本周三 11.25下午2:00 Seeing with the nano-eye: accessing structure, function, and dynamics of matter on its natural length and time scales
本周四 11.26 上午10：00 Advances in Tip-enhanced Raman Spectroscopy: from single molecule vibrational dynamics to atomic scale grain boundaries in 2D materials
报告地点：微尺度重点实验室 理化大楼 9004
报告人简介：Prof. Markus Raschke 是散射型近场光学显微镜（s-SNOM）的发明者之一，是世界知名的实验物理学家，其主要成就和贡献在于非线性光学和超快纳米光学。他的研究涉及光学和凝聚态。其中光学包括空间和时域的光学调控，纳米天线，等离子激元，近场光学显微镜，光的力学和热学效应；以及新的光学方法于凝聚态的应用包括复合材料和复杂氧化物的相变和动态行为，半导体纳米结构，聚合物的微观构成。
报告主题简介如下：
Title: Seeing with the nano-eye: accessing structure, function, and dynamics of matter on its natural length and time scales
To understand and ultimately control the properties of most functional materials, from molecular soft-matter to quantum materials, requires access to the structure, coupling, and dynamics on the elementary time and length scales that define the microscopic interactions in these materials. To gain the desired nanometer spatial resolution with simultaneous spectroscopic specificity we combine scanning probe microscopy with different optical, including coherent, nonlinear, and ultrafast spectroscopies. The underlying near-field interaction mediated by the atomic-force or scanning tunneling microscope tip provides the desired deep-sub wavelength nano-focusing enabling few-nm spatial resolution. I will introduce our generalization of the approach in terms of the near-field impedance matching to a quantum system based on special optical antenna-tip designs. The resulting enhanced and qualitatively new forms of light-matter interaction enable measurements of quantum dynamics in an interacting environment or to image the electromagnetic local density of states of thermal radiation. Other applications include the inter-molecular coupling and dynamics in soft-matter hetero-structures, surface plasmon/phonon interferometry as a probe of electronic structure and dynamics in 2D materials, and quantum phase transitions in correlated electron materials. These examples highlight the general applicability of the new near-field microscopy approach, complementing emergent X-ray and electron imaging tools, aiming towards the ultimate goal of probing matter on its most elementary spatio-temporal level.
Title:
Advances in Tip-enhanced Raman Spectroscopy: from single molecule vibrational dynamics to atomic scale grain boundaries in 2D materials
I will discuss advances in tip-enhanced spectroscopy in sensitivity, selectivity, time resolution, and overall parameter space in particular for Raman, photoluminescence, and nonlinear nano-imaging. In particular to gain insight into intra- and inter-molecular coupling and dynamics, we use tip-enhanced Raman spectroscopy (TERS) at variable and cryogenic temperatures, to slow and control the motion of a single-molecule. We resolve intrinsic linewidths of individual normal modes, allowing detailed and quantitative investigation of the vibrational fingerprint.
From temperature dependent line narrowing and splitting, we quantify ultrafast vibrational dephasing and intramolecular coupling. Through statistical correlation analysis of fluctuations of individual modes, we observe rotational dynamics and spectral diffusion of the molecule. In two-dimensional (2D) materials the physical properties are strongly influenced by nanoscale heterogeneities in the form of nucleation sites, defects, and edges. From combined tip-enhanced Raman scattering (TERS) and photoluminescence (TEPL) spectroscopy and imaging we resolve the nonlocal correlation and influence of grain boundaries and edges on structure and electronic excitation with sub-20 nm spatial resolution. From active AFM tip control and release of built in crystal strain we can assign PL spectral position and intensity to nanoscale strain effect.