Spectrophotometry - Essay Example

?SPECTRO-PHOTOMETRY ANALYZING EFFECTS OF VARYING THICKNESSES ON SPECTRA TABLE OF CONTENTS Number Topic Pages 2 Introduction 2 3 Experiment 2-3 4 Analysis On Experimental Results 3-10 5 Conclusion 11 Bibliography 1. ABSTRACT Transparent films of varying thicknesses have different effects on spectrum produced if light is passed through them. The effect on the spectra with the alteration in thickness and the dependency of the spectrum on the refractive index is a crucial point to understand when discussing spectrophotometry. Thus in this report an experiment is conducted focusing on the calculation of transmittance, reflectance values and the type of spectra produced. 2. INTRODUCTION Spectrophotometry is the study of numeric calculation of the magnitude of reflection and transmittance of different materials on the basis of the incident wave length. A spectrophotometer is a device which is used to measure the values of transmittance and reflection. Spectrophotometry is used in different fields and sciences like chemistry, biochemistry, physics and materials etc. Spectrophotometry also covers the subject of spectrum and its intensity, and other related issues with changing thicknesses. This report is actually based on the application of spectrophotometry. Dektak 3 ST is used in this experiment. It is a surface profile interpreting mechanism, adequately well on to the area of measuring surface grain or texture and capable of measuring change in thickness even in microns. A diamond tip stylus is used to identify the sample characteristics. The device is enough responsive to record all surface variations. The parametric measurement through Dektak 3 ST includes area, slope, radius measurement, step height, unevenness and roughness on a sample profile. A set of data plotting and video imaging can also be retrieved by using Dektak 3 ST. All thin films on which the spectroscopic analysis is made are actually made up of tin oxide. Tin oxide is a colorless transparent, amphoteric and inorganic material. Tin oxide is widely used in ceramics and majorly in ceramics glazing. Tin oxide is also used in the production of glasses and enamels. 3. EXPERIMENT The experiment is comprised of two phases, the first one proceeds with enkd-8000 machine and the second one proceeds with Dektak 3ST. In the beginning of the phase 1 of the experiment three glasses of tin dioxide having three different thicknesses are considered. The entire glass top surfaces of all are determined with the help of voltmeter. Then every glass is taken individually and analyzed in enkd-8000 machine. During the analysis of every glass, the file is clicked with the scanning option from 400 nm wavelength to 900 nm wavelength. After the selection of the wavelength the machine will take some time to analyze. Then after analysis is switched on in which performance summary information is selected. The selection will yield the CIE color space for the first glass. Now the whole process is being repeated for second and third glasses. All three analyses are made on P polarization When our analysis for P polarization is completed then any sample is selected for S polarization so a conclusion can be drawn by varying polarization. This is how the phase 1 of the experiment is completed. Considering the phase 2 of the experiment, all same three glasses of tin dioxide are used. Every glass is taken and then masked individually from the isolation tap then after zinc powder is being applied, then afterwards Hydrochloric acid is used for application on the applied zinc powder. Finally the hydrochloric acid is scrapped out and then samples are washed out. After this process if the glasses appear clean then apply acetone on it then again wash it with the help of water and then glass is being dried out. The same process is repeated for all three glasses. Dektak3ST machine is used to measure the thickness of all the samples of three glasses. The samples are positioned in the machine one by one. The run option is clicked by the mouse, and then scan option is clicked and after that the thickness is measured. A graph is obtained and from that graph we can choose the thickness from the desired position. Again all the samples are processed uniformly for the above process. 4. ANALYSIS ON EXPERIMENTAL RESULTS First of all the analysis is made on the first phase of our experiment. In the beginning transmittances and reflectances diagram against the wavelength is selected for all three P polarizations, the result is considered and discussed. Then in the first phase one sample based on P polarization and the same on S polarization is compared. Above is the transmittance and reflectance graph for sample 1. On the X axis it shows the wavelengths progression, on the Y axis it shows transmittance and reflectance values with the change in wavelength. As from the curve it can easily understood that at 400 nm wavelength the value of reflectance is around 0.08 while the value of transmittance is about 0.88. As we proceed on X with 420 nm a decreasing pattern on reflectance is observed while an increasing pattern for transmittance can be seen with values 0.04 for reflectance and 0.92 for transmittance. Then after from 420nm to 470nm a rising curve for reflectance and falling curve for transmittance is observed with values 0.15 for reflectance and 0.82 for transmittance. Then afterwards from 470nm to 670 nm wavelengths a suppressing pattern for reflectance and rising pattern for transmittance is observed with values at 670 nm 0.05 for reflectance and 0.93 for transmittance. Then after at 900 nm the value of transmittance is decreased to 0.91 while that of reflectance is of 0.07. The above graph is for sample 2. The reflectance value at 400nm wavelength is about 0.06 while that of transmittance is about 0.65. Then at 420nm reflectance is about 0.02 and that of transmittance is about 0.7. Then at 440nm the reflectance is about 0.08 and the transmittance is about 0.71. At 500nm the reflectance is about 0.025 and transmittance is about 0.78. Then at 600nm the value of reflectance is about 0.02 and that of transmittance is near around 0.85. About 700nm the value of reflectance has rose to 1.2 while that of transmittance has decreased to 0.82. At 790nm the value of transmittance is at peak on 0.9 while that of reflectance is 0.03. Finally on 900nm the value of transmittance is about 0.82 and the reflectance is about 0.12. The above graph is for sample 3 in P polarization. Here it can be observed that on 400nm that value of Reflectance is 0.05 while on the other hand transmittance is about 0.35. On 500nm wavelength a slight variation in reflectance is observed, it is about 0.06 while that of transmittance is about 0.55. On 600nm the value of reflectance is again with a slight deflect remains at 0.04 while that of transmittance is about 0.68 and as usual increasing. On 800 nm transmittance is about 0.82 while that of reflectance is about 0.03. Finally on 900nm the value of reflectance rises on 0.08 and that of transmittance is bit down 0.79. The same sample above is selected for S polarization analysis. The graph is shown below. Now here for S polarization the characteristic curve has changed a bit. A rise in the beginning at 400nm in reflectance value can be seen that is 0.09 while that value in P polarization was 0.05. On the other hand transmittance value is about 0.32 on 400nm which was 0.35 in P polarization. On 600 nm the value of reflectance is 0.08 which was 0.04 in P polarization and that of transmittance is 0.61 which was 0.68 in P polarization. On 840 nm the value of reflectance is about 0.06 and that of transmittance is about 0.78. At 900 nm the value of reflectance rises to 0.13 which was 0.08 in P polarization and transmittance is about 0.72 which was 0.79 in P polarization. The below table represents the percentage values of transmittances and reflectances with the thicknesses’ identified with the help of our experiment. The values for transmittances and reflectances are also noted for third sample on s polarization. The above picture is a graph that shows the average value of thickness on X axis and percentage value of transmittance on Y axis. Through this interpretation on varying average thickness with transmittance values can be easily understood. It shows that on 6934.4 average thicknesses the value of transmittance is 67.12 % and that it goes on increasing with decreasing thickness till 2472 average thickness with transmittance 81.87%. Then after on increasing values of thickness transmittance rose gradually but on slight magnitude. On 11904.66 average thickness the value changed to just 89.05%. A similar trend about reflectance can also be observed from a similar graph shown below; it is about reflectance and average thickness of the samples on X axis. The values of reflectances can be observed on Y axis. Now on 6934.44 average thicknesses the reflectance value is 4.63% as we go on decreasing the thickness the percentage reflectance value increases till 2472 average thickness and with the rise in reflectance value of about 6.82%. Then with an increasing average thickness the percentage reflectance value also increases till 8.77% reflectance on 11904.55 average thickness values. The below table explains average thicknesses with variation of all three samples. Since average thickness is discussed earlier, and the surface profile has some variations, here thickness variations are discussed on sample profile of each sample. In column 4 of the table difference between maximum thickness and average thickness is listed against each sample. In column 5 the difference between minimum thicknesses to average thicknesses is listed for every sample. In column 3 the average of the two differences is shown so as to ponder on error that is associated with the experiment. For first sample the possible error in the thickness value is about 185, for second sample it’s about 197.5 and for third it decreases to about 162. Sample Thickness Thickness (AVG) (MAX –MIN)/2 MAX-AVG MIN -AVG The first 11904.66 185 165 -205 The second 2472 197.5 178 -217 The third 6934.33 162 191.67 -132.33 CIE uniform color space revealed the spectrum characteristics values for each sample. For sample 1 L* =44.9 , a*= -14.57, b*= 12.08. In perspective of comprehension of the values for sample, the values reveal sample 1 of maximum thickness has the highest value of (L) means it has the lightest spectrum. The value of (a) is negative it shows that green is dominant on red; while (b) is positive which shows that yellow is dominant on blue. For sample 2 L* =30.64 , a*= -6.73, b*= 3.518 The (L) value for sample 2 shows that the spectrum is bit dark as compare to the sample 1. On the other hand value of (a) is also negative it shows that green is slightly dominant on red because the magnitude on negativity is low. The value of (b) is positive is down but again magnitude is down so yellow is again slightly dominant on blue. For sample 3 L* =25.110 , a*= -0.32, b*= -1.347 The third sample has a darker spectrum with lower value of (L). Value of (a) still negative but of very low magnitude it means that green is very slightly dominant on red. The value of (b) is negative it means that blue is very slightly dominant on yellow since the magnitude is also very low. 5. CONCLUSION By this experiment and with the analysis of the patterns achieved through experiments a detailed insight on the spectra against varying thicknesses of the films can be completely understood. Also the patterns of reflectances and transmittances against the different wavelengths coupled with the study of different samples help more in the process of understanding and creating insight about the behavior of the films with varying wavelengths and also the behaviors of reflectances and transmittances on varying thicknesses. The reflective indices of the spectra are also encountered during the experiment as the values of transmittances and reflectances are discussed in detail from different perspective. Also the change in polarization and the effect on transmittance and reflectance accordingly is also discussed. As a whole a comprehensive understanding is achieved with the help of this experiment and analysis Bibliography I. NIST. (n.d.). Spectrophotometry. Retrieved from Physical Measurement Labortary: http://www.nist.gov/pml/div685/grp03/spectrophotometry.cfm II. College Of William & Mary. (n.d.). Applied Research Centre. Retrieved from http://www.jlab.org/ARC/WM/121/NewDektak.html III. C.G.Harman, C. &. (1973). Ceramic Glazes. IV. Dennis Goldstein, M. D. (2003). Polarized Light (Vol. Second edition). V. E.Bourry. (1926). A Treatise On Ceramic Industries. VI. Eugene Hecht, A. W. (2002). Optics. VII. Schwedt, G. (1997). The Essential Guide to Analytical Chemistry. Read More