The I-Vs in Figure 5a are fitted well by a power law I ∝ V m , with m = 2.7 to 5.5, indicating that the predominant

charge carrier transport mechanism is the space-charge-limited current [47–50]. Due to the band bending of the quasi-conduction band near the metal-dielectric interfaces, a space charge layer is formed near the surface of the dielectric where electrons are depleted. Hence, under a voltage threshold, the electrons injected from the gold electrode are combined with the holes which are present in the space charge layer resulting in the decrease of free carriers. With FK228 the increase of voltage bias, the holes are fully filled after a voltage threshold, causing the rapid increase of free carriers. Similar results are obtained for the I-V characteristics under negative bias, where m = 2.3 to 3.4, Figure 5b. On the contrary, the a-TaN x film deposited on Si, despite it is thicker than the film deposited in Au, displays much lower voltage threshold, lower

total resistance, and parabolic to almost linear current behavior for higher bias voltages, Figure 5c. This is attributed to the presence of tantalum nanoparticles, as those identified in Figure 3d, which provide additional free charge carriers after a proper value of the applied field, changing the conductive behavior from almost parabolic, m = 1.8, to almost ohmic, m = 1.3 to 1.5, Figure 5c [49, 50]. The threshold value of the applied field is much lower compared to the a-TaN x deposited on Au, considering SCH727965 mw the lower threshold bias voltage and the thickness of the film. Furthermore, all the I-V characteristics under negative bias show a quite high leakage current with a very noisy profile, although the mean current still has a linear dependence to the voltage bias (Figure 5d). This high flow of electrons under negative voltage bias may be attributed to the usage of a low work function bottom electrode (Ag,

φ = 4.5 eV) compared with the high work function electrode (Au, φ = 5.1 eV) that is used in the other device. The charge transport at the metal-dielectric interface depends on the Schottky barrier height (SBH) which is defined as φ b = φ m – χ, where φ m and χ are the metal work function and electron affinity of the dielectric, respectively. Hence, in the case of an n-doped dielectric, lower metal work function Vildagliptin results in lower SBH and easier charge transport through the barrier. Next, the two devices are double swept from -10 to 10 V to detect possible hysteresis phenomena, Figure 6. Indeed, pronounced current hysteresis of the retrace during the forward and reverse biasing cycle of the tip is identified only for the a-TaN x film on Au. The hysteretic loops are attributed to the conservation, during the bias voltage decrement process, of the internal electric fields caused by the stored space charges near the surface. Hysteresis, in this work, is defined as delta I at a fixed voltage.