On silicon nanobubbles in space for scattering and interception of solar radiation to ease high-temperature induced climate change

A thin film of silicon-based nanobubbles was recently suggested that could block a fraction of the sun’s radiation to alleviate the present climate crisis. But detailed information is limited to the composition, architecture, fabrication, and optical properties of the film. We examine here the optical response of Si nanobubbles in the range of 300–1000 nm to evaluate the feasibility using semi numerical solution of Maxwell’s equations, following the Mie and finite-difference time-domain procedures. We analyzed a variety of bubble sizes, thicknesses, and configurations. The calculations yield resonance scattering spectra, intensities, and field distributions. We also analyzed some many-body effects using doublets of bubbles. We show, due to high valence electron density, silicon exhibits strong polarization/plasmonic resonance scattering and absorption enhancements over the geometrical factor, which afford lighter but more efficient interception with a wide band neutral density filtering across the relevant solar light spectrum. We show that it is sufficient to use a sub monolayer raft with ∼0.75% coverage, consisting of thin (∼15 nm) but large silicon nanobubbles (∼550 nm diameter), to achieve 1.8% blockage of solar light with neutral density filtering, and ∼0.78 mg/m2 silicon, much less than the mass effective limit set earlier at 1.5 g/m2. We evaluated solid counterpart nanoparticles, which may be produced in blowing/inflation procedures of molten silicon, as well as aging by including silicon oxide capping. The studies confirm the feasibility of a space bubble filtering raft, with insignificant imbalance of the correlated color temperature (CCT) and color rendering index characteristics of sunlight

Dynamic transition of nanosilicon from indirect to direct-like nature by strain-induced structural relaxation

Silicon nanoclusters exhibit light emission with direct-like ns–µs time dynamics; however, they show variable synthesis and structure, optical, and electronic characteristics. The widely adopted model is a core–shell in which the core is an indirect tetrahedral absorbing Si phase, while the shell is a network of re-structured direct-like H–Si–Si–H molecular emitting phases, with the two connected via back Si–Si tetrahedral bonds, exhibiting a potential barrier, which significantly hinders emission. We carried out first-principles atomistic computations of a 1-nm Si nanoparticle to discern the variabilities. Enlarging the network reduces the potential barrier monotonically to a finite limit not sufficient for strong emission to proceed while inducing a path to quenching of emission via a conical crossing between the excited and ground states. However, enlarging the network is found to induce strain and structural instability, which causes structural relaxation that creates a direct path for emission without crossing the barrier. Following emission, the particle relaxes back to the indirect ground structure, which completes the cycle. The results also confirm the pivotal role of HF/H2O2 etching in synthesizing the core–shells and affording control over the molecular network. Measurements using synchrotron and laboratory UV excitation of thin films of 1-nm Si particles show good agreement with the simulation results. It is plausible that the relaxation is behind the stimulated emission, gain, or microscopic laser action, reported earlier in macroscopic distributions of 1- and 3-nm Si nanoparticles

Wideband luminescence from bandgap-matched Mg-based Si core-shell geometry nanocomposite

We use wet treatment to integrate red-luminescent Si nanoparticles with Mg-based wide-bandgap insulators Mg(OH) and MgO (5.7 and 7.3 eV respectively). In the process, Mg2+ is reduced on Si nanoparticle clusters, while suffering combustion in water, producing a spatially inhomogeneous Mg(OH)2/MgO-Si nanoparticle composite with an inner material predominantly made of Si, and a coating consisting predominantly of magnesium and oxygen (“core-shell” geometry). The nanocomposite exhibit luminescence covering nearly entire visible range. Results are consistent with formation of Mg(OH)2/MgO phase with direct 3.43-eV bandgap matching that of Si, with in-gap blue-green emitting states of charged Mg and O vacancies. Bandgap match with nanocomposite architecture affords strong enough coupling for the materials to nearly act as a single hybrid material with novel luminescence for photonic and photovoltaic applications

Iron oxide-Si nanoparticle magnetic core-shell induced by the interaction of d-orbitals of Fe2+ with reconstructed Si dimer-like defects

Redox-type charge exchange between Si nanoparticles and aqueous metal ions m(x+) was recently used to synthesize core-shell nanocomposites in which their functionalities have been integrated. The process requires the electron (hole) affinities of the two to be different, with the efficiency of the charge exchange being strongly dependent on their difference. In this paper, we examine the interaction of Fe ions and red luminescent Si nanoparticles where the metal ion has comparable electron affinity to that of the Si nanoparticle. Scanning electron microscopy and fluorescent spectroscopy imaging show the formation of red luminescent core-shell clusters ranging from 100 nm to 500 nm. A permanent magnet is found to pull the structures indicating the formation of a magnetic phase. We use first principle atomistic computations at the unrestricted Hartree-Fock-DFT (density functional theory) level to obtain the charging energies and affinities of various ions of Fe and the Si nanoparticle. The computations indicate that Fe2+ cannot be oxidized to Fe3+ by the nanoparticle and it cannot strip one or two electrons from the nanoparticle and freely separate, resulting in bound complexes. Our analysis shows that a magnetic phase of iron oxide results from charge delocalization over the complex and a simultaneous interaction of the iron d-orbitals with the oxygen's lone electrons and the nanoparticle's reconstruction dimer-like defects. The core-shell integration at the nanoscale affords double functionality of luminescence and magnetism enhancing sensing, tracking, and delivery and enabling a variety of applications, including controlled drug delivery, underground oil and water exploration, and recovery

The prevalence of non-classic adrenal hyperplasia among Turkish women with hyperandrogenism

The prevalence of non-classic adrenal hyperplasia (NCAH) among Turkish women with hirsutism has not been established so far. Thus, we aimed to evaluate the prevalence of 21-hydroxylase (21-OH) deficiency by ACTH stimulation test among hirsute women. The study population consisted of 285 premenopousal women, aged 16-46 years (mean: 23.2 +/- 0.3). All were hirsute and hyperandrogenic. Androgen secreting tumors of the ovaries and the adrenal glands were excluded as well as thyroid dysfunction and hyperprolactinemia. All the patients were evaluated by 0.25 mg (i.v.) ACTH stimulation test and 17-OHP responses were obtained at 30 and 60 min. The diagnosis of NCAH due to 21-OH deficiency was considered in patients with the poststimulation 17-OHP level exceed 10 ng/ml. Six (2.1%) of the patients had NCAH due to 21-OH deficiency confirmed by genotyping. The rest of the patients were polycystic ovary syndrome (n = 166, 58.2%) and idiopathic hyperandrogenemia (n = 113, 39.7%). There were no patients with idiopathic hirsutism because patients with normal serum androgen levels were excluded. This first and most extensive national study investigating NCAH prevalence among Turkish population showed that NCAH is not prevalent in this population

The prevalence of non-classic adrenal hyperplasia among Turkish women with hyperandrogenism

The prevalence of non-classic adrenal hyperplasia (NCAH) among Turkish women with hirsutism has not been established so far. Thus, we aimed to evaluate the prevalence of 21-hydroxylase (21-OH) deficiency by ACTH stimulation test among hirsute women. The study population consisted of 285 premenopousal women, aged 16-46 years (mean: 23.2 +/- 0.3). All were hirsute and hyperandrogenic. Androgen secreting tumors of the ovaries and the adrenal glands were excluded as well as thyroid dysfunction and hyperprolactinemia. All the patients were evaluated by 0.25 mg (i.v.) ACTH stimulation test and 17-OHP responses were obtained at 30 and 60 min. The diagnosis of NCAH due to 21-OH deficiency was considered in patients with the poststimulation 17-OHP level exceed 10 ng/ml. Six (2.1%) of the patients had NCAH due to 21-OH deficiency confirmed by genotyping. The rest of the patients were polycystic ovary syndrome (n = 166, 58.2%) and idiopathic hyperandrogenemia (n = 113, 39.7%). There were no patients with idiopathic hirsutism because patients with normal serum androgen levels were excluded. This first and most extensive national study investigating NCAH prevalence among Turkish population showed that NCAH is not prevalent in this population