Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- Ultrasensitive gold micro-structured electrodes enabling the detection of extra-cellular long-lasting potentials in astrocytes populationsPublication . Mestre, Ana L. G.; Cerquido, Monica; INÁCIO, PEDRO; Asgarifar, Sanaz; Lourenco, Ana S.; Lurdes S. Cristiano, M.; Aguiar, Paulo; Medeiros, Maria C. R.; Araújo, Inês; Ventura, Joao; Gomes, Henrique L.Ultra-sensitive electrodes for extracellular recordings were fabricated and electrically characterized. A signal detection limit defined by a noise level of 0.3-0.4 mu V for a bandwidth of 12.5 Hz was achieved. To obtain this high sensitivity, large area (4 mm(2)) electrodes were used. The electrode surface is also micro-structured with an array of gold mushroom-like shapes to further enhance the active area. In comparison with a flat gold surface, the micro-structured surface increases the capacitance of the electrode/electrolyte interface by 54%. The electrode low impedance and low noise enable the detection of weak and low frequency quasi-periodic signals produced by astrocytes populations that thus far had remained inaccessible using conventional extracellular electrodes. Signals with 5 mu V in amplitude and lasting for 5-10 s were measured, with a peak-to-peak signal-to-noise ratio of 16. The electrodes and the methodology developed here can be used as an ultrasensitive electrophysiological tool to reveal the synchronization dynamics of ultra-slow ionic signalling between non-electrogenic cells.
- Small signal analysis of MPCVD diamond Schottky diodesPublication . Mendes, J. C.; L, Gomes H; Trippe, S. C.; Mukherjee, D.; Pereira, L.Polycrystalline diamond (PCD) grown by chemical vapor deposition (CVD) is an intrinsic semiconductor particularly attractive for high power/high temperature devices. Nevertheless, the physical models for injection and transport of electrical carriers are remarkable complex and depend on the microstructure and composition of carbon species in the film. In this work, free-standing CVD PCD films were deposited by microwave plasma CVD (MPCVD) and were characterized by Raman spectroscopy. Gold and aluminum circular contacts were deposited on the growth surface in order to fabricate a planar diode. The current-voltage characteristics were measured at different temperatures. The application of a non-homogeneous barrier model to fit the current-voltage characteristics reveals the existence of two barriers related with the grain/electrode and grain boundary/electrode interfaces. Small signal analysis was performed at room temperature to understand the nature of electrical process involved in the injection and carrier transport. The existence of parallel channels through with charge flows was confirmed and the fittings suggest the existence of a nearly equipotential surface at the interface diamond/electrode. The physical origin of the inclusion of a constant phase element in the equivalent circuit model is discussed. The results obtained are of particular importance to further devices fabrication. Prime novelty: An equivalent circuit model for the diamond Schottky diode is proposed
- Switching in polymeric resistance random-access memories (RRAMS)Publication . Gomes, Henrique L.; Benvenho, A. R. V.; De Leeuw, Dago M.; Cölle, M.; Stallinga, Peter; Verbakel, F.; Taylor, D. M.Resistive switching in aluminum-polymer-based diodes has been investigated using small signal impedance measurements. It is shown that switching is a two-step process. In the first step, the device remains highly resistive but the low frequency capacitance increases by orders of magnitude. In the second step, resistive switching takes place. A tentative model is presented that can account for the observed behavior. The impedance analysis shows that the device does not behave homogenously over the entire electrode area and only a fraction of the device area gives rise to switching.