A carbon nanotube bearing and Stodola rotor

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 171-181).A nano-scale rotor supported on a cantilevered multi-wall carbon nanotube (MWNT) shaft (Stodola configuration) is proposed. The nanotube is also expected to function as the bearing, since individual walls of a MWNT are not strongly bonded and can slide on each other with low friction. While MWNT based rotors have been previously constructed, they have so far been limited to horizontally oriented nanotubes. The rotor uses a vertically aligned tube, which allows superior control of the rotor geometry, enabling improved rotor balancing and axisymmetric features such as electrodes or blades. The rotor is proposed as a test stand for measuring inter-wall friction in MWNTs. The low friction in nanotubes has been studied with simulations and experiments, and while it is agreed that relative motion between walls is possible, there is much debate about the qualitative nature of the friction force between walls. Furthermore the reported quantitative values of friction vary by as much as ten orders of magnitude. The proposed rotor might be used to gather new friction data on rotating MWNT bearings at higher speeds that previously attempted. In addition, identical rotors fabricated on nanotubes of varying size, type, and crystalline quality might provide a large dataset that could be used to find correlations between friction behavior and these factors. Applications for the rotor beyond a friction testing apparatus could include pumps to work with existing micro-chemical sensors, gyroscopes, energy storage flywheels, and turbomachinery for power generation. A fabrication process for the proposed rotor was developed, and is being refined. An isolated vertically aligned MWNT is grown by chemical vapor deposition (CVD), from a nickel catalyst dot defined with electron-beam lithography. A silicon dioxide sacrificial layer is applied, followed by a polysilicon layer from which to cut out the rotor.(cont.) The rotor etch is performed by cryogenic reactive ion etching (RIE), patterned with electron-beam lithography. The rotor is released from the substrate by hydrofluoric acid vapor. One iteration of the fabrication process was completed, and further iterations are planned to complete a functional device. Actuation of the rotor would be achieved by directing jets of air at blades on the rotor, and an alternative electrostatic actuation concept is also proposed. A dynamic model of the rotor performance based on classical simple beam theory and rigid body dynamics indicates that speeds on the order of thousands to millions of revolutions per minute should be achievable, while avoiding the thirteen potential failure mechanisms analyzed.by Euguene Hightower Cook.S.M

Critical evaluation and novel design of a non-invasive and wearable health monitoring system

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.This study is about developing a non-invasive wearable health-monitoring system. The project aims to achieve miniaturisation as much as possible, using nanotechnology. The achieved results of the project are nothing but conceptual images of a convertible watch. The system is a non-invasive health measurement system. An important part of the study is researching the automation of blood pressure measurement by means of experiments which test the effect of exterior factors on blood pressure level. These experiments have been held to improve the automation and simplicity of BP measurements to establish a 24hr BP monitoring system. This study proposed a medical sensor that is part of the watch system, and that is most compatible with the elderly people product preferences in the UK. The “sensor strip” is in cm range, integrating a number of MEMS sensors, for the non-invasive detection of certain health aspects. The health aspects are chosen according to how close they are from the “health vital signs”, which are the first measurements executed by the doctor, if a patient is to visit him. An applied QFD study showed that the most suitable measurement technology to be used in the proposed sensor strip is the infrared technology. In addition to the sensor strip, EEG health detection is added, which is the reason why the watch is convertible. MEMS sensors, MEMS memory and an embedded processor are selected, since that this project also includes minimising the size of a device where the utilization of nanotechnology is vital. The final result of the study is only a conceptual design of a product with a carefully selected subsystems. The software design of the product will not be further developed to become a physical prototype of a consumer product

Future Missions to Titan: Scientific and Engineering Challenges

Saturn’s largest moon, Titan, has been an enigma at every stage of its exploration. For three decades after the hazy atmosphere was discovered from the ground in the 1940s, debate ensued over whether it was a thin layer of methane or a dense shield of methane and nitrogen. Voyager 1 settled the matter in favor of the latter in 1980, but the details of the thick atmosphere discovered raised even more intriguing questions about the nature of the hidden surface, and the sources of resupply of methane to the atmosphere. The simplest possibility, that an ocean of methane and its major photochemical product ethane might cover the globe, was cast in doubt by Earth-based radar studies and then eliminated by Hubble Space Telescope and adaptive optics imaging in the near-infrared from large ground-based telescopes in the 1990s. These data, however, did not reveal the complexity of the surface that Cassini-Huygens would uncover beginning in 2004. A hydrological cycle appears to exist in which methane (in concert with ethane in some processes) plays the role on Titan that water plays on Earth. Channels likely carved by liquid methane and/or ethane, lakes and seas of these materials—some rivaling or exceeding North America’s Great Lakes in size—vast equatorial dune fields of complex organics made high in the atmosphere and shaped by wind, and intriguing hints of geologic activity suggest a world with a balance of geologic and atmospheric processes that is the solar system’s best analogue to Earth. Deep underneath Titan’s dense atmosphere and active, diverse surface is an interior ocean discovered by Cassini and thought to be largely composed of liquid water. Cassini-Huygens has provided spectacular data and has enabled us to glimpse the mysterious surface of Titan. However the mission will leave us with many questions that require future missions to answer. These include determining the composition of the surface and the geographic distribution of various organic constituents. Key questions remain about the ages of surface features, specifically whether cryovolcanism and tectonism are actively ongoing or are relics of a more active past. Ammonia, circumstantially suggested to be present by a variety of different kinds of Cassini-Huygens data, has yet to be seen. Is methane out-gassing from the interior or ice crust today? Are the lakes fed primarily by rain or underground methane-ethane aquifers (more properly, “alkanofers”) and how often have heavy methane rains come to the equatorial region? We should investigate whether Titan’s surface supported vaster seas of methane in the past, and whether complex self-organizing chemical systems have come and gone in the water volcanism, or even exist in exotic form today in the high latitude lakes. The presence of a magnetic field has yet to be established. A large altitude range in the atmosphere, from 400–900 km in altitude, will remain poorly explored after Cassini. Much remains to be understood about seasonal changes of the atmosphere at all levels, and the long-term escape of constituents to space. Other than Earth, Titan is the only world in our solar system known to have standing liquids and an active “hydrologic cycle” with clouds, rains, lakes and streams. The dense atmosphere and liquid lakes on Titan’s surface can be explored with airborne platforms and landed probes, but the key aspect ensuring the success of future investigations is the conceptualization and design of instruments that are small enough to fit on the landed probes and airborne platforms, yet sophisticated enough to conduct the kinds of detailed chemical (including isotopic), physical, and structural analyses needed to investigate the history and cycling of the organic materials. In addition, they must be capable of operating at cryogenic temperatures while maintaining the integrity of the sample throughout the analytic process. Illuminating accurate chemistries also requires that the instruments and tools are not simultaneously biasing the measurements due to localized temperature increases. While the requirements for these techniques are well understood, their implementation in an extremely low temperature environment with limited mass, power and volume is acutely challenging. No such instrument systems exist today. Missions to Titan are severely limited in both mass and power because spacecraft have to travel over a billion miles to get there and require a large amount of fuel, not only to reach Titan, but to maintain the ability to maneuver when they arrive. Landed missions have additional limitations, in that they must be packaged in a sealed aeroshell for entry into Titan’s atmosphere. Increases in landed mass and volume translate to increased aeroshell mass and size, requiring even more fuel for delivery to Titan. Nevertheless, missions during which such systems and instruments could be employed range from Discovery and New Frontiers class in situ probes that might be launched in the next decade, to a full-up Flagship class mission anticipated to follow the Europa Jupiter System Mission. Capitalizing on recent breakthroughs in cryo-technologies and smart materials fabrication, we developed conceptual designs of sample acquisition systems and instruments capable of in situ operation under low temperature environments. The study included two workshops aimed at brainstorming and actively discussing a broad range of ideas and associated challenges with landing instruments on Titan, as well as more focused discussions during the intervening part of the study period. The workshops each lasted ~4 days (Monday-Thursday/Friday), included postdoctoral fellows and students in addition to the core team members, and generated active engagement from the Caltech and JPL team participants, as well as from the outside institutions. During the workshops, new instruments and sampling methodologies were identified to handle the challenges of characterizing everything from small molecules in Titan’s upper atmosphere to gross mixtures of high molecular weight complex organics in condensed phases, including atmospheric aerosols and “organic sand” in dunes, to highly dilute components in ices and lakes. To enable these advances in cryogenic instrumentation breakthroughs in a wide range of disciplines, including electronics, chemical and mechanical engineering, and materials science were identified

Detecting Delamination in Carbon Fiber Composites Using Piezoresistive Nanocomposites

Carbon fiber prepreg composites are utilized successfully as structural materials for different lightweight aerospace applications. Delamination is a critical failure mode in these composite materials. As composite plies separate from each other, the composite loses some of its ability for supporting expected loads. Therefore, detection of delamination at right time is a foremost significance. This study presents a new way for detecting delamination in composite plates using piezoresistive nanocomposites. This new procedure is setup and studied through both experimental and computational investigations. In this research, nanocomposites with 5% coarse graphene platelets are fabricated for detecting delamination. 8-ply carbon fiber prepreg composite samples are fabricated by placing a Teflon film between layers of prepreg. Piezoresistive nanocomposites are attached on top of prepreg laminate samples using epoxy resin. The change in electrical resistivity of these nanocomposites due to the induced strain from flexural test (three point bend test) on delaminated and neat composite laminates are monitored to demonstrate the delamination detection and neat composite laminates are monitored to demonstrate the delamination detection method. A non-linear finite element model is developed using Abaqus software suite to compliment the mechanical testing. Virtual Crack Closure Technique (VCCT) is used to model a delamination in the composite sample. Experimental results and the simulations in this study indicate that piezoresistive nanocomposites can be used for detecting delamination in carbon fiber composite materials

Carbon nanotube bearings in theory and practice

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 157-170).Carbon Nanotubes (CNTs) are attractive elements for bearings in Micro-Electro-Mechanical Systems (MEMS), because their structure comprises nested shells with no bonding and sub-nanometer spacing between them, enabling relative motion with low friction and wear. A few demonstrations of CNT bearings have been reported in the literature, and atomistic simulations have been used to probe the properties of these bearings. This thesis extends the state of knowledge about these bearing systems, by building on these prior works in both the experimental and simulation domains. The prototype CNT rotor device presented in this thesis, and accompanying fabrication process, improve on existing CNT bearing demonstrators by establishing a vertical bearing orientation (enabling superior rotor balance and speed, and flexibility of placement for drive mechanisms) and a more manufacturable process (employing CNTs grown in place by chemical vapor deposition, and evaluating trade-offs in growth parameters). The device consists of a silicon rotor, supported on a cantilevered CNT shaft, and actuated by impingement of air jets on blades around its perimeter. For the fabrication development, extensive and consistent studies on the compatibility of CNTs with a suite of standard MEMS process were conducted, yielding valuable information for future CNT-based device designers on the effects of these processes on CNTs. Additionally, manual manipulation and placement of loose CNTs into the required vertical alignment was demonstrated, providing an alternate fabrication route, as well as a useful research technique for development of CNT devices. Simulation of friction in a CNT bearing system has been a popular topic, yet many questions remain open. For example, the quantitative estimates of this friction reported to date range by as much as eight orders of magnitude, and simulation techniques employ a variety of disparate simulation paradigms and parameters. This thesis presents a new suite of consistently implemented but complementary and independent simulations, which span the approaches reported to date, yet agree quantitatively within the error margin. Furthermore, the quantitative relationships between friction and sliding speed, temperature, geometry, and simulation implementation parameters are determined, and a description of the causes of friction based on phonon analyses is offered.by Eugene Hightower Cook.Ph.D

Polaron physics in carbon nanotube electro-mechanical resonators

Carbon nanotube (CNT) mechanical resonators are unique systems because they combine remarkable mechanical properties with rich charge transport characteristics. Thanks to their intrinsically low-dimensional nature, their mass is extremely low. The mechanical resonance frequency reaches the GHz regime, can be widely tunable and they show quality factor as high as several million. Nanotubes hold great promise for sensing applications. Nanotubes are an excellent system to study quantum electron transport, which range from abry-Pérot interference to Coulomb blockade. These completely opposite regimes can be very efficiently coupled to the mechanics, since the two degrees of freedom, electrons and phonons, are embedded in the same system. In the first section of this thesis we develop a detection scheme utilizing a RLC resonator together with a low-temperature HEMT amplifier. This allows us to lower the current noise floor of the setup and carry out sensitive electrical noise measurements, demonstrating a displacement sensitivity of 0.5 pm/Hz^(1/2) and a force sensitivity of 4.3 zN/Hz^(1/2). This surpasses what has been achieved with mechanical resonators to date and paves the way for the detection of ndividual nuclear spins. We also improve the device fabrication enhancing the capacitive coupling between mechanical vibrations and electrons flowing though the nanotube. In the second part of this work, we study the electron-phonon coupling in CNT resonators in the Coulomb blockade regime and report on the long-sought-after demonstration of the ultra-strong coupling regime. Mechanical vibrations and electrons are so strongly coupled that it no longer makes sense to think of them as distinct entities, but rather as a quasi-particle: a polaron. First, we demonstrate that the polaronic nature of charge carriers modifies the quantum electron transport through the device. In previous electromechanical devices, the coupling was too weak to have any effect on the DC electrical conductance. Second, we show high tunability of polaron states by electrostatic means. This is something not possible to do with polarons in other systems, such as bulk crystals. Notably, this interaction creates a highly nonlinear potential for the phonon mode which establishes nanotube resonator as a possible platform for the demonstration of mechanical qubits.Los resonadores mecánicos de nanotubos de carbono (CNT) son sistemas únicos porque combinan propiedades mecánicas notables con ricas características de transporte de carga. Gracias a su naturaleza intrínsecamente de baja dimensión, su masa es extremadamente baja. La frecuencia de resonancia mecánica alcanza el régimen de GHz, puede ser ampliamente ajustable y muestra un factor de calidad de hasta varios millones. Los nanotubos son muy prometedores para las aplicaciones de detección. Los nanotubos son un excelente sistema para estudiar el transporte cuántico de electrones, que van desde la interferencia Fabry-Pérot hasta el bloqueo de Coulomb. Estos regímenes completamente opuestos se pueden acoplar de manera muy eficiente a la mecánica, ya que los dos grados de libertad, electrones y fonones, están integrados en el mismo sistema. En la primera sección de esta tesis desarrollamos un esquema de detección que utiliza un resonador RLC junto con un amplificador HEMT de baja temperatura. Esto nos permite reducir el ruido de fondo actual del setup y realizar mediciones de ruido eléctrico sensibles, demostrando una sensibilidad de desplazamiento de 0.5 pm/Hz^(1/2) y una sensibilidad de fuerza de 4.3zN/Hz^(1/2) . Esto supera lo que se ha logrado con resonadores mecánicos hasta la fecha y allana el camino para la detección de espines nucleares individuales. También mejoramos la fabricación del dispositivo mejorando el acoplamiento capacitivo entre vibraciones mecánicas y electrones que fluyen a través del nanotubo. En la segunda parte de este trabajo, estudiamos el acoplamiento de electrones y fonones en resonadores CNT en el régimen de bloqueo de Coulomb e informamos sobre el tan buscado después de la demostración del régimen de acoplamiento ultra fuerte. Las vibraciones mecánicas y los electrones están tan fuertemente acoplados que ya no tiene sentido pensar en ellos como entidades distintas, sino más bien como una casi partícula: un polaron. Primero, demostramos que la naturaleza polarónica de los portadores de carga modifica el transporte cuántico de electrones a través del dispositivo. En dispositivos electromecánicos anteriores, el acoplamiento era demasiado débil para tener algún efecto sobre la conducción eléctrica continua. En segundo lugar, mostramos una alta capacidad de sintonización de los estados de Polaron por medios electrostáticos. Esto es algo que no es posible hacer con los polarones en otros sistemas, como los cristales a granel. Notablemente, esta interacción crea un potencial altamente no lineal para el modo de fonón que establece el resonador de tubos de resonancia como una posible plataforma para la demostración de qubits mecánicosPostprint (published version

Polaron physics in carbon nanotube electro-mechanical resonators

Carbon nanotube (CNT) mechanical resonators are unique systems because they combine remarkable mechanical properties with rich charge transport characteristics. Thanks to their intrinsically low-dimensional nature, their mass is extremely low. The mechanical resonance frequency reaches the GHz regime, can be widely tunable and they show quality factor as high as several million. Nanotubes hold great promise for sensing applications. Nanotubes are an excellent system to study quantum electron transport, which range from abry-Pérot interference to Coulomb blockade. These completely opposite regimes can be very efficiently coupled to the mechanics, since the two degrees of freedom, electrons and phonons, are embedded in the same system. In the first section of this thesis we develop a detection scheme utilizing a RLC resonator together with a low-temperature HEMT amplifier. This allows us to lower the current noise floor of the setup and carry out sensitive electrical noise measurements, demonstrating a displacement sensitivity of 0.5 pm/Hz^(1/2) and a force sensitivity of 4.3 zN/Hz^(1/2). This surpasses what has been achieved with mechanical resonators to date and paves the way for the detection of ndividual nuclear spins. We also improve the device fabrication enhancing the capacitive coupling between mechanical vibrations and electrons flowing though the nanotube. In the second part of this work, we study the electron-phonon coupling in CNT resonators in the Coulomb blockade regime and report on the long-sought-after demonstration of the ultra-strong coupling regime. Mechanical vibrations and electrons are so strongly coupled that it no longer makes sense to think of them as distinct entities, but rather as a quasi-particle: a polaron. First, we demonstrate that the polaronic nature of charge carriers modifies the quantum electron transport through the device. In previous electromechanical devices, the coupling was too weak to have any effect on the DC electrical conductance. Second, we show high tunability of polaron states by electrostatic means. This is something not possible to do with polarons in other systems, such as bulk crystals. Notably, this interaction creates a highly nonlinear potential for the phonon mode which establishes nanotube resonator as a possible platform for the demonstration of mechanical qubits.Los resonadores mecánicos de nanotubos de carbono (CNT) son sistemas únicos porque combinan propiedades mecánicas notables con ricas características de transporte de carga. Gracias a su naturaleza intrínsecamente de baja dimensión, su masa es extremadamente baja. La frecuencia de resonancia mecánica alcanza el régimen de GHz, puede ser ampliamente ajustable y muestra un factor de calidad de hasta varios millones. Los nanotubos son muy prometedores para las aplicaciones de detección. Los nanotubos son un excelente sistema para estudiar el transporte cuántico de electrones, que van desde la interferencia Fabry-Pérot hasta el bloqueo de Coulomb. Estos regímenes completamente opuestos se pueden acoplar de manera muy eficiente a la mecánica, ya que los dos grados de libertad, electrones y fonones, están integrados en el mismo sistema. En la primera sección de esta tesis desarrollamos un esquema de detección que utiliza un resonador RLC junto con un amplificador HEMT de baja temperatura. Esto nos permite reducir el ruido de fondo actual del setup y realizar mediciones de ruido eléctrico sensibles, demostrando una sensibilidad de desplazamiento de 0.5 pm/Hz^(1/2) y una sensibilidad de fuerza de 4.3zN/Hz^(1/2) . Esto supera lo que se ha logrado con resonadores mecánicos hasta la fecha y allana el camino para la detección de espines nucleares individuales. También mejoramos la fabricación del dispositivo mejorando el acoplamiento capacitivo entre vibraciones mecánicas y electrones que fluyen a través del nanotubo. En la segunda parte de este trabajo, estudiamos el acoplamiento de electrones y fonones en resonadores CNT en el régimen de bloqueo de Coulomb e informamos sobre el tan buscado después de la demostración del régimen de acoplamiento ultra fuerte. Las vibraciones mecánicas y los electrones están tan fuertemente acoplados que ya no tiene sentido pensar en ellos como entidades distintas, sino más bien como una casi partícula: un polaron. Primero, demostramos que la naturaleza polarónica de los portadores de carga modifica el transporte cuántico de electrones a través del dispositivo. En dispositivos electromecánicos anteriores, el acoplamiento era demasiado débil para tener algún efecto sobre la conducción eléctrica continua. En segundo lugar, mostramos una alta capacidad de sintonización de los estados de Polaron por medios electrostáticos. Esto es algo que no es posible hacer con los polarones en otros sistemas, como los cristales a granel. Notablemente, esta interacción crea un potencial altamente no lineal para el modo de fonón que establece el resonador de tubos de resonancia como una posible plataforma para la demostración de qubits mecánico

From RF-Microsystem Technology to RF-Nanotechnology

The RF microsystem technology is believed to introduce a paradigm switch in the wireless revolution. Although only few companies are to date doing successful business with RF-MEMS, and on a case-by-case basis, important issues need yet to be addressed in order to maximize yield and performance stability and hence, outperform alternative competitive technologies (e.g. ferroelectric, SoS, SOI,…). Namely the behavior instability associated to: 1) internal stresses of the free standing thin layers (metal and/or dielectric) and 2) the mechanical contact degradation, be it ohmic or capacitive, which may occur due to low forces, on small areas, and while handling severe current densities.The investigation and understanding of these complex scenario, has been the core of theoretical and experimental investigations carried out in the framework of the research activity that will be presented here. The reported results encompass activities which go from coupled physics (multiphysics) modeling, to the development of experimental platforms intended to tackles the underlying physics of failure. Several original findings on RF-MEMS reliability in particular with respect to the major failure mechanisms such as dielectric charging, metal contact degradation and thermal induced phenomena have been obtained. The original use of advanced experimental setup (surface scanning microscopy, light interferometer profilometry) has allowed the definition of innovative methodology capable to isolate and separately tackle the different degradation phenomena under arbitrary working conditions. This has finally permitted on the one hand to shed some light on possible optimization (e.g. packaging) conditions, and on the other to explore the limits of microsystem technology down to the nanoscale. At nanoscale indeed many phenomena take place and can be exploited to either enhance conventional functionalities and performances (e.g. miniaturization, speed or frequency) or introduce new ones (e.g. ballistic transport). At nanoscale, moreover, many phenomena exhibit their most interesting properties in the RF spectrum (e.g. micromechanical resonances). Owing to the fact that today’s minimum manufacturable features have sizes comparable with the fundamental technological limits (e.g. surface roughness, metal grain size, …), the next generation of smart systems requires a switching paradigm on how new miniaturized components are conceived and fabricated. In fact endowed by superior electrical and mechanical performances, novel nanostructured materials (e.g. carbon based, as carbon nanotube (CNT) and graphene) may provide an answer to this endeavor. Extensively studied in the DC and in the optical range, the studies engaged in LAAS have been among the first to target microwave and millimiterwave transport properties in carbon-based material paving the way toward RF nanodevices. Preliminary modeling study performed on original test structures have highlighted the possibility to implement novel functionalities such as the coupling between the electromagnetic (RF) and microelectromechanical energy in vibrating CNT (toward the nanoradio) or the high speed detection based on ballistic transport in graphene three-terminal junction (TTJ). At the same time these study have contributed to identify the several challenges still laying ahead such as the development of adequate design and modeling tools (ballistic/diffusive, multiphysics and large scale factor) and practical implementation issues such as the effects of material quality and graphene-metal contact on the electrical transport. These subjects are the focus of presently on-going and future research activities and may represent a cornerstone of future wireless applications from microwave up to the THz range