Reaching silicon-based NEMS performances with 3D printed nanomechanical resonators

The extreme miniaturization in NEMS resonators offers the possibility to reach an unprecedented resolution in high-performance mass sensing. These very low limits of detection are related to the combination of two factors: a small resonator mass and a high quality factor. The main drawback of NEMS is represented by the highly complex, multi-steps, and expensive fabrication processes. Several alternatives fabrication processes have been exploited, but they are still limited to MEMS range and very low-quality factor. Here we report the fabrication of rigid NEMS resonators with high-quality factors by a 3D printing approach. After a thermal step, we reach complex geometry printed devices composed of ceramic structures with high Young’s modulus and low damping showing performances in line with silicon-based NEMS resonators ones. We demonstrate the possibility of rapid fabrication of NEMS devices that present an effective alternative to semiconducting resonators as highly sensitive mass and force sensors

Multi-material 3D printed shape memory polymer with tunable melting and glass transition temperature activated by heat or light

Shape memory polymers are attractive smart materials that have many practical applications and academic interest. Three-dimensional (3D) printable shape memory polymers are of great importance for the fabrication of soft robotic devices due to their ability to build complex 3D structures with desired shapes. We present a 3D printable shape memory polymer, with controlled melting and transition temperature, composed of methacrylated polycaprolactone monomers and N-Vinylcaprolactam reactive diluent. Tuning the ratio between the monomers and the diluents resulted in changes in melting and transition temperatures by 20, and 6 °C, respectively. The effect of the diluent addition on the shape memory behavior and mechanical properties was studied, showing above 85% recovery ratio, and above 90% fixity, when the concentration of the diluent was up to 40 wt %. Finally, we demonstrated multi-material printing of a 3D structure that can be activated locally, at two different temperatures, by two different stimuli; direct heating and light irradiation. The remote light activation was enabled by utilizing a coating of Carbon Nano Tubes (CNTs) as an absorbing material, onto sections of the printed objects

Induced Crystallization of Polyelectrolyte-Surfactant Complexes at the Gas-Water Interface

Synchrotron-X-ray and surface tension studies of a strong polyelectrolyte (PE) in the semi-dilute regime (~ 0.1M monomer-charges) with varying surfactant concentrations show that minute surfactant concentrations induce the formation of a PE-surfactant complex at the gas/solution interface. X-ray reflectivity and grazing angle X-ray diffraction (GIXD) provide detailed information of the top most layer, where it is found that the surfactant forms a two-dimensional liquid-like monolayer, with a noticeable disruption of the structure of water at the interface. With the addition of salt (NaCl) columnar-crystals with distorted-hexagonal symmetry are formed.Comment: 4 pages, 5 eps figure

3D Printing of Cellulose Nanocrystal-Loaded Hydrogels through Rapid Fixation by Photopolymerization

New ink compositions for direct ink writing (DIW) printing of hydrogels, combining superior rheological properties of cellulose nanocrystals (CNCs) and a water-compatible photoinitiator, are presented. Rapid fixation was achieved by photopolymerization induced immediately after the printing of each layer by 365 nm light for 5 s, which overcame the common height limitation in DIW printing of hydrogels, and enabled the fabrication of objects with a high aspect ratio. CNCs imparted a unique rheological behavior, which was expressed by orders of magnitude difference in viscosity between low and high shear rates and in rapid high shear recovery, without compromising ink printability. Compared to the literature, the presented printing compositions enable the use of low photoinitiator concentrations at a very short build time, 6.25 s/mm, and are also curable by 405 nm light, which is favorable for maintaining viability in bioinks

Over 6% Efficient Cu(In,Ga)Se2 Solar Cell Screen-Printed from Oxides on FTO

A new approach to fabricate copper, indium, gallium diselenide (CIGSe) solar cells on conductive fluorine-doped tin oxide (FTO) reached an efficiency of over 6% for a champion photovoltaic device. Commercial oxide nanoparticles are formulated into high-quality screen-printable ink based on ethyl cellulose solution in terpineol. The high homogeneity and good adhesion properties of the oxide ink play an important role in obtaining dense and highly crystalline photoabsorber layers. This finding reveals that solution-based screen-printing from readily available oxide precursors provides an interesting cost-effective alternative to current vacuum- and energy-demanding processes of the CIGSe solar cell fabrication.FCT PTDC/CTM-ENE/5387/2014 (PrintPV), Grant Agreement No. 016663, FCT SFRH/BD/121780/2016. Nanochemistry Research Group at INL for valuable discussions. This work was supported by ERDF COMPETE 2020 and Portuguese FCT funds under the PrintPV project (PTDC/CTM-ENE/5387/2014, Grant Agreement No. 016663). B.F.G. is grateful to the FCT for the SFRH/BD/121780/2016 gran

Electrical Sintering of Silver Nanoparticle Ink Studied by In-Situ TEM Probing

Metallic nanoparticle inks are used for printed electronics, but to reach acceptable conductivity the structures need to be sintered, usually using a furnace. Recently, sintering by direct resistive heating has been demonstrated. For a microscopic understanding of this Joule heating sintering method, we studied the entire process in real time inside a transmission electron microscope equipped with a movable electrical probe. We found an onset of Joule heating induced sintering and coalescence of nanoparticles at power levels of 0.1–10 mW/m3. In addition, a carbonization of the organic shells that stabilize the nanoparticles were found, with a conductivity of 4 105 Sm−1