Hardness multilayer systems

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

In conclusion, one should choose an appropriate multilayer system for different application purposes. For the case of fatigue wear, multilayer films consisting of two hard materials with different shear modulus, such as DLCAVC multilayer film [115], would satisfy the requirement for wear resistance. While for abrasive wear, multilayer films consisting of hard ceramic layers and soft metal layers, such as TiN/Ti and CrN/Cr [116,117] multilayer films are more competent. 

This work was followed by a number of researchers who confirmed the experimental results on various metallic multilayer systems (e.g. Cu/Ni [78-80] as well as on hard epitaxial and polycrystalline superlattices of nitrides, such as TiN/VN... 

TABLE 3—Maximum tion wavelength systems. hardness and modula-of several multilayer ... 

Whereas the disclination picture provides a convincing explanation of the properties of multilayers of fatty acids, being consistent with both the electron diffraction and optical evidence, it is not yet proven that, at room temperature, such systems are really in the hexatic state. It is equally probable that the existence of an initial hexatic monolayer on which subsequent layers are grown by epitaxy produces a material which is far from thermal equilibrium and has more of the nature of a glass state rather than of a mesophase. Indeed, the relative hardness of multilayers and their resemblance to true three-dimensional crystals of fatty acids tends to support this view. 

The variation of hardness with multilayer wavelength in a range of different types of structures. These include multilayers of (a) isostructural transition metal nitrides and carbides, which show the greatest hardening (b) nonisostructural multilayer materials, where slip cannot occur by the movement of dislocations across the planes of the composition modulation, because the slip systems are different in the two materials and (c) materials where different crystal structures are stabilized at small layer thicknesses, such as AIN deposited onto TiN. 

The importance of such effects was deduced from the data shown in Fig. 8.2 from the elegant experiments of Barnett and co-workers (Chu and Barnett, 1995). In the TiN/VN multilayers the two layers are both elastically strained with respect to one another and have different elastic moduli, that of TiN being greater than that of VN, which is similar to that of NbN. Shinn and Barnett (1994) have used this to study the effects of elastic modulus mismatch. As shown in Fig. 8.2, systems where there was a difference in elastic modulus showed a substantial increase in hardness. Where there was no difference in elastic modulus little or no hardening was observed, whilst hardening was obtained in a TiN/Vo.6Nb0.4N system where there was a modulus mismatch but no lattice mismatch (Mirkarimi et al., 1990 Hubbard et al., 1992). 

The three main approaches to multilayer resist imaging systems (see Chapter 16 for details) include (i) hard mask (HM) processes, (ii) top surface imaging (TSI) processes requiring latent image formation only near the surface of the resist, thus circumventing any transparency requirements, and (iii) bilayer resist (BLR)... 

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