published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

In this study, the templating role of bimolecular triple hydrogen bonded honeycomb network consisting perylene-3,4,9,10-tetracarboxydi-imide and melamine is investigated, using scanning tunneling microscopy. Although the stability of the network upon modification is a major obstacle toward higher complexity, three different approaches in this work highlight formation of successful architectures in a sequential way. 1. Insertion of pore modifier star shaped molecules based on tri(phenylene ethynylene)benzene core in the pores to construct a new template. 2. Insertion of iodinated molecules in the pores to study the network as a nanoreactor. 3. Electrochemical deposition of metals in the pores. Self-assembly monolayer of four different molecules based on tri(phenylene ethynylene)benzene core on uniform gold surface revealed different structures. The degree of the order within the structures depends highly on the symmetry of the molecules, and hence asymmetric molecule formed disordered structure. Upon insertion into the pores of the network, one of molecules did not match the pores size, while others fitted and illustrated rotation depending on the strength of their interaction with the network components and the substrate. The rotation is significantly reduced by modifying the molecules. These new architectures are used as templets hosting C₆₀ molecules which resulted in isolated single C₆₀ molecules. Self-assembly of iodinated molecule under different conditions on uniform gold surface leads to formation of different structures including monomers and dimers. Upon thermal treatment on the uniform surface oligomers are formed, whereas for the molecules confined in the pores of the network, the covalent bond formation was limited to dimerisation. Electrochemical copper deposition into the pores of the network under acidic condition (pH = 1 - 2) is not possible because of the stability of the network. However, by increasing pH of the electrolyte (pH = 5 – 7), a bilayer of Cu and anion is formed in the pores of the network, confirmed by scanning tunneling microscopy and X-ray photoelectron spectroscopy.

Silicon-based nanostructures are essential building blocks for nanoelectronic devices and nano-electromechanical systems (NEMS), and their mechanical and electrical properties play an important role in controlling the functionality and reliability of the nano-devices. The objective of this dissertation is twofold: The first is to investigate the mechanical properties of silicon nanolines (SiNLs) with feature size scaled into the tens of nanometer level. And the second is to study the electron transport in nickel silicide formed on the SiNLs. For the first study, a fabrication process was developed to form nanoscale Si lines using an anisotropic wet etching technique. The SiNLs possessed straight and nearly atomically flat sidewalls, almost perfectly rectangular cross sections and highly uniform linewidth at the nanometer scale. To characterize mechanical properties, an atomic force microscope (AFM) based nanoindentation system was employed to investigate three sets of silicon nanolines. The SiNLs had the linewidth ranging from 24 nm to 90 nm, and the aspect ratio (Height/linewidth) from 7 to 18. During indentation, a buckling instability was observed at a critical load, followed by a displacement burst without a load increase, then a fully recoverable deformation upon unloading. For experiments with larger indentation displacements, irrecoverable indentation displacements were observed due to fracture of Si nanolines, with the strain to failure estimated to be from 3.8% to 9.7%. These observations indicated that the buckling behavior of SiNLs depended on the combined effects of load, line geometry, and the friction at contact. This study demonstrated a valuable approach to fabrication of well-defined Si nanoline structures and the application of the nanoindentation method for investigation of their mechanical properties at the nanoscale. For the study of electron transport, a set of nickel monosilicde (NiSi) nanolines with feature size down to 15 nm was fabricated. The linewidth effect on nickel silicide formation has been studied using high-resolution transmission electron microscopy (HRTEM) for microstructural analysis. Four point probe electrical measurements showed that the residual resistivity of the NiSi lines at cryogenic temperature increased with decreasing line width, indicating effect of increased electron sidewall scattering with decreased line width. A mean free path for electron transport at room temperature of 5 nm was deduced, which suggests that nickel silicide can be used without degradation of device performance in nanoscale electronics.

Molding is a simple manufacturing process whereby fluid fills a master tool and then solidifies in the shape of the tool cavity. The precise nature of material flow during molding has long allowed fabrication of plastic components with sizes 1 mm 1 m. Polymer molding with precise critical dimension control could enable scalable, inexpensive production of micro- and nanostructures for functional or lithographic use. This dissertation reports experiments and simulations on molding of polymer micro- and nanostructures at length scales 1 nm 1 mm. The research investigates two main areas: 1) mass transport during micromolding and 2) polymer mechanical properties during nanomolding at length scales 100 nm. Measurements and simulations of molding features of size 100 nm 1 mm show local mold geometry modulates location and rate of polymer shear and determines fill time. Dimensionless ratios of mold geometry, polymer thickness, and bulk material and process properties can predict flow by viscous or capillary forces, shape of polymer deformation, and mold fill time. Measurements and simulations of molding at length scales 100 nm show the importance of nanoscale physical processes distinct from bulk during mechanical processing. Continuum simulations of atomic force microscope nanoindentation accurately model sub-continuum polymer mechanical response but highlight the need for nanoscale material property measurements to accurately model deformation shape. The development of temperature-controlled nanoindentation enables characterization of nanoscale material properties. Nanoscale uniaxial compression and squeeze flow measurements of glassy and viscoelastic polymer show film thickness determines polymer entanglement with cooperative polymer motions distinct from those observed in bulk. This research allows predictive design of molding processes and highlights the importance of nanoscale mechanical properties that could aid understanding of polymer physics.