Size-confined Si nanorods (NRs) have gained notable interestbecauseof their tunable photophysical properties that make them attractivefor optoelectronic, charge storage, and sensor technologies. However,established routes for fabrication of Si NRs use well-defined substratesand/or nanoscopic seeds as promoters that cannot be easily removed,hindering the investigation of their true potential and physical properties.Herein, we report a facile, one-step route for the fabrication ofSi NRs via thermal disproportionation of hydrogen silsesquioxane (HSQ)in the presence of a molecular tin precursor (SnCl4) ata substantially lower temperature (450 degrees C) compared to thoseused in the synthesis of size-confined Si nanocrystals (>1000 degrees C).The use of these precursors allows the facile isolation of phase-pureSi NRs via HF etching and subsequent surface passivation with 1-dodecenevia hydrosilylation. The diameters (7.7-16.5 nm) of the NRscan be controlled by varying the amount of SnCl4 (0.2-3.0%)introduced during the HSQ synthesis. Physical characterization ofthe NRs suggests that the diamond cubic structure is not affectedby SnCl4, HF etching, and hydrosilylation. Surface analysisof NRs indicates the presence of Si-0 and Sin+ species, which can be attributed to core Si and surface Si speciesbonded to dodecane ligands, respectively, and a systematic variationof the Si-0:Si-C ratio with the NR diameter. TheNRs show strong size confinement effects with solid-state absorptiononsets (2.51-2.80 eV) and solution-state (Tauc) indirect energygaps (2.54-2.70 eV) that can be tuned by varying the diameter(16.5-7.7 nm). Photoluminescence (PL) and time-resolved PL(TRPL) studies reveal size-dependent emission (1.95-2.20 eV)with short, nanosecond lifetimes across the visible spectrum, whichtrend closely with absorption trends seen in solid-state absorptiondata. The facile synthesis developed for size-confined Si NRs withhigh crystallinity and tunable optical properties will promote theirapplication in optoelectronic, charge storage, and sensing studies.

Ge1-xSnx nanocrystals (NCs) are a class of direct-gap semiconductors that show size- and composition-tunable energy gaps and enhanced absorption and emission properties compared to single-element Ge NCs. With decreasing size and increasing Sn content, optical transition oscillator strength and absorption increases, making these NCs attractive for optoelectronic devices, field effect transistors, and charge storage applications. Herein, we report the synthesis of Ge1-xSnx NCs with varying sizes (ranging from 4.7 +/- 0.6 to 8.6 +/- 1.9 nm) and varying Sn compositions (x = 0.01-0.08), followed by successful exchange of insulating surfactant ligands with molecular metal chalcogenides (MCCs), to produce solution-processed conductive NC thin films. Structural and surface analysis of pre- and post-exchanged NCs indicates a diamond cubic structure and replacement of amine surface ligands with the MCC. Electron micrographs of alloy NCs show a notable decrease in size upon ligand exchange, which is consistent with the etching induced by chalcogenide ligands. The size confinement effects have resulted in energy gaps that are significantly blue-shifted from bulk Ge for the Ge1-xSnx alloy quantum dots with composition-tunable solution-state (1.68-1.26 eV for x = 0.01-0.08) energy gaps and solid-state (1.54-1.20 eV for x = 0.01-0.08) absorption onsets. Electrical characterization of the uniform NC films (thickness = 197 +/- 5 nm) reveals that the films are insulating prior to ligand exchange and show >3 orders of magnitude increase in conductivity (3.5 x 10(-6) S/cm for Ge0.92Sn0.08 NCs) upon functionalization with MCC. The electrical conductivity of the films increases with the increasing Sn composition (1.2 x 10(-6)-3.5 x 10(-6) S/cm for x = 0.01-0.08), which is consistent with the increased spin-orbital coupling and reduction in energy gaps realized through homogeneous alloying of cubic Ge and alpha-Sn.