Spray method: Dependence of deposition efficiency on substrate temperature

Application of the spray method for the deposition of thin films has shown that the deposition efficiency is a decreasing function of the substrate temperature. The forces which determine the path and the time the droplets take to go from the nozzle to the substrate are analyzed. A theoretical curve of the deposition efficiency as a function of the substrate temperature has been obtained by a successive-approximation method. Experimental values of the efficiency obtained from the growth rate of the films are always a function of the substrate temperature. The good agreement of the theoretical curve with the experimental data confirms the validity of the method applied for our analysis.Work supported by Ministero della Universitá e della Ricerca Scientifica and Centro Regionale Ricerche Nucleari e Struttura della Materia     

Alkaloids Analysis of Habranthus cardenasianus (Amaryllidaceae), Anti-Cholinesterase Activity and Biomass Production by Propagation Strategies

Plants in the Amaryllidaceae family synthesize a diversity of bioactive alkaloids. Some of these plant species are not abundant and have a low natural multiplication rate. The aims of this work were the alkaloids analysis of a Habranthus cardenasianus bulbs extract, the evaluation of its inhibitory activity against cholinesterases, and to test several propagation strategies for biomass production. Eleven compounds were characterized by GC-MS in the alkaloid extract, which showed a relatively high proportion of tazettine. The known alkaloids tazettine, haemanthamine, and the epimer mixture haemanthidine/6-epi-haemanthidine were isolated and identified by spectroscopic methods. Inhibitory cholinesterases activity was not detected. Three forms of propagation were performed: bulb propagation from seed, cut-induced bulb division, and micropropagated bulbs. Finally, different imbibition and post-collection times were evaluated in seed germination assays. The best propagation method was cut-induced bulb division with longitudinal cuts into quarters (T1) while the best conditions for seed germination were 0-day of post-collection and two days of imbibition. The alkaloids analyses of the H. cardenasianus bulbs showed that they are a source of anti-tumoral alkaloids, especially pretazettine (tazettine) and T1 is a sustainable strategy for its propagation and domestication to produce bioactive alkaloids.     

Interaction of rotationally aligned and of oriented molecules in gas phase and at surfaces

Recent developments concerning the generation of molecular beams containing oriented/aligned molecules will be reviewed and applications of such tools to the study of elementary processes occurring both in homogeneous and heterogeneous phases will be presented. First we will discuss the case of symmetric top molecules oriented by hexapoles. Here the molecular polarization is obtained by the use of an external field and allows to control which end of the molecular projectile is going to collide with the target. Then we will review the so-called collisional alignment, a molecular polarization phenomenon occurring in supersonic expansions of gaseous mixtures. The key feature, in this case, is the velocity dependence of the alignment degree, which allows the use of mechanical devices to filter out of the beam the molecules having either a random (statistical) or a preferential (non-statistical) spatial distribution of their rotational angular momentum J with respect to the molecular beam axis. The physical mechanisms underlying the collisional alignment will be resumed and some relevant gas-phase experiments demonstrating its occurrence will be illustrated. Application of such methodologies to the investigation of the stereodynamics of elementary processes occurring in gas-surface interaction will be presented and discussed for both weakly and strongly interacting systems.     

Functionalized-graphene modified graphite electrode for the selective determination of dopamine in presence of uric acid and ascorbic acid

Graphene is chemically synthesized by solvothermal reduction of colloidal dispersions of graphite oxide. Graphite electrode is modified with functionalized-graphene for electrochemical applications. Electrochemical characterization of functionalized-graphene modified graphite electrode (FGGE) is carried out by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The behavior of FGGE towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) has been investigated by CV, differential pulse voltammetry (DPV) and chronoamperommetry (CA). The FGGE showed excellent catalytic activity towards electrochemical oxidation of AA, DA and UA compared to that of the bare graphite electrode. The electrochemical oxidation signals of AA, DA and UA are well separated into three distinct peaks with peak potential separation of 193mv, 172mv and 264mV between AA-DA, DA-UA and AA-UA respectively in CV studies and the corresponding peak potential separations in DPV mode are 204mv, 141mv and 345mv. The FGGE is successfully used for the simultaneous detection of AA, DA and UA in their ternary mixture and DA in serum and pharmaceutical samples. The excellent electrocatalytic behavior of FGGE may lead to new applications in electrochemical analysis.     

Direct electrochemical non-enzymatic assay of glucose using functionalized graphene

A non-enzymatic amperometric sensor is developed based on the graphite electrode modified with functionalized graphene for the determination of β, d (+)-glucose. Cyclic voltammetry and electrochemical impedance spectroscopy techniques are used to study the behavior. Atomic force microscopy was used to study the surface topography of the working electrode before and after its modification. The sensor enabled the direct electrochemical oxidation of β, d (+)-glucose in alkaline medium and responded linearly to the analyte over the range from 0.5?×?10^?3 to 7.5?×?10^?3?M with a limit of detection of 10?μM. The sensor is found to exhibit a better sensitivity of 28.4?μA?mM^?1?cm^?2, good stability, and shelf life. The sensitivity of the sensor to β, d (+)-glucose was not affected by the commonly co-existing interfering substances such as l-ascorbic acid, dopamine, uric acid, and acetaminophen.     

Optical study of single InAs on In0.12Ga0.88As self-assembled quantum dots: biexciton binding energy dependence on the dots size

Single self-assembled InAs quantum dots embedded in a In_0.12Ga_0.88As quantum well and emitting in the near infrared have been optically investigated. The dependence on the excitation power of the single quantum dot photoluminescence has been used to identify the emission of the biexciton complex. The biexciton binding energy, which has been measured for a dozen dots, increases with increasing exciton transition energy for the dot sizes investigated in the present work, as a consequence of stronger confinement in a smaller quantum dot. The obtained data is compared with experimental results available in the literature for InAs quantum dots. PACS 78.67.Hc; 73.21.La; 78.55.Cr     

A new procedure for thin-film deposition by solution spraying

The major reasons for the low photovoltaic efficiency of Cu₂S/CdS cells, in which the CdS film is deposited by spraying, are due to small film thicknesses which do not exceed 4 m and the small average grain size which ranges from 0.1 to 0.5 m.A new experimental solution spraying procedure is described that prevents both restrictions by controlling the substrate temperature. Average grain sizes of more than 1 m are obtained.Work supported by Ministere Pubblica Istruzione and Centro Regionale Ricerche Nucleari e di Struttura della Materia     

Dynamics of propene adsorption on Ag001

The interaction of propene with Ag(001) is investigated by high resolution electron energy loss spectroscopy and supersonic molecular beam methods under ultra high vacuum conditions. Propene adsorbs molecularly at 110 K and desorbs intact leaving a clean surface after annealing to 160 K. Two adsorption sites, characterized by slightly different vibrational modes, exist. The low frequency species is observed already at low coverage for molecules impinging at strongly hyperthermal energies while at lower translational energy it appears only at high coverage. The initial sticking probability S(0) decreases with increasing translational energy, as appropriate for nonactivated adsorption systems. The angle and energy dependence of S(0) indicate that scaling is intermediate between total and normal energy. From the coverage dependence of the sticking probability we infer that both a nonthermal intrinsic and a thermal extrinsic precursor exist.     

Determination of Pb in airborne particulate matter with a heavy matrix of silicon by SR-ETAAS

A study is undertaken to monitor Pb levels in airborne particulate matter collected on ash-free glass-fibre filters from urban and industrial areas of Argentina by electrothermal atomic absorption spectrometry with self-reversal background correction. For this sample with a heavy matrix of silicon, a simple acid treatment with aqua regia and HF is proposed aimed to minimize contamination and reduce sample treatment steps. Ultrasonic agitation was employed for sample homogenization. To overcome the problem of the high amounts of Si, main analytical variables including acid pretreatment conditions, temperature program of the graphite furnace and spectroscopic conditions were carefully studied and optimized. Continuum source and self-reversal methods for background correction were compared in order to avoid non-specific and spectral interferences due to the matrix. After optimization, synthetic acid solutions of Pb were employed for calibration. Calibration was linear within the range 1–40 µg L^{− 1} (correlation coefficient of 0.9995) when the 283.3 analytical line was used. Using optimized conditions limits of detection (3σ) of 0.6 µg L^{− 1} were achieved. The repeatability between injections (S_r%) was evaluated and was better than 4.2%. The precision (%RSD) for Pb determination in a single sample was estimated by analyzing three strips of the same filter. In all cases the RSD was better than 6.9%. For checking accuracy, an aliquot of a Standard Reference Material (NIST 2709, San Joaquin Soil) was subject to the same sample treatment and included in the overall analytical process. This method was successfully applied to the determination of Pb in airborne particulate matter collected in Buenos Aires city.