|AVS 57th International Symposium & Exhibition|
|Spectroscopic Ellipsometry Focus Topic||Thursday Sessions|
|Presenter:||K. Järrendahl, Linköping University, Sweden|
|Authors:||K. Järrendahl, Linköping University, Sweden
H. Arwin, Linköping University, Sweden
R. Magnusson, Linköping University, Sweden
P. Sandström, Linköping University, Sweden
C.-L. Hsiao, Linköping University, Sweden
J. Landin, Linköping University, Sweden
S. Valyukh, Linköping University, Sweden
J. Birch, Linköping University, Sweden
|Correspondent:||Click to Email|
A limited number of natural structures are known to reflect light that has circular or near circular polarization. This is for instance, the case for some scarab beetles were it is suggested that the polarization is caused by chiral structures in the form of helicoids in the cuticles . In this study, Mueller-matrix spectroscopic ellipsometry is applied in the spectral range of 250 to 1000 nm to investigate optical response and structures of the cuticle of various scarab beetles of the Cetoniinae subfamily. We will present our measurements showing how the polarization changes with wavelength as well as incidence angle and specify the conditions for when the reflected light is circularly left- or right-polarized. In most cases the reflected light is left-polarized as described by negative values of the M41 Mueller matrix element. For Cetonia aurata, a green beetle with metallic appearance, this is clearly seen in a rather narrow spectral range (470-550 nm). For other beetles (Potosia cuprea and Licola lugubris) similar polarization behavior is observed but the polarization features occur in a broader spectral region. We will show that there are even beetles (e.g. Plusiotis argentiola) reflecting both left- (M41 < 0) and right-polarized light (M41 > 0) in different parts of the spectral region. The Mueller data, including observations of the degree of polarization, are used to obtain structural and optical parameters from model calculations.
Our attempts to fabricate artificial structures with similar polarization properties will also be presented. Al1-xInxN thin films were grown on sapphire substrates by magnetron sputtering of indium and aluminum in a nitride atmosphere. Utilization of different seed layers and a substrate rotation gave chiral structures constituted by layers with a compositional gradient. Mueller-matrix results from these structures will be compared with the results from the natural structures. The Mueller data is also in this case very rich on information. In the initial steps to model these samples a similar approach as for the natural structures has been employed. Similarities and differences of the natural and artificial polarization response will be discussed in detail.