Studies of phase-change materials using ultrafast X-ray diffraction
(2025)- Abstract
- This thesis is focused on the investigation of the ultrafast structural response of the phase change material (PCM) Ge$_2$Sb$_2$Te$_5$ following laser excitation. Phase change materials are a group of materials capable of rapid, non-volatile, switching between an amorphous and a crystalline phase. The two phases exhibit high optical and electrical contrast, meaning the optical reflectivity and the electrical conductivity differ significantly between the two phases. These properties make PCM suitable for data storage, and they have been widely used, mainly in DVD-RW discs. GST has been successfully used for Phase Change Random Access Memory (PCRAM), and the non-thermal excitation pathways have been the interest of numerous... (More)
- This thesis is focused on the investigation of the ultrafast structural response of the phase change material (PCM) Ge$_2$Sb$_2$Te$_5$ following laser excitation. Phase change materials are a group of materials capable of rapid, non-volatile, switching between an amorphous and a crystalline phase. The two phases exhibit high optical and electrical contrast, meaning the optical reflectivity and the electrical conductivity differ significantly between the two phases. These properties make PCM suitable for data storage, and they have been widely used, mainly in DVD-RW discs. GST has been successfully used for Phase Change Random Access Memory (PCRAM), and the non-thermal excitation pathways have been the interest of numerous studies.
Conventionally, the phase change from the crystalline to the amorphous phase is driven by either optical or electric pulses on the order of 10 ns, where the material is melted and allowed to rapidly cool. If non-thermal pathways for amorphization exist, this could increase the write speed, up to 4 orders of magnitude.
This thesis presents ultrafast X-Ray Diffraction (XRD) studies investigating the ultrafast response of GST after femtosecond laser excitation, and compares the findings to previously suggested models, such as the suppression of the Peierls distortion, the umbrella flip model, and direct ultrafast amorphization. Furthermore, it is explained that the previous models do not satisfy the time-resolved behavior of the complete experimental findings, and a combination of these models is proposed as a more complete picture of the ultrafast dynamics. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/b7f654f6-49c4-45eb-a560-c82d51a6d28b
- author
- Nilsson, Eric LU
- supervisor
-
- Jörgen Larsson LU
- Olle Lundh LU
- opponent
-
- Prof. Balling, Peter, Aarhus University, Denmark.
- organization
- publishing date
- 2025
- type
- Thesis
- publication status
- published
- subject
- keywords
- X-ray diffraction, TRXRD, Ge2Sb2Te5, GST, phase change material, PCM
- pages
- 106 pages
- publisher
- Lund University , Department of physics
- defense location
- Lecture Hall Rydbergsalen, Department of Physics, Professorsgatan 1, Faculty of Engineering LTH, Lund University, Lund.
- defense date
- 2025-11-28 13:15:00
- ISBN
- 978-91-8104-748-6
- 978-91-8104-747-9
- language
- English
- LU publication?
- yes
- id
- b7f654f6-49c4-45eb-a560-c82d51a6d28b
- date added to LUP
- 2025-11-03 11:53:24
- date last changed
- 2025-11-05 13:08:29
@phdthesis{b7f654f6-49c4-45eb-a560-c82d51a6d28b,
abstract = {{This thesis is focused on the investigation of the ultrafast structural response of the phase change material (PCM) Ge$_2$Sb$_2$Te$_5$ following laser excitation. Phase change materials are a group of materials capable of rapid, non-volatile, switching between an amorphous and a crystalline phase. The two phases exhibit high optical and electrical contrast, meaning the optical reflectivity and the electrical conductivity differ significantly between the two phases. These properties make PCM suitable for data storage, and they have been widely used, mainly in DVD-RW discs. GST has been successfully used for Phase Change Random Access Memory (PCRAM), and the non-thermal excitation pathways have been the interest of numerous studies.<br/><br/>Conventionally, the phase change from the crystalline to the amorphous phase is driven by either optical or electric pulses on the order of 10 ns, where the material is melted and allowed to rapidly cool. If non-thermal pathways for amorphization exist, this could increase the write speed, up to 4 orders of magnitude.<br/><br/>This thesis presents ultrafast X-Ray Diffraction (XRD) studies investigating the ultrafast response of GST after femtosecond laser excitation, and compares the findings to previously suggested models, such as the suppression of the Peierls distortion, the umbrella flip model, and direct ultrafast amorphization. Furthermore, it is explained that the previous models do not satisfy the time-resolved behavior of the complete experimental findings, and a combination of these models is proposed as a more complete picture of the ultrafast dynamics.}},
author = {{Nilsson, Eric}},
isbn = {{978-91-8104-748-6}},
keywords = {{X-ray diffraction; TRXRD; Ge2Sb2Te5; GST; phase change material; PCM}},
language = {{eng}},
publisher = {{Lund University , Department of physics}},
school = {{Lund University}},
title = {{Studies of phase-change materials using ultrafast X-ray diffraction}},
url = {{https://lup.lub.lu.se/search/files/232052968/Eric_Nilsson_-_WEB.pdf}},
year = {{2025}},
}