Achieving good contacts is vital for harnessing the fascinating properties of two-dimensional (2D) materials. However, unsatisfactory 2D material-metal interfaces remain a problem that hinders the successful application of 2D materials for fabricating nanodevices. In this study, Kelvin probe force microscopy (KPFM) and other high-resolution microscopy techniques are utilized to characterize the surface morphology and contact interface between MoS 2 and common metals including Au, Ti, Pd, and Ni. Surface potential information, including the contact potential difference (V CPD ) and surface potential difference (∆V CPD ) of each MoS 2 -metal contact, is obtained. By comparing the surface potential distribution mappings with and without illumination, non-zero surface photovoltage (SPV) values and evident shift with amplitudes of 32 mV and 44 mV are observed for MoS 2 -Au and Ti, but not for MoS 2 -Pd and Ni. The Schottky barrier heights of MoS 2 -Au, Ti, Pd, and Ni are roughly evaluated from their I-V curves. Raman spectroscopy is also carried out to ensure more convincing results. All the results suggest that a smoother MoS 2 -metal interface results in better charge transport behaviors. Our analysis of the underlying mechanism and experimental findings offer a new perspective to better understand MoS 2 -metal contacts and underscore the fundamental importance of interface morphology for MoS 2 -based devices.
Recent progresses in the synthesis of large-area and stable atomically thin MoS2 have evoked enormous interest toward the future applications of two-dimensional (2D) electronics. Although considerable theoretical researches have been conducted to examine the zigzag and armchair lattice orientations of MoS2, which are closely related to the physical and chemical properties of this material, experimental investigations into these two orientations are still quite rare. In this paper, we present an experimental study on nanofabrication along the zigzag and armchair orientations of monolayer MoS2 using normal- and phase-mode AFM. After identifying the zigzag and armchair orientations, distinctly different nanofabrication forces along these two orientations are obtained, which are approximately 15.9 nN and 35.8 nN, respectively. To determine the underlying mechanism of this discrepancy, molecular dynamics simulation is performed. The simulated nanofabrication forces along the zigzag and armchair orientations are 12.16 ± 0.59 nN and 21.45 ± 0.74 nN, respectively, in good agreement with the experimentally measured ones. The results provide a better understanding of the zigzag and armchair lattice orientations of monolayer MoS2 as well as a promising approach to closed-loop fabrication of 2D materials with desirable lattice orientations.
In view of the high demand for low temperature coefficient reference current sources in integrated circuits, the advantages and disadvantages of several typical reference current sources in circuit structure and temperature characteristics are compared. In this paper, a low temperature coefficient reference current source is designed. Based on Hua Hong HHNECGE 0.35um process, the output current is 0.4uA, the temperature range is -40°C-125°C, and the temperature coefficient is 7.6ppm/°C under typical process angle. Other processes The temperature coefficient under the corner is at 10ppm/°C.
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