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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.

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).

International audience; 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.

A new amorphous alloy system $(TiZrNbCu)_{1-x}Co_x$ covering a broad composition range from the high-entropy (HEA) to Co rich alloys (x$\leqslant$ 0.43) has been fabricated, characterized and investigated. A comprehensive study of the chemical compositions, homogeneity, thermal stability, electronic structure and magnetic and mechanical properties has been performed. All properties change their variations with x within the HEA range. In particular, the average atomic volume deviates from the Vegard's law for x$\ge 0.2$, where also 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 onset of magnetic correlations magnetic susceptibility rapidly increases for x$\ge 0.25$. 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., 29 pages, 10 figures

The atomic structure, electronic structure and physical properties of $(TiZrNbCu)_{(1-x)}Ni_x$ (x $\leq$ 0.5) metallic glasses (MG) were studied in both the high-entropy (0, Comment: 40 pages, 8 figures

We present results of comprehensive study of electronic properties of (TiZrNbCu) 1 − x Nix metallic glasses performed in broad composition range x encompassing both, high entropy (HE) range, and conventional Ni-base alloy concentration range, x ≥ 0.35. The electronic structure studied by photoemission spectroscopy and low temperature specific heat (LTSH) reveal a split-band structure of density of states inside valence band with d-electrons of Ti, Zr, Nb and also Ni present at Fermi level N(EF), whereas LTSH and magnetoresistivity results show that variation of N(EF) with x changes in Ni-base regime. The variation of superconducting transition temperatures with x closely follows that of N(EF). The electrical resistivities of all alloys are high and decrease with increasing temperature over most of explored temperature range, and their temperature dependence seems dominated by weak localization effects over a broad temperature range (10–300 K). The preliminary study of Hall effect shows positive Hall coefficient that decreases rapidly in Ni-base alloys.

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.

We studied the growth mode and electronic properties of ultra-thin silver films deposited on Ni(1 1 1) surface by means of scanning tunnelling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES). The formation of the 4 d -quantum well states (QWS) was analysed within the phase accumulation model (PAM). The electronic structure of the 1 ML film is consistent with the silver layer which very weakly interacts with the supporting surface. The line-shape analysis of Ag-4 d xz,yz QWS spectrum support the notion of strong localization of these states within the silver layer. The asymmetry of the photoemission peaks implies that the decay of the photo-hole appears to be influenced by the dynamics of the electrons in the supporting surface.

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.

We have used scanning tunneling microscopy to study the growth of graphene on a periodically stepped Ir(3 3 2) substrate surface, which is a promising route for modification of graphene properties. We have found that graphene continuously extends over iridium terraces and steps. Moreover, new distinctive mesoscopic features of the underlying surface are formed involving large, flat terraces accompanied by groups of narrower steps. The distribution of the newly formed terraces is sensitive to the preparation temperature and only below 800 °C terrace width distribution closer to the intrinsic distribution of clean Ir(3 3 2) are found. We propose that the microscopic shape of steps found after graphene formation is strongly influenced by the orientation of graphene domains, where graphene rotated by 30° with respect to the substrate has a prominent role in surface structuring.

Grafen je atomski tanak materijal kojeg tvori heksagonalna mreža ugljikovih atoma i zbog svojih izuzetnih svojstava smatra ga se obećavajućim materijalom za upotrebu u budućim elektroničkim uređajima. Ali potencijalnu upotrebu u, na primjer, novim tranzistorima ograničava činjenica da je grafen polumetal, to jest da nema procjep u svojoj elektronskoj strukturi. Stoga je u istraživanju grafena veliki naglasak stavljen na razne načine modifikacije grafenske elektronske strukture i moguće otvaranje procjepa. Teorijski takav inženjering elektronske strukture mogao bi se postići, između ostalog, uvođenjem periodičkog potencijala ili naprezanja u grafenski sustav. Ovdje donosimo istraživanje rasta grafena na periodički stepenastoj površini Ir(332) [1] koje predstavlja potencijalnu eksperimentalnu realizaciju navedenih teorijskih predviđanja. Grafen je na površini Ir(332) dobiven kombinacijom dva procesa rasta: temperaturno kontroliranim rastom i depozicijom kemijskih para. Dobiveni sustav je karakteriziran s više strukturnih i spektroskopskih tehnika kao što je skenirajuća tunelirajuća mikroskopija i spektroskopija, nisko- energetska elektronska difrakcija, kutno razlučiva fotoemisijska spektroskopija itd. Pokazali smo da dobiveni grafen prekriva cijelu površinu uzorka ali i uzrokuje značajno restrukturiranje površine iridija, pri čemu se stvaraju široke terase omeđene visokim grupama stepenica. Strukturna i elektronska svojstva tako korugiranog grafena se uvelike razlikuju ovisno o rotaciji grafena u odnosu na površinu iridija i o položaju grafena na terasi ili na stepenicama. Rast grafena na stepeničastoj površini predstavlja dobar način ostvarivanja strukturne modulacije grafena što u konačnici utječe na njegova elektronska svojstva. [1]I.Šrut et al. Carbon 56(2013)193-200

Graphene, the one atom thick hexagonal array of carbon atoms, is considered to be a promising material for use in electronic devices. However, the fact that it is a zero gap semiconductor limits its utilization in novel transistors. Therefore, a great deal of effort has been put into finding different ways to alter graphene electronic structure and possibly open a gap. We investigate a growth on a periodically stepped surface, whose 1D potential could lead to unexpected and potentially useful charge carrier behavior, e.g. gap openings or Fermi velocity anisotropy [1]. We have grown graphene on an Ir(332) surface by processes of temperature controlled growth (TPG) and chemical vapor deposition (CVD) with varying sample temperature and ethylene pressure. The surface has been characterized by scanning tunneling microscopy (STM). We find that graphene growth alters uniformity of a clean (332) surface, forming broader terraces with several different moiré structures, followed by a series of narrow steps. Our results show that the width of these new formed terraces can be controlled by changing the sample temperature during CVD. In this way we open path to grow periodically modulated graphene with specifically altered electronic structure. [1] C.-H. Park, L. Yang, Y.-W. Son, M. L. Cohen, S. G. Louie , Nature Phys. 4 (2008) 213