Photoemission Electron Microscopy

Standard PEEM

Photoemission Electron Microscopy (PEEM) images sample surface with photo-emitted electrons that are generated by UV or x-ray light source. The photo-emitted electrons carry information about the local environment from where they are originated from. Our PEEM is equipped with an imaging energy analyzer, which enable us to perform spatially resolved photoemission spectroscopy (PES/UPS/XPS) with lateral resolution better than 15nm and at energy resolution better than 150meV. This technique provides information such as valence energy levels, and chemical bonding state of the near surface region of the sample. Besides direct imaging of sample surfaces, the microscope can also resolve photo-emitted electrons escaped from the sample at different azimuthal angles and at different energy (Photo-emitted electron diffraction/Angle-resolved Photoemission spectroscopy PED/ARPES). This technique let us study the electronic structure in materials and reconstruct the 3D Fermi surfaces at high spatial resolution.

In our laboratory, several UV light sources are currently available. Surface imaging can be done with a quasi-CW UV laser or an ultrafast pulsed UV laser, while conventional and time-resolved ARPES can be done using a He plasma discharge light source and an ultrafast pulsed extreme UV light source, respectively.

Electron microscope and its light sources

 

Time-Resolved Photoemission Electron Microscopy (TR-PEEM)

Traditionally, carrier dynamics is studied with ultrafast optics in which time resolution of femtosecond or better is accomplished using very short laser pulses. However, due to the diffraction limit, optic technique has limited spatial resolution and it is insufficient to spatially resolve carrier dynamics in devices or nanostructures at the nanometer length scale. In FSU, we overcome this resolution limit by imaging photoelectrons generated by the ultrafast laser pulse at high spatial resolution with the photoemission electron microscope. The electron microscope allows us to image samples at below 30nm spatial resolution, and pump - probe techniques allows us to resolve dynamics at time resolution better than 100fs. The unique combination of electron microscopy with ultrafast optics provide a means to visualize electron dynamics in materials at its fundamental time and length scale. Using this technique, we captured a video showing electron flow and charge transfer within a photovoltaic device structure [1]. This ultrafast nanoscale imaging technique gives us a unique way to investigate novel materials and quantum processes where the interaction of light and matter are still poorly understood. In the FSU, we are interested in the study of charge transport dynamics in 2D materials heterostructure and in the search of novel quantum phenomena at the nano- and femto- scale.

[1] M. K. L. Man, et al., Nature Nanotechnology 12, 36-40 (2017).

[2] E. L. Wong, et al.,Science Advances 4, eaat9722 (2018).

Schematic of the time-resolved PEEM setup

 

 

Page last updated on September 3, 2017 (MM/CP).