Kajian teoritis ragam polariton fonon dalam bahan ferroelektrik Bi4Ti3O12 (BTO)

WIDAYANTI, Dr. Kamsul Abraha

2006 | Tesis | S2 Fisika

Telah dilakukan telaah teoritis terhadap kurva dispersi polariton permukaan bahan ferroelektrik Bi4Ti3O12 (BTO). Arah perambatan gelombang tegak lurus terhadap sumbu mudah, dan medan luar sama dengan nol. Telaah ini memberikan deskripsi teoritis ragam bulk dan permukaan bahan Bi4Ti3O12 pada daerah frekuensi 0 – 100 cm-1. Kajian teoritik terlebih dahulu dilakukan untuk menurunkan perumusan relasi dispersi yang diperoleh melalui persamaanpersamaan Maxwell. Substitusi yang dilakukan untuk medan E dan H ke dalam persamaan diferensial gelombang serta penggunaan syarat batas dua medium menghasilkan relasi dispersi. Dinamika internal atau parameter-parameter sistem terkandung dalam permitivitas bahan. Diperoleh bahwa polariton permukaan hanya merambat dalam ragam TM (Transverse Magnetic) atau polarisasi p dan bersifat resiprokal, dimana perubahan arah vektor gelombang tidak menyebabkan perubahan frekuensi atau ω (q )=ω (− q), sedangkan pada ragam TE (Transverse Electric) tidak ditemukan adanya polariton permukaan melainkan hanya ditemukan polariton bulk. Perhitungan reflektivitas ATR menunjukkan keberadaan polariton permukaan ragam TM pada saat jarak antara prisma dan sampel mencapai nilai optimum 0,001 cm. Terbukti pula bahwa perhitungan reflektivitas ATR yang diperoleh bersesuaian dengan relasi dispersinya.

A theoretical study of the polariton dispersion curves on the surface of the ferroelectric material Bi4Ti3O12 (BTO) has been done. The direction of wave propagation is perpendicular to the easy axis without any external field. This study gives a theoretical description of the (BTO) surface and bulk modes at frequency range of 0-100cm-1. The dispersion relation is obtained through Maxwell equation. Substitution of H field and E field into the wave differential equation and application of boundary conditions will lead to the dispersion relations. The dynamics of internal or parameters system is included in the material permitivity. The surface polariton only propagate in TM mode (Transverse Magnetic) and they are resiprocal in the sense that the change of wave vector direction does not change the frequency, or ω(q)=ω(− q), whereas there is no surface modes that propagate in TE mode ( Transverse Electric), but only the bulk polariton has been found. The computation of ATR (Attenuated Total Reflection) reflectivity shows that the surface polariton can be detected when the distance between the Silicon prism and the sample reaches an optimum value of 0,001 cm. Surface modes are also provided by using ATR which is in agreement with the relation dispersion.

Kata Kunci : Polariton,Ferroelektrik BTO