Marco Peiteado

This study is part of an ongoing project in which we experimentally examine the effect of composition (refractive index) and surface roughness on the scattering matrix elements of a set of well-characterized rough regolith simulants. A set of four cylindrical Mars regolith simulants with controlled degrees of porosity and surface roughness is studied. Photopolarimetric measurements, spanning scattering angles from 94° to 177°, were conducted at a wavelength of 488 nm at the Instituto de Astrofísica de Andalucía Cosmic Dust Laboratory. These results are compared with those previously obtained at 640 nm. The higher absorption of the Mars simulants at 488 nm compared to 640 nm produces a significant effect on all elements of the scattering matrix. The trends previously observed in the diagonal elements of the scattering matrix and in the albedo as a function of surface roughness remain unaffected by the differences in refractive indices at both wavelengths. The comparison with the previous study enables the investigation of sample reddening across the scattering-angle range, with a trend also observed between surface roughness and reddening. Moreover, within our measured angular range, the effect of absorption is consistent with Umov’s law, whereas the effects of surface roughness do not appear to support its validity. Nearly all samples exhibit a shallow negative polarization branch.

The advancement of photocatalytic materials is critical for addressing environmental challenges such as water remediation, where efficient, robust, and reusable systems are in high demand. In this search, the development of hierarchically organized photocatalytic configurations with spatial control over active sites can significantly enhance performance. With this in mind, we present here a novel biomimetic approach for the patterned growth of TiO₂-ZnO photocatalytic heterostructures using solid-binding peptides (SBPs) as molecular linkers. Specifically, using bi-functional SBPs with selective affinity for both oxides, we achieve site-specific, molecularly guided deposition of TiO₂ nanoparticles onto pre-patterned ZnO-coated substrates. Leveraging the specific recognition capabilities and strong binding affinities of the engineered SBPs, the proposed biomimetic methodology allows for the fabrication of well-organized hybrid nanostructures under sustainable conditions. Photocatalytic degradation assays employing methyl orange as a model contaminant indicate that the patterned architecture enhances both the accessibility of the active photocatalytic sites and the recoverability of the material. This reusability is a critical parameter for the practical deployment of photocatalytic systems in water purification technologies. The obtained results underscore the potential of SBP-mediated molecular recognition as a versatile tool for green nanofabrication of functional materials with advanced architectural and catalytic properties.

Aims. We experimentally examined the impact of the surface roughness of regolith simulants on the elements of the light-scattering Mueller matrix. Methods. We processed a Mojave Mars Simulant (MMS2) powder sample to produce a set of aggregates with a controlled degree of porosity. The final samples present a cylindrical shape of 0.2 cm radius by 0.4 cm height. The measurements, spanning scattering angles from 94° to 177°, were conducted at a wavelength of 640 nm at the IAA Cosmic Dust Laboratory (CODULAB), which was specifically adapted for surface studies. This marks the first scattering experiment on surfaces performed at CODULAB. Results. Our measurements reveal the influence of surface roughness on the scattering matrix elements, with trends directly correlated with the degree of roughness. Additionally, we observe an inverse relationship between surface roughness and albedo. Across all samples, a shallow negative polarization branch near the backward direction is detected, a characteristic attributed to the single-particle and coherent backscattering mechanisms commonly observed in comets and asteroids. The results also highlight the significant role of large-scale surface structures in determining the scattering behavior, particularly through enhanced multiple scattering. Future work will explore the wavelength dependence of the scattering properties of these rough surfaces.

We report our recent advances in the design and synthesis of functional and hybrid composite nanomaterials with properties geared toward life sciences assays and as platforms for biomedical imaging applications. Using a stepwise reverse micelle procedure, we synthesized hybrid platelets comprising rare earth-doped strontium aluminate cores labeled Eu,Dy:SrAlO, where the phase nominally denoted as Sr0.95Eu0.02Dy0.03Al2O4 dominates the nature of the composite, as demonstrated by extensive X-ray diffraction investigations. These were coated with a biocompatible cerium oxide shell, giving rise to the hierarchical hybrids denoted CeO2@Eu,Dy:SrAlO. Such Eu/Dy codoped strontium aluminates exhibit broad luminescent emissions with high optical sensitivity. The CeO2 shell further imparts biocompatibility and water dispersibility, resulting in kinetically stable nanoplatelets which can translocate into living cells in lifetime imaging protocols that were optimized for imaging across nano- and microscales. Multiphoton fluorescence lifetime imaging microscopy (MP FLIM) confirmed the luminescent properties in thin films and living cellular environments. These nanohybrids represent a significant step forward in the development of functional molecules and materials, leveraging directed and self-assembly strategies for their synthesis. Their luminescence (detectable by fluorescence as well as phosphorescence emission intensity correlated with emission lifetime), negligible toxicity on the time scale of imaging assays and up to 72 h, and biocompatibility with cellular milieu enabled their tracing with living cells. Their cellular activity was estimated by standard MTT assays in PC-3 and provided a further insight into their behavior in biological environments. The inclusion of heavy cerium and strontium atoms enhanced X-ray attenuation, supporting multimodal imaging by integrating optical and X-ray-based methods, which paves the way for potential applications in computed tomography correlated to confocal microscopy coupled with fluorescence lifetime imaging. These findings highlight the versatility of these luminescent hybrids for bioimaging and as synthetic scaffolds toward nanomedicine applications, bridging advanced imaging modalities with functional materials design.

The experimental data base of scattering matrices of three well-characterized Martian dust analogues with narrow particle size distributions representative of Martian dust aerosols is used to check the the suitability of hexahedra model particles to reproduce the scattering behaviour of realistic polydisperse irregular particles at 488 and 640 nm. In general, the hexahedra model performs well. The scattering matrix elements as functions of the scattering angle can be reproduced with good accuracy for particle size distributions that contain small particles; however, the discrepancies increase with increasing particle size due to wavelength-scale surface roughness and internal structure found within large dust grains that are not accounted for by the smooth hexahedra model particles. We further perform sensitivity tests to study the effect of absorption, real part of the complex refractive index, and particle size distribution within the model to understand their contribution to the modelled scattering matrix elements. By using the best-fitting parameters from the sensitivity study, we have created a data base of optical properties that includes bulk extinction efficiencies, single-scattering albedos, asymmetry factors, extinction cross-sections, and phase matrices of the analogue samples from 200 to 2000 nm. The obtained values can be further used in radiative-transfer simulations. This work emphasizes the importance of accounting for the full scattering matrix as information on particle shape, size, and complex refractive index is lost when omitting polarization.

Within the RoadMap project, we investigated the microphysical aspects of particle collisions during saltation on the Martian surface in laboratory experiments. In earlier works, we followed the size distribution of ejected particles, their aerodynamic properties, and aggregation status upon ejection. We now focus on the electrification and charge distribution of ejected particles. We analyzed rebound and ejection trajectories of grains in a vacuum setup with a strong electric field of 100 kV m⁻¹ and deduced particle charges from their acceleration. The ejected particles have sizes of about 10–100 μm. They carry charges up to 10⁵ e or charge densities up to >10⁷ e mm⁻².

We present experimental scattering matrices of the JSC Mars-1, MMS-2, and MGS-1 simulants at 488 and 640 nm. The analogs were processed so that narrow size distributions representative of Martian dust aerosols during different dust cycles were obtained. We find that the forward peak of the phase function depends on particle size as it becomes narrower with increasing size, whereas the side- and backscattering directions depend on both composition and size so that increasing size and decreasing absorption produce a flatter curve. The position and maximum of the degree of linear polarization varies based on particle size and composition, and the negative polarization branch is more prominent for wavelength-scale particles diminishing with increasing size. The linear depolarization is strongly affected by size and composition. Finally, we compare sky-brightness curves measured by the Navcam and Hazcam engineering cameras on board the Mars Science Laboratory rover to the measured phase functions. The observations show a narrower peak at the forward direction and a flatter curve toward the side- and backscattering directions with an increasing dust load in the atmosphere, similar to what can be seen for the measured phase functions of the analogs with increasing particle size. In the case of the analogs, the flattening of the curve can be caused by an increase in multiple scattering within a particle by wavelength-scale surface roughness and/or internal inclusions. For the observed sky brightnesses, particle aggregation and multiple scattering among particles in denser dust conditions play a major role.

The interpretation of astronomical observations of comets, asteroids, and extrasolar objects such as protoplanetary and debris disks is essential for understanding the origin and evolution of planetary systems. Collecting electromagnetic radiation scattered or emitted by dust particles in these objects using powerful telescopes is often our only method to observe and characterize them. This work aims to enhance our understanding of the interaction between electromagnetic radiation and dust particles to improve the interpretation of remote observations of comets and data from future in situ missions like Comet Interceptor.We present experimental scattering matrices for a set of well-characterized porous cm-sized cylindrical aggregates as regolith simulants. The regolith production process involves two steps: Monomer synthesis: Micron-sized particles were generated by milling of two bulk samples: olivine and the Mojave Martian Simulant (MMS-2). Narrow size distributions were achieved through sieving, dispersion in a liquid media, and repeated gravity settling at different intervals. The size distributions of the resulting powders were measured using a MasterSizer 2000 particle sizer. Consolidation: Centimeter-sized pellets of the micron-sized grains obtained in step 1 were produced through mechanical compaction and subsequent consolidation by thermal treatment. In addition, porous samples were obtained by mixing the powder of interest with ethylcellulose as pore former, which was removed during the thermal treatment. This novel procedure allows us to obtain regolith sample sets in which only one physical property varies at a time, which is needed to disentangle the effect of different physical properties (grain size, surface roughness and composition) on the scattered light. The characterization of the samples includes optical microscopy, Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) imaging. As examples, Figures 1 and 2, show SEM images for the two end members of the MMS2 regolith set as far as surface roughness is concerned: MMS2-6 (the flattest) and MeC60-4 (the roughest), respectively. The AFM images displayed in Figures 3 and 4 provide the corresponding surfaces height profile.The experimental measurements of the scattered light by our regolith are performed at the IAA Cosmic Dust Laboratory at wavelengths of 488 and 640 nm. Due to the geometry of the regolith, the phase angle of the measured reflected light spans from 3 to 90 degrees. Preliminary results of the scattering matrix for the MMS2-6 and MeC60-4 regolith at the wavelength of 640 nm are shown in the Figure 5. The refractive index of the constituent particles at the measurement’s wavelength is equal to m=1.5 + i0.00035 (Martikainen et al 2023). In general, the increasing surface roughness affects all measured scattering matrix elements. That is specially the case for the F22/F11, F33/F11 and F44/F11 in the full measured phase angle range. It is interesting to note that in both cases the -F12/F11 ratio shows a shallow negative branch near the backward direction.These preliminary results show the potential of our studies with this new kind of samples. Additionally, comparison with scattering measurements of other regolith samples will enhance our understanding of how surface roughness and composition affect scattered light by different surfaces.Figure 1. SEM image of the surface of the sample MMS2-6.Figure 2. SEM image of the surface of the sample MeC60-4.Figure 3. AFM image about the height profile of the surface of the sample MMS2-6.Figure 4. AFM image about the height profile of the surface of the sample MeC60-4.Figure 5. Experimental scattering matrices of the surfaces of samples MMS2-6 (red) and MeC60-4 (green).