{"title":"Diffraction","authors":"Myeongkyu Lee","doi":"10.1201/9780429425356-5","DOIUrl":"https://doi.org/10.1201/9780429425356-5","url":null,"abstract":"—The structure of short(cid:2)period hexagonal GaN/AlN superlattices (SLs) has been investigated by X(cid:2) ray diffraction. The samples have been grown by metalorganic vapor(cid:2)phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al 2 O 3 substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μ m. The com(cid:2) plex of X(cid:2)ray diffraction techniques includes a measurement of θ –2 θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the deter(cid:2) mination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ –2 θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10 –2 ) have different signs. An analysis of diffraction peak half(cid:2)widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.","PeriodicalId":137593,"journal":{"name":"Optics for Materials Scientists","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134251824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Superposition of Waves","authors":"Myeongkyu Lee","doi":"10.3840/000018","DOIUrl":"https://doi.org/10.3840/000018","url":null,"abstract":"• Doppler Effect: If either a source of sound or a listener is moving with respect to the medium that carries the sound, the listener will perceive a different frequency than what was emitted. Let v be the speed of sound, vS be the speed of the source with respect to the medium, and vL be the speed of the listener with respect to the medium. (The direction from the listener to the source is taken to be positive.) If sound is emitted at","PeriodicalId":137593,"journal":{"name":"Optics for Materials Scientists","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121095105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Reflection and Refraction","authors":"Myeongkyu Lee","doi":"10.1201/9780429425356-2","DOIUrl":"https://doi.org/10.1201/9780429425356-2","url":null,"abstract":"where n1 and n2 are the indices of refraction of the two materials, θ1 is the incident angle, and θ2 is the refracted angle. The index of refraction is defined as the ratio of the speed of light in vacuum (space) over the speed of light in the material in question. Mathematically, n ≡ c/v. For air, n ≃ 1, and for water n = 1.33, whereas often n = 1.5 for glass. It has also been found that n will vary as a function of wavelength (or color) of light. Thus, white light entering a second material will have its different colors refracted at different angles and often the separate colors will become observable. A geometrical derivation for Snell’s Law can be found in most Physics texts. In general when light hits the interface between two different media, some of the light will be reflected and some will be refracted, with each obeying the above laws, accordingly. This is shown in figure 2. The amount reflected versus refracted depends on several variables, including the indices of refraction and the incident angle.","PeriodicalId":137593,"journal":{"name":"Optics for Materials Scientists","volume":"39 7","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2019-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113988700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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