Reduce Surface Contamination Research Articles

Characterization of hard disk substrates (NiP/Al, glass) using XPS

X-ray photoelectron spectroscopy (XPS) was applied to study the adsorbates on NiP-plated aluminium (NiP/Al) and glass substrates as used for hard disk production. For both substrates, XPS spectra of the surface as a function of the substrate heating treatment were taken. The substrate was heated in an ultrahigh vacuum (UHV) chamber for ∼3 s at the given temperature, which is comparable to the process time in production. The XPS measurements were performed at room temperature after cooling down of the disk. The untreated NiP/Al disk shows a surface contamination of ∼33 at.% carbon and 37 at.% oxygen. After heating to 150 °C, half of the carbon contamination is still left; 400 °C heating reduces carbon contamination from 33 at.% to 1 at.% and oxygen contamination from 37 at.% to 15 at.%. Producing an absolutely clean surface only by a short heating process seems to be impossible. Heating to temperatures above 350 °C leads to a segregation of magnesium to the surface. The glass substrate shows a much smaller contamination compared to the NiP/Al disk. Before heating, carbon contamination amounts to ∼8 at.%. After heating to 150 °C half of this amount is still left. Heating to 400 °C leads to a reduction to 1 at.% carbon contamination. The heating reduces surface contamination of all different carbon-containing molecules. After 300 °C there is only aliphatic carbon present on the surface. As for NiP/Al an absolutely clean surface cannot be achieved by using only a short heating process. Starting from temperatures of ∼300 °C, a segregation of K atoms to the bulk and Na atoms to the surface can be observed. Copyright © 2000 John Wiley & Sons, Ltd.

Use of platinum shadowing and magnetron sputter coating in an Oxford Cryotrans system to increase low temperature resolution of biological samples in a Hitachi field-emission Scanning Electron Microscope

Previous studies in this laboratory have shown that the resolution of biological specimens could be increased at least two fold in a conventional as well as a field emission SEM by substituting high vacuum evaporation of Pt for standard sputter coating. Because the EMscope SP2000A Sputter Cryo System and the Oxford CT 1500 Cryotrans System, which were used in these experiments, employed standard sputter coating, Pt shadowing and C evaporation were carried out in a modified Denton DFE-3 freeze-etch module on a DV-503 high vacuum evaporator and the coated specimens were transferred to the cryostage (EMscope) or the prechamber (Oxford) of the cryosystem. Not only did this procedure require a high vacuum evaporator but as a result of a through air transfer into LN2, considerable contamination condensed on the surface of the specimen. Most of this contamination consisted of water ice that could be easily sublimed; however, other unidentifiable contaminants remained. To increase the versatility of the cryosystem, reduce surface contamination of the specimen and evaluate alternative coating procedures, Oxford Cryotrans Systems were equipped and tested with a Pt evaporator and a high resolution magnetron sputter head. Low temperature observation and evaluation of the coated specimens were performed in a Hitachi S4100 field emission scanning electron microscope.

Large-scale MOVPE production systems

High-performance ICs and OEICs rely on complex epitaxial heterostructures with tight bandgap engineering. Related development and production require homogeneous material, manufacturing of batches of comparable wafers, in-situ multiwafer fabrication, reduced surface contamination and defect density along with proven heterostructure processes for many combinations of III—V materials. The application of substrate rotation always seemed to cause technical problems, such as particle generation, mechanical feed troughs etc., rather than to improve the process from a production point of view. This paper summarizes the breakthrough in III—V multiwafer MOVPE mass production applications using the planetary multiwafer reactor with gas foil rotation (5 × 3″/7 × 2″ or 5 × 4″/8 × 3″) which was originally developed and patented by Philips LEP for growth of GaAs/AlGaAs heterostructures and has been used successfully since then for HEMT production, laser fabrication, and GaInP deposition. In similar Planetary Reactors, GaAs- and InP-based materials for a wide range of optoelectronic applications have been produced. The use of low pressures is not only advantageous for the handling of phosphorus-containing compounds and reduction of overall gas consumption, but also allows to drastically reduce the amount of H 2 required for driving the wafer support. The variation of thickness in these multiwafer systems is reduced to the order of 1–2% for GaAs, AlGaAs, GaInP, InP, GaInAs and GaInAsP (1.55, 1.3, 1.05 μm). Thus, one major advantage in comparison to MBE is that these reactors are capable of handling both GaAs- and InP-based processes with high concentration of phosphorus. Processes for the production of visible lasers (AlGaInP), GaInP HBTs, or complex solar cell structures have also been developed. This finally makes this MOVPE technology by far superior over MBE for production application. The relatively simple realization of a variety of different wafer sizes emphasizes the efforts to create even larger reaction chambers capable for large-area epitaxial growth of different material systems. The use of silicon wafers as substrates for advanced device structures is no longer limited to 2″ or 3″ wafers, also 4″, 6″, and 8″ wafers can be used, and rectangular arrangements for solar cell production are being developed.

An Evaluation of Saline Irrigation and Comparison of Povidone-Iodine and Antibiotic in the Surface Decontamination of Donor Eyes

We evaluated the effect of saline irrigation on 38 pairs of donor eyes and determined the relative efficacy of antibiotic rinse/storage (neomycin-polymyxin B-gramicidin) and povidone-iodine immersion. Microbial growth was found in 49 (64.5%) of 76 eyes from which cultures were taken before irrigation, and only four (8.2%) became culture negative after irrigation. Of 27 eyes culture negative before irrigation, 15 (55.6%) became positive after irrigation. One eye of each pair was then assigned randomly to antibiotic rinse/storage and the other eye to 3-minute immersion in 1% povidone-iodine. Both antimicrobial treatments decreased the numbers of positive cultures, with povidone-iodine showing an advantage that did not reach significance. These results demonstrate that saline irrigation of donor eyes in situ does not reduce surface contamination and that povidone-iodine immersion should be considered as an alternative for donor eye decontamination.

Molecular beam epitaxy of GaAs and AlGaAs on Si

Epitaxial layers of GaAs and AlxGa1−x As (0.2≤x≤0.5) have been grown directly on single-crystal Si (100) substrates, without an intermediate Ge layer, by molecular beam epitaxy (MBE). To improve nucleation, after being chemically cleaned the Si substrates were preheated in the MBE system to reduce surface contamination and achieve ordered surface reconstruction prior to growth. Reflection electron diffraction, Rutherford backscattering channeling, and photoluminescence measurement were used to characterize the epitaxial layers. The AlGaAs layers were found to be superior to the GaAs layers.

Analysis of Al in silicon on sapphire films and bulk silicon

The detection threshold for analysis of Al in silicon on sapphire (SOS) and bulk Si by secondary ion mass spectrometry (SIMS) has been reduced to 10 14 Al atoms cm -3 by a new sample preparation method combined with a technique for reducing the mass 27 background in the spectrometer. The application of a photoresist layer prior to SOS sample subdivision reduces surface contamination by sapphire particles. In situ coating of the immersion lens cover plate of the CAMECA IMS-3f instrument with pure Si immediately before a SIMS analysis reduces the instrumental mass 27 background to below 10 14 cm -3.

Sampling Ultra-Pure Quartz and Glasses to Reduce Surface Contamination

One problem associated with the emission spectrographic analysis of low level trace constituents in high purity quartz or glasses is that of sampling. It is often difficult to ensure that the detected impurities do not result from surface contamination introduced before or during sampling.

Aqueous Quaternary Ammonium Antiseptics and Disinfectants

HOSPITAL personnel often assume that liquid antiseptics and disinfectants will sterilize treated objects. However, as these agents are usually used in hospitals, they do not eradicate contamination, but rather, can only be relied on to reduce surface contamination to a level unlikely to be hazardous. Too often, they do not even achieve this degree of decontamination, since the effectiveness of a liquid antiseptic or disinfectant depends on its strength, activity, and duration of contact with the contaminated surface, as well as the nature and extent of the contamination. In addition, these agents may themselves be contaminated with potential pathogens. For these reasons, these agents may not prevent, indeed, they may even cause, patient infection. Among the various agents used in hospitals, the aqueous quaternary ammonium compounds (AQACs) have been frequently implicated as a cause of infection because of intrinsic contamination or a lack of effectiveness against certain pathogens. Kaslow and

Sites of contamination and numbers of Erwinia carotovora present in stored seed potato stocks in Scotland

SUMMARYForty‐eight bulk and crate stored commercial seed potato stocks from the east of Scotland were examined for contamination by Erwinia carotovora in 1967 and 1968. Both E. carotovora var. carotovora and E. carotovora var. atroseptica were present, the latter, the blackleg pathogen, being detected four times more frequently. Most contamination was located on the tuber surface and in the lenticels; it was rare in the vascular ring and the organism was never detected in the cortex. The level of contamination of lenticels was only slightly affected after winter storage, which, however, substantially reduced surface contamination. More than 103 cells were detected on the surface of tubers in over half the stocks and in half the stocks each lenticel sampled contained more than 102 bacteria.

Studies on the coating of fuel particles for the ‘dragon’ reactor experiment

The requirements of fission product retaining coatings on coated fuel particles are reviewed and the scope of development necessary to meet these requirements for the initial charges of the Dragon Reactor Experiment is described. These studies on the coating of fuel particles were carried out using a laboratory scale fluidized bed type of coating furnace. Within the range of deposition temperatures investigated, laminar or metallographically structureless pyrolytic carbon was deposited with methane concentrations greater than 15 per cent, while the structure deposited at low methane concentrations was columnar. Appreciable temperature gradients were found in these small fluidized beds of fuel particles, particularly under the relatively static conditions of fluidization which favoured deposition of the columnar structure. The rate of deposition of pyrolytic carbon was found to increase linearly with methane concentration at a given temperature, and within specified limits of methane concentration such that the relationship was linear within each of two separate ranges of concentration corresponding to the different metallographic structures. The room temperature density of the deposited pyrocarbons showed minimum values for deposition temperatures of 1600–1700°C. Under the experimental conditions described, the carbon efficiency of deposition increased to the order of 100 per cent at deposition temperatures of 1600°C and above. The deposition of silicon carbide interlayers from methyltrichlorosilane is described. The surface contamination of coated particle fuel was shown to be sensitive to the temperature of deposition of the pyrocarbon, to the rate of deposition at a fixed temperature, and to the presence of silicon carbide interlayers. The latter reduced surface contamination to near background values.