Chemical functionalization is a promising route to band gap engineering of graphene. We chemically grafted nitrophenyl groups onto exfoliated single-layer graphene sheets in the form of substrate-supported or free-standing films. Our transport measurements demonstrate that nonsuspended functionalized graphene behaves as a granular metal, with variable range hopping transport and a mobility gap ~ 0.1 eV at low temperature. For suspended graphene that allows functionalization on both surfaces, we demonstrate tuning of its electronic properties from a granular metal to a gapped semiconductor, in which charge transport occurs via thermal activation over a gap ~ 80 meV. This non-invasive and scalable functionalization technique paves the way for CMOS-compatible band gap engineering of graphene electronic devices.

Sensors based upon surface-enhanced Raman spectroscopy (SERS) are attractive because they have narrow, vibrationally specific spectral peaks that can be excited using red and near-infrared light which avoids photobleaching, penetrates tissue, and reduces autofluorescence. Several groups have fabricated pH nanosensors by functionalizing silver or gold nanoparticle surfaces with an acidic molecule and measuring the ratio of protonated to deprotonated Raman bands. However, a limitation of these sensors is that macromolecules in biological systems can adsorb onto the nanoparticle surface and interfere with measurements. To overcome this interference, we encapsulated pH SERS sensors in a 30 nm thick silica layer with small pores which prevented bovine serum albumin (BSA) molecules from interacting with the pH-indicating 4-mercaptobenzoic acid (4-MBA) on the silver surfaces but preserved the pH-sensitivity. Encapsulation also improved colloidal stability and sensor reliability. The noise level corresponded to less than 0.1 pH units from pH 3 to 6. The silica-encapsulated functionalized silver nanoparticles (Ag-MBA@SiO(2)) were taken up by J774A.1 macrophage cells and measured a decrease in local pH during endocytosis. This strategy could be extended for detecting other small molecules in situ.

Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angström spatial precision is one of the critical challenges in the chemical sciences, as the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved a combination of 100 fs root-mean-squared temporal resolution and sub-Angstrom (0.76 Å) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions.

Silicon (Si) has been attracting extensive attention for rechargeable lithium (Li)‐ion batteries due to its high theoretical capacity and low potential vs Li/Li+. However, it remains challenging and problematic to stabilize the Si materials during electrochemical cycling because of the huge volume expansion, which results in losing electric contact and pulverization of Si particles. Consequently, the Si anode materials generally suffer from poor cycling, poor rate performance, and low coulomb efficiency, preventing them from practical applications. Up‐to‐date, there are numerous reports on the engineering of Si anode materials at microscale and nanoscale with significantly improved electrochemical performances. In this review, we will concentrate on various precisely designed protective layers for silicon‐based materials, including carbon layers, inorganic layers, and conductive polymer protective layer. First, we briefly introduced the alloying and failure mechanism of Si as anode materials upon electrochemical reactions. Following that, representative cases have been introduced and summarized to illustrate the purpose and advancement of protective coating layers, for instance, to alleviate pulverization and improve conductivity caused by volume expansion of Si particles during charge/discharge process, and maintain the surface stability of Si particles to form a stable solid‐electrolyte interphase layer. At last, possible strategies on the protective coating layer for stabilizing silicon anode materials that can be applied in the future have been indicated.

Pristine single layer graphene (SLG) has exceedingly high mobility, which is ∼ 4,000-20,000 cm 2 /Vs for typical devices supported on Si/SiO 2 substrates, and may reach as high as 250,000 cm 2 /Vs in suspended devices at room temperature. [ 1 ] Such high mobilities make graphene an extremely attractive candidate for the next generation electronic materials. However, the absence of a band gap, which is necessary for digital electronics, presents a technological challenge. One effective approach to band gap engineering is the (partial) saturation of the valences of some of the conjugated carbon atoms. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Nitrophenyl functionalization, in which a fully rehybridized sp 3 carbon atom is created in the lattice, dramatically modifi es the electronic and magnetic structure of graphene, with signifi cantly reduced fi eld effect mobility. [18][19][20][21][22] Since this type of functionalization scheme introduces resonant scatters [ 23 ] into the graphene lattice, we refer to this as destructive rehybridization. [ 24 ] Most approaches for chemical modifi cation of graphene involve the creation of sp 3 carbon centers at the cost of conjugated sp 2 carbon atoms in the graphene lattice. We have recently investigated the application of organometallic chemistry by studying the covalent hexahapto modifi cation of graphitic surfaces with zero-valent transition metals such as chromium. [ 12 , 25 ] The formation of the hexahapto ( η 6 )-arene − metal bond leads to very little structural reorganization of the π -system. In the reaction of the zero-valent chromium metal with graphene, the vacant d π orbital of the metal (chromium) constructively overlaps with the occupied π -orbitals of graphene, without removing any of the sp 2 carbon atoms from conjugation. [ 12 , 25 ] Previously we have shown that the formation of such bishexahapto transition metal bonds between the conjugated surfaces of the benzenoid ring systems present in the surfaces of graphene and carbon nanotubes can dramatically change their electrical properties. [ 12 , 24-27 ] These prior works focus on using the bis-hexahapto-metal bond as an interconnect for electrical transport between the conjugated surfaces, thereby increasing the dimensionality of the carbon nanotube and graphene materials and thus we were concerned with the use of the bishexahapto-metal bond as a conduit for electron transport between surfaces. In contrast, the goal of the present study is to investigate the effect of the hexahapto-bonded chromium atoms on the electronic properties of graphene itself (within the plane of a single layer), by using mono-hexahapto-metal bonds to the graphene surface.Single layer graphene (SLG) fl akes used in this study were extracted from bulk graphite using a standard mechanical exfoliation method and placed on a Si substrate with 300 nm SiO 2 . Contacts consisting of 10 nm of Cr and 150 nm of Au were deposited on SLG by e-beam lithography. The devices were then annealed in vacuum by passing a high current...