Silicon nanocrystals (SiNCs) with bright bandgap photoluminescence (PL) are of current interest for a range of potential applications, from solar windows to biomedical contrast agents. Here, we use the liquid precursor cyclohexasilane (Si6H12) for the plasma synthesis of colloidal SiNCs with exemplary core emission. Through size separation executed in an oxygen-shielded environment, we achieve PL quantum yields (QYs) approaching 70% while exposing intrinsic constraints on efficient core emission from smaller SiNCs. Time-resolved PL spectra of these fractions in response to femtosecond pulsed excitation reveal a zero-phonon radiative channel that anticorrelates with QY, which we model using advanced computational methods applied to a 2 nm SiNC. Our results offer additional insight into the photophysical interplay of the nanocrystal surface, quasi-direct recombination, and efficient SiNC core PL.

Efficient photoluminescence (PL) from silicon nanocrystal (SiNC) composites has important implications for emerging solar-collection technologies, yet a detailed understanding of the landscape of PL relaxation in vitrified colloidal SiNCs is still materializing. Here, we explore details of PL relaxation in photo-polymerized off-stoichiometric polymer/nanocrystal hybrids. Specifically, thiol-ene polymer/nanocrystal composites were synthesized from a tetra-functional thiol, tri-functional allyl, and a family of dodecyl-passivated colloidal SiNCs with peak PL wavelength spanning 700−950 nm. We find time-and air-stable emission from dilute composites with up to 70% quantum yield, and we investigate PL relaxation in the parameter space of nanocrystal size and temperature, focusing on changes in the partitioning of multimodal decay upon going from the colloid to composite. In light of previous work, our results reveal similarities between the impacts of crosslinking and cooling to cryogenic temperatures, both of which are characterized by a relative reduction in the availability of phonons.

We measured the disinfection of MRSA and Clostridium difficile spores using an ultraviolet C (UV-C) device, and we correlated those results to measurements and computer simulations of UV-C surface intensity. The results demonstrate both large differences in UV light intensity across various surfaces and how this leads to significant differences in disinfection.

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Silicon-carbide (SiC) nanocrystals (NCs) of controlled 2–4 nm size are produced in low-pressure nonthermal plasma from the simple alkylsilane precursor tetramethylsilane (TMS). Generating material on the slightly carbon-rich side of 50/50 Si/C, we establish a process for thermally removing residual carbon, which in turn promotes a degree of intrinsic solubility in polar solvents such as isopropanol (IPA). Using the size-dependent Tauc gap of luminescent silicon NCs (Si NCs) as a point of reference, we demonstrate quantum confinement in nanocrystalline β-SiC but without measurable luminescence. Surface-sensitive spectroscopic techniques reveal an oxide shell surrounding a nanocrystalline SiC core, where negative surface charge groups promote solubility while likely acting as efficient trap states for nonradiative recombination. An analytical model is presented that combines electrostatic repulsion with van der Waals attraction to explain experimental observations of concentration-dependent cluster formation and reversible NC aggregation. We anticipate that these materials will be of interest for use as nanofillers in polymer composites and in specialty coatings, while providing a foundation for exploring routes to band gap emission from nanocrystalline SiC.

We performed x-ray photoelectron spectroscopy measurements on a thin film of Si nanocrystals (SiNCs) while applying DC or AC external biases to extract the resistance and the capacitance of the thin film. The measurement consists of the application of 10 V DC or square wave pulses of 10 V amplitude to the sample at various frequencies ranging from 0.01 to 1 MHz while recording x-ray photoemission data. To analyze the data, we propose three different models with varying degrees of accuracy. The calculated capacitance of SiNCs agrees with the experimental value in the literature.

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