Development of a Cryogenic Femtosecond Aptureless Near-Field Scanning Optical Microscope for Nanostructure Research

开发用于纳米结构研究的低温飞秒无孔近场扫描光学显微镜

• 批准号: 9802784
• 负责人: Jeremy Levy
• 金额: $ 11.45万
• 依托单位: University of Pittsburgh
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-06-01 至 2001-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9802784&HistoricalAwards=false
• 关键词: Development; Cryogenic; Femtosecond; Aptureless; Near

9802784 Levy This award provides partial support to develop a variable- temperature "apertureless" near -field scanning optical microscope (ANSOM) for studying local electronic and lattice dynamics in nanostructured optoelectronic materials. The instrument will have unique and unprecedented capabilities, combining near-atomic spatial resolution, femtosecond temporal resolution, a wide operating temperature range (1.6K-400K), and operation in magnetic fields up to 10 Tesla. The instrument is specifically suited for the study of material properties which couple to refractive index changes. The contrast mechanism for ANSOM comes from measuring small phase shifts in scattered light from an atomic or magnetic force microscope tip. By modulating the tip-sample separation, it is possible to measure local sample polarizabilities (electric or magnetic) at length scales significantly smaller than those attainable by either conventional optical or fiber-based near-field scanning optical microscopes (NSOMs). The instrument design will also allow it to be used as a confocal scanning optical microscope, which can focus or collect light with high efficiency and diffraction-limited spatial resolution. There are presently several low-temperature NSOMs operating in laboratories around the world. Sub-wavelength spatial resolution for these instruments is obtained by scanning a tapered optical fiber close to the sample to form an image. However, both practical and fundamental constraints prevent the optical resolution from approaching that of atomic-force microscopy (AFM) or scanning tunneling microscopy (STM). The unique power of this instrument will come from the ability to combine traditional strengths of optical methods (e.g., time resolution or energy selectivity) with the spatial resolution of atomic force microscopy. It is possible using ANSOM to achieve spatial resolution below 10 A. The combination of spatial and temporal resolution will open many new research avenues related to dynamical processes in nanometer-scale condensed matter systems. The immediate scientific applications are threefold: (1) the study of exciton dephasing in semiconductor quantum dots, (2) spectroscopic and time-resolved studies of neutral excitations in single conjugated polymer chains, and (3) lattice dynamics and domain wall motion in ferroelectrics and quantum paraelectrics. Longer-range goals include the study of magnetization dynamics in ultrathin magnetic films, applications in biology (e.g., DNA sequencing), and optically detected magnetic resonance. The construction of this instrument will benefit from the design principles of earlier pioneers in the area of low-temperature scanning probe microscopy. Principles that ensure sufficient vibration isolation, coarse approach mechanisms, etc., have been incorporated into the proposed design. Many of the critical design parameters have been assessed from the construction of a room-temperature prototype, which is currently being used to study domain dynamics in ferroelectric thin films. The construction of this instrument will provide valuable experience for students at both the graduate and undergraduate level. The project will be overseen by the principal investigator, who will direct a postdoctoral researcher, a graduate student, and several undergraduate students. The graduate student will work closely with undergraduates on various subtasks related to the larger goal of building the proposed instrument, such as writing software drivers for instruments such as lock-in amplifiers and temperature controllers. The overall goals of the project will be discussed during group meetings so that undergraduates (and graduate students) can see how their project fits in with the larger goal. Support for both the graduate and undergraduate students comes from an NSF CAREER award DMR-9701725. %%% ***

9802784征收该奖项提供了部分支持，以开发可变温度的“无孔”近距离扫描光学显微镜（ANSOM），用于研究纳米结构的光电材料中的局部电子和晶格动力学。 该仪器将具有独特且前所未有的功能，将接近原子的空间分辨率，飞秒时间分辨率，较宽的工作温度范围（1.6k-400k）组合在一起，并在最高10特斯拉的磁场中运行。 该仪器专门适合研究材料特性的研究，这些特性夫妇折射指数的变化。 ANSOM的对比机制来自于从原子或磁力显微镜尖端中测量散射光中的小相移。 通过调节尖端样本的分离，可以在长度尺度上测量局部样品极化（电或磁性）的长度明显小于常规光学或基于纤维的近场扫描光学显微镜（NSOMS）可实现的范围。 仪器设计还将允许将其用作共聚焦扫描光学显微镜，该光学显微镜可以以高效率和衍射限制的空间分辨率聚焦或收集光线。 目前，世界各地的实验室中有几个低温NSOM。 通过扫描接近样品的锥形光纤以形成图像，可获得这些仪器的次波长空间分辨率。 但是，实际和基本约束都阻止了光学分辨率接近原子力显微镜（AFM）或扫描隧道显微镜（STM）的光学分辨率。 该仪器的独特力量将来自将光学方法（例如时间分辨率或能量选择性）与原子力显微镜的空间分辨率相结合的能力。 可以使用ANSOM在10 A以下实现空间分辨率。空间和时间分辨率的组合将开放许多与纳米级凝结物质系统中动态过程相关的新研究途径。 直接的科学应用是三重的：（1）在半导体量子点中进行激子dephasing的研究，（2）单个共轭聚合物链中中性激发的光谱和时间分辨研究，以及（3）晶格动力学和域壁运动在铁罗电和量子Parealectrics和量子Paraelectrics中。 长期目标包括研究超薄磁性膜中的磁化动力学，生物学应用（例如DNA测序）以及光学检测到的磁共振。 该仪器的构建将受益于低温扫描探针显微镜区域的早期先驱者的设计原理。 确保足够的振动隔离，粗制接近机制等的原理已被纳入拟议的设计中。 从室温原型的构建中，已经评估了许多关键设计参数，该原型目前用于研究铁电薄膜中的域动力学。 该乐器的建设将为研究生和本科级别的学生提供宝贵的经验。 该项目将由首席研究员监督，他将指导博士后研究员，研究生和几位本科生。 研究生将与与建立拟议仪器的更大目标有关的各种子任务的大学生紧密合作，例如为仪器编写软件驱动程序，例如锁定放大器和温度控制器。 该项目的总体目标将在小组会议期间讨论，以便本科生（和研究生）可以看到他们的项目如何适合更大的目标。 对研究生和本科生的支持来自NSF职业奖DMR-9701725。 %%% ***