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TL;DR: In this article, a rigorous expression for the transmission of a thin absorbing film on a transparent substrate is manipulated to yield formulae in closed form for the refractive index and absorption coefficient.
Abstract: The rigorous expression for the transmission of a thin absorbing film on a transparent substrate is manipulated to yield formulae in closed form for the refractive index and absorption coefficient. A procedure is presented to calculate the thickness to an accuracy of better than 1% with similar accuracies in the values of n. A method to correct for errors due to slit width is also given. Various formulae to calculate the absorption coefficient accurately over almost three orders of magnitude are discussed. Only data from the transmission spectrum are used and the procedure is simple, fast and very accurate. All formulae are in closed form and can be used on a programmable pocket calculator.
3,482 citations
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TL;DR: It is found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa, indicating that atmospheric oxygen was present at significant levels during the deposition of these units.
Abstract: Several lines of geological and geochemical evidence indicate that the level of atmospheric oxygen was extremely low before 2.45 billion years (Gyr) ago, and that it had reached considerable levels by 2.22 Gyr ago. Here we present evidence that the rise of atmospheric oxygen had occurred by 2.32 Gyr ago. We found that syngenetic pyrite is present in organic-rich shales of the 2.32-Gyr-old Rooihoogte and Timeball Hill formations, South Africa. The range of the isotopic composition of sulphur in this pyrite is large and shows no evidence of mass-independent fractionation, indicating that atmospheric oxygen was present at significant levels (that is, greater than 10-5 times that of the present atmospheric level) during the deposition of these units. The presence of rounded pebbles of sideritic iron formation at the base of the Rooihoogte Formation and an extensive and thick ironstone layer consisting of haematitic pisolites and oolites in the upper Timeball Hill Formation indicate that atmospheric oxygen rose significantly, perhaps for the first time, during the deposition of the Rooihoogte and Timeball Hill formations. These units were deposited between what are probably the second and third of the three Palaeoproterozoic glacial events.
1,277 citations
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TL;DR: In this paper, the authors report systematic changes in mudrock composition through time on a single con- tinental cmstal block and show that the changes reflect both sediment recycling processes and changes through time in the composition of crystalline material being added to the sedimentary system and are related to tectonic evolution as the block matures from a series of accreted arc terranes to a stable craton.
1,155 citations
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TL;DR: The Kaapvaal craton of South Africa, which formed and stabilized between 3.7 and 2.7 Gyr ago, is one of the oldest reasonably sized examples of these continental fragments as mentioned in this paper.
Abstract: About 30% of the Earth is covered by continents, but only about 10 small kernels of these continentsae—known as Archaean cratonsae—are continental fragments formed before 2.5 Gyr ago. The Kaapvaal craton of South Africa, which formed and stabilized between 3.7 and 2.7 Gyr ago, is one of the oldest reasonably sized examples of these continental fragments. It consists of a mosaic of subdomains that have been welded together by processes similar to those of modern-day plate tectonics. The earliest subdomains may have owed their origin to the onset of efficient recycling from the Earth's hydrosphere into the mantle.
700 citations
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TL;DR: In this paper, the effects of thickness variation, surface roughness and variation in refractive index on the transmission spectrum of thin thin films were analyzed and analytical expressions were derived from which all the optical constants of an inhomogeneous film can be calculated from the optical transmission spectrum.
Abstract: Inhomogeneities in thin films have a large influence on the optical transmission spectrum. If not corrected for, this may lead to too large calculated values for the absorption coefficient or the apparent presence of an absorption band tail as well as serious errors in the values of refractive index and thickness. The effects of thickness variation, surface roughness and variation in refractive index on the transmission spectrum are analysed. Analytical expressions are derived from which all the optical constants of an inhomogeneous film can be calculated from the transmission spectrum.
644 citations
Authors
Showing all 1720 results
Name | H-index | Papers | Citations |
---|---|---|---|
Donald R. Lowe | 62 | 180 | 15262 |
Frank Vanhaecke | 61 | 521 | 16098 |
Josua P. Meyer | 56 | 543 | 12316 |
Tomasz Kapitaniak | 53 | 353 | 8876 |
Alvaro M. Viljoen | 51 | 278 | 9092 |
Lewis D. Ashwal | 50 | 141 | 6119 |
Nicolas J. Beukes | 46 | 126 | 9102 |
Gary Stevens | 43 | 116 | 5511 |
J.D. van Wyk | 43 | 316 | 7105 |
Reiner Klemd | 42 | 128 | 6655 |
Toshiaki Tsunogae | 41 | 209 | 5436 |
Jens Gutzmer | 38 | 199 | 5476 |
Ian A. Dubery | 37 | 185 | 4811 |
B.-E. Van Wyk | 33 | 170 | 3731 |
Andreas Roodt | 33 | 320 | 3437 |