Optical studies of Ge islanding on Si(111)

We report an experimental study of the optical properties of island layers resulting from molecular beam epitaxial deposition of Ge on Si(111) substrates. The combination of electroreflectance spectroscopy of the E1 transition and Raman scattering allows us to separately determine the strain and composition of the islands. For deposition at 500 °C a deposited layer of 1.36 nm of Ge assembles into 80 nm diameter islands 11 nm thick. The average Si impurity content in the islands is 2.5% while the average in-plane strain is 0.5%. Both strain and Si impurity content in islands decrease with increasing Ge depositio

Optical Reflection Spectroscopy of Thick Corrosion Layers on 304 Stainless Steel

Corrosion resistant structural materials of both iron and nickel based alloys are used in the electric power industry for the construction of the coolant loops of both conventional and nuclear power generating stations. These materials, in the presence of high temperature (e.g. 287 C), high pH (e.g. 10.0 {at} 20 C) water with dissolved hydrogen will oxidize and form corrosion films that are double metal oxides (or spinels) of the form AB{sub 2}O{sub 4}. This work describes optical reflectivity techniques that have been developed to study the growth of these films in situ. The optical technique uses a dual-beam specular reflection spectrometer to measure the spectrum of reflected light in small angle (i.e. < 15{sup o}) scatter. The reflection spectra are then calibrated using a set of corrosion coupons with corrosion films that are well known. Results are compared with models based on multilayer reflection and Mie scattering from a particle size distribution. Surface roughness is found to be the dominant cause of reduced reflection as the films grow

Final Report for Nucleation and growth of semiconductor nanocrystals by solid-phase reaction

This final report describes the technical output of a scientific program aimed at understanding the formation and structure of II-VI nanocrystals formed by solid phase precipitation within a glass environment. The principle probes were optical absorption spectroscopy to determine crystallite sizes, Raman scattering to determine composition, and x-ray absorption spectroscopy to study the evolution of local reactant environments

Determination of the complex refractive indices of Titan haze analogs using photothermal deflection spectroscopy

International audienceThe spectrometers of the Cassini mission to the Saturn system have detected haze layers reaching up to 800 km in Titan's atmosphere. Knowledge of the complex refractive index (k) of the haze is important for modeling the surface and atmosphere of Titan and retrieving some information about the functional groups present in the aerosols. Plasma discharges or ultraviolet radiation are commonly used to drive the formation of solid organics assumed to be good analogs of the Titan aerosols. [Tran, B.N., Ferris, J.P., Chera, J.J., 2003a. The photochemical formation of a Titan haze analog. Structural analysis by X-ray photoelectron and infrared spectroscopy. Icarus 162, 114–124; Tran, B.N., Force, M., Briggs, R., Ferris J.P., Persans, P., Chera, J.J., 2008. Photochemical processes on Titan: Irradiation of mixtures of gases that simulate Titan's atmosphere. Icarus 177, 106–115] reported the index of refraction of analogs synthesized by far ultraviolet irradiation of various gas mixtures. k was determined in the 200–800 nm wavelength range from transmission and reflection spectroscopy. However, this technique is limited by (i) uncertainties in the absorption values because of the small amounts of organics available, (ii) light scattering by the surface roughness and particulates in the sample. These limitations prompted us to perform new measurements using photothermal deflection spectroscopy (PDS), a technique based on the conversion of absorbed light into heat in the material of interest. By combining traditional spectroscopy (λ 500 nm), we determined values of k over the 375–1550 nm range. k values as low as 10−4 above 1000 nm were determined. This is one order of magnitude lower than the measurements generally used as a reference for Titan's aerosols analogs [Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Callicott, T.A., Williams, M.W., 1984. Optical-constants of organic Tholins produced in a simulated Titanian atmosphere—from soft-X-ray to microwave-frequencies. Icarus 60(1), 127–137]. We recommend that these results were used in models to describe the optical properties of the aerosols produced in Titan's stratosphere

Strain-induced quenching of optical transitions in capped self-assembled quantum dot structures

Strain-induced quenching of optical transitions has been found in capped self-assembled quantum dot structures. Light absorption at the E 1 and E 1 + Δ 1 critical points of InSb islands buried in InP disappears for nominal InSb thicknesses lower than 10 monolayers as a consequence of the strain produced inside the islands by the cap layer. Certainly, this strain increases as the InSb deposition diminishes, changing the band lineup of the system from type-I to type-II and therefore drastically reducing the oscillator strengths of the island-related E 1 and E 1 + Δ 1 transitions

Strain-induced quenching of optical transitions in capped self-assembled quantum dot structures

Strain-induced quenching of optical transitions has been found in capped self-assembled quantum dot structures. Light absorption at the E 1 and E 1 + Δ 1 critical points of InSb islands buried in InP disappears for nominal InSb thicknesses lower than 10 monolayers as a consequence of the strain produced inside the islands by the cap layer. Certainly, this strain increases as the InSb deposition diminishes, changing the band lineup of the system from type-I to type-II and therefore drastically reducing the oscillator strengths of the island-related E 1 and E 1 + Δ 1 transitions

Hyperdoped silicon sub-band gap photoresponse for an intermediate band solar cell in silicon

Hyperdoping silicon with impurities is considered an attractive method to develop an intermediate band solar cell in silicon with the potential to increase the photovoltaic cell efficiency beyond that of the Shockley-Queisser limit by utilizing sub-band gap photons for energy generation. Unfortunately, to date sub-band gap photoresponse has not been observed in singlecrystal hyperdoped silicon at room temperature, which is crucial for the development of intermediate band solar cells. In this contribution, we report and analyze room-temperature sub-band gap photoresponse of single-crystal silicon hyperdoped with gold. We further discuss the potential of using gold-hyperdoped silicon for IBSC in silicon