MgO layer

Further improvement of the structural and optical properties of the PLD Bragg mirrors was achieved by substituting ZnO by yttria stabilized zir-conia (YSZ, with typically 9 at. % Y2O3), as demonstrated in Fig. 7.29. A considerable increase of the maximum reflectivity of the Bragg structures from about 90-99% was realized by doubling the number of YSZ-MgO layer pairs from 5.5 to 10.5 as shown in Fig. 7.29 (top). The experimentally obtained single layer thicknesses of the 5.5 and 10.5 pair structure are given in the caption and show smaller variation compared to the MgO-ZnO structure of Fig. 7.28. Indeed, the SNMS isotope intensity depth profile... 

Fig. 7.29. Top Reflectivity at normal incidence of two PLD grown Bragg mirrors with 5.5 and 10.5 YSZ-MgO layer pairs obtained from the ellipsometry model analysis. By doubling the layer number, the reflectivity was increased from 90 to 99%. The UV-vis ellipsometry data were fitted best with layer thicknesses of 38-46 nm YSZ/48-54nm MgO for the 5.5 layer pair Bragg, and 46.4 0.7 nm YSZ and 51.9 0.5 nm MgO for the 10.5 pair Bragg. Measured and calculated by R. Schmidt-Grand. Bottom SNMS isotope intensity depth profile of this 5.5 x YSZ/MgO Bragg structure...

Insert of Figure 13.2 shows the positron lifetime spectra for MgO (open circles), Au-implanted MgO (crosses) and Au nanoparticles embedded in MgO (solid circles). These spectra were deconvoluted using Laplace inversion [CONTIN, 7] into the probability density functions (pdf) as a function of vacancy size. Figure 13.2 shows the pdf spectra for the MgO samples accordingly. The positron lifetime components obtained for the MgO layer are 0.22 0.04 ns with 89 3% contribution and 0.59 0.07 ns with 11 3% contribution. For the Au-implanted sample without annealing, the major lifetime component is at 0.32 ns. For the Au nanoparticle-embedded MgO, lifetime components are 0.41 0.08 ns at 90% and 1.8 0.3 ns at 7%. 

Figure 13.3 (left) Two-dimensional spectrum of annihilation radiation of positrons injected into a p-Si (100), with 8 fl-cm. The diagonal feature indicates the condition of E) + E2= 1.022 MeV (right) Normalized annihilation lines as a function of photon energy for Au nanoparticle layer (solid circles), MgO layer (open circles), and Au film (solid line) [6],... 

Fig. 8. Electron energy loss spectra of 15 ML thick MgO layers, (a) as grown (b) after Ar sputtering (c) after additional deposition of 4 ML of Mg (d) after deposition of 4 ML of Mg and post oxidation with O2 and consequent annealing. Reproduced from ref. [128], Copyright 1999 Elsevier.

Coordinates of the centres of mass and orientations of the two acetylene molecules (1 and 2) in the (2x2) unit cell on MgO(lOO). The values obtained from LEED-IV data [24], neutron diffraction (ND) [26], and semi-empirical potential calculations [24,25] are tabulated. The definitions of x, y, and O are given in Fig. 4. 9 is the polar tilt of the molecule away from the surface plane, and z is with respect to the surface MgO layer. The two calculated z values are for effective charges of 1.2 and 2, respectively. 

The microstructures of ceramic matrices grown from two different classes of alloys have been reported. The external growth surface of ceramic matrices grown from an Al-Si-Mg alloy in the absence of a reinforcement was covered by a thin ( 1- to 4-gm) layer of MgO that sometimes contained up to 5% MgAl204 [33]. The external MgO layer typically was separated from the interconnected A1203 matrix by a thin aluminum alloy (1- to 3-gm) layer. Only rarely was an A1203 grain found in direct contact with the external oxide layer. Within the bulk of the composite, the metallic channels typically were 3 to 8 /tm in width. 

Fig. 2.1. Calculated surface layer LDOS (Local Density of States) for 0- to 3-MgO layers on Ag(lOO). Reproduced from [19]. Copyright 2001 American Physical Society...

Figure 35. Grazing-emission X-ray fluorescence analysis features. Top left Model layered structure showing how the thin film depth profile can affect fluorescence signal. Top right Calculated fluorescence signal from the model layered structure. Right Actual observed fluorescence signal versus grazing exit angle for MgO layers prepared by various methods on a Si wafer. Modified from deBokx et al. (1997).

Figure 9. (a) Pd particle (5 nm) in cross-sectional viewP (b) Averaged distance between the (200) lattice planes of Pd, normal to the interface in the successive layers from the interface with MgO (layer number 1) to the top. ... 

The oxidation of Mg particles spreads from the surface toward the center of a particle, as can be seen from the SEM and EPMA shown in Fig. 6.50, and the rate-controlling factor is greatly dependent on the depth of the MgO layer and the... 

Sectional view by SEM MgO layer image by EPMA Unreacted MgO image by EPMA... 

Fig. 6.50 Sectional images of a large, nearly spherical Mg particle taken by SEM and EPMA showing growth of the MgO layer in a radial direction.

Figure 4. Schematic of surface microstructure during DM0 growth. A thin alloy film is formed between a surface MgO layer and the growing alumina skeleton and is continuous with underlying alloy channels. The reactions at A, B, and C are described in the text.

The steady-state microstructure described above is a simpUfication. The MgO layer is far from uniform, both with respect to position and time [50,56,66], and thicknesses <0.1 pm has occasionally been observed [66]. In some samples the interface between aluminum and MgO was found to contain spinel [47], while the solidified metallic phase frequently contained nanocrystals of MgO [66]. Even less consistent with the steady state hypothesis was the apparent equilibrium between aluminum and MgO in the presence of a magnesium concentration that was necessarily, and experimentally, close to the three-phase equilibrium with spinel and alumina [50]. Cation de-mixing of spinel, as a source of MgO (periclase), seems unlikely when spinel is the minor phase or apparently absent. An alternative hypothesis assumes that oxidation of magnesium in the vapor phase is responsible for the presence of MgO, an assumption that is supported by the demonstration of... 

The results of this approach to extracting ri2 v) and fe(v) from the experimental spectra of MgO layers on the surface of Al mirrors are discussed below. 

These layers were deposited by magnetron sputtering on A1 substrates maintained at temperatures of 25° and 250°C. The spectrum obtained by IRRAS for the film deposited at 25°C (Fig. 3.68a) shows an intense vlo absorption band at 725 cm . In the spectrum of the film deposited at 250°C, the maximum of this band is shifted to higher frequencies, and its FWHM is smaller than that in the spectrum of the film obtained at 25°C. The resulting spectral dependences of n2(v) and k2 v) for the MgO layers are presented in Fig. 3.68Z . The optical constants of the layer sputtered on the 250°C substrate are close to those of a MgO crystal. The lower frequency and larger bandwidth of the / 2(v) band suggest an amorphous phase in the layer. 

Figure 3.68. (a) IRRAS spectra of MgO layer on Al substrate, recorded In p-polarized radiation at >1 = 60°, d2 = 100 nm at temperatures t = 25°C (solid line) and t = 250°C (dashed line). Reprinted, by permission, from 1.1. Shaganov, O. P. Konovalova, and O. Y. Rusakova, Sov. J. Opt. Technol. 55, 402 (1988) p. 403, Fig. 1, Copyright 1988 Optical Society of America, (b) Dispersion of optical constants k and n of MgO (1) polycrystalline film deposited at t = 250°C (dashed lines) (2) amorphous film deposited at f = 25°C (solid lines) (3) MgO monocrystal (dashed-dotted lines). Reprinted, by permission, from O. P. Konovalova, O. Y. Rusakova, and 1.1. Shaganov, in N. G. Bakhshiev (Ed.), Spectrochemistry of Inter- and Intramolecular Interactions, issue 4, Leningrad State University Press, Leningrad, 1988, p. 206 p. 209, Fig. 2. Copyright 1988 St. Petersburg University Press.

MgO layers. MgO (10 g) and kieselguhr G (10 g) are passed through a 60-mesh sieve fol lowed by mixing with 80 ml of distilled water. The slurry is transferred to the plates with a commercial spreader. The plates are allowed to dry for 12 h. 

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