Using silicon/reduced graphene oxide (Si/rGO) composites as lithium-ion battery (LIB) anodes can effectively buffer the volumetric expansion and shrinkage of Si. Herein, we designed and prepared Si/rGO-b with a sandwiched structure, formed by a duple combination of ammonia-modified silicon (m-Si) nanoparticles (NP) with graphene oxide (GO). In the first composite process of m-Si and GO, a core–shell structure of primal Si/rGO-b (p-Si/rGO-b) was formed. The amino groups on the m-Si surface can not only hybridize with the GO surface to fix the Si particles, but also form covalent chemical bonds with the remaining carboxyl groups of rGO to enhance the stability of the composite. During the electrochemical reaction, the oxygen on the m-Si surface reacts with lithium ions (Li⁺) to form Li₂O, which is a component of the solid–electrolyte interphase (SEI) and is beneficial to buffering the volume expansion of Si. Then, the p-Si/rGO-b recombines with GO again to finally form a sandwiched structure of Si/rGO-b. Covalent chemical bonds are formed between the rGO layers to tightly fix the p-Si/rGO-b, and the conductive network formed by the reintroduced rGO improves the conductivity of the Si/rGO-b composite. When used as an electrode, the Si/rGO-b composite exhibits excellent cycling performance (operated stably for more than 800 cycles at a high-capacity retention rate of 82.4%) and a superior rate capability (300 mA h/g at 5 A/g). After cycling, tiny cracks formed in some areas of the electrode surface, with an expansion rate of only 27.4%. The duple combination of rGO and the unique sandwiched structure presented here demonstrate great effectiveness in improving the electrochemical performance of alloy-type anodes.

Diamond has extraordinary and unique properties attractive for a variety of technological applications. Radiation treatment by high-energy electrons or ions serves as a versatile tool for material modification and structural transformation. Herewith we report the rapid formation of diamond by electron irradiation of graphene oxide (GO) in just a few seconds. The structural transformation of GO to diamond was accomplished in an electron beam of energy 120 keV and electron flux density (1~8) × 107 e/nm2·s. When the electrons irradiated GO, diamondoids were formed on the surface. Electron bombardment of GO resulted in breakage of the C-O and C-C bonds, causing migration of carbon atoms as well as the oxygenic functional groups on the GO plane. In a typical case, carbon dimers were incorporated into a sp2-hybridized network to form adamantane on the GO surface. The similarity of hybridization between the carbon atoms linked to oxygenic functional groups of GO and the carbon atoms in diamondoids is a key to the successful transformation of GO to diamondoids. The atomic structure of adamantane, unimantane, and 15-polymantane were observed and analyzed by high-resolution electron microscopy (HREM) and image simulations. The formation and growth of diamond, analyzed with in situ HREM, were revealed in both modes of crystal growth: (i) nucleation and growth and (ii) oriented attachment.

Electron microscopy is essential for nanoparticle research because it provides the critical structural data of particle size, morphology, crystallography, and elemental composition that are essential for tailoring and for predicting nanoparticles’ optical, electronic, catalytic, and mechanical properties. The weak scattering from nanoparticles results in low contrast in electron microscope images. Therefore, observing and interpreting such images requires special care to avoid erroneous conclusions. This study investigates the imaging contrast of diamond structures on different supporting films. When the nanodiamond is overlapped with a carbon film, particle edge details cannot be explained, and the overlapping interference lattices produce a pattern of interference fringes that is much coarser than the original pattern. Single graphene oxide (GO) sheets, as the ideal support film, are highly electron-transparent for the study of nanoparticles. As a low-background and high-transparency support to identify the dominant structural information of the nanodiamond, GO is superior to carbon support film. Quantitative contrast analysis reveals that GO film improves the contrast-to-noise ratio (CNR) by a factor of 3.0 for 8 nm particles compared with conventional amorphous carbon films. The {111} lattice-fringe detection rate increases from 35% on carbon film to 85% on GO for the same particle size. These results establish GO as a quantitatively superior support film for high-resolution electron microscopy (HRTEM) imaging of sub-10 nm nanoparticles.