MgO single-crystal substrates

Silver has been reported to reduce the transformation temperature of FePt nanoparticles made by both sputtering and chemical synthesis [15, 16]. Furthermore, Ag, MgO and FePt have very similar lattice parameters (aAg = 0.40 nm) and therefore allows for a study of the transformation temperature without destroying the perpendicular texture. Here we describe the study of FePt/Ag multilayers deposited on MgO single crystal substrates at temperatures up to 400 °C. The X-ray diffraction patterns of the (FePt 2 nm/Ag 16 nm) pseudo-multilayers deposited on MgO [001] substrates at different temperatures are shown in Fig. 23. The superlattice (001) peak is present in all samples at temperatures above 280 °C, indicating the formation of Z,lo phase. 

Fig. 33. X-ray pole figures of the (108) peak of (a) a seed film prepared by RF plasma evaporation on a MgO single-crystal substrate and (b) a Y123 LPE-grown film. Note that several types of grain orientation exist for the seed film, however the obtained LPE film demonstrates a good crystallinity because formation of inplane aligned island crystallites on the 100 MgO surface is followed by their coalescence and a spiral growth development over the whole surface (Ishida et al. 1997).

On a heated substrate the deposited material forms islands as the increased surface mobility and surface tension cause the deposit to coalesce on the surface. With increased deposition the islands grow laterally until the islands become interconnected to form a continuous layer. For FePt the substrate temperature also transforms the sample into the FCT. The island sizes vary with the nominal thicknesses of the deposited layer. Figure 20 is a plot of the coercivity vs. layer thickness for FePt deposited on MgO (001) single crystal substrates at the two temperatures listed on the plot. The coercivity follows a functional form very similar to that predicted for particles in Fig. 2. 

Pd particles (1-15 nm) were prepared by ultra high vacuum (UHV) condensation of the metal on clean MgO or ZnO microcrystals, on ZnO (00.1) thin epitaxial layers synthesized in situ and on clean (001) MgO single crystals, air cleaved and in situ cleaned. The metal was evaporated from a Knudsen cell at a calibrated flux b The temperatures of the substrates were between 400 °C... 

Chemical vapour deposition (CVD), or more specifically, organo-metallic CVD can also be used to prepare ferrite thin films (Itoh, Takeda Naka, 1986). A mixture of acetylacetonate complexes of the desired metal is evaporated in a quartz boat (number 1 in Fig. 3.27) and is reacted with O2, which is introduced directly in the deposition zone. By adding a second furnace (B), an additional component evaporating at a different temperature can be transported to the substrate. Glass or MgO single crystals can be used as the substrates an annealing up to 1(X)0°C is performed on the film to improve its crystallisation. Spinel thin films (Ni, Ni-Zn) have been prepared by this method. 

Plasmas are also used to provide a more reactive Oj atmosphere during molecular beam epitaxy of magnetite (Lind et al., 1991). In this technique, electrons are accelerated to impinge on a metallic target (Fe) to release metal atoms and deposit them on a substrate (the (001) face of MgO single crystals). Instead of flooding the deposition chamber with diatomic O2 gas, an oxygen plasma provides a reactive mixture of O and O" which... 

We will consider the example of diffusion couples prepared by depositing an In20s thin film on a cleaved bulk single-crystal substrate of MgO and identify the location of the initial interface by an array of Pt particles as illustrated in Figure 25.14. The Pt particles are prepared... 

In the chemical vapor deposition (CVD) method, NbN films are fabricated by decomposing NbCls gas in NH3 and Hj gases at a high temperature, about 1000°C. When MgO single crystal is used as a substrate, single-crystal NbN film can be grown (5). 

A central problem with nitride growth by any technique is the lack of suitable lattice-matched substrates. Gas phase heteroepitaxy is currently done with 6H-SiC [32], 3C-SiC [33], MgO [34], and AI2O3. Single-crystal SiC is quite expensive to use as substrate. Despite the large lattice mismatch of 14%... 

Figure 20. Coercivity vs. Layer thickness for FePt deposited on heated (450 and 490 °C) single crystal MgO (001) substrates.

FT-RAIRS measurements of CO have also been used to identity facets of oxide supported Cu particles [78, 82]. The low sensitivity of RAIRS on single crystal ZnO(OOOl) prevented the observation of adsorbed CO or CO2, despite their observation in NEXAFS [78], although the local metallic dielectric allowed CO to be observed on the Cu particles. There appear to be no examples of HREELS being used to carry out vibrational spectroscopy of adsorbates on oxide supported metal particles. A HREELS study of Ag on MgO(lOO) films [95] was used only to characterise the Ag induced attenuation in the substrate Fuchs-Kliewer phonons, and the appearance of the metal/oxide interfacial plasmon at higher energies. HREELS has also been used to characterise the oxide/oxide interface between NiO and thin film MgO(lOO) [96]. Similar measurements of substrate phonon attenuation were made in HREELS studies on Pt films grown on ZnO(OOOl) [97]. 

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