Surface height profile imaging with optically trapped spheres

使用光学捕获球进行表面高度轮廓成像

• 批准号: 325733426
• 负责人: Professor Dr. Alexander Rohrbach
• 金额: --
• 依托单位: Institut für Mikrosystemtechnik (IMTEK)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/325733426?language=en
• 关键词: Surface; height; profile; imaging; optically

Surfaces play a special role in nature and technology, since they do not only separate outside from inside, but control chemical reactions, and regulate the exchange of pressure, light, heat, and moisture. To understand the properties of surfaces on a molecular scale, special measurement technology is required to spatially probe and resolve smallest structures without destroying them. Several different scanning probe microscopy (SPM) techniques, among which the most prominent are the atomic force microscope (AFM) and the scanning tunneling microscope (STM), illustrate the enormous demand for imaging surfaces with the most various structures, features and functions. However, despite the impressive success-story of AFM technology, it turned out that the tips of AFM cantilevers are often too stiff for many applications, thus damaging the soft sample. Similar to AFM, but much more sensitive, an optically trapped probe can be scanned across a structured surface to measure the height profile from the displacements of the probe. This technique is called Photonic Force Microscopy (PFM). Optical traps have been playing important roles in the bio-nano-sciences due to their ability to flexibly apply smallest forces on tiny structures in fluid environments. Combined with advanced 3D particle tracking techniques such as back-focal-plane interferometry, they allow sensing miniscule forces exerted on these structures. In a recent publication (Friedrich 2015) we have demonstrated that by a combination of a time-shared twin-optical trap and nanometer-precise three-dimensional interferometric particle tracking reliable height-profiling and surface imaging is possible with a spatial resolution below the diffraction limit. This technique exploits the high energy thermal position fluctuations of the trapped probe, leading to a sampling of the surface 5000 times softer than in AFM. In this research proposal we aim to improve the PFM technology in three different directions: First, the spatial resolution shall be improved significantly, by using smaller probes, which requires a short (green) laser wavelength to stably trap them. Second, the so-called tapping mode shall be implemented, where the probe is oscillated vertically with the goal to reduce the probe sticking and to increase the scanning velocity. A third goal is to expand the range of applications for this scanning probe microscopy by imaging also opaque surfaces, which requires precise optical trapping and tracking of the probe also in reflection mode.

表面在自然和技术中起着特殊的作用，因为它们不仅将外部与内部分开，还可以控制化学反应，并调节压力，光，热和水分的交换。为了理解表面在分子尺度上的特性，需要特殊的测量技术才能在不破坏它们的情况下空间探测和解决最小的结构。几种不同的扫描探针显微镜（SPM）技术，其中最突出的是原子力显微镜（AFM）和扫描隧道显微镜（STM），说明了对具有最多各种结构，特征和功能的成像表面的巨大需求。但是，尽管AFM技术的成功率令人印象深刻，但事实证明，AFM悬臂的尖端对于许多应用程序而言通常太僵硬，从而损坏了软样品。与AFM相似，但更敏感，可以在结构化的表面扫描光学捕获的探针，以测量探针位移的高度轮廓。该技术称为光子力显微镜（PFM）。光学陷阱由于能够灵活地在流体环境中的微小结构上施加最小的力，因此在生物纳米露西中发挥了重要作用。结合先进的3D粒子跟踪技术，例如后面平面干涉法，它们允许在这些结构上施加的微小力。在最近的出版物（Friedrich 2015）中，我们已经证明，通过时间共享的双光陷阱和纳米精确的三维干涉粒子跟踪可靠的高度构图和表面成像的结合，可以将空间分辨率与衍射极限低于衍射极限。该技术利用了被困探针的高能量热位置波动，导致表面采样5000倍，比AFM柔软。在这项研究建议中，我们旨在通过三个不同的方向提高PFM技术：首先，应使用较小的探针，该探针需要大量（绿色）激光波长来稳定地捕获它们，从而显着改善空间分辨率。其次，应实现所谓的敲击模式，其中探针垂直振荡，以减少探针粘附并增加扫描速度的目标。第三个目标是通过成像还不透明表面扩展此扫描探针显微镜的应用范围，这还需要在反射模式下精确的光学诱捕和探针跟踪。