This Small Grants for Exploratory Research (SGER) project will examine a spectacular property of certain ferroelectric crystals: Conversion of diffuse thermal heat energy (normally associated primarily with lattice vibrations) into spontaneous emission of electrons from the surface of the crystal. The phenomenon is somewhat analogous to "photoemission" but here a poorly understood thermal conversion process replaces the photon. The thermally emitted electrons have energies of 100Kilovolts or more. Under easily obtained laboratory conditions, and with a small crystal, the emitted electron current can exceed a nano-ampere. The energies of the emitted electrons are measured by conventional methods and show that emission can be pulsed, and that it depends on the heating cycle of the crystal. The goal of this project is to understand, optimize and control these phenomena, for which a complete theory is not yet available. Environmental conditions such as temperature, crystal size, coercive field, and vacuum pressure will be varied to increase the electron current and energy, hopefully to the Megavolt range. Students will be trained in a range of modern laboratory techniques. The basic science that results from understanding this effect could open a window to a new class of collective solid-state dynamics. For example, localization of the effect could lead to an electron source for a compact projection transmission electron microscope. %%% This Small Grants for Exploratory Research (SGER) project will examine a spectacular, property of certain crystals: Ferroelectric crystals such as lithium niobate are extraordinary materials in that internal electric fields as large as 100 million volts/cm can be produced spontaneously owing to the arrangements of positive and negative ions in the crystal lattice. These fields can be put to work: Upon smoothly increasing the temperature of a small 1 cm^3 crystal, electrons are emitted and used to create x-rays. The goal of this project is to elucidate the fundamental scientific process whereby the energy involved in a gentle and diffuse heating becomes focused on electrons and causes them to be emitted with energies characteristic of the x-rays found in medical x-ray devices. A key goal is to determine the maximum energy, power, and current achievable in this compact geometry. Broad technological consequences could be realized if one is successful in localizing the high-energy emission to a nanoscale tip. In this case the energy transduction made possible by ferroelectricity might lead to a prototype compact projection transmission electron microscope. Students will be trained in a laboratory techniques ranging from solid-state chemistry to nuclear spectroscopy to x-ray generation and detection.
