IMR: Development of an Acoustic Phonon Spectroscopy System for Materials Research, Education and Outreach

将开发仪器，以允许光学产生和时间分辨测量在大多数材料中传播的几乎所有波长的相干声波。这一非凡的范围将允许在相同的长度尺度范围内对结构无序进行桌面实验研究，从近1毫米（即明显宏观的）到短至10纳米。它还将提供直接的实验访问动态变化的结构，发生在一个类似的宽范围的时间尺度，从快于1皮秒到许多微秒，给定的声学频率范围约为10兆赫至500千兆赫，将获得访问。这种独特的材料研究能力将用于复杂液体，无定形固体和部分无序晶体的基础研究，其关键特性由这些长度和时间尺度上的结构变化介导。该仪器还将用于表征先进的结构，包括薄膜和多层组件的兴趣，在微电子和许多其他应用。该仪器将提供在体材料和薄膜材料中跨越大部分布里渊区的相干窄带声学声子。 波长为米或毫米的声波通常用于探测类似大小的结构，例如地幔内的特征，干墙后面的2 × 4梁，或子宫内的手指和脚趾（及其运动）。超声成像和探测的相同原理也可以应用于更小的长度尺度，并且有大量的微米和纳米尺寸的结构需要表征。这些包括微电子器件中的多层薄膜;纳米球，纳米棒和其他为纳米技术制造的结构;异质材料的成分，如合金，悬浮液和凝胶;甚至在粘性液体，聚合物和生物流体的自然波动或流动过程中形成的瞬态不规则性。但是，产生波长如此短的声波，引导它们沿着或穿过感兴趣的材料，然后检测它们往往是令人生畏的挑战。近年来，已经开发了新的方法，通过这些方法，可以使用精细定制的激光脉冲来产生和检测具有特定波长或频率的声波。在某些情况下，使用激光的“梳”将声波图案直接压印到感兴趣的材料上，就像突然轻轻接触水面的真实的梳可能产生波长与梳间距匹配的声波一样（除了激光条纹仅相隔几微米！）。在其他情况下，激光脉冲的定时序列用于将声波发射到材料中，就像水族馆侧面的连续水龙头可能会将声波发送到其中的水中（除了光脉冲仅为皮秒，即10 X（-12）秒）。声波不仅可以产生，而且可以通过光学方式检测，因此不需要与样品进行机械接触。这些方法已被用于测量纳米厚度的膜层和横向尺寸的微小功能，粘弹性波动的瞬态演变，管理聚合物加工或生物系统的响应，以及其他小结构和它们的动态主机。在这个项目中，将开发设备，允许光学产生和检测声波，基本上所有可能的波长和频率，可以在广泛的材料和结构元件内传播。这些设备的设计不仅使这些测量成为可能，而且还很可靠，因此高中生可以在外展实验室进行测量，博士也可以进行测量。理工科学生。通过这种方式，一个新的窗口进入微米级和纳米级的结构和行为将被广泛使用。

Instrumentation will be developed to permit optical generation and time-resolved measurement of coherent acoustic waves at nearly all wavelengths that propagate through most materials. This extraordinary range will permit tabletop experimental study of structural disorder on the same range of length scales, from nearly 1 millimeter, i.e. clearly macroscopic, to as short as 10 nanometers. It also will provide direct experimental access to dynamical changes in structure that occur over a similarly wide range of time scales, from faster than 1 picosecond to many microseconds, given by the acoustic frequency range of roughly 10 MHz - 500 GHz to which access will be gained. This unique materials research capability will be used for fundamental study of complex liquids, amorphous solids, and partially disordered crystals whose key properties are mediated by structural variation on these length and time scales. The instrumentation also will be used for characterization of advanced structures including thin films and multilayer assemblies of interest in microelectronics and many other applications. The instrumentation will provide access to coherent, narrowband acoustic phonons across most of the Brillouin zone in bulk and thin film materials. Non-Technical Summary Sound waves with wavelengths of meters or millimeters are commonly used to probe structures of comparable size, such as features within the earth's mantle, two-by-four beams behind drywall, or fingers and toes (and their motions) inside the womb. The same principles of ultrasonic imaging and probing can apply to much smaller length scales as well, and there are plenty of micrometer and nanometer size structures that need characterization. These include multilayer thin films in microelectronics devices; nanospheres, nanorods, and other structures fabricated for nanotechnology; the constituents of heterogeneous materials like alloys, suspensions, and gels; and even transient irregularities that form during natural fluctuations or flow in viscous liquids, polymers, and biological fluids. But generating acoustic waves with such short wavelengths, directing them along or through the material of interest, and then detecting them often present daunting challenges. In recent years, novel methods have been developed through which finely tailored laser pulses may be used to generate and detect acoustic waves with specified wavelengths or frequencies. In some cases, a "comb" of laser light is used to imprint the acoustic wave pattern directly onto the material of interest, just as a real comb that suddenly, gently touches a water surface might generate acoustic waves whose wavelength matches the comb spacing (except that the laser light fringes are only microns apart!). In other situations, a timed sequence of laser pulses is used to launch an acoustic wave into a material, just like sequential taps on the side of an aquarium might send acoustic waves into the water within it (except that the light pulses are only picoseconds, i.e. 10X( -12) seconds, apart!). The acoustic waves are not only generated but also detected optically, so no mechanical contact with the sample is needed. These methods have been used to measure nanometer thicknesses of film layers and lateral dimensions of tiny features, transient evolution of viscoelastic fluctuations that govern polymer processing or biological system responses, and a host of other small structures and their dynamics. In this project, equipment will be developed that will permit optical generation and detection of acoustic waves with essentially all possible wavelengths and frequencies that can propagate within a wide range of materials and structural elements. The equipment will be designed to make these measurements not only possible but robust, such that they can be made by high school students in an outreach lab as well as by Ph.D. science and engineering students. In this manner, a new window into microscale and nanoscale structure and behavior will be made widely available.