A novel process which does not require the traditional Chemical Vapor Deposition (CVD) synthesis techniques and which works at temperatures lower than the conventional techniques was developed for synthesis of carbon nanotubes (CNT). The substrates used for this study involved MEMS (Micro Electrical Mechanical Systems) elements and passive elements. These were coated with Fullerene using Physical Vapor Deposition or through a solution in an organic solvent. Catalyst precursors were deposited on these Fullerene coated substrates using “wet processes”. These substrates were then heated using either the integrated microheaters or external heaters in an inert atmosphere to obtain CNT. Thus, in this process we tried to obviate the Chemical Vapor Deposition (CVD) process for synthesis of CNT (SWCNT and MWCNT). The synthesized CNT will be characterized using Scanning Electron Microscopy and Raman spectroscopy techniques. Also, conductivity measurements were carried out for the synthesized tubes using Dry (contact based) and Wet (electro-chemical) methods. This work also proves the concept for the feasibility for a portable hand held instrument for synthesis of CNT with tunable “on demand” chirality.

High-resolution lattice periodicity images of a variety of well-defined surfaces, including graphite, mica, and Au(111), validated the good stability of our atomic force microscope (AFM) system. Combining self-assembled monolayer (SAM) and AFM technology, we demonstrated the capabilities of pattern fabrication as well as modification of surface functionality. AFM-based nanolithography operating conditions, such as scan rate, deflection setpoint, and number of scan were studied to obtain the optimized quality of the fabricated patterns. Thiolated-DNA probe molecules could be patterned at a nanometer scale on a gold substrate. However, we found that the surface coverage began to drop notably with the probe length (number of DNA bases). Therefore, the displaced DNA molecules during nanoshaving were reversibly adsorbed, and patterning became unreliable. We were unsuccessful in detecting the subsequent hybridization reactions at these nanopatterns from AFM measurements. To realize the DNA hybridization, further studies on the incubation temperature, probe length and even DNA sequences are required to demonstrate that this AFM-based gene diagnostic method is truly operational.

This thesis presents the development of a novel atomic force microscope (AFM) based nanofabrication technique termed as thermochemical nanolithography (TCNL). TCNL uses a resistively heated AFM cantilever to thermally activate chemical reactions on a surface with nanometer resolution. This technique can be used for fabrication of functional nanostructures that are appealing for various applications in nanofluidics, nanoelectronics, nanophotonics, and biosensing devices. This thesis research is focused on three main objectives. The first objective is to study the fundamentals of TCNL writing aspects. We have conducted a systematic study of the heat transfer mechanism using finite element analysis modeling, Raman spectroscopy, and local glass transition measurement. In addition, based on thermal kinetics analysis, we have identified several key factors to achieve high resolution fabrication of nanostructures during the TCNL writing process. The second objective is to demonstrate the use of TCNL on a variety of systems and thermochemical reactions. We show that TCNL can be employed to (1) modify the wettability of a polymer surface at the nanoscale, (2) fabricate nanoscale templates on polymer films for assembling nano-objects, such as proteins and DNA, (3) fabricate conjugated polymer semiconducting nanowires, and (4) reduce graphene oxide with nanometer resolution. The last objective is to characterize the TCNL nanostructures using AFM based methods, such as friction force microscopy, phase imaging, electric force microscopy, and conductive AFM. We show that they are useful for in situ characterization of nanostructures, which is particularly challenging for conventional macroscopic analytical tools, such as Raman spectroscopy, IR spectroscopy, and fluorescence microscopy.

In the past decade, nanomechanical resonators have found use in the work towards understanding mesoscopic quantum systems and the necessary validation of quantum mechanics on this scale. In 2010, the observation and state manipulation of a nanomechanical quantum system was achieved for the first time by O'Connell et al.. In 2002, Knobel and Cleland proposed to use a radio frequency superconducting single-electron transistor (RF-SSET), a fast and sensitive charge amplifier, to sense the quantum-limited motion of a piezoelectrically coupled nanomechanical resonator. The work presented in this thesis is towards the realization of the RF-SSET component of this device. An in-house fabrication recipe for making SETs with tunnel junction areas < 100^2 nm^2 and resistances between 20 kΩ and 150 kΩ was developed, in the end producing six SETs with resistances (36 ± 8) kΩ that were not susceptible to aging effects. Three measurement circuits were designed and used to characterize one of these SETs in the superconducting state (SSET) and operated in the DC and RF modes in a cryostat at a base temperature of 320~mK. Lock-in measurements revealed the SSET junction capacitances as 206 and 305 aF, contributing to a charging energy of (296 ± 11) x 10^(-6) eV. The resonant LC tank, which permitted RF operation, was also characterized at base temperature. The charge sensitivity of the RF-SSET was 6.8 x 10^(-5) e/√Hz (with uncertainty between 9.6 x 10^(-4) e/√Hz and 3.5 x 10^(-5) e/√Hz). With moderate improvements to the impedance matching network formed with the LC tank and greater junction resistances, an RF-SSET charge sensitivity on the order of 10^(-6) e/√Hz, required for sensing the quantum-limited motion of the nanomechanical resonator, should be achieved. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-08-10 17:38:43.798

Thermochemical Nanolithography (TCNL) is a scanning probe microscope (SPM) based lithographic technique modified with a semi-conducting cantilever. This cantilever is capable of locally heating a surface and with a well-engineered substrate, this spatially confined heating induces chemical or physical transformation. While previous works focused primarily on proof of principle and binary studies, there is limited research on controlling and understanding the underlying mechanisms governing the technique. In this thesis, a chemical kinetics model is employed to explain the driving mechanisms and to control the technique. The first part focuses on studying surface reactions. By coupling a thermally activated organic polymer with fluorescence microscopy, the chemical kinetics model is not only verified but also applied to control the surface reactions. The work is then expanded to include 3D effects, and some preliminary results are introduced. Finally, applications are discussed.

The possibilities of novel catalytic scanning probe lithography (cSPL) on starch using α-amylase was investigated. For this thin homogeneous layers of starch with good coverage were prepared by spin coating a starch solution on a silicon base. Amylase immobilized to an atomic force microscopy (AFM) cantilever tip were prepared and dragged along a spin coated starch surface. This after verifying the enzyme immobilization method using (3-Aminopropyl)triethoxysilane (APTES) on a silicon surface. In addition an unmodified cantilever tip were dipped in amylase solution and were dragged along a starch surface to investigate possibilities of dip-pen nanolithography (DPN). The preliminary experiments with AFM based enzymatic lithography were promising but non-conclusive. There are still many parameters not fully explored such as water availability, activity and reach of the amylase, speed of the enzymatic process and difference in structure between the starch and the shorter saccharides that are left after the hydrolysis

In this report we detail our work fabricating and measuring graphene quantum dots. We investigate a technique, relatively widely used in several other materials but not yet well investigated in graphene, known as Atomic Force Microscope Lithography (AFML). We then use AFML to fabricate graphene quantum dot systems. Transport measurements are carried out on our graphene quantum dots at low temperatures and high parallel magnetic fields and we try to understand the behaviour of spins in graphene. In our initial investigations into AFML we use graphene samples electrically contacted using standard electron-beam lithography. We were able to cut the graphene lattice by applying a negative voltage to the AFM tip and moving the tip across a grounded graphene surface. We have shown, by measuring the current through the AFM tip during lithography, that cutting of graphene is not current driven. Using a combination of transport measurements and scanning electron microscopy we show that , while indentations accompanied by tip current appear in the graphene lattice for a range of tip voltages, real cuts are characterized by a strong reduction of the tip current above a threshold voltage. The flexibility of the technique was then demonstrated by the fabrication, measurement, modification and re-measurement of graphene nanodevices with resolution down to 15 nm. We subsequently developed a shadow-masking technique to electrically contact graphene samples thus eliminating the use of chemical resists and the associated contamination of the graphene surface. With these pristine samples we were able to oxidise and hydrogenate the graphene using AFML. A graphene quantum dot was then fabricated using AFML oxidation. We also fabricated a graphene quantum dot using e-beam lithography in combination with oxygen plasma etching. We studied electron spin physics in these structures by J:1pplying large parallel magnetic fields at low temperatures and performing electrical transport measurements. We do not find an ordered filling sequence of spin states, which we assign to edge disorder and surface charge impurities.

This dissertation focuses on characterization of the mesoscopic fluid film, testing its behavior in different application scenarios, including its role in near-field scanning probe microscopy imaging, contribution to the phononic mechanism in nanotribology phenomena, utilizing it as a natural environment in the study of carbohydrate-protein interactions, and harnessing it as bridge to transport ions in the fabrication of nanostructures on responsive polymer materials. Due to their high resolution and versatile applications in a variety of fields, the family of scanning probe microscopy (SPM) has found widespread acceptance as an analytical and fabrication tool. However, the working mechanism of SPM that allows maintaining the probe-sample distance constant is still controversial. At the heart the problem is a lack of precise knowledge about the nature of the probe-sample interaction. One key factor is the presence of a mesoscopic fluid-like layer that naturally forms at any surface at ambient condition in which most SPMs are operated. Its mesoscopic nature (~20 nm in thickness) results in extraordinary behavior compared to the properties of bulk liquid. For example, the effective shear viscosity of confined mesoscopic fluids is enhanced, and viscoelastic relaxation times are prolonged. Despite the wide use of SPM techniques in ambient air, the basis of their working mechanisms is still not well understood. The probe-sample interaction is monitored using a combination of tuning-fork based shear force microscopy and our recently developed near-field acoustic technique. To characterize the mesoscopic fluid film a series of experiments are performed under different conditions in order to explore the benefits of having extra probing (acoustic) technique in addition to the shear-force approach. The presence of mesoscopic fluid layers as a natural environment enables the detection of protein-carbohydrate interactions. We demonstrated the capability of our shear-force/acoustic technique to monitor the rupture of chemical bonds between carbohydrate and protein pairs. Finally, we present fabrication of nanostructures via electric-field assisted dip-pen nanolithography by exploiting the responsive feature of a particular class of polymers, where the mesoscopic fluid layer also plays an important role in pattern creation.

<p>Fabricating complex submicron 3D structures can be achieved by multi-photon lithography, especially two-photon lithography is commonly used to obtain precision and flexibility in printing sophisticated sub-micron 3D structures. Several disadvantages stemmed from a two-photon lithography experiment setup, including cost, the necessity of a large laboratory space to use a femtosecond laser and a high-order process. A two-step absorption is chosen instead of two-photon lithography as a primary excitation process achieving the same degree of quadratic optical non- linearity as two-photon lithography at a lower cost with a relatively compact laboratory size. The working mechanism of Two-step absorption is the following. Quadratic nonlinearity comes from radicals from excited triplet states photoinitiators. Ground states of photoinitiators get excited by the incident laser. Those excited singlet photoinitiators go through the intersystem crossing, becoming the ground triplet state of photoinitiators. There are two branches after the ground triplet states, especially for photoinitiator benzil molecules with the incident laser on. Either it becomes a radical without photons received from the incident laser or gets excited again to an excited triplet state by the incident laser. Those excited triplet-state photoinitiator molecules become radicals that occur in polymerization. However, those from the ground triplet states add linearity to polymerization. When it comes to multiple exposures, the linearity becomes problematic, especially outside the region and tails of the voxel. For example, suppose the intensity at two tails of the voxel is 1% relative to the maximum intensity at the focal point. In that case, the absorbed dose will be added up to the maximum intensity at the focal point when it comes to 100 exposures. Quadratic nonlinearity and linearity are jumbled together in the current two-step absorption process. In this work, optimization of photoinitiator concentration was conducted to reduce the linearity. Confined and high throughput 3D structure fabrications are achieved by controlling initiator depletion. Simulations are also developed with multi-physics models to compare with the empirical results.</p>

This thesis presents work done investigating methods for constructing patterns on the nanometer scale. Various methods of nanolithography using atomic force microscopes (AFMs) are investigated. The use of AFMs beyond their imaging capabilities is demonstrated in various experiments involving nanografting and surface electrochemical modification. The use of an AFM to manipulate a monolayer of thiols deposited on a gold substrate via nanografting is shown in our work to enable chemical modification of the surface of the substrate by varying the composition of the monolayer deposited on it. This leads to the selective deposition of various polymers on the patterned areas. Conditions for enhancing the selective deposition of the self-assembled polymers are studied. Such conditions include the types of polymers used and the pH of the polyelectrolyte solutions used for polymer deposition. Another method of nanolithography is investigated which involves the electrochemical modification of a monolayer of silanes deposited on a silicon substrate. By applying a potential difference and maintaining the humidity of the ambient environment at a certain level we manage to change the chemical properties of select areas of the silane monolayer and thus manage to establish selective deposition of polymers and gold nanoparticles on the patterned areas. Parameters involved in the patterning process using surface electrochemical modification, such as humidity levels, are investigated. The techniques established are then used to construct circuit elements such as wires. / Ph. D.