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  • 1
    Electronic Resource
    Electronic Resource
    Net shape ceramic microcomponents by modified sol–gel casting (2000)
    Springer
    Microsystem technologies 6 (2000), S. 200-204 
    Details
    ISSN: 1432-1858
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Technology
    Notes: Abstract  Development of ceramic microcomponents can open up the current silicon-based MEMS (micro-electro-mechanical systems) technology to new applications, especially for use in high temperature, chemically reactive environments. We report a study of sol–gel technologies applied to the fabrication of microcomponents. Organic/inorganic hybrid materials, particularly silica-based hybrids, were developed by sol–gel processing. A weak silica network was made possible by using acid catalyst, low functionality organic precursor in the sol preparation. Since the weak network has a high tendency to collapse, the result is a denser material. Incorporation of organic ligands modifies the surface chemistry of gel network so that a greater drying stress was developed and a denser hybrid structure was achieved without high temperature treatment. In addition, the incorporation of organic ligands prevented formation of cracks. Nanoscale oxide particles were dispersed and incorporated into the gel network by surface condensation. The incorporation of titania nanoparticles into sols greatly reduced the volume shrinkage of gels and enhanced the mechanical strength of the components. In this work, silica sol was also applied to coat metallic microcomponents and a thin uniform coating was formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005420000051
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  • 2
    Electronic Resource
    Electronic Resource
    Role of hydroxide impurities in the thermoluminescent behavior of lithium fluoride (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 2217-2220 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of OH ion impurities on thermoluminescent sensitivity and supralinearity in LiF:Mg, Ti is analyzed. Available evidence is shown to be consistant with the presence of Ti-OH and Mg-OH complexes. The track interaction model is used to explain the data, with competing centers decreasing sensitivity and supralinearity at high concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334365
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  • 3
    Electronic Resource
    Electronic Resource
    Band-edge photoluminescence degradation in GaAs (1991)
    Springer
    Journal of materials science 2 (1991), S. 72-78 
    Details
    ISSN: 1573-482X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper reports on the degradation of the band-edge photoluminescence (PL) signal seen in various types of GaAs samples during low-power argon laser irradiation. This degradation was observed to take place over a period of minutes and was found to be a function of the position on the wafer as well as the temperature of the wafer and laser power. The decrease in PL intensity did not recover after several hours with the laser off. Surface, thermal and system parameters were eliminated as possible sources of the PL degradation seen. We propose that the observed PL degradation is partly due to a bulk material parameter, and that the method of measuring PL degradation could be used as a more reliable and reproducible method of whole-wafer characterization than the current procedure of mapping PL intensities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00694755
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  • 4
    Electronic Resource
    Electronic Resource
    Measurement of ionic diffusion in lithium fluoride by nuclear magnetic resonance techniques (1966)
    Springer
    Journal of materials science 1 (1966), S. 117-126 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Rates of diffusion of 7Li and 19F were investigated in doped crystals of lithium fluoride using the technique of motional narrowing of nuclear magnetic resonance lines. Major doping elements were divalent Mg and Mn ions, present in amounts between 3 and 240 × 10−6 cation site fraction. Extrinsic vacancies introduced by this doping increased Li ion diffusion and caused 7Li motional narrowing to begin at lower temperatures for greater impurity contents. Diffusivities were determined from the motional narrowing curves using a method of analysis which reduces uncertainties due to magnetic field inhomogeneity and other temperature independent contributions to line broadening. Resulting log D vs 1/T plots showed the expected intrinsic, free vacancy extrinsic, and divalent ion-vacancy association regions of Li ion diffusivity. Activation energies determined for these regions were 1.87±0.09, 0.66±0.03, and 0.91±0.05 eV, respectively. These values yielded the energy for motion of a cation vacancy as 0.66 eV and the energy of formation of a Schottky defect as 2.42 eV. Experimental results obtained earlier in powdered LiF: Mn samples are clarified, and indications concerning the effects of other impurities on Li ion diffusion are presented and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550100
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of the equilibrium concentration of impurities on the reproducibility of thermoluminescence in MgO (1981)
    Springer
    Journal of materials science 16 (1981), S. 1191-1196 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A study of thermoluminescent (TL) sensitivity and reproducibility is undertaken in crystals of MgO exposed to ultraviolet radiation in the as-received condition, and heat treated in air or in a mixtue of CO/CO2 at either 1000 or 1400° C. The changes in the concentrations of transition metal ions such as Fe3+, Cr3+, Mn2+ and V2+, caused by the heat treatments, are followed using electron spin resonance. It is shown that the equilibrium concentrations of Fe3+ and V2+ ions, which can be altered by heat treatments, play an important role in the reproducibility of the TL in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01033831
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  • 6
    Electronic Resource
    Electronic Resource
    Thermoluminescent mechanisms involving transition metal ion impurities and V-type centres in MgO crystals exposed to ultraviolet radiation (1982)
    Springer
    Journal of materials science 17 (1982), S. 2585-2593 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Thermoluminescent (TL) mechanisms involving Fe, Cr, Mn and V ions in both divalent and trivalent valence states, and V-type centres were studied in MgO single crystals of varying impurity content after exposure to ultraviolet radiation. Using the ESR technique, it is shown that samples containing primarily divalent impurities show no V-type centres related to the TL mechanism, which is that of charge transfer between the impurities. V-type centres, when present, are seen to be more stable in purer samples than in less pure samples, resulting in a shift of the TL peaks to higher temperatures. The TL mechanism in this case includes charge transfer between V-type centres and the impurities. The supralinear behaviour of TL peak 1 is associated with the R-emission lines of Cr3+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00543891
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  • 7
    Electronic Resource
    Electronic Resource
    Iron impurities in Si3N4 processing (1985)
    Springer
    Journal of materials science 20 (1985), S. 1807-1814 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The atomic environment of iron impurities is investigated during the processing cycle of reaction-bonding silicon nitride (RBSN). Several analysis techniques are utilized, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and electron spin resonance (ESR), to examine iron impurities in the starting silicon powder, in sintered silicon compacts, and in RBSN materials. Results indicate that iron impurities in as-received metallurgical grade silicon powder are incorporated in the silicon bulk as a highly distorted FeSi2 compound. No surface iron or iron-based particulate is observed in the starting material. Upon sintering, the iron environment becomes an ordered FeSi2 structure. In the RBNS material, the FeSi2 structure is again distorted, as observed by both EXAFS and ESR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00555287
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  • 8
    Electronic Resource
    Electronic Resource
    Thermally activated flow parameters in the deformation of MgO single crystals (1973)
    Springer
    Journal of materials science 8 (1973), S. 1567-1572 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Strain-rate cycling methods have been used to determine the thermally activated flow parameters in the compressive deformation of MgO single crystals. Activation volumes of the order of 100b 3 have been measured for deformation below room temperature, indicating dislocation-point defect interactions as the rate controlling mechanism for hardening at these temperatures, whileV * values of the order of 1000b 3 have been measured at and above room temperature. This, together with the fact that the effective stress remains constant with strain at these temperatures identifies the interaction of dislocations with dislocation dipoles as the rate controlling mechanism in this temperature range. The Gibbs free energy for deformation,ΔG, equals the activation enthalpy,ΔH, at low temperatures and the deviation ofΔG fromΔH above room temperature may be attributed to entropy effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754891
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  • 9
    Electronic Resource
    Electronic Resource
    Thermoluminescence and activation energies in Al2O3, MgO and LiF (TLD-100) (1973)
    Springer
    Journal of materials science 8 (1973), S. 407-414 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Thermoluminescent characteristics of Al2O3 and MgO single crystal samples obtained from several sources have been determined after X-ray and ultra-violet irradiation. The glow peak spectrum above room temperature, the emission spectrum, the impurity content and distribution and the activation parameters for the observed glow peaks are reported. Czochralski-grown Al2O3 samples indicate a major glow peak, the position of which shifts to lower temperatures with increasing dose, an observation with interesting implications in thermoluminescent radiation dosimetry. MgO also has characteristics which could be useful in dosimetry, especially in the ultra-violet region. Activation parameter comparisons are made for the observed glow peaks in Al2O3 and MgO and in LiF (TLD-100). After considering a number of theoretical and experimental problems and uncertainties, it is concluded that determinations of activation parameters are less meaningful than observations of other thermoluminescent characteristics in the understanding of thermoluminescent behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550162
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  • 10
    Electronic Resource
    Electronic Resource
    Temperature dependence of yielding and work-hardening rates in magnesium oxide single crystals (1974)
    Springer
    Journal of materials science 9 (1974), S. 121-128 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The mechanical properties of MgO single crystals have been analysed for their yielding and work-hardening behaviour as a function of purity and deformation temperature. The Fleischer theory accounts for the observed temperature dependence of the critical resolved shear stress well. Depending on temperature and impurity content, the MgO single crystals are shown to exhibit two-stage work-hardening behaviour, with the hardening shown to be athermal in nature. At and below room temperature, a temperature-dependent contribution results from dislocation-point defect interactions, while the primary athermal contribution arises out of dislocation-dislocation dipole interactions. The CRSS and work-hardening behaviour of MgO single crystals indicates a close relationship to the deformation characteristics of NaCl-structure alkali halides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00554762
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