| dc.identifier.uri | http://hdl.handle.net/11401/76325 | |
| dc.description.sponsorship | This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree. | en_US |
| dc.format | Monograph | |
| dc.format.medium | Electronic Resource | en_US |
| dc.language.iso | en_US | |
| dc.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dc.type | Thesis | |
| dcterms.abstract | Sapphire (α -Al2O3 ) is well-known as an important technological material primarily for the application as substrates for GaN based LEDs ( Light emitting diodes ). Additionally, sapphire is also characterized by properties such as high transparency, excellent scratch- resistance, chemical stability, high mechanical strength, good thermal conductivity and electric insulation. These make it attractive for wide use as optical windows, bearings, armor protections etc. The structure of sapphire is rhombohedral (a = b = c = 5.13 Å, α =β =γ =55.1°). But it can also be considered as pseudo-hexagonal (a = b = 4.759213Å, c = 12.9915867Å, α =β =90°, γ =120°). The crystal structure is a slightly distorted hexagonal closed-packing of large oxygen ions (O2- anions) with small aluminum ions (Al3+ cations) occupying two thirds of octahedral interstices. The sapphire samples in this study were grown by the Edge-defined film-fed growth (EFG). Compared to other growth techniques such as Czochralski method, Kyropoulos method, heat exchanger method, the EFG method offers the advantage of obtaining near final shape of single crystal sapphire wafers. However, the growth conditions must be optimized to obtain low defect density ribbons. Therefore, to understand defect nucleation and propagation in these crystals, Synchrotron White Beam X-ray Topography has been employed in conjunction with optical microscopy and chemical etching in this study. Of particular interest in EFG sapphire is the nucleation of polycrystallinity that lowers yield. Transmission X-ray topography reveals the overall defect distribution around the region of polycrystallinity and the range of tilts and strains. Section X-ray topography is used to trace the evolution of strain and/or dislocations leading to onset of polycrystallinity. X-ray reticulography is used to quantitatively map the variation in strains and tilts around the region of polycrystallinity. All defects found in sapphire will be specifically discussed regarding their formation, effects and behaviors with the characterization techniques described. | |
| dcterms.abstract | Sapphire (α -Al2O3 ) is well-known as an important technological material primarily for the application as substrates for GaN based LEDs ( Light emitting diodes ). Additionally, sapphire is also characterized by properties such as high transparency, excellent scratch- resistance, chemical stability, high mechanical strength, good thermal conductivity and electric insulation. These make it attractive for wide use as optical windows, bearings, armor protections etc. The structure of sapphire is rhombohedral (a = b = c = 5.13 Ã…, α =β =γ =55.1°). But it can also be considered as pseudo-hexagonal (a = b = 4.759213Ã…, c = 12.9915867Ã…, α =β =90°, γ =120°). The crystal structure is a slightly distorted hexagonal closed-packing of large oxygen ions (O2- anions) with small aluminum ions (Al3+ cations) occupying two thirds of octahedral interstices. The sapphire samples in this study were grown by the Edge-defined film-fed growth (EFG). Compared to other growth techniques such as Czochralski method, Kyropoulos method, heat exchanger method, the EFG method offers the advantage of obtaining near final shape of single crystal sapphire wafers. However, the growth conditions must be optimized to obtain low defect density ribbons. Therefore, to understand defect nucleation and propagation in these crystals, Synchrotron White Beam X-ray Topography has been employed in conjunction with optical microscopy and chemical etching in this study. Of particular interest in EFG sapphire is the nucleation of polycrystallinity that lowers yield. Transmission X-ray topography reveals the overall defect distribution around the region of polycrystallinity and the range of tilts and strains. Section X-ray topography is used to trace the evolution of strain and/or dislocations leading to onset of polycrystallinity. X-ray reticulography is used to quantitatively map the variation in strains and tilts around the region of polycrystallinity. All defects found in sapphire will be specifically discussed regarding their formation, effects and behaviors with the characterization techniques described. | |
| dcterms.available | 2017-09-20T16:50:01Z | |
| dcterms.contributor | Dudley, Michael | en_US |
| dcterms.contributor | Raghothamachar, Balaji | en_US |
| dcterms.contributor | Venkatesh, T. A. | en_US |
| dcterms.creator | Li, Zheyu | |
| dcterms.dateAccepted | 2017-09-20T16:50:01Z | |
| dcterms.dateSubmitted | 2017-09-20T16:50:01Z | |
| dcterms.description | Department of Materials Science and Engineering. | en_US |
| dcterms.extent | 51 pg. | en_US |
| dcterms.format | Application/PDF | en_US |
| dcterms.format | Monograph | |
| dcterms.identifier | http://hdl.handle.net/11401/76325 | |
| dcterms.issued | 2014-12-01 | |
| dcterms.language | en_US | |
| dcterms.provenance | Made available in DSpace on 2017-09-20T16:50:01Z (GMT). No. of bitstreams: 1
Li_grad.sunysb_0771M_11793.pdf: 4573783 bytes, checksum: 6cff50dd615805818e75bc36bf9a492b (MD5)
Previous issue date: 1 | en |
| dcterms.publisher | The Graduate School, Stony Brook University: Stony Brook, NY. | |
| dcterms.subject | sapphire, SWBXT, Synchrotron White Beam X-ray Topography | |
| dcterms.subject | Materials Science | |
| dcterms.title | Synchrotron White Beam X-ray Topography Study of EFG Sapphire Ribbons | |
| dcterms.type | Thesis | |
