Papers by Keyword: Atomic Force Microscope (AFM)

Abstract: 4H-SiC epitaxial layers on Carbon-face (C-face) substrates were grown by a low-pressure hot-wall type chemical vapor deposition system. The C-face substrates were prepared by fine mechanical polishing using diamond abrasives with the grit size of 0.25 %m and in-situ HCl etching at 1400°C, which produced surface roughness of 0.27 nm. The use of the smooth substrates made it possible to decrease the substrate temperature and specular surface morphologies were realized at C/Si ratios of 1.5 or less both for a substrate temperature of 1550°C and for that of 1500°C. Surface roughness of 0.26 nm and the residual donor concentration of 6.7×1014 cm-3 were obtained for a C-face epitaxial layer grown at a C/Si ratio of 1.5 and at a substrate temperature of 1550°C. Schottky barrier diodes were fabricated on a non-doped C-face epitaxial layer grown at 1500°C and it was verified that a high quality metal-semiconductor interface was formed on the epitaxial layer.

Abstract: Physical vapor deposition technique has been employed to develop a thin film of OLED, and atomic force microscopy was used to investigate the boundary characteristics such as uniformity of emitting layer, roughness, and surface morphology. In order to determine the deposition characteristic which associated with the materials failure in OLED, finite element simulation, together with alternative analytical modeling has been carried out by means of island growth mechanism analysis. The boundary growth of thin film can be determined from the velocity of island boundary using simple rate equations. The results obtained are compared with experimental observation. Generally good agreement has been achieved.

Abstract: To develop a better surface conformation of titanium dental implants, we examined the in vitro biocompatibility of a thin natural apatite (NA) film deposited by laser ablation. Thin (2000-Å) hydroxyapatite (HA) and NA films were deposited on titanium discs using an ArF excimer laser operating at a repletion rate of 10 Hz and annealed by heating at 360°C for 1 h. Energy dispersive analysis of the NA film revealed peaks of Na and Mg in addition Ca and P. X-ray diffraction showed that crystalline HA was present in the HA and NA films. Primary mouse osteoblast grew faster and had higher alkaline phosphatase activity when grown in NA films than on HA films or a bare titanium surface. In addition, osteocalsin production by these cells was higher on HA and NA than bare titanium, but there was no significant difference between cells grown on HA and NA. Thus surface modification with NA film may contribute to successful osteoblast function and differentiation at titanium interface.

Abstract: This paper briefly introduces the nano-bio related-research being carried out in our research group. The work is based on a fusion of neuroscience and bio-molecular science with nanotechnology. This interdisciplinary research is extremely promising for creating a new technology and developing a new knowledge. Nano-bio research could be a key to understanding the signal processing mechanism that lies behind memory and the learning system in our brain. Developing a novel biocompatible device that runs with biological functions is one of our research goals.

Abstract: Morphological information can be related to significant properties of solid bodies, like their friction, adhesion and wear. The primary aim of the present contribution is to provide evidences of the crucial role played by roughness in contact mechanics, based on Atomic Force Microscopy investigations at the nanoscale. We report experimental results concerning poly(dimethylsiloxane) colloidal probes indenting smooth substrates and discuss the dependence of load-penetration curves and pull-off forces on system details. We suggest their use to perform novel contact mechanics experiments on nanostructured rough surfaces.

Abstract: Glassy carbon (GC) discs and platinum microcylindrical electrodes were modified with a layer of nickel(II) tetrakis 3-methoxy-4 hydroxyphenyl porphyrin (poly-TMHPP-Ni) of different loadings (Γ) between 0.6 and 10 nmol/cm2, and subsequently with a Nafion layer. The topography and in some cases the thickness of films were measured by means of contact mode AFM. SEM and optical microscopy observations were used for the comparative studies on a larger scale. The useful range of the coverage with modifying polymer was investigated. The optimal value of loading for the sensor was found to be in the range of 6-8 nmole of poly-TMHPP-Ni per cm2. We observed the Nafion layer uniformity in nanometric scale.

Abstract: Electrodes, assigned as GC/Pt-C and GC/Pt-Ru-C, were formed by deposition of Ptbased catalysts (47.5 wt % Pt + high surface area carbon) and (54 wt. % Pt-Ru alloy + high surface area carbon) on glassy carbon (GC) discs. X-ray diffraction measurements were used for the determination of the average crystallite size and phase composition of both catalysts. Crystallite size for Pt-C catalyst was 2.9 nm for Pt-fcc. In the diffraction pattern of the Pt-Ru-C catalyst two phases, e.g. Pt-Ru-fcc and Ru-hcp were refined using the Rietveld method. Crystallite sizes were 3.9 nm for Pt-Ru-fcc and 2.8 nm for Ru-hcp. STM observations of the surface of GC/Pt-C and GC/Pt-Ru-C electrodes revealed the presence of metal particles of the size in the range 2-6 nm and Pt-C or Pt- Ru-C agglomerates in the range of several tenth of nm. The thickness of the Nafion covering layer determined by AFM is ca. 100 nm. A simplified scheme of the investigated electrodes was created.

Abstract: With the development of science and technology, Atomic Force Microscope is widely applied to the field of machining process in nanometer scale. Due to the limitation of the inventive purpose of AFM, only height mode and deflection mode can be applied in AFM-tip micromachining. It can’t control the machining depth during the micromachining process at present. In this paper, a new micromachining system is set up, which composed of a high precision three-dimensional stage, an AFM, a diamond probe and a special control device. By utilizing variation parameters PID algorithm and controlling the machining depth directly, the micromachining system can resolve the problem mentioned above.

Abstract: Since adhesion plays a significant role in microtribology, properties of adhesion work of several materials, such as Si, and mica are investigated by AFM. Experimental results indicate that, measured adhesion work varies with contacting velocity, surface roughness and so on, which is more than a constant. Meanwhile, under invariable loads, friction force of these materials is also measured over a wide range of velocity, which is found that adhesion work of the sample surface directly influences the velocity dependent property of micro friction force. This makes the observed micro frictional behaviour significantly differs from the traditional macro friction laws, in which friction force is proved be independent of sliding velocity. Additionally, with zero or negative load, friction forces are proved to be determined by adhesion work and adhesion contact area. Finally, a relationship between micro friction force and adhesion work is outlined.

Abstract: Atom Force Microscopy (AFM) can be employed to create surfaces in Si substrate with recessed features. The resulting patterns can serve as masters to make the required elastomeric stamps for soft lithography. Morphology analysis of patterned features on Si substrate and polydimethylsiloxane (PDMS) stamp by AFM imaging confirms that pattern can be successfully transferred from Si substrates to PDMS stamps. It is shown that this method for creating masters can be performed with an AFM, making this method particularly straightforward, economical and accessible to a large technical community that are provided with AFM for measurement.