SummaryA well-organized monolayer of alkylated perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) has been formed onto CVD graphene transferred on a transparent substrate. Its structure has been probed by scanning tunnelling microscopy and its optical properties by polarized transmission spectroscopy at varying incidence. The results show that the transition dipoles of adsorbed PTCDI are all oriented parallel to the substrate. The maximum absorption is consistent with the measured surface density of molecules and their absorption cross section. The spectrum presents mainly a large red-shift of the absorption line compared with the free molecules dispersed in solution, whereas the relative strengths of the vibronic structures are preserved. These changes are attributed to non-resonant interactions with the graphene layer and the neighbouring molecules.

Among the transduction mechanisms of interest for sensing and/or actuation applications at nano/micro scale, the piezoelectric effect has been widely exploited owing to the solid state nature of piezoelectrics, the large ability of specific classes of materials for the mechanical-to-electrical energy conversion and easy integration. However, every piezoelectric (also generally ferroelectric) presents well-known intrinsic drawbacks such as required poling step and related aging. In contrast, uniquely flexoelectric materials do not suffer from these disadvantages because flexoelectricity, a universal effect in all dielectric solids defined as the electrical polarization induced by a strain gradient, does not imply preliminary electric field-induced macroscopic polarization. Besides, strain gradient may be easily obtained by bending plate or cantilever-shaped structure and in this case it is nothing but the local curvature of the flexible system. Thus, as strain gradient (curvature) inversely scales with both elastic stiffness and thickness, this study will focus on the evaluation of the potentialities of flexoelectric effect in soft polymer films for electromechanical applications, with an emphasis on the thickness influence. In this way, analytical results combined to experimentally obtained effective flexoelectric coefficients for some typical polymer classes may provide guidelines for the development of soft and low frequency flexoelectric mechanical transducers.

All organic soft dielectrics are growing more and more interest in the electronic industry owing to their light weight, low cost and the flexibility they yield compared to the rigid devices. In the specific field of microwave communicating devices planar printed (patch) antennas on a soft dielectric substrate are sought for their conformability and advantageous compactness. In this article, two soft thermoplastic elastomer blends based on polypropylene (PP) or lowdensity polyethylene (LDPE) were tested. The fabrication process and the established characterization steps have been fully presented. More specifically, in order to characterize the dielectric film up to 40 GHz, the microstrip ring resonator with coplanar waveguide access has been adapted to a new configuration specimen sample. The results of the characterizations obtained showed very encouraging performances for microwave applications. Indeed, the measured dielectric constant and loss tangent up to 40 GHz were found to be ε r ≈ 2.45 and tan δ ≈ 0.01 for both blends. The fabrication and the radiation characteristics of a patch antenna on a new performing PP or LDPEbased elastomer blends as the soft dielectric substrate was demonstrated and analysed. The proof of the concept of the investigated device consists of a microstrip patch antenna with an operation frequency of about 10 GHz. These dielectric features render the polyolefin based blends very promising as a soft material for microwave engineering, which is confirmed by the measured antenna properties: the gain, the directivity as well as the efficiency have been calculated from the measured radiation pattern and were recorded as 4.6 dB, 7.7 dB and 46% respectively for the rPP based blend and 4.8 dB, 8.1 dB and 51% for the LDPE based blend.