Final Polishing Step Research Articles

The effect of sample preparation on spreading resistance measurements of doped semiconductors

The spreading resistance profiling (SRP) technique was used to investigate the carrier concentration and segregation behavior of doped semiconductors. This technique is dependent on many parameters, in particular the surface finish of the wafers. The free-carrier concentration of the gallium (Ga)-doped germanium (Ge) 〈111〉 Czochralski grown crystal wafers were first measured using Hall effect measurements. The wafers were then prepared for SRP measurement with four different surface preparation procedures. These procedures were differentiated by the final polishing step used, namely; 0.1 μm diamond polished-surface, 1 μm alumina-polished surface, mechanochemical-polished surface using colloidal silica, and a mechanochemical-polished surface which was then etched using a (1 : 1 : 1) HF : H 2O 2 : CH 3COOH etch. The measured SRP data for each surface were related to the Hall effect measurements by a probe calibration factor (PCF). A model was developed which related the total damage layer in each sample to the PCF. The total damage layer consists of the surface damaged region and the subsurface damaged region. Using estimates from the literature, a linear relationship between the total damaged layer and the PCF was found.

Treatment of wool scouring effluent using anaerobic biological and chemical flocculation

The most widely used treatment of wool scouring effluent (WSE) in Australia is lagooning (anaerobic and aerobic). As the pressure to devise a more environmentally acceptable treatment method increases there is a need to study alternative, efficient biological treatment systems for WSE. In this study, laboratory and pilot-scale anaerobic biological and chemical flocculation treatment processes were investigated for removing the pollutants (mainly wool grease) from WSE. Anaerobic biological treatment utilises the natural microbial flora to destabilise and bioflocculate the WSE resulting in the settling of wool grease from the bulk liquid. Batch trials showed a grease reduction by anaerobic bioflocculation of between 30% (pilot scale) and 50% (laboratory scale) over 8 days. However, the destabilisation of the wool grease emulsion after only 2–3 days resulted in a total grease reduction of >80% after addition of a polymeric flocculant. A laboratory anaerobic bioflocculation-chemical flocculation process gave promising results by removing >90% grease at hydraulic retention times of 1–2 days. In the pilot-scale the same process resulted in up to 80% grease removal efficiency. The results of this study indicate that anaerobic biological and chemical treatment of WSE is a promising alternative treatment system compared to other chemical or natural (lagooning) treatment systems. Our approach suggests adding a flocculant to aid the separation of biologically coagulated grease from the bulk liquid. A final low-level aerobic polishing step will be necessary to meet effluent disposal guidelines

Direct purification of lysozyme using continuous counter-current expanded bed adsorption

We describe the application of a novel technique for the continuous counter-current chromatography of proteins. The unit operation has shown potential in extracting targeted species from unclarified feedstocks, delivering clarified streams of purified product. The adsorbent used in this equipment consists of a perfluorocarbon matrix, coated with poly(vinyl alcohol), and derivatized with the triazine dye Procion Red HE-7B. Purification of lysozyme from egg-whites and enriched bovine milk could be carried out continuously. The former was extracted in 90.5% yield at a rate of 7400 U/min, achieving a purification factor of 19.4. Lysozyme from the enriched milk sample was extracted continuously at a rate of 41 000 U/min, in 66.0% yield. The continuous product streams in both cases were fully clarified, thus enabling their direct application to a final polishing step, if desired.

Recovery and Characterization of a Rotavirus Outer Capsid Protein Expressed in a Recombinant Insect Cell System

Recombinant OSU VP4 protein, an outer capsid antigen of porcine rotavirus, was purified to a high level from the spent broth of baculovirus-infected Spodoptera frugiperda insect cells. Initial clarification of the broth with a 0-60% ammonium sulfate cut retained 93% of the total VP4. Q-sepharose ion exchange chromatography performed at pH 6.5 yielded 67% of the initial amount of VP4 in the pooled fractions, with more than four times the purity of the original sample. Gel filtration chromatography followed ion exchange. VP4 eluted from this column at a volume corresponding to a protein of a molecular weight of approximately 85 kDa, the single chain molecular weight of VP4. This step retained 34% of the initial VP4, with a 28-fold purification. Affinity chromatography, using heparin and glycophorin as ligands, was chosen as a final polishing step. The selective binding of VP4 to the two ligands suggested that VP4 may play a role during in vivo rota-viral infection. These specific interactions based on the biological properties of rotaviruses achieved a VP4 purity level of 85-95%. The overall purification scheme recovered about 1.5 mg per liter of VP4 spent broth from about 50 mg/liter (5% of total protein) present initially in the broth.

Polish-induced damage in GaAs: A systematic TEM investigation

Gallium Arsenide Integrated Circuit (IC) Technology demands extremely flat and almost “damage-free” GaAs wafers to maximize the yield in the manufacturing of ICs. These devices are fabricated on oriented surfaces of the crystals, which have been polished to a high degree of Harness and smoothness. The polishing procedures typically involve the use of abrasives successively to result in finer surfaces with a final chemical polishing step to remove the surface damage caused by the abrasives. However, if the final polishing step does not result in damage-free surfaces, local variations in the crystallographic orientation of the surface may lead to defective device structures. Extensive reviews are available in literature on the aspects of etching of GaAs substrates, including procedures for the preparation of polished substrates and on the revelation of defects by selective etchants.

Is Remediated Groundwater Meeting SDWA Requirements?

Treating groundwater for drinking purposes is quite different from treating it for site remediation. However, given that aquifer cleanup goals are becoming more stringent, it has been suggested that drinking water treatment technology be integrated into groundwater remediation strategies as a final polishing step and as a means of meeting the requirements of the Safe Drinking Water Act. This article discusses how traditional drinking water treatment technologies could be used for dealing with hazardous waste sites, including cost, performance, and applicability. Pump and treat technology as used in groundwater remediation is compared with that employed in drinking water applications.

Silicon-on-Insulator Wafer Bonding-Wafer Thinning Technological Evaluations

The realization of wafer-scale Silicon-on-Insulator by Van der Waals wafer bonding and subsequent thinning of one of the wafers is described for 100 mm wafers. The bonding of two silicon wafers is brought about by Van der Waals forces which are found to be sufficiently strong for a tight bond at wafer distances of less than 1 nm. This condition requires wafer surfaces which are extremely flat and free of dust particles. Usually the bonding susceptibility is enhanced by a short polishing step. Van der Waals bonding (dipole bonding) is sufficiently strong to withstand the thinning procedure, but bonding is often enhanced by an anneal step (chemical bonding) before thinning. Four thinning procedures are described: 1. Electroless chemical thinning: Selective etching of highly doped bulk material of an active wafer using an electrochemically controlled HF–HNO3–HAc–H2O etchant down to a low-dope, low etch-rate epilayer. 2. Chemical thinning: Electrochemically controlled chemical etching of p-type bulk material of an active wafer down to a p/n junction, where electrochemical passivation of an n-type silicon epilayer occurs. 3. Thinning down to a tribochemical polish stop: In this technique an active wafer is polished until grooves filled with Si3N4 are encountered. The removal rate then becomes small while SOI remains in the areas between the grooves. 4. Polish without stopper: By adapting the existing optical polishing technology, extreme control of flatness and parallelism of wafer surfaces can be achieved. It then becomes possible to polish homogeneously down to SOI layers a few microns thick over a 100 mm wafer. In procedures 1 and 2 an acceptable surface quality is obtained by applying a final tribochemical polishing step. Experimental results of the four technologies are presented. In these technologies, tribochemical polishing is crucial. The necessity of this polishing technology as an off-line facility is discussed in the broader context of ICs of the future.

PRELIMINARY STUDIES ON A COMBINED SEAWEED MARICULTURE‐TERTIARY WASTE TREATMENT SYSTEM1

ABSTRACTA pilot‐plant scale waste recycling‐mariculture system was developed at the Woods Hole Oceanographic Institution's Environmental Systems Laboratory in 1973. Basically, the concept of this system is to grow unicellular marine algae in continuous flow cultures on mixtures of seawater and secondarily treated sewage effluent, and feed the algae to bivalve molluses, maintained in a separate culture system. A final polishing step in the system consists of macroscopic algae (seaweeds) which remove the dissolved nutrients regenerated by the animal culture prior to discharge of the final effluent. In addition to serving as a final polishing step in the phytoplankton‐shellfish waste recycling system, seaweeds are also used as a one‐step waste recycling‐mariculture system.Currently, in the seweed systems, red alage are being grown which contain either agar or carrageenam both of which are in short supply and therefore have a high economic value. Yields from these seaweed mariculture systems are notably high compared to other maricultural and agricultural crops. Results indicate that seaweed farms will be an ecomomically profitable enterprise especially for developing countries in warm climates.

Analytical Examination of Oil/Water Separation by Coalescence

ABSTRACT The physical separation process of coalescence has been studied analytically under controlled conditions in regard to the separation of oil from oily water mixtures. Variations in coalescer performance were studied as a function of the oily water feed to a three stage prototype separation system of which coalescence was the final stage. The data were analyzed statistically and it was shown that increasing suspended solids concentration, increasing oil viscosity, and increasing oil concentration decreased coalescer element lifetime, however, above a certain level increasing oil concentration had no effect. Variations in the total flow rate in the range of one to four gallons per minute per square foot did not have a significant effect on coalescer element life. Under all conditions studied, the effluent water contained less than 15 parts per million oil, only ten percent of the samples analyzed contained more than this amount. The results indicate that coalescence is useful as a final polishing step in an oil/water separation system.