A. Amaral

Interactions of D-ribose with polyatomic anions, and alkaline and alkaline-earth cations: possible clues to environmental synthesis conditions in the pre-RNA world

The interaction of some of the most abundant anions in seawater (borate, sulfate and carbonate/bicarbonate) with D-ribose was studied by 1H, 11B and 13C NMR spectroscopy. The results confirmed that only borate improves the stability of D-ribose and favours significant amounts of the ribofuranose isomer, which is the form occurring in present day living organisms. The effect of cations (Na+, K+, Mg2+, Ca2+ and Sr2+) on ribose–borate-bound species was also studied, and it was found that the divalent cations induce a small increase in the relative amounts of ribopyranose isomers in solution and a corresponding decrease in the abundance of the ribofuranose isomers. It was also found that the stability of ribose–borate-bound species, when compared with free ribose over a wide range of temperature and pH values, is higher for compounds with borate, which are stable even at a relatively low pH (6.6) and a relatively high temperature (60 °C). The stability of ribose under moderate pH and relatively high temperature conditions, in the presence of species that occur in seawater, is important for the viability of the early synthetic steps that led to the first nucleotides, which predated the formation of more complex structures, such as RNA.

Effect of rf power on the properties of ITO thin films deposited by plasma enhanced reactive thermal evaporation on unheated polymer substrates

Abstract The influence of the radiofrequency (rf) deposition power on the properties of indium tin oxide (ITO) thin films deposited onto unheated polymer substrates is studied. The deposition technique used is the radiofrequency plasma enhanced reactive thermal evaporation (rf-PERTE). Results show that (1) the total transmittance at 500 nm is always around 80% and (2) that the electrical resistivity is 10−3 Ω cm for ITO films deposited in the rf power range 45–50 W. X-ray diffraction analysis showed the presence of a crystalline phase. Scanning electron microscopy (SEM) revealed that the surface morphology of the ITO films does not vary significantly with rf power.

Ultrasensitive microchip sensor based on boron-containing polyfluorene nanofilms

A fluorene-based π-conjugated copolymer with on-chain dibenzoborole units was used in the development of a nanocoated gold interdigitated microelectrode array device which successfully detects fluoride in a broad range of concentrations (10(-11)-10(-4) M) in aqueous solution, upon impedance spectroscopy measurements. A calibration curve obtained over this range of concentrations and a new analytical method based on impedance spectroscopy measurements in aqueous solution is proposed. The sensor nanofilm was produced by spin-coating and diagnosed via spectroscopic ellipsometry, AFM, and electrically conductivity techniques. Changes in the conductivity due to the boron-fluoride complex formation seem to be the major mechanism behind the dependence of impedimetric results on the fluoride concentration.

Effect of thickness on the properties of ITO thin films deposited by RF- PERTE on unheated, flexible, transparent substrates

Abstract The influence of thickness on the main properties of indium tin oxide (ITO) thin films deposited onto flexible, transparent polymer substrates at room temperature was studied. The deposition technique used was radio-frequency (RF) plasma-enhanced reactive thermal evaporation (RF-PERTE) of a 90% In–10% Sn alloy in the presence of oxygen. Results show that (1) the total transmittance is always approximately 80% at a wavelength of 500 nm when the thickness of the ITO films exceeds 70 nm and (2) ITO thin films with electrical resistivity of 6.2×10 −3 Ω cm, free carrier mobility of approximately 1.2 cm 2 V −1 s −1 and free carrier concentration of approximately 8.6×10 20 cm −3 are obtained, for films 100 nm thick. SEM investigations revealed that the surface morphology of the growing ITO thin film is dominated by the surface features of the flexible, transparent polymer substrate in the micron and submicron ranges, and does not vary significantly with thickness.

Properties of high growth rate amorphous silicon deposited by MC-RF-PECVD

Hydrogenated amorphous silicon (a-Si : H) thin films have been deposited on glass and crystalline silicon substrates by magnetically confined RF-PECVD (MC-RF-PECVD) at different RF power densities in order to verify the influence of this deposition parameter on the density of states (DOS) and growth rate (RG). It was found that the highest growth rate, 7.8 ( A is obtained for a-Si : H films deposited with an RF power density of 14.3 mW/cm 3 . For the DOS calculation, constant photocurrent method (CPM) data have been used. The lowest value of DOS is approximately 8 � 10 15 /eV/cm 3 and was obtained for a-Si : H films produced with an RF power density in the range of 10–20 mW/cm 3 . Infrared spectroscopy shows that when the RF power density increases, the concentration of SiH3 groups decreases and the concentration of SiH groups increases. At 8 mW/cm 3 , a maximum of the SiH2 concentration is obtained. At this point, a maximum of the optical gap (1.9 eV) is observed and a minimum of the dark conductivity is verified. We conclude that the best films are achieved in an RF power density range (7.1–21.4 mW/cm 3 ) for which an increase of SiH and a decrease of both SiH2 and SiH3 are simultaneously obtained. Thereafter, for higher power densities, an inversion of DOS and growth rate behaviour are observed due to ion bombardment. r 2002 Elsevier Science Ltd. All rights reserved.

ITO thin films deposited by RTE on flexible transparent substrates

Indium-tin oxide (ITO) thin films were successfully deposited onto transparent flexible substrates of hydroxypropylcellulose (HPC) cross-linked with 1,4-di-isocyanatobutane (BDI). The effect of O 2 plasma exposure on the transmittance and sheet resistance of the ITO coated flexible substrates has been studied. Atomic force microscopy (AFM) shows that these type of substrates have a large surface roughness (4.8 nm) which originates high values in the diffuse transmittance. The best properties of the resulting ITO films on flexible substrates are an average total transmittance in the visible region of about 80% and a sheet resistance of about 4 x 10 4 Ω/sq.

Flexible cellulose derivative PDLC type cells

In this work we perform a study of 250 ≈ μm thick flexible electro-optical PDLC type cells made from a biocompatible cellulose derivative film and several conductive substrates. The deposition of an ITO layer by reactive thermal evaporation on a polymeric substrate was referred to in the literature very recently and this type of coated substrate was used in the present work. In order to consider the influence of the substrates on the electro-optical behaviour of the cells, five cells were made using different substrates (three flexible polymers and two glass for comparison). Three of the substrates were coated under the same conditions, and the other two were commercially available substrates.

Influence of the a-Si:H structural defects studied by positron annihilation on the solar cells characteristics

The influence of the power density, P , on the density and structure of defects of undoped a-Si:H thin films, deposited by r.f.- D PECVD, is studied by the constant photocurrent method, (CPM), and by slow positron beam spectroscopy, respectively.Deep defect density, N , remains approximately constant at 10 cm , typical of device quality material, for P in the range 7-20 16 y3 DD D mWOcm , as calculated from CPM.Out of this range, N increases roughly one order of magnitude for both lower and higher y3 DD

Study of Defects in Hydrogenated Amorphous Silicon by Constant Photocurrent Method and Positron Annihilation

The influence of the power density, P D , on the density and structure of defects of undoped a-Si:H thin films, deposited by rf -PECVD, is studied by constant photocurrent method, CPM, and by slow positron beam spectroscopy, respectively. Deep defect density, N DD , remains approximately constant at 10 -16 cm -3 , typical of device quality material, for P D in the range 7 - 20 mW.cm -3 calculated from CPM. NDD increases roughly one order of magnitude for both low and for high power densities. Positron annihilation spectroscopy reveals the presence of two kinds of vacancy type defects in the films: large vacancy clusters or voids for P D ∼ 7 mW.cm -3 and small vacancy type defects as P D increases to ∼30 mW.cm -3 . The relative abundance of the structural defects is shown to be controlled by the power density used during the deposition without affect the electronic deep defect density, significantly.