ICMCTF2011 Session FP: Symposium F Poster Session

In this study, we report that the high-density ZnS/ZnO core-shell nanowires were successfully synthesized on a Si substrate using thermal evaporation at a temperature of 1000°C for 1 hr. A field emission scanning electron microscope (FESEM) shows that the ZnS/ZnO core-shell nanowires have a diameter of 50 to 100 nm and a length of several micrometer. An x-ray diffraction (XRD) pattern shows the planes of (100), (002), (110) for the ZnS/ZnO core-shell nanowires. An x-ray photoelectron spectroscopy (XPS) gives Zn₂p₃, S₂p₃ and O 1s. A high-resolution transmission electron microscope (HRTEM) shows that both of ZnS and ZnO are of single crystalline hexagonal wurtzite with a common growth direction of [0002]. An energy dispersive x-ray spectrometer (EDS) indicates peaks of Zn, S and O. The cathodoluminescence (CL) spectra shows that ZnS/ZnO core-shell nanowires exhibit a green emission. The conductivity of ZnS/ZnO core-shell is better than the ZnS nanowire. The photo-sensing measurement demonstrates the ZnS/ZnO core-shell nanowire-based photodetectors have both high sensitivity and low response time, which proves that ZnS/ZnO core-shell nanowires have potential application in future UV photodetectors.

In literature, theoretical studies on phase stability and structure of oxynitrides are rare which limits understanding as well as application of this material system. The aim of this study is to contribute towards understanding of the influence of oxygen on stability and elastic properties of TiAlN.

Using ab initio calculations, defects in TiAlN as well as oxygen incorporation in TiAlN were studied. Vacancies, substitutions, interstitials and combinations thereof in different configurations have been investigated in terms of crystal energies, enthalpies of formation and bulk moduli.

The enthalpies of formation per vacancy are 2.5 eV, 2.0 eV and 3.4 eV for Ti, Al and N, respectively. The enthalpy of formation of the second metal vacancy is 0.3 - 0.5eV higher than for the first, while a second nitrogen vacancy has the same enthalpy of formation as the first one. No indication for interaction of vacancies was observed. Irrespective of the kind of vacancies, the bulk modulus B is reduced linearly with the number of vacancies. Compared to stoichiometric TiAlN B decreases by 7 % when the stoichiometry is changed to (Ti,Al)₁N_0.94 or (Ti,Al)_0.94N₁.

The energy of mixing of TiAlN and hypothetical isostructural TiAlO is negative which may imply the possibility to form TiAlNO in NaCl structure. The influence on enthalpy of formation of metal vacancies is calculated as well as on enthalpy of formation of interstitial oxygen. It is shown that oxygen on the nitrogen sublattice leads to spontaneous incorporation of interstitial oxygen. Possible reasons are discussed.

Thin films of TiAlNO are prepared using High power impulse magnetron sputtering of a TiAl target in mixed nitrogen and oxygen atmosphere. It is shown that high oxygen flux leads to the formation of amorphous films. The influence of temperature on structure, composition and elastic properties is determined.

Nano-textured surfaces (NTSs) can reduce friction and adhesion forces due to the decrease in effective contact area and thus have potential to be applied to micro-electro-mechanical systems to increase their reliability. Here, we report a novel NTS consisting of aluminum nanoislands protruding from a continuous aluminum film on silicon substrate, deposited by thermal evaporation. This surface combines the favorable tribological properties of nanoscale surface-texturing with the enhanced strength provided by a continuous film as compared to isolated nanoislands deposited on a substrate. Characterization of this novel aluminum surface includes scanning electron microscopy, transmission electron microscopy, atomic force microscopy, x-ray diffraction, and energy-dispersive x-ray spectroscopy. Tribological test results showed improved frictional performance as compared to a smooth silicon surface.

Uniform tungsten oxide (W₁₈O₄₉) nanowires were simply synthesized by thermal chemical vapor deposition (CVD) without using any catalyst in a tube furnace via the two-step process 8 00 and 1000°C, respectively. The nanowires have diameters of 15–20 nm and lengths of several micrometers. Morphology, composition, and crystal structure were characterized by scanning electron microscopy (SEM); x-ray diffraction (XRD); transmission electron microscopy (TEM); and energy-dispersive x-ray (EDX), and Raman. SEM images of high-density W₁₈O₄₉ nanowires clearly demonstrate that the nanowires have a uniform one-dimensional morphology high aspect ratio. The result of XRD, TEM, and EDX confirmed the formation of W₁₈O₄₉ nanowires ( lattice constants, a = 1.832 nm; b = 0.3784 nm; c = 1.403 nm) containing W and O atoms, with [010] as the major growth direction. The vapor-solid (VS) mechanism is responsible for the growth of W₁₈O₄₉ nanowires in this experiment since no catalyst were used. We investigated the temperature dependence electrical transport properties of individual W₁₈O₄₉ nanowires. The conductivity is 2.6 Ω^-1cm^-1 at 290K and 42.4Ω^-1cm^-1 at 500K, respectively. The electron activation energy was calculated to be about 0.26eV.

Vertically aligned carbon nanotubes were synthesized using FeNi or Fe sputtering catalyst layers on glass substrates by direct current-plasma enhanced chemical vapor deposition (DC-PECVD) method at low temperature. Electronic field had different intensities in different positions of a PECVD chamber, and strong electronic field produced high concentration of reactive radicals, which enhanced CNTs growth. Therefore, CNTs exhibited different growth rates in different positions due to different intensities of electronic field. With increasing in concentration of O₂ the growth rate of CNTs increased. Adding O₂ can remove amorphous carbon from CNTs and enhance CNTs growth, while adding H₂ can lead to high activity and wetting ability of metal catalyst and enhance growth of CNT. But O₂/H₂ ratio was a key factor on CNTs growth. In DC-PECVD, the CNTs were well aligned vertically. FeNi thin film catalysts exhibited higher activity and better wetting ability than the Fe island thin film catalysts. This article discussed the growth mechanisms of CNTs based on plasma physics, position of substrate, concentration of O₂ and H₂, and catalysts.

In the present study, our developing rf/dc oxygen ashing apparatus is first applied to efficient removal of used DLC coated dies, punches and tools. Different from conventional dc-plasma ashing, the interlayer between main DLC coating and substrate is also removed efficiently without severe damage to substrate. In the present experiment, original mirror-shaped WC (Co) substrate surface is reproduced even after removal processing via rd/dc plasma ashing. Next, nano-laminated DLC film is re-coated onto the recycled substrate. This recycled DLC coated dies and tools are further used in the further steps of progressive stamping. Quality of stamped products is compared

Tantalum thin films have been of importance since the early 1960’s for their use in fabricating resistors and capacitors. Tantalum is of particular interest today because it is a strong candidate to replace electrodeposited (ED) chromium coatings used for various tribological applications, such as the interior lining of large caliber gun barrels. Typically, coatings used for this application require thicknesses 100 µm or more. Modulated pulse power (MPP) magnetron sputtering is a promising deposition technique to deposit thick films due to the ability to generate high metal ion fluxes with low ion energies. Thin and thick tantalum coatings ranging from 2 – 100 µm were deposited by MPP at 2 kW, 5 mTorr and – 50 V substrate bias. The microstructure and properties of the coatings were characterized by glancing incident angle X-ray diffraction and conventional X-ray diffraction, nanoindentation, scratch test and scanning electron microscopy. The effect of the coating thickness on the coating residual stress, phase formation, grain size, surface roughness and mechanical properties will be presented in detail.

The results of the EDS analysis of sample 1 showed that the calcium/ phosphorus (Ca/P) ratio of the enamel was approximately 1.54, the Ca/P ration of the dentin was approximately 1.02, and the Ca/P ratio of the cementum was approximately 0.96. The results of the EDS analysis on the crown, root, and total tooth powder of sample 2 showed that the Ca/P ratios of the total tooth were 1.46 and 1.24, which were comparable to the values of tricalcium phosphate (TCP) and octacalcium phosphate (OCP). The crown portion had a ratio of 1.75, which was comparable to the hydroxyapatite (HA) value, and the root portion had a ratio of 1.32, which was similar to the amorphous calcium phosphate (ACP) value. In XRD, HA and TCP were detected in all samples. We confirmed that the dental crown portion was primarily composed of high-crystalline calcium phosphate while the root portion was composed of poor-crystalline calcium phosphate. Favorable bony remodeling by osteoconduction could be anticipated if the dentin and cementum portion of the tooth, which was the largest portion of the tooth, was used as the bone graft materials because they contained low-crystalline apatite.

The incorporation of metal or metal carbide nanoparticles into or onto carbon nanofibers (CNFs) has recently highlighted new applications of carbon structures at the nanoscale. These nanofibers are considered as a promising candidate for sensors application at the nanoscale. Nickel-carbon composite nanofibers (c-Ni/CNFs) are attractive for various applications due to their promising properties. The elaboration of this type of material is considered as a challenge in the field of nanoscience. The purpose of this work is to report a new, easy and cheap method in order to prepare organized c-Ni/CNFs. This method consists in combining two plasma processes PVD and PECVD (Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition) for direct growth of horizontal and aligned c-Ni/CNFs on silicon nanopatterned substrate prepared by laser interference lithography. Before integrating these nanofibers in complex nanodevices we characterize it by various analysis techniques. The observation of these nanofibers with scanning electron microscopy demonstrates their very high length (up to several millimeters) and their good flexibility. Their diameter is about 150 nm. Micro-Raman spectroscopy performed on a single nanofiber, after being dispersed on a silicon substrate, shown that the carbon phase was amorphous. The chemical composition of the nanofibers was determined by XPS, and the presence of nickel nanoparticles was demonstrated by high resolution transmission electron microscopy imaging. After the optimization of the growth of the nanofibers, the impacts of the deposition time and of the dimensions of the nanopatterned silicon substrate on the growth of the nanofibers are studied. By controlling these two parameters (deposition time and the dimensions of the nanopatterned substrate) it is possible to control the diameter of the nanofibers between 80 nm (the lower value reached by this process) and 400 nm. This synthesis technique gives the opportunity of synthesizing nickel/carbon nanofibers with a very high length, with a controlled diameter and microstructure.

X-ray tubes using cold cathodes as electron source has recently attracted great attention in a wide range of applications, especially in x-ray radiography such as diagnostic medical imaging and embedded-type radiation brachytherapy, because they have a lot of advantages, including possibility of miniaturization, fast response, low power consumption, and low fabrication cost, over the x-ray systems using conventional thermionic cathodes. Carbon nanotubes (CNTs) have been considered to be one of the most promising materials for point-type cold electron sources due to their mechanical and chemical stability as well as superior electron emission properties. The CNT-based field emission cold cathodes have been fabricated either by direct growth of CNTs on substrates or by indirect technique. The direct growth by CVD process has several problems, such as difficulties in controlling each CNT, the complexity of the fabrication process, and high growth temperature. The indirect printing method, by contrast, is a relatively simple process and can be done for a lower cost than the direct growth method, but also has many technical limitations including non-uniform dispersion of the CNT powders, poor adhesion between the substrate and the CNT layer, and emission degradation by residues of binder.

Nanocomposites of polyaniline nanofibers and polyimide were fabricated and studied using small angle neutron scattering (SANS). The immiscible nature of the conformationally dissimilar polyaniline nanofiber and polyimide host is established by a series of experiments involving neutron scattering. Based on these techniques, we conclude that the crystal structure of the polyimides is not disrupted, and that there is no mixing on a molecular level between the two components. The morphology of the conducting salt component was analyzed by SANS data and was treated by two common models: Debye-Bueche (D-B) and inverse power law (IPL). Due to deviations in the linear curve fitting over a large scattering range, neither the D-B nor the IPL model could be used to characterize the size and shape of all PANI-0.5-CSA/polyimide blend systems. At 1 and 2% concentration, the D-B model suggested salt domains between 20 and 70 Å with fractal geometries implied by the IPL model. As salt concentrations are increased to 5%, the structures are observed to change, but there is no simple structural model that provides a suitable basis for comparison.

Recently, carbon nanotubes (CNTs) have been researched to develop a cold cathode electron source in x-ray system for medical applications such as diagnosis and brachytherapy of cancers. In order to realize a high-resolution x-ray image by using CNTs, their field-emission properties should be enhanced and, at the same time, the fine focusing of the electron beam should be required. For this purpose, tip-type CNT-emitters were proposed by our previous works, where the CNTs were directly grown on conical-type metal-tip substrates. The results showed that the tip-type CNTs had much better electron-emission properties and smaller beam areas than conventional CNTs that used flat-type substrates like Si wafer. However, the peel-off phenomenon of the CNTs after a prolonged operation occurred at the summit part of the tip, which led to the degradation of the emission current. For this reason, more studies on stable and sustaining electron emission from CNTs are still required for the practical use of CNT-emitters as cold cathodes. It is unfortunate, however, that this issue has hardly been considered in the literature.

In this study, we have aimed to develop a tip-type CNT-emitter that can provide highly stable and at the same time less fluctuated emission currents by investigating the effects of tip-curvatures and selective CNT-growth on their field-emission properties. The CNTs were directly grown on conical-type metal tips employing an inductively coupled plasma-chemical vapor deposition system. The conical tips were made through electrochemical etching of a tungsten wire and prepared to have different tip-curvatures (which were controlled by changing the conical angle of the tip from approximately 10^o to 180^o) by varying the etching time, the molarity of chemical (KOH), and the applied voltage between a anode and a cathode. Prior to growth of CNTs, a thin film of Ni as a catalyst was deposited and then treated using NH₃ plasma to form Ni islands for nucleation. Here, the area of the plasma-treated Ni layer was defined using a chemical etching method so that the CNTs were selectively grown only on the region where the Ni islands existed. For all the grown CNTs, their morphologies and microstructures were analyzed by scanning electron microscopy. Furthermore, their electron-emission properties including the current fluctuation and the long-term variation of emission current were measured and characterized in terms of tip-curvatures and selectively-grown CNT areas. In addition, to analyze the trajectory and beam size of electrons emitted from the CNTs, the field-emission microscopic images and the corresponding intensity profiles of brightness were extracted.

In this work, species as N₂⁺, N₂, O and O⁺ was analyzed by optical emission spectroscopy (OES) into the plasma of Ar-N₂-O₂ gas mixture. Argon and nitrogen flux was fixed in 2 and 4 sccm, respectively and varied the oxygen flux between 2 and 4 sccm. It was observed the influence of both gas and species concentrations in the surface properties after thermochemical plasma treatment. Surface tension measurements on the samples showed increasing in the dispersive coordinate proportionally to oxygen flow and it promoted an increasing in the angle contact. The DRX has presented a solid solution of nitrogen and titanium oxides (resultado importante?). The AFM measurements have shown different topographies and roughness values. Based on those characterization analysis it has been seen which a relation among luminous intensities and surface parameters. Nanohardness assays and elasticity module also presented variance accord to the luminous intensity of N₂⁺ species.