Browsing by Subject "Polymer fibers"

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Open Access
Silicon nanocrystal doped polymer nanowire arrays
(2013) Çelebi, Muhammet
In this thesis, we successfully produced silicon nanocrystal embedded polymer micro and nanowire arrays by using a new top—to—bottom nanofabrication approach. Silicon nanocrystal (Si-Nc) quantum dots are photoluminescent materials that give bright optical illumination under UV light excitation. Si-Ncs were used to fabricate large area luminescent thin polymer ﬁlms before production of the ﬁbers. Among many of Si—Nc fabrication methods that are available, we chose a chemical route which takes the advantage of high product yield and ease of production steps, although the resultant size distribution is not uniform as other methods such as electrochemical treatment of Si wafers. Dopant Si—Ncs in polymer sheets shows some improved properties compared to free standing silicon nanocrystals, like longer luminescent life time in normal atmospheric conditions and in high temperatures as high as 300 °C. With utilizing these properties, thermal drawing of Si—Nc doped polymer ﬁbers is possible without harming the luminescence properties. Hence, throughout the work, different types of ﬁlms were investigated and polycarbonate ﬁlms were chosen for both their thermal and optical properties such as durable luminescence at high temperatures and low absorption at visible wavelengths. Consequently, with combining these properties with our iterative thermal size reduction method, we successfully produced silicon nanocrystal doped polymer micro and nanowire arrays. In literature, there are similar works treating the same idea of producing luminescent ﬁbers, which were realized with different techniques and material sets, like dye/QD doped nanoﬁbers or ﬁbers produced with conjugated polymers. However, the methods used to produce these type of geometries lacks in some aspects such as limited length, uniformity, alignment, reproducibility, etc. On the other hand, our iterative thermal drawing method is very successful for producing indeﬁnitely long, uniform and easily aligned ﬁbers. Our production steps can be summed in ﬁve steps which are: Si—Nc synthesis, ﬁlm preparation, ﬁlmrolling, consolidation, and two consecutive ﬁber drawing. Keeping the track of characterization of the product in each step is important. Hence, for silicon nanocrystals, we took photoluminescence (PL) intensity measurements, SEM/TEM images and temperature dependent PL measurements. Also for doped ﬁlms, we performed temperature dependent PL measurements and for the resultant ﬁbers we carried out cross—section SEM and PL characterizations. Silicon nanocrystal embedded micro and nanowires can be utilized as ﬁber gain medium, single photon source, directional emitter, light emitting diodes and optical sensing elements. Also, they increases light extraction efﬁciencies with guiding advantages and this can result to ﬂuorescence enhancement for luminescent active material dopants.