Heavy pnictogen chalcohalides offer various shades from the same palette, like “Paysage” by Nicolas de Staël. Their versatility and tunability lead to a new world of possible applications.

Lead halides in an asymmetric layered structure form memristive devices which are controlled by the electronic structure of the PbX2|metal interface. In this paper, we explain the mechanism that stands behind the I–V pinched hysteresis loop of the device and shortly present its synaptic-like plasticity (spike-timing-dependent plasticity and spike-rate-dependent plasticity) and nonvolatile memory effects. This memristive element was incorporated into a reservoir system, in particular, the echo-state network with delayed feedback, which exhibits brain-like recurrent behavior and demonstrates metaplasticity as one of the available learning mechanisms. It can serve as a classification system that classifies input signals according to their amplitude.

Coordination compounds with a tin center surrounded by both organic and inorganic ligands ([SnI4{(C6H5)3PO}2], [SnI4{(C6H5)2SO}2], and [SnI4(C5H5NO)2]) acting as molecular semiconductors are in the spotlight of this article. This is a new class of hybrid semiconducting materials where optoelectronic properties of inorganic core (SnI4) were tuned by organic ligands. The valence band is located at the inorganic portion of the molecule while the conduction band is made of carbon-based orbitals. This suggests the great importance of hydrogen bonds where iodine atoms play the role of an acceptor. Weak intermolecular interactions between iodine atoms and aromatic rings are essential in a band structure formation. These materials form orange-red crystals soluble in most of organic solvents. Their semiconducting properties are addressed experimentally via photovoltage measurements, as well as theoretically, using DFT and semiempirical approaches.

No abstract

No abstract

The enormous amount of data generated nowadays worldwide is increasingly triggering the search for unconventional and more efficient ways of processing and classifying information, eventually able to transcend the conventional von-Neumann-Turing computational central dogma. It is, therefore, greatly appealing to draw inspiration from less conventional but computationally more powerful systems such as the neural architecture of the human brain.This neuromorphic route has the potential to become one of the most influential and long-lasting paradigms in the field of unconventional computing. The material-based workhorse for current hardware platforms is largely based on standard CMOS technologies, intrinsically following the above mentioned von-Neumann-Turing prescription; we do know, however, that the brain hardware operates in a massively parallel way through a densely interconnected physical network of neurons. This requires challenging the intrinsic definition of the single units and the architecture of computing machines. Memristive and the recently proposed memfractive systems have been shown to display basic features of neural systems such as synaptic-like plasticity and memory features, so that they may offer a diverse playground to implement synaptic connections. Their combination with reservoir computing approaches can further increase their versatility since reservoir networks do not require extra optimization of internal connections. In this review, we address various material-based strategies of implementing unconventional computing hardware: (i) electrochemical oscillators based on liquid metals and (ii) mem-devices exploiting Schottky barrier modulation in polycrystalline and disordered structures made of oxide or perovskite-type semiconductors. Both items (i) and (ii) build the two pillars of neuromimetic computing devices, which we will denote as synthetic neural networks. We complement the more experimental aspects of the review with an overview of few atomistic and phenomenological modelling approaches of memdevices as well as of reservoir computing networks. We expect that the current review will be of great interest for scientists aiming at bridging unconventional computing strategies with specific materials-based platforms.

The intriguing properties of triiodide organic salts ([(C6H5)3AsO]2H+I3−, (C6H5CH2)3NH+I3− ⋅C6H5CH3, and [(C6H5CH2)3NO]2H+I3−) have been analyzed in detail using experimental and theoretical techniques. The analysis of crystal structures, density of states distribution and photocurrent generation of this purely ionic materials indicates insulating character of the ground state, whereas semiconducting character in higher excited states is observed. These peculiar properties of the studied compounds are the consequence of a specific electronic structure: very flat dispersion diagrams of the valence and conduction band and highly dispersive character on the higher conduction band. Weak triiodide‐triiodide interactions play the key role in the visible absorption range of these salts, while the charge transfer involving high energy carbon‐centered states is responsible for photocurrent generation. The complexity of the electrochemical reactions and the interactions of the I3− anion with light, solubility in organic solvents and the simplicity of preparation make these materials interesting candidates for application in unconventional optoelectronic devices.

The operation of an FTO/[SnI4{(C6H5)2SO}2]/Cu memristor is based on the Schottky barrier modulation due to electron trapping/detrapping at the interface states. The presented memristive bipolar device has an asymmetric current–voltage characteristic and multiple resistance states, which can be achieved by the application of impulses with different amplitudes and durations. STDP measurement performed with symmetric sawtooth voltage pulses results in the asymmetric Hebbian-like learning pattern. The incorporation of the device in a particular type of the reservoir systema single node echo state machineallowed observation of signal processing in a feedback-loop equipped system: classification according to the initial pulse amplitude and generation of pulse sequences of a random length.