Boron, SIMS analysis

Be-evaporation at JET and boronization in other devices act as metallic markers and allow studies of material transport. Surface analysis of JET and TEXTOR tiles show very clearly that long-range transport is only observed for carbon. In addition to markers, 13C marked methane has been recently injected in various machines. As an example, Secondary Ion Mass Spectroscopy (SIMS) analysis of JET tiles show a strong enrichment of 13C on top of the surface of the inboard divertor tiles whereas no corresponding 13C was found in the outboard divertor. This proves that impurities are dragged towards the inboard divertor. However, the near top surface shows much more C and D than measured in deeper layers and on tiles from previous MKIIGB operation and no 13C could be identified on the shadowed regions of the divertor tiles. 

We can consider the hydroboration step as though it involved borane (BH3) It sim phfies our mechanistic analysis and is at variance with reality only m matters of detail Borane is electrophilic it has a vacant 2p orbital and can accept a pair of electrons into that orbital The source of this electron pair is the rr bond of an alkene It is believed as shown m Figure 6 10 for the example of the hydroboration of 1 methylcyclopentene that the first step produces an unstable intermediate called a tt complex In this rr com plex boron and the two carbon atoms of the double bond are joined by a three center two electron bond by which we mean that three atoms share two electrons Three center two electron bonds are frequently encountered m boron chemistry The tt complex is formed by a transfer of electron density from the tt orbital of the alkene to the 2p orbital... 

Bech Nielsen et al. (1988) also made a channeling study of the 2H in B-2H complexes that was similar in principle to that just described but differed in details of technique and in some of the conclusions arrived at. Also, they did not investigate the position of the boron atoms. They used Si uniformly doped with a high (1 x 1019 B/cm3) boron concentration, rather than implanted boron. The surface was etched off after hydrogenation, but no SIMS data was presented to confirm the uniform hydrogen concentration assumed. The penetration depth of the H was given as —7000 A. The channeling measurements were performed at 30 K. For analysis of their data Bech Nielsen et al. used the same model, based on the assumption of statistical equilibrium (SE) of the channeled ions, already described in connection with the measurements of implanted deutrium... 

Hawthorne, F.C., Cooper, M.A., Bottazzi, R, OttoUni, L., Scott Ercit,T., Grew, E.S. (1995) Micro-analysis of minerals for boron by SREF, SIMS and EMPA a comparative study. Can. Mineral, 33,389-397. 

Microanalytical LC-MS methods for the analysis of BR-derived boronates have also been developed, using either atmospheric pressure chemical ionization (APCl) or electrospray ionization (ESI). APCl-based LC-MS has been used to analyze naphthaleneboronate derivatives of BRs in this case, optimal results were obtained by using a reverse-phase HPLC acetonitrile-water gradient to elute a CIS column [67]. Typical ions observed in the positive-ion spectra of the naphthaleneboronates included a pseudomolecular ion [M -i- H]" and a fragment ion [M -i- H-H20]. The most abundant ion from the fragmentation of BL derivatives is the parent ion, while the [M -I- H-H20] ion is the most abundant in the mass spectra of CS, teasterone and typhasterol. Full-scan mass spectra were readily obtained from 400 ng of free BRs, whereas the limit of detection in SIM mode was around 2 ng. The most... 

In the case of static SIMS, a reduced volume is examined. To offset the parallel loss in detection limits/sensitivities associated with the analysis of smaller volumes, the secondary ion transmission functions of Time-of-Flight SIMS instruments (these are best snited to Static SIMS applications) can approach 100%, with all ions simnltaneously recorded. As a result, surface detection limits for Iron on a Silicon snbstrate is in the low 10 atoms/cm range, whereas that for Boron on Silicon is in the mid 10 atoms/cm range (note the different units used). These detection limits can extend fnrther for the more electropositive/electronegative elements when analyzed under appropriate conditions. 

Figure 5.5 The various means of relaying depth resolution in SIMS depth profile analysis. Note Intensities are plotted on a linear scale. In the inset is the same data with the intensity plotted on a natural logarithmic scale (decay lengths are described using natnral logarithmic arguments). The data is of the sixth Boron delta layer from the Boron delta layer Silicon structure (a structure with atomically abmpt interfaces with the composition following a delta-like function with depth) examined under 0.5 keV Oj primary ion conditions at normal incidence, i.e. from that shown in Figure 5.25.

Uniformly copper-doped and boron-doped silicon thin films fabricated by the ion beam sputter deposition method were analyzed by FIR-ICP-MS using an isotope dilution approach to provide a certified reference material for quantitative surface analysis by SIMS. 

---