We have clearly discriminated the single-, bilayer-, and multiple-layer graphene (<10 layers) on Si substrate with a 285 nm SiO 2 capping layer by using contrast spectra, which were generated from the reflection light of a white light source. Calculations based on Fresnel's law are in excellent agreement with the experimental results (deviation 2%). The contrast image shows the reliability and efficiency of this new technique. The contrast spectrum is a fast, nondestructive, easy to be carried out, and unambiguous way to identify the numbers of layers of graphene sheet. We provide two easy-to-use methods to determine the number of graphene layers based on contrast spectra: a graphic method and an analytical method. We also show that the refractive index of graphene is different from that of graphite. The results are compared with those obtained using Raman spectroscopy.The recent success in extracting graphite sheets in multiple layers, and even monolayer graphene, from highly ordered pyrolytic graphite (HOPG) using a technique called micromechanical cleavage 1,2 has stimulated great interest in both the fundamental physics study and the potential applications of graphene. 3 Graphene has a two-dimensional (2D) crystal structure, which is the basic building block for other sp 2 carbon nanomaterials, such as nanographite sheets and carbon nanotubes. The peculiar properties of graphene arise from its unique electronic band structure, in which the conduction band touches the valence band at two points (K and K′) 4,5 in the Brillouin zone, and in the vicinity of these points, the electron energy has a linear relationship with the wavevector, E ) pkV f . Therefore, electrons in an ideal graphene sheet behave like massless Dirac-Fermions. 6,7 Some of these unique properties have been observed experimentally 8-21 and many new ideas 22-29 about the fundamental physics and device applications of single-and multiple-layer graphene have been proposed. Presently micromechanical cleavage is still the most effective way to produce high-quality graphene sheets, and a quick and precise method for determining the thickness of graphene sheets is essential for speeding up the research and exploration of graphene. Although atomic force microscopy (AFM) measurement is the most direct way to identify the number of layers of graphene, the method has a very slow throughput and may also cause damage to the crystal lattice during measurement. Furthermore, an instrumental offset of ∼0.5 nm (caused by different interaction forces) always exists, which is even larger than the thickness of a monolayer graphene and data fitting is required to extract the true thickness of graphene sheets. 30 Unconventional quantum Hall effects [8][9][10] are often used to differentiate monolayer and bilayer graphene from multiple layers. However, it is not a practical and efficient way. Researchers have attempted to develop more efficient ways to identify different layers of graphene without destroying the crystal lattice. Raman spectroscopy is a poten...

Reduced graphene oxide (rGO)-conjugated Cu(2)O nanowire mesocrystals were formed by nonclassical crystallization in the presence of GO and o-anisidine under hydrothermal conditions. The resultant mesocrystals are comprised of highly anisotropic nanowires as building blocks and possess a distinct octahedral morphology with eight {111} equivalent crystal faces. The mechanisms underlying the sequential formation of the mesocrystals are as follows: first, GO-promoted agglomeration of amorphous spherical Cu(2)O nanoparticles at the initial stage, leading to the transition of growth mechanism from conventional ion-by-ion growth to particle-mediated crystallization; second, the evolution of the amorphous microspheres into hierarchical structure, and finally to nanowire mesocrystals through mesoscale transformation, where Ostwald ripening is responsible for the growth of the nanowire building blocks; third, large-scale self-organization of the mesocrystals and the reduction of GO (at high GO concentration) occur simultaneously, resulting in an integrated hybrid architecture where porous three-dimensional (3D) framework structures interspersed among two-dimensional (2D) rGO sheets. Interestingly, "super-mesocrystals" formed by 3D oriented attachment of mesocrystals are also formed judging from the voided Sierpinski polyhedrons observed. Furthermore, the interior nanowire architecture of these mesocrystals can be kinetically controlled by careful variation of growth conditions. Owing to high specific surface area and improved conductivity, the rGO-Cu(2)O mesocrystals achieved a higher sensitivity toward NO(2) at room temperature, surpassing the performance of standalone systems of Cu(2)O nanowires networks and rGO sheets. The unique characteristics of rGO-Cu(2)O mesocrystal point to its promising applications in ultrasensitive environmental sensors.

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We demonstrate, both theoretically and experimentally, that cation vacancy can be the origin of ferromagnetism in intrinsic dilute magnetic semiconductors. The vacancies can be controlled to tune the ferromagnetism. Using Li-doped ZnO as an example, we found that while Li itself is nonmagnetic, it generates holes in ZnO, and its presence reduces the formation energy of Zn vacancy, and thereby stabilizes the zinc vacancy. Room temperature ferromagnetism with p type conduction was observed in pulsed laser deposited ZnO:Li films with certain doping concentration and oxygen partial pressure.

CoFe2O4/graphene oxide hybrids have been successfully fabricated via a facile one-pot polyol route, followed by chemical conversion into FeCo/graphene hybrids under H2/NH3 atomosphere.

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The unique magnetic vortex structure allows ferrimagnetic vortex‐domain iron oxide nanorings to possess negligible remanence and large hysteresis loss, which not only promotes colloid stability but also maximizes the specific absorption rate. It overcomes the super‐paramagnetic limitation and allows a new class of nanoparticle agent to be designed for high‐performance thermal‐based biomedical applications.

Large-scale synthesis of monodisperse ultrasmall metal ferrite nanoparticles as well as understanding the correlations between chemical composition and MR signal enhancement is critical for developing next-generation, ultrasensitive T magnetic resonance imaging (MRI) nanoprobes. Herein, taking ultrasmall MnFeO nanoparticles (UMFNPs) as a model system, we report a general dynamic simultaneous thermal decomposition (DSTD) strategy for controllable synthesis of monodisperse ultrasmall metal ferrite nanoparticles with sizes smaller than 4 nm. The comparison study revealed that the DSTD using the iron-eruciate paired with a metal-oleate precursor enabled a nucleation-doping process, which is crucial for particle size and distribution control of ultrasmall metal ferrite nanoparticles. The principle of DSTD synthesis has been further confirmed by synthesizing NiFeO and CoFeO nanoparticles with well-controlled sizes of ∼3 nm. More significantly, the success in DSTD synthesis allows us to tune both MR and biochemical properties of magnetic iron oxide nanoprobes by adjusting their chemical composition. Beneficial from the Mn dopant, the synthesized UMFNPs exhibited the highest r relaxivity (up to 8.43 mM s) among the ferrite nanoparticles with similar sizes reported so far and demonstrated a multifunctional T MR nanoprobe for in vivo high-resolution blood pool and liver-specific MRI simultaneously. Our study provides a general strategy to synthesize ultrasmall multicomponent magnetic nanoparticles, which offers possibilities for the chemical design of a highly sensitive ultrasmall magnetic nanoparticle based T MRI probe for various clinical diagnosis applications.