Single-walled Carbon Nanotube/graphene Van Der Waals Junctions For High-performance Nanodevices

Semiconducting single-walled carbon nanotubes?S-SWCNTs?with diameter-and chirality-dependent direct bandgaps?0.6¹.2 eV?have great potential for high-performance nanosensors due to their unique features of broadband?UV-NIR?light absorbance,large specific-surface-area,sensitive to ambient environment.Especially,the electronic transport in the axial direction of S-SWCNTs belongs to the ballistic transport,and the mean free path of carriers in the axial direction is at micro-scale.However,the mean free path of carriers in the radial direction of SWCNTs is only a few nanometres,which seriously suppressed radial carrier transport in SWCNTs.Thus,there are big challenges for further promoting the performance of such SWCNT sensors.Fortunately,the SWCNT/graphene van der Waals junctions are valid for improving the efficiency of carrier separation and charge transfer,moreover,controlling the optical and electronic properties in atom-scale.Herein,by systematically investigating the mechanism of charge transfer of SWCNT/graphene van der Waals junctions,different high-performance sensing nanodevices based on SWCNT/graphene van der Waals junctions have been studied,including photodetectors,humidity sensors and multifunctional nanosensors.Furthermore,the performance and mechanism of these nanodevices are discussed in detailed.The significant results achieved in the dissertation are given as following:?1?Systematically investigating the charge transfer at the?6,5?SWCNT/graphene van der Waals junctions.The results imply that the hole-doping in graphene converts to electron-doping when the applied bias voltage changes,and the critical voltage is 4V;both i-Ge and n-Ge substrate inject holes into graphene,and thus enhancing the electron-doping from?6,5?SWCNT to graphene;the electrons of water molecule injected to?6,5?SWCNT directly,and therefore changing the charge transfer of?6,5?SWCNT/graphene van der Waals junctions.?2?Firstly using separated graphene?SGR?to fabricate a broadband photodetector based on?6,5?SWCNT/graphene all-carbon van der Waals junctions.It has been demonstrated that the structure of SGR greatly decreases dark current of the device and the?6,5?SWCNT/SGR network still keeps ideal carrier transport.The responsivity,detectivity and conductive gain of the device are 3275.6 A/W,4.25×10¹22 Jones and 4×10⁶,respectively.The ultrafast response time of the device is 44?s.?3?Proposing the strategy for substrate-assisted enhancement of the photoelectric performance,a self-driven NIR photodetector based on?6,5?SWCNT/graphene van der Waals junctions has been fabricated.The device exhibits high responsivity of 833 A/W and detectivity of 4.6×10¹³Jones.?4?An all-carbon?6,5?SWCNT/graphene van der Waals junction humidity sensor has firstly been demonstrated by combining non-functionalized?6,5?SWCNTs with graphene.The humidity sensor exhibits high sensitivity of 1820%?80%RH?.When operated at zero or weak bias,the device still shows outstanding sensitivity with ultrafast response/recovery time of 198 ms/110 ms.Additionally,a new mechanism based on charge transfer and linkage effect has been demonstrated.?5?Firstly fabricating a self-driven multifunctional nanosensor based on?6,5?SWCNT/graphene van der Waals junctions.The sensitivity for light signal and humidity signal of the sensor is 20%and 43%,respectively,and the response for the two types of signal of the device is independent.