Surface Depth Profiling Research Articles

Estimation of planktonic wind drift by transmissometry1

Halsted Bay (Lake Minnetonka, Minnesota) was surveyed with a transmissometer. Continuous surface transects and depth profiles revealed a pattern of distribution of phytoplankton that can best be described as wind drift. The relative composition of the phytoplankton, as well as its concentration, was modified by wind: blue‐green algae drifted downwind, while all other groups remained uniformly distributed. Regression analysis showed a linear relationship of alpha (beam attenuation coefficient) with total cell volume, chlorophyll a concentration, and dry weight of suspended particles.

Diffusion kinetics of Au through Pt films about 2000 and 6000 Å thick studied with Auger spectroscopy

The diffusion kinetics of Au through Pt films were studied because of the frequent use of PtAu metallizations in semiconductor technology and because Au is often undesirable in active semiconductor regions etc. that are in contact with the Pt. PtAu couples with approximately 2000 Å and 6000 Å Pt films were heat treated between 250° and 350°C in 1 atm N 2 ambient. Surface composition and depth profiles were measured using Auger spectroscopy and ion milling. Au was found to diffuse initially through thin Pt films (< 6000 Å) by grain boundary migration and more than 10 15 atoms cm −2 of Au crossed the Pt film when the bulk of the Pt contained very little Au (⪅1 at.%). For 2250 Å Pt films on Au, the time t( X = 0.5) for half-saturation of the Pt surface with Au was given by t(0.5) = 1.2 X 10 −7 X exp (0.96 eV/ kT) min, where X is the fractional Au concentration in the first 7 Å of the surface. This diffusion rate is relatively fast; e.g. t(0.5)≈7 min for a 2250 Å Pt film at 350°C. At t(0.5) the bulk of the Pt contained less than 1 at.% Au and t(0.5) was proportional to Pt film thickness near 2000 to 6000 Å.