Mojib Saei

Crystalline Nanojoining Silver Nanowire Percolated Networks on Flexible Substrate

Optoelectronic performance of metal nanowire networks are dominated by junction microstructure and network configuration. Although metal nanowire printings, such as silver nanowires (AgNWs) or AgNWs/semiconductor oxide bilayer, have great potential to replace traditional ITO, efficient and selective nanoscale integration of nanowires is still challenging owing to high cross nanowire junction resistance. Herein, pulsed laser irradiation under controlled conditions is used to generate local crystalline nanojoining of AgNWs without affecting other regions of the network, resulting in significantly improved optoelectronic performance. The method, laser-induced plasmonic welding (LPW), can be applied to roll-to-roll printed AgNWs percolating networks on PET substrate. First principle simulations and experimental characterizations reveal the mechanism of crystalline nanojoining originated from thermal activated isolated metal atom flow over nanowire junctions. Molecular dynamic simulation results show an angle-dependent recrystallization process during LPW. The excellent optoelectronic performance of AgNW/PET has achieved Rs ∼ 5 Ω/sq at high transparency (91% @λ = 550 nm).

Super-strengthening and stabilizing with carbon nanotube harnessed high density nanotwins in metals by shock loading

CNTs reinforced metal composites has great potential due to their superior properties, such as light weight, high strength, low thermal expansion and high thermal conductivity. The current strengthening mechanisms of CNT/metal composite mainly rely on CNTs’ interaction with dislocations and CNT’s intrinsic high strength. Here we demonstrated that laser shock loading the CNT/metal composite results in high density nanotwins, stacking fault, dislocation around the CNT/metal interface. The composites exhibit enhanced strength with excellent stability. The results are interpreted by both molecular dynamics simulation and experiments. It is found the shock wave interaction with CNTs induces a stress field, much higher than the applied shock pressure, surrounding the CNT/metal interface. As a result, nanotwins were nucleated under a shock pressure much lower than the critical values to generate twins in metals. This hybrid unique nanostructure not only enhances the strength, but also stabilize the strength, as the nanotwin boundaries around the CNTs help pin the dislocation movement.

Large Scale Laser Crystallization of Solution-based Alumina-doped Zinc Oxide (AZO) Nanoinks for Highly Transparent Conductive Electrode.

A new method combining aqueous solution printing with UV Laser crystallization (UVLC) and post annealing is developed to deposit highly transparent and conductive Aluminum doped Zinc Oxide (AZO) films. This technique is able to rapidly produce large area AZO films with better structural and optoelectronic properties than most high vacuum deposition, suggesting a potential large-scale manufacturing technique. The optoelectronic performance improvement attributes to UVLC and forming gas annealing (FMG) induced grain boundary density decrease and electron traps passivation at grain boundaries. The physical model and computational simulation developed in this work could be applied to thermal treatment of many other metal oxide films.

Superplastic Formation of Metal Nanostructure Arrays with Ultrafine Gaps

Laser shock compression of plasmonic nanoarrays results in ultrafine tunable line-gaps at sub-10 nm scale by collaborative superplastic flow. From molecular dynamics analysis, the metal nanostructures change from crystalline to liquid-like metals, expanding quickly but never fusing together, even when they are very close. This technique enables good tunability of surface plasmon resonances and significantly enhanced local fields.

Dry Etching with Nanoparticles: Formation of High Aspect-Ratio Pores and Channels Using Magnetic Gold Nanoclusters

Methods for generating nanopores in substrates typically involve one or more wet-etching steps. Here a fundamentally different approach to produce nanopores in sheet substrates under dry, ambient conditions, using nanosecond-pulsed laser irradiation and magnetic gold nanoclusters (MGNCs) as the etching agents is described. Thermoplastic films (50-75 µm thickness) are coated with MGNCs then exposed to laser pulses with a coaxial magnetic field gradient, resulting in high-aspect ratio channels with tapered cross sections as characterized by confocal fluorescence tomography. The dry-etching process is applicable to a wide variety of substrates ranging from fluoropolymers to borosilicate glass, with etch rates in excess of 1 µm s-1 . Finite-element modeling suggests that the absorption of laser pulses by MGNCs can produce temperature spikes of nearly 1000 °C, which is sufficient for generating photoacoustic responses that can drive particles into the medium, guided by magnetomotive force.