arXiv subjects

Renato P. Camata

Publications and source records attributed to Renato P. Camata.

6 recordsLinked to original sources

arXiv2025

Pulsed laser synthesis of mesoporous metal chalcogenide thin films

Mesoporous films of the metal chalcogenide $β$-FeSe were grown on MgO substrates by KrF pulsed laser deposition (PLD) in an argon background. At 100 mTorr, gated intensified charge-coupled device imaging and ion probe measurements showed that the plasma plume responsible for crystal growth initially comprised three components, with distinct expansion velocities. Plume interactions with the substrate heater and ablation target gave rise to complex dynamics, including collisions between the charged leading edge -- rebounding between the substrate and the target -- and slower-moving species in the plume interior. Film growth was dominated by species with kinetic energies $\le$0.5 eV/atom. X-ray reflectivity and atomic force microscopy revealed that films grown in this environment -- with a substrate temperature of 350$^\circ$C, a laser fluence of 1.0 J cm$^{-2}$, and a 7.5 mm$^2$ spot area -- formed a porous framework with 15% porosity and pore sizes below 100 nm. X-ray diffraction indicated that the porous films were epitaxial with respect to the substrate and likely grew by oriented-attachment of gas-phase molecular clusters or very small nanoparticles, in contrast to the conventional epitaxy of vacuum films from atomic constituents. The in-plane orientation of the mesoporous films was $β$-FeSe[100]$\parallel$[110]MgO, attributed to the soft landing of pre-formed crystallites on the MgO substrates, where protruding Se rows of $β$-FeSe aligned with corrugations of the MgO surface. This work implies that growth of candidate electrocatalyst materials by PLD in inert gas background may allow mesoporous frameworks with a single crystallographic orientation that expose specific crystal facets for electrochemical reactions and active site engineering.

cond-mat.mtrl-sci↗

arXiv2023

Machine learning the relationship between Debye temperature and superconducting transition temperature

Recently a relationship between the Debye temperature $Θ_D$ and the superconducting transition temperature $T_c$ of conventional superconductors has been proposed [npj Quantum Materials $\mathbf{3}$, 59 (2018)]. The relationship indicates that $T_c \le A Θ_D$ for phonon-mediated BCS superconductors, with $A$ being a pre-factor of order $\sim 0.1$. In order to verify this bound, we train machine learning (ML) models with 10,330 samples in the Materials Project database to predict $Θ_D$. By applying our ML models to 9,860 known superconductors in the NIMS SuperCon database, we find that the conventional superconductors in the database indeed follow the proposed bound. We also perform first-principles phonon calculations for H$_{3}$S and LaH$_{10}$ at 200 GPa. The calculation results indicate that these high-pressure hydrides essentially saturate the bound of $T_c$ versus $Θ_D$.

cond-mat.supr-con↗

arXiv2021

Geometrical and energy scaling in the pulsed laser deposition plasma during epitaxial growth of FeSe thin films

Pulsed laser deposition (PLD) is a versatile technique for growing epitaxial heterostructures of a wide variety of novel materials combinations. Achieving low-defect layers with atomically sharp interfaces by PLD requires careful management of crystal growth conditions. Control over the flux of depositing particles, their kinetic energy, and the substrate temperature, is generally sufficient to obtain high-quality single crystal epitaxy in vacuum. In this article, we show that measurements of plasma parameters such as the electron temperature, the electron density, and the Mach number of the plasma fluid expansion may provide additional insights into the tuning of the crystal growth and processing environment of PLD. We report Langmuir probe measurements during growth of FeSe thin films on (100)-oriented SrTiO$_3$. We discuss two distinct plasma regimes that are accessible by KrF laser ablation of FeSe when pulse energies in the 20-630 mJ range are used. The two regimes can be characterized by the relative number of photons to absorbing centers in the laser-plasma interaction volume. Thin films grown under the conditions created by these two distinct plasma regimes are analyzed by x-ray diffraction and x-ray reflectivity and their epitaxial configurations correlated to the PLD conditions associated with these plasmas.

physics.app-ph↗

arXiv2021

Experimentally constrained multidimensional simulation of laser-generated plasmas and its application to UV nanosecond ablation of Se and Te

We carry out simulations of laser plasmas generated during UV nanosecond pulsed laser ablation of the chalcogens selenium (Se) and tellurium (Te), and compare the results to experiments. We take advantage of a 2D-axisymmetric, adaptive Cartesian Mesh (ACM) framework that enables plume simulations out to centimeter distances over tens of microseconds. Our model and computational technique enable comparison to laser-plasma applications where the long-term behavior of the plume is of primary interest, such as pulsed laser synthesis and modification of materials. An effective plasma absorption term is introduced in the model, allowing the simulation to be constrained by experimental time-of-flight kinetic energy distributions. We show that the effective simulation qualitatively captures the key characteristics of the observed laser plasma, including the effect of laser spot size. Predictions of full-scale experimentally-constrained Se and Te plasmas for 4.0 J/cm$^2$ laser fluence and 1.8 mm$^2$ circular laser spot area show distinct behavior compared to more commonly studied copper (Cu) plumes. The chalcogen plumes have spatial gradients of plasma density that are steeper than those for Cu by up to three orders of magnitude. Their spatial ion distributions have central bulges, in contrast to the edge-only ionization of Cu. For the irradiation conditions explored, the range of plasma temperatures for Se and Te is predicted to be higher than for Cu by more than 0.50 eV.

physics.plasm-ph↗

arXiv2019

Laser-generated plasmas in length scales relevant for thin film growth and processing: simulation and experiment

In pulsed laser deposition, thin film growth is mediated by a laser-generated plasma, whose properties are critical for controlling the film microstructure. The advent of 2D materials has renewed the interest in how this ablation plasma can be used to manipulate the growth and processing of atomically thin systems. For such purpose, a quantitative understanding of the density, charge state, and kinetic energy of plasma constituents is needed at the location where they contribute to materials processes. Here we study laser-induced plasmas over expansion distances of several centimeters from the ablation target, which is the relevant length scale for materials growth and modification. The study is enabled by a fast implementation of a laser ablation/plasma expansion model using an adaptive Cartesian mesh solver. Simulation outcomes for KrF excimer laser ablation of Cu are compared with Langmuir probe and optical emission spectroscopy measurements. Simulation predictions for the plasma-shielding threshold, the ionization state of species in the plasma, and the kinetic energy of ions, are in good correspondence with experimental data. For laser fluences of 1-4 J/cm$^2$, the plume is dominated by Cu$^0$, with small concentrations of Cu$^{+}$ and electrons at the expansion front. Higher laser fluences (e.g., 7 J/cm$^2$) lead to a Cu$^{+}$-rich plasma, with a fully ionized leading edge where Cu$^{2+}$ is the dominant species. In both regimes, simulations indicate the presence of a low-density, high-temperature plasma expansion front with a high degree of ionization that may play a significant role in doping, annealing, and kinetically-driven phase transformations in 2D materials.

physics.app-ph↗

arXiv2019

X-ray diffraction analysis to support phase identification in FeSe and Fe$_7$Se$_8$ epitaxial thin films

X-ray diffraction (XRD) data and analysis for epitaxial iron selenide thin films grown by pulsed laser deposition (PLD) are presented. The films contain $β$-FeSe and Fe$_7$Se$_8$ phases in a double epitaxy configuration with the $β$-FeSe phase (001) oriented on the (001) MgO growth substrate. Fe$_7$Se$_8$ simultaneously takes on two different epitaxial orientations in certain growth conditions, exhibiting both (101)- and (001)- orientations. Each of these orientations are verified with the presented XRD data. Additionally, XRD data used to determine the PLD target composition as well as mosaic structure of the $β$-FeSe phase are shown.

cond-mat.mtrl-sci↗