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Amorphous Layer (amorphous + layer)
Selected AbstractsCatalyst-Free Synthesis and Characterization of Metastable Boron Carbide NanowiresADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Aruna Velamakanni Abstract Catalyst-free growth of boron carbide nanowires is achieved by pyrolysis of diborane and methane at 650,750,°C and around 500 mTorr in a quartz tube furnace. Electron-diffraction analysis using a novel diffraction-scanning transmission electron microscopy (D-STEM) technique indicates that the crystalline nanowires are single-crystal orthorhombic boron carbide. TEM images show that the nanowires are covered by a 1,3,nm thick amorphous layer of carbon. Elemental analysis by electron energy loss spectroscopy (EELS) shows only boron and carbon while energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) show the presence of oxygen as well as boron and carbon. [source] Combining Ar ion milling with FIB lift-out techniques to prepare high quality site-specific TEM samplesJOURNAL OF MICROSCOPY, Issue 3 2004Z. HUANG Summary Focused ion beam (FIB) techniques can prepare site-specific transmission electron microscopy (TEM) cross-section samples very quickly but they suffer from beam damage by the high energy Ga+ ion beam. An amorphous layer about 20,30 nm thick on each side of the TEM lamella and the supporting carbon film makes FIB-prepared samples inferior to the traditional Ar+ thinned samples for some investigations such as high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). We have developed techniques to combine broad argon ion milling with focused ion beam lift-out methods to prepare high-quality site-specific TEM cross-section samples. Site-specific TEM cross-sections were prepared by FIB and lifted out using a Narishige micromanipulator onto a half copper-grid coated with carbon film. Pt deposition by FIB was used to bond the lamellae to the Cu grid, then the coating carbon film was removed and the sample on the bare Cu grid was polished by the usual broad beam Ar+ milling. By doing so, the thickness of the surface amorphous layers is reduced substantially and the sample quality for TEM observation is as good as the traditional Ar+ milled samples. [source] Hydrolysis of ,-Tricalcium Phosphate in Simulated Body Fluid and Dehydration Behavior During the Drying ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2007Xiang Wei The hydrolysis of ,-tricalcium phosphate (,-TCP) in a simulated body fluid (SBF) at 37°C was investigated. The hydration rate was found to be slower in SBF than that in deionized water. The concentration of ions in SBF was monitored by ICP. The hydrolysis product, which was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infra red, and X-ray photoelectron spectroscopy, was determined to be carbonate-containing, calcium-deficient hydroxyapatite (CO3,CDHAp) with Mg2+, Na+, and Cl, impurities similar to the biological apatite. An amorphous layer on the ,-TCP surface was found to be the precursor of the apatite phase, which may either form crystalline apatite or may decompose back to ,-TCP at a lower temperature. [source] Cubic-Formation and Grain-Growth Mechanisms in Tetragonal Zirconia PolycrystalJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003Koji Matsui The microstructure in Y2O3 -stabilized tetragonal zirconia polycrystal (Y-TZP) sintered at 1300°,1500°C was examined to clarify the role of Y3+ ions on grain growth and the formation of cubic phase. The grain size and the fraction of the cubic phase in Y-TZP increased as the sintering temperature increased. Both the fraction of the tetragonal phase and the Y2O3 concentration within the tetragonal phase decreased with increasing fraction of the cubic phase. Scanning transmission electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) measurements revealed that cubic phase regions in grain interiors in Y-TZP generated as the sintering temperature increased. High-resolution electron microscopy and nanoprobe EDS measurements revealed that no amorphous layer or second phase existed along the grain-boundary faces in Y-TZP and Y3+ ions segregated at their grain boundaries over a width of ,10 nm. Taking into account these results, it was clarified that cubic phase regions in grain interiors started to form from grain boundaries and the triple junctions in which Y3+ ions segregated. The cubic-formation and grain-growth mechanisms in Y-TZP can be explained using the grain boundary segregation-induced phase transformation model and the solute drag effect of Y3+ ions segregating along the grain boundary, respectively. [source] A comparative investigation of the damage build-up in GaN and Si during rare earth ion implantationPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008Florence Gloux Abstract The medium range implantation of rare earth ions at room temperature in GaN layers leads to the formation of point defect clusters, basal and prismatic stacking faults from the lowest fluence. When a threshold fluence of about 3 × 1015 at/cm2 is reached, a highly disordered ,nanocrystalline layer' (NL) is observed to form at the surface. This layer is made of a mixture of misoriented nanocrystallites and voids. Beyond this NL, I1, I2 and E basal stacking faults (BSFs) have been identified, as well as in GaN implanted at lower fluences than the threshold. Prismatic stacking faults (PSFs) with Drum atomic configuration connect the I1 BSFs. A similar investigation of the damage in Eu implanted Si shows a completely different behaviour; in this case, from the relatively low fluence 1 × 1014 at/cm2, amorphization starts in patches at the projected range and extends very rapidly towards the surface and the bulk, to form a uniform amorphous layer already at 2 × 1014 at/cm2. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ta-C/Si heterojunction diodes with apparently giant ideality factorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Marc Brötzmann Abstract A common feature of many wide band gap heterojunction diodes is an unexplained large ideality factor n > 2. In this context we investigate the diode characteristics of heterojunction diodes consisting of a crystalline semiconductor material such as Si covered with a thin semiconducting film of amorphous or disordered material. As thin amorphous film we use tetrahedral amorphous carbon (ta-C). These heterojunctions exhibit a pronounced rectifying behavior, low saturation current and low parasitic currents. Moreover, we observe an apparently giant ideality factor reaching values of n > 75. As a consequence, the turn on voltage is around 3 , 10 V and the I-V curves can be measured for bias up to 40 V without reaching saturation or electrical breakdown. We present a quantitative model for the unusual diode characteristics of these Metal , Amorphous Semiconductor , Semiconductor diodes (MASS-diodes). We demonstrate that the I-V characteristics of the heterojunctions are well described by a serial arrangement of an ideal Schottky-diode, a Frenkel-Poole type resistance and an Ohmic contact resistance, emulating a p-n- or Schottky diode characteristic with giant ideality factor and referred to as the FPID-model. We propose that heterojunctions exhibiting apparently large ideality factors n , 2 may possess an interfacial disordered or amorphous layer with Frenkel-Poole conduction properties. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] TEM characterization of VLS-grown ZnTe nanowiresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008H. Kirmse Abstract ZnTe nanowires were grown via a vapour-liquid-solid pro- cess. Nano-sized droplets of a gold-based eutectic act as catalysts. The comprehensive transmission electron microscopy studies reveal that the nanowires are single crystals with numerous stacking faults and twins. The dimension of the wires is several micrometers in length and a few tens of nanometers in diameter. At the sidewall of the nanowires additional nanocrystals of ZnO embedded in an amorphous layer are identified. The formation process of the nanowires can be understood as a two-step process. The first step is the one-dimensional growth along the wire axis by consuming all the material deposited near the droplet. In a second step, facets are formed due to lateral growth of the nanowire. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A novel characteristic of porous titanium oxide implantsCLINICAL ORAL IMPLANTS RESEARCH, Issue 6 2007Takashi Sawase Abstract Objective: The anatase form of titanium dioxide (TiO2) is one of the most common crystalline forms of TiO2 and is normally produced by oxidation of titanium via thermal oxidation or anodizing. This crystalline form exhibits photocatalytic activity when it is irradiated with ultraviolet A (UVA) light. The aim of the current study was to analyze the crystal structure of anodic-oxidized TiUnite® implants and to confirm the photocatalytic properties in vitro and in vivo. Material and methods: Cross-sectional observations by transmission electron microscopy were used to determine the surface crystal structure on the TiUnite implant. Subsequently, photocatalytic activity was confirmed by degradation of methylene blue, and hydrophilicity was measured based on the water contact angle. Furthermore, the in vivo effects of the photocatalytic activity of this compound were investigated. Results: An amorphous layer that was about 10 ,m thick was observed on the TiUnite implant surface. In the amorphous layer, the anatase form of the crystalline TiO2 was identified. Photocatalytic activity was clearly demonstrated by the bleaching effect of methylene blue under UVA illumination. The contact angle decreased from 44° to 11° after UVA illumination. Although these data suggest increased hydrophilicity for the TiUnite implant, the bone-to-metal contact at 4 weeks was not influenced. Conclusion: The anodic-oxidized TiUnite implant has inherent photocatalytic activity. UVA illumination increases the surface hydrophilicity of the implant. However, this increase in hydrophilicity does not improve bone apposition to the implant surface at 4 weeks. [source] Determination of mean free path for energy loss and surface oxide film thickness using convergent beam electron diffraction and thickness mapping: a case study using Si and P91 steelJOURNAL OF MICROSCOPY, Issue 2 2006D. R. G. MITCHELL Summary Determining transmission electron microscope specimen thickness is an essential prerequisite for carrying out quantitative microscopy. The convergent beam electron diffraction method is highly accurate but provides information only on the small region being probed and is only applicable to crystalline phases. Thickness mapping with an energy filter is rapid, maps an entire field of view and can be applied to both crystalline and amorphous phases. However, the thickness map is defined in terms of the mean free path for energy loss (,), which must be known in order to determine the thickness. Convergent beam electron diffraction and thickness mapping methods were used to determine , for two materials, Si and P91 steel. These represent best- and worst-case scenario materials, respectively, for this type of investigation, owing to their radically different microstructures. The effects of collection angle and the importance of dynamical diffraction contrast are also examined. By minimizing diffraction contrast effects in thickness maps, reasonably accurate (±15%) values of , were obtained for P91 and accuracies of ±5% were obtained for Si. The correlation between the convergent beam electron diffraction-derived thickness and the log intensity ratios from thickness maps also permits estimation of the thickness of amorphous layers on the upper and lower surfaces of transmission electron microscope specimens. These estimates were evaluated for both Si and P91 using cross-sectional transmission electron microscopy and were found to be quite accurate. [source] Combining Ar ion milling with FIB lift-out techniques to prepare high quality site-specific TEM samplesJOURNAL OF MICROSCOPY, Issue 3 2004Z. HUANG Summary Focused ion beam (FIB) techniques can prepare site-specific transmission electron microscopy (TEM) cross-section samples very quickly but they suffer from beam damage by the high energy Ga+ ion beam. An amorphous layer about 20,30 nm thick on each side of the TEM lamella and the supporting carbon film makes FIB-prepared samples inferior to the traditional Ar+ thinned samples for some investigations such as high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). We have developed techniques to combine broad argon ion milling with focused ion beam lift-out methods to prepare high-quality site-specific TEM cross-section samples. Site-specific TEM cross-sections were prepared by FIB and lifted out using a Narishige micromanipulator onto a half copper-grid coated with carbon film. Pt deposition by FIB was used to bond the lamellae to the Cu grid, then the coating carbon film was removed and the sample on the bare Cu grid was polished by the usual broad beam Ar+ milling. By doing so, the thickness of the surface amorphous layers is reduced substantially and the sample quality for TEM observation is as good as the traditional Ar+ milled samples. [source] | ||||||||||||||||