In situ studies of particle properties during their formation and growth with optical second-harmonic generation

目的是发展光学二次谐波产生（二次谐波散射，SHS）和双光子荧光（2-PF）作为原位研究< 50 nm纳米颗粒的形成，生长和表面改性的方法。SHS作为一种非侵入性的非线性散射光谱技术，对纳米颗粒的尺寸、形状和表面的变化非常敏感。在小于50 nm的纳米颗粒表面的配体交换可以用具有高时间分辨率的SHS进行跟踪，并且除了获得热力学信息之外，还允许区分不同的吸附步骤和表面位点。另外，半导体量子点（尺寸小至2 - 3 nm）的颗粒特性可以从2-PF中获得。此外，2-PF还可以研究颗粒缺陷的形成。金属和半导体纳米颗粒的颗粒形成将分别在T型混合器中与SHG和2-PF一起研究。结合原位紫外-可见光谱和透射电镜的颗粒生长的动力学进行了研究。通过改变系统参数，研究了稳定剂对颗粒形成动力学的影响。对于ZnO量子点，我们将特别关注粒子生长过程中缺陷的形成，下一步将利用原位SHS研究不同尺寸金属纳米粒子表面的配体交换，以解决配体交换的动力学和热力学对不同尺寸粒子的依赖性。除了产生动力学信息外，还将确定配体的表面覆盖度，从而确定配体交换的效率。对于邻苯二酚在ZnO上的快速吸附，将使用T-混合器。在最后一步中，将研究同时应用SHS和2-PF进行颗粒测量。因此，2-PF和SHS量子点的依赖于粒子的大小，激发波长和表面改性将进行研究。

The objective is the development of optical second harmonic generation (second harmonic scattering, SHS) and two-photon fluorescence (2-PF) as methods for in situ investigations of particle formation, growth and surface modifications of nanoparticles < 50 nm. SHS as a non-invasive nonlinear scattering spectroscopy is highly sensitive to changes of particle size, particle shape and of the surface of nanoparticles. The ligand exchange at the surface of nanoparticles < 50 nm can be followed with SHS with high time resolution and allowed for the discrimination of different adsorption steps and surface sites besides gaining thermodynamic information. Alternatively, particle properties of semiconducting quantum dots (down to sizes of 2 -3 nm) can be obtained from 2-PF. In addition, 2-PF enables the investigation of the formation of defects of the particles.Particle formation of metallic and semiconducting nanoparticles will be studied in a T-mixer with SHG and 2-PF, respectively. In combination with in situ UV-Vis spectroscopy and TEM the kinetics of particle growth will be studied. By variation of system parameters the influence of the stabilizer on the particle formation kinetics will be investigated. For ZnO quantum dots a special focus will be put on the formation of defects during particle growth.In the next step, the ligand exchange at the surface of metallic nanoparticles of different sizes will be studied with in situ SHS in order to resolve the dependence of kinetics and thermodynamics of the ligand exchange on differently sized particles. Besides yielding kinetic information the surface coverage of the ligands and thereby the efficiency of the ligand exchange will be determined. For the fast adsorption of catechol on ZnO the T-mixer will be used.In the last step, the simultaneous application of both SHS and 2-PF for particle measurement will be studied. Therefore, 2-PF and SHS of quantum dots will be investigated in dependence of the particle size, excitation wavelength and surface modification.