We demonstrate that dodecanethiol monolayer passivation can significantly enhance the anode performance of germanium (Ge) nanowires in lithium-ion batteries. The dodecanethiol-passivated Ge nanowires exhibit an excellent electrochemical performance with a reversible specific capacity of 1130 mAh/g at 0.1 C rate after 100 cycles. The functionalized Ge nanowires show high-rate capability having charge and discharge capacities of ∼555 mAh/g at high rates of 11 C. The functionalized Ge nanowires also performed well at 55 °C, showing their thermal stability at high working temperatures. Moreover, full cells using a LiFePO(4) cathode were assembled and the electrodes still have stable capacity retention. An aluminum pouch type lithium cell was also assembled to provide larger current (∼30 mA) for uses on light-emitting-diodes (LEDs) and audio devices. Investigation of the role of organic monolayer coating showed that the wires formed a robust nanowire/PVDF network through strong C-F bonding so as to maintain structure integrity during the lithiation/delithiation process. Organic monolayer-coated Ge nanowires represent promising Ge-C anodes with controllable low carbon content (ca. 2-3 wt %) for high capacity, high-rate lithium-ion batteries and are readily compatible with the commercial slurry-coating process for cell fabrication.

Graphene in the form of graphene/nanocrystal nanocomposites can improve the electrochemical performance of nanocrystals for lithium-ion (Li-ion) battery anodes, which is especially important for high-capacity Li-alloy materials such as Si and Ge. For practical full-cell applications, graphene composite electrodes consisting of a large portion of active materials (i.e., a surface of graphene sheets evenly distributed with dense nanoparticles) are required. We have developed a facile solution-based method to synthesize subgram quantities of nanocomposites composed of reduced graphene oxide (RGO) sheets covered with a high concentration (∼80 wt %) of single-crystal 4.90(±0.80) nm diameter Ge nanoparticles. Subsequently, carbon-coated Ge nanoparticles/RGO (Ge/RGO/C) sandwich structures were formed via a carbonization process. The highnanoparticle-loading nanocomposites exhibited superior Li-ion battery anode performance when examined with a series of comprehensive tests, such as receiving a practical capacity of Ge (1332 mAh/g) close (96.2%) to its theoretical value (1384 mAh/g) when cycled at a 0.2 C rate and having a high-rate capability over hundreds of cycles. Furthermore, the performance of the full cells assembled using a Ge/RGO/C anode and an LiCoO 2 cathode were evaluated. The cells were able to power a wide range of electronic devices, including an light-emitting-diode (LED) array consisting of over 150 bulbs, blue LED arrays, a scrolling LED marquee, and an electric fan. Thus, this study demonstrates a proof of concept of the use of graphene-based nanocomposites toward practical Li-ion battery applications.

Tetragonal chalcopyrite CuIn-(S1−x Se x )2 (0 ≤ x ≤ 1) nanocrystals were synthesized by reacting a mixture of CuCl, InCl3, S, and Se in the presence of oleylamine at 265 °C. The S/Se composition ratio in the CuIn(S1−x Se x )2 could be tuned across the entire composition range of x from 0 to 1 by modulating the S/Se reactant mole ratio. The tetragonal lattice constants, that is, a and c, increase linearly with the increase of Se content, following Vegard’s law. The band gap energies of CuIn(S1−x Se x )2 nanocrystals could be tuned in the range between 0.98 and 1.46 eV and change nonlinearly with respect to x, deriving a bowing parameter of 0.17 eV. In addition, the method developed in this study was scalable to achieve gram-scale production of stoichiometry-controlled CuIn(S1−x Se x )2 and CuIn1−x Ga x Se2 nanocrystals.

Solid and hollow structures of Cu 2−x Te nanocrystals are synthesized by the injection of a Te−TOP solution at different reaction times. Both types of Cu 2−x Te nanocrystals exhibit an intense absorption peak (localized surface plasmon resonance (LSPR)) in the near-infrared region, arising from excess holes in the valence band, and high molar extinction coefficients of 2.6 × 10 7 M −1 cm −1 at 1150 nm and 8.1 × 10 7 M −1 cm −1 at 1200 nm are demonstrated for the solid-type and hollow-type Cu 2−x Te nanocrystals, respectively. The experimentally observed extinction spectra and calculated extinction spectra based on the electrostatic approximation are studied. The LSPR responses in the near-infrared (NIR) region for both solid and hollow Cu 2−x Te nanocrystals are affected by the refractive index of the medium, whereas the NIR resonance shift is more obvious in the hollow-type Cu 2−x Te nanocrystals. Furthermore, the localized surface plasmon band of the Cu 2−x Te nanostructures can be tuned by post processing via oxidation and reduction methods (controlling their degree of copper deficiency).

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Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal oxide, magnetic material and semiconductor were successfully grown on chemically converted graphene (CCG), which is simultaneously reduced from GO during the synthesis. High boiling-point solvents afford sufficient thermal energy to assure the high-quality crystalline nature of NCs, therefore the post-annealing process is obviated. Controlled experiments revealed that OLA-GO triggers heterogeneous nucleation and serves as excellent nuclei anchorage media. The protocol developed here brings one step closer to achieve "unity in diversity" on the preparation of nanocrystal-graphene hybrids.

Utilizing monophenylsilane as the precursor and liquid injection chemical vapor deposition (LICVD) as the fabrication method offers a novel synthetic approach for the facile, ambient pressure, and continuous vapor-liquid-solid (VLS) synthesis of high quality Si nanowires.