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通过大多数材料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范围内对结构无序进行桌面实验研究，从近1毫米(即明显的宏观)到短至10纳米。它还将提供对结构动态变化的直接实验通道，这些动态变化发生在同样广泛的时间范围内，从快于1皮秒到许多微秒，给出了将获得接入的大约10 MHz-500 GHz的声频范围。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，这些晶体的关键性质是由这些长度和时间尺度上的结构变化所调节的。该仪器还将用于表征先进的结构，包括微电子和许多其他应用中感兴趣的薄膜和多层组件。该仪器将提供在块状和薄膜材料中的大部分布里渊区获得相干、窄带声学声子的途径。非技术概述波长为米或毫米的声波通常用于探测类似大小的结构，如地球地幔内的特征、石膏板后面2乘4的光束，或子宫内的手指和脚趾(及其运动)。超声波成像和探测的相同原理也可以应用于更小的长度尺度，并且有大量微米和纳米尺寸的结构需要表征。这些包括微电子设备中的多层薄膜；纳米球、纳米棒和其他为纳米技术制造的结构；合金、悬浮液和凝胶等非均质材料的成分；甚至在粘性液体、聚合物和生物液体中自然波动或流动时形成的瞬时不规则。但产生波长如此短的声波，引导它们沿着感兴趣的材料或穿过感兴趣的材料，然后检测它们，往往会带来令人望而生畏的挑战。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，激光的“梳子”被用来将声波图案直接压印在感兴趣的材料上，就像真正的梳子突然轻轻接触水面可能会产生与梳子间距相匹配的声波一样(只是激光条纹之间只有微米的距离！)。在其他情况下，定时的激光脉冲序列被用来向材料发射声波，就像水族馆一侧的连续敲击可能向水族馆内的水中发射声波一样(除了光脉冲只有皮秒，即10X(-12)秒)。声波不仅是产生的，而且是光学检测的，因此不需要与样品进行机械接触。这些方法已被用于测量薄膜层的纳米厚度和微小特征的横向尺寸，控制聚合物加工或生物系统响应的粘弹性波动的瞬时演变，以及许多其他小结构及其动力学。在这个项目中，将开发一种设备，允许光学产生和检测基本上所有可能的波长和频率的声波，这些波长和频率可以在各种材料和结构元件中传播。这些设备的设计将不仅使这些测量成为可能，而且还将使其变得坚固可靠，以便高中生可以在外展实验室中进行测量，也可以由理工科博士生进行测量。通过这种方式，一个了解微米和纳米级结构和行为的新窗口将被广泛使用。

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.