Underlayer alloy

Summary of geometry of Cu 100 -c(2x2)-Pd(Pt) underlayer alloys determined by SATLEED. Positive values for buckling in layer 2 corresponds to adsorbate atoms relaxed towards the vacuum interface. Positive values for buckling in layer 4 corresponds to Cu atoms below Pd (or Pt) relaxed towards the adsorbate. The values in brackets below the interlayer spacings indicate the percentage contraction (negative) or expansion (positive) relative to the bulk value of Cu 100 of 1.807 A. The final entry corresponds to aPt multilayer alloy with a minimum of two ordered c(2x2) CuPt layers within the LEED probing depth. 

Iridium follows the trend for formation of underlayer alloys for elements with similar metallic radii/crystal structure to copper yet having considerably higher surface energy. However, Ir differs from the tendency for c(2x2) underlayer ordering shown by Pd and Pt. In this case, formation of one-dimensionally close packed Ir rows may occur due to the higher Ir-Ir bond energy combined with the slightly smaller f.c.c. mismatch of 6.2%. 

Go Binary and Ternary Alloyed Thin Films. Most of the thin-film media for longitudinal and perpendicular recording consist of Co—X—Y binary or ternary alloys. In most cases Co—Cr is used for perpendicular recording while for the high density longitudinal media Co—Cr—X is used X = Pt, Ta, Ni). For the latter it is essential to deposit this alloy on a Cr underlayer in order to obtain the necessary in-plane orientation. A second element combined with Co has important consequences for the Curie temperature (T ) of the alloy, at which the spontaneous magnetisation disappears. The for... 

Amorphous NiP alloys with > 10% P (generally obtained by deposition from acidic electrolytes) are non-magnetic (see [66] and references therein), as required of the underlayer for thin-film media. Although the structure of these alloys is generally assumed to be a solid solution of P in Ni, a recent report [67] has suggested that NiP with 7.4-10% P deposited from acid sulfate electrolytes is better represented by a microcrystalline structure composed of 4-5 nm fee NiP solid-solution grains. 

The strong dependence of the magnetic properties on the microstructure of the magnetic alloy implies that the substrate will also influence the magnetics, since the substrate will affect the nucleation and growth, the structure, and the PO of the material deposited on it. For electrochemically deposited films, most studies have examined underlayer effects as secondary to other aspects of magnetic thin films. A few relevant papers dealing primarily with the effects of underlayers can nevertheless be mentioned here. 

The two metallizations most commonly used to fabricate transducers on AW devices are gold-on-chromium and aluminum. Au is often chosen for chemical detection applications because of its inertness and resistance to corrosion a layer 100-200 nm diick is necessary to provide adequate electrical conductivity. Unfortunately, the inertness of Au also prevents its adhesion to quartz and other oxides utilized for AW device substrates. Therefore, an underlayer of Cr (2-10 nm thick) is utilized to promote the adhesion of Au to the substrate the electropositive (reactive) nature of Cr allows it to form strcxig bonds with oxide surfaces, while alloying between the Cr and Au chemically binds the two metal layers... 

Fig.8. Variation with temperature of the average segregant concentration at the Ll2(100) surface (solid lines) and at the first underlayer (dotted lines) in AB3 model alloy calculated in the FCEM approximation for different segregation/order factors r (marked near the plots). Arrows indicate order-disorder transition temperatures (for r =3.5, Ts=Tb).

A few cases have recently been discovered of ordered two-dimensional alloy underlayers consisting of a mixed alloy second layer capped by a copper monolayer. 

Figure 18. Schematic model of a Cu 100 -c(2x2) underlayer ordered alloy including top and side views along the [Oil] azimuth. The side view defines the major geometric parameters. Open circles indicate top, third and deeper layer Cu atoms, filled circles indicate second layer adsorbate and hatched atoms are second layer Cu.

Figure 20. Schematic models of suggested structures for the Cu 100 /Pd monolayer alloy (a) a p(2x2) clock rotated Pd monolayer above a c(2x2) CuPd second layer (b) a double layer c(2x2) CuPd alloy (c) a p(2x2) CuPd overlayer with 100% decrease in atomic density above a clock rotated CuPd underlayer (d) a p(2x2) CuaPd outermost layer above a c(2x2) CuPd underlayer. The surface unit cell is shown in each case by dotted lines [160].

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