Surface studies of supported model catalysts

In the framework of the thermal-spike model the present paper deals with the effect of the electronic stopping power (Se) in metals irradiated by swift heavy ions. Using the strength of the electron-phonon coupling g(z) with the number of valence electrons z as the unique free parameter, the increment of lattice temperature induced by swift-heavy-ion irradiation is calculated. Choosing z=2, the calculated threshold of defect creation by Se for Ti, Zr, Co and Fe is about 11, 27.5, 28 and 41 keV nm-1, in good agreement with experiment. Taking the same z value, the calculation shows that Al, Cu, Nb and Ag are Se insensitive. Moreover, in Fe, the differences in the damage created by U ions of different energies but exhibiting the same value of Se may be interpreted by a velocity effect. Using z=2, other calculations suggest that Be (Se>or=11 keV nm-1), Ga (Se>or=5 keV nm-1) and Ni (Se>or=49 keV nm-1) should be sensitive to Se but Mg should not. These examples put the stress on the effect of the physical parameters governing the electron-phonon coupling constant apart from z determination: the sound velocity linked to the Debye temperature and the lattice thermal conductivity. Furthermore, a simple criterion is proposed in order to predict the Se sensitivity of metals.

/pdf/the-se-sensitivity-of-metals-under-swift-heavy-ion-2g5eyh0z6p.pdf

The Se sensitivity of metals under swift-heavy-ion irradiation: a transient thermal process

Recently, films produced by depositing pre-formed mass-selected atomic clusters in the size range 1–10 nm have generated a great deal of attention. The ability to control the size, density and in some cases the morphology of the deposited particles allows unprecedented flexibility in the creation of new types of nanostructure. The technique enables research on the fundamental behaviour of matter at mesoscopic length scales and in addition has enormous potential in the creation of new materials whose properties can be widely varied. This review will describe the technology used to produce the particles and deposit them, and discuss the details of the landing on the surface and subsequent surface kinetics. The equilibrium structures and morphologies of the particles will be reviewed as also how the organisation of the particle assemblies is influenced by the particle–surface and inter-particle interactions. As a result of the reduced average atomic coordination, the quantum size effect and the modified screening response in nanoscale systems, the clusters display novel electronic and magnetic properties and these will be described for a range of elements including transition metals, noble and simple metals, and rare-earths. In addition to the native properties, the effect of the interaction with the substrate and other deposited particles will be explored. Finally, the work on coated particles and particles embedded in matrices will be reviewed and the potential to create new materials and devices will be discussed.

Nanoclusters deposited on surfaces

Gas phase nanoparticle production, manipulation and deposition is of primary importance for the synthesis of nanostructured materials and for the development of industrial processes based on nanotechnology. In this review we present and discuss this approach, introducing cluster sources, nanoparticle formation and growth mechanisms and the use of aerodynamic focusing methods that are coupled with supersonic expansions to obtain high intensity cluster beams with a control on nanoparticle mass and spatial distribution. The implication of this technique for the synthesis of nanostructured materials is also presented and applications are highlighted.

https://iopscience.iop.org/article/10.1088/0022-3727/39/22/R02/pdf

Cluster beam deposition: a tool for nanoscale science and technology

Nanoscale structural information underlies research aimed at fabricating catalysts in a more controlled way. Surface science methods can provide that information, but the complexity of heterogeneous systems in general hinders the application of these methods to their full potential. In the last decades, a solution to this problem has been found in the use of model systems, ranging from well-defined single crystals of the supported phase to films or particles of that phase on flat or spherical model supports. In this paper, we review the literature on the latter model systems, that is, particles on a model support. Attention is payed to both preparation and use of such model systems.

https://pure.tue.nl/ws/files/1495087/617871.pdf

Surface Science Approach to Modeling Supported Catalysts

M\"ossbauer spectroscopy of damage induced by energetic Ar, Kr, and Xe ions in the giga-electron-volt range in two ferrimagnetic oxides, ${\mathrm{Y}}_{3}$${\mathrm{Fe}}_{5}$${\mathrm{O}}_{12}$ and ${\mathrm{BaFe}}_{12}$${\mathrm{O}}_{19}$, is presented. The enhancement of the paramagnetic phase observed after an irradiation with high-energy deposition (Xe and Kr ions) compared to low-energy deposition (Ar ions) supports a damage mechanism based on the electronic stopping power. Threshold energy-deposition values close to 17 and 25 MeV ${\mathrm{cm}}^{2}$ ${\mathrm{mg}}^{\mathrm{\ensuremath{-}}1}$ have thus been determined for ${\mathrm{Y}}_{3}$${\mathrm{Fe}}_{5}$${\mathrm{O}}_{12}$ and ${\mathrm{BaFe}}_{12}$${\mathrm{O}}_{19}$, respectively. Furthermore, drastic changes in the bulk orientation of the hyperfine magnetic field ${H}_{f}$ have been observed in yttrium iron garnet: The ${H}_{f}$ distribution is isotropic for Ar irradiations and anisotropic for Xe irradiations, while two types of ${H}_{f}$ distributions are observed for Kr irradiations, depending on the values of the deposited energy compared to that of the threshold energy. Comparison with latent-track models is performed.

Damage processes and magnetic field orientation in ferrimagnetic oxides Y 3 Fe 5 O 12 and BaFe 12 O 19 irradiated by high-energy heavy ions: A Mössbauer study

Crystalline ${\mathrm{Ni}}_{3}$B ribbons have been irradiated at low temperature with GeV heavy ions (Kr,Xe,U) in order to study the disordering process induced in this material by ion electronic energy loss. The atomic rearrangements produced by irradiation were monitored in situ via electrical resistance measurements and characterized after annealing at room temperature by electron diffraction. The results show a huge electrical resistivity increase above an electronic-energy-loss threshold, which can be ascribed to partial amorphization of the irradiated alloy.

Evidence for amorphization of a metallic alloy by ion electronic energy loss.

Cluster-beam deposition of thin metallic antimony films: Cluster-size and deposition-rate effects.

The energy deposited on target electrons by a swift heavy ion has been studied for several years. The deposited energy density in the vicinity of the ion path is large as the velocity of the incident ion is low. The influence of the ion velocity on irradiation effect induced by electronic energy loss ( S e ) has been clearly demonstrated after irradiation experiments performed on the insulator Y 3 Fe 5 O 12 and suspected in metals. In that case the damage creation is enhanced at low ion velocities. In the present work, pure bismuth samples have been irradiated at 100 K by 42.9 MeV amu −1 Xe and 4 MeV amu −1 Kr ions with similar S e values (∼ 17 KeV nm −1 ). The resistivity increment Δϱ was measured in situ as a function of the ion fluence, Φt. The analyses of Δϱ(Φt) curves show that the Kr irradiation leads to a damage efficiency which is two to four times larger than that obtained after Xe irradiation. In addition, 2, 10 and 20 MeV amu −1 Pb-ion irradiations were performed at 20 K. The comparison of deduced latent track radii for the same S e values with previous results gives that lower velocity in irradiations produce larger tracks. These phenomena evidence that a strong ion velocity effect exists in bismuth. The thermal spike model with the ion velocity dependence of the initial energy deposition is used to determine the track radii as a function of S e values. We now find an agreement between calculated and experimental track radii in relation with the ion velocity. Moreover the electron number density n e of the quasi-free gas in bismuth is found to be 1.5 times the atomic density n a ( n e = 1.5n a ) and the S e threshold for continuous latent track formation, S et , is ranged from 24 to 31 keV nm −1 for ion energies ranging from 2 to 25 MeV amu −1 .

Velocity effect on the damage creation in metals in the electronic stopping power regime

Iron and copper thin metallic films (thickness ≤ 100 nm) deposited on sapphire substrates (α-Al2O3) were mixed at room temperature by various rare gas ions (Ne, Ar, Kr and Xe) in large energy and dose ranges. Microstructural and chemical characterization of the mixed interfaces were performed using three complementary techniques: high resolution transmission electron microscopy (HRTEM), X-ray photoemission spectroscopy (XPS) and conversion electron Mossbauer spectrometry (CEMS) in the particular case of Fe/Al2O3 samples. The final atom distributions at the mixed interface are the result of the ballistic phase of mixing and no long range diffusion of mixed elements in Al2O3 has been observed. The result is a very narrow and damaged interface (amorphous or not in the case of Fe/Al2O3 or Cu/Al2O3, respectively) containing a very high concentration of metallic atom recoils. The composition and nature of this interfacial layer, which completely depends on the energy deposition at the interface, which is controlled by the mixing parameters (mass of the incident ion, energy and fluence) are the origin of the spectacular adhesion enhancement observed. In the particular case of the Fe/Al2O3 interface, the formation of iron recoils in Al2O3 in the Fe2+ state and the formation of the spinel phase seem to be correlated with the quality of the interfacial joint in terms of adhesion. Thermal annealings in a low temperature range (< 600°C) promote the spinel phase formation and produce an additional positive effect on adhesion.

G. Fuchs

Papers

Damage processes and magnetic field orientation in ferrimagnetic oxides Y 3 Fe 5 O 12 and BaFe 12 O 19 irradiated by high-energy heavy ions: A Mössbauer study

Evidence for amorphization of a metallic alloy by ion electronic energy loss.

Cluster-beam deposition of thin metallic antimony films: Cluster-size and deposition-rate effects.

Velocity effect on the damage creation in metals in the electronic stopping power regime

Ion beam mixing of metal-ceramic interfaces