Xinliang Zheng

Hydrophobic graphene nanosheets decorated by monodispersed superparamagnetic Fe3O4 nanocrystals as synergistic electromagnetic wave absorbers

The comprehension of the interactions between the building blocks in hybrids can give us an insight into the design and application of highly efficient electromagnetic wave absorption materials. Herein, we report a facile in situ thermal decomposition route for the fabrication of superparamagnetic Fe3O4 nanocrystals anchored on hydrophobic graphene nanosheets as synergistic electromagnetic wave absorbers. The microstructures and interactions of the Fe3O4–graphene hybrids are systematically investigated, and the results suggest that the Fe3O4 nanocrystals are uniformly decorated and chemically bonded on the surface of graphene nanosheets without obvious conglomeration or large vacancies. The Fe3O4–graphene hybrids show hydrophobic and superparamagnetic characteristics. Combing the benefits of superparamagnetic Fe3O4 nanocrystals and electrically conducting graphene, the Fe3O4–graphene hybrids show a maximum reflection loss (RL) of −40 dB at 6.8 GHz with a matching thickness of 4.5 mm, and the effective absorption bandwidth (RL < −10 dB) is 4.6–18 GHz with an absorber thickness of only 2–5 mm. However, due to the lack of dielectric loss, only a weak RL of −5 dB is obtained in bare Fe3O4 nanocrystals. The remarkably enhanced electromagnetic wave absorption properties of the Fe3O4–graphene hybrids are owing to effective impedance matching and synergistic interaction. Moreover, compared with other reported graphene-based electromagnetic wave absorption materials, the hydrophobic Fe3O4–graphene hybrids prepared in this work are considered to be more stable and suitable to be applied in some particular environmental conditions, such as rain.

Graphene as broadband terahertz antireflection coating

We examined the potential of stacked multilayer graphene as broadband terahertz (THz) antireflection coating based on the impedance matching effect in experiment and theory. The reflected pulses from the quartz and silicon substrates were observed to change with the layer number and doping concentration of the graphene coating. Remarkable broadband impedance matching was achieved due to optimized THz conductivity. Theoretical analysis based on Drude model and thin film Fresnel coefficients have been used to explain the experimental phenomena, which indicated the shift of Fermi level caused by chemical doping. This work paves the way for graphene-based broadband THz antireflection coating.

Solution-processable reduced graphene oxide films as broadband terahertz wave impedance matching layers

The potential of solution-processable reduced graphene oxide (rGO) films as wave impedance matching layers has been examined in a broad terahertz (THz) spectral bandwidth. The THz sheet conductivities of rGO films measured by THz time-domain spectroscopy were observed to be tunable and sensitive to the film thicknesses and reduction degrees, which can be efficiently controlled by our solution-processable fabrication method. Remarkable broadband impedance matching was achieved with a suitable rGO film, as shown by the suppression of the internal reflected THz pulses from the substrate in the spectra. The underlying mechanisms have been revealed both experimentally and theoretically. This work paves the way for developing rGO-based broadband and large-scale anti-reflection layers for THz components.

Passively Mode-Locked Radially Polarized Nd-Doped Yttrium Aluminum Garnet Laser Based on Graphene-Based Saturable Absorber

We report the first demonstration of a graphene-mode-locked, radially polarized Nd-doped yttrium aluminum garnet (Nd:YAG) laser, generating ~15.6 ps pulses with output power up to 2 W. The peak wavelength is at ~1064 nm with a pulse repetition rate of 112 MHz. The maximum output pulse energy and peak power are 18 nJ and 1.08 kW respectively. Our radially polarized all-solid-state laser is a simple and low-cost optical source for a range of applications, such as optical trapping and high-resolution microscopy.

High repetition rate Q-switched radially polarized laser with a graphene-based output coupler

We demonstrate a Q-switched radially polarized all-solid-state laser by transferring a graphene film directly onto an output coupler. The laser generates Q-switched radially polarized beam (QRPB) with a pulse width of 192 ns and 2.7 W average output power. The corresponding single pulse energy is up to 16.2 μJ with a high repetition rate of 167 kHz. The M2 factor and the polarization purity are ∼2.1 and 96%, respectively. Our QRPB source is a simple and low-cost source for a variety of applications, such as industrial material processing, optical trapping, and microscopy.

Synthesis and loading-dependent characteristics of nitrogen-doped graphene foam/carbon nanotube/manganese oxide ternary composite electrodes for high performance supercapacitors

The ternary composite electrodes, nitrogen-doped graphene foam/carbon nanotube/manganese dioxide (NGF/CNT/MnO2), have been successfully fabricated via chemical vapor deposition (CVD) and facile hydrothermal method. The morphologies of the MnO2 nanoflakes presented the loading-dependent characteristics and the nanoflake thickness could also be tuned by MnO2 mass loading in the fabrication process. The correlation between their morphology and electrochemical performance was systematically investigated by controlling MnO2 mass loading in the ternary composite electrodes. The electrochemical properties of the flexible ternary electrode (MnO2 mass loading of 70%) exhibited a high areal capacitance of 3.03F/cm2 and a high specific capacitance of 284F/g at the scan rate of 2mV/s. Moreover, it was interesting to find that the capacitance of the NGF/CNT/MnO2 composite electrodes showed a 51.6% increase after 15,000 cycles. The gradual increase in specific capacitance was due to the formation of defective regions in the MnO2 nanostructures during the electrochemical cycles of the electrodes, which further resulted in increased porosity, surface area, and consequently increased electrochemical capacity. This work demonstrates a rarely reported conclusion about loading-dependent characteristics for the NGF/CNT/MnO2 ternary composite electrodes. It will bring new perspectives on designing novel ternary or multi-structure for various energy storage applications.

One-pot, template-free synthesis of hydrophobic single-crystalline La(OH)3 nanowires with tunable size and their d0 ferromagnetic properties

Hydrophobic single-crystalline La(OH)3 nanowires with tunable size have been successfully fabricated by a facile one-pot liquid–solid-solution (LSS) assisted hydrothermal method without any template and their morphology, chemistry and crystal structure were characterized on the nanoscale. Their average diameter and length strongly depend on the reaction time and the selection of solvents, which is due to the Ostwald ripening and oriented attachment mechanisms. XRD patterns and SAED analysis of numerous nanowires show that the La(OH)3 nanowires have a pure hexagonal structure without any impurities. TEM image and HAADF-STEM element mapping analysis indicate that the La(OH)3 nanowires have a uniform size, smooth surface and pure chemical phase. HRTEM images and CBED patterns of individual La(OH)3 nanowires suggest that each nanowire is single crystalline. Magnetic measurements reveal that the La(OH)3 nanowires show a d0 room-temperature ferromagnetic behavior. This study highlights the basic morphological, chemical and structural information for La(OH)3 nanowires, which is critical for their applications in nanodevices and nanoelectronics.

Anomalous Ferromagnetism and Electron Microscopy Characterization of High-Quality Neodymium Oxychlorides Nanocrystals

High-quality neodymium oxychlorides nanocrystals with cubic shape were synthesized by a nonhydrolytic thermolysis route. The morphology and crystal structure of the neodymium oxychlorides nanocubes were characterized by transmission electron microscopy at the nanoscale. Transmission electron microscope (TEM) image shows that the neodymium oxychlorides nanocrystals are nearly monodispersed with cube-like shape. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns of numerous neodymium oxychlorides nanocubes suggest a pure crystal phase with tetragonal PbFCl matlockite structure. HRTEM image of individual neodymium oxychlorides nanocubes indicate that each nanocubes have a single-crystalline nature with high quality. Unlike the anti-ferromagnetism of the bulk, the neodymium oxychlorides nanocubes show clearly anomalous ferromagnetic characteristic at room temperature. This finding provides a new platform for the exploration of diluted magnetic semiconductors, rare earth-based nanomaterials and so on.

Magnetic Superatoms Based Spintronics: A DFT Study

A kind of magnetic superatom is designed by doping transition metal element into Na8 clusters. Their electronic structure and spin-polarized transport properties are investigated using the first principles method. Our calculation shows that electrode materials have notable influence on the superatoms’ geometrical stability. Lithium lead is a good choice. Among all the superatoms, TiNa8 and NiNa8 give the highest transmission spin polarization (TSP), for negative and positive values, respectively. Relation between TSP and the magnetic moment of isolated superatom may lead to some promising designs in molecular spintronics devices.