title: Experimental evidence of new tetragonal polymorphs of silicon formed through ultrafast laser-induced confined microexplosion.
abstract: Ordinary materials can transform into novel phases at extraordinary high pressure and temperature. The recently developed method of ultrashort laser-induced confined microexplosions initiates a non-equilibrium disordered plasma state. Ultra-high quenching rates overcome kinetic barriers to the formation of new metastable phases, which are preserved in the surrounding pristine crystal for subsequent exploitation. Here we demonstrate that confined microexplosions in silicon produce several metastable end phases. Comparison with an ab initio random structure search reveals six energetically competitive potential phases, four tetragonal and two monoclinic structures. We show the presence of bt8 and st12, which have been predicted theoretically previously, but have not been observed in nature or in laboratory experiments. In addition, the presence of the as yet unidentified silicon phase, Si-VIII and two of our other predicted tetragonal phases are highly likely within laser-affected zones. These findings may pave the way for new materials with novel and exotic properties.
authors.affiliation: Laser Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Rapp
authors.affiliation: Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: B
authors.initials: B
authors.lastname: Haberl
authors.affiliation: Department of Physics and Astronomy, University College London, London WC1E 6BT, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Pickard
authors.affiliation: Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: J E
authors.initials: JE
authors.lastname: Bradby
authors.affiliation: Laser Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: E G
authors.initials: EG
authors.lastname: Gamaly
authors.affiliation: Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: J S
authors.initials: JS
authors.lastname: Williams
authors.affiliation: Laser Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: A V
authors.initials: AV
authors.lastname: Rode