We prepared nanoscopically flat open-ended SWNT substrates from SWNT spun fibers by using the microtome cutting technique or the focused ion beam cutting technique followed by various etching and cleaning schemes or alternatively from vertically aligned SWNT film by flipping-over. Deposited catalyst was docked to the open ends of SWNTs, and carbon feedstocks were catalyzed into continued single-walled carbon nanotube growth resembling 1D molecular epitaxy. The data obtained from Raman spectroscopy indicates that the (n, m) structure of the newly grown SWNT was cloned from that of the pre-existing SWNT substrate. Such results lead us to believe that this method will provide us with a means of chirality-controlled SWNTs growth on a macroscopic scale using a fairy general and scalable setup in the future.

This work reports the successful production of neat macroscopic membranes of aligned single-walled carbon nanotubes (SWNTs) via filtration in intense magnetic fields of 25 Tesla and 7 Tesla. These membranes comprise a novel material that allows an unprecedented capability to characterize and manipulate aligned SWNTs, providing access to the more remarkable properties of SWNTs. Surface areas in excess of 100 cm 2 and thickness in excess of seven microns were produced. A density within a factor of two of close packing was achieved. These assemblies exhibit anisotropy in Raman resonance, electrical transport, thermal transport, and reflection of polarized light. These samples provide a macroscopic window to exploring the properties of SWNTs and pave the way for many potential applications. The successful extension of this process to 7 Tesla provides a more pragmatic path towards aligned assemblies of carbon nanotubes. Variations in the properties of the materials made under different magnetic field intensities were observed.* *This dissertation includes a CD that is compound (contains both a paper copy and a CD as part of the dissertation). The CD requires the following application: Notepad.

This thesis will discuss the principles, techniques and applications of the Radio Frequency Single Electron Transistor (RF-SET). In the first part, the operating principles of Single Electron Transistors (SETS) in the normal and superconducting states will be introduced. The general techniques of fabricating and calibrating SETs will also be introduced. In the second part, two of our recent experiments are reviewed. One is related to the sensitivity and linearity of superconducting RF-SETs. We found that the RF-SET achieves the best balance of charge sensitivity and linearity in the subgap regime, as opposed to the usual preferred working point in the above-gap regime. The second experiment relates to the real-time counting of single electrons. We demonstrated that the RF-SET can be used as a fast and ultra-sensitive electrometer which can even detect tunneling of a single electron inside a tunable quantum dot (QD) formed in a two dimensional electron gas (2DEG).

We have developed a coherent time-domain THz magneto-spectroscopy system. It can be used for measuring the refractive index, complex conductivities, and cyclotron resonance of different semiconductor structures as well as for investigating fundamental physical phenomena. As a first application, we have carried out time-domain cyclotron resonance studies of an ultrahigh-mobility two-dimensional electron gas at low temperatures. We observed coherent cyclotron resonance oscillations that persist as long as ∼ 50 ps. We show that the basic physics of these oscillations can be described as the free induction decay of a coherent superposition between the lowest unfilled Landau level and the highest filled Landau level prepared by an incident THz pulse. Using the 0 Tesla data as a reference, we successfully extracted the real and imaginary conductivities for different magnetic fields in the frequency domain. Finally, I will discuss a few future experiments that will be performed with this novel system.

Bose-Einstein condensation (BEC) in ultra-cold magnetically-trapped $\sp7$Li vapor was experimentally observed and quantitative measurements of condensate number were made. Compared to other BEC experiments, lithium is unique due to its negative s-wave scattering length, corresponding to effectively attractive interactions. Due to this attraction, condensates are expected to undergo mechanical collapse if the condensate number exceeds a critical value. In this experiment, an upper limit of about 1000 condensate atoms is found, in agreement with theoretical predictions. In the experiment, the atoms are confined by a set of six permanent magnets in the Ioffe configuration. Optical forces are used to slow and guide atoms from a thermal atomic beam into the magnetic trap. With about $10\sp8$ atoms loaded into the trap, the vapor is laser-cooled to near 200 $\mu$K and then evaporatively cooled by application of a resonantly-tuned microwave field. Evaporative cooling produces a million-fold increase in phase-space density, reaching quantum-degenerate conditions with about 10$\sp5$ atoms at temperatures near 300 $\mu$K. After cooling, the trapped atom distribution is observed by in situ imaging via an optical probe. Calculated atom distributions are fit to the image data. In initial data, the imaging resolution was insufficient to see the spatially-narrow condensate peak, but as phase-space densities approached the expected phase transition, the images suddenly became distorted. Initial fits to the data suggested as many as 10$\sp5$ condensate atoms, in strong disagreement with theoretical predictions. An imaging model, accounting for imperfections in the imaging optics, shows that the sudden appearance of the distortions is a consequence of BEC, and that these distortions led to the initial over-estimation of cloud phase-space density and condensate number. Improved imaging was obtained using large probe detunings, a Phase-Contrast Polarization Imaging (PCPI) technique, and near-diffraction-limited imaging optics. The PCPI method exploits the birefringence of the trapped atoms. From the resulting images, quantitative estimates of condensate number are obtained and compared with theory.

Functional magnetic resonance imaging (fMRI) is a non-invasive technique that allows for visualization of active brain regions. Although white matter (WM) constitutes approximately 50% of brain tissue, fMRI activation in WM has conventionally been dismissed. There are two main reasons WM fMRI remains controversial: 1) the blood oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and volume, which are lower in WM than gray matter and 2) fMRI signal has been associated with post-synaptic potentials as opposed to action potentials. Despite these observations, there is no direct evidence against measuring fMRI activation in WM. This thesis is comprised of four manuscripts that investigate fMRI activation in WM at 4T. The first study evaluated whether it was possible to detect WM activation using an interhemispheric transfer task and examined whether certain MRI contrast mechanisms were more sensitive to activation in WM. Activation was detected in the anterior corpus callosum at the individual and group level and we discovered that T2 weighted imaging may provide increased sensitivity to activation in WM. The second study used two established interhemispheric transfer tasks to examine whether callosal activation could be experimentally manipulated using a within subjects design. The results replicated previous findings and demonstrated an ability to map functional activation in the corpus callosum that was task dependent. The third study examined WM fMRI activation in a different structure and focused on the posterior limb of the internal capsule using a motor task; activation was elicited at both individual and group levels. The fourth study linked advances in the ability to detect WM fMRI activation to current clinical approaches to the assessment of WM dysfunction. An adapted Symbol Digit Modalities Test was used to evaluate WM activation in healthy controls. The results revealed individual level activation in both the corpus callosum and internal capsule. Taken together this stream of research represents a major advance in the methods used to non-invasively study brain function. Future applications may include improved assessment methods for patients with WM dysfunction.

DEAP (Dark Matter Experiment with Argon and Pulse Shape Discrimination) is an experiment that aims to directly detect dark matter particles via nuclear recoils in liquid argon. The experiment uses the scintillation property of liquid argon as a means to discriminate the γ and β backgrounds from the expected signal. DEAP-1 is a 7 kg single phase liquid argon detector. It was constructed to demonstrate the scalability for a larger (3600 kg) detector. The detector was originally operated at Queen’s University, where the background rejection level achieved was 6.3×10−8 for the recoil detection efficiency of 97.1%. The detector was relocated to SNOLAB, where the background in the energy region of interest was reduced by a factor of 7.7 (from 4.61±0.17 mHz to 0.60±0.05 mHz.). The background rejection level of 9.64×10−9 (10.4 part per billion) was achieved from the combined data set (Queen’s University and SNOLAB) for a recoil detection efficiency of 35.5 ± 1.3 %. With the current background rate, the background rejection level required for the 3600 kg detector (1.8×10−9 ) is projected to be achieved in 382 days at the neutron efficiency of 9.1±0.6 %. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-01-26 09:28:25.432

The PICASSO experiment located 2 km underground in SNOLAB is directly searching for dark matter signals by looking for interactions between dark matter particles and an active target made of superheated droplets of freon C4F10. During the interaction, energy is deposited to the freon triggering a phase transition, inducing pressure waves which are detected by piezo-electric sensors. A temperature dependent analysis of the amplitudes of the signals for detector 71 showed that, above 25 ◦C, between 20 and 80 % of the events were saturated implying that the preamplifiers had too high a gain. Decreasing this gain by a fixed factor was not found to be a suitable solution to the problem. Ideally, a temperature dependent gain should be established. In addition, some channels have intrinsic problems and should be repaired. A threshold analysis was used to establish the trigger efficiency which was found to be 90% above 25 ◦C but only 50% at lower temperatures with the current setting of the threshold. A temperature dependent threshold setting has been proposed. A new setup at Queen’s University has been built and a gamma calibration using three different radioactive sources (22Na,137Cs,57Co) was undertaken leading to a new detector response curve for gammas. For a proper analysis, new and more appropriate cuts were implemented. The analysis confirmed the expectation that the PICASSO detectors are mostly blind to gammas below 50 ◦C. However, the detectors appear to be more sensitive to 122 keV gammas than to 622 keV gammas by a factor of about 10. The sensitivity for 22Na also differs by a large factor from what was expected from old calibrations on detectors with much smaller bubbles. The rate plots exhibit a strong exponential increase in rate above 40 ◦C which is not due to any of the gamma sources used, but could be due to neutrons or low energy x-rays. This remains under investigation. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-09-24 18:28:21.308

SuperCDMS, the next stage of the Cryogenic Dark Matter Search (CDMS), uses cylindrical germa- nium crystals as particle detectors to measure phonon and ionization signals resulting from particle interactions. The aim of CDMS is to identify and measure interactions from dark matter particles (WIMPs). Phonons produced during a particle interaction are absorbed by sensors on the detector surface and are measured through the change in the sensors' temperature dependent resistance. Electrodes on the detector surface create an electric eld causing charges released during an inter- action to drift through the detector and produce an ionization signal. Surface events, which are interactions that occur within a few m from the electrodes, cause a reduced ionization signal due to di usion of some of the initially hot charge carriers into the electrode. Because the ability of CDMS to discriminate between a WIMP interaction and background radiation is based on the ratio of phonon to ionization energies, surface events cause a signal similar to a WIMP interaction and are currently the largest source of background. A detector test facility at Queen's University has been commissioned to characterize detectors and test new detector technology. Multiple detectors have been characterized and many tungsten samples have been measured. Two sets of experiments were performed to test new detector designs. To possibly reduce surface events, an insulating layer was deposited on a germanium detector be- neath the electrode to prevent back di usion of charge into the electrode. To possibly simplify the phonon sensor production process, di erent cryogenic glues were used to attach silicon wafers with a tungsten lm to the crystal surface and phonon propagation through these glues was measured. The most e ective cryogenic glue for coupling tungsten samples to CDMS detectors was found to be Araldite epoxy. Both experiments were successful at measuring interactions. Energy calibrations were performed on both charge and phonon sensors. Further research is required to determine the success of reducing surface events with an insulating layer. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-05-30 10:39:02.976

Spin-polarized low energy electrons from a GaAs source were used to probe magnetized nickel(111) surface. Intensity curves as well as spin-orbit and exchange induced polarization asymmetries were obtained for the $(00)-20\sp\circ, (00)-30\sp\circ,$ $(00)-45\sp\circ, (10)$ and $(-10)$ beams. Comparison with a preliminary theoretical study yields no quantitative information on the magnetic moment per surface atom.