Annual Report 2012 - Latvijas Universitātes Cietvielu fizikas institūts

HOLOGRAPHIC LITHOGRAPHY IN AMORPHOUS
CHALCOGENIDE THIN FILMS
J.Teteris, J.Aleksejeva and M.Reinfelde
The recording of the surface-relief and refractive index modulated gratings with
a period of 0.15 – 1.0 μm was performed by solid immersion holographic method. The
grating period for two intersecting light beams in a coupling prism with refractive index
n can be expressed as Λ=λ 0 /2 n sinθ, where λ 0 is the wavelength of laser light in
vacuum, n is refractive index of the prism and θ is the half-angle between the laser
beams inside the prism. The right angle prisms with n= 1.5 – 2.6 were used. Amorphous
As-S-Se based photoresist with refractive index n 1 =3.2 at 0.488 μm was used for the
recording of surface-relief gratings. After recording, wet etching of the photoresist was
performed to obtain a surface-relief grating. The grating period and profile were
measured by AFM. If the recording was performed in air (n=1) and the angle between
the beams was equal to 90 o , a grating with a period of 0.345 μm was obtained. If the
intersection of the laser beams is performed in a prism with a refractive index of 1.75, a
grating period of 0.197 μm was obtained. The application of a prism as an immersion
medium decreases the period of the recorded grating n times. The transmission,
reflection and polarization properties of the subwavelength transmission gratings in
As 2 S 3 amorphous films were studied. The angular selectivity of holographic recording in
amorphous chalcogenide thin films has been improved significantly by a decrease of
grating period.
SURFACE RELIEF FORMATION DURING HOLOGRAPHIC RECORDING
U.Gertners and J.Teteris
The key element for the production of surface-relief holographic optical elements
is photoresist or light sensitive material. Changes of the chemical properties induced in
resist material by light or e-beam exposure enable the surface relief structuring by wet or
dry etching. Therefore this process includes two steps: recording and development by
etching. Recently a number of organic and inorganic materials have been studied for
direct surface relief formation during the exposure process by a light or e-beam. It is
very promising for practical application enabling the possibility to simplify technology
of the surface patterning.
In this research the study of direct holographic recording of the surface-relief
gratings on amorphous As-S and As-S-Se films has been presented from the side of light
polarization. Because of direct surface relief formation, efficiency of the relief formation
also depends on softening temperature of the sample what in this case is about 170 0 C.
Results have shown that the surface relief formation efficiency is many times larger in
case of extra softening by additional incoherent light during recording. The mechanism
of the direct recording of surface relief on amorphous chalcogenide films based on the
photoinduced plasticity has been discussed.
NANOSTUCTURED SURFACES FOR OPTICAL ANTIREFLECTION
J.Aleksejeva and J.Teteris
The demand for optically antireflective layers during last years has increased.
Particularly such high demand is in the branches where large surfaces will be covered
(greenhouses, solar cells etc.) At present work we show the results obtained for surface
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