Real time UV-visible absorption measurements of stopped flows of AgNO 3 and (NH 4 ) 2 S are used to study the nucleation and growth of silver sulfide nanoparticles (Ag 2 S NP). Ag 2 S NP in the size range of 2 to 10 nm are formed a few seconds after the flow containing the reactants stops. The absorbance near the band edge of the semiconductor nanoparticle is used to monitor the number of particles formed with time and study the nucleation process. Transmission electron microscopy measurements are used to correlate particle size and the indirect band gap energy, determined from the onset of light absorption. A linear relation is established between Ag 2 S NP particle size and indirect band gap energy. The nucleation and growth process are not well separated in time. The initial nucleation and growth rates are found to increase with initial [AgNO 3 ] o /[(NH 4 ) 2 S] o ratios larger than 1. Silver-rich sulfides are proposed to be involved in the nucleation stage and growth process of Ag 2 S NP. Density functional calculations are consistent with that interpretation: Ag 3 S + is found to have a lower energy than the Ag 2 S and AgSH molecules or the AgSand Ag 2 SH + ions. The results are discussed in terms of classic nucleation theory and the possible growth mechanisms are discussed.

Atomic force microscopy (AFM), scanning electron microscopy (SEM), white light imaging measurements, and Raman microscopy were employed for the characterization of hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) nanoparticles deposited on glass substrate surfaces. The RDX nanoparticles were prepared by exposure of glass substrate surfaces to an aerosol jet containing RDX. The spectroscopic signature of RDX particles and the two known forms of the material, β and R RDX, are compared. Raman measurements reveal that RDX nanoparticles and β deposits have similar spectroscopic signatures between 750 and 1000 cm -1 .

Calcium sulfide (CaS) nanoparticles are cadmium free fluorescent nanostructures with potential applications in nanomedicine and photovoltaic cells. We report on the synthesis and optical properties of CaS nanoparticles prepared by the reaction of Ca(CH3CO2)2 and DMSO in a microwave. The absorption spectra of CaS prepared from this method consists of a well-defined peak in the UV and a long wavelength tail that extends above 700 nm. Emission bands centered at around 500 nm with a long wavelength tail that extends above 600 nm are observed upon excitation at 405 nm. STM measurements reveal the formation of CaS nanoparticles with an average diameter of (3.2 ± 0.7) nm. The direct and indirect band gaps are estimated to be (0.403 ± 0.003) eV and (4.135 ± 0.006) eV, respectively. Theoretical calculations on small CaS clusters are used to establish the physical properties of calcium sulfide nanoclusters, including the optical absorption spectra. Unique to CaS nanostructures is the absorption of light at wavelengths longer that in the bulk material instead of the blue shift associated with quantum confinement effects in semiconductors. Indeed, the strong absorption bands in the visible region of the spectra of the CaS nanostructures do not have a counterpart in the gas or solid phases. The optical absorption spectra are proposed to have a significant contribution from indirect transitions which are discussed in terms of the dispersion of the phonon frequency.

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We report on the effect of naked CaS nanostructures on the proliferation of carcinoma cancer cells and normal fibroblasts in vitro. The CaS nanostructures were prepared via the microwave-mediated decomposition of dimethyl sulfoxide (DMSO) in the presence of calcium acetate Ca(CH3CO2)2. Light scattering measurements revealed that dispersions contain CaS nanostructures in the size range of a few Å to about 1 nanometer, and are formed when DMSO is decomposed in the presence of Ca(CH3CO2)2. Theoretical calculations at the DFT/B3LYP/DGDZVP level of theory on (CaS)n clusters (n = 1, 2, 3, and 4) are consistent with clusters in this size range. The absorption spectra of the CaS nanostructures are dominated by strong bands in the UV, as well as weaker absorption bands in the visible. We found that a single dose of CaS nanoclusters smaller than 0.8 nm in diameter does not affect the survival and growth rate of normal fibroblasts and inhibits the proliferation rate of carcinoma cells in vitro. Larger CaS nanostructures, approximately (1.1 ± 0.2) nm in diameter, have a similar effect on carcinoma cell proliferation and survival rate. The CaS nanoclusters have little effect on the normal fibroblast cell cycle. Human carcinoma cells treated with CaS nanocluster dispersion exhibited a decreased ability to properly enter the cell cycle, marked by a decrease in cell concentration in the G0/G1 phase in the first 24 h and an increase in cells held in the SubG1 and G0/G1 phases up to 72 h post-treatment. Apoptosis and necrotic channels were found to play significant roles in the death of human carcinoma exposed to the CaS nanoclusters. In contrast, any effect on normal fibroblasts appeared to be short-lived and non-detrimental. The interaction of CaS with several functional groups was further investigated using theoretical calculations. CaS is predicted to interact with thiol (R-SH), hydroxide (R-OH), amino (R-NH2), carboxylic acid (R-COOH), ammonium (R-NH3+), and carboxylate (R-COO−) functional groups. None of these interactions are predicted to result in the dissociation of CaS. Thermodynamic considerations, on the other hand, are consistent with the dissociation of CaS into Ca2+ ions and H2S in acidic media, both of which are known to cause apoptosis or cell death. Passive uptake and extracellular pH values of carcinoma cells are proposed to result in the observed selectivity of CaS to inhibit cancer cell proliferation with no significant effect on normal fibroblast cells. The results encourage further research with other cell lines in vitro as well as in vivo to translate this nanotechnology into clinical use.