Characterization of the Resistance and Force of a Carbon Nanotube/Metal Side Contact by Nanomanipulation

A high contact resistance restricts the application of carbon nanotubes (CNTs) in fabrication of field-effect transistors (FETs). Thus, it is important to decrease the contact resistance and investigate the critical influence factors such as the contact length and contact force. This study uses nanomanipulation to characterize both the resistance and the force at a CNT/Au side-contact interface inside a scanning electron microscopy (SEM). Two-terminal CNT manipulation methods, and models for calculating the resistance and force at contact area, are proposed to guide the measurement experiments of a total resistance and a cantilever’s elastic deformation. The experimental results suggest that the contact resistance of CNT/Au interface is large (189.5 kΩ) when the van der Waals force (282.1 nN) dominates the contact force at the interface. Electron-beam-induced deposition (EBID) is then carried out to decrease the contact resistance. After depositing seven EBID points, the resistance is decreased to 7.5 kΩ, and the force increases to 1339.8 nN at least. The resistance and force at the contact area where CNT was fixed exhibit a negative exponential correlation before and after EBID. The good agreement of this correlation with previous reports validates the proposed robotic system and methods for characterizing the contact resistance and force

Additive nanomanufacturing: a review

Additive manufacturing has provided a pathway for inexpensive and flexible manufacturing of specialized components and one-off parts. At the nanoscale, such techniques are less ubiquitous. Manufacturing at the nanoscale is dominated by lithography tools that are too expensive for small- and medium-sized enterprises (SMEs) to invest in. Additive nanomanufacturing (ANM) empowers smaller facilities to design, create, and manufacture on their own while providing a wider material selection and flexible design. This is especially important as nanomanufacturing thus far is largely constrained to 2-dimensional patterning techniques and being able to manufacture in 3-dimensions could open up new concepts. In this review, we outline the state-of-the-art within ANM technologies such as electrohydrodynamic jet printing, dip-pen lithography, direct laser writing, and several single particle placement methods such as optical tweezers and electrokinetic nanomanipulation. The ANM technologies are compared in terms of deposition speed, resolution, and material selection and finally the future prospects of ANM are discussed. This review is up-to-date until April 2014

Electron beam induced deposition (EBID) of carbon interface between carbon nanotube interconnect and metal electrode

Electron Beam Induced Deposition (EBID) is an emerging additive nanomanufacturing tool which enables growth of complex 3-D parts from a variety of materials with nanoscale resolution. Fundamentals of EBID and its application to making a robust, low-contact-resistance electromechanical junction between a Multiwall Carbon Nanotube (MWNT) and a metal electrode are investigated in this thesis research. MWNTs are promising candidates for next generation electrical and electronic devices, and one of the main challenges in MWNT utilization is a high intrinsic contact resistance of the MWNT-metal electrode junction interface. EBID of an amorphous carbon interface has previously been demonstrated to simultaneously lower the electrical contact resistance and to improve mechanical characteristics of the MWNT-electrode junction. In this work, factors contributing to the EBID formation of the carbon joint between a MWNT and an electrode are systematically explored via complimentary experimental and theoretical investigations. A comprehensive dynamic model of EBID using residual hydrocarbons as a precursor molecule is developed by coupling the precursor mass transport, electron transport and scattering, and surface deposition reaction. The model is validated by comparison with experiments and is used to identify different EBID growth regimes and the growth rates and shapes of EBID deposits for each regime. In addition, the impact of MWNT properties, the electron beam impingement location and energy on the EBID-made carbon joint between the MWNT and the metal electrode is critically evaluated. Lastly, the dominant factors contributing to the overall electrical resistance of the MWNT-based electrical interconnect and relative importance of the mechanical contact area of the EBID-made carbon joint to MWNT vs. that to the metal electrode are determined using carefully designed experiments.Ph.D.Committee Chair: Dr. Andrei G. Fedorov; Committee Member: Dr. Azad Naeemi; Committee Member: Dr. Suresh Sitaraman; Committee Member: Dr. Vladimir V. Tsukruk; Committee Member: Dr. Yogendra Josh

Low-dimensional carbon nanotube and graphene devices

P.iii (acknowledgements) missing from electronic version.Electronic devices in which the electrons are confined to fewer than three spatial dimensions are an important tool for physics research and future developments in computing technology. Recently discovered carbon nanotubes (1991) and graphene (2004) are intrinsically low-dimensional materials with remarkable electronic properties. Combined with semiconductor technologies they might be used to fabricate smaller devices with more complex functionality. This thesis addresses two routes towards this goal. The detection of charge transport through quantum dots using a GaAs point contact is a potential tool for quantum computation. This project aimed to fabricate and measure hybrid devices with carbon nanotube quantum dots on top of GaAs point contacts. Dispersion and AFM manipulations of nanotubes on GaAs were studied, revealing comparatively weak binding. Transport measurements indicated that GaAs induces disorder in nanotubes, creating multiple tunnel barriers. Preliminary attempts were made at CVD growth and ink-jet printing of nanotubes directly onto GaAs. Although only one atom thick, graphene is macroscopic in area and must be patterned to confine conduction; room temperature transistor behaviour requires graphene ribbons only a few nanometres wide. This work fabricated such structures using a charged AFM tip, achieving reliable cutting even on single layer graphene and feature sizes as small as 5 nm. The cutting mechanism was found to be chemical oxidation of carbon by a polarised water layer, with an activation energy determined by the energy of dissociation of water at the graphene surface. The critical variables were the voltage difference between the tip and graphene and the atmospheric humidity. An unstable solid oxide intermediate was also observed. Thermal annealing revealed the presence of a layer of water beneath flakes. Finally, EFM measurements were made of graphene at 20 mK, enabling estimates of the local carrier density and revealing spatial variations in the electronic structure on a scale consistent with electron and hole puddles

Carbon nanotube thermal interfaces and related applications

The development of thermal interface materials (TIMs) is necessitated by the temperature drop across interfacing materials arising from macro and microscopic irregularities of their surfaces that constricts heat through small contact regions as well as mismatches in their thermal properties. Similar to other types of TIMs, CNT TIMs alleviate the thermal resistance across the interface by thermally bridging two materials together with cylindrical, high-aspect ratio, and nominally vertical conducting elements. Within the community of TIM engineers, the vision driving the development of CNT TIMs was born from measurements that revealed impressively high thermal conductivities of individual CNTs. This vision was then projected to efforts focused on packing many individual CNTs on a single substrate that efficiently conduct heat in parallel and ultimately through many contact regions at CNT-to-substrate contacts. This thesis encompasses a comprehensive investigation of the viability of carbon nanotube based thermal interface materials (CNT TIMs) to efficiently conduct heat across two contacting materials. The efforts in this work were initially devoted to engaging CNT TIMs with an opposing substrate using two bonding techniques. Using palladium hexadecanethiolate, Pd(SC16H35)2 the CNT ends were bonded to an opposing substrate (one-sided interface) or opposing CNT array (two-sided interface) to enhance contact conductance while maintaining a compliant joint. The palladium weld is particularly attractive for its mechanical stability at high temperatures. The engagement of CNT TIMs with an opposing substrate was also achieved by inserting a solder foil between the CNT TIM and opposing substrate and subsequently raising the temperature of the interface above the eutectic point of the solder foil. This bonding technique creates a strong weld that not only reduces the thermal resistance significantly but also minimizes the change in thermal resistance with an applied compressive load. The thermal performance was further improved by infiltrating the CNT TIM with paraffin wax, which serves as an alternate pathway for heat conduction across the interface that ultimately reduces the bulk thermal resistance of the CNT TIM. For CNT TIMs synthesized at the Birck Nanotechnology Center at Purdue University, the thermal resistance was shown to scale linearly with their aggregate, as-grown height. Thus, the bulk thermal resistance can alternatively be tuned by adjusting the as-grown height. The linear relationship between thermal resistance and CNT TIM height provides a simple and efficient methodology to estimate the contact resistance and effective thermal conductivity of CNT TIMs. In this work, the contact resistance and effective thermal conductivity were estimated using two measurement techniques: (i) one-dimensional, steady-state reference bar and (ii) photoacoustic technique. A discrepancy in the estimated contact resistance exists between the two measurement techniques, which is due to the difficulty in measuring the true contact area. In contrast, the effective thermal conductivities estimated from both measurement techniques moderately agreed and were estimated to be on the order of O(1 W/mK). The final chapter is in collaboration with Sandia National Laboratories and focuses on the development of an apparatus to measure the thermal conductivity of insulation materials critical for the operation of molten salt batteries. Molten salt batteries are particularly useful power sources for radar and guidance systems in military applications such as guided missiles, ordinance, and other weapons. Molten salt batteries are activated by raising the temperature of the electrolyte above its melting temperature using pyrotechnic heat pellets. The battery will remain active as long as the electrolyte is molten. As a result, the thermal processes within the components and interactions between them are critical to the overall performance of molten salt batteries. A molten salt battery is typically thermally insulated using wrappable and board-like insulation materials such as Fiberfrax wrap, Fiberfrax board, and Min-K insulation. The Fiberfrax board and Min-K insulation are composites of alumino-silicate and fumed silica-titania, respectively. In Chapter 9, the thermal conductivities of the Fiberfrax board and Min-K insulation were measured under different uniaxial compressive states and ambient environments. The thermal conductivity of the mixed separator pellets (LiCl/MgO/KCl) was also measured along with its contact resistances with interfacing members. To measure the thermal quantities, a steady-state reference bar with thermocouples was employed. The resulting values serve as inputs to a thermal model that aims to predict lifetimes of the batteries. (Abstract shortened by ProQuest.

Carbon nanotube thermal interfaces and related applications

The development of thermal interface materials (TIMs) is necessitated by the temperature drop across interfacing materials arising from macro and microscopic irregularities of their surfaces that constricts heat through small contact regions as well as mismatches in their thermal properties. Similar to other types of TIMs, CNT TIMs alleviate the thermal resistance across the interface by thermally bridging two materials together with cylindrical, high-aspect ratio, and nominally vertical conducting elements. Within the community of TIM engineers, the vision driving the development of CNT TIMs was born from measurements that revealed impressively high thermal conductivities of individual CNTs. This vision was then projected to efforts focused on packing many individual CNTs on a single substrate that efficiently conduct heat in parallel and ultimately through many contact regions at CNT-to-substrate contacts. This thesis encompasses a comprehensive investigation of the viability of carbon nanotube based thermal interface materials (CNT TIMs) to efficiently conduct heat across two contacting materials. The efforts in this work were initially devoted to engaging CNT TIMs with an opposing substrate using two bonding techniques. Using palladium hexadecanethiolate, Pd(SC16H35)2 the CNT ends were bonded to an opposing substrate (one-sided interface) or opposing CNT array (two-sided interface) to enhance contact conductance while maintaining a compliant joint. The palladium weld is particularly attractive for its mechanical stability at high temperatures. The engagement of CNT TIMs with an opposing substrate was also achieved by inserting a solder foil between the CNT TIM and opposing substrate and subsequently raising the temperature of the interface above the eutectic point of the solder foil. This bonding technique creates a strong weld that not only reduces the thermal resistance significantly but also minimizes the change in thermal resistance with an applied compressive load. The thermal performance was further improved by infiltrating the CNT TIM with paraffin wax, which serves as an alternate pathway for heat conduction across the interface that ultimately reduces the bulk thermal resistance of the CNT TIM. For CNT TIMs synthesized at the Birck Nanotechnology Center at Purdue University, the thermal resistance was shown to scale linearly with their aggregate, as-grown height. Thus, the bulk thermal resistance can alternatively be tuned by adjusting the as-grown height. The linear relationship between thermal resistance and CNT TIM height provides a simple and efficient methodology to estimate the contact resistance and effective thermal conductivity of CNT TIMs. In this work, the contact resistance and effective thermal conductivity were estimated using two measurement techniques: (i) one-dimensional, steady-state reference bar and (ii) photoacoustic technique. A discrepancy in the estimated contact resistance exists between the two measurement techniques, which is due to the difficulty in measuring the true contact area. In contrast, the effective thermal conductivities estimated from both measurement techniques moderately agreed and were estimated to be on the order of O(1 W/mK). The final chapter is in collaboration with Sandia National Laboratories and focuses on the development of an apparatus to measure the thermal conductivity of insulation materials critical for the operation of molten salt batteries. Molten salt batteries are particularly useful power sources for radar and guidance systems in military applications such as guided missiles, ordinance, and other weapons. Molten salt batteries are activated by raising the temperature of the electrolyte above its melting temperature using pyrotechnic heat pellets. The battery will remain active as long as the electrolyte is molten. As a result, the thermal processes within the components and interactions between them are critical to the overall performance of molten salt batteries. A molten salt battery is typically thermally insulated using wrappable and board-like insulation materials such as Fiberfrax wrap, Fiberfrax board, and Min-K insulation. The Fiberfrax board and Min-K insulation are composites of alumino-silicate and fumed silica-titania, respectively. In Chapter 9, the thermal conductivities of the Fiberfrax board and Min-K insulation were measured under different uniaxial compressive states and ambient environments. The thermal conductivity of the mixed separator pellets (LiCl/MgO/KCl) was also measured along with its contact resistances with interfacing members. To measure the thermal quantities, a steady-state reference bar with thermocouples was employed. The resulting values serve as inputs to a thermal model that aims to predict lifetimes of the batteries. (Abstract shortened by ProQuest.

Cutting Edge Nanotechnology

The main purpose of this book is to describe important issues in various types of devices ranging from conventional transistors (opening chapters of the book) to molecular electronic devices whose fabrication and operation is discussed in the last few chapters of the book. As such, this book can serve as a guide for identifications of important areas of research in micro, nano and molecular electronics. We deeply acknowledge valuable contributions that each of the authors made in writing these excellent chapters