Pietro Lanza

Spectrophotometric determination of traces of boron in silicon by means of solvent extraction

A spectrophotometric method for the determination of boron in silicon based on the extraction of the methylene blue-fluoroborate complex has been improved. Some important points, such as the dissolution of silicon with hydrofluoric acid and hydrogen peroxide, the effect of various anions on the blank absorbance and the best working conditions for forming and extracting the complex, have been studied. The method is applied to the determination of boron in silicon containing at least 1 p.p.m. of boron, with a relative standard deviation of ±5%.

The behaviour of copper(II)-selective electrodes in chloride-containing solutions

Abstract Calibration curves for copper(II) in solutions containing various chloride ion concentrations are examined in detail. The mechanism of the interferences on the behaviour of the copper(II)-selective electrode is discussed. The anomalous slopes observed can be explained by considering the sensitivity of the electrode membrane to the silver ions released from the electrode surface by chemical interaction with the solution. The effects of the formation of silver-chloride complexes and of the changes in the membrane are described.

Differential-pulse polarographic determination of molybdenum in steel

A method for the determination of molybdenum in steel, based on catalytic electroreduction by the molybdate ion, is described. After a suitable sample dissolution, iron is removed by cation exchange and molybdenum is eluted with 0.5 M nitric acid. The eluate is diluted 1 + 1 with 4 M ammonium nitrate solution, and polarographic analysis carried out over the range from 0 to –1.0 V versus a saturated calomel electrode. The method is applicable to the determination of molybdenum in the 0.001–5% of molybdenum range and good agreement is reported for a number of certified British Chemical Standard and commercial steels.

Potentiometric determination of boron in silicon with an ion-selective electrode

Abstract A potentiometric method is proposed for the determination or boron in silicon, based on dissolution of silicon by treatment with hydrofluoric acid and ammonium fluoride in the presence of hydrogen peroxide, and conversion of boron to fluoroborate ion. The fluoroborate activity is measured with the Orion fluoroborate-selective electrode. Some important points, such as the effect of various interfering ions and the hydrolysis of fluoroborate ion, are described in detail. The method is applied to the determination of boron in silicon containing at least 10 p.p.m. of boron, with a relative standard deviation of ±4%.

The differential pulse polarographic determination of chromium in gallium arsenide

The method described for the determination of chromium in gallium arsenide is based on the catalytic current produced by nitrate in the electrolytic reduction of the chromium(VI)-diethylenetriaminepentaacetate complex. Matrix effects, primarily caused by gallium, are discussed in detail. The method is suitable for determinations of chromium at levels as low as about 1 μg g−1 with about 50 mg of sample; the r.s.d. is better than 10%.

Spectrophotometric evaluation of phosphorus profiles in silicon

Abstract A new method for the determination of phosphorus concentration profiles in semiconductor silicon slices makes use of spectrophotometry for concentration measurements and anodic oxidation for sectioning. Silicon layers in the 5–50-nm range can be removed reproducibly. The profile determination of phosphorus doping is possible for concentrations as low as 10 19 atoms P cm -3 . Measurements of these profiles by the proposed procedure give excellent agreement with electrical evaluations. The method is simple and reliable, and expensive apparatus is not required. A medium-depth profile is normally completed in eight hours.

Stoichiometry of superconducting YBa2Cu3Oy. Determination of Cu(III)/Cu(II) ratio and oxygen content

Abstract The electrical properties of the high T c superconductor YBa 2 Cu 3 O y depend on its oxygen content. The oxygen content is indirectly determined by iodimetric measurement of the oxidation state of copper. A combination of two titrations, with and without addition of KI, prior to dissolving the sample permits the determination of the two species Cu(II) and Cu(III). A simplified automatic titration with potentiometric detection of the end-point is described. The method is suitable for rapid and reliable determinations of the Cu(III)/Cu(II) ratio and total copper content and for controlling the stoichiometry of the compound. Samples of the superconductor were analysed and the stoichiometric coefficient y for oxygen was determined with excellent results. Typically, y =6.811 ± 0.0063 (s.d.) ( n =5). A comparison of the total copper content (found by direct analytical determination) with the copper concentration calculated from the stoichiometric formula gives an evaluation of possible deterioration of the sample.

Potentiometric study on the interaction of Ag+ ions with gelatin

Abstract From a study of the Ag + - gelatin system it can be deduced that complex formation is possible in the whole pH-range examined (1.5–10). The ligand groups of gelatin, carboxyl, α- and ϵ-amino and imidazole groups, can be active simultaneously; the predominant action of one or other group depends on the pH. In alkaline environment (pH > 8) the Ag + complex directly affects the peptide link. From the observed pAg-values and the measurement of the number of H + ions displaced/Ag + ion complexed, it can be deduced that the interaction Ag + - gelatin leads essentially to the formation of chelate complexes.

Differential pulse polarographic determination of traces of phosphorus in semiconductor silicon

Abstract A method for the indirect determination of phosphorus in semiconductor silicon is presented. After silicon dissolution with hydrofluoric and nitric acids and matrix volatilization, molybdophosphoric acid is formed in 0.25 M hydrochloric acid and then extracted into n-butyl acetate. Back-extraction with 2 M ammonium nitrate—1 M ammonia solution and addition of nitric acid gives a suitable supporting electrolyte for measurement of the catalytic molybdenum wave. Differential pulse polarography provides a detection limit of ca. 5 ng g - with a precision of about ±2%, with linear calibration curves up to at least 0.1 μg P ml -1 .

Separation and determination of traces of metallic impurities in silver halides

Abstract A method for the enrichment and determination of elements present in trace amounts in high-purity silver halides is described. Concentrated solutions of potassium iodide are used as solvents for the samples. The elements determined are concentrated by solvent extraction: zinc, cadmium, lead, copper, cobalt and nickel as dithizonates, and iron, aluminium and manganese as oxinates. The complexes formed are then determined spectrophotometrically. The relative lower limits of detection are of the order of 1 p.p.m. with an accuracy better than 10%.