Interlayer interactions at the heterointerfaces of van der Waals heterostructures (vdWHs), which consist of vertically stacked two-dimensional materials, play important roles in determining their properties. The inter...Interlayer interactions at the heterointerfaces of van der Waals heterostructures (vdWHs), which consist of vertically stacked two-dimensional materials, play important roles in determining their properties. The interlayer interactions are tunable from noncoupling to strong coupling by controlling the twist angle between adjacent layers. However, the influence of stacking sequence and individual component thickness on the properties of vdWHs has rarely been explored. In this work, the influence of the stacking sequence of WSe2 and graphene in vdWHs of graphene-on-WSe2 (graphene/WSe2) or WSe2-on-graphene (WSe2/graphene), as well as their thickness, on their interlayer interaction was systematically investigated by ultralow-frequency (ULF) Raman spectroscopy. A series of ULF breathing modes of WSe2 nanosheets in these vdWHs were observed with frequencies highly dependent on graphene thickness. Interestingly, the ULF breathing modes of WSe2 red-shifted in graphene/WSe2 and WSe2/graphene configurations, and the amount of shift in the former was much larger than that in the latter. In contrast, no obvious ULF shift was observed by varying the twist angle between WSe2 and graphene. This indicates that the interlayer interaction is more sensitive to the stacking sequence compared with the twist angle. The results provide alternative approaches to modulate the interlayer interaction of vdWHs and, thus, tune their optical and optoelectronic properties.展开更多
Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D...Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D confined adsorbates on the properties of 2D materials is rarely explored. Herein, we combined atomic force microscopy(AFM), Kelvin probe force microscopy(KPFM) and Raman spectroscopy especially the ultralow frequency(ULF) Raman spectroscopy to explore the influence of 2D confined organic adlayer thickness on the ULF breathing modes of few-layer MoS2 and WSe2nanosheets. As the thickness of organic adlayers increased, red shift, coexistence of blue and red shifts as well as blue shift of ULF breathing mode was observed. KPFM measurement confirmed the enhanced n-doping and p-doping behaviors of organic adlayers as their thickness increased,respectively. Our results will provide new insights into the interaction between 2D confined adsorbates and bottom surface of 2D nanosheets, which could be useful for modulating properties of 2D materials.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 21571101 and 51322202)the Natural Science Foundation of Jiangsu Province in China (Grant Nos. BK20161543 and BK20130927)+1 种基金the Joint Research Fund for Overseas Chinese, Hong Kong and Macao Scholars (Grant No. 51528201)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 15KJB430016).
文摘Interlayer interactions at the heterointerfaces of van der Waals heterostructures (vdWHs), which consist of vertically stacked two-dimensional materials, play important roles in determining their properties. The interlayer interactions are tunable from noncoupling to strong coupling by controlling the twist angle between adjacent layers. However, the influence of stacking sequence and individual component thickness on the properties of vdWHs has rarely been explored. In this work, the influence of the stacking sequence of WSe2 and graphene in vdWHs of graphene-on-WSe2 (graphene/WSe2) or WSe2-on-graphene (WSe2/graphene), as well as their thickness, on their interlayer interaction was systematically investigated by ultralow-frequency (ULF) Raman spectroscopy. A series of ULF breathing modes of WSe2 nanosheets in these vdWHs were observed with frequencies highly dependent on graphene thickness. Interestingly, the ULF breathing modes of WSe2 red-shifted in graphene/WSe2 and WSe2/graphene configurations, and the amount of shift in the former was much larger than that in the latter. In contrast, no obvious ULF shift was observed by varying the twist angle between WSe2 and graphene. This indicates that the interlayer interaction is more sensitive to the stacking sequence compared with the twist angle. The results provide alternative approaches to modulate the interlayer interaction of vdWHs and, thus, tune their optical and optoelectronic properties.
基金supported by the National Natural Science Foundation of China (21571101 and 51322202)the Natural Science Foundation of Jiangsu Province in China (BK20161543 and BK20130927)+1 种基金the Joint Research Fund for Overseas Chinese, Hong Kong and Macao Scholars (51528201)Natural Science Foundation of Jiangsu Higher Education Institutions of China (15KJB430016)
文摘Recently, it has been reported that physisorbed adsorbates can be trapped between the bottom surface of twodimensional(2D) materials and supported substrate to form2 D confined films. However, the influence of such 2D confined adsorbates on the properties of 2D materials is rarely explored. Herein, we combined atomic force microscopy(AFM), Kelvin probe force microscopy(KPFM) and Raman spectroscopy especially the ultralow frequency(ULF) Raman spectroscopy to explore the influence of 2D confined organic adlayer thickness on the ULF breathing modes of few-layer MoS2 and WSe2nanosheets. As the thickness of organic adlayers increased, red shift, coexistence of blue and red shifts as well as blue shift of ULF breathing mode was observed. KPFM measurement confirmed the enhanced n-doping and p-doping behaviors of organic adlayers as their thickness increased,respectively. Our results will provide new insights into the interaction between 2D confined adsorbates and bottom surface of 2D nanosheets, which could be useful for modulating properties of 2D materials.
