Trace determination of silicon by heavy ion activation analysis

The Si(¹¹B, x)^34mCl and Si(¹⁹F, x)^44mSc reactions have been studied in order to work out their capabilities in determining traces of silicon. The first one has been tested with beam energies ranging from 19 to 27 MeV¹¹B; only Mg and Al have shown nuclear interferences and a 30-min 27 MeV¹¹B irradiation yields a 14 ng detection limit. The second reaction, investigated in between 35 and 46 MeV¹⁹F, yields a 16 ng detection limit with a 2 hrs 46 MeV¹⁹F irradiation; at that energy only Al and P present nuclear interferences.     

Trace fluoride determination with specific ion electrode

A method is described for determining 10^-5–10^-4M fluoride in a variety of solutions potentiometrically with a fluoridc-specific electrode, by a standard addition method. Any change of ionic strength or the nature of the solution that might alter activity coefficients or junction potentials is minimized. The relationship between potential and fluoride concentration thus follows the Nernst equation, and the unknown concentration can be calculated. Experimental data are given for solutions of sodium choride, sodium nitrate, acidified sodium silicate and sodium hydroxide, lithium chloride, and phosphoric acid. Metal ions (e.g., Al³⁺, UO₂²⁺, Fe³⁺, Th⁴⁺) that interfere by forming complexes with fluoride can be precomplexed with phosphoric acid. The relative error is estimated at 10%, and the relative standard deviation is less than 5% over the concentration range 10^-5–10^-4M fluoride.     

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

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%.     

Studies in heavy ion activation analysis trace determination possibilities with9Be bombardment

⁹Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (E_lab=14, 32 and 63 MeV⁹Be²⁺). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a⁹Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.     

Determination of boron in silicon by SIMS with the matrix ion species ratio method

Summary In quantitative SIMS, the oxygen content of the sample surface proves to be a very important analytical parameter. The matrix ion species ratio method (MISR) was used to investigate the influence of the presence of oxygen on the determination of boron in silicon. By analysing standard samples at conditions of different oxygen coverage, the relation between the sensitivity of boron and the oxygen content of the sample surface, as indexed by the SiO⁺/Si³⁺ matrix ion species ratio, was established. The influence of the primary ion current density on this relation was investigated. The MISR procedure proves to be a suitable method to perform quantitative determinations (relative error < 10%) in conditions of changing oxygen content on the sample surface.

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Bestimmung von Bor in Silicium durch SIMS mit der Matrix Ion Species Ratio Method

     

Trace determination of volatile sulfur compounds by solid-phase microextraction and GC-MS

A method was developed for the simultaneous determination of the following nine volatile sulfur compounds in gas samples: carbon disulfide, carbonyl sulfide, ethyl sulfide, ethyl methyl sulfide, hydrogen sulfide, isopropanethiol, methanethiol, methyl disulfide and methyl sulfide. The target compounds were preconcentrated by solid-phase microextraction (SPME) and determined by gas chromatography combined with mass spectrometry. Experimental design was employed to optimize the extraction time and temperature and concurrent detection of the nine compounds was achieved by using an SPME fiber coated with Carboxen-polydimethylsiloxane (75 microns). Detection limits ranged from 1 ppt (v/v) for carbon disulfide to 350 ppt (v/v) for hydrogen sulfide and calibration functions were linear up to 20 ppb (v/v) for all the compounds investigated.     

Deuterium and oxygen-18 determination of microliter quantities of a water sample using an automated equilibrator

We describe a modified version of the equilibration method and a correction algorithm for isotope ratio measurements of small quantities of water samples. The deltaD and the delta(18)O of the same water sample can both be analyzed using an automated equilibrator with sample sizes as small as 50 microL. Conventional equilibration techniques generally require water samples of several microL. That limitation is attributable mainly to changes in the isotope ratio ((18)O/(16)O or D/H) of water samples during isotopic exchange between the equilibration gas (CO(2) or H(2)) and water, and therefore the technique for microL quantities of water requires mass-balance correction using the water/gas (CO(2) or H(2)) mole ratio to correct this isotopic effect. We quantitatively evaluate factors controlling the variability of the isotopic effect due to sample size. Theoretical consideration shows that a simple linear equation corrects for the effects without determining parameters such as isotope fractionation factors and water/gas mole ratios. Precisions (1-sigma) of 50-microL meteoric water samples whose isotopic compositions of -1.4 to -396.2 per thousand for deltaD are +/-0.5 to +/-0.6 per thousand, and of -0.37 to -51.37 per thousand for delta(18)O are +/-0.01 to +/-0.11 per thousand.     

Quantitative analysis of boron profiles in silicon using ion microprobe mass spectrometry

Single crystal silicon samples of various boron concentrations are studied using an ion microprobe. Argon and oxygen ion beams are used for the scanning and the determination of the boron profiles. Erosion rates are discussed.     

Determination of oxygen-18 in inorganic compounds

A relatively simple and rapid method has been developed for the analysis of the oxygen-18 content of many inorganic compounds including water. The samples are heated with silver cyanide at 500 degrees and the carbon dioxide formed is separated from the other products by means of a methylcyclohexane slush at -130 degrees and analysed mass spectrometrically.     

Trace determination of beryllium by heavy ion activation analysis

A novel procedure for measuring the concentration of trace beryllium in different samples has been studied using¹¹B heavy ion activation analysis. The specific reaction,⁹Be/¹¹B, 2n/¹⁸F, is sensitive and selective when using a 10 MeV¹¹Be³⁺ bombardment energy. The detection limit for a nondestructive analysis is 0.1 ng for a 2 h irradiation in a A cm^–2 beam current. A precision of 12% was achieved at the 50 g g^–1 level. Beryllium has been determined in a standard beryllium-copper alloy NBS-SRM C1123. Glass samples containing up to 61 trace elements were also analyzed nondestructively. When using a clean vacuum irradiation chamber, the technique might allow ultra-trace determinations, dealing with solid samples of a few milligrams.     

Spectrographic determination of ultramicro amounts of boron in high-purity silicon tetrachloride and trichlorosilane

A new sensitive method is proposed for the determination of boron in highpurity silicon tetra chloride and trichlorosilane. The method consists of complexing boron with triphenylchloromethane, removal of excess silicon tetrachloride, hydrolysis of the complex, and improved spectrographic excitation of liberated boric acid.The best sensitivity attainable is 0.03μg B, which corresponds to 0.06 p.p.b. B for a 500-g sample.     

Spectrophotometric determination of trace and ultratrace levels of boron in silicon and chlorosilane samples

Summary Spectrophotometric methods for the determination of boron in the low g/g and ng/g range in high-purity silicon and dichloro- and trichlorosilanes were investigated in detail. The procedures established involve dissolution of silicon samples and the hydrolyzed products of chlorosilane samples in hydrofluoric acid-containing reagents followed by evaporation of the silicon matrix as H₂SiF₆. The boron retained in the treated sample solution was then determined by a spectrophotometric method using carminic acid as a chromatic reagent. Special effort has been paid to the control of the analytical blank and reproducible determination of boron. The results indicate that addition of mannitol and proper control of the evaporation process are effective in preventing volatilization of boron during the evaporation of silicon matrix and can thus attain high recovery of boron and reproducible analysis. Through meticulous control of the analytical blank and experimental conditions, the limit of detection for boron determination with the established method can be as low as ng/g levels. Application of the methods to the determination of boron in various stages of purification of silicon and trichlorosilane as well as in borophosphosilicate film was conducted.     

Simultaneous oxygen,carbon, nitrogen,sulfur and silicon determination in coal by proton induced gamma-ray analysis

The technique of gamma-ray analysis of light elements (GRALE) is extended to measure the concentration of carbon, nitrogen, oxygen, sulfur and silicon in coal samples. The composition of the sample is determined by analyzing the spectrum of gamma rays emitted following inelastic scattering of protons bombarding the target. A large volume lithium drifted germanium detector is used as a gamma-ray detector in this work. Coal samples are irradiated with 9.5 MeV protons in a helium atmosphere for 1000 sec. Results with standard coal samples indicate that the method has an accuracy of ∼5% of the concentration of each element and a precision of ∼4% for elements constituting at least 1% of the coal by weight.     

A simple method for oxygen-18 determination of milligram quantities of water using NaHCO3 reagent

This paper presents a modified H(2)O-CO(2) equilibration method for stable oxygen isotopic composition (delta(18)O) analysis of water. This method enables rapid and simple delta(18)O analysis of milligram quantities of water, by employing solid reagent NaHCO(3) as the CO(2) source, a small (0.6 mL) glass vial for the equilibration chamber, and an isotope-monitoring gas chromatography/mass spectrometry (irm-GC/MS) system for delta 18O(CO2) analysis. This method has several advantages, including simple handling for the H(2)O-CO(2) equilibration (without purging and/or evacuation treatments), rapid and easy delta(18)O analysis of equilibrated CO(2), and highly sensitive and highly precise delta(18)O analysis of H(2)O, using samples as small as 10 mg and with a precision of less than +/-0.12 per thousand. The time needed to attain oxygen isotopic equilibration between CO(2) and water is also comparable (17 h for 10 mg H(2)O and 10 h for 100 mg H(2)O) to other previous methods using CO(2) gas for the CO(2) source. The extent of delta(18)O variation of sample water from its initial delta(18)O value due to isotope exchange with added NaHCO(3) is also discussed. It is concluded that the correction needed is negligible (less than 0.1 per thousand ) as long as the oxygen atom ratio (O(NaHCO3)/O(H2O)) is less than 3.3 +/- 10(-3) and provided the delta18O(H2O) determination is made by comparing delta(18)O of CO(2) equilibrated with sample water and that equilibrated with standard water of a moderately close delta(18)O value, less than 30 per thousand difference.     

On aromatic stability of oxygen- imino-, and sulfur-bridged [18]annulenes

Oxygen-, imino-. and/or sulfur-bridged [18]annulenes are studied using the A_s-index of aromatic stabilization. Theoretical predictions, which indicate that these compounds should differ among themselves in their aromatic properties, correlate nicely with the available experimental findings. Unknown compounds of this class: [18]annulene imino-dioxide and [18]annulene oxide-imino-sulfide are predicted to be aromatic and good candidates for preparation. The same prediction is also reached for 1,10-diaza[18]annulene.     

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%.     

Trace determination of iron on a silicon wafer surface by silicon direct bonding and neutron activation analysis

In order to determine iron on silicon wafer surface at a level of 10¹⁴ atoms·m^–2 the efficiency of a well-type Ge detector for⁵⁹Fe -ray emissions was measured and a low temperature silicon direct bonding technique was developed. With silicon direct bonding at a temperature of 350 to 650°C iron remains near the interface of the bound silicon. The iron contamination of the interface escaped from the interface can be ignored with this technique. The value of iron obtained was (2.7 to 5.9)·10¹⁴ atoms · m^–2 in the surface on silicon wafers.