Enhanced physical properties of porous silicon for improved hydrogen gas sensing

In the current communication, porous silicon samples were prepared by pulsed photoelectrochemical etching using a hydrofluoric acid-based solution. The structural and gas-sensing properties of the samples were studied. Apart from the cycle time T and pause time T_off of the pulsed current, a novel parameter, in the shape of the current named ‘delay time T_d’ was introduced. Our results showed that by optimization of delay time, the porosity of samples can be controlled due to the chemical preparation of silicon surface prior to electrochemical anodization. The fourier-transform infrared measurements of porous silicon (PS) layers on Si substrate showed that the typical PS surface was characterized by chemical species like Si–H and Si–O–Si terminations. The two-minute delay before applying electrical current was considered sufficient for the fabrication of higher porosity (83%), more uniform, and more stable structures. The photoluminescence (PL) peak of the optimized sample showed higher intensity than the other samples. An obvious PL blue shift also revealed a change in the crystallographic characteristics of silicon due to quantum confinement effects. Metal–semiconductor–metal diodes with Schottky contacts of nickel were fabricated on PS samples and the potential application of optimized substrates for the improved sensitivity, stability, response time and recovery time of hydrogen gas sensors was subsequently studied.     

The effect of LiCF<Subscript>3</Subscript>SO<Subscript>3</Subscript> on the complexation with potato starch-chitosan blend polymer electrolytes

This work examines the effect of lithium trifluoromethanesulfonate (LiCF₃SO₃) and glycerol on the conductivity and dielectric properties of potato starch-chitosan blend-based electrolytes. The electrolytes are prepared via solution cast technique. From X-ray diffraction (XRD) analysis, the blend of 50 wt.% starch and 50 wt.% chitosan is found to be the most amorphous blend. Fourier transform infrared (FTIR) spectroscopy studies show the interaction between the electrolyte materials. The room temperature conductivity of pure starch-chitosan film is found to be (2.85 ± 1.31) × 10^?10 S cm^?1. The incorporation of 45 wt.% LiCF₃SO₃ increases the conductivity to (7.65 ± 2.27) × 10^?5 S cm^?1. Further conductivity enhancement up to (1.32 ± 0.35) × 10^?3 S cm^?1 has been observed on addition of 30 wt.% glycerol. This trend in conductivity is verified by XRD and dielectric analysis. The temperature dependence of conductivity of all electrolytes are Arrhenian.     

Separation of bromide, bromate, iodide, iodate, nitrite, nitrate and selenite anions by capillary zone electrophoresis

Summary Capillary zone electrophoresis (CZE) has been used for the separation of bromide, bromate, iodide, iodate, nitrite, nitrate and selenite anions. The separation was achieved using a fused silica capillary (72 cm long x 50 m i.d.) filled with an acidic phosphate buffer (pH=3, 25 mmol/l), and with on-column UV detection at 200 nm. The influence of different experimental parameters such as pH, ionic strength and voltage, was studied. The nitrate concentration of a Rhine water sample was then determined under selected conditions and the results were compared to those obtained by high performance ion chromatography (HPIC).On leave from the Universitat de Barcelona (postdoctoral fellowship from ECC-BCR).     

Certification of total arsenic, dimethylarsinic acid and arsenobetaine contents in a tuna fish powder (BCR-CRM 627)

Tuna fishes were collected in the Straits of Messina (Italy), were dissected and dorsal muscles minced, freeze-dried, ground and sieved. The obtained powder was stabilised by γ-irradiation and filled into brown glass bottles. The homogeneity and stability at +20?°C and +40?°C were verified with regards to the total arsenic, dimethylarsinic acid and arsenobetaine contents. Ten laboratories participated in the certification study. All participants had demonstrated beforehand their ability to produce accurate results for the As speciation in fish tissue. The certified values are: total arsenic (4.8 ± 0.3) mg/kg, arsenobetaine (52 ± 3) μmol/kg, dimethylarsinic acid (2.0 ± 0.3) μmol/kg. The material is available from the BCR since early 1998.     

Improvement scheme for the determination of arsenic species in mussel and fish tissues

Six interlaboratory studies were organised by the Standard, Measurement and Testing Programme of the European Commission on the determination of arsenic species (arsenobetaine, arsenocholine, monomethylarsonic acid, dimethylarsinic acid, As(III) and As(V)) in marine matrices and soil. A step-by-step approach was used and a meeting was held at the end of each study to help the participants to discover errors and to improve their analytical methods. The successive steps investigated the calibration procedures on various solutions, the separation and derivatisation techniques on solutions and extracts and the extraction on mussel and fish tissues. All materials used for the study were monitored for their stability. Verified calibration solutions and compounds were distributed to the participants in each exercise in order to trace calibration problems. The agreement between the results improved regularly and at the end of the six campaigns allowed the certification of a reference material of tuna-fish tissue (BCR-CRM 627) for its total arsenic, arsenobetaine and dimethylarsinic acid contents. Received: 31 March 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Certification of total arsenic, dimethylarsinic acid and arsenobetaine contents in a tuna fish powder (BCR-CRM 627)

Tuna fishes were collected in the Straits of Messina (Italy), were dissected and dorsal muscles minced, freeze-dried, ground and sieved. The obtained powder was stabilised by γ-irradiation and filled into brown glass bottles. The homogeneity and stability at +20 °C and +40 °C were verified with regards to the total arsenic, dimethylarsinic acid and arsenobetaine contents. Ten laboratories participated in the certification study. All participants had demonstrated beforehand their ability to produce accurate results for the As speciation in fish tissue. The certified values are: total arsenic (4.8 ± 0.3) mg/kg, arsenobetaine (52 ± 3) μmol/kg, dimethylarsinic acid (2.0 ± 0.3) μmol/kg. The material is available from the BCR since early 1998. Received: 31 March 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

ChemInform Abstract: The Ground-State Potential Energy Surface of Diazene

has been studied by using a complete active space MCSCF wave function generated by distributing eight electrons among eight orbitals.