Investigation of ferroelectrics and magnetic particles for novel applications: X-rays, cell mechanics, and electron and ion beams.

摘要

The first demonstration of significant field emitted electron and ion current at pressures in the 10-7 to 10-8 mbar range generated with a lithium niobate crystal are reported here. These experiments are also the first to use a field emission tip mounted on a pyroelectric crystal. Further work with lithium tantalate produced electron beams with energies up to 110 keV, generated with only a few degrees temperature change. The ability to generate large voltages with small crystals (this sample was 15 mm in length with a 10 mm diameter) for such small temperature changes has many practical applications. With the use of a specially designed copper tip, 11 keV electron beams with a beam diameter of 13 microns were produced. Due to the piezoelectric nature of this crystal, it could act as tuning fork AFM to image surfaces and then electron dispersive x-ray analysis could be performed by heating the crystal. Results with a grounded tungsten tip used to create controlled bursts of x-rays of known energy are presented next. The energy can be tailored by changing either the tip radius or the tip crystal separation. Bursts of up to 80,000 x-rays/scm2 were produced in this manner. Two such bursts would be enough to expose a dental x-ray film, demonstrating the usefulness of pyroelectrics for medical imaging. The use of a pyroelectric crystal as a current source in air is also reported. Relatively steady currents of 300-500 nA are produced by heating the sample with a heat gun. These results show that it is not necessary to have complicated thermal cycling to successfully harvest pyroelectric current; turbulent hot air is all that is required. In the final chapter of this dissertation, an interferometric imaging technique is used for mechanical measurements on fibroblast cells with nickel beads and mirrors. The Young's moduli of fibroblasts are determined with this method and compare favorably with literature values. The advantages of the interferometric microscope, coupled with the versatility and known geometry of the probes, make this new technique a powerful addition to the tools currently available for studying cell mechanics.