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The valence band (VB) structure of an Al0.5TiZrPdCuNi high-entropy alloy (HEA) obtained using x-ray photoelectron spectroscopy has been compared to that recently calculated by Odbadrakh et al. [J. Appl. Phys. 126, 095104 (2019)]. Both the experimental and theoretical VBs show a split-band structure, typical for alloys consisting of the early (TE) and late (TL) transition metals. Accordingly, several electronic structure (ES) properties of this alloy, both in the glassy and crystalline state, are compared with those of similar TE-TL alloys. The comparison shows a strong effect of alloying with Al on the density of states at the Fermi level, N(EF), and on the magnetic susceptibility of Al0.5TiZrPdCuNi HEA, similar to that in conventional glassy alloys, such as Zr-Cu-Al ones. Despite some similarity in the theoretical and experimental density of states of the VBs, there are significant differences between them, which should be taken into account in any future studies of ES in HEAs and other compositionally complex alloys. [ABSTRACT FROM AUTHOR]

In this article, we describe the characterization of a newly fabricated amorphous alloy system (TiZrNbCu)1−xCox covering a broad composition range from high-entropy (HEA) to Co-rich alloys (x ≤ 0.43). We investigated thermal stability, atomic and electronic structure, and magnetic and mechanical properties as a function of chemical composition x. One of the important findings is that all studied properties change their dependence on concentration x within the HEA range. In particular, it has been found that the average atomic volume deviates from Vegard's law for x > 0.2, the concentration for which the average atomic packing fraction suddenly changes. The valence band structure, studied with ultraviolet photoemission spectroscopy, shows a split-band shape with 3d-states of Co approaching the Fermi level on increasing x. Due to the onset of magnetic correlations, magnetic susceptibility rapidly increases for x > 0.25. Very high microhardness increases rapidly with x. The results are compared with those for similar binary and quinary metallic glasses and with those for Cantor type of crystalline alloys. [ABSTRACT FROM AUTHOR]

A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high-entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and atomic volumes close to those predicted by Vegard's law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu. Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to conventional MGs with the same composition is briefly discussed. [ABSTRACT FROM AUTHOR]

In this paper, we present a study of the sub-monolayer gold intercalation of graphene on Ir(111) using scanning tunnelling microscopy (STM). We found that Au islands grow following different kinetics than growth on Ir(111) without graphene. Graphene appears to increase the mobility of Au atoms by shifting the growth kinetics of Au islands from dendritic to a more compact shape. Graphene on top of intercalated gold exhibits a moiré superstructure, with parameters significantly different from graphene on Au(111) but almost identical to graphene on Ir(111). The intercalated Au monolayer shows a quasi-herringbone reconstruction with similar structural parameters as on Au(111). [ABSTRACT FROM AUTHOR]

Photoemission spectroscopy (PES) is an underrepresented part of current and past studies of compositionally complex alloys (CCA) such as high-entropy alloys (HEA) and their derivatives. PES studies are very important for understanding the electronic structure of materials, and are therefore essential in some cases for a correct description of the intrinsic properties of CCAs. Here, we present several examples showing the importance of PES. First, we show how the difference between the split-band structure and the common-band structure of the valence band (VB), observed by PES, can explain a range of properties of CCAs and alloys in general. A simple description of the band crossing in CCAs composed from the early and late transition metals showing a split band is discussed. We also demonstrate how a high-accuracy PES study can determine the variation in the density of states at the Fermi level as a function of Cu content in Ti-Zr-Nb-Ni-Cu metallic glasses. Finally, the first results of an attempt to single out the contributions of particular constituents in Cantor-type alloys to their VBs are presented. The basic principles of PES, the techniques employed in studies presented, and some issues associated with PES measurements are also described. [ABSTRACT FROM AUTHOR]

Enhancement of hydrogen (H) absorption kinetics improves the performance of hydrogen-purifying membranes and hydrogenstorage materials, which is necessary for utilizing hydrogen as a carbon-free energy carrier. Pd-Au alloys are known to show higher hydrogen solubility than pure Pd. However, the effect of Au on the hydrogen penetration from the surface into the subsurface region has not been clarified so far. Here, we investigate the hydrogen absorption at Pd-Au surface alloys on Pd(110) by means of thermal desorption spectroscopy (TDS) and hydrogen depth profiling with nuclear reaction analysis (NRA). We demonstrate that alloying the Pd(110) surface with submonolayer amounts of Au dramatically accelerates the hydrogen absorption. The degree of acceleration shows a volcano-shaped form against Au coverage. This kinetic enhancement is explained by a reduced penetration barrier mainly caused by a destabilization of chemisorbed surface hydrogen, which is supported by density-functional-theory (DFT) calculations. The destabilization of chemisorbed surface hydrogen is attributed to the change of the surface electronic states as observed by angle-resolved photoemission spectroscopy (ARPES). If generalized, these discoveries may lead to improving and controlling the hydrogen transport across the surfaces of hydrogenabsorbing materials. [ABSTRACT FROM AUTHOR]

The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of the corresponding CAs. However, this transition has thus far been studied in only two types of alloy systems: crystalline alloys of iron group metals (such as the Cantor alloy and its derivatives) and both amorphous (a-) and crystalline alloys, TE-TL, of early (TE = Ti, Zr, Nb, Hf) and late (TL = Co, Ni, Cu) transition metals. Here, we briefly overview the main results for the transition from HEAs to CAs in these alloy systems and then present new results for the electronic structure (ES), studied with photoemission spectroscopy and specific heat, atomic structure, thermal, magnetic and mechanical properties of a-TE-TL and Cantor-type alloys. A change in the properties of the alloys studied on crossing from the HEA to the CA concentration range mirrors that in the ES. The compositions of the alloys having the best properties depend on the alloy system and the property selected. This emphasizes the importance of knowing the ES for the design of new compositional complex alloys with the desired properties. [ABSTRACT FROM AUTHOR]

Modifications of graphene's electronic band structure can be achieved through periodic bending strain and related potential in samples grown on stepped substrates, opening a viable route to implement the periodicity effects in this ultimate two-dimensional (2D) material. We studied graphene grown on stepped Ir(332), which can be benchmarked to a well-known graphene on flat Ir(111) recognized for a weak van der Waals (vdW) interaction. The structural characterization indicated that graphene growth induces reversible, well defined faceting of iridium surface into alternating terraces and step bunches, while spectroscopy techniques revealed substantial changes of graphene's electronic structure. Crucially, highly concentrated Ir step edges, resulting in locally strong chemical bonding of graphene, introduce a dominant energy parameter which overwhelms the induced strain and presents a driving force for the surface faceting. This sets a general framework for the understanding of graphene mediated faceting of stepped substrates whenever the corresponding low index surface exhibits dominantly vdW interaction with graphene, which can be also supplemented to other 2D materials. Interestingly, the graphene π band becomes pronouncedly anisotropic due to the presence of a periodic potential originating from steps, and lateral variation of the charge carrier concentration enabling a straightforward electronic band engineering in graphene. [ABSTRACT FROM AUTHOR]

Glass is important as a substrate for coatings in a wide range of applications or as a substrate for the fabrication of optical micro/nano structures. Coating by wet chemistry methods often demands modifications of the glass surface properties involving several steps. In addition, the micro/nano structuring is usually a several-step process. New methods that are simpler and more efficient are being proposed. One of them is glass poling that has been used to obtain surface relief on glass and, together with electric field assisted dissolution, for metal nanostructures in glass/metal systems. In this work, we demonstrate that poling increases the susceptibility of the glass surface for coating with Ag nanoparticles synthesized in situ by silver salt reduction. It is shown that a selectively poled glass surface can be used as a template to obtain optical microstructures consisting of Ag nanoparticles in only three simple steps. As a proof-of-concept, the method is used to fabricate diffraction gratings with an optical response that can be tuned by adjusting the Ag concentration. This approach is more versatile than the standard structuring by electric field assisted dissolution, as it does not require application of an elevated temperature once the coating is formed, which might change or destroy the properties of the thermally sensitive coating species or morphologies.