Vakumda buharlaştırma yöntemiyle hazırlanan alüminyum ince filmlerin optik özellikleri
Küçük Resim Yok
Tarih
1991
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Ege Üniversitesi
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
ÖZET Bu çalışmada, önce vakumda buharlaştırma yöntemiyle hazırlanan yansıtıcı opak alüminyum filimlerin optik özellikleri elipsometrik yöntemle incelendi. Elipsometri, polarize ışığın polarizasyon halinde yansıma sonucu ortaya çıkan değişimin ölçülmesidir. Polarizasyon hali ; elektrik alan vektörünün gelme düzlemine paralel p - bileşeni ile gelme düzlemine dik s - bileşeni arasındaki genlik ve faz bağıntılanyla karakterize edilir. Yansıma, p ve s polarize bileşenlerinin faz ve genliklerinin değişmesine neden olur. Yansımada meydana gelen faz değişimi A, genlik oranları değişme faktörü tgw olmak üzere elipsometrinin temel bağıntısı rip = A rip ei5rp İA - = e tg \j/ ei5- şeklindedir. Burada rlp ve r1s gelme düzlemine paralel ve dik bileşenler için yüzeyin kompleks genlik yansıtma katsayılarıdır. Bu katsayılar ile gelme açısı ve yüzeyin optik sabitleri arasındaki ilişki Fresnel bağıntıları ile verilir. Elipsometre ile yapılan ölçümler, A ve \|/ parametrelerinin belirlenmesini ve yüzeyin optik sabitlerinin hesaplanmasını sağlar. Cam taşıyıcılar üzerinde elde edilen yaklaşık 300 A kalınlığındaki Al filmlerin görünür ışık bölgesindeki n, k optik sabitleri ve alüminyumun asal gelme açısı elipsometrik yöntemle belirlendi. Asal gelme açısının 77.5 ° olduğu bulundu. Elde edilen optik sabitler kullanılarak örneklerin görünür ışık bölgesindeki dik geliş reflektansın hesaplandı. Reflektansın görünür bölge boyunca % 90 civarında olduğu ve pek fazla değişmediği tespit edildi. Belirlenen optik sabitlerden yararlanarak alüminyumun e = £j - i 62 kompleks dieîektrik sabitinin e1 gerçel ve 62 sanal kısımları hesaplandı. Bunların foton enerjisiyle değişimi incelenerek yorumlandı. o 5500 A dalgaboylu ışık ile elipsometrik ölçümler yapılarak filmlerin havada eskitilmesiyle optik sabitlerin nasıl değiştiği incelendi. Havada bekletilme sonucu optik sabitlerin başlangıçta hızla küçüldüğü ve dördüncü günden sonra değişimin yavaşladığı tespit edildi. Bu değişimin filmin yüzeyinde zamanla büyüyen bir oksit tabakasından kaynaklandığı belirtildi. Çalışmanın ikinci kısmında kuvars taşıyıcılar üzerinde elde edilen çok ince Al filmlerin absorpsiyon özellikleri, filmden geçen ışık şiddetinin ölçülmesine dayanan spektrofotometrik yöntemle incelendi. Filmlerin ölçülen optik absorbans spektrumlarının taşıyıcı sıcaklığı ve filmin yüzey yoğunluğu 43ile değişimi araştırıldı. Yüzey yoğunlukları aynı (2,58 ug / cm2) fakat farklı sıcaklıktaki taşıyıcılar üzerinde elde Âl ince filmlerin absorbans spektrumları karşılaştırıldı. Oda sıcaklığındaki taşıyıcı üzerinde oluşan filmlerin absorbans spektrumunun, alüminyumun elektronik özelliklerinden beklenen normal yapıda olduğu saptandı. Buna karşılık sıcak taşıyıcılar üzerinde oluşan filmlerin absorbans spektrumlarında 430 nm civarında taşıyıcı sıcaklığı arttıkça şiddetlenen bir absorpsiyon bandı ortaya çıktığı bulundu. Bu absorpsiyon bandının tanecikli film yapısından kaynaklanabileceği ve Maxwell - Gamett teorisiyle açıklanabileceği öne sürüldü, öngörünün doğruluğunu kontrol etmek amacıyla 200 °C sıcaklıktaki taşıyıcılar üzerinde elde edilen filmlerde absorpsiyon bandının filmlerin yüzey yoğunluğu ile değişimi incelendi. Yüzey yoğunluğu büyüdükçe absorpsiyon bandının Maxwell - Garnett teorisinden beklendiği gibi şiddetlenerek uzun dalgaboylarına kaydığı gösterildi. 44
SUMMARY In this study, at first optical properties of reflecting opaque Al films obtained by the method of vacuum evaporation have been investigated by the ellipsometric method. Ellipsometry is the measurement of the effect of reflection on the state of polarization of polarized light. The state of polarization is characterized by the amplitude and phase relationship between the two component of the electric field vector. One component designated p is parallel to the plane of incidence. The other designated s is normal to the plane of incidence. Reflection causes a change in phases of the p and s polarized components and a change in their amplitudes. The basic equation of ellipsometry is rlp _ A ris rip ris ei5rp i A = e tg y e rs where A is the phase change arising from reflection, tg \j/ is the variation factor of the amplitude ratio, ?ip and rls are complex amplitude reflection coefficients of the surface for p and s components. Relations between the reflection coefficients, the angle of incidence and the optical constants of reflecting surface is given by the Fresnel equations. Measurements taken by an ellipsometer supply the determination of A and \|/ parameters and the calculation of the optical constants of the surface under examination. o The optical constants n and k of Al films, about 300 A in thickness, obtained on the glass substrates and the principal angle of incidence were determined by the ellipsometric method. The principal angle of incidence was found to be 77.5 °. The normal incidence reflectances in the visible region of samples were calculated using the optical constants determined ellipsometrically. It was shown that the reflectance of these Al films is about 90 % along whole visible region and does not change very much. The real and imaginary parts of the complex dielectric constant e = e^ - i e2 of Al were calculated using the determined optical constants. The variation of the real and imaginary parts e^ and E2 of complex dielectric constant with photon energy were examined and also explained. The change of the optical constants with ageing of films in air was examined by o ellipsometric measurements at the wavelength of 5000 A. As a result, it was shown that the optical constants initially decrease rapidly and after the fourth day the variation is slow. It has been pointed out that the observed change of the optical constants are due to the oxide layer growing on the films surface as the films age in air. In the second part of the study, the absorption properties of very thin Al films deposited on quartz substrates were examined by the spectrophotometric method which is based on measurements of 45light intensity transmitted through the film. The effects of the substrate temperature and the surface density of films on the measured optical absorbance spectra were investigated. Absorbance spectra of thin Al films having same surface densities (2.58 (ig / cm2) but deposited on substrates at different temperatures were compared. It was found that the absorbance spectra of films deposited on substrates at room temperature have a normal structure expected from electronic properties of aluminum. However, an absoption band was observed near the wavelength of 430 nm in the absorbance spectra of films deposited on hot substrates. It was shown that the intensity of this absorption band increases by rising substrate temperature. It has been proposed that this absorption band is due to the granular film structure and could be explained by means of Maxwell - Garnett theory. To control the validity of this proposal, the variation of absorption band with the surface density of films was examined. It was shown that the intensity of the band increases by growing surface density and also shifts to longer wavelengths as expected from Maxwell - Garnett theory. 46
SUMMARY In this study, at first optical properties of reflecting opaque Al films obtained by the method of vacuum evaporation have been investigated by the ellipsometric method. Ellipsometry is the measurement of the effect of reflection on the state of polarization of polarized light. The state of polarization is characterized by the amplitude and phase relationship between the two component of the electric field vector. One component designated p is parallel to the plane of incidence. The other designated s is normal to the plane of incidence. Reflection causes a change in phases of the p and s polarized components and a change in their amplitudes. The basic equation of ellipsometry is rlp _ A ris rip ris ei5rp i A = e tg y e rs where A is the phase change arising from reflection, tg \j/ is the variation factor of the amplitude ratio, ?ip and rls are complex amplitude reflection coefficients of the surface for p and s components. Relations between the reflection coefficients, the angle of incidence and the optical constants of reflecting surface is given by the Fresnel equations. Measurements taken by an ellipsometer supply the determination of A and \|/ parameters and the calculation of the optical constants of the surface under examination. o The optical constants n and k of Al films, about 300 A in thickness, obtained on the glass substrates and the principal angle of incidence were determined by the ellipsometric method. The principal angle of incidence was found to be 77.5 °. The normal incidence reflectances in the visible region of samples were calculated using the optical constants determined ellipsometrically. It was shown that the reflectance of these Al films is about 90 % along whole visible region and does not change very much. The real and imaginary parts of the complex dielectric constant e = e^ - i e2 of Al were calculated using the determined optical constants. The variation of the real and imaginary parts e^ and E2 of complex dielectric constant with photon energy were examined and also explained. The change of the optical constants with ageing of films in air was examined by o ellipsometric measurements at the wavelength of 5000 A. As a result, it was shown that the optical constants initially decrease rapidly and after the fourth day the variation is slow. It has been pointed out that the observed change of the optical constants are due to the oxide layer growing on the films surface as the films age in air. In the second part of the study, the absorption properties of very thin Al films deposited on quartz substrates were examined by the spectrophotometric method which is based on measurements of 45light intensity transmitted through the film. The effects of the substrate temperature and the surface density of films on the measured optical absorbance spectra were investigated. Absorbance spectra of thin Al films having same surface densities (2.58 (ig / cm2) but deposited on substrates at different temperatures were compared. It was found that the absorbance spectra of films deposited on substrates at room temperature have a normal structure expected from electronic properties of aluminum. However, an absoption band was observed near the wavelength of 430 nm in the absorbance spectra of films deposited on hot substrates. It was shown that the intensity of this absorption band increases by rising substrate temperature. It has been proposed that this absorption band is due to the granular film structure and could be explained by means of Maxwell - Garnett theory. To control the validity of this proposal, the variation of absorption band with the surface density of films was examined. It was shown that the intensity of the band increases by growing surface density and also shifts to longer wavelengths as expected from Maxwell - Garnett theory. 46
Açıklama
Anahtar Kelimeler
Fizik ve Fizik Mühendisliği, Physics and Physics Engineering, Buharlaştırma yöntemi, Vaporization method, Optik özellikler, Optical properties, İnce filmler, Thin films