Like-oriented superimposed diffraction gratings formed by E-beam recording
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ANDRIESH, Andrei, SERGEEV, Sergei, TRIDUKH, Ghennadi, ROBU, Stephan V.. Like-oriented superimposed diffraction gratings formed by E-beam recording. In: Materials Science and Condensed Matter Physics, 13-17 septembrie 2010, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2010, Editia 5, pp. 67-68.
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Materials Science and Condensed Matter Physics
Editia 5, 2010
Conferința "Materials Science and Condensed Matter Physics"
Chișinău, Moldova, 13-17 septembrie 2010

Like-oriented superimposed diffraction gratings formed by E-beam recording


Pag. 67-68

Andriesh Andrei1, Sergeev Sergei1, Tridukh Ghennadi1, Robu Stephan V.2
 
1 Institute of Applied Physics,
2 Moldova State University
 
 
Disponibil în IBN: 14 aprilie 2021


Rezumat

One of the way of increasing of recording density consists in producing of the group of superimposed elements onto common space region of the medium of registration. Such possibility is provided by the accumulation of the registration medium modifications induced by recording irradiation. The study of likeoriented superimposed gratings formed by e-beam recording was carried out. The structures composed of two (N =2) and three (N=3) diffraction gratings were formed by the alternate e-beam recording, which was realized in the scanning electron microscope BS 300. Beam current, determining the dose of electron irradiation, was ranged from 0.6 to 4 nA. The amorphous As-S films, which exhibit the wide dose range of induced increasing of index of refraction, were used as a registration medium. The layers prepared from copolymer carbazolylethylmethacrylate with methylmethacrylate (CEM:MMA) were proved as well. Different structures composed of like-oriented gratings consisted of: (i) gratings with close period values differed in 50 – 200 nm; (ii) gratings with doubly differed period values; (iii) mutually shifted gratings with equal period values. Generally grating period (Λ) ranged from 0.45 mm to 4 mm. The phase grating structures composed of index modulation gratings were formed in the As-S layers by direct e-beam recording. The relief grating structures were formed in the As-S layers by chemical development in KOH water solution of the previously studied index grating structures. The relief grating structures in the CEM:MMA layers were formed by direct e-beam recording. The diffraction efficiency (h1) was measured in the first diffraction order at normal (or occasionally 45 grad) incidence of He-Ne laser beam (wavelength 0.6328 mm). The diffraction efficiencies of constituent gratings (h1N ) were compared with ones of the same single gratings (h1S). For N=2 and N=3 grating structures the influence of recording current value on diffraction properties was studied. For grating structures composed of like-directed gratings with different values of grating period the diffraction efficiencies of constituent gratings usually were smaller than ones of same single gratings. Nevertheless, for the structures composed of index gratings with close values of grating period and formed at low beam current the effect of efficiency increasing, caused by superimposition, has been revealed. For structures formed at high beam current values the ratio of intensities of diffracted beams depended on writing sequence of corresponding gratings. The chemical development resulted in increasing of diffraction efficiencies but probably produced profile distortion of each constituent relief grating involving in complex structure. Therefore, in the case of the relief structures the efficiencies of constituent gratings were smaller, than ones of the same single gratings even for low recording currents. The relief structure composed by gratings of close period values produced multi-beam light diffraction, involving set of additional diffracted beams, so-called “hosts”. Intensities of hosts were relatively low in the case of relief structures formed by chemical treatment in As-S films, but rather high in the case of relief structures formed by direct e-beam writing in CEM:MMA layers. Relief superimposed gratings with periods Λ1= 0.45 μm and Λ2= 0.5 μm were formed in As2S3 layers due to high resolution of this material. Diffraction structures composed of gratings with doubly differing periods (Λ1= 2 μm, Λ2 = 4 μm and Λ3= 8 μm) produced multi-beam light diffraction characterized by apparent non-monotone distribution of intensity along diffracted orders. Significant multiplication of diffraction efficiency caused by superposition of gratings with equal values of period has been revealed. The relief structure composed of three shifted gratings of 4 μm period produced diffraction efficiency about 27 % in comparison with one of 7 % for single grating after identical chemical treatment. Moreover in the former case the intensity of 2-nd order diffracted beam was negligibly low. Thus the different types of diffraction structures composed of like-oriented gratings can be formed. Diffraction properties of each type of structure can be varied by choosing both of conditions of forming and grating parameters.