Upcycling fish scales through heating for steganography and Rhodamine B adsorption application.

With increasing population and limited resources, a potential route for improving sustainability is increased reuse of waste materials. By re-looking at wastes, interesting properties and multifunctionalities can be discovered in materials previously explored. Despite years of research on bio-compatible fish scales, there is limited study on the fluorescence property of this abundant waste material. Controlled denaturation of collagen and introduction of defects can serve as a means to transform the fluorescence property of these fish scale wastes while providing more adsorption sites for pollutant removal, turning multifunctional fish scales into a natural steganographic material for transmitting text and images at both the macroscopic and microscopic levels and effectively removing Rhodamine B pollutants (91 % removal) within a short contact time (10 minutes). Our work offers a glimpse into the realm of engineering defects-induced fluorescence in natural material with potential as bio-compatible fluorescence probes while encouraging multidimensional applicability to be established in otherwise overlooked waste resources.

Dynamic Tuning of Moiré Superlattice Morphology by Laser Modification.

In artificial van der Waals (vdW) layered devices, twisting the stacking angle has emerged as an effective strategy to regulate the electronic phases and optical properties of these systems. Along with the twist registry, the lattice reconstruction arising from vdW interlayer interaction has also inspired significant research interests. The control of twist angles is significantly important because the moiré periodicity determines the electron propagation length on the lattice and the interlayer electron-electron interactions. However, the moiré periodicity is hard to be modified after the device has been fabricated. In this work, we have demonstrated that the moiré periodicity can be precisely modulated with a localized laser annealing technique. This is achieved with regulating the interlayer lattice mismatch by the mismatched lattice constant, which originates from the variable density of sulfur vacancy generated during laser modification. The existence of sulfur vacancy is further verified by excitonic emission energy and lifetime in photoluminescence measurements. Furthermore, we also discover that the mismatched lattice constant has the equivalent contribution as the twist angle for determining the lattice mismatch. Theoretical modeling elaborates the moiré-wavelength-dependent energy variations at the interface and mimics the evolution of moiré morphology.

Nanopath-Beacons for Directed Silver Dendrites' Migration across Graphene Oxide Terrain.

With their special hierarchical fractal and highly symmetric formation, silver dendrites have a large surface area and plentiful active sites at edges, which have allowed them to exhibit unique properties ranging from superhydrophobic surfaces to biosensors. Yet, many suggested synthesis processes either require a long reaction time or risk contamination from sacrificial elements. Limited research in directing while enhancing the growth of these silver dendrites also hinders the application of these unique microstructures as site-selective hydrophobicity of surfaces and location-dependent SERS (surface-enhanced Raman spectroscopy). A possible solution to this is to utilize WO3 nanocubes as beacons to accelerate and conduct the growth of these silver dendrites through the electrochemical migration process. These nanocubes effortlessly altered the applied electric field distributed between the electrodes, depending on their orientations and positions. As the silver dendrites branched from the nanocubes, the dendrites themselves further concentrated the electric field to encourage the growth of more loose fractal silver dendrites. The combinatory effect successfully directs the growth of silver dendrites along the concentrated electric field paths. Both changes to the electric field and directed growth of silver dendrites are underscored using Multiphysics COMSOL simulations and time-lapse microscopy. This work provided insight into the possibility of designing microstructures to direct and accelerate the growth of silver dendrites.

Performance Improvement by Ozone Treatment of 2D PdSe2.

Atomic-scale defects in two-dimensional transition metal dichalcogenides (TMDs) often dominate their physical and chemical properties. Introducing defects in a controllable manner can tailor properties of TMDs. For example, chalcogen atom defects in TMDs were reported to trigger phase transition, induce ferromagnetism, and drive superconductivity. However, reported strategies to induce chalcogen atom defects including postgrowth annealing, laser irradiation, or plasma usually require high temperature (such as 500 °C) or cause unwanted structural damage. Here, we demonstrate low-temperature (60 °C) partial surface oxidation in 2D PdSe2 with low disorder and good stability. The combination of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory calculations provide evidence of atomic-scale partial oxidation with both atomic resolution and chemical sensitivity. We also experimentally demonstrate that this controllable oxygen incorporation effectively tailors the electronic, optoelectronic, and catalytic activity of PdSe2. This work provides a pathway toward fine-tuning the physical and chemical properties of 2D TMDs and their applications in nanoelectronics, optoelectronics, and electrocatalysis.

High-Performance, Room Temperature, Ultra-Broadband Photodetectors Based on Air-Stable PdSe2.

Photodetection over a broad spectral range is crucial for optoelectronic applications such as sensing, imaging, and communication. Herein, a high-performance ultra-broadband photodetector based on PdSe2 with unique pentagonal atomic structure is reported. The photodetector responds from visible to mid-infrared range (up to ≈4.05 µm), and operates stably in ambient and at room temperature. It promises improved applications compared to conventional mid-infrared photodetectors. The highest responsivity and external quantum efficiency achieved are 708 A W-1 and 82 700%, respectively, at the wavelength of 1064 nm. Efficient optical absorption beyond 8 µm is observed, indicating that the photodetection range can extend to longer than 4.05 µm. Owing to the low crystalline symmetry of layered PdSe2 , anisotropic properties of the photodetectors are observed. This emerging material shows potential for future infrared optoelectronics and novel devices in which anisotropic properties are desirable.

Nanosurfer flash-mobs: electric-field-choreographed silver migration on graphene oxide.

We report for the first time the ability to direct and control the migration path of silver nanoparticles across graphene oxide (GO). With the help of a focused laser beam, we demonstrated choreographed nanoparticle assembly on GO via a directed electric-field. Silver migration and the resultant dendrite formation on GO were characterized through electrical testing coupled with fluorescence microscopy. The proposed mechanism for silver migration in GO involves the interlayer water between GO sheets serving as the electrolyte for the electrochemical process. This interlayer water facilitates the disappearance of dendrites through oxidation and dissolution into the water. Furthermore, we demonstrate that the shape of the formed Ag dendrites can be controlled by a combination of an applied electric field and patterned regions of a reduced GO film created by a focused laser beam. This paves the way for an alternative low-cost silver nanoparticle assembly method requiring only a low-powered laser and low voltage.

Laser assisted blending of Ag nanoparticles in an alumina veil: a highly fluorescent hybrid.

We report a functional hybrid made of silver nanoparticles (AgNPs) embedded in an amorphous aluminium oxide (alumina) film. This laser-initiated process allows formation of AgNPs and amorphous alumina in localized regions defined by the scanning laser beam. Due to metal enhanced fluorescence, this hybrid exhibits strong blue fluorescence emission under ultraviolet excitation. Upon irradiating with electrons at dosages of 1 to 20 mC cm-2, AgNPs become more metallic while the Al film is further oxidised. As a result, the fluorescing property is intensified. Using a hybrid irradiated with 10 mC cm-2, the electronic conductivity of the sample is improved by 11.5 times compared to that of the as-synthesized hybrid film. Excitation by UV light on the sample results in an increase in the detected current of nearly 29 times. Given that the electron beam patterned message is selectively visible only under UV or blue light irradiation, this hybrid film is thus a possible platform for steganographic transmission.

Hybrid Bilayer WSe2 -CH3 NH3 PbI3 Organolead Halide Perovskite as a High-Performance Photodetector.

A high-performance 2D photodetector based on a bilayer structure comprising a WSe2 monolayer and CH3 NH3 PbI3 organolead halide perovskite is reported. High performance is realized by modification of the WSe2 monolayer with laser healing and perovskite functionalization. After modification, the output of the device was three orders of magnitude better than the pristine device; the performance is superior to that of most of the 2D photodetectors based on transition-metal-dichalcogenides (TMDs). This result indicates that combinatory TMDs-halide perovskite hybrids can be promising building blocks in optoelectronics.

Micro-dressing of a carbon nanotube array with MoS2 gauze.

Few-layer MoS2 film has been successfully assembled over an array of CNTs. Using different focused laser beams with different wavelengths, site selective patterning of either the MoS2 film or the supporting CNT array is achieved. This paves the way for applications and investigations into the fundamental properties of the hybrid MoS2/CNT material with a controlled architecture. Through Raman mapping, straining and electron doping of the MoS2 film as a result of interaction with the supporting CNT array are detected. The role of the MoS2 film was further emphasized with a lower work function being detected from Ultra-violet Photoelectron Spectrsocopy (UPS) measurements of the hybrid material, compared to the CNT array. The effect of the changes in the work function was illustrated through the optoelectronic behavior of the hybrid material. At 0 V, 3.49 nA of current is measured upon illuminating the sample with a broad laser beam emitting laser light with a wavelength of 532 nm. With a strong response to external irradiation of different wavelengths, and changes to the power of the excitation source, the hybrid material has shown potential for applications in optoelectronic devices.

Laser modified ZnO/CdSSe core-shell nanowire arrays for Micro-Steganography and improved photoconduction.

Arrays of ZnO/CdSSe core/shell nanowires with shells of tunable band gaps represent a class of interesting hybrid nanomaterials with unique optical and photoelectrical properties due to their type II heterojunctions and chemical compositions. In this work, we demonstrate that direct focused laser beam irradiation is able to achieve localized modification of the hybrid structure and chemical composition of the nanowire arrays. As a result, the photoresponsivity of the laser modified hybrid is improved by a factor of ~3. A 3D photodetector with improved performance is demonstrated using laser modified nanowire arrays overlaid with monolayer graphene as the top electrode. Finally, by controlling the power of the scanning focused laser beam, micropatterns with different fluorescence emissions are created on a substrate covered with nanowire arrays. Such a pattern is not apparent when imaged under normal optical microscopy but the pattern becomes readily revealed under fluorescence microscopy i.e. a form of Micro-Steganography is achieved.