Shih-Siang Lin

Pulsed laser synthesis of carbon-overdoped tungsten with a body-centered orthorhombic structure and planar defects

C-overdoped W crystallites with a new body-centered orthorhombic (BCO) structure were synthesized by inward diffusion of C from a substrate upon pulsed laser heating in vacuum. Analytical electron microscopic observations indicated that the BCO-type W has occasional long-range ordering of atoms for the particulates, whereas {110}-shuffling for the nanocondensates tended to form a (111) 30° twist boundary and a (01)/(101) interface with a fair coincidence site lattice upon (hkl)-specific coalescence. The co-existent bcc-W nanocondensates have well-developed ~{110} and ~{112} vicinal surfaces to adjoin as tilt boundaries. The refractory phase assemblages have bimodal UV-visible absorptions for potential machining and optoelectronic/catalytic applications in a harsh environment.

Pulsed laser ablation synthesis of magnesiowüstite based phases with special defect clusters, interfaces and internal stress: implications for natural occurrence and engineering applications

Nanocondensates of rocksalt-type (R) magnesiowustite and minor spinel-type (S) magnesioferrite with paracrystalline distribution of defect clusters were fabricated by pulsed laser ablation of MgO–Fe2O3 solid solution (9 : 1 molar ratio) under specified power densities in air and characterized by X-ray/electron diffraction and optical absorption spectroscopy. The predominant magnesiowustite nanocondensates have well-developed {100}, {110}, {111} facets for (hkl)-specific coalescence as unity and bicrystal with exact/almost {110} 70.5° twist boundary, {111} twin boundary, (1)/(001) heterointerface, and (100)R/(310)S interphase interface constrained by [01]R//[001]S. The magnesiowustite nanocondensates have a minimum band gap of ca. 3 eV for potential opto-electronic catalytic applications and a significant internal compressive stress of ca. 2.5 GPa when fabricated at a relatively high power density, shedding light on its natural high-pressure occurrence.

Pulsed laser synthesis of diamond-type nanoparticles with enhanced Si–C solid solubility and special defects

Diamond-type Si–C particles with enhanced solid solubility were synthesized by pulsed laser ablation of 6H-SiC (102) wafer in tetraethyl orthosilicate and characterized using X-ray/electron diffraction and optical spectroscopy. The C-overdoped Si, Si1+xC and Si-overdoped C nanoparticles underwent (hkl)-specific coalescence to form special grain boundaries, i.e. {111} twin boundary, (110) 70.5° twist boundary and [11](123)/(011) tilt boundary, and polycrystals up to several microns in size. Paracrystalline distribution of defect clusters and shock-induced 1-D 4×(111) faulting were also identified in the C-overdoped Si nanocrystals. The co-existent turbostratic graphene with varied Si–O–H content not only formed ribbons surrounding the diamond-type nanoparticles but also spherulites with bimodal basal spacing distribution due to dynamic constitutional supercooling. The overall refractory particles with significant photoluminescence (532, 603 nm) and violet light absorbance (3.1 eV) have potential opto-catalytic/electronic/abrasive applications and shed light on their natural occurrence in dynamic settings.

(CoxMg1−x)O nanocondensates by pulsed laser ablation of bulk alloy in air

Pulsed laser ablation of bulk CoO–MgO (solid solutions in 1:9, 1:1 or 9:1 molar ratios) in air was used to fabricate alloyed nanocondensates which were investigated by X-ray diffraction, transmission electron microscopy and UV-visible absorption characterization. The nanocondensates were formed as rocksalt-type (CoxMg1−x)O protoxide with well-developed {100} faces for coalescence as single crystals or (100) twist boundary with misorientation by 26.6°. Additional Mg-doped (8 at.%) Co3−δO4 spinel in the form of cubic nanocondensates and nearly spherical particulates with {011} and {121} facets were produced from the Co-rich target. The predominant (CoxMg1−x)O protoxide nanocondensates were able to turn the carbonaceous support into turbostratic graphene shell upon radiant heating and showed tailored paracrystalline distribution of defect clusters (ca. 1.5–2 nm interspacing), internal compressive stress (up to ca. 2 GPa), and UV absorption (3.2–3.5 eV) for potential opto-electronic catalytic applications.

(hkl)-Specific defects of MgO–CoO alloy produced by pulsed laser ablation in water

Metal oxides with (hkl)-specific defects of rocksalt-type based structure were fabricated by pulsed laser ablation of powdery MgO–CoO alloy (molar ratio 9:1, 5:5, 1:9 denoted as M9C1, M5C5 and M1C9, respectively, against CoO) in water and characterized using transmission electron microscopy. The resultant submicron-sized particles have a well-developed {100} surface with {110} edges and abundant dislocations for M9C1, whereas a rough surface and paracrystalline distribution of defect clusters (ca. 1.5–2 nm interspacing) along with spinel-type intergrowth for Co-richer compositions were obtained. Such paracrystals tended to form arrays following the ~{111} vicinal planes of the rocksalt-type host, i.e. {112} and {113} for M5C5 and {115} for Co1−xO, under the influence of a mutual dopant and/or the hydrogenation effect. A stable [110](11)/(12) asymmetrical tilt boundary with a fair coincidence site lattice also occurred by ~{111}-specific coalescence of the spinel particles for the M1C9 specimen. The composition-dependent formation of paracrystalline distribution of defect clusters and internal compressive stress (up to ca. 1 GPa) of the rocksalt-type host with characteristic UV absorbance are addressed.