In intense pulsed light sintering (IPL), pulsed large-area visible light from a xenon lamp is absorbed by nanoparticle films or patterns and converted to heat, resulting in rapid sintering of the nanoparticles. This work experimentally characterizes IPL of silver nanoparticle films. A newly observed turning point in the evolution of film temperature during IPL is correlated to the observation, in literature and in this work, that film densification levels off beyond a critical pulse fluence and number of pulses. A computational model is developed that couples electromagnetic finite element analysis, heat transfer models and densification models to predict the evolution of film temperature and density during IPL. This model is able to capture the experimentally observed turning point in temperature during IPL, whereas current models of IPL are unable to do so. It is shown that the temperature turning point occurs due to a coupling between optical absorption and densification in the nanoparticle film, mediated by a change in nanoscale shape of the deposited nanoparticles due to interparticle neck growth. Further, it is found that the optical fluence per pulse has a greater effect on the achievable film density in IPL, as compared to the number of pulses.

Intense Pulsed Light sintering (IPL) uses pulsed, visible light to sinter nanoparticles (NPs) into films used in functional devices. While IPL of chalcogenide NPs is demonstrated, there is limited work on prediction of crystalline phase of the film and the impact of optical properties of the substrate. Here we characterize and model the evolution of film temperature and crystalline phase during IPL of chalcogenide copper sulfide NP films on glass. Recrystallization of the film to crystalline covellite and digenite phases occurs at 126 °C and 155 °C respectively within 2–7 seconds. Post-IPL films exhibit p-type behavior, lower resistivity (~10−3–10−4 Ω-cm), similar visible transmission and lower near-infrared transmission as compared to the as-deposited film. A thermal model is experimentally validated, and extended by combining it with a thermodynamic approach for crystal phase prediction and via incorporating the influence of film transmittivity and optical properties of the substrate on heating during IPL. The model is used to show the need to a-priori control IPL parameters to concurrently account for both the thermal and optical properties of the film and substrate in order to obtain a desired crystalline phase during IPL of such thin films on paper and polycarbonate substrates.

No abstract

Incremental forming of thermoplastic surfaces has recently received significant interest due to the potential for simultaneous reduction in thermal energy consumption and in part-shape specific tooling. This paper examines the mechanical properties and the chain orientation of the formed material in single point incremental forming (SPIF) of amorphous polyvinyl chloride (PVC) and semicrystalline polyamide sheets. Tensile and stress relaxation properties of the formed polymers are compared to those of the unformed polymer. The effect of incremental depth and tool rotation speed on the above properties, and on the temperature rise of the sheet during SPIF, is quantified. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) are used to compare the chain orientation and crystallinity of the formed and the unformed polymers. It is observed that the formed material has greater toughness and ductility, but lower yield stress and reduced Young's modulus, as compared to the unformed material. We also observe deformation-induced chain reorientation in the formed polymer, with minimal change in the degree of crystallinity. The link between the SPIF process parameters, temperature rise of the polymer during SPIF, change in chain orientation, and change in mechanical properties of the polymer is discussed.

We report a scalable method for producing efficient Cu2ZnSn(S,Se)4 photovoltaic cells by combining binary metal sulfide nanoparticles synthesized in aqueous solutions.