e-Journal of Surface Science and Nanotechnology Vol. 15(2017)

We have studied the optical second harmonic generation (SHG) of a rubbed novel polyimide (PI) film having steroidal structure side chains prepared by spin coating on an indium tin oxide (ITO)-coated glass substrate. The second order nonlinear susceptibility χ_ijk⁽²⁾ elements were obtained from the fitting of the SHG data. The symmetry of the polymer chains roughly belonged to Cs symmetry with the rubbing direction parallel to the mirror plane. The average polar (tilt) angle of the rubbed PI chains was determined to be around 16° by using the measured χ_ijk⁽²⁾ elements. [DOI: 10.1380/ejssnt.2017.7]

Thermal decomposition of SiC has been used for the fabrication of high quality monolayer graphene and graphene nanoribbons on semi-insulating substrates. In this work, we propose a selective oxygen etching method to remove buffer layers on SiC surfaces that are connected to monolayer graphene formed from step edges. A thermal treatment in an extreme low partial pressure oxygen diluted by argon atmosphere was found to be effective to etch only the buffer layers and remain monolayer graphene areas intact, which might be significant for the application of graphene to electric/spintronic devices. The etching processes of surface buffer layer investigated by in situ scanning electron microscopy and scanning tunneling microscopy revealed an etching rate dependence on a distance from a step edges, suggesting a distribution of crystallinity of surface buffer layer on a terrace. [DOI: 10.1380/ejssnt.2017.13]

Chemical imaging techniques such as mass spectrometry (MS) imaging and imaging spectroscopy have grown to be important in a variety of fields. Infrared spectrum information, for example is essential to evaluate organic and biological samples. Recently, near-field spectroscopy techniques have been developed that enable higher spatial resolution above the one usually obtainable due to wavelength limitations. In terms of chemical imaging for organic materials, time-of-flight secondary ion mass spectrometry (TOF-SIMS) is one of the powerful techniques because of extremely high sensitivity and high spatial resolution of approximately 100 nm. Since TOF-SIMS does not always provide complete information on complex samples, a complementary technique of similar spatial resolution is required. Near-field infrared microscope (NFIR) is the most promising candidate for a complementary analysis method along with TOF-SIMS. It is, however, often difficult to interpret NFIR data because of the low signal intensity in near-field infrared. Multivariate analysis techniques such as principal component analysis (PCA), which have successfully been applied to TOF-SIMS imaging data, would also likely be helpful for NFIR data interpretation. In this study, a multicomponent model polymer sample was measured with NFIR and then the image data along with the complex NFIR spectra were analysed by PCA. As a result, the components in the model sample can be separately displayed based on groups of peaks specific to every component indicated by PCA. [DOI: 10.1380/ejssnt.2017.19]

The crystallinity, surface morphology and topography of the femtosecond pulsed laser deposited Nd:YAG film under in-situ and post deposition heat treatment were examined. Heat treatment improved the crystallinity of the film with the increase in the reflecting planes shown in X-ray diffraction data. Scanning electron micrograph of the heat treated film surface indicates a small degree of melting. Surface topography of the as-deposited Nd:YAG film under AFM shows size variation to within few tens of nanometers indicating the generation of nanoparticles. Temperature dependence of the cross section area, height and surface roughness of the film was determined and explained by the volume free energy of the film. Our results demonstrate the novel use of femtosecond laser to ablate and deposit laser crystal as well as heat treatment to engineer the structural properties of the film. [DOI: 10.1380/ejssnt.2017.25]

Magnetite (Fe₃O₄) nanoparticles, are promising inorganic nanomaterials for future biomedical applications due to their low toxicity and unique magnetic properties. However, the synthesis of these particles can often be expensive, energy intensive, and non-scalable, requiring the addition of surfactants to stabilize the material to control the particle size and avoid agglomeration. We wish to report a simple, green, surfactant-free electrochemical synthesis of these materials using a closed aqueous system at ambient temperature. Particle diameter, between 19 and 33 nm, was controlled by simply modifying the distance between the electrodes. These magnetite nanoparticles were then fully characterized using both spectroscopy and microscopy. Vibrational magnetometry indicates that as the size of the particle decreases, the magnetic hysteretic gap decreases, although for samples below 25 nm no inter-sample difference was observed. To support this experimental data, we carried out a Density Functional Theory (DFT) analysis of magnetite containing more than three iron atoms in the cluster, an essential proposition as magnetite contains three distinct iron species. These calculations were used to support the experimental observations, and closely reproduced both the experimental IR spectrum, and the XRD pattern. In vitro cytotoxicity assays showed dose responsive behavior for the nanoparticles, and demonstrated that they are non-toxic at clinically relevant concentrations; below 200 μg/mL we observed no toxicity in a 48-hour standard assay. This work represents the first DFT based simulation of this detailed magnetite cluster, and demonstrates that this sustainable synthetic method is capable of producing nanomaterials with a physical and biological profile that might make them suitable for biomedical applications. [DOI: 10.1380/ejssnt.2017.31]

We consider the computation of a long-range interaction energy between a single graphene sheet and a silicon substrate, which arises from vacuum fluctuations. The interaction energy obtained by summation of the Lennard Jones potential between a carbon atom in a single graphene sheet and a silicon atom is compared with the dispersion energy (Casimir energy) obtained by combining the Lifshitz theory and the Dirac model for graphene. Deviation of the pairwise summation of the Lennard-Jones potential from the Casimir energy is corrected by adding a power function term, whose coefficient depends on the distance between atoms. We also consider the interaction between a graphene sheet and a silicon dioxide substrate. [DOI: 10.1380/ejssnt.2017.40]

Rh nanoparticles have been fabricated by the evaporation method using the He gas in the Rh evaporation chamber, connected with the pre-evacuation chamber of BL6N1 at Aichi Synchrotron Radiation Center (Aichi SR). The electronic and geometric properties of the Rh nanoparticles have been verified without atmosphere exposure (in situ XPS) and after atmosphere exposure (ex situ XPS) using SR-XPS and TEM. The size of Rh nanoparticles is estimated 1.8±0.5 nm in diameter and deposited on a substrate. Judging from the result of the in situ XPS analysis with photon energy of 2.0 keV and 3.5 keV, the surface of the deposited Rh nanoparticles without atmosphere exposure is the metallic state. On the other side, the outermost surface changes into Rh oxide after atmosphere exposure even in a short time. For a long time atmosphere exposure moreover, the Rh oxide increases in the depth direction, and the deep area is in the higher oxidation state. [DOI: 10.1380/ejssnt.2017.50]

Dust figures can be used to visualize the distributions of positive and negative charges that remain on the surface of an insulator using two types of charged powder; one is attached to the insulator and positive charges, and the other is attached to negative charges. In this study, dust figures were used to visualize the spreading pattern of an atmospheric-pressure plasma jet when an insulator was irradiated with the plasma jet in air. Observation using a high-speed camera indicates that streamers existed in the plasma and served as a source of both positive and negative charges. An ebonite plate was used as an insulator. White rosin powder and red lead (colored orange) powder were used to obtain positive and negative charge diagrams, respectively. When the ebonite plate was irradiated with an atmospheric-pressure argon (Ar) plasma jet in air, a disc- or ring-shaped dust figure was formed because of the residual positive and negative charges. The shape and size of the dust figure depended on the spreading pattern of the plasma jet on the ebonite plate. The dependence of the dust figure formed by both charges on the irradiation time (1–60 s) and distance (2–40 mm) of the plasma, the applied voltage (4–10 kV), and the Ar gas flow rate (5 or 10 L/min)was determined. [DOI: 10.1380/ejssnt.2017.55]

We have successfully fabricated hollow core-shell type Si/C nanocomposites using a simple process. Si powder was grinded to form Si nanoparticles, mixed with sucrose as a carbon source and ammonium chloride as an expansion agent, and finally annealed in Ar atmosphere. During the annealing, carbon hollow spheres encapsulating Si nanoparticles were spontaneously fabricated through dehydrogenation reaction of the sucrose to form carbon balloons and the balloon expansion by ammonium gas generated during ammonium chloride decomposition. Volume of the empty spaces in the core-shell structure can be controlled by the rising rate in the annealing temperature. This method is suitable for industrial production of hollow Si/C nanocomposites because of its simplicity. [DOI: 10.1380/ejssnt.2017.69]

Surface topography influences cell growth and differentiation. In this study, we used a nano-imprinting method to develop a titanium sheet with 500 nm-, 1 μm-, and 2 μm-wide grooved and pillared structures. We investigated the effects of the surfaces with the micro- and nano-structures on Ca9-22 cell adhesion and proliferation. Ca9-22 cells were cultured in DMEM containing 10% fetal bovine serum and counted adhered cells at 1 and 24 h postculture. Scanning electron microscopy was used to assess cell morphology. Immunofluorescence cell staining was used to evaluate vinculin formation to observe the presence of focal contacts at 24 h. There was no difference in cell adhesion between cells cultured on a plane or groove after 1 h. However, at 24 h, the adhesion of cells cultured on the groove was reduced. In addition, the cell adhesion count on the pillar was less than that of cells cultured on a plane at both 1 hour and 24 h post-seeding. Furthermore, in the groove of the Ti sheet after 1 and 24 h, cell expansion occurred in the grooved direction. These results demonstrate that the micro and nano-grooved and pillared structures on the titanium sheet control Ca9-22 cell adhesion and orientation. [DOI: 10.1380/ejssnt.2017.1]

Biomineralization is the process of forming hard exo- or endoskeltons by biological organisms. The physical properties and the morphology of the composite material that is formed depends on the mode of crystal-growth, which depends on the diffusion of the constituents (metal cations, their anions, and additives). We chose a model system, strontium carbonate / silica, because the precipitation of SrCO₃ and SiO₂ is pH dependent. A lower pH accelerates SiO₂ formation while it slows down SrCO₃ crystallization, and vice versa. Thus, the precipitation of the composite can occur in an alternating fashion, regulating the morphology of the carbonate precipitate. The solution of SrCl₂ and water glass is poured into a shallow container and a glass slide is floated on top, eliminating the effects of bulk precipitation and convection. The pH is adjusted to a starting value of 12, and a small amount of dimethyl carbonate is added. This compound slowly hydrolyses and gives off carbon dioxide, the carbonate source for the crystal growth. The crystal morphology is clearly dendritic and shows several distinct periods of growth. First, a few crystals grow from a common seed, and after a while, the blocking of surface sites on the carbonate crystals by water glass, leads to the start of a more needle-like growth with a significant increase of branching density. Finally, after seven days, coral-like structures are formed. [DOI: 10.1380/ejssnt.2017.65]