Graphene-epoxy flexible transparent capacitor obtained by graphene-polymer transfer and UV-induced bonding.

A new approach is reported for the preparation of a graphene-epoxy flexible transparent capacitor obtained by graphene-polymer transfer and UV-induced bonding. SU8 resin is employed for realizing a well-adherent, transparent, and flexible supporting layer. The achieved transparent graphene/SU8 membrane presents two distinct surfaces: one homogeneous conductive surface containing a graphene layer and one dielectric surface typical of the epoxy polymer. Two graphene/SU8 layers are bonded together by using an epoxy photocurable formulation based on epoxy resin. The obtained material showed a stable and clear capacitive behavior.

The Physics behind the Modulation of Thermionic Current in Photodetectors Based on Graphene Embedded between Amorphous and Crystalline Silicon.

In this work, we investigate a vertically illuminated near-infrared photodetector based on a graphene layer physically embedded between a crystalline and a hydrogenated silicon layer. Under near-infrared illumination, our devices show an unforeseen increase in the thermionic current. This effect has been ascribed to the lowering of the graphene/crystalline silicon Schottky barrier as the result of an upward shift in the graphene Fermi level induced by the charge carriers released from traps localized at the graphene/amorphous silicon interface under illumination. A complex model reproducing the experimental observations has been presented and discussed. Responsivity of our devices exhibits a maximum value of 27 mA/W at 1543 nm under an optical power of 8.7 µW, which could be further improved at lower optical power. Our findings offer new insights, highlighting at the same time a new detection mechanism which could be exploited for developing near-infrared silicon photodetectors suitable for power monitoring applications.

A new strategy to prevent biofilm and clot formation in medical devices: The use of atmospheric non-thermal plasma assisted deposition of silver-based nanostructured coatings.

In industrialized countries, health care associated infections, the fourth leading cause of disease, are a major health issue. At least half of all cases of nosocomial infections are associated with medical devices. Antibacterial coatings arise as an important approach to restrict the nosocomial infection rate without side effects and the development of antibiotic resistance. Beside nosocomial infections, clot formation affects cardiovascular medical devices and central venous catheters implants. In order to reduce and prevent such infection, we develop a plasma-assisted process for the deposition of nanostructured functional coatings on flat substrates and mini catheters. Silver nanoparticles (Ag NPs) are synthesized exploiting in-flight plasma-droplet reactions and are embedded in an organic coating deposited through hexamethyldisiloxane (HMDSO) plasma assisted polymerization. Coating stability upon liquid immersion and ethylene oxide (EtO) sterilization is assessed through chemical and morphological analysis carried out by means of Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). In the perspective of future clinical application, an in vitro analysis of anti-biofilm effect has been done. Moreover, we employed a murine model of catheter-associated infection which further highlighted the performance of Ag nanostructured films in counteract biofilm formation. The anti-clot performances coupled by haemo- and cytocompatibility assays have also been performed.

Contamination-free graphene by chemical vapor deposition in quartz furnaces.

Although the growth of graphene by chemical vapor deposition is a production technique that guarantees high crystallinity and superior electronic properties on large areas, it is still a challenge for manufacturers to efficiently scale up the production to the industrial scale. In this context, issues related to the purity and reproducibility of the graphene batches exist and need to be tackled. When graphene is grown in quartz furnaces, in particular, it is common to end up with samples contaminated by heterogeneous particles, which alter the growth mechanism and affect graphene's properties. In this paper, we fully unveil the source of such contaminations and explain how they create during the growth process. We further propose a modification of the widely used quartz furnace configuration to fully suppress the sample contamination and obtain identical and clean graphene batches on large areas.

Combining light-harvesting with detachability in high-efficiency thin-film silicon solar cells.

Efforts to realize thin-film solar cells on unconventional substrates face several obstacles in achieving good energy-conversion efficiency and integrating light-management into the solar cell design. In this report a technique to circumvent these obstacles is presented: transferability and an efficient light-harvesting scheme are combined for thin-film silicon solar cells by the incorporation of a NaCl layer. Amorphous silicon solar cells in p-i-n configuration are fabricated on reusable glass substrates coated with an interlayer of NaCl. Subsequently, the solar cells are detached from the substrate by dissolution of the sacrificial NaCl layer in water and then transferred onto a plastic sheet, with a resultant post-transfer efficiency of 9%. The light-trapping effect of the surface nanotextures originating from the NaCl layer on the overlying solar cell is studied theoretically and experimentally. The enhanced light absorption in the solar cells on NaCl-coated substrates leads to significant improvement in the photocurrent and energy-conversion efficiency in solar cells with both 350 and 100 nm thick absorber layers, compared to flat-substrate solar cells. Efficient transferable thin-film solar cells hold a vast potential for widespread deployment of off-grid photovoltaics and cost reduction.

Novel back-reflector architecture with nanoparticle based buried light-scattering microstructures for improved solar cell performance.

A new back-reflector architecture for light-management in thin-film solar cells is proposed that includes a morphologically smooth top surface with light-scattering microstructures buried within. The microstructures are pyramid shaped, fabricated on a planar reflector using TiO2 nanoparticles and subsequently covered with a layer of Si nanoparticles to obtain a flattened top surface, thus enabling growth of good quality thin-film solar cells. The optical properties of this back-reflector show high broadband haze parameter and wide angular distribution of diffuse light-scattering. The n-i-p amorphous silicon thin-film solar cells grown on such a back-reflector show enhanced light absorption resulting in improved external quantum efficiency. The benefit of the light trapping in those solar cells is evidenced by the gains in short-circuit current density and efficiency up to 15.6% and 19.3% respectively, compared to the reference flat solar cells. This improvement in the current generation in the solar cells grown on the flat-topped (buried pyramid) back-reflector is observed even when the irradiation takes place at large oblique angles of incidence. Finite-difference-time-domain simulation results of optical absorption and ideal short-circuit current density values agree well with the experimental findings. The proposed approach uses a low cost and simple fabrication technique and allows effective light manipulation by utilizing the optical properties of micro-scale structures and nanoscale constituent particles.