Self-Powered Bidirectional Photoresponse in High-Detectivity WSe2 Phototransistor with Asymmetrical van der Waals Stacking for Retinal Neurons Emulation.

An artificial retina system shows a promising potential to achieve fast response, low power consumption, and high integration density for vision sensing systems. Optoelectronic sensors, which can emulate the neurobiological functionalities of retinal neurons, are crucial in the artificial retina systems. Here, we propose a WSe2 phototransistor with asymmetrical van der Waals (vdWs) stacking that can be used as an optoelectronic sensor in artificial retina systems. Through the utilization of the gate-tunable self-powered bidirectional photoresponse of this phototransistor, the neurobiological functionalities of both bipolar cells and cone cells, as well as the hierarchical connectivity between these two types of retinal neurons, are successfully mimicked by a single device. This self-powered bidirectional photoresponse is attributed to the asymmetrical vdWs stacking structure, which enables the transition from an n-p to p+-p homojunction in the WSe2 channel under different polarities of gate bias. Moreover, the detectivity and ON/OFF ratio of this phototransistor reach as high as 1.8 × 1013 Jones and 5.3 × 104, respectively, and a rise/fall time <80 µs is achieved, as well, which reveals good photodetection performance. The proof of this device provides a pathway for the future development of neuromorphic vision devices and systems.

Learning English vocabulary from word cards: A research synthesis.

Researchers' interest in the learning of vocabulary from word cards has grown alongside the increasing number of studies published on this topic. While meta-analyses or systematic reviews have been previously performed, the types of word cards investigated, and the number of word card studies analyzed were limited. To address these issues, a research synthesis was conducted to provide an inclusive and comprehensive picture of how the use of word cards by learners results in vocabulary learning. A search of the Web of Science and Scopus databases resulted in 803 potential studies, of which 32 aligned with the inclusion criteria. Coding of these studies based on an extensive coding scheme found most studies assessed receptive vocabulary knowledge more often than productive vocabulary knowledge, and knowledge of vocabulary form and meaning were assessed more often than knowledge of vocabulary use. Results of effect size plots showed that more of the reviewed studies showed larger effects for the use of paper word cards than digital word cards, and for the use of ready-made word cards than self-constructed word cards. Results also indicated more studies showed larger effects for using word cards in an intentional learning condition compared with an incidental learning condition, and for using word cards in a massed learning condition compared with a spaced learning condition. Although a correlation was found between time spent using word cards and vocabulary learning outcomes, this correlation was not statistically significant. Learners that were more proficient in English learned more words from using word cards than those less proficient. These results suggest that future researchers should report learner proficiency, adopt reliable tests to assess vocabulary learning outcomes, compare the effectiveness of ready-made word cards and self-constructed word cards, and investigate the learning of different aspects of word knowledge. Teachers should provide learners guidance in how to use word cards and target word selection for self-construction of word cards. In addition, teachers should encourage learners to create word cards for incidentally encountered unknown words and use massed learning when initially working with these new words before using spaced learning for later retrieval practice.