The fellow during the grant was active in mainly three different areas, developed simultaneously during the period of the grant, to guarantee that the output was maximum, always pointing toward the objectives set in the proposal. More specifically:
Firstly, the fellow during the whole duration of the grant has been engaged with setup development. Initially, we found out that the amplified laser system in our labs at the moment, did not have the appropriate pulse temporal duration for obtaining the ultrabroadband spectrum we were hoping for, but we were limited at ~3THz. For this reason, we decided to use the laser facilities of the Max Planck Institute for Polymer research (MPIP), in Mainz Germany, since the host group is assigned as an official Max Planck partner group. By using their ultrabroadband THz spectrometer, based on air-plasma, we characterized several families of MOFs with THz time-domain spectroscopy (THz-TDS) and for one sample, namely the Cu-HHTP (HHTP=hexahydroxy triphenylene) we were able to identify a phonon, residing at 1.8THz. The low frequency where this phonon appeared allowed us to investigate it at IMDEA, with the resources we had, observing a clear electron-phonon interaction. In the meantime, we obtained a new amplified laser system, with an oscillator output of a duration of <10fs, which will allow us reaching the desired bandwidth and consequently will allow us to study more conductive MOFs with phonons appearing at higher frequencies. Moreover, the new setup design also allows measurements in transmission and reflection, which will give us the opportunity to study any samples independently of its opacity at THz frequencies.
Secondly, following the research lines of the host group, the fellow engaged in other projects, closely related to the proposal’s objectives. He performed temperature dependent THz-TDS measurements on the HHTP MOFs with different metal centers and found out that the electrical properties of the samples is greatly affected by the nature of the metal center. Moreover, the fellow also performed temperature dependent THz-TDS measurements on the Cu2(OHPTP) MOF, a sample of great interest since it shows a bandgap in the near IR, making it very relevant for logic and solar cell applications. From these measurements he found out that this material has excellent mobility and also a large scattering time, very beneficial for these applications where long range charge migration is needed.
Finally, measurements on other side projects took place, due to the scientific relation of the fellow with colleagues at Fritz Haber Institute in Berlin, producing a total of three extra publications. In brief the fellow used a Lithium Niobate high-field THz source for performing THz-pump/Raman probe on electrolyte solutions. He used a newly built SFG/DFG spectrometer to experimentally derive the nonlinear Fresnel Factors of metals for the first time and did complementary measurements on z-cut alpha-quartz crystals proving its applicability on THz applications.
The project has been very productive scientifically, with 4 publications in high impact journals, and 4 additional ones in peer-review or preparation phases. Furthermore, it has been presented 3 conferences and one internal IMDEA seminar.
