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

Towards Single-Chip Nano-Systems

Important scientific discoveries are being propelled by the advent of nano-scale sensors that capture weak signals from their environment and pass them to complex instrumentation interface circuits for signal detection and processing. The highlight of this research is to investigate fabrication technologies to integrate such precision equipment with nano-sensors on a single complementary metal oxide semiconductor (CMOS) chip. In this context, several demonstration vehicles are proposed. First, an integration technology suitable for a fully integrated flexible microelectrode array has been proposed. A microelectrode array containing a single temperature sensor has been characterized and the versatility under dry/wet, and relaxed/strained conditions has been verified. On-chip instrumentation amplifier has been utilized to improve the temperature sensitivity of the device. While the flexibility of the array has been confirmed by laminating it on a fixed single cell, future experiments are necessary to confirm application of this device for live cell and tissue measurements. The proposed array can potentially attach itself to the pulsating surface of a single living cell or a network of cells to detect their vital signs

Atomic Force Microscopy Cantilever-Based Nanoindentation: Mechanical Property Measurements at the Nanoscale in Air and Fluid

An atomic force microscope (AFM) fundamentally measures the interaction between a nanoscale AFM probe tip and the sample surface. If the force applied by the probe tip and its contact area with the sample can be quantified, it is possible to determine the nanoscale mechanical properties (e.g., elastic or Young\u27s modulus) of the surface being probed. A detailed procedure for performing quantitative AFM cantilever-based nanoindentation experiments is provided here, with representative examples of how the technique can be applied to determine the elastic moduli of a wide variety of sample types, ranging from kPa to GPa. These include live mesenchymal stem cells (MSCs) and nuclei in physiological buffer, resin-embedded dehydrated loblolly pine cross-sections, and Bakken shales of varying composition. Additionally, AFM cantilever-based nanoindentation is used to probe the rupture strength (i.e., breakthrough force) of phospholipid bilayers. Important practical considerations such as method choice and development, probe selection and calibration, region of interest identification, sample heterogeneity, feature size and aspect ratio, tip wear, surface roughness, and data analysis and measurement statistics are discussed to aid proper implementation of the technique. Finally, co-localization of AFM-derived nanomechanical maps with electron microscopy techniques that provide additional information regarding elemental composition is demonstrated

Characterization of Electrophoretic Deposited Zinc Oxide Nanopartices for the Fabrication of Next-Generation Nanoscale Electronic Applications

Several reports state that it is crucial to analyze nanoscale semiconductor materials and devices with potential benefits to meet the need for next-generation nanoelectronics, bio, and nanosensors. The progress in the electronics field is as significant now, with modern technology constantly evolving and a greater focus on more efficient robust optoelectronic applications. This dissertation focuses on the study and examination of the practicality of Electrophoretic Deposition (EPD) of zinc oxide (ZnO) nanoparticles (NPs) for use in semiconductor applications. The feasibility of several synthesized electrolytes, with and without surfactants and APTES surface functionalization, is discussed. The primary objective of this study is to demonstrate that the electrophoretic method for depositing ZnO NPs can also be used to produce ZnO films onto p-type silicon, functionalized p-type silicon, and aluminum substrates. This investigation uses ZnO NPs deposited at room temperature onto silicon, functionalized silicon, and aluminum substrates via EPD. The experimental work examines EPD solution formulations, EPD optimization for ZnO NP coverage, imaging of the surfaces, and electrical characterizations. Thin films produced were examined using Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS), Ultraviolent Photoelectron Spectroscopy (UPS), and Atomic Force Microscopy (AFM), electrical impedance, and current-voltage (I-V) measurements. The results obtained are viewed in the context of providing valuable information in the ongoing search for reproducible and robust yet economical means of NP and thin-film deposition. This work fabricates a proof-of-concept pn junction composed of n-type ZnO NPs electrophoretically deposited onto p-type Si. This investigation presents a potential opportunity for integrating this deposition method into applications where ZnO contributes to the reliability, affordability, and highly increased sensitivity needed for the next generation of nanoscale devices and systems. The EPD of ZnO nanoscale thin films is important to several research areas, including biosensors, photophilic dye-sensitized solar cells, optoelectronic devices, and thin-film transistors. ZnO NPs have recently attracted attention due to their excellent optoelectronic performance and low cost of production [1-11]. Combining EPD with ZnO NPs will result in a more accessible technique of nanomaterial deposition, research tools for thin films and nanostructures, and improved materials for next-generation electronic

Fabrication and Manipulation of Metallic Nanofeatures and CVD Graphene through Nanopatterning and Templating

Nanotechnology holds exciting potential to significantly advance research in many fields such as sensors, environmental sustainability and cleanup, energy harvesting and storage, as well as nanoelectronics. The resulting high demand for implementation into these areas has simultaneously created a large need for effective fabrication methods for nanostructured materials. It is important the fabrication methods are capable of significant control over size, orientation, and structural configuration of nanomaterials for effective function in these applications. Nanopatterning and templating are a promising means to achieve extreme selectivity over these parameters, and additionally be used as tools to control the growth and structure of large-scale materials through nanoscale manipulation. In this research, nanopatterning and templating are implemented to create metallic nanowire structures on surfaces of silicon substrates with highly selectivity over nanowire placement and design. Additionally, templating is incorporated in graphene growth on metallic substrates to influence the quality of graphene films, and further film patterning is used to improve the graphene electrical and optical properties. The first part of this work focuses on the fabrication of copper metallic nanowires through resist patterning coupled with electroless copper deposition. An atomic force microscope is used to selectively remove portions of a self-assembled monolayer resist on a silicon substrate, with patterns reaching down to widths of 20 nm. Electroless metal plating provides a facile way to deposit metal in selectively activated areas on surfaces with nanoscale dimensions. Here, it is employed to deposit copper selectively within these nanopatterned lines to create copper nanowire features. Through variation of the electroless metal solution conditions, the dimensions of the AFM-patterned line, and the doping of the underlying silicon substrate, the dimensions and uniformity of copper deposition within AFM-patterned lines can be influenced. Furthermore, this method provides a successful level of control to construct copper nanowire features between gold microelectrodes, which allows the electrical properties of these nanowires to be examined. The ability to selectively place nanowire features on a substrate surface with dimensions down to the tens of nanometers, as well as the capability to manipulate the nanowire size and uniformity, make this a promising method to construct metallic nanofeatures for complex nanodevices and circuitry. The second portion of this research investigates techniques to develop high quality graphene films produced by chemical vapor deposition (CVD) on copper substrates. Chemical vapor deposition shows great potential for developing graphene films of large area, but unfortunately CVD graphene oftentimes possesses low conductivity values due to an increased amount of misaligned grain boundaries and point defects, and oftentimes exhibits low optical transparency. The focus of this research is to better understand the role the copper substrate plays in CVD graphene formation, and to find ways to directly enhance CVD graphene quality through changes in the copper substrate template. The surface morphology, optical transmittance, and electrical properties of CVD graphene manufactured on two copper substrates with different surface structures were investigated. It was found that differences in the copper substrate grain alignment and crystal lattice could significantly influence the deposition and quality of graphene on copper substrates. Furthermore, the possibility of developing graphene films on nonmetallic substrates, as well as enhancing its properties through chemical doping, is demonstrated by nanopatterning and templating of graphene films

Cancer Nanomedicine

This special issue brings together cutting edge research and insightful commentary on the currentl state of the Cancer Nanomedicine field