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The precise knowledge of the values of the optical constants (index of refraction, n, and extinction coefficient, k) for nanostructured porous silicon (nanoPS) is a necessary condition to predict the behavior of any optical and photonic devices based on this material. With this objective in mind, a simulation computational program based on the matrix method was used to determine the values of the optical constants in the visible range of self-standing nanoPS films from their experimental reflectance and transmittance spectra. Furthermore, the spectral absorption coefficient (α) was determined from the spectral k values, which motivated to the determination of the values and type of bandgap (direct or indirect) for different porosities

Lithium manganese oxides (LMOs) are key materials due to their role in Li-ion batteries and lithium recovery from aqueous lithium resources. In the present work, we investigated the effect of the crystallization temperature on the formation by hydrothermal synthesis of LMO nanocomposites with high Li/Mn ratios. It is demonstrated that LMOs with a high Li/Mn ratio can be formed by systematically favoring the lithium-rich layered monoclinic phase (Li2MnO3) in a mixture of monoclinic and spinel crystalline phases. LMO nanocomposites have been characterized in terms of morphology, size, crystallinity, chemical composition and surface properties. Moreover, lithium adsorption experiments were conducted using acid-treated LMOs (HMOs) to evaluate the functionality of the nanocomposites as lithium adsorbent materials in a LiCl buffer solution. This study spotlights the structural, compositional, and functional properties of different LMO nanocomposites obtained by the hydrothermal method using the same Li and Mn precursor compounds at slightly different crystallization temperatures. According to our knowledge, this is the first report of the successful application of the lithium-rich Li2MnO3 phase in lithium manganese oxide nanocomposites as lithium adsorbent materials. Therefore, specific LMO nanocomposites with controlled amounts of the layered phase can be engineered to optimize lithium recovery from aqueous lithium resources.

Creating novel liquid crystalline (LC) photonic metamaterial structures is a highly promising approach for the development of tunable photonic devices particularly when nanoporous structures are used in which the LC can infiltrate and modify their properties. In the present work, a tunable scattering device made of partially oxidized porous silicon microparticles mixed with LC is proposed and demonstrated. Being porous in nature, the microparticles trap the LC molecules and enhance the scattering in the voltage OFF state. Due to the random orientational order inside the particles, the averaged refractive index (RI) inside these nanopores is close to that of the isotropic LC RI in the OFF state. Averaging between this LC and the oxidized porous Si brings the average RI of the microparticle down and maximizes the index mismatch with the surrounding LC regions. When the porosity is large enough, a high RI mismatch between the particles and its surrounding in the OFF state is obtained. In the ON state, the molecules orient along the electric field direction, decreasing the RI mismatch and increasing the transparency of the system. The scattering decreases gradually and reversibly with the applied voltage while at zero voltage state it decreases with temperature. At the high voltage state the scattering increases with temperature with some enhancement at the clearing point due to the LC order parameter fluctuations. A slight decrease of the clearing point is observed as a result of weakening the intramolecular interaction and lowering the order parameter. Using fluorescent confocal microscopy the changes in the LC and microparticles domains are monitored showing some reversible dragging of the microparticles towards one of the substrates as the voltage increases. Being a tunable light scattering device, it has a great potential for smart window and light shutter applications.

As subwavelength nanostructures are receiving increasing attention for photonic and plasmonic applications, we grew nanostructured porous silicon (n-PS) and hybrid n-PS/Ag layers onto silicon substrates and measured their reflection and absorption characteristics as functions of the wavelength, angle of incidence, and polarization state of incident light. The experimental results show that the absorption characteristics of the hybrid n-PS/Ag layer can be controlled by selecting the appropriate combination of its thickness and porosity, together with the density of infiltrant silver nanoparticles. The observed wideband optical absorption characteristics of the hybrid n-PS/Ag layers might be useful in light-harvesting devices and photodetectors, since the overall efficiency will be increased as a result of increased field-of-view for both s- and p-polarization states of incident light, R.J.M.-P. thanks Ministerio de Educación, Cultura y Deporte (Spain) for funding under grant reference number PRX17/00095. P.D.M. and A.L. thank the Charles Godfrey Binder Endowment at Penn State for continued support of their research activities. R.R. thanks the Egyptian Ministry of Higher Education, Missions section, for funding under Joint Supervision grant, call 2015–2016

Hybrid organic-inorganic self-powered photodetectors with three different configurations were fabricated and their optoelectronic performance was determined. Si is the inorganic active layer and the transparent conductor poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is the organic layer. The basic photodetector structure under study is Au/PEDOT:PSS/Si/Al. This device shows high responsivity under low irradiation levels, as well as a wideband response in the visible and near-infrared wavelength ranges. To improve the performance of this basic device, its structure was modified by the addition of a nanostructured porous silicon (PSi) layer on top of the Si substrate. The resulting Au/PEDOT:PSS/PSi/Si/Al devices have been found to show improved photoresponse under high irradiation levels together with narrowband spectral responsivity in the infrared region. To further improve the optoelectronic performance of the photodetectors, Si + PSi micro-arrays were used instead of single PSi layers, leading to devices with the structure Au/PEDOT:PSS/(Si + PSi micro-arrays)/Si/Al. These devices possess a much improved performance, showing a responsivity of 1172.87 mA W-1, a specific detectivity of 5.81 × 1013 Jones, and a fast response speed of 396/412 μs at 0 V bias under white-light illumination (100 μW). Furthermore, a broadband spectral responsivity was achieved, with a maximum value of 473 mA W-1 at 853 nm. This improved behavior is associated with the combined effect of an effective reduction of the reflectance due to the presence of PSi and an improvement of the electrical conduction given by the presence of heavily-doped Si regions, This research was partially funded by the Universidad Autónoma de Madrid, FPI-UAM grant and by the Egyptian Ministry of Higher Education, Missions Section under Egyptian Joint Supervision Grant. This work was part of ATTRACT that has received funding from the European Union’s Horizon 2020 Research and Innovation Programme