Hoppa till innehåll
EN In english

Invers fotoemission med hög energiopplösning

Diarienummer
ITM17-0432
Projektledare
Liu, Xianjie
Start- och slutdatum
190101-231231
Beviljat belopp
5 995 625 kr
Förvaltande organisation
Linköping University
Forskningsområde
Materialvetenskap och materialteknologier

Summary

We will develop equipment to directly probe the unoccupied states of (hybrid) organic electronic materials (semiconductors and conductors) with high energy resolution and minimal beam damage. We will construct a high-resolution inverse photoemission (IPES) apparatus to work in near-ultraviolet (NUV) to visible (Vis) range with a total energy resolution better than 0.1 eV, improving upon the IPES state-of-the-art by more than a factor of 3! Existing IPES equipment is incapable of the precise determination of the electron accepting and transporting levels crucial for design of (hybrid) organic electronic devices and materials. We will use an electron beam energy between 0 and 5 eV, which is necessary to minimize beam damage in organic semiconductors, dictating the choice of energy range for the photon detection system (NUV-Vis). The apparatus will contain a monochromatic electron source using a hemispherical deflection analyzer and a photon detection system consisting of a NUV-Vis bandpass filter and a photomultiplier and/or a grating spectrometer combined with a toroidal reflection mirror (to enlarge the acceptance angle) and a back-thinned CCD. The work will be carried over a three-year period by two post-docs supervised by the applicant. The post-project goal is to leverage the unique IPES performance to establish a word-leading activity in measurements of unoccupied states in (hybrid) organic semiconductor films and if possible commercialize the new IPES instrument.

Populärvetenskaplig beskrivning

Precise determination of the electron- and hole-transporting states in electronic materials is crucial for design and use in applications. Photoemission spectroscopy (PES) probes directly the occupied states that transport holes and the kinetic energy and hence the binding energy of the photoemitted electrons can be detected at a few meV resolution. Sweden has a state-of-the-art light source (MAX IV), a world-leading PES spectrometer manufacturer (Scienta Omicron) and a +50-year history as innovation leaders in this technique. Inverse photoemission spectroscopy (IPES), i.e. electron in – photon out, is a direct probe of the unoccupied (electron-transporting) states and thus complements PES. Unfortunately, IPES intensity is five orders of magnitude lower than PES and increased electron beam density decreases the energy resolution and potentially damages organic samples. Current IPES has a resolution of 0.5 eV, which is far from the accuracy needed (below 0.1 eV) to be used for materials and device design. Other indirect methods to probe unoccupied states, like optical absorption, exist but require estimates of excitonic binding energies that typically are not known with any precision for e.g. organic semiconductors. Hence, many critical questions regarding fundamental (opto)electronic processes in (hybrid) organic semiconductors are still unresolved due to the lack of reliable measurements of the unoccupied states. Our goal is to construct a high energy resolution IPES by using a monochromatic electron source with an energy width better than 0.1eV at a low beam energy between of 0 and 5 eV. The former is far better than the best current electron source in IPES (0.25 eV). The latter can avoid the sample damage as the damage threshold of organic materials is at ~5 eV. The emitted light is then between 180 and 700 nm (near ultraviolet and visible range), where light can be guided/analyzed with commercial available equipment with a resolution down to meV. This facilitates a total resolution of IPES better than 0.1 eV. A reflection mirror will be used to enhance the light collection in a large solid angle and transfer the focused light into an optical bandpass filter and/ or optical spectrometer detector in air to analyze the light intensity. Our IPES will strongly boost the (hybrid) organic electronics research in Sweden and in the world, through publishing accurate and precise measurements and by publishing and/or commercializing the IPES design.