Solar probe: a rendezvous with the Sun

Summary A study has been promoted by NASA to evaluate the scientific return and the technological problems of a close-to-the-Sun mission (Solar Probe). It has come out that using current technology it is possible to deliver at 4 solar radii from the Sun's centre a scientific payload with such performances to allow a great improvement of our understanding of the coronal phenomena. The mission concept currently under study uses planetary encounters to reach the required orbit. The final orbit period is 2.5 years, the estimated mission duration about 9 years. The orbit inclination is such as to give the maximum coverage in terms of heliographic latitude. During the perihelion phases a conical structure shields the spacecraft from the intense solar radiation. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Anomalies of the partition coefficient and properties of crystals in the region of low concentrations of an isomorphous admixture. 1. Unusual decomposition of solid solutions of the NaCl—CdCl2 system

Solid solutions NaCl—CdCl₂ were studied in an interval of CdCl₂ concentrations of 0.05—3 mol.% by Raman spectroscopy. The molecular form Na₂CdCl₄ decomposes: Na₂CdCl₄ 2Na⁺ + Cd²⁺ + 2Cl₂ ^– + 2e^–; 2Na + 2e^– 2Na⁰. Free sodium atoms form color centers of crystal (F centers) in the region of jumpwise changing the partition coefficient of CdCl₂ in NaCl (K jump).     

Flavour democracy calls for the fourth generation

It is argued with the help of an illustrative model, that the inter species hierarchy among the fermion masses and the quark mixing angles can be accommodated naturally in the standard model with (approximate) flavor democracy provided there are three exactly massless neutrinos and four families of sequential quark-leptons with all members of the fourth family having roughly equal masses. The special problem of light neutrino masses (if any) and possible solutions are also discussed.     

Neutrinoless Double Beta Decay: Status of Evidence

The present experimental status in the search for neutrinoless double beta decay is reviewed, with emphasis on the first indication for neutrinoless double beta decay found in the HEIDELBERG-MOSCOW experiment, giving first evidence for lepton number violation and a Majorana nature of the neutrinos. Future perspectives of the field are briefly outlined.     

The ACE-FTS atlas of the infrared solar spectrum

The ACE-FTS is a space-borne Fourier transform spectrometer onboard SCISAT-1. The satellite was launched in August 2003 and since February 2004 the ACE-FTS has been performing solar occultation measurements in order to infer the chemical composition of the terrestrial atmosphere. The individual spectra recorded at the highest limb tangent altitudes (above 160 km) are by definition “high sun” spectra and contain no atmospheric contribution. In this work, an empirical solar spectrum covering the 700 to 4430 cm⁻¹ spectral range has been constructed from an average of 224,782 individual ACE-FTS solar spectra. Line assignments have been made for about 12,000 lines. The spectrum and two line lists are provided in the supplemental material attached to this work. Due to the excellent noise level achieved in the ACE-FTS solar atlas presented here, numerous weak absorption features are assigned which were not detectable in the ATMOS solar observations.     

Nanocluster n-CdO thin film by sol-gel for solar cell applications

The nanocluster-CdO film was successfully synthesized by sol-gel method using cadmium acetate and 2-metoxyethanol as starting materials and monoethanolamine as a stabilizer. The structural properties of the CdO film were investigated by atomic force microscopy (AFM). AFM results indicate that the CdO film is consisted of nanoclusters with grain size of 75-85 nm. The optical band gap E_g of nanocluster-CdO film was found to be 2.27 eV. The heterostructure, formed from two semiconductor layers having different optical band gaps, p-Si/n-CdO is prepared as a solar cell device. The electrical properties of the device were characterized by current-voltage and capacitance-conductance-voltage methods. The photovoltaic properties of p-Si/n-CdO device have been investigated. The p-Si/n-CdO heterojunction solar cell shows the best values of V_oc = 0.41 and J_sc = 2.19 mA/cm² under AM1.5 illumination. It is evaluated that this work is useful as a basis for the search of nanomaterial CdO and more competitive p-Si/n-CdO based solar cells, despite the fact that V_oc and J_sc are lower than those reported in the literature.     

Crystallization and surface segregation in CuIn0.7Ga0.3Se2 thin films on Cu foils grown by pulsed laser deposition

This work reports unexpected crystallization and segregation behavior of CuIn_0.7Ga_0.3Se₂ (CIGS) thin films deposited on flexible Cu foils by pulsed laser deposition. A composite-type microstructure containing nanometer-scaled CIGS crystallites embedded in amorphous Cu-rich matrix is observed even at the high temperature of 500 °C. The findings are attributed to very fast condensation of the ablated species and random nucleation induced from the amorphous matrix. Cu-rich particulates tend to precipitate on the film surface, and their average size, shape, number density and composition exhibit a strong dependence on the substrate temperature up to 500 °C. The similar crystallization properties of the films on Cu foils and glass substrates are noticeable to the use of Cu foils for flexible solar cells.     

Surface profile optimization of antireflection gratings for solar cells

The solar cell efficiency can be improved by antireflection gratings. In this paper, the antireflection gratings with different symmetrical surface profiles are investigated by numerical simulations based on the Rigorous Coupled-Wave Analysis. Simulated results show that the antireflection performance of sharp profile such as quadratic profile has a significant improvement compared with triangular and parabolic profiles, while the top cutoff in the grating tip will severely influence the antireflection performance. Meanwhile, proper length of flat region between grating features in the nonclose-packed triangular antireflection grating can have better antireflection performance than the close-packed counterpart for the same grating period and height. Such antireflection gratings with different surface profiles may offer attractive solutions to current commercial silicon solar cell, as well as organic and other semiconductor material based solar cells.