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High Power Target systems are key elements in future neutrino and other rare particle production in accelerators. These systems transform an intense source of protons into secondary particles of interest to enable new scientific discoveries. As beam intensity and energies increase, target systems face significant challenges. Radiation damages and thermal shocks in target materials were identified as the leading cross-cutting challenges of high-power target facilities. Target material R&D to address these challenges are essential to enable and ensure reliable operation of future-generation accelerators. Irradiation facilities and alternative methods are critical to provide a full support of material R&D and better address these critical challenges., Comment: contribution to Snowmass 2021

The local epitaxial growth of pulsed laser deposited Ca$_2$MnO$_4$ films on polycrystalline spark plasma sintered Sr$_2$TiO$_4$ substrates was investigated to determine phase formation and preferred epitaxial orientation relationships ($ORs$) for isostructural Ruddlesden-Popper (RP) heteroepitaxy, further developing the high-throughput synthetic approach called Combinatorial Substrate Epitaxy (CSE). Both grazing incidence X-ray diffraction and electron backscatter diffraction (EBSD) patterns of the film and substrate were indexable as single-phase RP-structured compounds. The optimal growth temperature (between 650 $^{\circ}$C and 800 $^{\circ}$C) was found to be 750 $^{\circ}$C using the maximum value of the average image quality (IQ) of the backscattered diffraction patterns. Films grew in a grain-over-grain pattern such that each Ca$_2$MnO$_4$ grain had a single $OR$ with the Sr$_2$TiO$_4$ grain on which it grew. Three primary $ORs$ described 47 out of 49 grain pairs that covered nearly all of RP orientation space. The first $OR$, found for 20 of the 49, was the expected RP unit-cell over RP unit-cell $OR$, expressed as [100][001]$_{film}$||[100][001]$_{sub}$. The other two $ORs$ were essentially rotated from the first by 90$^{\circ}$, with one (observed for 17 of 49 pairs) being rotated about the [100] and the other (observed for 10 of 49 pairs) being rotated about the [110] (and not exactly by 90$^{\circ}$). These results indicate that only a small number of $ORs$ are needed to describe isostructural RP heteroepitaxy and further demonstrate the potential of CSE in the design and growth of a wide range of complex functional oxides., Comment: Submitted to J. Appl. Phys

The formation of nano-hillocks on CaF2 crystal surfaces by individual ion impact has been studied using medium energy (3 and 5 MeV) highly charged ions (Xe19+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV) heavy ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy while for swift heavy ions a minimum electronic energy loss is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via electronic energy loss the potential energy threshold for hillock production can be substantially lowered. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, as demonstrated when plotting the results in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to case where kinetic and potential energies are deposited into the surface., Comment: 12 pages, 4 figures

We developed a new sub-nanosecond time-resolved instrument to study the dynamics of UV-visible luminescence under high stopping power heavy ion irradiation. We applied our instrument, called SPORT, on a fast plastic scintillator (BC-400) irradiated with 27-MeV Ar ions having high mean electronic stopping power of 2.6 MeV/\mu m. As a consequence of increasing permanent radiation damages with increasing ion fluence, our investigations reveal a degradation of scintillation intensity together with, thanks to the time-resolved measurement, a decrease in the decay constant of the scintillator. This combination indicates that luminescence degradation processes by both dynamic and static quenching, the latter mechanism being predominant. Under such high density excitation, the scintillation deterioration of BC-400 is significantly enhanced compared to that observed in previous investigations, mainly performed using light ions. The observed non-linear behaviour implies that the dose at which luminescence starts deteriorating is not independent on particles' stopping power, thus illustrating that the radiation hardness of plastic scintillators can be strongly weakened under high excitation density in heavy ion environments., Comment: 5 figures, accepted in Nucl. Instrum. Methods B

The high energy density of electronic excitations due to the impact of swift heavy ions can induce structural modifications in materials. We present a X-ray diffractometer called ALIX, which has been set up at the low-energy IRRSUD beamline of the GANIL facility, to allow the study of structural modification kinetics as a function of the ion fluence. The X-ray setup has been modified and optimized to enable irradiation by swift heavy ions simultaneously to X-ray pattern recording. We present the capability of ALIX to perform simultaneous irradiation - diffraction by using energy discrimination between X-rays from diffraction and from ion-target interaction. To illustrate its potential, results of sequential or simultaneous irradiation - diffraction are presented in this article to show radiation effects on the structural properties of ceramics. Phase transition kinetics have been studied during xenon ion irradiation of polycrystalline MgO and SrTiO3. We have observed that MgO oxide is radiation-resistant to high electronic excitations, contrary to the high sensitivity of SrTiO3, which exhibits transition from the crystalline to the amorphous state during irradiation. By interpreting the amorphization kinetics of SrTiO3, defect overlapping models are discussed as well as latent track characteristics. Together with a transmission electron microscopy study, we conclude that a single impact model describes the phase transition mechanism., Comment: 12 pages, 8 figures, Accepted to Review of Scientific Instruments

Calcium cobaltite thin films with a ratio Ca/Co=1 were grown on (101)-NdGaO3 substrate by the pulsed laser deposition technique. The structure of the deposited metastable phase is solved using a precession electron diffraction 3D dataset recorded from a cross-sectional sample. It is shown that an ordered oxygen-deficient Ca2Co2O5+d perovskite of the brownmillerite-type with lattice parameters a= 0.546nm, b=1.488nm and c=0.546nm (SG: Ibm2) has been stabilized using the substrate induced strain. The structure and microstructure of this metastable cobaltite is further discussed and compared to related bulk materials based on our transmission electron microscopy investigations, Comment: 13 pages, 10 figures, 2 tables, accepted in Phys. Rev. B

The thermal hysteresis of the electronic transport properties were studied for V2O3 thin films. The temporal evolution of the resistance shows the out-of-equilibrium nature of this hysteresis with a very slow relaxation. Partial cycles reveal not only a behavior consistent with phase coexistence, but also the presence of spinodal temperatures which are largely separated. The temperature spreading of phase coexistence is consistent with the bulk phase diagram in the pressure-temperature plane, confirming that the film is effectively under an effective pressure induced by the substrate., Comment: Accepted for publication in Europhysics Letters

The spectacular metal-to-insulator transition of V2O3 can be progressively suppressed in thin film samples. Evidence for phase separation was observed using microbridges as a mesoscopic probe of transport properties where the same film possesses domains that exhibit a metal-to-insulator transition with clear first order features or remain metallic down to low temperatures. A simple model consisting of two parallel resistors can be used to quantify a phase coexistence scenario explaining the measured macroscopic transport properties. The interaction between film and substrate is the most plausible candidate to explain this extended phase coexistence as shown by a correlation between the transport properties and the structural data., Comment: extended version accepted in Journal of Physics: Condensed Matter. More references and figures. More details are given on the structural part

High quality vanadium sesquioxide V2O3 films (170-1100 {\AA}) were grown using the pulsed laser deposition technique on (0001)-oriented sapphire substrates, and the effects of film thickness on the lattice strain and electronic properties were examined. X-ray diffraction indicates that there is an in-plane compressive lattice parameter (a), close to -3.5% with respect to the substrate and an out-of-plane tensile lattice parameter (c) . The thin film samples display metallic character between 2-300 K, and no metal-to-insulator transition is observed. At low temperature, the V2O3 films behave as a strongly correlated metal, and the resistivity (\rho) follows the equation \rho =\rho_0 + A T^2, where A is the transport coefficient in a Fermi liquid. Typical values of A have been calculated to be 0.14 \mu\Omega cm K^{-2}, which is in agreement with the coefficient reported for V2O3 single crystals under high pressure. Moreover, a strong temperature-dependence of the Hall resistance confirms the electronic correlations of these V2O3 thin films samples., Comment: 4 pages, 4 figures

Epitaxial La2NiMnO6 thin films have been grown on (001)-oriented SrTiO3 using the PLD technique. The thin films are semiconducting and FM with a TC close to 270K, a coercive field of 920Oe, and a saturation magnetization of 5muB per f.u. TEM, conducted at RT, reveals a majority phase having "I-centered" structure with a=c=1.4asub and b=2asub along with a minority phase-domains having "P-type" structure (asub being the lattice parameter of the perovskite structure). A discusion on the presence of Ni/Mn long-range ordering, in light of recent literature on double perovskites La2NiMnO6 is presented., Comment: To be published in Applied Physics Letters