Recent years have witnessed major advances in development of massive nonlayer structured ultrathin materials, providing great enrichment to the 2D nanomaterial family. The intriguing physical and chemical properties brought by nonlayered nanomaterials have attracted tremendous research interest. In this work, a systematica study of the optical properties of 2D nonlayered β‐diindium trisulfide (β‐In2S3) is reported. The thickness‐dependent photoluminescence (PL), Raman spectra, and absorption property are measured for ultrathin β‐In2S3 flakes and found distinguished from its bulk counterpart. These peculiar features originate from the superficial indium oxide in ultrathin β‐In2S3, as revealed by low‐temperature PL and X‐ray photoelectron spectroscopy measurement. The Raman vibration modes are identified by Raman spectra measurements combined with calculations using density functional theory. Importantly, the tetragonal β‐In2S3 flakes exhibit strong in‐plane anisotropic Raman response under the angle‐resolved polarized Raman spectroscopy measurements. The results in this paper provide an in‐depth understanding of the emerging 2D nonlayered material In2S3 and pave a fundamental step for its potential applications in future electronics and optoelectronics.
Memtransistor, a hybrid structure that integrates the function of memristor and transistor, is a promising device prototype for the realization of complex neuromorphic learning owing to its diverse functionality and additional flexibility in emulating synaptic behaviors. Memtransistor of two-dimensional (2D) chalcogenide materials have received many interests as it has distinctive memristive mechanism quite different from conventional oxide memristors. Here, we report a memtransistor based on the twodimensional thin films (2DTFs) of non-layered β-In2S3. The In2S3 2DTFs grown by physical vapor deposition method have microscopically visible grain boundaries (GBs) formed by the stacking and interconnecting of 2D In2S3 flakes. The memtransistors of In2S3 2DTFs show tunable bipolar resistive states with resistance ratio up to 10 5 , endurance over 200 cycles, and a retention time of 10 4 s. Illumination of laser light from visible and near-infrared are able to induce intermediate resistance states in memtransistors, enabling optical-modulated multilevel memory storage. Also, the memtransistors are able to emulate the synaptic function of long-term potentiation (LTP) and long-term depression (LTD) with tunable synaptic weight in response to presynaptic stimuli of drain/gate pulses. Interestingly, the plasticity of LTP and LTD behavior can be switched in a highly tunable manner by simply varying the gate voltages. The diverse optoelectronic properties and controllable functionality of memtransistors based on the emerging 2D In2S3 offer a useful guide to potential application in electronic memory and artificial synapses.
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