SGER: Mechanism for Emission of Penetrating Radiation from Ferroelectric Crystals

这一小型探索性研究(SGER)项目将研究某些铁电晶体的一种壮观特性：将扩散热能(通常主要与晶格振动有关)转换为晶体表面的自发电子发射。这种现象有点类似于“光电发射”，但在这里，人们对热转换过程知之甚少，而是用光子来代替。热发射的电子的能量为100千伏特或更多。在容易获得的实验室条件下，用一个小晶体，发射的电子电流可以超过纳米安培。用传统的方法测量了发射电子的能量，表明发射是脉冲的，而且它取决于晶体的加热周期。这个项目的目标是了解、优化和控制这些现象，对于这些现象，还没有完整的理论可用。温度、晶体大小、矫顽场和真空压力等环境条件将会改变，以增加电子电流和能量，有望达到Megavolt范围。学生们将接受一系列现代实验室技术的培训。理解这一效应所产生的基础科学可能会打开一扇窗户，让我们了解一类新的集体固态动力学。例如，这种效应的本地化可能会导致一种用于紧凑型投影透射电子显微镜的电子源。%这个小型探索研究拨款(SGER)项目将研究某些晶体的一种壮观的性质：像铌酸锂这样的铁电晶体是非常特殊的材料，因为由于晶格中正离子和负离子的排列，可以自发产生高达1亿伏/厘米的内电场。这些场可以发挥作用：当平稳地提高1厘米^3小晶体的温度时，电子被发射出来，并用来产生X射线。这个项目的目标是阐明基本的科学过程，在温和和扩散加热中涉及的能量集中在电子上，并使它们以医用x射线设备中的x射线特有的能量发射。一个关键目标是确定在这种紧凑的几何结构中可以实现的最大能量、功率和电流。如果一个人成功地将高能发射定位到纳米级尖端，就可以实现广泛的技术后果。在这种情况下，铁电性使能量传递成为可能，这可能导致一种紧凑的投影电子显微镜的原型。学生将在实验室接受从固态化学到核光谱学再到X射线产生和检测的各种技术培训。

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.