#### Transcript Determining Optical Constants for UO2+x

Determining Optical Properties of Uranium Oxide Richard Sandberg Brigham Young University Special Thanks to Kristi Adamson, Shannon Lunt, Elke Jackson, Dr. David Allred, Nathan Orton, Mike Diehl, Dr. Steven Turley D. Allred: 2. age: Why study Uranium Oxide? bout 5 years ago my search group was ked to design, deposit d characterize a ML lector coating for a ika of mirrors for the age spacecraft’s UV instrument. It is in bit now in a polar orbit d produces images of e earth’s agnetosphere like the e shown here, taken m a distance of about ,000 Km above the orth Pole. The small ntral circle is the rth’s aurora. The uzy structure, reddish re in false color is the e subject of the strument. He +1 ions IMAGE Satellite Mirror Project High Theoretical Reflectivity Applications: Medical Equipment Space Observation Lithography hether we anium e. Creating our samples . y be t as an Oxidation d surface. optical ) if their th. • Reactive DC Magnetron Sputtering OC if we are • evices. talk about ible and UV us get to d help us ss of layers. e faces in air. t now UO2 etely stable an U. ble to Mo] Creates a uranium oxide film • We create samples with thickness of 15–30 nanometers Allred: acterizat lide it for . 2 XPS ometry subject . ut that ometry is ensitive ence, as ill see. e going e more ort on an we ed 1 ago. Characterizing Samples Why these tools? X-Ray Diffraction- thickness Atomic Force Microscopy-thickness & roughness X-Ray Photoelectric Spectroscopychemical state Ellipsometry- thickness & valence state David D. Allred: Determining Composition With XPS Peaks indicate electron binding energy Peaks shift with varying oxidation states 2.2K 2K 1.8K 1.6K 1.4K 1.2K 1K 800 600 400 200 1099 1049 999 949 899 849 799 749 699 649 599 549 499 449 399 349 299 249 199 149 99 49 vid D. Allred: IDE 6: psometry arized light hits mple. flects ptically arized light. s is then lyzed to get ative ratio of p to olarization and angle of ation of the pse. e of the engths of psometry is at only ratios e required. ere are 2 ios: Delta and i. Ellipsometry Polarized light hits sample Reflects elliptically polarized light : ng Constants from y Finding Constants From Ellipsometry n that this is spectroscopic . Delta and Psi are n a few seconds at about ngths in a few seconds. n use many angles. So get usand pieces of data used ness, and n and k as Energy. But thicknesses fairly curate if N and k are There can be some noise ent n and K. A better way rize the functions so that 3etermine 15 or so model. Lorentz Oscillator models were used to extract reflectance and n and k Ellipsometry Limitations Comparison to Literature They used bulk samples, we use thin films We know our layers are hybrid of Lorentz is one that different layers eed n and k to get nted to compare what we Allred: Band model when our group ellipso to get s of a thin film en relatively orward. But r UO2. There electrons in U not involved in onding. These s produce the gap of the 2. The reason s diagram is to s. We also hat UO2 can considerable hiometry. s UO(2+x). As nges, k, and to extent, n Suggestion of Band Model for UO2 (D: Electron density of states) From Naegele et al 1976 Allred: Reflectances) of Our Samples Sample 2 Generated and Experimental 0.8 2 4 Photon Energy (eV) 6 8 Sample 4 Generated and Experimental 0.50 Model Fit Exp pRb 0° 0.40 Reflection Reflection 0.0 0 8 0.20 Now LOOK at the 0.10 of the maxima. 3.5 0.00 0 2 mple 1 and 6 eV for ember these. 0.4 0.2 0.20 Sample 2 was 0.15 d with very 0 little 2 4 6 Photon Energy (eV) It is mostly U metal. hy its reflectance is Sample 3 he right hand side; ctances 0.50 of metalsGenerated are and Experimental e IR. The right hand Model Fit 0.40 Exp pRb 0° bout .8 eV which is 0.30 UV starts at ons in IR. Model Fit Exp pRb 0° 0.6 Reflection Reflection are not available in Reflectance ture for all U oxide ions so we have Sample 1 d n and k to ces. Calculated Generated and Experimental 0.40 ces. Reflectances are Model Fit 0.35 Exp pRb 0° own. Reflectances are ncidence. 0.30 Directly the samples. We plot 0.25 Energy. 0.30 0.20 0.10 4 Photon Energy (eV) 6 8 0.00 0 2 4 Photon Energy (eV) 6 8 D. Allred: (Reflectances from the e.) Reflectance of UOx single crystals according to Naegele et al 1976 t the maxima. 4.3 eV 0.25 and 5.3 eV for 2. k at the low energy side. 2-13%.0.2 Now go back to See here only 1 stays as hese two from literature nergy. Reflectance 0.15 aks in the calculated R d 4 may be real or they 0.1 artifacts of the Lorentz rs. They could be real. hat as the composition of 0.05 e changes the maxima position. Our samples e layered. ] 0 1 2 case we note that our s really are different erature. We have done work to trust our data. 3 4 5 6 Energy (eV) x=2.25 x=2 7 8 9 10 vid D. Allred: e 11. tress that we ready now to EUV asurements. Further Research Depth Profiling At-wavelength reflection measurements Monochrometer Longer time scale for oxidation Thank you Richard Sandberg Brigham Young University E-mail [email protected] Phone (801) 368-7779