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Fabrication And Properties Of Graphene Based Nano-devices

Posted on:2014-01-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:K ZhangFull Text:PDF
GTID:1221330395989301Subject:Condensed matter physics
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Graphene, a two dimensional monolayer building block of a carbon allotrope, has emerged as an exotic material of21st century, and received world-wide attentions due to its exceptional charge transport, thermal, optical, and mechanical properties. Recent progress has shown that the graphene-based materials have a profound impact on and wide application for electronic and optoelectronic devices, chemical sensors, and energy storage. However, the absence of a bandgap is a hurdle for graphene to be used in the logic device, which requires high on/off switch ratio. In this regards, many strategies, such as constraining the graphene in nanoribbons or nanomash, controlling the stacking geometry of bilayer graphene, applying strain and chemical doping, have been proposed to open up the bandgap of the graphene and enhance the performance of field effecte transistor of graphene. On the other hand, one dreams that all carbon electrical circuits can be realized through direct writing on the graphene, which can be as improvement and alternation for the silicon based integrated circuits.To fulfill such ultimate goals, we focus our work on the fundamental research such as how to direct write graphene FET and circuits, how to design high performance graphene chemical sensor, and how to fabricate cost-effective and feasible nano-devices by combining technologies of atomic force microscope and e-beam lithography. Therfore, this dissertation has four chapters and the contents are outlined as follows.In chapter one, we first summarize the unique structure and physical properties of graphene, and describe some typical applications of graphene device. Then we introduce the principle and multiple working modes of the atomic force microscope, which is a powerful tool used in our research. At last, we present the motivation and aim of our work.In chapter two, the work of direct writing graphene nano-devices through localized catalytic reduction by the atomic force microscope is presented. It is found that the catalytic reduction of graphene oxide can occur by the Pt coated AFM tip under hydrogen ambience, and the reduction process is affected by the substrate temperature, tip load force and scanning velocity. The reduction is further confirmed by Raman spectroscopy and the electrical conducting experiments. With the control experiments, we verify the results that the Pt coated tip is as the catalyst while the hydrogen gas as the reducing agent in the reduction process. We also reveal that, through density functional theory calculation, the reduction process consists of six steps and the energy change during each step is the motivation for the reaction. In order to show the virtue of our proposed localized catalytic reduction techniuqe, we successfully direct write various highly conductive graphene interconnection nanoribbons and field effect transistors with Pt tip. The conductance and the carrier mobility of the fabricated graphene nanodevice can reach as high as104S/m and20cm2/VS respectively, which are among the highest quality of rGO nanoribbons. Finally, we suggest that, if we could combine our localized catalytic nanolithography with the local heating tip, the performance of fabricated graphene device can be further improved.In chapter three, we focus on the study of chemical gas sensing of rGO devices. Two methods, microwave-heating reduction and field induced reductuion, are proposed to fabricate the rGO devices. We demonstrate that the former can get large quantities of rGO with controllable reduction degree, while the latter can avoid chemical contaminations efficiently. Various rGO sensor devices with different reduction degree are fabricated on to the SiO2substrates by spin coating method and their respondences to the NO2circumstance are investigated systemically. For the fully reduced rGO device, the sensitivity can reach to35.5%/ppm when the NO2concentration is below1ppm. The performance is much higher than the similar sensor made from either the mechanically exfoliated graphene or the thermal reduced graphene. However, when NO2concentration increases beyond1ppm, the sensitivity of our device drops to4%/ppm, still compared to that previous reported. As for the partially reduced rGO device, the sensitivity can reach53±23%/ppm in the range of10ppm NO2concentration, ten times higher than that of the fully reduced rGO sensor. Moreover, the sensitivity can increase to196±104%/ppm with further decrease rGO reduction degree. All behaviors of above devices indicate that the defects on the rGO surface play a critical role in gas adsorption and charge transfer. Therefore, we expect that the high performance of NO2gas sensor can be made by appropriately modifying the rGO surface.In chapter four, we try to realize some critical nanostructure such as nanogap by combining the novel nanofabrication methods with the traditional lithographies. For example, with the help of Jeol heating and dielectrophoresis, we successfully prepared the10nm-less separation nanoelectrodes, which is the important prerequisite to realize the molecular device. We also demonstrate several sub-100nm nanostructures fabricated by either the anodic oxidation or the dip pen lithography. All these studies are helpful to realize the efficient, simple and cost saving fabrication for nanodevices.
Keywords/Search Tags:graphene, reduced graphene oxide, graphene nanoribbon, nanolithography, field effect transistor, nanosensor, scanning probemicroscopy
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