feed gases diluted in Ar (50%-50% by volume) were used to study etching of p-type Si(100) in a rf inductively coupled, Faraday-shielded plasma, with a focus on the photo-assisted etching component. Etching rates were measured as a function of ion energy. Etching at ion energies below the threshold for ion-assisted etching was observed in all cases, with Br 2 /Ar and HBr/Cl 2 /Ar plasmas having the lowest and highest sub-threshold etching rates, respectively. Sub-threshold etching rates scaled with the product of surface halogen coverage (measured by X-ray photoelectron spectroscopy) and Ar emission intensity (7504 Å). Etching rates measured under MgF 2 , quartz, and opaque windows showed that sub-threshold etching is due to photon-stimulated processes on the surface, with vacuum ultraviolet photons being much more effective than longer wavelengths. Scanning electron and atomic force microscopy revealed that photo-etched surfaces were very rough, quite likely due to the inability of the photo-assisted process to remove contaminants from the surface. Photo-assisted etching in Cl 2 /Ar plasmas resulted in the formation of 4-sided pyramidal features with bases that formed an angle of 45 with respect to h110i cleavage planes, suggesting that photo-assisted etching can be sensitive to crystal orientation. V
Plasticizers influence the physical properties of edible films by their interaction with the film-forming polymers. Using near-infrared chemical imaging, it is possible to characterize the interaction between compounds through the analysis of their relative presence throughout the film (abundance) and their variability. These parameters and standard mechanical properties were used to characterize the interaction between gelatin, chitosan and several plasticizers, pure or in binary combinations. Triacetin showed the least interaction with the polymers, while polyethylene glycol 400 and glycerol showed high interaction with them. In addition, we observed that the tensile strength of the film was well correlated with the variability of gelatin and chitosan.
This study describes changes observed in the near-infrared (NIR) diffuse reflectance (DR) spectra of pharmaceutical tablets after these tablets were subjected to different levels of strain (exposure to shear) during the mixing process. Powder shearing is important in the mixing of powders that are cohesive. Shear stress is created in a system by moving one surface over another causing displacements in the direction of the moving surface and is part of the mixing dynamics of particulates in many industries including the pharmaceutical industry. In continuous mixing, shear strain is developed within the process when powder particles are in constant movement and can affect the quality attributes of the final product such as dissolution. These changes in the NIR spectra could affect results obtained from NIR calibration models. The aim of the study was to understand changes in the NIR diffuse reflectance spectra that can be associated with different levels of strain developed during blend shearing of laboratory samples. Shear was applied using a Couette cell and tablets were produced using a tablet press emulator. Tablets with different shear levels were measured using NIR spectroscopy in the diffuse reflectance mode. The NIR spectra were baseline corrected to maintain the scattering effect associated with the physical properties of the tablet surface. Principal component analysis was used to establish the principal sources of variation within the samples. The angular dependence of elastic light scattering shows that the shear treatment reduces the size of particles and produces their uniform and highly isotropic distribution. Tablet compaction further reduces the diffuse component of scattering due to realignment of particles.
Species excitation mechanisms were studied, using optical emission spectroscopy, in a helium 200 kHz radio frequency (RF) plasma jet, emerging into the open air at 1 atm. The jet impinged on a dielectric substrate of either MgF2 or quartz. Optical emissions between 115 and 950 nm were recorded through the substrate either along the jet axis or at a steep angle to isolate emissions originating from the region near the substrate surface. Time-resolved emission was observed close to the substrate surface only during a brief period near the positive peak of the applied RF voltage. No emission close to the substrate was observed during the negative voltage with the exception of a weak emission from N2 (C3Πu → B3Πg) just prior to the peak negative voltage. N2+, H, O, OH, and NO emissions along the discharge axis, from impurities in the He feed, or air diffusing into the He jet just downstream of the end of the tube (nozzle), were dominated by Penning ionization of N2 and dissociative excitation of water and O2 by He metastables (He*). Unlike the fully modulated electron-impact excited emission from N2 and He, emissions produced by collisions with He* were weakly modulated during the RF period and were shifted in phase with respect to the peak positive or peak negative voltage. This was attributed to vacuum ultraviolet emissions, in the radiation-trapped environment of atmospheric pressure, that produced He* outside the discharge tube even during the period when the plasma was confined inside the tube. N2 emission revealed a weak ionization wave propagating during the positive voltage period, well before the peak positive voltage. At peak positive voltage, ionization and excitation in the gap between the nozzle and the substrate maximized. The plasma positively charged the substrate, resulting in the brief N2 emission observed during the negative voltage period, as electrons drifted toward the substrate to neutralize the positive charge.
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