Reflectance difference spectroscopy

Reflectance difference spectroscopy (RDS) is a spectroscopic technique which measures the difference in reflectance of two beams of light that are shone in normal incident on a surface with different linear polarizations.Peter Y. Yu, Manuel Cardona ,"Fundamentals of Semiconductors" It is also known as reflectance anisotropy spectroscopy (RAS).{{Citation | last1 = Weightman | first1 = P | last2 = Martin | first2 = D S | last3 = Cole | first3 = R J | last4 = Farrell | first4 = T | title = Reflection anisotropy spectroscopy | journal = Reports on Progress in Physics | volume = 68 | pages = 1251 | year = 2005 | doi = 10.1088/0034-4885/68/6/R01 | issue = 6|bibcode = 2005RPPh...68.1251W | s2cid = 94037903 }}

It is calculated as:

:$RDS=\; 2\; \backslash frac\{r\_\{\backslash alpha\}-r\_\{\backslash beta\}\}\{r\_\{\backslash alpha\}+r\_\{\backslash beta\}\},\; r\; \backslash in\; \backslash mathbb\{C\}$

$r\_\{\backslash alpha\}$ and $r\_\{\backslash beta\}$ are the reflectance in two different polarizations.

The method was introduced in 1985 for the study optical properties of the cubic semiconductors silicon and germanium.{{Citation | last1 = Aspnes | first1 = D. E. | last2 = Studna | first2 = A. A. | title = Anisotropies in the Above-Band-Gap Optical Spectra of Cubic Semiconductors | journal = Physical Review Letters | volume = 54 | pages = 1956–1959 | year = 1985 | doi = 10.1103/PhysRevLett.54.1956 | pmid = 10031185 | issue = 17| bibcode = 1985PhRvL..54.1956A }} Due to its high surface sensitivity and independence of ultra-high vacuum, its use has been expanded to in situ monitoring of epitaxial growth{{Citation | last1 = Richter | first1 = W. | last2 = Zettler | first2 = J.-T. | title = Real-time analysis of III--V-semiconductor epitaxial growth | journal = Applied Surface Science | volume = 100--101 | pages = 465–477 | year = 1996 | doi = 10.1016/0169-4332(96)00321-2 | bibcode = 1996ApSS..100..465R }} or the interaction of surfaces with adsorbates.{{Citation | last1 = May | first1 = M. M. | last2 = Lewerenz | first2 = H.-J. | last3 = Hannappel | first3 = T. | title = Optical in situ Study of InP(100) Surface Chemistry: Dissociative Adsorption of Water and Oxygen | journal = Journal of Physical Chemistry C | volume = 118 | pages = 19032 | year = 2014 | issue = 33 | doi = 10.1021/jp502955m | doi-access = free }} To assign specific features in the signal to their origin in morphology and electronic structure, theoretical modelling by density functional theory is required.