Surface Metal Concentration Research Articles

Adsorption and Desorption of Contaminant Metals on Si Wafer Surface in SC1 Solution

ABSTRACTVariation in the surface concentration of Fe, Ni, Cu and Zn on Si wafers due to treatment in NH4OH/H2aO2/H2O solution called SC1 is investigated. The metal concentration on the wafer surface depends on the initial surface concentration, concentration in the solution, adsorption probability, desorption rate constant and the treatment time. The surface metal concentration behavior is explained by taking into account the effects of these parameters. The variation in the desorption rate constant with the metal species, the concentration in the solution, treatment temperature and mixing ratio of SC1 is discussed.

Comparative study of adsorption behavior of copper, lead, and zinc onto goethite in aqueous systems

The adsorption of lead(II) and zinc(II) onto goethite was studied as a function of pH, total dissolved metal concentration, surface area of goethite, and ionic strength. The results for zinc and lead were compared with those for copper reported earlier. The adsorption edge of lead ranges from pH 4 to 7, similar to that of copper, but the adsorption edge of zinc is displaced by 1.5 pH units toward higher pH. A fourfold increase in goethite surface area had a significant effect on the adsorption edge of lead, but a tenfold increase in the ionic strength of the medium did not affect the adsorption edge of lead and zinc. At neutral pH, 50 percent of the zinc was still available for transport and reactions in aqueous solution, whereas almost 100 percent of the lead and copper were bound to the goethite surface. The distribution coefficients increase sharply with the increase in pH and ranged from 60 to 30,000 ml/g in 2.5 pH units for lead and from 60 to 3000 ml/g in 1.5 pH units for zinc, depending on the goethite surface area and metal concentration. Distribution coefficients were used to calculate the number of protons released per mole of metal adsorbed during the adsorption process, with the average number of protons released per mole of lead and zinc adsorbed estimated to be 0.97±0.07 and 1.32±0.06, respectively. Proton coefficients of copper, lead, and zinc were correlated to their ionic radii and apparent equilibrium binding constant. Although the adsorption behavior of copper and lead were similar and both have the same charge, the drop in pH per mole of metal adsorbed is more in copper than in lead.

Photostimulated Removal of Trace Metals

Photostimulated removal of trace amounts of gold, chromium, and copper from the surface of an undoped silicon substrate was studied. The initial, intentional metal surface contamination is at least . The metal‐contaminated silicon substrates were immersed into deionized water and irradiated with ultraviolet and visible light. The decrease in surface metal concentration for each of these metals is comparable to standard acid cleanup chemistries.

RADAR OBSERVATIONS OF ASTEROIDS AND COMETS

ABSTRACT Radar observations of asteroids and comets provide information about these objects' sizes, shapes, spin vectors, decimeter-scale morphology, topographic relief, regolith porosity, and metal concentration. On average, small, near-earth asteroids are rougher at decimeter scales than comets or mainbelt asteroids. Asteroid 2 Pallas is smoother than the moon at decimeter scales but much rougher than the moon at some much larger scales. There is at least a five-fold variation in the radar albedos of main-belt asteroids, implying substantial variation in these objects' surface porosities or metal concentrations. The highest albedo estimate, for 16 Psyche, is consistent with a metal concentration near unity and lunar porosities. The radar polarization signature of the near-earth object 2101 Adonis is anomalous, resembling that of Jupiter's satellite Callisto more than that of any other radar-detected planetary target. The echo spectra of comet IRAS-Araki-Alcock reveal an irregular, ≡7-km sized nucleus and an associated debris swarm, at least 103 times larger than the nucleus and comprised of particles at least a centimeter in size.

Ion scattering spectroscopy and secondary ion mass spectrometry (ISS/SIMS) studies of zeolites

In an attempt to determine the applicability of ion scattering spectroscopy (ISS) and secondary ion mass spectrometry (SIMS) techniques to the analysis of zeolite systems, surface analyses of various natural and ion-exchanged synthetic zeolite samples have been carried out. A number of different mineral single crystals were studied both in an exchanged and in a natural form; also, ionexchanged synthetic powder samples, both hydrated and dehydrated, were subjected to analysis. The analyses were performed to obtain an elemental composition of the surface to determine such information as Si Al ratios and changes in the relative concentrations of exchanged metal species. The use of a high current density Ne 20 ion beam made possible depth profiling studies to monitor changes in Si Al ratios and metal ion concentrations as a function of depth from the surface. Depth profiling of both powder and single crystal metal-exchanged samples revealed that bulk and surface Si Al ratios are essentially the same. Changes in surface metal concentration of metal-exchanged samples as the result of dehydration were also observed in accord with previously reported results. Quantification of data was attempted through the use of relative elemental sensitivity factors and published sputter yields corrected for instrumental conditions. The results, even considering their semi-quantitative nature, display a good agreement with data obtained from previous scanning Auger microscopy, X-ray photoelectron studies, and fast atom bombardment mass spectrometry studies of zeolites as well as with other independent means of analysis to indicate the value of ISS/SIMS analyses to the study of zeolites.