Characterization of iron-phosphate-silicate chemical garden structures

Chemical gardens form when ferrous chloride hydrate seed crystals are added or concentrated solutions are injected into solutions of sodium silicate and potassium phosphate. Various precipitation morphologies are observed depending on silicate and phosphate concentrations, including hollow plumes, bulbs, and tubes. The growth of precipitates is controlled by the internal osmotic pressure, fluid buoyancy, and membrane strength. Additionally, rapid bubble-led growth is observed when silicate concentrations are high. ESEM/EDX analysis confirms compositional gradients within the membranes, and voltage measurements across the membranes during growth show a final potential of around 150-200 mV, indicating that electrochemical gradients are maintained across the membranes as growth proceeds. The characterization of chemical gardens formed with iron, silicate, and phosphate, three important components of an early earth prebiotic hydrothermal system, can help us understand the properties of analogous structures that likely formed at submarine alkaline hydrothermal vents in the Hadean-structures offering themselves as the hatchery of life.     

Determination of optical parameters of Ga0.75In0.25Se layered crystals

The optical properties of the Ga_0.75In_0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380–1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10–300 K. The rate of change of band gap energy (γ = –6.2 × 10^–4 eV/K) and absolute zero value of the band gap (E_gi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index values. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical constants of layered structured Ga0.75In0.25Se crystals from the ellipsometric measurements

We have carried out the spectroscopic ellipsometry measurements on Ga_0.75In_0.25Se single crystals in the 1.2–6.0 eV spectral range at room temperature. The optical constants, real and imaginary parts of the dielectric function, refractive index and extinction coefficient, were found as a result of analysis of ellipsometric data. The critical point analysis of the second derivative spectra of the dielectric function revealed four interband transition structures with critical point energy values of 3.19, 3.53, 4.10 and 4.98 eV. The results of the analysis were compared with those of the ellipsometric studies performed on GaSe which is the main constituent of the Ga_0.75In_0.25Se crystal. The obtained critical point energies are in good agreement with the energies of the GaSe crystal reported in the literature.