ABSTRACT
Five materials with antimicrobial function, by adding silver, were investigated to evaluate total silver concentration in the polymers and migration of silver nanoparticles from the materials in contact with food. The migration test was carried out by contacting plastic material with food simulant. Migration concentrations and average silver particle sizes were determined by mass spectrometry with inductively coupled plasma, performed in single particle mode (spICP-MS). Additionally, silver particles size and shape were characterized by scanning electron microscopy (SEM) with chemical identification by energy-dispersive X-ray spectroscopy (EDS). Most of samples showed detectable total silver concentrations and all samples showed migration of silver nanoparticles, with concentrations found between 0.00433 and 1.35 ng kg-1. Indeed, the migration study indicated the presence of silver nanoparticles in all food simulants, with sizes bellow 95 nm. The average particle size determined for acetic acid was greater than that observed in the other simulants. In the images obtained by SEM/EDS also confirmed the presence of spherical silver nanoparticles, between 17 and 80 nm. The findings reported herein will aid the health area concerning of human health risk assessments, aiming at regulating this type of material from a food safety point of view.
ABSTRACT
The metastable wurtzite crystal phase in gallium phosphide (WZ GaP) is a relatively new structure with little available information about its emission properties compared to the most stable zinc-blend phase. Here, the effect of growth conditions of WZ GaP nano- and microstructures obtained via chemical beam epitaxy on the optical properties was studied using power- and temperature-dependent photoluminescence (PL). We showed that the PL spectra are dominated by two strong broad emission bands at 1.68 and 1.88 eV and two relatively narrow peaks at 2.04 and 2.09 eV. The broad emissions are associated with the presence of carbon and a small number of extended crystal defects, respectively. For the sharp emissions, two main radiative recombination channels were observed with ionization energies estimated in the range of 50-80 meV and lower than 10 meV. No variation of the low-temperature PL spectra was observed for samples grown at different P precursor flows, while increasing Ga content enhanced the dominant broad emission at around 1.68 eV, suggesting that the group III organometallic precursor is the main source of impurities. Finally, Be-doped samples were grown, and their characteristic optical emission at 2.03 eV was identified. These results contribute to the understanding of impurity-related luminescence in hexagonal GaP, being useful for further crystal growth optimization required for the fabrication of optoelectronic devices.
ABSTRACT
Non-planar Fin Field Effect Transistors (FinFET) are already present in modern devices. The evolution from the well-established 2D planar technology to the design of 3D nanostructures rose new fabrication processes, but a technique capable of full characterization, particularly their dopant distribution, in a representative (high statistics) way is still lacking. Here we propose a methodology based on Medium Energy Ion Scattering (MEIS) to address this query, allowing structural and compositional quantification of advanced 3D FinFET devices with nanometer spatial resolution. When ions are backscattered, their energy losses unfold the chemistry of the different 3D compounds present in the structure. The FinFET periodicity generates oscillatory features as a function of backscattered ion energy and, in fact, these features allow a complete description of the device dimensions. Additionally, each measurement is performed over more than thousand structures, being highly representative in a statistical meaning. Finally, independent measurements using electron microscopy corroborate the proposed methodology.
