Luminescent properties and reduced dimensional behavior of hydrothermally prepared Y <inf>2</inf>SiO <inf>5</inf>: Ce nanophosphors

Hydrothermally prepared nanophosphor Y2 Si O5: Ce crystallizes in the P 21 c structure, rather than the B2b structure observed in bulk material. Relative to bulk powder, nanophosphors of particle size ∼25-100 nm diameter exhibit redshifts of the photoluminescence excitation and emission spectra, reduced self absorption, enhanced light output, and medium-dependent radiative lifetime. Photoluminescence data are consistent with reduced symmetry of the P 21 c structure and are not necessarily related to reduced dimensionality of the nanophosphor. In contrast, medium-dependent lifetime and enhanced light output are attributed to nanoscale behavior. Perturbation of the Ce ion electric field is responsible for the variable lifetime. © 2006 American Institute of Physics

Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions

The establishment of covalent junctions between carbon nanotubes (CNTs) and the modification of their straight tubular morphology are two strategies needed to successfully synthesize nanotube-based three-dimensional (3D) frameworks exhibiting superior material properties. Engineering such 3D structures in scalable synthetic processes still remains a challenge. This work pioneers the bulk synthesis of 3D macroscale nanotube elastic solids directly via a boron-doping strategy during chemical vapour deposition, which influences the formation of atomic-scale “elbow” junctions and nanotube covalent interconnections. Detailed elemental analysis revealed that the “elbow” junctions are preferred sites for excess boron atoms, indicating the role of boron and curvature in the junction formation mechanism, in agreement with our first principle theoretical calculations. Exploiting this material’s ultra-light weight, super-hydrophobicity, high porosity, thermal stability, and mechanical flexibility, the strongly oleophilic sponge-like solids are demonstrated as unique reusable sorbent scaffolds able to efficiently remove oil from contaminated seawater even after repeated use

Effect of Sex and Prior Exposure to a Cafeteria Diet on the Distribution of Sex Hormones between Plasma and Blood Cells

It is generally assumed that steroid hormones are carried in the blood free and/or bound to plasma proteins. We investigated whether blood cells were also able to bind/carry sex-related hormones: estrone, estradiol, DHEA and testosterone. Wistar male and female rats were fed a cafeteria diet for 30 days, which induced overweight. The rats were fed the standard rat diet for 15 additional days to minimize the immediate effects of excess ingested energy. Controls were always kept on standard diet. After the rats were killed, their blood was used for 1) measuring plasma hormone levels, 2) determining the binding of labeled hormones to washed red blood cells (RBC), 3) incubating whole blood with labeled hormones and determining the distribution of label between plasma and packed cells, discounting the trapped plasma volume, 4) determining free plasma hormone using labeled hormones, both through membrane ultrafiltration and dextran-charcoal removal. The results were computed individually for each rat. Cells retained up to 32% estrone, and down to 10% of testosterone, with marked differences due to sex and diet (the latter only for estrogens, not for DHEA and testosterone). Sex and diet also affected the concentrations of all hormones, with no significant diet effects for estradiol and DHEA, but with considerable interaction between both factors. Binding to RBC was non-specific for all hormones. Estrogen distribution in plasma compartments was affected by sex and diet. In conclusion: a) there is a large non-specific RBC-carried compartment for estrone, estradiol, DHEA and testosterone deeply affected by sex; b) Prior exposure to a cafeteria (hyperlipidic) diet induced hormone distribution changes, affected by sex, which hint at sex-related structural differences in RBC membranes; c) We postulate that the RBC compartment may contribute to maintain free (i.e., fully active) sex hormone levels in a way similar to plasma proteins non-specific binding

Effect of Sex and Prior Exposure to a Cafeteria Diet on the Distribution of Sex Hormones between Plasma and Blood Cells

It is generally assumed that steroid hormones are carried in the blood free and/or bound to plasma proteins. We investigated whether blood cells were also able to bind/carry sex-related hormones: estrone, estradiol, DHEA and testosterone. Wistar male and female rats were fed a cafeteria diet for 30 days, which induced overweight. The rats were fed the standard rat diet for 15 additional days to minimize the immediate effects of excess ingested energy. Controls were always kept on standard diet. After the rats were killed, their blood was used for 1) measuring plasma hormone levels, 2) determining the binding of labeled hormones to washed red blood cells (RBC), 3) incubating whole blood with labeled hormones and determining the distribution of label between plasma and packed cells, discounting the trapped plasma volume, 4) determining free plasma hormone using labeled hormones, both through membrane ultrafiltration and dextran-charcoal removal. The results were computed individually for each rat. Cells retained up to 32% estrone, and down to 10% of testosterone, with marked differences due to sex and diet (the latter only for estrogens, not for DHEA and testosterone). Sex and diet also affected the concentrations of all hormones, with no significant diet effects for estradiol and DHEA, but with considerable interaction between both factors. Binding to RBC was non-specific for all hormones. Estrogen distribution in plasma compartments was affected by sex and diet. In conclusion: a) there is a large non-specific RBC-carried compartment for estrone, estradiol, DHEA and testosterone deeply affected by sex; b) Prior exposure to a cafeteria (hyperlipidic) diet induced hormone distribution changes, affected by sex, which hint at sex-related structural differences in RBC membranes; c) We postulate that the RBC compartment may contribute to maintain free (i.e., fully active) sex hormone levels in a way similar to plasma proteins non-specific binding

Investigation on the chemical, structural and mechanical properties of carbon-germanium films deposited by dc-magnetron sputtering

Amorphous carbon-germanium films were deposited by de-magnetron sputtering onto Si substrates leading to a set of films with GejC ratios ranging from 0 to 2. Nuclear techniques. Rutherford backscattering spectrometry and elastic recoil detection analysis, provided both the composition and the atomic density of the films. Raman results suggest that carbon and germanium atoms are segregated into distinct amorphous domains. X-ray diffraction analysis was also performed and the results confirmed the amorphous character of the films. already determined by Raman spectroscopy. The internal stress of the films was obtained by measuring the bending of the substrates and the hardness was measured by a nanoindentation technique. These mechanical properties were correlated to the Ge content of the films; an important reduction in both hardness and internal stress with the Ge incorporation was observed

Raman spectroscopy and scanning electron microscopy investigation of annealed amorphous carbon-germanium films deposited by d.c. magnetron sputtering

The precipitation of germanium nanocrystals in amorphous carbon\u2013germanium films allows for the development of innovative devices, but the accurate control of both size and size distribution of Ge quantum dots in these matrices still constitutes a challenging step. In this paper, both the structure and morphology of amorphous carbon\u2013germanium films (a-Ge1 12xCx), deposited by d.c. magnetron sputtering onto silicon substrates and annealed in vacuum at temperatures up to 550 \ub0C, are investigated by Raman spectroscopy and scanning electron microscopy. The main features of Raman spectra obtained from carbon-rich films (x>0.43) are the D and G bands, characteristic of graphitic carbon films. The ratio between the intensities of the bands, ID/IG, increases with the annealing temperature, suggesting a progressive increase of the graphitic domains within the films. Raman spectra obtained in the low frequency region from both as-deposited and annealed germanium-rich films (x<0.43) show broad bands associated with transverse acoustic and transverse optic Ge\u2013Ge modes. Ge\u2013Ge optic modes merge up into a well-shaped peak at 300 cm 121 in the germanium-richest sample, and underwent annealing treatment at 550 \ub0C, thus indicating the precipitation of crystalline Ge. Scanning electron microscopy analysis shows an apparently uniform nucleation of Ge crystallites at the sample surface. Microprobe Raman scattering results suggest the formation of a nearly homogeneous distribution of Ge nanocrystals in germanium-rich films annealed at 550 \ub0C

Growth kinetics and relationship between structure and mechanical properties of a-C(N): H films deposited in acetylene-nitrogen atmospheres

Amorphous hydrogenated carbon\u2013nitrogen films, a-C~N!:H, were deposited by plasma enhanced chemical vapor deposition using acetylene\u2013nitrogen mixtures. Film composition and density were determined by means of ion beam techniques being the film microstructure studied by infrared and Raman spectroscopies. Films were obtained with nitrogen content up to 22 at. %. As for films -obtained using other gas mixtures, the deposition rate showed a strong decrease upon nitrogen incorporation, although with a smaller rate. The film growth kinetic is discussed and some specific features of acetylene\u2013nitrogen precursor gas mixtures are pointed out. A remarkable decrease on the C atom sp3 fraction was inferred for nitrogen contents higher than 10 at. %, and was correlated to the film density behavior. The mechanical hardness and internal stress were relatively insensitive to low nitrogen incorporation, with a systematic decreasing behavior for nitrogen contents above 10 at. %

Comparative study of anneal-induced modifications of amorphous carbon films deposited by dc magnetron sputtering at different argon plasma pressures

This work investigates the evolution of the structural, mechanical and tribological properties of amorphous carbon films (a-C ) undergoing thermal annealing. Two different types of a-C film were studied: hard, stressed and dense films, henceforth called \u2018diamond-like\u2019, and soft, more relaxed and less dense films, called \u2018polymer-like\u2019. The two sets of films were deposited by dc magnetron sputtering at 0.36 and 1.4 Pa argon plasma pressures, respectively, and both were annealed in vacuum for 1 h at temperatures between 300 and 700\ub0C. Raman results provided indications of a remarkable increase of the sp2 hybridized domains, that occurs mainly at temperatures higher than 400\ub0C for the diamond-like films and in a continuous way for the polymer-like films. The friction coefficient of both types of film approaches the same value with increasing temperature, whereas the surface roughness is nearly constant. For diamond-like films, the hardness and compressive internal stress are nearly constant up to 500\ub0C, and then undergo a fast decrease. In contrast, the hardness of the polymer-like film continuously decreases with temperature, whereas the compressive stress remains constant

Effects of ion beam irradiation on self-trapped defects in single-crystal Lu<inf>2</inf>SiO<inf>5</inf>

Ion irradiation effects on emission bands related to self-trapped defects in Czochralski-grown Lu2SiO5 (LSO) crystals has been investigated. Irradiation was carried out using 53 keV He+ and 40 keV H+ beams with doses of 1 and 2×1016 atoms/cm2, respectively, at room temperature. Post-irradiation radioluminescence measurements were carried out in the 5-300 K temperature range using Mo-target X-ray excitation. Two emission bands were observed at 256 and 315 nm and assigned to self-trapped excitons (STE) and self-trapped holes (STH), respectively. The intensity of the bands was determined by the ballistic damage induced by irradiation, and no effects due to the chemical nature of implanted species were observed. Thermal-quenching activation energies of these defects as a function of irradiation conditions were extracted by applying the Mott-Seitz two-level model. Each band presents strikingly different behavior following irradiation; activation energy of the STH increases two-fold whereas the STE decreases three-fold. The results indicate a major role of surface effects on the radioluminescence of LSO. For comparative purposes, irradiated Lu2O3 was also investigated. © 2006 Elsevier B.V. All rights reserved

Fluorine incorporation into amorphous hydrogenated carbon films deposited by plasma-enhanced chemical vapor deposition: structural modifications investigated by X-ray photoelectron spectrometry and Raman spectroscopy

Fluorinated hydrogenated amorphous carbon films were grown by plasma-enhanced chemical vapor deposition\u17dPECVD.. Two sets of films were deposited. For the first set, the self-bias voltage\u17dVB.was kept constant and equal to 350 V, while the CF4 partial pressure in CH4CF4gas mixtures was changed from 0 to 80%. For the second one, a fixed 2:1 CF4CH4proportion in the precursor atmosphere was employed while VB was varied from 50 V to 500 V. The carbon chemical environment was investigated by X-ray photoelectron spectroscopy\u17dXPS., while structural changes in the carbon matrix were probed by Raman spectroscopy. The increase of both the CF4partial pressure and the VBleads to an increase of the fluorine concentration within the film. While in the first case the increase of the fluorine content leads to a relative increase of the CFn XPS bands, in the second one the relative intensity of the CFn bands are nearly the same within the range of VB values investigated. In particular, the CF2band grows for higher CF4partial pressures, while it is negligible in the self-bias study. The analysis of the Raman spectra shows that a progressive structural modification from a diamond-like towards a polymer-like material occurs for higher CF4partial pressures as well as for lower VB. This trend is accompanied by a noticeable broadening of the C1s XPS peak on the side of lower binding energies