North Carolina State University, Department of Chemical and Biomolecular Engineering, 911 Partners Way, Centennial Campus, Raleigh, North Carolina 27695, USA. scarelgx@jmu
Appl Spectrosc. 2010 Jan;64(1):120-6. doi: 10.1366/000370210790571954.
Experimental transmission infrared spectra of gamma-Al(2)O(3) and ZnO films are collected from heat-treated thin oxide films deposited with uniform thickness on Si(100) using atomic layer deposition. We show that the Berreman thickness, i.e. the upper limit for a linear relationship between oxide film thickness and phonon absorbance in the infrared region in transmission configuration, is a concept that applies to both transverse and longitudinal optical phonons. We find that for aluminum oxide films the Berreman thickness is 125 nm, and we estimate that it is around approximately 435 nm for zinc oxide films. Combining experiment and simulation, we also show that the Berreman thickness is the maximum distance allowed between interfaces for Snell's law and Fresnel's formulas to determine the optical properties in the infrared region and in transmission configuration for a layer system including an oxide film. Below the Berreman thickness, a Taylor series expansion of the absorbance coefficient determines the linear relationship between phonon absorbance and oxide film thickness t, so that as t --> 0 absorption A(p) is proportional to 4pi omega(ph)t, where omega(ph) indicates optical phonon frequency. Above the Berreman thickness, field boundary conditions at the air/oxide film interface effectively contribute with a single interface in explaining optical phonon absorbance. Preliminary infrared spectra in reflection configuration for gamma-Al(2)O(3)/Si(100) are discussed, and the obtained data support the conclusions reported for the transmission configuration.
实验传输红外光谱的γ - Al （ 2 ） O （ 3 ）和 ZnO 薄膜收集热处理后薄膜沉积的均匀厚度的硅（ 100 ）使用原子层沉积。我们表明， Berreman 厚度，即上限的线性关系之间的氧化物膜厚度和声子吸收在红外区域的传输配置，是一个概念，适用于横向和纵向光学声子。我们发现，对于氧化铝薄膜的 Berreman 厚度为 125nm ，我们估计，这是大约 435nm 为氧化锌薄膜。结合实验和模拟，我们还表明， Berreman 厚度是最大允许距离之间的接口为斯涅尔定律和菲涅耳公式来确定光学性质在红外区域和传输配置的层系统包括一个氧化物膜。在 Berreman 厚度以下，泰勒级数展开的吸收系数决定了线性关系之间的声子吸收和氧化物膜厚度吨，使吨 - > 0 吸收一（ p ）成正比 4pi omega （ ph ）吨，其中 omega （ ph ）表示光频声子。在 Berreman 厚度以上，外地边界条件的空气/氧化物膜界面有效地有助于与一个单一的接口，在解释光频声子吸收。初步红外光谱在反射配置的γ - Al （ 2 ） O （ 3 ） /硅（ 100 ）进行了讨论，并获得的数据支持的结论报告的传输配置。
