Tracking dynamic cellular processes necessitates fluorescent materials that are photostable, biocompatible, water-soluble, nanosized, and nontoxic. In this study, highly fluorescent carbon dots (CDs) were produced from cheap and readily available sources, citric acid (CA) and Philippine citrus (Citrus japonica Thunb.) or calamansi juice (CJ) via a microwave-assisted method. A number of synthetic conditions were investigated systematically to optimize the preparation of CDs from CA and CJ. The formation mechanism, surface chemistry, and photoluminescence of CA-based CDs (CA-CDs) and CJ-based CDs (CJ-CDs) were evaluated after each stage of pyrolysis in detail using different characterization techniques, such as dynamic light scattering, diffusion-ordered spectroscopy, atomic force microscopy, ζ potential, X-ray diffraction, Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, and absorption/emission spectroscopy. Gram-scale pyrolysis of CA with ethylenediamine (EDA) and CJ with EDA were carried out to provide CA-CDs (CA-18) within 18 min total pyrolysis time at 97% yield and CJ-CDs (CJ-14) within 14 min total pyrolysis time at 7% yield. Aqueous suspensions of CA-18 and CJ-14 CDs gave comparable bright blue luminescence at 462 nm. CA-CDs were shown to be nontoxic for mung beans up to 2 mg/mL, whereas CJ-CDs with higher surface negative charges inhibited growth above 0.5 mg/mL. This study demonstrates that bright CA- and CJ-CDs can be produced in gram-scale quantities using inexpensive methods. The size, amount, and extent of EDA incorporation are important in contributing to the formation of highly emissive particles.

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A laboratory-scale small angle x-ray scattering (SAXS) system was designed to detect free silicon nanoclusters generated in the gas phase during silicon film deposition by an inductively coupled mesoplasma chemical vapor deposition system at different SiH4 partial pressures and rf powers. Analysis of the SAXS profiles collected from the vicinity of the plasma-substrate boundary layer has revealed the presence of a polydisperse system of spherical scatterers having a loosely bound structure with around 2–3nm in size. A small amount of larger-sized nanoclusters was found to form as the rf power decreased, and emergence of such large nanoclusters was seen to be associated with the transition from an epitaxial to agglomerated microstructure of the films so deposited.

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