Memristor with a ferroelectric HfO2 layer: in which case it is a ferroelectric tunnel junction.

New interest in the implementation of ferroelectric tunnel junctions has emerged following the discovery of ferroelectric properties in HfO2 films, which are fully compatible with silicon microelectronics technology. The coercive electric field to switch polarization direction in ferroelectric HfO2 is relatively high compared to classical perovskite materials, and thus it can cause the migration of non-ferroelectric charges in HfO2, namely charged oxygen vacancies. The charge redistribution would cause the change of the tunnel barrier shape and following change of the electroresistance effect. In the case of ambiguous ferroelectric properties of HfO2 ultrathin films, this oxygen-driven resistive switching effect can mimic the tunnel electroresistance effect. Here, we demonstrate two separate resistive switching regimes, depending on the applied voltage, in the same memristor device employing a ferroelectric Hf0.5Zr0.5O2 (4.5 nm) layer. The first regime originates from the polarization reversal, whereas the second one is attributed to the accumulation/depletion of the oxygen vacancies at the electrode interface. The modulation of the tunnel barrier causes the enhancement of R OFF/R ON ratio in ∼20 times compared to the tunnel electroresistance effect. The developed device was used to formulate the criteria for unambiguous discrimination between the ferroelectric-and non-ferroelectric resistive switching effects in HfO2-based ferroelectric tunnel junctions.

Charge states and lattice sites of dilute implanted Sn in ZnO.

The common charge states of Sn are 2+ and 4+. While charge neutrality considerations favour 2+ to be the natural charge state of Sn in ZnO, there are several reports suggesting the 4+ state instead. In order to investigate the charge states, lattice sites, and the effect of the ion implantation process of dilute Sn atoms in ZnO, we have performed 119Sn emission Mössbauer spectroscopy on ZnO single crystal samples following ion implantation of radioactive 119In (T ½ = 2.4 min) at temperatures between 96 K and 762 K. Complementary perturbed angular correlation measurements on 111mCd implanted ZnO were also conducted. Our results show that the 2+ state is the natural charge state for Sn in defect free ZnO and that the 4+ charge state is stabilized by acceptor defects created in the implantation process.

[Migraine and temporomandibular joint dysfunction: mechanisms of comorbidity].

OBJECTIVE: to analyze the frequency of different forms of temporomandibular joint dysfunction (TMJD) in episodic and chronic migraine and to study mechanisms of their comorbidity. MATERIAL AND METHODS: Sixty-three patients with chronic migraine (CM) and 40 patients with episodic migraine (EM) were examined. Anxiety and depression were assessed with the HADS, quality-of-life related to headache was measured with the HIT-6. To evaluate the antinociceptive system function, we studied blink reflex (BR) and nociceptive flexion reflex (NFR). RESULTS: The higher frequency of TMJD was identified in patients with CM compared to those with EM (47.5 and 28.5%, respectively), CM patients more frequently had disturbances related to the myofascial pain syndrome of masticatory muscles. R3 BR and NFR thresholds were significantly decreased in CM patients as well. CONCLUSION: TMJD is a component of the pathogenesis in many patients with CM. Masticatory muscles may generate nociceptive impulses in CNS, ie be a source of peripheral sensitization, that promote pain chronification, including migraine. Dysfunction of masticatory muscles may reflect the central sensitization and disturbance of efferent pain control.