Beyond the hydrogen wave: new frontier in the detection of trace elements by stripping voltammetry

Stripping voltammetry is limited in acidic conditions to relatively high deposition potentials because of the interfering effects of the hydrogen produced at the working electrode. We report here a simple procedure to perform reliable and sensitive trace metal analysis in such conditions. Measurements are made at a gold microwire electrode. After applying a simple electrochemical conditioning procedure, hydrogen does not block the electrode, allowing reproducible analysis and smooth stripping signals to be obtained. Advantages of working inside the hydrogen wave are exemplified through the detection of the often considered electroinactive antimony(V). Sb(V) is detected in relatively low acidic conditions (pH ≤ 1) using low deposition potentials (≤-1.8 V). The detection limit is 5 pM (0.63 ppt), the lowest ever reported for an electroanalytical technique and one of the lowest analytical methods. The method is simple, robust, and free from the common arsenic interference due to selective electrochemical hydride generation of arsine over stibine during the deposition step. Analytical methods were optimized and tested on mineral, river, tap, and coastal seawater. Results favorably compare against Certified Reference Materials data (NASS-4 and SLRS-3) and ICPMS analysis. Deposition well below the hydrogen wave pushes the frontier of stripping voltammetry, and new analytical applications in this combined range of acidity and deposition potential are to be expected.     

Sensitivity characteristics of mixtures of mono- and dinitrotoluene with nitrogen tetroxide and tetranitromethane

In the recovery of acids from the nitration of toluene to TNT, it is possible under certain conditions to obtain mixtures of nitroaromatic compounds, primarily mono- and dinitrotoluene with nitrogen tetroxide (N₂O₄) and/or tetranitromethane (TNM). Since these mixtures contain rather strong oxidizers and a fuel, they have the potential of being highly sensitive liquid explosives. Studies showed such mixtures are not exceptionally sensitive to mechanical impact and friction or thermal initiation. However, these mixtures at oxygen balanced proportions are extremely sensitive to induced shock and are capable of propagating explosive reactions at film thicknesses less than 0.5 mm. In the standard NOL card gap test, oxygen balanced mixtures of N₂O₄ with nitrobody exhibited an attenuator thickness of greater than 155 cm as compared to 3.8 cm for TNT.Shock sensitive mixtures of N₂O₄ and nitrobody can collect in fume and acid recovery operations. It is suspected that such mixtures were the cause of some of the explosions in TNT acid recovery operations in the past which have been attributed to TNM.     

The process specification system for MMST

A specification application (SPEC) was created as part of the Microelectronics Manufacturing Science and Technology (MMST) program at Texas Instruments Incorporated. The overall goal of the MMST program was the development of the next generation wafer fabrication system by improving key areas in the fabrication of wafers, including cycle time, cost, and quality. This paper presents the key features of SPEC used to meet the MMST goals. SPEC composes process flow specifications from equipment, step, sequence, and wafer specification hierarchies. Specifications can be reused and can be machine independent. These specifications are integrated into a specification management framework that provides both revision and change notice control. SPEC integrates with other MMST applications to process wafers; including material release into the factory, material movement, machine scheduling, and direct control of equipment-all key features of a paperless factory. During the processing of a wafer, SPEC uses the latest version of a specification. SPEC played a key role in the MMST program especially during the 1000 wafer pilot production run which achieved a single wafer cycle time of less than 72 h     

Interactions of meat-associated bacteriocin-producing Lactobacilli with Listeria innocua under stringent sausage fermentation conditions

The kinetics of the antilisterial effect of meat-associated lactobacilli on Listeria innocua LMG 13568 were investigated during laboratory batch fermentations. During these fermentations, which were performed in a liquid meat simulation medium, a combination of process factors typical for European-style sausage fermentations was applied, such as a temperature of 20 degrees C and a representative pH and salting profile. Two bacteriocin-producing sausage isolates (Lactobacillus sakei CTC 494 and Lactobacillus curvatus LTH 1174), which have already proven efficacy in sausage trials, and one nonbacteriocinogenic, industrial strain (Lactobacillus sakei I), were evaluated. Staphylococcus carnosus 833 was included in the experiment because of its role in flavor and color development. When grown as a monoculture or upon cocultivation with L. sakei I and S. carnosus 833, L. innocua LMG 13568 developed slightly, despite the stress of low temperature, pH, lactic acid, salt, and nitrite. In contrast, when either of the bacteriocin producers was used, the L. innocua LMG 13568 population was rapidly inactivated with more than 3 log CFU ml(-1) after 2 days of fermentation. A bacteriocin-tolerant L. innocua LMG 13568 subpopulation (4 X 10(-4)) remained after bacteriocin inactivation. Thus, when the initial level of L. innocua LMG 13568 equaled 3 log CFU ml(-1), all cells were inactivated and no bacteriocin-tolerant cells were detected, even after 7 days of incubation. S. carnosus was not inactivated by the Lactobacillus bacteriocins and displayed slight growth.     

Contact resistance behavior of the Pd2 Si-AlCuSi system

Aluminum to silicon contact resistance, R_c , is influenced by the choice of intermediate contact and interconnection metallurgies, as well as anneal cycles associated with metallization and post-metallization passivation processes in single and multi-level metal VLSI technologies. This is particularly evident for the metallurgical system comprised of palladium silicide, Pd₂ Si, and AlCuSi. This system has been investigated to ascertain the relationships between R , anneal time, and anneal temperature for various Pd Si thicknesses of AlCuSi contacts to N⁺ single-crystal silicon and polysilicon. The evaluations revealed that R_c and R_c distribution are inversely proportional to Pd₂ Si thickness, and increase with anneal time and temperature. The results are compared to the known physical chemical interactions of Pd Si and Al. The studies demonstrate that by proper selection of process parameters and contact structure design, stable Al-Si contact resistance can be achieved for semiconductor device applications when Pd is used as an intermediate contact metallurgy.