Search

Abstract: The effect of the material of the metal plates (Au, Ta, W) and exposure to a high-power blue laser on the memristive characteristics of metal-insulator-semiconductor (MIS) capacitors with a Si3N4 film 6 nm thick fabricated on the basis of n+-Si is studied. It is shown that bipolar switching by the current appears only in capacitors with Au. The causes of the absence of bipolar switching in capacitors with Ta and W are explained. The switching of capacitors with Ta by the current and light and the photomemory effect are detected. It is shown that, despite the high doping level of the semiconductor substrate, it decreases the MIS memristor response rate due to a high density of surface states localized at the Si3N4/n+-Si interface. However, illumination allows a significant increase in the response rate due to a decrease in the semiconductor resistivity. The surface state densities are determined. To improve the frequency characteristics of MIS memristors, it is necessary to achieve a low surface state density. [ABSTRACT FROM AUTHOR]

Abstract—: The effect of optical illumination on the resistive switching in ultrathin (~4 nm) ZrO2(Y) films with embedded single-layer Au nanoparticle arrays 2-3 nm in size is studied via tunneling atomic force microscopy. The ZrO2(Y) films with Au nanoparticles are grown by layerwise magnetron deposition onto glass substrates with a conductive indium-tin-oxide sublayer, followed by annealing at 450°C. An increase in hysteresis due to bipolar resistive switching in the ZrO2(Y) films is observed on the cyclic current-voltage curves of the microscope probe-to-sample contact. The effect is found to manifest itself in a dense Au nanoparticle array (~660 nm) when the contact area is photoexcited through a transparent substrate exposed to the radiation of a semiconductor laser at the plasmon-resonance wavelength. The effect is attributed to the photon-assisted field emission of electrons from Au nanoparticles to the conduction band of ZrO2(Y) in a strong electric field between the microscope probe and the indium-tin-oxide substrate under plasmon-resonance conditions. [ABSTRACT FROM AUTHOR]

1. The intracellular mechanism of heterosynaptic facilitation (HSF) formation in identified neurons from the snail Planorbis corneus has been studied. 2. Facilitation of excitatory postsynaptic currents (EPSC) were induced by (a) stimulation of pallial nerve, and (b) addition to extracellular saline of serotonin, NaF, papaverine, theophylline, caffeine or dibutril-cAMP. 3. A depression of EPSC in solutions containing tolbutamide, a cAMP-dependent protein kinase inhibitor was observed. 4. In some cases the similar facilitation or depression of the current induced by acetylcholine application (ACh-current) was found in the same neuron. 5. The effects on ACh-current were distorted in solutions containing caffeine, a well-known activator of calcium ions release from the intracellular depot. 6. According to our findings, we suggest that adenylate cyclase activity of postsynaptic cells could underlie the formation of HSF and it is likely that this activity was modulated by intracellular concentration of calcium ions.

Monoamines (NE, DA) were studied for their effect on heterosynaptic facilitation of n-cholinergic synaptic transmission in identified giant neurons of the cerebral ganglion of Planorbis corneus. It was shown that NE and DA blocked n-cholinergic EPSP and facilitated acetylcholine potential evoked by ionophoretic acetylcholine application. The monoamines blocked heterosynaptic facilitation as well. Washing of the monoamines after blocking heterosynaptic facilitation evoked recovery and long maintenance of the synaptic facilitation. It is concluded that DA and NE release may be the mechanism for conducting the intensity and duration of the heterosynaptic facilitation in the natural activity of the central nervous system of molluscs.

It is shown that heterosynaptic facilitation of the synaptic transmission in the giant neurons of the cerebral ganglion in Planorbis corneus develops due to the diffuse neurohumoral effects on the pre- and postsynaptic structures but not as a result of the local synaptic influences on the presynaptic mechanisms. Using the new biological object it has been confirmed that serotonin from the perfuse solution was a source of the facilitatory action on the n-cholinergic synaptic transmission. It was established that conditioning stimulations facilitated not only the n-cholinergic synaptic transmission but also the ionophoretic acetylcholine potentials. Amplitudes of EPSPs and acetylcholinic potentials increased 4-6 times, while the postsynaptic membrane impedance increased only by 20%. Based on such data it is summarized that sensitization of n-cholinergic receptors of the postsynaptic membrane contributed much to the heterosynaptic facilitation. The possible role of n-cholinergic receptors of the postsynapcit membrane in the processes of the heterosynaptic facilitation and of the conditional training is discussed.

Heterosynaptic facilitation evoked in the giant neuron of the Planorbis corneus cerebral ganglion by stimulation of the remote visceral nerve was more effective than facilitation achieved by paired stimulation of cerebral nerves. Its effectiveness depended not on the efficacy of the heterosynaptic input to the giant neuron, but on the strength of the connections between the chosen heterosynaptic input with neurons surrounding the giant cell. This finding as well as prolonged latency and slow rise-time of facilitation may indicate that the latter is of neurosecreory origin. The existence of a mechanism of drastic increase in the efficacy of synaptic connections may play an important role in animal habituation and during conditioning in particular, though such plasticsynaptic changes do not reflect the specificity of the conditioned reflex.