Thin HfO2 films were grown by atomic layer deposition
on chemical vapor-deposited large-area graphene. The graphene was
transferred, prior to the deposition of the HfO2 overlayer,
to the HfO2 bottom dielectric layer pregrown on the Si/TiN
substrate. Either HfCl4 or Hf[N(CH3)(C2H5)]4 was used as the metal precursor for the
bottom layer. The O2 plasma-assisted process was applied
for growing HfO2 from Hf[N(CH3)(C2H5)]4 also on the top of graphene. To improve
graphene transfer, the effects of the surface pretreatments of the
as-grown and aged Si/TiN/HfO2 substrates were studied and
compared. The graphene layer retained its integrity after the plasma
processes. Studies on resistive switching on HfO2-graphene-HfO2 nanostructures revealed that the operational voltage ranges
in the graphene-HfO2 stacks were modified together with
the ratios between high- and low-resistance states.
Nanolaminates of ZrO2 and HfO2 were grown by atomic layer deposition, using metal halides and water as precursors, on silicon and fused quartz substrates at 300 °C. The crystalline phase composition, optical refraction, and mechanical performance of the multilayers were influenced by the relative contents of the constituent metal oxides. The crystal growth in as-deposited HfO2 dominantly led to the monoclinic phase, whereas ZrO2 was partially crystallized as its metastable and hard tetragonal polymorph. The hardness and elasticity of the nanolaminate structures could be modified by varying the amounts of either oxide contributing to the crystallographic order formed in the solid films. The refractive indexes depended on the nanolaminate structure.
Comparative analysis of dry sliding wear behavior of nanocrystalline diamond (NCD) films and NCD films coated with a thin Al 2 O 3 layer (Al 2 O 3 /NCD) is the main goal of the present study. Plasma-enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD) methods were used to prepare the NCD and alumina films, respectively. Sliding wear tests were conducted at room temperature (RT), 300 and 450 • C in air. Independent of type of specimen, superlubricating behavior with the coefficient of friction (COF) in the range of 0.004-0.04 was found for the tests at 300 • C. However, the COF value measured on the Al 2 O 3 /NCD films in the tests at 450 • C is lower than that for the NCD film. A relatively short run-in period and a stable COF value of about 0.15 were observed at this temperature for the Al 2 O 3 /NCD films. The width of the wear scars measured on the Al 2 O 3 /NCD films after the tests at 450 • C is significantly smaller in comparison with the NCD film. The apparent wear volume of the wear scar on the NCD film tested at 450 • C was noticeably higher than that on the Al 2 O 3 /NCD films.
Introduction Nanostructured Co3O4 in thin film form may possess and demonstrate a variety of properties making the material attractive for several applications. Co3O4 has been investigated as an important electrode material [1-4], gas sensor [5, 6], catalyst [7, 8], or superhydrophobic coating [9]. Co3O4 films have demonstrated resistive switching properties potentially enabling their application in resistive random access memory devices [10, 11]. Cobalt oxide, Co3O4, containing Co 2+ and Co 3+ ions, is recognized as magnetic semiconductor material [12]. Antiferromagnetic behavior with characteristic magnetization-field curves can be demonstrated by Co3O4 nanoparticles [13]. Regarding the possible applications in spintronics, it may occur necessary to activate ferromagnetic coupling in Co3O4 nanoparticles by hybridization with foreign materials, e.g. graphene oxide [14]. Co3O4 films have been grown by oxidation of electron-beam evaporated Co layers [15], pulsed laser deposition [5, 10] chemical bath deposition [1, 6], chemical solution deposition [8, 11], hydrothermal method [2, 13], solvothermal synthesis [9], spray pyrolysis [16]
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