Welcome to Nanomaterials Research Lab!!!

We are a group of researchers who delve into the studies of the physical properties of a wide variety of nanostructured materials, aiming to understand the dependence of the physical properties on the morphology, chemical stoichiometry, surface effect and nanostructure of the nanomaterials created. 

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Research Highlights:

2021: Scintillating zinc oxide ensconced in a carbon nanotube forest engineered by laser micro-welding

" Scintillating zinc oxide ensconced in a carbon nanotube forest engineered by laser micro-welding", Applied Surface Science, 562, 150231, 2020

Herein, we report defect-introduction via focused-laser-beam (FLB) modification to introduce carbon defects into zinc oxide (ZnO) thin film. The approach begins with a carbon nanotube (CNT) array covered by a thin layer of sputtered Zn on top of the array. When FLB irradiates the covered CNT array under ambient conditions, effective laser energy absorption by CNT results in ZnOCNT nanohybrid formation, it also enables site-selective transformation to be achieved. By adjusting the laser power, the degree of carbon incorporation into the pristine Zn system can be tuned and this exerts some degree of control over the fluorescent properties of the nanohybrid. Generating a higher defect density increases the intensity and changes the wavelength of the fluorescence emitted by ZnO under ultraviolet (UV) excitation and enhances its field emission properties. In particular, the turn-on electric field (ETO) of the nanohybrid decreases. A lower ETO reduces the probability of arc formation, a significant problem currently undermining the industrial feasibility of field emission displays (FED). Electron emission from these samples can be enhanced by exciting the laser-treated sample with an external laser source. The normalised current produced increases by as much as 6µA/(mW/mm2) when the sample is excited by a 405 nm monochromatic laser.

2020: Electrically Tailored Metachrosis in ZnO-C Nanowires

"Electrically Tailored Metachrosis in ZnO-C Nanowires", ACSNano, 14, 5845, 2020

Carbon incorporated zinc oxide (ZnO:C) nanowires (NWs) are found to be remarkable morphing NWs. We show that the physical properties of ZnO:C NWs are engineered via the passage of electric current to produce fluorescence differences and negative differential resistance as well as electroluminescence. When a ZnO:C NW is subjected to an applied voltage bias and under ultraviolet (UV) excitation, electron–hole separation due to the voltage biasing suppresses their fluorescence at low voltages. At medium voltages, the NW exhibits metastable chemical changes that translates to tunable and reversible optical alterations akin to metachrosis found in chameleons. Concurrently, the NW displays electrical alterations with negative differential resistance behaviors. At higher voltages, these NWs are permanently modified with distinct heterogeneous chemical stoichiometry, fluorescence, and electronic properties. Such heterogeneity within the NW allows for emergence of junctions capable of electroluminescence.

2020: Heteromoiré Engineering on Magnetic Bloch Transport in Twisted Graphene Superlattices

"Heteromoiré Engineering on Magnetic Bloch Transport in Twisted Graphene Superlattices", Nano Letters, 20, 7572, 2020

Localized electrons subject to applied magnetic fields can restart to propagate freely through the lattice in delocalized magnetic Bloch states (MBSs) when the lattice periodicity is commensurate with the magnetic length. Twisted graphene superlattices with moiré wavelength tunability enable experimental access to the unique delocalization in a controllable fashion. Here, we report the observation and characterization of high-temperature Brown–Zak (BZ) oscillations which come in two types, 1/B and B periodicity, originating from the generation of integer and fractional MBSs, in the twisted bilayer and trilayer graphene superlattices, respectively. Coexisting periodic-in-1/B oscillations assigned to different moiré wavelengths are dramatically observed in small-angle twisted bilayer graphene, which may arise from angle-disorder-induced in-plane heteromoiré superlattices. Moreover, the vertical stacking of heteromoiré supercells in double-twisted trilayer graphene results in a mega-sized superlattice. The exotic superlattice contributes to the periodic-in-B oscillation and dominates the magnetic Bloch transport.

2020: Band Nesting Bypass in WS2 Monolayers via Förster Resonance Energy Transfer

"Band Nesting Bypass in WS2 Monolayers via Förster Resonance Energy Transfer", ACS Nano, 14, 5946, 2020

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) have attracted intensive interest due to the direct-band-gap transition in the monolayer form, positioning them as potential next-generation materials for optoelectronic or photonic devices. However, the band-nested suppression of the recombination efficiency at higher excitation energies limits the ability to locally control and manipulate the photoluminescence of WS2 for multifunctional applications. In this work, we exploit an energy transfer method to modulate the fluorescence properties of TMDs under a larger excitation range spanning from UV to visible light. Self-assembled lanthanide (Ln)/TMD hybrids have been designed based on a low-cost and highly efficient solution-processed approach. The emission energy from Ln3+ sources can be effectively transferred to the TMD monolayers under low power exposure (0.13 mW) at room temperature, activating the characteristic monolayer fluorescence in place of Ln3+ emission signatures. The Ln/TMDs photonics can potentially tune the excitation of TMDs to provide variable yet controllable emissions. This provides a solution to the suppression of direct exciton recombination in monolayer TMDs at the band nesting resonant energy region. Our work on such Ln/TMD systems would overcome the limited excitation energy range in TMDs and extend their functionalities for optoelectronic or photonic applications.

2020: Unlocking the potential of carbon incorporated silver-silver molybdate nanowire with light

"Unlocking the potential of carbon incorporated silver-silver molybdate nanowire with light", Applied Materials Today, 20, 100670, 2020

We present a novel form of Ag2MoO4-based hybrid nanowire (NW) with a few remarkable attributes. Firstly, the NW is embedded and decorated with Ag NPs. Secondly, carbon atoms are intentionally incorporated within the matrix of the NW. Thirdly the hybrid nanowires are created via a facile process. Namely, focused laser micropatterning of Ag NPs on GO film as seeding sites and subsequent formation of the hybrid NWs by placing the patterned GO films on heated Mo foil on a hotplate. This unique process resulted in the production of hybrid Ag/Ag2MoO4 NWs that emit unique red fluorescence emission. And finally remarkable photodoping effect is observed from a single strand of optically tuned carbon-doped silver nanoparticles embedded silver molybdate nanowire. We demonstrate applications of these hybrid NWs as micro-display and time limiting, logic components for secure transmission of messages.

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