Epitaxial growth of boron-doped graphene by thermal decomposition of B4C

Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a B4C thin film

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B₄C on SiC and graphene on B₄C had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on B₄C acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on B₄C was highly boron doped, and the hole concentration could be controlled over a wide range of 2 × 10¹³ to 2 × 10¹⁵ cm^-2. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Graphene Quantum Dots for Optical Bioimaging

Graphene quantum dots (GQDs) have shown great potential in bioimaging applications due to their excellent biocompatibility, low cytotoxicity, feasibility for surface functionalization, physiological stability, and tunable fluorescence properties. This Review first introduces the intriguing optical properties of GQDs that are suitable for biological imaging, and is followed by the GQDs' synthetic strategies. The emergent and latest development methods for tuning GQDs' optical properties are further described in detail. The recent advanced applications of GQDs in vitro, particularly in cell imaging, targeted imaging, and theranostic nanoplatform fabrication, are included. The applications of GQDs for in vivo bioimaging are also covered. Finally, the Review is concluded with the challenges and prospectives that face this nascent yet exciting field.

Co2B and Co Nanoparticles Immobilized on the N-B-Doped Carbon Derived from Nano-B4C for Efficient Catalysis of Oxygen Evolution, Hydrogen Evolution, and Oxygen Reduction Reactions

A novel hybrid electrocatalyst of Co₂B and Co nanoparticles immobilized on N-B-doped carbon derived from nano-B₄C (Co₂B/Co/N-B-C/B₄C) is in situ synthesized by pyrolysis of nano-B₄C supporting Co(OH)₂ nanoparticles with melamine. The Co₂B and Co nanoparticles are formed and anchored on the generated N and B codoped carbon and undecomposed B₄C. The hybrid exhibits remarkable catalytic performances toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR)-a very small potential of 1.53 V at 10 mA cm^-2 for the OER and a high catalytic kinetics and superior durability for the ORR-which are superior to the RuO₂ and Pt/C catalyst, respectively. Most impressively, the hybrid delivers a very small potential gap of 710 mV, which is lower than those of most bifunctional electrocatalysts reported. In addition, the hybrid also shows a satisfying hydrogen evolution reaction performance offering a small overpotential of 220 mV at 10 mA cm^-2 and wonderful stability. The excellent trifunctional catalytic performances issue from synergetic effects of Co₂B, metal Co, Co/N-doped carbon, and B self-doped carbon coexisting in the hybrid with good interaction mutually. This work provides a new-type efficient multifunctional catalyst for regenerative fuel cell and overall water-splitting technologies.

Facile Synthesis of Boron-Doped rGO as Cathode Material for High Energy Li-O2 Batteries

To improve the electrochemical performance of the high energy Li-O2 batteries, it is important to design and construct a suitable and effective oxygen-breathing cathode. Herein, a three-dimensional (3D) porous boron-doped reduction graphite oxide (B-rGO) material with a hierarchical structure has been prepared by a facile freeze-drying method. In this design, boric acid as the boron source helps to form the 3D porous structure, owing to its cross-linking and pore-forming function. This architecture facilitates the rapid oxygen diffusion and electrolyte penetration in the electrode. Meanwhile, the boron-oxygen functional groups linking to the carbon surface or edge serve as additional reaction sites to activate the ORR process. It is vital that boron atoms have been doped into the carbon lattices to greatly activate the electrons in the carbon π system, which is beneficial for fast charge under large current densities. Density functional theory calculation demonstrates that B-rGO exhibits much stronger interactions with Li5O6 clusters, so that B-rGO more effectively activates Li-O bonds to decompose Li2O2 during charge than rGO does. With B-rGO as a catalytic substrate, the Li-O2 battery achieves a high discharge capacity and excellent rate capability. Moreover, catalysts could be added into the B-rGO substrate to further lower the overpotential and enhance the cycling performance in future.

Electronic Structure Modification of Ion Implanted Graphene: The Spectroscopic Signatures of p- and n-Type Doping

A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations is used to describe the electronic structure modifications incurred by free-standing graphene through two types of single-atom doping. The N K and C K electron energy loss transitions show the presence of π* bonding states, which are highly localized around the N dopant. In contrast, the B K transition of a single B dopant atom shows an unusual broad asymmetric peak which is the result of delocalized π* states away from the B dopant. The asymmetry of the B K toward higher energies is attributed to highly localized σ* antibonding states. These experimental observations are then interpreted as direct fingerprints of the expected p- and n-type behavior of graphene doped in this fashion, through careful comparison with density functional theory calculations.

Diffusion Bonding of Ceramics by Spark Plasma Sintering (SPS) Apparatus

Alumina, Silicon Carbide, Boron Carbide and Magnesium Aluminate Spinel were directly joined by a Spark Plasma Sintering (SPS) apparatus. The optimal parameters for joining (temperature, holding time and applied pressure) were experimentally found. The joined regions were investigated using scanning electron microscopy (SEM) ultrasonic and micro hardness testing. Alumina, Boron Carbide and Silicon Carbide parts were successfully joined at 1300, 1800 and 1900°C, respectively, for 30 min under argon atmosphere (10- 2 torr) and 40 MPa uniaxial pressure. Spinel parts were successfully joined at 1300°C for 60 min. Micro hardness of the interfacial regions were similar to those of the bonded specimens. The effect of a prolonged heat treatment on the microstructural evolution of the joined regions was investigated and the grain growth mechanism was discussed.