Tesis doctoral de Amelia Barreiro Megino
After a motivation into the field of molecular electronics in the first chapter, an introduction into the properties of carbon nanotube based devices as compared to si technology is given. The state-of-the-art of cntfets, cntfet logic circuits, cnt optoelectronic devices, cnt interconnects and graphene fets is reviewed. Special emphasis is given to state-of-the-art nems. After that, an outlook to carbon-based electronics is given. In this chapter, the aim of this work is elucidated, too. some basic concepts that could be useful for a better understanding of this thesis are summarized in the second chapter, such as the characteristic lengths in mesoscopic physics, classical and ballistic conduction, as well as the transport properties in mesoscopic disordered systems, the principal band structures of solids and the quantum hall effect. graphene is introduced in the third chapter. Its electronic properties as well as the anomalous quantum hall effect are discussed and, finally, the phonon dispersion relation of graphene is presented. in the fourth chapter, an introduction to cnts is given. First of all, the structural and electronic properties are reviewed. A short introduction to the phonon dispersion relation is given. Thereafter an overview to the current synthesis and purification methods of cnts and the different characterisation methods for cnts is given. the main results of this thesis can be separated into three parts: first, nanotube growth; second, mwnt based nems and their properties; and third, high bias transport properties of graphene and application of a high-bias to achieve the current-induced cleaning technique. These three parts are summarized as in the following. first, a comprehensive study of the growth of swnts with a controlled diameter distribution using different methods is presented. These results are analyzed in chapter 5. on one hand, the influence of gas flow on nanotube diameter during the synthesis of high-purity, very long swcnts via aerosol-assisted chemical vapour deposition is reported. The sample morphology, nanotube yield, defect concentration and amount of carbonaceous impurities, as well as the mean diameter and the diameter distribution of the swcnts were analysed by combined scanning- and transmission electron microscopy, fourier transform raman spectroscopy and optical absorption spectroscopy. The results show that by using a solution of ferrocene and sulphur in m-xylene the addition of sulphur as a promoter was found to enhance the swcnt growth and to increase the yield. A reduction of the mean diameter and a change in the diameter distribution are observed when the total gas flow is increased. on the other hand, a new method to grow bulk quantities of swcnts by a catalytic chemical vapor deposition process with the possibility to vary the pressure has been developed and is reported in this thesis. Thermal decomposition of ferrocene provides both catalytic particles and carbon source for swcnt growth using ar as a carrier gas. Upon an increase of the pressure the mean diameter of the swcnts decreases. In fact, high abundances of swcnt with diameters as small as 0.7 nm, which is the limit for stable caps with isolated pentagons, can be obtained. An additional advantage of this method is that as no external carbon sources are required, swcnt synthesis can be achieved at temperatures as low as 650 ºc. second, we report on an artificial nanofabricated motor in which one short carbon nanotube moves relative to another coaxial nanotube. A cargo is attached to an ablated outer wall of a multiwalled carbon nanotube that can rotate and/or translate along the inner nanotube. The motion is actuated by imposing a thermal gradient along the nanotube, which allows for subnanometer displacements, as opposed to an electromigration or random walk effect. These results are presented in chapter 7. Depending on the device, the moveable shell either moves and/or rotates along and/or around the mwnt axis. The longitudinal, rotational or spiral motion is attributed to the potential barrier of the relative barrier between two shells, which depends on the chirality of the shells and, to our knowledge, this is the first experimental evidence of the chirality effect on the mechanical motion. Then, we compare our nanotube based thermal motors with molecular motors. Apart from that, we can obtain the thermal conductivity of suspended mwnts at high bias. third, we report on the high bias properties of graphene and its application. A simple yet highly reproducible method to suppress contamination of graphene at low temperature inside a cryostat is presented in the 8th chapter. The method is based on the application of a large current through the graphene devices, which generates several tens of mw dissipation over a few µm2 large surface. This extremely high current density is shown to remove contamination adsorbed on the surface and to improve the mobility of the samples. Remarkably, this simple cleaning technique allows us to obtain very high quality devices that enable the observation of the anomalous, half-integer quantum hall effect that is the signature of a clean, single graphene layer. Evidence of very high quality samples is demonstrated by measuring an additional plateau at the landau level n=0 at relatively low magnetic field (9 t). Interestingly, this plateau is visible only after the current-induced cleaning process. in the 9th chapter we present a detailed study of the high-current transport properties grapheme devices patterned in a 4-point configuration. The high current regime has special interest for application, e.G. For interconnects and graphene based fets.The current tends to saturate as the voltage across graphene is increased but never reaches the complete saturation as in metallic nanotubes. Measurements are compared to a model based on the boltzmann equation, which includes electron scattering processes due to charged and neutral impurities, and graphene optical-phonons. The saturation is incomplete because of the competition between disorder and optical-phonon scattering. This result holds promise for high-speed graphene electronics.
Datos académicos de la tesis doctoral «Carbon based electronics: from nanotube based thermal motors to graphene in the high-current limit«
- Título de la tesis: Carbon based electronics: from nanotube based thermal motors to graphene in the high-current limit
- Autor: Amelia Barreiro Megino
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 24/07/2009
Dirección y tribunal
- Director de la tesis
- Adrian Bachtold
- Tribunal
- Presidente del tribunal: eduardo Hernández
- thomas Pichler (vocal)
- (vocal)
- (vocal)