhesion at the interfaces between the carbon fibers and epoxy resin matrix in the present composite system.

The large surface area of inert carbon nanotubes (CNTs) and carbon fibers (CFs) renders insufficient interaction between the CNTs and CFs with the organic matrix. The filler–matrix interactions consequently become important to ensure sufficient wetting and filler dispersion in the matrix. The optimized functionalization method for both the CNTs and CFs will improve the viability of the entities for applications. In this report, we present a comparison between single-walled, multi-walled CNTs and pitch-based CFs in terms of their susceptibility to oxidation. The effects of functionalization reactions and extent of reaction are analyzed in terms of morphology, destruction of graphitization and hydrophobicity of the CNTs and CFs.

The shape and size control of barium compound nanoparticles (barium chromate, barium sulfate, barium carbonate) was examined using the water-in-oil microemulsion as nanometer-sized reaction medium. The barium compound nanoparticles were synthesized using the microemulsion formed by AOT as an anionic surfactant and iso-octane as an organic solvent. Chromate, sulfate, or carbonate-containing microemulsion solution and Ba(AOT)₂ reverse micelle solution were mixed. After a few days, the morphology of the product material was observed using TEM. Then, bundle of the nanowire, chain structure of the nanorod, superlattice structure of the nanodot, and dispersed nanodot were synthesized by changing material concentration and material molar ratio. It has been shown that the aspect ratio of the generated particles decreased with increase in the anionic ion concentration. In contrast, the aspect ratio did not change even if the barium ion concentration changed. The surfactant AOT has selectively adsorbed on the specific crystal faces and suppressed their crystal growth. And, the generated particles were self-organized by the hydrophobic interaction of hydrophobic group of the AOT molecule adsorbed onto the particle. In conclusion, it was clarified that the supersaturation ratio and the particle–surfactant interaction were important factors for controlling the shape and size of the inorganic nanoparticles.

Carboxyl PAMAM dendrimer (3.5 generation) was covalently coupled onto amine modified glass surface to prepare a monolayer of high density functional linkers. Activation of the carboxyl PAMAM surface and the subsequent immobilization of antibodies resulted in a high density protein microarray as compared to linear carboxyl linker surface. In addition, fluorescent labeled cell lysate showed extremely low nonspecific adsorption to the PAMAM modified surface, comparable to inert PEG surface. Thus, the carboxyl PAMAM modified surface is ideal for the generation of high density protein arrays for the detection of dilute antigens with superior sensitivity.

The effect of UV–IR radiation and electron on polymers has been widely studied. However, independent irradiation effects in different energy domain of electron are of greater interest. We have installed 10 keV electron beam which has zero background of UV–IR using solenoid guided electron beam upto 100 nA/cm². The effect of electron beam changes the microstructure upto a few microns of polymers, which results in the variation in the physical, chemical, and gas permeation properties. The polymer membrane of 25 μm is exposed to an electron beam with 50 μm grid structure on the top. The RGA spectra of polymers during the irradiation were recorded. The optical micrograph shows a depression on the surface due to electron impact and scission of the polymer chains. The gas permeation also gets modified in such a way that permeation rate was higher from the irradiation side.