ABSTRACT
Interest has grown in services that consume a significant amount of energy, such as large language models (LLMs), and research is being conducted worldwide on synaptic devices for neuromorphic hardware. However, various complex processes are problematic for the implementation of synaptic properties. Here, synaptic characteristics are implemented through a novel method, namely side chain control of conjugated polymers. The developed devices exhibit the characteristics of the biological brain, especially spike-timing-dependent plasticity (STDP), high-pass filtering, and long-term potentiation/depression (LTP/D). Moreover, the fabricated synaptic devices show enhanced nonvolatile characteristics, such as long retention time (≈102 s), high ratio of Gmax/Gmin, high linearity, and reliable cyclic endurance (≈103 pulses). This study presents a new pathway for next-generation neuromorphic computing by modulating conjugated polymers with side chain control, thereby achieving high-performance synaptic properties.
Subject(s)
Polymers , Synapses , Polymers/chemistry , Synapses/physiology , Neuronal Plasticity/physiology , Neural Networks, ComputerABSTRACT
Recently, two-dimensional transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) have attracted great attention due to their unique properties. To modulate the electronic properties and structure of TMDs, it is crucial to precisely control chalcogenide vacancies and several methods have already been suggested. However, they have several limitations such as plasma damage by ion bombardment. Herein, we introduced a novel solvent-assisted vacancy engineering (SAVE) method to modulate sulfur vacancies in MoS2. Considering polarity and the Hansen solubility parameter (HSP), three solvents were selected. Sulfur vacancies can be modulated by immersing MoS2 in each solvent, supported by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses. The SAVE method can further expand its application in memory devices representing memristive performance and synaptic behaviors. We represented the charge transport mechanism of sulfur vacancy migration in MoS2. The non-destructive, scalable, and novel SAVE method controlling sulfur vacancies is expected to be a guideline for constructing a vacancy engineering system of TMDs.
ABSTRACT
For evaluating the effect of light absorption in vertically structured thin film light-emitting diodes (VLEDs), we investigate the dependence of the efficiencies on the several specific parameters including thickness and doping concentration (N(D)) of the n-GaN layer, a design of hetero-structures of the n-GaN layer, and a number of pairs of multi-quantum wells (MQWs). Generally, there is a complementary relation between internal quantum efficiency (IQE) and light extraction efficiency (LEE). However, we confirmed that LEE determined by light absorption is more dominant than IQE in VLED structures with a textured surface, from numerical simulation and experimental results. Effect of light absorption is more prominent in the vertical chip with a textured surface than in that with a flat surface, because a travel length of light extracted from the textured surface is longer. Minimizing light absorption in VLEDs is a key technology for improving light output, and light absorption speaks for the index of enhancement by the general technologies for improving LEE.
ABSTRACT
The optical transmission spectra of several samples of gold nanoparticle layers were examined using a modified Drude model proposed with a novel elastic scattering parameter, gamma'. Although the measured transmission spectra deviated from the simple calculation from Mie scattering, it was explained well by the modified model assuming elastic and inelastic scattering in the form of the collision frequency of free electrons within a metal particle due to the particle boundary. The particle-size and inter-particle-distance dependences of gamma' were extracted within the framework of the proposed model from the curve of best fit of the transmittance spectra.
