The work presented in this thesis may be considered in two main parts; firstly a description of the design and operation of a display type photoelectron spectrometer. Secondly a series of experiments investigating the electronic properties of thin epitaxial films (1-5 atomic layers) of cobalt grown on a clean single crystal copper (001) substrate. Conventional angle resolved photoelectron spectrometers of the deflection type are only capable of observing one point in the (E,θ,φ) space at a time. This is often perfectly acceptable if one is concerned with optimal resolution in order to perform accurate band mapping experiments. However certain experiments are essentially impossible, for instance the observation of the emitted photocurrent over all θ,φ at the fermi energy. This is partly because of the time limitations imposed by the necessity to keep the sample atomically clean in the U.H.V. environment. Several previous workers have tackled this problem by designing spectrometers that observe large sections of θ,φ space simultaneously, for a given energy. The first part of this work concerns the design and implementation of a display type spectrometer which embodies some new and quite novel features. Thin epitaxial films of ferromagnetic materials grown on non-magnetic substrates have long been of interest. Partly as a prototypical surface for the investigation of surface magnetism, and partly for the investigation of the changes induced in the magnetic properties as the dimensionality is reduced or as the lattice size is changed. The second part of this thesis concerns experiments using three different spectroscopies on a system of this type, specifically Co on Cu(001). Firstly, a photoemission study using the display spectrometer is presented, observations of the spin-split bands as a function of wavevector parallel to the surface are shown. Secondly an Auger electron study of the growth mode of the epitaxial film, together with a LEED I/V study of the changing lattice strain as a function of film thickness are presented. Although none of these measurements directly probe the magnetism of the films, they provide very necessary information in order to understand their behaviour.

Graduation date: 1992

AbstractThis thesis includes an elementary introduction and background to nuclear magnetic resonance (NMR) detection. The content is essentially concerned with the mathematical analysis of the spectrometer electronics. The construction and testing was routine using established high frequency techniques. The spectrometer circuitry incorporates both vacuum tube and solid state devices. The special characteristics of each device were utilized to best meet the particular circuit requirements.The electronic portion of this spectrometer functioned properly. Final testing of the total system is awaiting the completion of the induction probe presently under development.Ball State UniversityMuncie, IN 47306

This thesis begins with a theoretical description of the quadrupole nucleus, its interaction with a molecular electric field and its detection.The design parameters for the minaturized cryogenic NQR Spectrometer are presented along with an analysis of the operation of a superregenerative oscillator-detector. A review of the problems encountered in the development of the spectrometer is also presented.Ball State UniversityMuncie, IN 47306

Call number: LD2668 .T4 1985 S54 / Master of Science

Graduation date: 2002

A multi-detector spectrometer was constructed to measure garmia-gamma angular correlations in 154Gd from the decay of 154Eu. Gamma-ray multipole mixing ratios were extracted from the data. A modified fast-slow coincidence electronics arrangement with selective routing of data was used. One Ge(Li) detector and three NaI detectors were used in the system for rapid data acquisition. "Real-plus-random" and "random" coincidences were accumulated simultaneously with detectors set at selected angles. Mixing ratios for the first transition in the cascades of 1274-123--keV (2--2+-0+), 1005-123-keV (3+-2+-0+), and 723-996-keV (2--2+-O+) were measured as '5(1274) = 0.02 0.02, '5(1005) = -28+10' '5(723) = 0.02 0.02.'The measured correlation for the 592-1005 keV cascade (2--3+-2+) was analyzed by searching a 157 by 157 array of values for '5(592) and 8(1005); agreement was tested using a Q2 criterion. The best agreement for the mixing ratio of the 592-keV transition was 8(592) = 0.08 0:22; for the 1005-keV transition 8(1005) = -9.5+7. The value 8(1005) _ -9.5+7 is taken to be the better value as a result of experimental considerations. The value for the 592-keV transition had not been previously measured.Ball State UniversityMuncie, IN 47306

This thesis is concerned with the design and realisation of components for a new state of the art 94GHz Electron Spin Resonance (ESR) spectrometer capable of operating in both pulsed and CW modes. The complete spectrometer is designed to provide phase coherent 1kW peak power sub-nanosecond π/2 pulses having variable duration and repetition rate. The mm-wave response of a paramagnetic sample to these pulses is detected with a superheterodyne detector. Such a system would offer a step change in performance, promising unprecedented resolution and sensitivity. These aims should be compared with the performance of commercial (Bruker) instruments capable of delivering 200mW 30ns π/2 pulses. For this type of system, both the long term (thermal) and short term (phase) stability of oscillators and sources employed are extremely important. Consideration of phase noise, frequency, tunability and power output shows that multiplied sources offer substantial benefits compared to fundamental sources. A delay line discriminator method of phase noise measurement, suitable for use with the low frequency oscillators is described and implemented. This is extended to 94GHz using a down convertor with a quasi-optically stabilised Gunn oscillator. These tools are used to select an optimum oscillator-multiplier combination to produce a low noise 94GHz source. Anew method of pulse generation, which has produced +23dBm peak power 250ps rectangular and 115ps Gaussian envelope phase coherent pulses, is described. These are believed to be the shortest phase coherent pulses at 94GHz available. This system will be used to provide ns pulses suitable for amplification to 1kW using a Klystron amplifier. A heterodyne detector has been constructed which employs the same oscillator/multiplier techniques identified above to produce the required local oscillator signal. It is demonstrated that by careful consideration of multiplication factors a system employing one variable and one fixed oscillator allows all the signals required in the spectrometer to maintain phase coherence. It is demonstrated that the complete demodulator responds to pulses on a ns time scale and has a noise temperature of 737K.

CD containing a copy of the thesis, software and extra documentation is held with print copy. / Nuclear Magnetic Resonance (NMR) is a relatively complex technique and normally requires expensive equipment. However, with advances in computing, electronics and permanent magnet technologies, NMR is becoming more feasible as a non-invasive tool for industry. The strength of NMR is its ability to probe at the molecular level and hence gain information about molecular structure, organisation, abundance and orientation. This thesis describes the development of an instrumentation platform technology that is compact and therefore portable. It has been produced to aid the development of NMR based tools or sensors for research and industry and will lead to a series of low cost, portable NMR systems for the non-destructive testing of materials such as polymer composites, rubber, timber, bricks and concrete. The instrumentation is largely electronics based and consists of a series of modules that can be interconnected to produce a solution. The first of two main modules is called the system core. What is common to all NMR applications is the generation of precisely timed signals, the capturing of signals and the processing/display of data. This has been implemented by developing a general purpose Digital Signal Processor (DSP) based instrumentation and control module that uses a Universal Serial Bus interface to communicate with a host computer. A graphical user interface is provided by an application running under Windows® XP. The second main module is a radio frequency transceiver that has been developed using digital receiver technology. The signals, after some amplification, are digitized with a 14-bit, 62.5MH.z analogue to digital converter. The sampled signal is then mixed digitally with synthesized sine and cosine functions to generate lower frequency quadrature outputs which are then digitally filtered and decimated before being passed onto the DSP for further processing and storage. A direct digital synthesizer with an analogue output is used to generate any required excitation signals. All synthesizers have phase and frequency hopping capabilities and are phase locked to each other and the DSP. The system was designed to interface to a range of NMR probes. The type of probe is determined by the intended application and each probe has specific requirements such as the type of radio frequency power amplifier, duplexer and preamplifier needed. This results in a number of instrumentation variations and a modular instrument enclosure was used to cater for these variations. The instrument was first configured for an NMR probe called the NMR-MOUSE. Tests were performed with this probe to verify the correct operation and performance of the instrument. The instrument was then reconfigured for a new probe called the NMR-MOLE and further testing was performed. This probe was still undergoing development and had not been previously tested. Finally, a dedicated compact instrument measuring 360 x 240 x 55 mm and weighing 3.6 kg was developed for the NMR-MOUSE probe.

An (e,2e) electron scattering spectrometer has been constructed and used for the first time to investigate the spectral momentum density of the valence bands of a solid target. This technique provides fundamental information about the electronic structure of both crystalline and amorphous solids. The three fundamental quantities, the band structure, electron density of states, and electron momentum distribution can be simultaneously derived from the measured (e,2e) cross section. A review of single electron and (e,2e) scattering theory is given with an emphasis on scattering from solids. The effects of multiple scattering are discussed and a method of deconvoluting those effects from the measured (e,2e) cross section is developed. There is a detailed description of the spectrometer design and operation with particular attention given to the electron optics and voltage distribution. The algorithms and software for computer aided data acquisition and analysis are also outlined, as is error analysis. The techniques employed in the preparation and characterization of extremely thin film samples of a-C and single crystal graphite are described. An analysis of the data taken for a-C samples is given. The data are compared with the results of complementary experiments and theory for graphite, diamond, and a-C which are given in a review of the literature. The existence of a definite dispersion relation ε(q) in amorphous carbon is demonstrated. The a-C band structure appears to be more similar to that of graphite than to that of diamond, however it differs significantly from both in some respects. The measured spectral momentum density seems compatible with a model of a-C based on small, randomly-oriented islands of quasi-2D graphite-like continuous random network structures. However, no definitive interpretations can be made until higher resolution experiments are performed on both a-C and single crystal graphite. / Ph. D.