Project C1 is dedicated to the theoretical description, modelling and optimization of thermal emission in and from multiscaled materials. The main application area is thermophotovoltaics (TPV), where the emitted thermal energy is converted into electrical energy for power generation. Two approaches are pursued. First, selective far field emitters are developed which are stable at temperatures above 1000°C. In addition, near field systems are investigated which enable to transfer large radiative power by radiation even at temperatures below 1000°C.
In order to tailor efficient TPV-emitters which match specific photovoltaic receivers we realize spectrally selective emitters that show an emission close to that of a black body at short wavelengths, but substantially reduced emission at long wavelengths. We demonstrate such band-edge emitters based on a W-HfO2 refractory metamaterial in cooperation with C7  and a monolayer of monodisperse ZrO2-spheres on a tungsten substrate in cooperation with C4 and C6 . Both structures are stable up to 1000°C.
The study of near field emission concentrates on the thermal radiation in hyperbolic materials  and across nanometer vacuum gaps.
Fig. 1: Absorptivity/Emissivity of the ZrO2-monolayer on tungsten after annealing. Inset: structure (dark blue: W, orange: HfO2, light blue: ZrO2).
|Prof. Dr. rer. nat. Manfred Eich, |
|Dr. rer. nat. Alexander Petrov,|
1. P. Dyachenko et al.: Controlling thermal emission with refractory epsilon-near-zero metamaterials via topological transitions. Nature Commun. 7, 11809, 2016 - with C7, Z3
2. P. Dyachenko et al.: Tungsten band edge absorber/emitter based on a monolayer of ceramic microspheres. Optics Express. 23, A1236-A1244, 2015 - with C2, C4, C6
3. S.-A. Biehs et al.: Blackbody theory for hyperbolic materials. Phys. Rev. Lett. 115, 174301, 2015
... and more on the list of publications.
In project C1, metallic-dielectric multilayers are needed to rea-lize and investigate selective thermophotovoltaic emitters. These should be stable at very high temperatures of 1400°C and above. Scientific work on this, in particular on sputter deposition and high temperature behavior of tungsten hafnium oxide layers, has already been carried out at the HZG within the framework of C7 led by Dr. Michael Störmer in the 2nd funding period (FP). With regard to the 3rd FP, the scientific questions raised so far have now given way to more complex technical questions. From the preliminary work we know that the parameters for precise, nanometer-accurate deposition of multilayers of metals and dielectrics is not transferable from one material combination to another and requires very sophisticated technical knowledge and the appropriate sputtering equipment as well as equipment and experience with X-ray reflectometry (XRR) and X-ray diffraction (XRD). In the planned subcontract to the HZG, among other things, parameters of magnetron sputtering for various high-temperature stable material combinations are to be determined and optimized. Layer thicknesses and deposition rates will be determined by XRR and profilometry. Structure and phase determination is performed by XRD and elemental analysis (EDX, XPS). Depositions of multilayers will be performed on various substrates (sapphire, MEMS chips, silicon, MgO and MgAl2O4) with metals (Ir, Re, Pt, W, as well as W-Re, W-Sc) and dielectrics (HfO2, Y2O3, CeO2, Al2O3, ZrO2, HfC) without and with dopants. Coatings are investigated under vacuum conditions and at temperatures up to 2000°C (including in-situ XRD). Phase and phase transformations are determined.