Papers by Keyword: Transition Metals

Abstract: New complex based on cobalt (II) acrylate and 4′-phenyl-2,2′:6′,2″-terpyridine (PhTpy) was synthesized and characterized using a number of analytical techniques including IR and UV- vis spectroscopy, elemental, X-Ray and TGA/DSC analysis. The complex has high thermal stability and crystallinity. It is found that decomposition of the complex is accompanied by thermal polymerization of acrylic fragments that is a potential way for the preparation nanoparticles of metals or their oxides stabilized by the polymer matrix.

Abstract: Undoped and transition metals (TM = Cr, Ni, Mn and Cd) doped zinc oxide (ZnO) thin films were prepared by sol-gel dip-coating method on glass substrates at 300 °C. In this study, the effect of dopant material on the structural, morphological, optical, electrical and mechanical properties of ZnO thin films is investigated by using XRD, AFM, UV-Vis, Hall effect and nanoindentation techniques, respectively. Nanocrystalline films with a ZnO hexagonal wurtzite structure and two preferred orientations (002) and (103) were obtained. UV-Vis transmittance spectra showed that all the films are highly transparent in the visible region (> 80 %). Moreover, the optical band gap of the films decreased to 3.13 eV with an increasing orbital occupation number of 3d electrons. AFM-topography shows that the films are dense, smooth and uniform, except for the high roughness RMS =26.3 nm obtained for Cd-doped ZnO. Finally, the dopant material is found to have a significant effect on the mechanical behavior of ZnO as compared to the undoped material. For Ni and Cd dopants, analysis of load and unload data yields an increase in the hardness (8.96 ± 0.22 GPa) and Young’s modulus (122 ± 7.46 GPa) of ZnO as compared to Cr and Mn dopants. Therefore, Ni and Cd are the appropriate dopants for the design and application of ZnO-based nanoelectromechanical systems.

Abstract: Structural-phase state of the diamond-metallized coating interphase boundary after thermal diffusion metallization of diamond grains by transition metals Fe, Ni and Co were studied. Metallization were conducted under temperature-time mode corresponding to the sintering of cemented carbide matrices with Cu impregnation. The structural-phase state of the metallized coating and diamond-coating interphase boundary was studied by scanning electron microscopy, X-ray phase analysis and Raman spectroscopy. A metallized coating strongly adhered to the diamond forms during thermal diffusion metallization of diamond by iron. The metallized coating has a complex structural phase composition of iron, a solid solution of carbon in iron and graphite phases. Nickel and cobalt cause intense catalytic graphitization of diamond with the formation of numerous traces of erosion on its surface under the heating conditions specified in the experiment. The observed weak adhesive interaction of these metals with diamond is probably due to the high melting temperatures of the Ni-C and Co-C eutectics, which does not allow the metals to react with diamond under given experimental conditions.

Abstract: Structural-phase state of the diamond-metallized coating interphase boundary after thermal diffusion metallization of diamond grains by transition metals Cr, Ti were studied. Metallization were conducted under temperature-time mode corresponding to the sintering of cemented carbide matrices with Cu impregnation. The structural-phase state of the metallized coating and diamond-coating interphase boundary was studied by scanning electron microscopy, X-ray phase analysis and Raman spectroscopy. It was found that a thin continuous metal carbide coating chemically bonded to the diamond and consisting of the corresponding metal, their carbides and small amount of graphite phases is formed during thermal diffusion metallization of diamond by Cr and Ti under the conditions specified in the experiment. It was shown that graphite is formed not by a continuous layer, but in the form of local inclusions. This ensures a strong adhesion of the metallized coating to the diamond through the carbides of the corresponding metals. The results can be useful in the development of compositions and technological methods that provide an increased level of diamond retention in the matrices of tools based on cemented carbide powder mixtures.

Abstract: In this research, the possibility of applying multilayer multielement super hard coatings by Cathodic Arc is investigated. More precisely the structure of the coating consisting of quaternary CrAlSiN and ternary AlSiN layers is examined by electron microscopy, X-ray diffraction and X-ray photoelectron microscopy analytical methods. The as-deposited samples were found to have distinguishable layers. The CrAlSiN layer is characterized by an extra sequence of repeated nanolayers. The AlSiN layer consisted of nanosized grains having a preferential orientation. Finally the surface layer was found to contain a solid solution of CrxAl1-xN, while Si3N4was identified only by XPS most probably due to its amorphous structure.

Abstract: The antibacterial property of several types of transition metals such as silver, nickel, zinc, and copper substituted hydroxyapatite (HA) composite coatings was investigated against staphylococcus aureus (S. aureus). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). Transition metals-substituted hydroxyapatite/PEEK coatings were successfully deposited using cold spraying parameters of 10-14 bars at preheated air temperature between 150 and 160 °C. The results indicated that copper substituted hydroxyapatite showed the best antimicrobial property against S. aureus.

Abstract: The change in phase stability of Group-VB transition metals (V, Nb, and Ta) due to pressure and alloying is explored by means of first-principles electronic-structure calculations. It is shown that under compression stabilization or destabilization of the ground-state body-centered cubic (bcc) phase of the metal is mainly dictated by the band-structure energy. In the case of alloying the change in phase stability is defined by the interplay between the band-structure and Madelung energies. We show that band-structure effects determine phase stability when a particular Group-VB metal is alloyed with its nearest neighbors within the same d-transition series: the neighbor with less and more d electrons destabilize and stabilize the bcc phase, respectively. When V is alloyed with neighbors of a higher (4d- or 5d-) transition series, both electrostatic Madelung and band-structure energies stabilize the bcc phase. Utilizing the self-consistent ab initio lattice dynamics approach, we show that pressure-induced mechanical instability of bcc V, which results in formation of a rhombohedral (rh) phase at around 60-70 GPa at room temperatures, will prevail significant heating and compression. Furthermore, alloying with Cr decreases the temperature at which stabilization of the bcc phase occurs at elevated pressure.

Abstract: The review reports on the results of our research work on nanostructured metal films onto porous silicon. Principal steps of the techniques allowing fabrication of metal films completely inheriting morphological pattern of different types of porous silicon are presented. It is shown, that giving of the nanostructured pattern to metal films by means of porous silicon template opens their new structural, optical, mechanical and electrical properties, which can be successfully applied in nanoelectronics and biomedicine, particularly including devices based on superconductivity effect, SERS analysis with picomolar sensitivity and transdermal drug delivery by electroporation.

Abstract: The article discusses the formation of coatings with magnetic properties on non-magnetic substrates by the method of additive technology of metal powders using high power pulsed laser radiation. An instrumental base for the development of methods for creating local magnetic zones of a given configuration has been described. Approaches to create methods of additive welding of solid solution magnetic zones on the basis of micro-powders of metal alloys have been developed. The coatings with soft magnetic properties on the basis of powders of bronze and iron-containing "Inconel" alloy on non-magnetic substrates were obtained by laser welding. The structural inhomogeneity at the interface of the substrate and the solid solution were studied. Data on hardness and magnetic properties were obtained for formed magnetically soft materials.

Abstract: Early transition metals (TMs) of the 3d and 4d rows are undesired contaminants in solarandelectronic-grade Si. From the theoretical standpoint, understanding the properties of these TMs insilicon still remains a challenging problem owing to the strong correlations among the TM d-electrons.The present study proposes a first-principles Hubbard-corrected DFT+U approach, with on-site parametersaccounting separately for electron Coulomb (U) and exchange (J) effects. We use this approachtogether with conventional DFT to determine electrical levels and migration barriers of early3d (Ti, V and Cr) and 4d (Zr, Nb and Mo) TMs in Si. Comparisons with experimental data allowedus to uniquely assign the deep levels in the gap appraising also the effect of on-site correlation. Ourresults also resolve existing controversies in the literature concerning the type and origin of the donorlevels of Cr and Mo. For all the metals, with the exception of Cr, high barriers of interstitial diffusionare obtained, thus confirming that most of these TMs are slow diffusers in silicon.