Secondary Ion Mass Spectrometry

Fluorine and chlorine X‑ray count rates are known to vary significantly during electron probe microanalysis (EPMA) of apatite. Since the rate, timing, and magnitude of this variation are a function of apatite orientation and composition, as well as EPMA operating conditions, this represents a significant problem for volatile element analysis in apatite. Although the effect is thought to be an intrinsic crystallographic response to electron-beam exposure, the mechanisms and causes of the count rate variability remain unclear. We tackle this by examining directly the effects of electron-beam exposure on apatite, by performing secondary ion mass spectrometry (SIMS) depth profiles of points previously subject to electron-beam irradiation. During irradiation of fluorapatite, oriented with the c-axis parallel to the electron beam, halogens become progressively concentrated at the sample surface, even under a relatively low power (15 nA, 10–15 kV) beam. This surface enrichment corresponds to an observed increase in EPMA FKa X‑ray count rates. After prolonged irradiation, the surface region starts to lose halogens and becomes progressively depleted, corresponding with a drop in EPMA count rates. Under normal EPMA operating conditions there is no halogen redistribution in fluorapatite oriented with the c-axis perpendicular to the electron beam, or in chlorapatite. We infer that anionic enrichment results from the migration of halogens away from a center of charge build-up caused by the implantation of electrons from the EPMA beam, assisted by the thermal gradient induced by electron-matter interactions. The process of surface enrichment is best explained by halogen migration through interstitial crystallographic sites in the c-axis channel. This suggests that once the thermal and electric fields are removed, halogens may relax back to their original positions on very long timescales or with sample heating.

Silicon samples implanted at medium fluences (2 × 1014-2 × 1015 ions/cm2) with arsenic, phosphorus and BF2 at 0° and 7° of tilt were analyzed by secondary ion mass spectrometry (SIMS) to investigate the effects of direct axial channeling on the as-implanted chemical profiles for a variety of experimental settings which are common in microelectronic device fabrication. The importance of axial channeling for each species is discussed and related to the actual implant energy and to the fluence required to obtain acontinuous amorphous silicon layer; arsenic (60-150 keV) and phosphorus (80-150 keV) dopant profiles are deeply affected by the implant tilt angle; on the contrary, boron resulting from the dissociation of BF2 molecule at 70 keV, has turned out to be less sensitive to implant angle configuration. The ineffectiveness of 7° of tilt in avoiding axial channeling is pointed out.

Fluid-saturated experiments were conducted to investigate the partitioning of boron among haplogranitic melt, aqueous vapor and brine at 800 °C and 100 MPa. Experiments were carried out in cold-seal pressure vessels for 1 to 21 days, and utilized powdered synthetic subaluminous haplogranite glass doped with 1000 ppm B (crystalline H3BO3) and variable amounts of NaCl and H2O at a fluid/haplogranite