Characterization of Thermoplastic Polyurethane (TPU) and Ag-Carbon Black TPU Nanocomposite for Potential Application in Additive Manufacturing.

Electromechanical, adhesion, and viscoelastic properties of polymers and polymer nanocomposites (PNCs) are of interest for additive manufacturing (AM) and flexible electronics. Development/optimization of inks for AM is complex, expensive, and substrate/interface dependent. This study investigates properties of free standing films of a thermoplastic polyurethane (TPU) polymer and an Ag⁻carbon black (Ag-CB) TPU PNC in a lightly loaded low strain compression contact as a rough measure of their suitability for AM. The TPU exhibited high hysteresis and a large viscoelastic response, and sufficient dwell time was needed for polymer chain relaxation and measurable adhesion. A new discovery is that large enough contact area is needed to allow longer time constant polymer ordering in the contact that led to higher adhesion and better performance/reliability. This has previously unknown implications for interface size relative to polymer chain length in AM design. The standard linear model was found to be a good fit for the viscoelastic behavior of the TPU. The PNC exhibited no adhesion (new result), low electrical resistance, and relatively small viscoelastic response. This implies potential for AM electrical trace as well as switch applications.

Observation of the intrinsic bandgap behaviour in as-grown epitaxial twisted graphene.

Twisted graphene is of particular interest due to several intriguing characteristics, such as its the Fermi velocity, van Hove singularities and electronic localization. Theoretical studies recently suggested the possible bandgap opening and tuning. Here, we report a novel approach to producing epitaxial twisted graphene on SiC (0001) and the observation of its intrinsic bandgap behaviour. The direct deposition of C60 on pre-grown graphene layers results in few-layer twisted graphene confirmed by angular resolved photoemission spectroscopy and Raman analysis. The strong enhanced G band in Raman and sp(3) bonding characteristic in X-ray photoemission spectroscopy suggests the existence of interlayer interaction between adjacent graphene layers. The interlayer spacing between graphene layers measured by transmission electron microscopy is 0.352 ± 0.012 nm. Thermal activation behaviour and nonlinear current-voltage characteristics conclude that an intrinsic bandgap is opened in twisted graphene. Low sheet resistance (~ 160 Ω â–¡(-1) at 10 K) and high mobility (~2,000 cm(2) V(-1) s(-1) at 10 K) are observed.

Voltage-impulse-induced non-volatile ferroelastic switching of ferromagnetic resonance for reconfigurable magnetoelectric microwave devices.

A critical challenge in realizing magnetoelectrics based on reconfigurable microwave devices, which is the ability to switch between distinct ferromagnetic resonances (FMR) in a stable, reversible and energy efficient manner, has been addressed. In particular, a voltage-impulse-induced two-step ferroelastic switching pathway can be used to in situ manipulate the magnetic anisotropy and enable non-volatile FMR tuning in FeCoB/PMN-PT (011) multiferroic heterostructures.

Epitaxial graphene growth by carbon molecular beam epitaxy (CMBE).

A novel growth method (carbon molecular beam epitaxy (CMBE)) has been developed to produce high-quality and large-area epitaxial graphene. This method demonstrates significantly improved controllability of the graphene growth. CMBE with C(60) produces AB stacked graphene, while growth with the graphite filament results in non-Bernal stacked graphene layers with a Dirac-like electronic structure, which is similar to graphene grown by thermal decomposition on SiC (000-1).