Arsenic depth profile

FIGURE 2. Depth profile of germanium compounds in Baltic Sea (modified from Reference 11) MeGe, monomethylgermanium Me2Ge, dimethylgermanium Asi, total dissolved inorganic arsenic... 

Arsenic. The inorganic species arsenate [As(V)] and arsenite [As(III)] were measured in the depth profile of the lake over the seasonal cycle (Figure 6) (32). The relevant reduction and oxidation processes will be briefly considered. The equilibrium constants for the various reactions are calculated on the basis of the thermodynamic data given in refs. 66 and 67. According to the thermodynamic sequence, the reduction of As(V) to As(III) occurs in a p range similar to that of the reduction of Fe(OH)3(s) to Fe(II) (Figure 2). 

Gault, A.G., Islam, F.S., Polya, D.A. et al. (2005) Microcosm depth profiles of arsenic release in a shallow aquifer, West Bengal. Mineralogical Magazine, 69(5), 855-63. 

Warren, C., Burgess, W.G. and Garcia, M.G. (2005) Hydrochemical associations and depth profiles of arsenic and fluoride in Quaternary loess aquifers of northern Argentina. Mineralogical Magazine, 69(5), 877-86. 

Similar depth profiles are routinely done for phosphorus and arsenic-doped silicon films. 

Figure 11 Vertical depth profiles taken in July, 1999 of various physical, chemical, and biological properties of Mono Lake, California, when the lake was in a meromictic condition, (a) Dissolved oxygen, light transmissivity, and chlorophyll a content (b) arsenate and arsenite (c) methane and sulfide (d) temperature and density (e) direct counts of bacterial cells and sulfate. (From Ref. 57.)...

Figure 12 Vertical depth profiles of arsenate with rates of respiratory arsenate and sulfate reduction in the water column of meromictic Mono Lake, California, made during October, 1999. Sulfate-reduction profiles from the last period of meromixis (1986) when the lake was 4 m shallower are shown for comparison. (From Ref. 57.)...

SIMS is used for quantitative depth profile determinations of trace elements in solids. These traces can be impurities or deliberately added elements, such as dopants in semiconductors. Accurate depth prohles require uniform bombardment of the analyzed area and the sputter rate in the material must be determined. The sputter rate is usually determined by physical measurement of the crater depth for multilayered materials, each layer may have a unique sputter rate that must be determined. Depth prohle standards are required. Government standards agencies like NIST have such standard reference materials available for a limited number of applications. For example, SRM depth profile standards of phosphorus in silicon, boron in silicon, and arsenic in silicon are available from NIST for calibration of SIMS instmments. P, As, and B are common dopants in the semiconductor industry and their accurate determination is critical to semiconductor manufacture and quality control. 

As an example of RBS applied to a polymer system, figure 3.22 shows the spectrum obtained from a sample of the conjugated polymer poly(phenylene, vinylene) after exposure to arsenic pentafluoride vapour (Masse et al. 1990). This dopant diffuses into the polymer and reacts with it to form an electrically conducting complex and RBS is well suited to following the kinetics of the doping process by providing concentration-depth profiles of the elemental components of the dopant as a function of time. The peaks in the spectrum... 

Barozzi, M., Giubertoni, D., Anderle, M., Bersani, M. (2004) Arsenic shallow depth profiling accurate quantification in Si02/Si stack. Applied Surface Science, 231-232,632-635. 

Comparison of the elemental depth profiles of the SEI (Figure 22) shows that, as with the LiPF electrolyte, the SEI formed on soft carbon is thinner. After 10 minutes of sputtering, the carbon concentration from the underlying HOPG approaches 80%, while for the hard carbon it does not exceed 30%. Eithium content remains relatively constant during sputtering, whereas the concentrations of carbon, oxygen, fluorine, and arsenic decrease monotonically. 

M. Bersani, P. Honicke, B. Beckhoff and A. Sanz-Medel, Quantitative depth profiling of boron and arsenic ultra low energy implants by pulsed radiofrequency glow discharge time of flight mass spectrometry, J. Anal. At. Spectrom., 2011, 26, 542-549. 

A profile of a 500-eV arsenic implant by Hitzman and Mount [127] shows the effect of Cs+ primary ion energy and incidence angle on depth resolution (Fig. 4.38). These As- profiles also demonstrate the high sensitivity of the SIMS technique. 

Figure 38 Effect of beam energy and angle of incidence on depth resolution. Profiles of arsenic in silicon using Cs+ primary beam. (From Ref. 127.)...

Sulfur in core MTR. 1 (Fig. 7 Table 5) is generally less than 0.2 wt%, but it increases up core to a sharp maximum at 9 cm depth with two additional subordinate peaks centered at 23 and 37 cm, corresponding to about 1945 and 1970, respectively. The Zn distribution is similar to that of sulfur in that it increases up core, and likewise has two peaks at 23 and 37 cm, although it lacks a distinct peak near 10 cm. Pb content has a peak at 23 cm with another at 37 cm. The Cu profile, on the other hand, is dominated by the peak at 10 cm, but is otherwise nearly constant. Arsenic varies, but has a clear peak at 9 cm and a poorly defined one at 25 cm. 

Extensive studies have shown that arsenic can accumulate in the soil when arsenic compounds are repeatedly applied to crops [1]. On fields treated with calcium arsenate for insect control, the arsenic concentrations decreased with soil depth [1]. Appreciable amounts of arsenic could also move down in the soil profile with the percolating soil water [13]. 

---