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.

Novel silicon phases and nanostructures for solar energy conversion

“…7 This structure is notably different from the other tetrahedrally bonded phases, as its gap is larger that that of Si-I (see Fig. 7 and Table I).…”

“…A recent study employed ultrashort laser pulses to locally induce pressures and temperatures significantly higher than those attained in diamond anvil cell or indenter experiments, 7 thus permitting, upon cooling, the freezing of local regions of Si into phases that are otherwise inaccessible due to kinetic barriers. These experiments allowed for the experimental observation of ST12, and the existence of bt8 was reported for the first time, as well as that of two additional tetragonal and two monoclinic phases.…”

Tipping solutions: emerging 3D nano-fabrication/ -imaging technologies

“…To push resolution limits to the nanoscale, advancements in lasers and optical microscopy were combined and evolved into microscale 3D fabrication techniques, where photons of a wavelength λ can be focused into a diffraction-limited spot size of ~λ/2, and controlled at timescales of a few femtoseconds. Such energy delivery has a broadly appreciated flexibility in energy deposition and reaches sub-wavelength structuring in 3D through several processes: formation of new phases of materials [12,13], precise ablation [14][15][16], and/ or polymerization [17,18]. More advanced laser fabrication methods can reach sub-micron resolution by exploiting nonlinear processes, such as multiphoton polymerization [19][20][21] and stimulated emission depletion techniques [22,23].…”

Photoluminescence from voids created by femtosecond-laser pulses inside cubic-BN

“…For comparison, dense array of ablation patterns were fabri- cated with 800 nm/150 fs pulses focused with N A = 0.95 on the surface of c-BN. Judgement of the void presence at the center of irradiated spot inside c-BN was made by a sharp optical contrast change which was identical to the void formation in crystalline sapphire, quartz and glasses of different refractive indices 22,23 ; focused ion milling will be implemented next to reveal an internal structure of the void as it was made for voids at the Si-SiO 2 interface 24 . Photoluminescence and its transients were measured under laser diode 405 nm/30 ps or 510 nm/100 ps (Pi-LAS; advanced Laser Diode systems) excitation using N A = 0.7 objective lens and a single photon counting avalanche photo diode (SPCM-AQRH-14) as a detector.…”