The glancing angle deposition (GLAD) technique is now used by over one hundred research groups, each requiring a fundamental understanding of and new techniques for modulating the properties of GLAD in order to optimize their results. In this thesis, the structural characteristics of nanostructured columnar films were therefore investigated and quantified using gas adsorption porosimetry, focused ion beam tomography, optical methods, scanning electron microscopy (SEM) image analysis. Questions such as ``What is their surface area?'', ``How porous are they?'', ``How do the films evolve as they grow?'', and ``Can the structural characteristics be manipulated?'' were answered. Surface areas, determined from krypton gas adsorption, were found to be high, making GLAD promising for applications requiring large and rough surface interfaces. Specifically, peak specific surface areas of 700 +/- 150 m^2g^{-1}, 325 +/- 40 m^2g^{-1}, 50 +/- 6 m^2g^{-1} were measured for silica (SiO_2), titania (TiO_2) and indium tin oxide (ITO), respectively. Broad pore distributions, with peaks in the low mesoporous regime of 2 nm to 5 nm, were also determined. The internal surface area may also be up to three times as high as that of the externally exposed surface. As well, despite the fact that GLAD column broaden as they grow, the surface area increases linearly with film thickness. Focused ion beam milling, with concurrent SEM imaging, was then employed to investigate and reconstruct the three-dimensional structure of GLAD films in the tens of nanometers regime not measurable by krypton gas adsorption porosimetry. The measured growth scaling trends agreed with previous findings, but were determined using only one sample, instead of multiple samples of increasing thickness. Mean column diameters, center-to-center spacings, void spacings, and column densities were found to scale with thickness as w = (9.4 +/- 3.0) t^{0.35 +/- 0.09} nm, c = (24.8 +/- 5.2) t^{0.31 +/- 0.08} nm, v = (15.2 +/- 3.8) t^{0.25 +/- 0.06} nm, and d = (3400 +/- 2500) t^{-0.65 +/- 0.15} columns um^{-2}, respectively. Finally, spatially graded nanostructures were demonstrated by extending the GLAD technique to include macroscopic shadowing. Optically transparent, graded thickness and pitch helical films were fabricated with polarization selectivity over a spatial range of 30 mm, concurrent with 70 nm spectral tunability. These structures will be useful for tunable frequency photonic devices. / Micro-Electrical-Mechanical Systems (MEMS) and Nanosystems

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

This thesis describes the development, characterization andoptimization of compact, high-brightness, liquid-jet-targetx-ray sources. Two different source types have been developedfor different wavelength regions and applications. A laser-plasma source for generating soft x-ray andextreme-ultraviolet radiation has been further developed forsoft x-ray microscopy and extreme-ultraviolet lithography. Thiswork focused on improved target stability, increased conversionefficiency and decreased debris production. For x-raymicroscopy applications using carbon-containingliquid-jetdroplet targets, the droplet stability has beeninvestigated and a method for source stabilization introduced.This source has also been optimized in terms of flux per debriswith respect to target material and size. Forextreme-ultraviolet lithography applications, aliquid-xenon-jet-target laser-plasma source system has beengreatly improved, especially in terms of stability andconversion efficiency. This source has also been characterizedin terms of, e.g., source size, angular distribution, andrepetition-rate capability. For extremeultraviolet lithography,the possible use of tin as a target material has also beenstudied and conversion efficiency and debris measurementsperformed. A new anode concept for electron-impact hard x-ray sourcesbased on high-speed liquidmetal jets has been introduced.Initial calculations show that this new target concept couldpotentially allow more than a hundred-fold increase in sourcebrightness compared to existing state-of-the-art technology. Alow-power, proof-of-principle, experiment has been performed,verifying the basic source concept. Scaling tohigh-poweroperation is discussed and appears plausible. A main obstaclefor high-power operation, the generation of a microscopichigh-speed jet in vacuum, is investigated usingdynamic-similarity experiments and shown to be feasible.Finally, initial medium-power experiments, approaching currentstate-of-the-art sources in terms of brightness, have beenperformed.

The fabrication characteristic of etching and deposition of focused ion beam (FIB) on the submicron structure of silica and quartz glass was investigated. FIB has several advantages such as high sensitivity, high material removal rate, and direct fabrication in some selected areas without the use of etching mask, etc. In this study, silicon and quartz glass materials etched by FIB were used for fast fabrication of 3-D submicron structures to investigate the differences between the samples before and after fabrication. The expansion effect of silicon with sputtered platinum on surface is compared with Pyrex glass with sputtered chromium on surface. The result shows the side wall of structure in the center wouldn¡¦t be vertical after etching and trimming on the quartz glass and the silicon substrate. Trenches with different depth and width on the surface of silicon were etched by FIB and measured by Atomic Force Microscope. Lines with different interval were deposited by FIB on the surface of quartz glass and were measured by Atomic Force Microscope.

The daily uncertainty concerning tumor localization is one of the major problems during the course of radiation therapy. Image guided-radiation therapy (IGRT) can be used to improve the localization and adjustment of the planning target volume. The aim of this work was to evaluate both the IGRT technique used for prostate cancer patients at the department of the Karolinska University Hospital and an alternative on-line adaptive radiation therapy (ART) method with an On-Board Imager (OBI). In the first part of the thesis 2D and 3D image registration with an OBI were compared. Ten prostate cancer patients were involved in the analyses. Two different statistical tests were used to determine significant systematic deviations between the two methods. The second part concerns daily dose verifications and dose plan reoptimization of one intensity modulated radiation therapy (IMRT) prostate cancer patient treated with IGRT. The study was based on cone-beam computed tomography (CBCT) images acquired at 6 different treatment fractions. The risk of developing late rectal and bladder toxicity was quantified using normal tissue complication probability (NTCP) calculations. Additional measurements on an Alderson phantom were performed to verify the accuracy of using the CBCT images for dose calculations. A statistically significant difference between the 2D-2D and the 3D-3D match applications could be observed in lateral and longitudinal direction. However, the effect differed among the patients. The phantom measurements showed small dose deviations between the CT and CBCT image, with a mean dose increase to the prostate and seminal vesicles (SV) of 2.5 %. The daily dose to the prostate and SV of the IMRT patient showed to be satisfactory. The daily dose to the rectum did not exceed the prescribed rectal dose except at one treatment fraction and the highest risk of developing late rectal toxicity was about 10.4 %. Large daily bladder dose variations were observed and at two treatment fractions the bladder dose restrictions were exceeded. With a reoptimization process of the dose plan, the dose to the bladder could be reduced while conserving the dose to the target. This work shows that for these specific patient cases appropriate doses to the prostate and SV can be delivered with IGRT. However, introducing a suitable ART method could lead to a reduction of inter-fractional rectal and bladder dose variations.

An algorithm for modeling two species plasmas, which evolves the number density, flow velocity, and temperature equations coupled to Maxwell's electric and magnetic field equations, is discussed. Charge separation effects and the displacement current are retained. Mathematical derivations of normal modes in cold and hot plasmas, as represented by dispersion relations resulting from a linear analysis of the two fluid equations, are presented. In addition, numerical theory in relation to the ideas of geometry, temporal and spatial discretization, linearization of the fluid equations, and an expansion using finite elements is given. Numerical results generated by this algorithm compare favorably to analytical results and other published work. Specifically, we present numerical results, which agree with electrostatics, plasma oscillations at zero pressure, finite temperature acoustic waves, electromagnetic waves, whistler waves, and magnetohydrodynamics (MHD) waves, as well as a Fourier analysis showing fidelity to multiple dispersion relations in a single simulation. Final consideration is given to two species plasma stability calculations with a focus on the force balance of the initial conditions for a resistive MHD tearing mode benchmark and a static minimum energy plasma state.

External radiotherapy with proton and ion beams needs accurate tools for the dosimetric characterization of treatment fields. Monte Carlo (MC) particle transport codes, such as FLUKA and GEANT4, can be a valuable method to increase accuracy of dose calculations and to support various aspects of ion beam therapy (IBT), such as treatment planning and monitoring. One of the prerequisites for such applications is however that the MC codes are able to model reliably and accurately the relevant physics processes. As a first focus of this thesis work, physics models of MC codes with importance for IBT are developed and validated with experimental data. As a result suitable models and code configurations for applications in IBT are established. The accuracy of FLUKA and GEANT4 in describing nuclear fragmentation processes and the production of secondary charged nuclear fragments is investigated for carbon ion therapy. As a complementary approach to evaluate the capability of FLUKA to describe the characteristics of mixed radiation fields created by ion beams, simulated microdosimetric quantities are compared with experimental data. The correct description of microdosimetric quantities is also important when they are used to predict values of relative biological effectiveness (RBE). Furthermore, two models describing Compton scattering and the acollinearity of two-quanta positron annihilation at rest in media were developed, validated and integrated in FLUKA. The detailed description of these processes is important for an accurate simulation of positron emission tomography (PET) and prompt-γ imaging. Both techniques are candidates to be used in clinical routine to monitor dose administration during cancer treatments with IBT. The second objective of this thesis is to contribute to the development of a MC-based treatment planning tool for protons and ions with atomic number Z ≤ 8 using FLUKA. In contrast to previous clinical FLUKA-based MC implementations for IBT which only re-calculate a given treatment plan, the developed prototype features inverse optimization of absorbed dose and RBE-weighted dose for single fields and simultaneous multiple-field optimization for realistic treatment conditions. In a study using this newly-developed tool, the robustness of IBT treatment fields to uncertainties in the prediction of RBE values is investigated, while comparing different optimization strategies. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Submitted. Paper 6: Manuscript.</p>

A novel photon flux monitor has been designed and tested for use at the Duke University High Intensity Gamma Source, where the photon beam produced is essentially mono-energetic but it is not tagged. Direct counting of the number of photons using a high-efficiency detector is not possible because of the high photon fluxes expected. Therefore, a direct counting detector with a low, accurately known efficiency was required.<p> The photon flux monitor based on a five scintillator paddle system detects recoil electrons and positrons from photoelectric, Compton and pair-production processes. It has been designed to be insensitive to gain and detector threshold changes and to be usable for photon energies above 5 MeV. It has been calibrated using direct counting with a NaI detector and its efficiency has been shown to be well predicted by a GEANT4 simulation.<p> Results of measurements, calibration and calculations required to characterize the 5-paddle photon flux monitor are presented. The photon flux monitor has met its design specifications of being able to determine the number of photons incident on it during the live time of a measurement to within a systematic error of 2%.<p> A paper based on the work for this thesis has been published in the Nuclear Instruments and Methods in Physics Research Journal.

Radiotherapy is one method of treating di erent diseases like cancer. It requires a treatment plan that clearly delineates target and non-target volumes, and the beams and their intensities to deliver the prescribed dose. Historical treatment plans often contain volume names that are unaccounted for. An approach is applied where desired volumes are detected and renamed to conform to current search standards. The mapped names provide an avenue for searching historical plans when performing outcomes analysis in the future to help improve quality in radiation therapy. A specific form known as intensity modulated radiation therapy is applied to total marrow irradiation, a method to remove all marrow in the body prior to bone marrow transplant. A set-covering approach is used, solved using heuristics and commercial packages to compare outcomes. Constraint programming is used in an attempt to better and to improve on the heuristic solutions.

Radiotherapy is one method of treating di erent diseases like cancer. It requires a treatment plan that clearly delineates target and non-target volumes, and the beams and their intensities to deliver the prescribed dose. Historical treatment plans often contain volume names that are unaccounted for. An approach is applied where desired volumes are detected and renamed to conform to current search standards. The mapped names provide an avenue for searching historical plans when performing outcomes analysis in the future to help improve quality in radiation therapy. A specific form known as intensity modulated radiation therapy is applied to total marrow irradiation, a method to remove all marrow in the body prior to bone marrow transplant. A set-covering approach is used, solved using heuristics and commercial packages to compare outcomes. Constraint programming is used in an attempt to better and to improve on the heuristic solutions.