Zahir Muhammad

Stable 1T-MoSe2 and Carbon Nanotube Hybridized Flexible Film: Binder-Free and High-Performance Li-Ion Anode

Two-dimensional stable metallic 1T-MoSe2 with expanded interlayer spacing of 10.0 Å in situ grown on SWCNTs film is fabricated via a one-step solvothermal method. Combined with X-ray absorption near-edge structures, our characterization reveals that such 1T-MoSe2 and single-walled carbon nanotubes (abbreviated as 1T-MoSe2/SWCNTs) hybridized structure can provide strong electrical and chemical coupling between 1T-MoSe2 nanosheets and SWCNT film in a form of C-O-Mo bonding, which significantly benefits a high-efficiency electron/ion transport pathway and structural stability, thus directly enabling high-performance lithium storage properties. In particular, as a flexible and binder-free Li-ion anode, the 1T-MoSe2/SWCNTs electrode exhibits excellent rate capacity, which delivers a capacity of 630 mAh/g at 3000 mA/g. Meanwhile, the strong C-O-Mo bonding of 1T-MoSe2/SWCNTs accommodates volume alteration during the repeated charge/discharge process, which gives rise to 89% capacity retention and a capacity of 971 mAh/g at 300 mA/g after 100 cycles. This synthetic route of a multifunctional MoSe2/SWCNTs hybrid might be extended to fabricate other 2D layer-based flexible and light electrodes for various applications such as electronics, optics, and catalysts.

A Ternary Alloy Substrate to Synthesize Monolayer Graphene with Liquid Carbon Precursor

Here we demonstrate a ternary Cu2NiZn alloy substrate for controllably synthesizing monolayer graphene using a liquid carbon precursor cyclohexane via a facile CVD route. In contrast with elemental metal or bimetal substrates, the alloy-induced synergistic effects that provide an ideal metallic platform for much easier dehydrogenation of hydrocarbon molecules, more reasonable strength of adsorption energy of carbon monomer on surface and lower formation energies of carbon chains, largely renders the success growth of monolayer graphene with higher electrical mobility and lower defects. The growth mechanism is systemically investigated by our DFT calculations. This study provides a selective route for realizing high-quality graphene monolayer via a scalable synthetic method by using economic liquid carbon supplies and multialloy metal substrates.

Synthesis of Ni9S8/MoS2 heterocatalyst for Enhanced Hydrogen Evolution Reaction

We demonstrate a heterostructure Ni9S8/MoS2 hybrid with tight interface synthesized via an improved hydrothermal method. As compared to pure MoS2, the increased surface area and the shorten charge transport pathway in the layered hybrid significantly promote the photocatalytic efficiency for hydrogen evolution reaction (HER). In particularly, the optimized Ni9S8/MoS2 hybrid with 20 wt % Ni9S8 exhibits the highest photocatalytic activity with HER value of 406 μmolg-1h-1, which is enhanced by 70% compared to that of pure MoS2 nanosheets (285.0 μmolg-1h-1). Moreover, the value is 4 times more than the commercial MoS2 (92.0 μmolg-1h-1), indicating the high potential of the hybrid in the catalytic fields.

Ferromagnetism in CVT Grown Tungsten Diselenide Single Crystals with Nickel Doping

Two dimensional (2D) single crystal layered transition materials have had extensive consideration owing to their interesting magnetic properties, originating from their lattices and strong spin-orbit coupling, which make them of vital importance for spintronic applications. Herein, we present synthesis of a highly crystalline tungsten diselenide layered single crystal grown by chemical vapor transport technique and doped with nickel (Ni) to tailor its magnetic properties. The pristine WSe2 single crystal and Ni-doped crystal were characterized and analyzed for magnetic properties using both experimental and computational aspects. It was found that the magnetic behavior of the 2D layered WSe2 crystal changed from diamagnetic to ferromagnetic after Ni-doping at all tested temperatures. Moreover, first principle density functional theory (DFT) calculations further confirmed the origin of room temperature ferromagnetism of Ni-doped WSe2, where the d-orbitals of the doped Ni atom promoted the spin moment and thus largely contributed to the magnetism change in the 2D layered material.

Active {010} facet-exposed Cu2MoS4 nanotube as high-efficiency photocatalyst

Rational design and facet-engineering of nanocrystal is an effective strategy to optimize the catalytic performance of abundant and economic semiconductor-based photocatalysts. In this study, we demonstrate a novel ternary Cu2MoS4 nanotube with the {010} facet exposed, synthesized via a hydrothermal method. Compared with two-dimensional Cu2MoS4 nanosheet with the {001} facet exposed, this one-dimensional nanotube exhibits highly enhanced performance of photodegradation and water splitting. Both theoretical calculations and experimental results suggest that the conduction band minimum (CBM) of the {010} facet crystal shows lower potential than that of the {001} facet. In particular, the up-shifted CBM in Cu2MoS4 nanotube is significantly beneficial for the absorption of dye molecules and reduction of H+ to H2. These results may open a new route for realizing high-efficiency photocatalysts based on Cu2MX4 by facet engineering.

Tuning the composition of ternary Bi2Se3xTe3(1-x) nanoplates and their Raman scattering investigations

We present the composition engineering and Raman scattering study of Bi2Se3xTe3(1-x) nanoplates that were synthesized by chemical vapor deposition method using different substrates, including fluorophlogopite mica, SiO2/Si. The characterizations revealed high crystallinity and layered-structure in the ternary Bi2Se3xTe3(1-x) products. Raman spectra of Bi2Se3xTe3(1-x) ranging from 80-200 cm-1 as a function of different Se-doping levels shows that intrinsic Raman peaks of Bi2Se3xTe3(1-x) nanoplates shift to higher frequency as the ratio of doped-Se increasing. The discontinuity of Raman peaks was found and discussed.

Electron doping induced semiconductor to metal transitions in ZrSe 2 layers via copper atomic intercalation

Atomic intercalation in two-dimensional (2D) layered materials can be used to engineer the electronic structure at the atomic scale and generate tuneable physical and chemical properties which are quite distinct in comparison with the pristine material. Among them, electron-doped engineering induced by intercalation is an efficient route to modulate electronic states in 2D layers. Herein, we demonstrate a semiconducting to metallic phase transition in zirconium diselenide (ZrSe2) single crystals via controllable incorporation of copper (Cu) atoms. Our angle resolved photoemission spectroscopy (ARPES) measurements and first-principles density functional theory (DFT) calculations clearly revealed the emergence of conduction band dispersion at the M/L point of the Brillouin zone due to Cu-induced electron doping in ZrSe2 interlayers. Moreover, electrical measurements in ZrSe2 revealed semiconducting behavior, while the Cu-intercalated ZrSe2 exhibited a linear current–voltage curve with metallic character. The atomic intercalation approach may have high potential for realizing transparent electron-doping systems for many specific 2D-based nanoelectronic applications.

Magnetic Isotropy/Anisotropy in Layered Metal Phosphorous Trichalcogenide MPS3 (M = Mn, Fe)Single Crystals

Despite the fact that two-dimensional layered magnetic materials hold immense potential applications in the field of spintronic devices, tunable magnetism is still a challenge due to the lack of controllable synthesis. Herein, high-quality single crystals MPS3 (M= Mn, Fe) of millimeter size were synthesized through the chemical vapor transport method. After systemic structural characterizations, magnetic properties were studied on the bulk MPS3 layers through experiments, along with first principle theoretical calculations. The susceptibilities as well as the EPR results evidently revealed unique isotropic and anisotropic behavior in MnPS3 and FePS3 crystals, respectively. It is worth noting that both of these materials show antiferromagnetic states at measured temperatures. The estimated antiferromagnetic transition temperature is 78 K for bulk MnPS3 and 123 K for FePS3 crystals. The spin polarized density functional theory calculations confirmed that the band gap of the antiferromagnetic states could be generated owing to asymmetric response all over the energy range. The ferromagnetic state in MnPS3 and FePS3 is less stable as compared to the antiferromagnetic state, resulting in antiferromagnetic behavior. Additionally, frequency-dependent dielectric functions for parallel and perpendicular electric field component vectors, along with the absorption properties of MPS3, are thoroughly investigated.

Low temperature ferromagnetic properties of CdS and CdTe thin films

The magnetic property in a material is induced by the unpaired electrons. This can occur due to defect states which can enhance the magnetic moment and the spin polarization. In this report, CdS and CdTe thin films are grown on FTO glass substrates by chemical bath deposition and close-spaced sublimation, respectively. The magnetic properties, which are introduced from oxygen states, are found in CdS and CdTe thin films. From the hysteresis loop of magnetic moment it is revealed that CdS and CdTe thin films have different kinds of magnetic moments at different temperatures. The M–H curves indicate that from 100 K to 350 K, CdS and CdTe thin films show paramagnetism and diamagnetism, respectively. A superparamagnetic or a weakly ferromagnetic response is found at 5 K. It is also observed from ZFC/FC curves that magnetic moments decrease with temperature increasing. Spin polarized density functional calculation for spin magnetic moment is also carried out.

Band-Limited Filters and Bragg Reflectors in Perturbed Defect Nanostructures of Chiral Sculptured Thin Films

Sculptured thin films (STFs) are engineered films having tailored morphology and high porosity. Henceforth, we can elicit desired optical responses upon light excitation in these films. The oblique deposition of the nanocolumns and the resulting anisotropic properties have been discovered over the past decade. Their discovery has lead to unique and predictable optical, mechanical, electrical, magnetic, thermal, and biological properties. To study the optical response of such STFs, we introduced a central defect in a perturbed chiral STF (CSTF), which transmits light of one circular polarization state and reflects the other in a spectral Bragg regime. The perturbed CSTF reflects light of both circular polarization states in the Bragg regime if the amplitude of modulation of vapor incident angle increases. A structurally chiral layer defect or either central twist defect in a perturbed matched CSTF fabricated a narrow bandpass (ultranarrow bandstop filter) and Bragg reflectors depending upon the thickness and periods of these nanostructures. However, both the ultranarrow bandstop filter and Bragg reflectors have become polarization insensitive by the appropriate modulation of the tilt nanohelixes of perturbed CSTFs. Moreover, simulation revealed that the polarization-insensitive Bragg mirrors, laser mirror, and Bragg reflector were fabricated using such CSTF structures having structural defect. These structural nanomaterials are very tolerant when the amplitude of modulation of vapor incident angle is sufficiently large. It has been also examined that different STFs structures of different refractive indices and porosity are fabricated by changing deposition angle and angle of inclination through modulation and glancing angle deposition.