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Obtaining pure group IV 2D films on well-behaved substrates is at present a major goal in materials science and of great interest for the associated industries. This goal still represents a challenge in surface science because often these materials tend to form alloys. As a consequence, some of the proposed 2D films resulted in topics of controversy regarding the top-layer elemental composition and interpretation of the honeycomb patterns measured by STM. Very recently, germanene on Al(111) was proposed to be a system having a larger gap than silicene and a quantum-spin Hall effect. This system was studied by several techniques including scanning tunnel microscopy, low-energy electron diffraction, photoemission, and density functional theory. None of the techniques used until now have the capability to detect unambiguously the presence of substrate atoms within the ultrathin film (i.e., separated from the corresponding substrate), thus leaving open the question of the composition or purity of the layer. Here we follow previous guidelines to grow a Ge film on Al(111) with the expected 3 × 3 arrangement that was assumed to be characteristic of germanene, and then we study in situ the properties of the films with ion scattering and recoiling spectrometry, a technique particularly suited for determining the elemental composition of the last surface layer. Our results unambiguously show the formation of a mixture of well-ordered Ge and Al atoms for all of the temperatures and conditions tested, in clear disagreement with the pure single germanene layer proposed in previous works. These conclusions led us to investigate by DFT calculations other possible structures compatible with our present results and the previously reported ones. The most favorable alloyed structures obtained by DFT were then compared with new I–V low-energy electron diffraction curves, and from this comparison, a top surface model composed of five Ge atoms and three Al atoms is proposed to replace the germanene model.

Measurements of the energy loss of protons and deuterons channeled in a very thin single-crystal foil of gold were performed, covering the range of very low velocities. The experimental results provide clear evidence of the deviation of the energy loss from the proportionality with ion velocity predicted theoretically, showing a transition between two well-defined regimes. We explain this behavior by a theoretical analysis that takes into account the electronic band structure properties of the medium, separating the contribution of the conduction band ͑described as a free Fermi gas͒ from the contribution of the nearly free d electrons of gold, which are affected by a threshold behavior due to the shift of the density of states of this band with respect to the Fermi level. The theoretical model yields a very good description of the experimental findings.

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Energy-loss measurements and theoretical calculations for Be and B ions in Zn are presented. The experimental ion energies range from 40 keV/u to 1 MeV/u, which includes the energy-loss maximum and covers a lack of experimental data for these systems from intermediate to high energies. The measurements were performed using the Rutherford backscattering technique. The ab initio calculations are based on the extended Friedel sum rule-transport cross-section method for the valence electrons and the Shellwise local plasma approximation for the bound electrons. A comparison of these calculations to the present experimental data for Be and B and previous values for H, He, and Li ions on the same target is included. This confirms the applicability of the employed theoretical framework also for ions of intermediate atomic number.

The synthesis of antimonene and related 2D Sb films on top of metallic substrates has recently become a very active subject due to the strong spin−orbit coupling and the envisaged topological properties of this novel material. Gold has been used as a standard substrate for other 2D films, but in the case of Sb, no success has yet been reported mainly due to the formation of AuSb 2 surface alloy. In this work, we have used low energy electron diffraction, time-of-flight direct recoil spectroscopy, X-ray photoemission spectroscopy, and scanning tunneling microscopy together with density functional theory calculations to provide a full characterization of the growth and the structural properties of Sb deposited on Au(111). We show that the controlled deposition of Sb on Au(111) at room temperature results in a surface alloy at submonolayer coverage, but around 1 ML a pure 2D Sb film with a ( ) 3 0 1 2 commensurate structure is achieved. The obtained 2D material has high stability and can be produced not only by direct deposition of Sb over the clean Au substrate but also by starting from a thicker Sb film followed by annealing of the sample at about 500 K, which is easier and reliable for potential applications.

We present a combined experimental-theoretical study of the energy loss of C and O ions in Zn in the energy range 50-1000 keV/amu. This contribution has a double purpose, experimental and theoretical. On the experimental side, we present stopping power measurements that fill a gap in the literature for these projectiletarget combinations and cover an extended energy range, including the stopping maximum. On the theoretical side, we make a quantitative test on the applicability of various theoretical approaches to calculate the energy loss of heavy swift ions in solids. The description is performed using different models for valence and inner-shell electrons: a nonperturbative scattering calculation based on the transport cross section formalism to describe the Zn valence electron contribution, and two different models for the inner-shell contribution: the shellwise local plasma approximation (SLPA) and the convolution approximation for swift particles (CasP). The experimental results indicate that C is the limit for the applicability of the SLPA approach, which previously was successfully applied to projectiles from H to B. We find that this model clearly overestimates the stopping data for O ions. The origin of these discrepancies is related to the perturbative approximation involved in the SLPA. This shortcoming has been solved by using the nonperturbative CasP results to describe the inner-shell contribution, which yields a very good agreement with the experiments for both C and O ions. The study of the energy loss of ions in solids is a problem of interest for basic and applied research in many areas, such as ion implantation, radiation damage, and space research. Although a large number of experiments and calculations have been produced over the years, there is a demand for new data for various projectile-target combinations. Additionally, the development of a consistent theoretical framework is a subject of great current interest [1,2]. In recent years, we have performed a set of studies that combine experimental and theoretical research with the aim of providing a theoretical framework that could serve as a basis for more accurate predictions of the energy loss of swift ions in various solid materials. It is worthwhile to mention that for ions heavier than Li, the experimental stopping power data are scarce except for some particular materials (C, Al, Si, Ag, Au) [3]. In zinc, no energy loss measurements for C and O ions have been reported in the literature.In previous papers, we have studied in a systematic way the stopping coefficients for a series of ions of increasing atomic numbers: H, He, Li, Be, and B in zinc [4][5][6][7][8], and with our theoretical formulation, we have been able to explain changes in the stopping power curves, reaching a very good agreement between the experimental and theoretical results. This agreement was achieved by a detailed theoretical study of the contribution of each individual charge state of the projectile and each electronic shell of the target. This was made by separ...