Properties Of Granular Thin Films Research Articles

Structural, optical, and electrical properties of e-beam deposited metamaterials of granular CdSe thin films on glass substrates with a thin buffer layer of HfO2 dielectric

Structural, optical, and electrical properties of granular thin films of CdSe deposited on HfO2 dielectric layer are reported. The thin films were deposited on fluorine-doped tin oxide (FTO) coated glass substrates by e-beam evaporation technique. Structural analysis revealed the amorphous nature of the HfO2, whereas wurtzite type hexagonal crystal structure was observed in the CdSe thin films. Microstructural analysis showed the granular nature of both the deposited layers. The optical and electrical properties of the thin films were studied in detail. The dielectric properties of the deposited layers were studied in correlation with their microstructure. The appearance of negative permittivity (NP) in the films indicates towards metamaterial type characteristics which has various potential applications viz. high permittivity capacitors, microwave filters, coil free resonators, and thin film transistors (TFTs).

Correlation between the structural state and magnetoresistive properties of granular CoxAg100-x alloy thin films

Extensive investigations into structural, magnetotransport and magnetic properties of granular thin films with a thickness of 20 nm based on Co and Ag in a wide range of component concentrations were carried out: 17 ≤ x ≤ 89 where x is at.% of Co. The samples were obtained by the method of electron beam co-evaporation using two independent electron guns at room temperature. The correlation between the structural-phase state and magnetotransport and magnetic properties was established by TEM method. The threshold of structural percolation in granular films was observed for x ≈ 60%. At lower concentration x < 64%, the films had a phase composition of Ag (fcc) + Co (hcp) and were characterized by an isotropic giant magnetoresistance (GMR). The maximum GMR values of 7.2% and 7.5% in transverse and longitudinal geometry, respectively, were observed at x = 55 at.%. For higher concentrations (x > 70%) the films demonstrated anisotropic magnetoresistance (AMR), which was assumed to be associated with the appearance of ferromagnetic interactions between the cobalt granules.

Thickness dependence of magnetic properties of granular thin films with interacting particles

The effect of film thickness on magnetic properties of Cu80Co20 granular alloy was studied. It was observed that the susceptibility peak temperature, TM, strongly increases with the film thickness, t, for t&amp;lt;100 nm. The long-range nature of this effect points to magnetic dipole interaction as responsible mechanism. This dependence of TM can be explained within the framework of Dormann’s theory of dipolar interaction between magnetic particles. The coercive field has different thickness dependence and it is related to formation of magnetic domain structure of Co particles in the granular alloy.

Morphological analysis of discontinuous thin films on various substrates

We study and characterize the morphology of granular gold films deposited on amorphous and polycrystalline substrates using some of the more efficient tools of the mathematical morphology. This analysis shows the occurrence of characteristic lengths in the morphology which are strongly dependent on the nature of the substrate. This implies that a completely random model such as the theory of percolation can only be considered as a first approximation to interpret the dielectric and optical properties of granular thin films.

Some properties of granular thin films of high-field superconductors

The resistance as a function of temperature, the superconducting critical temperature, and the upper critical field of NbN and Nb3Ge thin films have been measured. These measurements may be explained in terms of a model of a granular superconductor. The properties of NbN and Nb3Ge may be universal characteristics of high-field granular superconductors.