Thickness-dependent dielectric and structural properties of 4000g/mol polyethylene thin films
JOURNAL OF NON-CRYSTALLINE SOLIDS, cilt.690, 2026 (SCI-Expanded, Scopus)
- Yayın Türü: Makale / Tam Makale
- Cilt numarası: 690
- Basım Tarihi: 2026
- Doi Numarası: 10.1016/j.jnoncrysol.2026.124252
- Dergi Adı: JOURNAL OF NON-CRYSTALLINE SOLIDS
- Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus, Chemical Abstracts Core, Chimica, Compendex, INSPEC, Academic Search Ultimate (EBSCO), Engineering Source (EBSCO)
- İstanbul Üniversitesi Adresli: Evet
Özet
Polyethylene (PE) thin films (Mn = 4000 g/mol) were deposited by thermal evaporation in the thickness range 20-1000 nm between aluminum electrodes. Fourier-transform infrared spectroscopy revealed a partially crosslinked structure containing additional C-H bending (800-1280 cm-1), CHs bending (1367 cm-1), and C--O stretching (1725 cm-1) bands beyond the characteristic PE vibrations, indicating chain scission and recombination during deposition. Broadband dielectric spectroscopy performed over frequencies from 0.1 Hz to 107 Hz and temperatures from 233 to 373 K revealed dielectric constants (kappa ') of 3.8 to 20.3 at 1 kHz, substantially higher than that of bulk polyethylene (approximate to 2.3). The observed dielectric behavior was attributed to normal-mode polarization arising from oligomeric species at frequencies below 1 kHz and to the orientational polarization of dipolar species generated during deposition at frequencies higher than 1 kHz. The dielectric constant increased with film thickness, indicating a gradual transition toward bulk-like dielectric behavior at higher thicknesses. Electric modulus analysis revealed alpha-relaxation peaks shifting from 344 K to 273 K with increasing thickness, corresponding to dielectric-relaxation-based estimates of Tg. AC conductivity followed Jonscher's power law with an overlapped large-polaron tunneling mechanism. These findings demonstrate the importance of film thickness in tailoring the dielectric properties of thermally evaporated PE thin films for dielectric-layer and flexible electronic applications.