Ultrafast Materials Physics – Molecular Movies

Our goal is to understand the fundamental physical phenomena underlying chemical reactions and the transport of charges and energy. This understanding enables cheap and environmentally benign materials for solar-energy harvesting [Canton2015, Harlang2015], new insights in the mechanisms for photocatalysis [van Driel 2016], and new functional materials [Katsouras 2016 (PVDF paper)].

Using optical laser pulses or electrical fields as triggers, we can take snapshots of the structural dynamics response of functional materials with powerful X-ray pulses from large-scale X-ray facilities such as synchrotrons and X-ray Free Electron lasers

Current activities

Currently, our focus is on the dynamics of photo-active chemical compounds in solution, with a special emphasis on novel, iron-based materials for solar energy harvesting with dye-sensitized solar cells. One key aspects of this research is to understand how photo-excited electrons in dye molecules experience and influence the potential energy landscape that govern how well suited a dye may be for solar energy applications. However, such molecules do not exist in isolation, and the surrounding solvent medium may directly influence the photochemical reactions and another current avenue of research is therefore the solute-solvent interactions, also known as “solvation”.

Our research is currently focused on

  • Measuring and understanding the ultrafast electronic dynamics in the very first instants after a photo-excitation event and understanding the intimate interplay between electronic and structural dynamics. [Biasin2016, Cammarata2017]
  • Mapping the potential landscape(s) in novel iron-based photo-sensitizer molecules,
  • Understanding how changes in the environment (solvation) influences these landscapes. [Driel2016]
  • Electron localization in photochemical reactions
  • Method development, both in terms of experiments [Ejdrup 2009 detector timing, Haldrup 2016 (Combined XES+XDS, MHz experiments) Katsouras 2016] and in terms of new methods for data reduction and data analysis of terabyte-sized data sets with sub-picosecond time resolution. [Haldrup2014, Driel2015].
  • Understanding, interpreting and utilizing the effects that arise due to an anisotropic orientation distribution of excited-state structures due to a linearly polarized pump laser pulse.

Experimental activities

Large-scale X-ray facilities allows us to combine:

  • The atomic resolution of X-ray scattering with
  • The sensitivity to electronic states delivered by X-ray spectroscopy.

- As highlighted in a few recent papers, [Haldrup2016]

At synchrotron X-ray sources we combine the superior average brilliance, high stability and high-energy X-rays to enable high-resolution studies down to time scales of picoseconds. At X-ray free Electron lasers we take advantage of the incredibly high peak brilliance to study the dynamics of atoms and molecules down to time scales of only a few tens of femtoseconds. We are currently involved in investigations utilizing the following facilities:

  • The ESRF synchrotron in Grenoble, France, (link)
  • The APS synchrotron near Chicago, USA, (link)
  • The LCLS X-ray Free Electron Laser at Stanford, USA, (link)
  • The SACLA X-ray Free Electron Laser in Japan, (link)
 

 We further have a strong collaboration with the new XFEL facilities being built in Europe, in particular with the European XFEL being built in Hamburg, Germany, but also with the SwissFEL being built near Zurich, Schwiterland.

 We build and design key components for the FXE instrument (link) at the European XFEL together with the Danish company JJ X-ray A/S (link) as part of the Danish membership contribution to the European XFEL (link) on behalf of the ministry of Science and Education (link).

Theory and Simulations

In order to interpret the many TBs of incredibly highly resolved X-ray data which we obtain though our experimental activities, we also need a solid theoretical framework. In our group we currently focus on

  • Algebraic methods for data reduction and interpretation [Haldrup2014]
  • Methods for directly connecting simulation results with experimental data [Dohn2015]

But we also utilize the tools of computational chemistry such as

  • Classical Molecular Dynamics (MD)
  • Density Functional Theory (DFT) calculations, and hybrids such as
  • QM/MM or AIMD, combining DFT with MD [Dohn2015]  

Student projects

We always welcome motivated students, all the way from 1st year project to the PhD level! Such projects can be highly tailored to match the interests and skills of the student to our research activities, and we have projects focused on simulation, experiments and data analysis. If you wish to work with us, then drop by or send us an email!

Recent and current student projects have covered such diverse topics as:

  • Benchmarking an energy-resolving detector for structural studies of self-assembled molecular wires
  • Characterizing slit scattering in X-ray experiments
  • Building a Matlab-based tool for quick, easy and robust Fourier transforms in both time and space
  • Analysis of XFEL data on the ultrafast dynamics of the photo-active complex Tl-PtPOP
  • Analysis of XFEL data on ultrafast dynamics in candidate compounds for iron-based photo-sensitizers

-Almost all of our activities rely to one degree or another on Matlab programming, so if you are not familiar with Matlab already, a project with our group will for sure make you an experienced user of this versatile programming tool.

Collaborations

All of our work is highly interdisciplinary in scope, and we therefore always collaborate with both national and international partners, both at universities and at large-scale facilities. Our current collaboration partners include

  • The Theoretical Chemistry group of Prof. K.B. Møller at DTU Chemistry
  • The Theoretical Physics group of Prof. K. Thygesen at DTU Physics
  • The Chemical Physics group at Lund University
  • The group of Prof. Sebastian Westenhoff at Gothenburg University
  • The FXE group at the European XFEL
  • The group of G. Vanko at RFKI in Budapest, Hungary
  • Prof. Michael Wullf and the staff the Id09b beamline at ESRF
  • Prof. Lin X. Chen at Northwestern University/Advanced Photon Source
  • The Gaffney/Cordones-Hahn groups at PULSE, Stanford, USA

Contact

Kristoffer Haldrup
Senior Researcher
DTU Physics
+45 22 98 37 20

Contact

Martin Meedom Nielsen
Professor
DTU Physics
+45 45 25 32 26
http://www.fysik.dtu.dk/english/Research/NEXMAP/Research/Ultrafast-Materials-Physics
19 AUGUST 2018