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Monoclinic BiVO4 (BVO) properties favor its use as the main absorber in photoanodes applied for photoelectrochemical water splitting. However, hindrances as the high rate of recombination of the electrons and holes photogenerated and as the poor charge carrier transport limit its direct, practical use. Doping, building a heterojunction with other semiconductors and decorating the surface with catalysts like cobalt phosphate and ruthenium oxide are among the many existing approaches to improve BVO performance. The deposition of catalyst or cocatalyst normally involve the use of potentially hazardous techniques as chemical vapor deposition (CVD). In this work, we present a simple route for enhancing photoelectrochemical results in BVO samples. The decoration with metallic ruthenium is performed via magnetron sputtering DC, a reliable, inexpensive and safe-to-use physical deposition technique, followed by a thermal treatment in air within a muffle furnace for 6 h at 400 °C. A gain of about 45% in the photocurrent at 1.23 V vs reversible hydrogen electrode (RHE) and in the overall spectrum area in comparison with pristine BVO samples was registered by cyclic voltammetry measurements in a 0.5 M phosphate buffer solution under full spectrum illumination from a 100 W Xenon lamp. The morphological and chemical modifications that resulted in such photocurrent rise were characterized using Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and X-ray Photogenerated Spectroscopy (XPS).

This chapter presents a specific reliability study of some GEANT4-DNA (version 10.02.p01) processes and models for proton transportation considering ultra-thin layers (UTL). The Monte Carlo radiation transport validation is fundamental to guarantee the simulation results accuracy. However, sometimes this is impossible due to the lack of experimental data and, it is then that the reliability evaluation takes an important role. Geant4-DNA runs in an energy range that makes impossible, nowadays, to perform a proper microscopic validation (cross-sections and dynamic diffusion parameters) and allows very limited macroscopic reliability. The chemical damage cross-sections reliability (experiment versus simulation) is a way to verify the consistency of the simulation results which is presented for 2 MeV incident protons beam on PMMA and PVC UTL. A comparison among different Geant4-DNA physics lists for incident protons beams from 2 to 20 MeV, interacting with homogeneous water UTL (2 to 200 nm) was performed. This comparison was evaluated for standard and five other optional physics lists considering radial and depth profiles of deposited energy as well as number of interactions and stopping power of the incident particle.

We report on surface modification of poly(methyl methacrylate) (PMMA) thin films deposited onto silicon wafers induced by fast ions in a wide range of electronic stopping powers [14 keV/nm (2.1 GeV Bi), 2.2 keV/nm (17 MeV Au) and 0.019 keV/nm (2 MeV H)]. Marked differences were observed on surface morphology induced by low and high dE/dx ions. The effect of the 2 MeV H beam on the PMMA surface was a weak smoothing, whilst for the heavier Bi and Au ions, pronounced roughening occurs with development of porosity and other surface features in a broad range of spatial frequencies. For the heavy ions, surface changes develop in basically two regimes. At the single ion regime at low fluences, most of the changes can be attributed to sputtering and flow of material in individual ion impacts. At the track overlap regime, porosity emerge in a pattern of holes, with an areal density not directly related to the ion fluence, but still spread uniformly across the film. A good correlation between the input of energy and the changes in surface morphology was obtained when (dE/dx)1.85 was used as the scaling factor.

Impacts of swift heavy ions of different energy loss in amorphous and crystalline Lennard-Jones (LJ) thin films (2–60 nm) were simulated using classical molecular dynamics to study cratering and sputtering in model molecular thin films. Crater size is determined mostly by evaporation and melt flow from the hot ion track, while rim size is determined both by melt flow and by coherent displacement of particles due to the large pressure developed in the excited region, with minor influence of particles from the substrate. Sputtering yields from both crystalline and amorphous samples are similar (including the scaling with energy loss), due to the extremely high temperature and disordered condition of the track region from where most ejected particles originate in the early stages of the track evolution. Cratering, however clearly depends on the crystallinity of the film. Craters and rims are much smaller in crystalline films mainly due to faster energy dissipation, higher stress threshold for plasticity and smaller free-volume in the ordered phase. We also found a large dependence of the induced surface effects on film thickness below a critical thickness value. The pressure pulse due to the ion impact is weaker and cooling of the excited track is more efficient in short tracks, both contributing to the decreased radiation damage efficiency on ultrathin layers. Despite the simplicity of the LJ model, the simulations in the amorphous films reproduce remarkably well several of the experimental features seen recently on polymer thin and ultrathin films irradiated by swift heavy ions. Fil: Gutierres, L. I.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Lima, N.W.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Thomaz, R. S.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Papaléo, R. M.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina

In this chapter, we review fundamental issues related to the damaging processes of PMMA films induced by high-energy ions with kinetic energies from a few keV to a few GeV, covering the regimes of energy deposition dominated by nuclear collisions and by electronic excitation. Emphasis is given to present an overview of the bond-breaking processes, the changes in the polymer chemical structure, and the corresponding modifications in selected macroscopic physical properties (optical, mechanical, and electrical).

Thin films of poly(methyl methacrylate) and poly(vinyl chloride) of different thickness are used to investigate the effect of spatial confinement on the efficiency of bond breaking induced by 2 MeV H^{+} and 2.1 GeV Bi ions. Effective cross sections for oxygen and chlorine loss are extracted for films down to a thickness of about 5 nm and are compared to theoretical estimations based on radial energy density profiles simulated with geant-dna. The cross sections are to a large extent thickness independent, indicating that bond breaking is dominated by short-range processes. This is in contrast to the strongly reduced efficiencies found recently for cratering induced by high-energy ions in similar ultrathin polymer films [Phys. Rev. Lett. 114, 118302 (2015)PRLTAO0031-900710.1103/PhysRevLett.114.118302].

Investigations on the chemical modifications induced by swift heavy ions in PMMA thin films were carried out using beams of high d E /d x (2.2 GeV Bi, 14,090 eV/nm) and low d E /d x (2 MeV H, 19 eV/nm). The induced chemical modifications were monitored by XPS for films with initial thickness of 50 and 100 nm. For both beams, the irradiation decreased the amount of carbon atoms bound to oxygen (C O and C O C), with a larger decrease of the carboxyl moiety, as expected. However, the chemical changes induced by light and heavy ions were qualitatively different. For the same mean deposited energy density, proton irradiation induced a decrease of the relative intensity of the carbon–oxygen bonds up to ∼20% larger than the irradiation with Bi ions. This suggests a greater importance of particle ejection by unzipping of PMMA chains at high d E /d x , which tends to keep the O/C ratio closer to the pristine value.

In this paper, the surface effects of individual heavy ions impacting thin polymerlike films were investigated, using molecular dynamics simulations with the finite extensible nonlinear elastic (FENE) potential to describe the molecular chains. The perturbation introduced by the ions in the lattice was modeled assuming that the initial excitation energy in the ion track is converted into an effective temperature, as in a thermal spike. The track was heated only within the film thickness h, leaving a nonexcited substrate below. The effect of decreasing thickness on cratering and sputtering was evaluated. The results were compared to experimental data of thin polymer films bombarded by MeV-GeV ions and to simulations performed with the Lennard-Jones potential. While several qualitative results observed in the experiments were also seen in the simulations, irrespective of the potential used, there are important differences observed on FENE films. Crater dimensions, rim volume, and sputtering yields are substantially reduced, and a threshold thickness for molecular ejection appears in FENE simulations. This is attributed to the additional restrictions on mass transport out of the excited track region imposed by interchain interactions (entanglements) and by the low mobility of the molten phase induced by the spike. Fil: Lima, N. W.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Gutierres, L. I.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Gonzalez, R. I.. Universidad de Chile; Chile Fil: Müller, S.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Thomaz, R. S.. Universidade Católica Do Rio Grande Do Sul; Brasil Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Papaléo, R.M.. Universidade Católica Do Rio Grande Do Sul; Brasil

We show direct experimental evidence that radiation effects produced by single MeV heavy ions on a polymer surface are weakened when the length of the ion track in the material is confined into layers of a few tens of nanometers. Deviation from the bulk (thick film) behavior of ion-induced craters starts at a critical thickness as large as ∼40nm, due to suppression of long-range additive effects of excited atoms along the track. Good agreement was found between the experimental results, molecular dynamic simulations, and an analytical model. Fil: Papaléo, R. M.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Thomaz, R.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: Gutierres, L.I.. Pontificia Universidade Católica do Rio Grande do Sul; Brasil Fil: De Menezes, V.M.. Universidade Federal Da Fronteira Sul; Brasil Fil: Severin, D.. GSI Helmholtz Centre; Alemania Fil: Trautmann, C.. GSI Helmholtz Centre; Alemania. Universitat Technische Darmstadt; Alemania Fil: Tramontina Videla, Diego Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Grande, P. L.. Universidade Federal do Rio Grande do Sul; Brasil