Accurate electrical and analytical measurements allowed us to determine a relationship between resistivity and phosphorus concentration in doped silicon. This relationship is compared with that obtained by other authors in the case of n-type silicon, and the differences due to the various doping agents are discussed. Differences between concentrations determined by analytical techniques and by Hall effect measurements are reported.
The addition of trifluoromethane (CHFJ to the aerosol carrier gas in inductively coupled plasma mass spectrometry was assessed as a method of improving detection limits (DL) for elements such as As, Se, Cu and Zn in matrices containing interfering species. It was observed that in each case the analyte response was significantly increased with a coincident decrease in the blank signal. The improved DL for As in CIand Ca2+ matrices (interferences 40Ar%I+ and 43Ca'60z were 0.02 and 0.04 ng ml-' compared with 0.65 and 0.28 ng ml-', respectively, without CHF,; for 78Se (interference 40Af'8Ar+) 0.032 compared with 0.88 ng ml-'; for 63Cu in Na2S0, or Na,HPO, matrices (interferences ,'AP3Na+ and 31P1602+) 0.022 and 0.089 compared with 0.35 and 0.53 ng ml-', respectively; and for 64Zn in an Na,HPO, matrix (interferences H3'P1602+ and 31P160170+) 0.011 compared with 0.42 ng ml-', The reduction of the interference is attributed to competitive reactions between the matrix species and the CHF, or species derived from it in the plasma. The analyte enhancement effect is not yet clear. It has been suggested that this effect is related to elements with ionization potential (IP) in the 9-11 eV region and is affected by organic compounds added to the aerosol carrier gas stream. Copper (IP 7.73 ev), Al (5.99 eV), Br (1 1.30 eV) and I (1 0.44 ev) are exceptions to this assumption. Analytical curves of the studied elements at low ppb and sub-ppb levels (in the interfering matrices) further demonstrated the advantage of adding CHF, in trace elemental analysis.
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