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Scanning Tunnelling Microscopic Image Simulation And Nanodevice Design Based On Monolayer And Multilayer Graphene

Posted on:2009-03-05Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z F WangFull Text:PDF
GTID:1101360242995922Subject:Condensed matter physics
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As silicon devices scaled down to 30 nanometers, conventional CMOS techniques are fast approaching its physical limitations. The developing of quantum electronic devices based on new materials, therefore, becomes important. Graphene is one of the most promising materials to build nanoelectronics. This novel two-dimensional material has excellent crystal structure and exhibits many interesting electronic properties. Integrated graphene-based circuits can be fabricated by using modern etching techniques. Electrons in conventional semiconducting device are described by the Schrodinger equation, but electrons in graphene are described by the relativistic Dirac equation. This special characteristic provides us a possible way to apply the quantum electrodumamics to study this two dimensional condensed matter material.In the first chapter of my thesis, I will give a brief introduction about the limitations that current silicon techniques are facing, and discuss the discovery of carbon nanotubes and their applications in nanoelectronics. I will then discuss the property of graphene including the special mass less Dirac fermions in graphene and the fabrication techniques.In the second chapter, I first introduce the tight binding model and then provide the analytical solution of the eigenstates and eigenvalues ofπorbit in monolayer and multilayer graphenes. I will also discuss how to obtain the corresponding real-space Green's function. Based on the effective mass approximation, I will derive an analytical expression of Green's function in real-space, which is constructed by multiplying the space isotropic and anisotropic functions. Combing with the Dyson equation, I simulate the scanning tunneling microscope image of single impurity and quantum corral on a graphene. I also discuss the effect of single vacancy and double vacancies, long range and short-rang potential on a bilayer graphene. These results exhibit an intrinsic three-fold symmetric pattern on graphene when the impurities do not destroy such symmetry. My further study on multilayer graphene also shows that the surface electronic properties of the bilayer graphene can capture most properties of multilayer graphene. This finding is significant because it indicates that we can use a graphite sample to indirectly study the surface properties of a bilayer graphene.In the third chapter, I study the ballistic transport properties of graphene nanoribbon using the Landauer model. Under the tight binding framework, I designed several quantum devices that show many novel physical phenomena and they are: 1. Z-shaped quantum-dot device. We connect the armchair and zigzag graphene nanoribbon to form a Z-shaped junction. The quantum dot can be trapped in the center metallic junction region. In addition, the quantum dot is not destroyed by impurities, substrate effect and irregular edge effect. 2. Zigzag graphene nanoribbon negative differential resistance device. The zigzag graphene nanoribbon is divided into two parts with different doping. The selective tunneling rules induce a nonlinear transport behavior in such a device. I provide an easy way to describe this special rule. 3. Armchair graphene nanoribbon switch device. Armchair graphene nanoribbon with different width can be either metalic or semiconducting. By connecting graphene nanoribbon with different width, the resulting device can modulate the gate voltage to achieving switching effect. I also find a selective tunneling effect in this device, which can be used to design the tunable quantum dot.
Keywords/Search Tags:Graphene, Scanning tunneling microscope, Quantum dot, Negative differential resistance, Switch
PDF Full Text Request
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