Porous silicon (PSi) on p${}^{++}$-type (111) silicon substrate has been fabricated by electronically etching method in hydrofluoric acid (HF) media from 5 to 110 mA/cm${}^2$ of anodizing current density. The problem of determining the optical properties of (111) PSi is board through implementing a photoacoustic (PA) technique coupled to an electrochemical cell for real-time monitoring of the formation of porous silicon thin films. PA amplitude allows the calculation of the real part of the films refractive index and porosity using the reflectance self-modulation due to the interference effect between the PSi film and the substrate that produces a periodic PA amplitude. The optical properties are studied from specular reflectance measurements fitted through genetic algorithms, transfer matrix method (TMM), and the effective medium theory, where the Maxwell Garnett (MG), Bruggeman (BR), and Looyenga (LLL) models were tested to determine the most suitable for pore geometry and compared with the in situ PA method. It was found that (111) PSi exhibit a branched pore geometry producing optical anisotropy and high scattering films.

Global trends in health, climate, and population growth drive the demand for high-nutrient plants like spinach, which thrive under controlled conditions with minimal resources. Despite technological advances in agriculture, current systems often rely on traditional methods and need robust computational models for precise plant growth forecasting. Optimizing vegetable growth using advanced agricultural and computational techniques, addressing challenges in food security, and obtaining efficient resource utilization within urban agriculture systems are open problems for humanity. Considering the above, this paper presents an enclosed agriculture system for growth and modeling spinach of the Viroflay (Spinacia oleracea L.) species. It encompasses a methodology combining data science, machine learning, and mathematical modeling. The growth system was built using LED lighting, automated irrigation, temperature control with fans, and sensors to monitor environmental variables. Data were collected over 60 days, recording temperature, humidity, substrate moisture, and light spectra information. The experimental results demonstrate the effectiveness of polynomial regression models in predicting spinach growth patterns. The best-fitting polynomial models for leaf length achieved a minimum Mean Squared Error (MSE) of 0.158, while the highest MSE observed was 1.2153, highlighting variability across different leaf pairs. Leaf width models exhibited improved predictability, with MSE values ranging from 0.0741 to 0.822. Similarly, leaf stem length models showed high accuracy, with the lowest MSE recorded at 0.0312 and the highest at 0.3907.

This work investigates the changes in the optical response of photonic crystals based on porous silicon (PSi) as a function of temperature. Using the transfer matrix method in combination with thermo-optical properties, we numerically calculate the optical response of two types of photonic crystals: Distributed Bragg Reflectors (DBRs) and Fabry–Perot microcavities (FPMs). The results reveal that the photonic bandgap shifts with increasing temperature and pressure, with the defect mode in the microcavity notably shifting to longer wavelengths as the temperature rises. Additionally, we explore the transformation of PSi into porous quartz (PQz) via thermal oxidation, which preserves the porosity and multilayer structure, while altering the chemical composition. This results in geometrically identical photonic systems with distinct chemical properties, offering enhanced stability. Our simulations show that PSi structures exhibit a redshift in the photonic bandgap due to thermal expansion, while PQz structures remain optically stable even at elevated temperatures. This work highlights the potential of PQz as a robust material for high-temperature photonic applications, with tunable optical properties and stable performance under extreme conditions. The findings emphasize the feasibility of using porous-silicon-based photonic crystals for advanced optical devices in harsh environments.