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Rare gas adsorption was studied on suspended individual single walled carbon nanotubes and graphene. The devices were fabricated as field effect transistors. Adsorption of N2 and CO, which formed a Root 3 X Root 3 commensurate solid monolayer, produced a dramatic reduction of the two-terminal conductance of graphene by as much as a factor of three. This effect is possibly connected with the opening of a band gap expected to occur in such structures.
Rare gas adsorption was studied on suspended individual single walled carbon nanotubes and graphene. The devices were fabricated as field effect transistors. Adsorption on graphene was studied through two-terminal conductance. On nanotube devices adsorption was studied through conductance while the coverage (density) of the adsorbates was determined from the mechanical resonance frequency shifts. The adsorbed atoms modified the conductance of the nanotube field effect transistors, in part through charge transfer from the adsorbates to the nanotube. By tracking the shifts of conductance as a function of gate voltage, G=G(Vg), and comparing these shifts with the periodicity of the Coulomb blockade oscillations we quantified the charge transfer to the nanotubes with high accuracy. For all studied gases (He, Ar, Kr, Xe, N2, CO, and O2) the charge transfer had a similar magnitude and was rather small, on the order of 10^-5 to 10^-3 electrons per adsorbed atom. The nanotube devices displayed two classes of adsorption behavior. On some devices the monolayers exhibited first-order phase transitions analogous to those that occur in adsorbed monolayers on graphite. On other devices phase transitions within the adsorbed monolayers were absent. We present evidence that a highly uniform layer of contaminants deposits on the surface of suspended nanotube devices either upon cooldown in the cryostat or at room temperature from air. These contaminants modify the adsorption behavior preventing the adsorbed monolayers from exhibiting the first order phase transitions expected to occur on a clean surface. A similar type of contamination leading to virtually identical effects occurs on suspended graphene. In the low coverage regions of isotherms on nanotubes we observe Henry's law behavior, demonstrating a high uniformity of the surface and allowing us to accurately determine the single particle binding energy to this surface. The determined binding energies were 776+-10 K for Ar, and 997+-37 K for Kr. In the second part of the dissertation we present the first measurements of adsorption on a pristine graphene surface, exposed through aggressive electric current annealing. On graphene the rare gas adsorbates form monolayers with phases analogous to those on graphite, but with phase transitions occurring at slightly higher pressures due to a reduction of binding energy. The condensations of monolayers with phases not commensurate with the graphene lattice resulted in a slight shift of the charge neutrality point of monolayer graphene corresponding to a change of carrier concentration on the order of 10^9 e/cm^2. Adsorption of N2 and CO, which formed a Root 3 X Root 3 commensurate solid monolayer, produced a dramatic reduction of the two-terminal conductance of graphene by as much as a factor of three. This effect is possibly connected with the opening of a band gap expected to occur in such structures. We observe hysteretic behavior in the adsorbed Root 3 X Root 3 commensurate monolayers on freestanding graphene, which is likely due to the interaction of two adsorbed monolayers on opposite surfaces of the graphene sheet.
Research in adsorption of gases by carbon nanomaterials has experienced considerable growth in recent years, with increasing interest for practical applications. Many research groups are now producing or using such materials for gas adsorption, storage, purification, and sensing. This book provides a selected overview of some of the most interesting scientific results regarding the outstanding properties of carbon nanomaterials for gas adsorption and of interest both for basic research and technological applications. Topics receiving special attention in this book include storage of H, purification of H, storage of rare gases, adsorption of organic vapors, gas trapping and separation, and metrology of gas adsorption.
The focus of this work is a study of the adsorption of noble gases on individual, suspended, single-walled carbon nanotubes (SWNTs). The surface of a SWNT is a cylindrical cousin of graphite, but the binding energy is smaller and the cylindrical geometry and lack of grain boundaries could be expected to lead to substantially different behavior. The coverage (areal density) on a nanotube can be measured with high precision from the mechanical resonance frequency shifts, yielding isotherms as a function of gas pressure analogous to volumetric isotherms on bulk substrates. The electrical conductance of the nanotubes can also be measured at the same time and the effects of the adsorbates on the conductance thereby investigated. We found that adsorbed noble gases form monolayers on SWNTs, analogous to those on conventional 2-dimensional (2D) substrates, with a variety of 2D phases as a result of atom-atom interactions. Based on a combination of the coverage and conductance isotherms, the behavior of the adsorbates on SWNTs was established, including the 2D phases, 2D critical and triple-point temperatures, binding energies, isosteric heats, and latent heats. The majority of measurements were on Ar and Kr, fewer on 4He and Xe. The binding energy of the noble gases on a SWNT was found to be lower than on graphite, as anticipated. For example, the binding energy for Ar on one device was about 725 K ℗ł 50 K, about 30% lower than graphite. The lower binding energy allows isotherm measurements at lower temperatures compared because the required pressure are higher. In all cases we found that only a single atomic layer is formed before reaching the saturated vapor pressure of the adsorbate. Remarkably, although the binding energies of Ar were consistent between multiple SWNTs, the adsorbates on different devices did not behave in the same way. The device can be classified into two classes. Those in Class I show sharp first-order transitions between 2D phases, very similar to those on graphite, and the maximum monolayer coverage on SWNTs is consistent with that on graphite taking into account the radius of nanotube. Large and sharp risers at constant pressures in the coverage or conductance isotherms indicate the 2D liquid-vapor or commensurate solid-vapor conversion. Small and smoother risers following the large ones in the isotherms indicate the 2D incommensurate solid-liquid phase transitions. In contrast, devices in Class II do not show clear phase transitions, have non-vertical isotherms in regions where first-order jumps would be expected, and the monolayers seem to be not complete when the saturated vapor pressure is reached. The difference in isosteric heat between devices of the two classes within the region where the first-order transition is expected, may be due to the 2D L-V latent heat. The existence of the two different classes of behavior remains puzzling. It appears that in class II nanotubes the effects of atom-atom attractive interactions are suppressed, due possibly either to geometrical effects or the different electrical properties of different nanotube species.
This book comprehensively reviews recent and emerging applications of carbon nanotubes and graphene materials in a wide range of sectors. Detailed applications include structural materials, ballistic materials, energy storage and conversion, batteries, supercapacitors, smart sensors, environmental protection, nanoelectronics, optoelectronic and photovoltaics, thermoelectric, and conducting wires. It further covers human and structural health monitoring, and thermal management applications. Key selling features: Exclusively takes an application-oriented approach to cover emerging areas in carbon nanotubes and graphene Covers fundamental and applied knowledge related to carbon nanomaterials Includes advanced applications like human and structural health monitoring, smart sensors, ballistic protection and so forth Discusses novel applications such as thermoelectrics along with environmental protection related application Explores aspects of energy storage, generation and conversion including batteries, supercapacitors, and photovoltaics This book is aimed at graduate students and researchers in electrical, nanomaterials, chemistry, and other related areas.
How Can We Lower the Power Consumption of Gas Sensors? There is a growing demand for low-power, high-density gas sensor arrays that can overcome problems relative to high power consumption. Low power consumption is a prerequisite for any type of sensor system to operate at optimum efficiency. Focused on fabrication-friendly microelectromechanical systems (MEMS) and other areas of sensor technology, MEMS and Nanotechnology for Gas Sensors explores the distinct advantages of using MEMS in low power consumption, and provides extensive coverage of the MEMS/nanotechnology platform for gas sensor applications. This book outlines the microfabrication technology needed to fabricate a gas sensor on a MEMS platform. It discusses semiconductors, graphene, nanocrystalline ZnO-based microfabricated sensors, and nanostructures for volatile organic compounds. It also includes performance parameters for the state of the art of sensors, and the applications of MEMS and nanotechnology in different areas relevant to the sensor domain. In addition, the book includes: An introduction to MEMS for MEMS materials, and a historical background of MEMS A concept for cleanroom technology The substrate materials used for MEMS Two types of deposition techniques, including chemical vapour deposition (CVD) The properties and types of photoresists, and the photolithographic processes Different micromachining techniques for the gas sensor platform, and bulk and surface micromachining The design issues of a microheater for MEMS-based sensors The synthesis technique of a nanocrystalline metal oxide layer A detailed review about graphene; its different deposition techniques; and its important electronic, electrical, and mechanical properties with its application as a gas sensor Low-cost, low-temperature synthesis techniques An explanation of volatile organic compound (VOC) detection and how relative humidity affects the sensing parameters MEMS and Nanotechnology for Gas Sensors provides a broad overview of current, emerging, and possible future MEMS applications. MEMS technology can be applied in the automotive, consumer, industrial, and biotechnology domains.
It is about 15 years that the carbon nanotubes have been discovered by Sumio Iijima in a transmission electron microscope. Since that time, these long hollow cylindrical carbon molecules have revealed being remarkable nanostructures for several aspects. They are composed of just one element, Carbon, and are easily produced by several techniques. A nanotube can bend easily but still is very robust. The nanotubes can be manipulated and contacted to external electrodes. Their diameter is in the nanometer range, whereas their length may exceed several micrometers, if not several millimeters. In diameter, the nanotubes behave like molecules with quantized energy levels, while in length, they behave like a crystal with a continuous distribution of momenta. Depending on its exact atomic structure, a single-wall nanotube –that is to say a nanotube composed of just one rolled-up graphene sheet– may be either a metal or a semiconductor. The nanotubes can carry a large electric current, they are also good thermal conductors. It is not surprising, then, that many applications have been proposed for the nanotubes. At the time of writing, one of their most promising applications is their ability to emit electrons when subjected to an external electric field. Carbon nanotubes can do so in normal vacuum conditions with a reasonable voltage threshold, which make them suitable for cold-cathode devices.
This book focuses on several areas of intense topical interest related to applied spectroscopy and the science of nanomaterials. The eleven chapters in the book cover the following areas of interest relating to applied spectroscopy and nanoscience: · Raman spectroscopic characterization, modeling and simulation studies of carbon nanotubes, · Characterization of plasma discharges using laser optogalvanic spectroscopy, · Fluorescence anisotropy in understanding protein conformational disorder and aggregation, · Nuclear magnetic resonance spectroscopy in nanomedicine, · Calculation of Van der Waals interactions at the nanoscale, · Theory and simulation associated with adsorption of gases in nanomaterials, · Atom-precise metal nanoclusters, · Plasmonic properties of metallic nanostructures, two-dimensional materials, and their composites, · Applications of graphene in optoelectronic devices and transistors, · Role of graphene in organic photovoltaic device technology, · Applications of nanomaterials in nanomedicine.
Size Up the Short- and Long-Term Effects of GrapheneThe Graphene Science Handbook is a six-volume set that describes graphene's special structural, electrical, and chemical properties. The book considers how these properties can be used in different applications (including the development of batteries, fuel cells, photovoltaic cells, and supercapac
Graphene has already gained a unique reputation among novel synthetic materials. Dedicated efforts and enormous resources are being invested in creating viable commercial products. The high electrical and thermal conductivities in graphene are well known, and most of the applications of this material are pivoted to these properties. In addition to electronic and thermal management applications there are several other vital areas where graphene can be used successfully. This book is compiled in two volumes. Volume 1 is specifically meant for beginners who want to know the science and technology associated with this nanomaterial. This volume consists of chapters that are specifically written for readers who are looking for the applications of graphene and its derivatives. The first objective of this book is to provide readers with numerical/physics based models for assessment of graphene for targeted applications. The second objective of this book is to introduce readers to the industrial applications of graphene. Chapters are carefully written so that readers can choose methodologies for screening of graphene materials for a particular application. This second volume is written for broader readership including young scholars and researchers with diverse backgrounds such as chemistry, physics, materials science, and engineering. It can be used as a textbook for graduate students, and also as a review or reference book for researchers from different branches of materials science.