Exotic silicon phases synthesized through ultrashort laser-induced microexplosion: Characterization with Raman microspectroscopy

L. A. Smillie; M. Niihori; L. Rapp; B. Haberl; J. S. Williams; J. E. Bradby; C. J. Pickard; A. V. Rode

doi:10.1103/PhysRevMaterials.4.093803

Exotic silicon phases synthesized through ultrashort laser-induced microexplosion: Characterization with Raman microspectroscopy

L. A. Smillie, M. Niihori, L. Rapp, B. Haberl, J. S. Williams, J. E. Bradby, C. J. Pickard, A. V. Rode

High Pressure

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Abstract

Exotic metastable phases of silicon formed under high pressure are expected to have attractive semiconducting properties including narrow band gaps that open up novel technological applications. Confined microexplosions induced by powerful ultrashort laser pulses have been demonstrated as an advanced tool for the creation of new high-pressure phases that cannot be synthesized by other means. Tightly focused laser pulses are used to generate localized modifications inside the material structure, providing the possibility for precise controlled band-gap engineering. In this study, noninvasive Raman spectroscopy was used for analysis of laser-modified zones in silicon and to determine the metastable high-pressure phases contained. Low laser energies induced the formation of amorphous-only silicon, while higher energies led to crystalline silicon polymorphs within the modifications, albeit under considerable residual stress up to 4.5 GPa. The presence of the structurally similar r8-Si, bc8-Si, and bt8-Si phases is revealed, as well as other yet to be identified phases, and the stacking-related 9R Si polytype is evidenced, presumably stress-induced by the highly compressed laser-modified zone. The ab initio random structure searching approach is used to calculate the Raman signatures and to help identify different Si polymorphs. These findings by Raman spectroscopy from ultrashort laser-induced microexplosion sites may yield insights into the local structure and properties of new silicon metastable phases and the prospect of utilizing exotic phases for extending current applications.

Original language	English
Article number	093803
Journal	Physical Review Materials
Volume	4
Issue number	9
DOIs	https://doi.org/10.1103/PhysRevMaterials.4.093803
State	Published - Sep 2020

Funding

This work has been partially supported by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The US Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan . The authors acknowledge the support by the Australian Government through the Australian Research Council's Discovery scheme, Project No. DP170100131. The authors acknowledge the facilities and the scientific and technical assistance of Microscopy Australia at the Advanced Imaging Precinct, Australian National University. B.H. was supported by resources at the Spallation Neutron Source and the High Flux Isotope Reactor, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory (ORNL). C.J.P. is supported by the Royal Society through a Royal Society Wolfson Research Merit award.

Funders	Funder number
U.S. Department of Energy
Office of Science
Oak Ridge National Laboratory
UT-Battelle	DE-AC05-00OR22725
Royal Society
Australian Research Council	DP170100131

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10.1103/PhysRevMaterials.4.093803

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title = "Exotic silicon phases synthesized through ultrashort laser-induced microexplosion: Characterization with Raman microspectroscopy",

abstract = "Exotic metastable phases of silicon formed under high pressure are expected to have attractive semiconducting properties including narrow band gaps that open up novel technological applications. Confined microexplosions induced by powerful ultrashort laser pulses have been demonstrated as an advanced tool for the creation of new high-pressure phases that cannot be synthesized by other means. Tightly focused laser pulses are used to generate localized modifications inside the material structure, providing the possibility for precise controlled band-gap engineering. In this study, noninvasive Raman spectroscopy was used for analysis of laser-modified zones in silicon and to determine the metastable high-pressure phases contained. Low laser energies induced the formation of amorphous-only silicon, while higher energies led to crystalline silicon polymorphs within the modifications, albeit under considerable residual stress up to 4.5 GPa. The presence of the structurally similar r8-Si, bc8-Si, and bt8-Si phases is revealed, as well as other yet to be identified phases, and the stacking-related 9R Si polytype is evidenced, presumably stress-induced by the highly compressed laser-modified zone. The ab initio random structure searching approach is used to calculate the Raman signatures and to help identify different Si polymorphs. These findings by Raman spectroscopy from ultrashort laser-induced microexplosion sites may yield insights into the local structure and properties of new silicon metastable phases and the prospect of utilizing exotic phases for extending current applications.",

author = "Smillie, {L. A.} and M. Niihori and L. Rapp and B. Haberl and Williams, {J. S.} and Bradby, {J. E.} and Pickard, {C. J.} and Rode, {A. V.}",

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Exotic silicon phases synthesized through ultrashort laser-induced microexplosion: Characterization with Raman microspectroscopy

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