Optical phase change in bismuth through structural distortions induced by laser irradiation

Semimetal bismuth (Bi) is known to possess a wide range of peculiar properties, owing to its unique electronic band structure. Its electronic band can easily be distorted by structural changes, and thereby undergo transitions between semimetal to either semiconductor or metal states. Utilising a foc...

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Bibliographic Details
Published in:Radiation effects and defects in solids 2020-03, Vol.175 (3-4), p.291-306
Main Authors: Handegård, Ørjan S., Kitajima, Masahiro, Nagao, Tadaaki
Format: Article
Language:English
Subjects:
Bismuth
Change detection
Crystal defects
Droplets
Irradiation
Laser beam heating
laser irradiation
Lasers
Noble metals
Oxidation
Phase change
Phonons
Raman spectra
Raman spectroscopy
Silicon substrates
structural defects
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Summary:Semimetal bismuth (Bi) is known to possess a wide range of peculiar properties, owing to its unique electronic band structure. Its electronic band can easily be distorted by structural changes, and thereby undergo transitions between semimetal to either semiconductor or metal states. Utilising a focused laser beam, one can easily introduce structural defects, along with phase changes, oxidation, and morphological modifications. Confocal Raman microscopy indicated that the as-fabricated Bi droplets inhibit the Raman signal from the underlying silicon (Si) substrate. After a laser flash heating step, the intensity of Si optical phonons was strongly enhanced at the positions of Bi droplets, and exceeding the intensity from the bare Si substrate. Thus, such laser irradiating step on the Bi droplets induces an optical phase change. The optical phase change was detected as going from inhibition to strong enhancement of the underlying Si substrate Raman signal. From the observed Bi optical phonon modes (E g and A 1g ), alterations in the Raman peaks due to laser exposure indicated that the ordered crystallinity in pristine Bi droplets became deteriorated. The effects of atomic displacements and loss of structural order in Bi droplets impacts its dielectric response. The observed Si Raman signal enhancement is similar to the surface-enhanced Raman scattering effect typically known for noble metals.
ISSN:1042-0150
1029-4953
DOI:10.1080/10420150.2019.1701461