Infrared spectroscopic ellipsometry

A. Rossler, Infrared Spectroscopic Ellipsometry (Akademie-Verlag, Berlin,... 

H. Roseler Infrared Spectroscopic Ellipsometry (Akademie Verlag, Berlin, 1990) O.S. Heavens Optical Properties of Thin Films (Butterworths Scientific Publications, London, 1955) S. Adachi Optical Properties of Crystalline and Amorphous Semiconductors (Kluwer, Boston, 1999)... 

Little is known about infrared refractive indices of organic compounds, and only very few such studies related to liquid crystals are reported. To some extend this is due to the fact that special techniques and even dedicated equipment are required. On the other hand birefringence can be derived from the polarization pattern produced by the phase difference between the ordinary and the extraordinary beam. This experiment had been outlined by Born and Wolf (1980) and was applied to liquid crystals by Wu et al. (1984). The procedure is primarily suitable in transparent regions, for a more comprehensive optical characterization it should be extended to complete ellipsometry (Reins et al., 1993). Results obtained by infrared-spectroscopic ellipsometry are shown in Figs. 4.6-5 and 4.6-6. 

Figure 6.4-13 Procedure of photometric infrared-spectroscopic ellipsometry.

C. W. Meuse, "Infrared spectroscopic ellipsometry of self-assembled monolayers", Langmuir, 2000, 16, 9483-9487. 

Up to date, diverse of ellipsometry has been developed, such as imaging ellipsometry [38-40], infrared spectroscopic ellipsometry [41-50], Mueller matrix ellipsometry [51-63], etc. Here, we wiU not make a full introduction about the developments of ellipsometry. As an example, a rotating-polarizer-analyzer ellipsometer (RPAE) will be introduced as follows. 

The optical phonon spectrum is one of the most fundamental characteristics of the crystals. It reflects the specific features of the interatomic interactions and gives very comprehensive and detailed information about the thermal and optical properties involving the efficiency of the optoelectronic devices. The vibrational properties in all the nitride systems have heen investigated in detail over the years by Raman scattering (RS) spectroscopy. Recent studies of nonpolar a-plane GaN by RS confirmed the finding in the c-plane GaN [107, 108]. However, in some cases there is a lack of agreement between the values of some phonon deformation potentials and strain-free phonon-mode positions in GaN and AlN, as determined theoretically and by employing RS spectroscopy. The nonpolar materials allow an access to the complete set of phonons by infrared spectroscopic ellipsometry (IRSE). This provides an alternative tool to study the vihrational properties and to establish very important and useful fundamental parameters of the nitrides. 

As we have seen in Section 3.1.1, the ratio of the reflection coefficients in p-and s-polarizations, p, can be represented in terms of the ellipsometric angles Y and A (Eq. (3.33)). These quantities are determined by the sample properties and being measured as a function of the incident radiation frequency provide spectroscopic information about the sample. This is the basic idea of spectroscopic ellipsometry or, in the IR region, infrared spectroscopic ellipsometry (IRSE). 

Table1.9 Phonon mode frequencies (in units ofcm ) ofwurtzite ZnO at the center of the Brillouin zone obtained from infrared spectroscopic ellipsometry (IRSE) and Raman scattering measurements in comparison with theoretical predictions.

One of the reports of dielectric functions of ZnO is that by Ashkenov et al. [135] who characterized thin films grown by pulsed laser deposition on c-plane sapphire and a single-crystalline sample grown by seeded chemical vapor transport method. The static dielectric constant was obtained from infrared spectroscopic ellipsometry measurements. The high-frequency dielectric constant was calculated through the Lyddane-Sachs-Teller (LST) relation, (Equation 1.31), using the static constant and the TO- and LO-phonon mode frequencies. The results are compared with the data from some of the previous studies in Table 3.8. 

Bundesmann, C. (2005) Phonons and plasmons in ZnO-based alloy and doped ZnO thin films studied by infrared spectroscopic ellipsometry and Raman scattering spectroscopy, PhD Thesis, Universitat Leipzig (Shaker, Aachen, 2006). 

Rappich J, Hiurichs K (2009) In situ study of nitrohenzene grafting (m Si(l 11)-H surfaces by infrared spectroscopic ellipsometry. Electrochem Commun 11 2316-2319... 

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