Chemical doping with foreign atoms is an effective method to intrinsically modify the properties of the host materials. In this paper, we report a facile strategy to prepare nitrogen and boron doped monolayer graphene by using urea and boric acid as solid precursors. By adjusting the elemental precursors, the nitrogen content could be modulated from 0.9 to 4.8% for nitrogen doped graphene and the boron content from 0.7 to 4.3% for boron doped graphene respectively, as estimated by X-ray photoelectron spectroscopy. The mobilities of the nitrogen and boron doped graphene-based back-gate field-effect transistors are about 350-550 cm 2 V À1 s À1 and 450-650 cm 2 V À1 s À1 respectively. Our results are better than plasma treated nitrogen and boron doped graphene. Therefore the synthesis of nitrogen and boron doped graphene sheets by a solid doping elemental precursor method is considered to be an efficient approach to producing graphene with excellent optical and electrical performances at relatively low cost.

A simple but efficient strategy to synthesize millimeter‐sized graphene single crystal grains by regulating the supply of reactants in the chemical vapor deposition (CVD) process is demonstrated. Polystyrene is used as a carbon source. Pulse heating on the carbon source is utilized to minimize the nucleation density of graphene on copper foil, while a gradual increase in the temperature of the carbon source and the flow rate of hydrogen is adapted to drive the continuous growth of the graphene grains. As a result, the nucleation density of graphene grain can be controlled to as low as ≈100 nuclei/cm2, and a single crystal grain can grow up to dimensions of ≈1.2 mm. Raman spectroscopy, transmission electron microscopy (TEM), and electrical‐transport measurements show that the graphene grains obtained are of high quality. The strategy presented provides very good controllability and enables the possibility of large graphene single crystals, which is of vital importance for practical applications.

With the potential uses of photothermal therapy (PTT) in cancer treatment with excellent efficacy, and the growing concerns about the nanotoxicity of hyperthermia agents such as carbon nanotubes and gold-based nanomaterials, the importance of searching for a biocompatible hyperthermia agent cannot be emphasized too much. In this work, a novel promising hyperthermia agent employing magnetic Fe3O4 particles with fairly low toxicity was proposed. This hyperthermia agent showed rapid heat generation under NIR irradiation. After modification with carboxymethyl chitosan (CMCTS), the obtained Fe3O4@CMCTS particles could disperse stably in PBS and serum without any aggregation. The modification of CMCTS could decrease the adsorption of bovine serum albumin (BSA) and improve the cellular uptake. In a comparative study with hollow gold nanospheres (HAuNS), Fe3O4@CMCTS particles exhibited a comparable photothermal effect and fairly low cytotoxicity. The in vivo magnetic resonance (MR) images of mice revealed that by attaching a magnet to the tumor, Fe3O4@CMCTS particles accumulated in the tumor after intravenous injection and showed a low distribution in the liver. After being exposed to a 808 nm laser for 5 min at a low power density of 1.5 W cm(-2), the tumors on Fe3O4@CMCTS-injected mice reached a temperature of ~52 °C and were completely destroyed. Thus, a kind of multifunctional magnetic nanoparticle with extremely low toxicity and a simple structure for simultaneous MR imaging, targeted drug delivery and photothermal therapy can be easily fabricated.

In this paper, we consider the minimum-time reorientation problem of an axisymmetric rigid spacecraft with two independent control torques mounted perpendicular to the spacecraft symmetry axis. The objective is to reorient the spacecraft from an initial attitude, with some angular velocity, to a nal attitude with a certain angular velocity in minimum time. All possible control structures, including both singular and nonsingular arcs, are studied completely by deriving the corresponding formulas and the necessary optimality conditions. It is shown that a second-order singular control can be part of the optimal trajectory. It is also shown that for an inertially symmetric and a nonspinning axisymmetric rigid body, it is possible for in nite-order singular controls to be part of or the whole optimal trajectory. In particular, for a nonspinning axisymmetric rigid body, the second-order singular trajectory is shown to be an eigenaxis rotation. An ef cient method for numerically solving the optimal control problem, based on a cascaded computationalscheme that uses both a direct method and an indirect method, is also presented. Numerical examples demonstrate optimal reorientation maneuvers with both nonsingular and singular subarcs, and comparisons are made between eigenaxis rotations and the true time-optimal rotations.

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