T graphene, a two-dimensional carbon allotrope with tetrarings, is investigated by first-principles calculations. We demonstrate that buckled T graphene has Dirac-like fermions and a high Fermi velocity similar to graphene even though it has nonequivalent bonds and possesses no hexagonal honeycomb structure. New features of the linear dispersions that are different from graphene are revealed. π and π* bands and the two comprising sublattices are the key factors for the emergence of Dirac-like fermions. T graphene and its two types of nanoribbon are expected to possess additional properties over graphene due to its different band structure.

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Temperature-dependent Raman scattering is performed on unsupported vertical graphene sheets, which are approximate to free graphene without supporting the substrate. Here the observed G peak line shift with temperature is completely consistent with the theoretical prediction based on the first-principles calculation on free graphene, and our result is helpful to understand intrinsic anharmonic phonon characteristics of free graphene and the divergence on the G peak line shift with temperature. However, the observed linewidth variation is different from the prediction. To reveal the origins, a simplified Klemens model is used, and the dominating anharmonic phonon scattering mechanism is explored. In addition, line shift and linewidth variations of D and 2D peaks of the graphene sheets with temperature are revealed, and the possible mechanisms dominating the results are discussed.

Interfacial integration of a shape-engineered electrode with a strongly bonded current collector is the key for minimizing both ionic and electronic resistance and then developing high-power supercapacitors. Herein, we demonstrated the construction of high-power micro-supercapacitors (VG-MSCs) based on high-density unidirectional arrays of vertically aligned graphene (VG) nanosheets, derived from a thermally decomposed SiC substrate. The as-grown VG arrays showed a standing basal plane orientation grown on a (0001̅) SiC substrate, tailored thickness (3.5-28 μm), high-density structurally ordering alignment of graphene consisting of 1-5 layers, vertically oriented edges, open intersheet channels, high electrical conductivity (192 S cm), and strong bonding of the VG edges to the SiC substrate. As a result, the demonstrated VG-MSCs displayed a high areal capacitance of ∼7.3 mF cm and a fast frequency response with a short time constant of 9 ms. Furthermore, VG-MSCs in both an aqueous polymer gel electrolyte and nonaqueous ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate operated well at high scan rates of up to 200 V s. More importantly, VG-MSCs offered a high power density of ∼15 W cm in gel electrolyte and ∼61 W cm in ionic liquid. Therefore, this strategy of producing high-density unidirectional VG nanosheets directly bonded on a SiC current collector demonstrated the feasibility of manufacturing high-power compact supercapacitors.

Intrinsic diamagnetism of graphene is studied both theoretically and experimentally, to unravel the magnetic response of chiral massless fermions. Comprehensive formulas predicting the variation of graphene magnetization with magnetic field and temperature are developed. Graphene magnetization M at low temperatures is particularly large and M ∝ − √ B, intrinsically different from normal materials. The quantum Berry phase of π and linear energy dispersion are responsible for this intriguing macroscopic behavior. The temperature dependence of magnetization is successfully formulated by a Langevin-like function. The de Haas-van Alphen oscillations are predicted in the case of doping. Correspondingly, experiments at different temperatures are conducted on highly pure, mass-produced graphene flakes derived from SiC single crystals, which exhibit very strong diamagnetism. The measured results agree well with the theoretical ones in both magnitude and trend.

Double-layer graphene epitaxially grown on silicon carbide was used to Q-switch a Tm:YAG laser. Stable Q-switched laser pulses at the central wavelength of 2.01 μm were obtained. The maximum average output power, pulse repetition rate, and single pulse energy were 38 mW, 27.9 kHz, and 1.74 μJ, respectively. Our results illustrate that graphene can be used as a saturable absorber at the 2 μm region.

Tantalum arsenide is experimentally verified as a Weyl semimetal recently. However, it is difficult to grow large TaAs single crystals due to the decomposition prior to reaching its melting point. Here we report an improved chemical vapor transport method using iodine as an agent to get large-size, high-quality TaAs single crystals up to 1 cm. X-ray diffraction confirmed that they are tetragonal TaAs. Specific heat of TaAs was measured from 2 K to room temperature, and hence the entropy and enthalpy were obtained, which are helpful in designing the optimal growth conditions. The as-grown crystals exhibit polyhedral morphology consisting of {101}, {001}, {103}, and {112} facets. The key points in crystal growth include using tantalum in the form of foils instead of powder as the starting material, tilting ampule to enhance convections and controlling the concentration of agent iodine. These measures should be applicable to the growth of other transition metal arsenides and phosphides.

Graphene covered SiC powder (GCSP) has been fabricated by well established method of high temperature thermal decomposition of SiC. The structural and photocatalystic characteristics of the prepared GCSP were investigated and compared with that of the pristine SiC powder. Under UV illumination, more than 100% enhancement in photocatalystic activity is achieved in degradation of Rhodamine B (Rh B) by GCSP catalyst than by pristine SiC powder. The possible mechanisms underlining the observed results are discussed. The results suggested that GCSP as a composite of graphene based material has great potential for use as a high performance photocatalyst.