This study experimentally and numerically investigated the fatigue response of laser-welded (LW) lap-shear samples in copper (Cu) sheets of dissimilar thicknesses. Fatigue tests were first conducted, and the resulting fatigue data and failure modes were recorded. To investigate the failure processes and mechanisms, microscopic examinations, including microhardness tests for Cu LWs, were conducted before and after the failure. The experimental results showed the interfacial failure under high-load-range and low-load-range conditions and the top sheet separation under median-load-range conditions. Next, finite element analyses for LW lap-shear samples were conducted to calculate the global stress intensity factors (GSIFs) and local stress intensity factors (LSIFs) for interfacial and kinked cracks, respectively. The GSIFs, LSIFs, and Paris law were further used to derive the two fatigue models to analyze the evolution of interfacial and kinked cracks, respectively. Finally, two fatigue models estimated a series of fatigue lives that matched the general trends of experimental data.

In this study, we employed molecular dynamics (MD) simulations to investigate ablation induced by the application of pulsed laser irradiation to a thin α -Fe substrate. We observed several mechanisms underlying the removal of material, including ultrafast melting, cluster ejection, and thermal vaporization. We also examined the effects of laser fluence on the resulting surface morphology as well as the amount of material ablated and deposited around the craters

Ultrathin glass is a promising substrate material for web processing (also called roll-to-roll processing) of flexible electronics, but is highly susceptible to breaking and cracking due to the almost inevitable presence of substrate-edge defects. Recently, a novel technique for removing the micro cracks on the edges of ultrathin glass substrates was devised at ITRI. It amounts to shining a CO2 laser on one edge of a substrate, which induces spontaneous peeling of a thin layer containing preexisting cracks on the edge from the substrate, resulting in an essentially crack-free new substrate edge. Exploiting the thinness of ultrathin glass substrates, here we propose a simplified two-dimensional thermal model for the laser peeling process, and obtain an analytic expression for the transient temperature variation in a substrate being peeled. This enables us to locate the "thermally affected zone" in the substrate, which turns out to be impressively similar in size and shape to the substrate-edge peels observed in experiments. Moreover, a quantitative criterion for the minimum cooling rate required for the progression of the peeling process is obtained. The results here thus provide useful insights into the laser peeling mechanism, and can be used to expedite the optimization of process parameters. Some preliminary purely numerical results using a finite element method (FEM) based software also are briefly discussed here.

Laser peeling is a surface defect removal process involving irradiating laser pulses on edges of ultra-thin glasses. Mechanical- or laser-cutting induced edge defects on glass edges are removed by peeling off a thin layer containing the cutting defects. The new edge-surfaces of the glasses are defect-free and much less prone to cracking failure. In this paper the mechanism of this material removal process is investigated. From experimental observations and theoretical calculations, it is shown that the laser glass peeling is a brittle fracture process driven by residual stress associated to glass surface phase change phenomenon, as opposed to the typical laser ablation material removal. A quantitative fracture mechanics model that simulates the laser induced glass peeling process is also presented. (C) 2016 Elsevier Ltd. All rights reserved.

A laser-based thin-film processing scheme for printing and annealing of graphene oxide is reported. This method is able to print and simultaneously reduce the graphene oxide to graphene. The resulting graphene thin film is with good transmittance and its resistance is dramatically reduced from 200 MΩ to 80 KΩ.

We report on effects of doping graphene in poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate), PEDOT:PSS, as a PEDOT:PSS/graphene nanocomposite hole injection layer on the performance enhancement of polymer light-emitting diodes (PLEDs). Graphene oxides were first synthesized and then mixed in the PEDOT:PSS solution with specifically various amounts. Graphenes were reduced in the PEDOT:PSS matrix through thermal reduction. PLED devices with hole-injection nanocomposite layer containing particular doping concentration were fabricated, and the influence of doping concentration on device performance was examined by systematically characterizations of various device properties. Through the graphene doping, the resistance in the hole-injection layer and the turn-on voltage could be effectively reduced that benefited the injection and transport of holes and resulted in a higher overall efficiency. The conductivity of the hole-injection layer was monotonically increased with the increase of doping concentration, performance indices from various aspects, however, did not show the same dependence because faster injected holes might alter not only the balance of holes and electrons but also their combination locations in the light-emitting layer. Results show that optimal doping concentration was the case with 0.03 wt% of graphene oxide.

A method for rapidly fabricating dense and high-aspect-ratio silver nanowires, with wire diameter of 200 nm and wire length more than 30 µm, is reported. The fabrication process simply involves filling the silver nitrate solution into the pores of an anodic-aluminum-oxide (AAO) membrane through capillary attraction and irradiating the dried template AAO membrane using a pulsed ArF excimer laser. Through varying the thickness and pore diameter of the employed AAO membrane, the primary dimensions of the targeted silver nanowires can be plainly specified; and, by amending the initial concentration of the silver nitrate solution and adjusting the laser operation parameters, laser fluence and number of laser pulses, the surface morphology and size of the resulting nanowires can be finely regulated. The wire formation mechanism is considered through two stages: the period of precipitation of silver particles from the dried silver nitrate film through the laser-induced photoreduction; and, the phase of clustering, merging and fusing of the reduced particles to form nanowires in the template pores by the thermal energy owing to photothermal effect. This approach is straightforward and takes the advantage that all the fabrication processes can be executed in an ambient environment and at room temperature. In addition, by the excellence in local processing that the laser possesses, this method is suitable for precisely growing nanowires.

We report on an approach for fabricating transparent electrodes on a plastic substrate by annealing AZO nanoparticles using a pulsed UV laser. For the resulting AZO film, the resistivity is 7.6×10−2 Ω-cm and the transmittance is over 80% within the wavelength from 400 to 800 nm. This method is straightforward and executable in the ambient environment and at room temperature.

A method for fabricating silver nanowires is reported. Based on irradiation from a pulsed CO(2) laser with a high repetition rate, dense and high aspect ratio silver nanowires are grown from an anodic aluminum oxide template within several seconds. The morphology and composition of the fabricated nanostructures are characterized, and the detailed mechanisms for the growth are addressed. This method is straightforward and takes the advantage of heating the template and reducing nanowires locally, which is suitable for low temperature fabrication. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3358129] All rights reserved.

Through incorporating with the technique of rapid polydimethysiloxane (PDMS) lift-off, this study reports on a new laser transfer method that is applicable to printing metallic thin film on a flexible substrate. Aluminum line patterns, with line widths of 40 and 100 µm and deposited on poly(ethylene terephthalate) (PET) substrate, are presented. The patterned film is demonstrated to be a good conductor, with resistivity of 2.95×10−6 Ω-cm, and with very good adhesion strength through the scotch-tape test.

This study reports on a new photoreduction approach for growing dense and continuous silver nanowires from an anodic aluminum oxide (AAO) template. Silver nanoparticles are first reduced then merged to form nanowires in the AAO pores from dried silver nitride by laser irradiation. The morphology and composition of the grown nanostructures are characterized and the detailed photochemical growth mechanism is addressed. This method is rapid, low-cost, local reduction and can be executed in the ambient environment.

In this study, we propose a new laser-induced implantation based approach for embedding electronic interconnects in this study. Direct implantations of silver particles, vaporized by a pulsed laser from a silver film initially pre-coated on a transparent glass substrate, into poly(vinyl alcohol) (PVA)-encapsulated organic electronic devices as electronic conducting circuits are demonstrated. Two test carriers are the devices of organic thin-film transistors and polymeric light-emitting diodes. Device property characterizations indicate the implanted circuits can work smoothly. The implantation process is driven by the high-energy ejected particles that soften and melt the PVA layer and penetrate into it until their momentums are totally lost. The penetration depth increases with the number of laser pulses and is becoming saturated as the pulse number is getting high. A conducting circuit, with length of 2μm, can be completely embedded within 3 laser pulses. Due to its flexibility in embedding metals into an encapsulated device, this technique can be used for repairing internal circuit damage. Besides, all steps can be executed in the ambient environment and at room temperature that is suitable for plastic substrate processing.