Memristors are two-terminal passive circuit elements that have been developed for use in non-volatile resistive random-access memory and may also be useful in neuromorphic computing. Memristors have higher endurance and faster read/write times than flash memory and can provide multi-bit data storage. However, although two-terminal memristors have demonstrated capacity for basic neural functions, synapses in the human brain outnumber neurons by more than a thousandfold, which implies that multi-terminal memristors are needed to perform complex functions such as heterosynaptic plasticity. Previous attempts to move beyond two-terminal memristors, such as the three-terminal Widrow-Hoff memristor and field-effect transistors with nanoionic gates or floating gates, did not achieve memristive switching in the transistor. Here we report the experimental realization of a multi-terminal hybrid memristor and transistor (that is, a memtransistor) using polycrystalline monolayer molybdenum disulfide (MoS) in a scalable fabrication process. The two-dimensional MoS memtransistors show gate tunability in individual resistance states by four orders of magnitude, as well as large switching ratios, high cycling endurance and long-term retention of states. In addition to conventional neural learning behaviour of long-term potentiation/depression, six-terminal MoS memtransistors have gate-tunable heterosynaptic functionality, which is not achievable using two-terminal memristors. For example, the conductance between a pair of floating electrodes (pre- and post-synaptic neurons) is varied by a factor of about ten by applying voltage pulses to modulatory terminals. In situ scanning probe microscopy, cryogenic charge transport measurements and device modelling reveal that the bias-induced motion of MoS defects drives resistive switching by dynamically varying Schottky barrier heights. Overall, the seamless integration of a memristor and transistor into one multi-terminal device could enable complex neuromorphic learning and the study of the physics of defect kinetics in two-dimensional materials.

Memristive systems offer biomimetic functions that are being actively explored for energy-efficient neuromorphic circuits. In addition to providing ultimate geometric scaling limits, 2D semiconductors enable unique gatetunable responses including the recent realization of hybrid memristor and transistor devices known as memtransistors. In particular, monolayer MoS 2 memtransistors exhibit nonvolatile memristive switching where the resistance of each state is modulated by a gate terminal. Here, further control over the memtransistor neuromorphic response through the introduction of a second gate terminal is gained. The resulting dual-gated memtransistors allow tunability over the learning rate for non-Hebbian training where the long-term potentiation and depression synaptic behavior is dictated by gate biases during the reading and writing processes. Furthermore, the electrostatic control provided by dual gates provides a compact solution to the sneak current problem in traditional memristor crossbar arrays. In this manner, dual gating facilitates the full utilization and integration of memtransistor functionality in highly scaled crossbar circuits. Furthermore, the tunability of long-term potentiation yields improved linearity and symmetry of weight update rules that are utilized in simulated artificial neural networks to achieve a 94% recognition rate of handwritten digits.

Using scalable solution processing, layered gallium telluride (GaTe) nanoflake dispersions are produced in surfactant-free, low-boiling-point, water–ethanol cosolvent mixtures. During exfoliation, chemical degradation of the ambient-reactive GaTe crystals is minimized by using deoxygenated solvents in a sealed tip ultrasonication system. The structural and chemical integrity of the solution-processed GaTe nanoflakes is subsequently confirmed with a comprehensive suite of microscopic and spectroscopic analyses. Furthermore, field-effect transistors and phototransistors based on individual solution-processed GaTe nanoflakes show electronic and optoelectronic properties, respectively, that are comparable to micromechanically exfoliated GaTe. Minimal solution-processing residues from the surfactant-free, low-boiling-point cosolvent dispersion medium coupled with the high intrinsic hole doping of GaTe produces the highest electrical conductivity among solution-processed layered nanoflake thin films without post-treatment. Large-area photodetectors based on these electrically percolating thin films of solution-processed GaTe nanoflakes show a positive correlation between responsivity and illumination intensity, with a high photoconversion gain that is explained by a combination of defect-mediated optical processes and photothermal effects. Overall, this study establishes solution-processed layered GaTe nanoflakes as a leading candidate for high-performance, large-area, thin-film photodetectors.

Background/AimsFew studies have evaluated the use of a smartphone application (app) for educating people undergoing colonoscopy and optimizing bowel preparation. Therefore, this study was designed to develop a smartphone app for people to use as a preparation guide and to evaluate the efficacy of this app when used prior to colonoscopy.MethodsIn total, 142 patients (male:female=84:58, mean age=43.5±9.3 years), who were scheduled to undergo a colonoscopy at Myongji Hospital, were enrolled in this study. Seventy-one patients were asked to use a smartphone app that we had recently developed to prepare for the colonoscopy, while the 71 patients of the sex and age-matched control group were educated via written and verbal instructions.ResultsThe quality of bowel cleansing, evaluated using the Boston Bowel Preparation Scale, was significantly higher in the smartphone app group than in the control group (7.70±1.1 vs. 7.24±0.8, respectively, p=0.007 by t-test). No significant differences were found between the two groups regarding work-up time and the number of patients with polyps.ConclusionsIn this study, targeting young adults (≤50 years), the bowel preparation achieved by patients using the smartphone app showed significantly better quality than that of the control group.