Josep Miquel Vidal Hernández

En Josep Miquel Vidal Hernández, físic, fundador de l'Institut Menorquí d'Estudis (del qual ara era coordinador científic) i de l'Obra Cultural de Menorca (impulsora de l'Enciclopèdia de Menorca, de la qual era director), membre de l'equip rector de la Universitat Catalana d'Estiu (UCE). Nascut el 1939 a Maó, ens va deixar el passat 9 de gener sense que ens haguéssim preparat abans, ni ell ni nosaltres. Amb un munt de projectes començats o a mig fer. És per això que volem recollir ací algunes de les petjades que ha deixat ben impreses, en els records, en les emocions, en les activitats fetes, en el seu treball en col·laboració amb diferents persones relacionades amb la física i amb la Societat Catalana de Física. El que presentem només n'és una mostra, no podem pas pretendre ser exhaustius. Recollim ací unes pinzellades d'alguns dels físics i d'algunes de les persones estretament vinculades amb la divulgació de la física que van viure i compartir amb en Josep Miquel Vidal algunes d'aquestes activitats

Flexible, transparent electrodes using carbon nanotubes

We prepare thin single-walled carbon nanotube networks on a transparent and flexible substrate with different densities, using a very simple spray method. We measure the electric impedance at different frequencies Z(f) in the frequency range of 40 Hz to 20 GHz using two different methods: a two-probe method in the range up to 110 MHz and a coaxial (Corbino) method in the range of 10 MHz to 20 GHz. We measure the optical absorption and electrical conductivity in order to optimize the conditions for obtaining optimum performance films with both high electrical conductivity and transparency. We observe a square resistance of 1 to 8.5 k[greek capital letter omega] for samples showing 65% to 85% optical transmittance, respectively. For some applications, we need flexibility and not transparency: for this purpose, we deposit a thick film of single-walled carbon nanotubes on a flexible silicone substrate by spray method from an aqueous suspension of carbon nanotubes in a surfactant (sodium dodecyl sulphate), thereby obtaining a flexible conducting electrode showing an electrical resistance as low as 200 [greek capital letter omega]/sq. When stretching up to 10% and 20%, the electrical resistance increases slightly, recovering the initial value for small elongations up to 10%. We analyze the stretched and unstretched samples by Raman spectroscopy and observe that the breathing mode on the Raman spectra is highly sensitive to stretching. The high-energy Raman modes do not change, which indicates that no defects are introduced when stretching. Using this method, flexible conducting films that may be transparent are obtained just by employing a very simple spray method and can be deposited on any type or shape of surface.Postprint (published version

THz-conductivity of CVD graphene on different substrates

Optoelectronic properties of CVD graphene are charac-terized over a wide frequency range: THz, IR, visible and near-UV. We used Raman spectroscopy to characterize the synthesized graphene films. All graphene layers were deposited on various substrates, some ones transparent or flexible, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), quartz and silicon. Transmission Terahertz time-domain spectroscopy (THz-TDS) method, in the range from 100 GHz to 3 THz, is used to analyze the transmittance, sheet conductivity and attenuation of graphene and the complex refractive index of substrates. From IR, near-UV and visible spectroscopy we obtained the transmittance of the substrate and the sample at those frequency ranges, and we deduced the graphene transmittance on each substrate. We found that it is close to 97% in most cases.Peer ReviewedPostprint (published version