Mgb2 powder

SrTiO₃ (100) single-crystal substrates were purchased from SHINKOSHA CO., LTD. Mg powder (212–600 μm, 99.9%, Wako, Osaka, Japan) and MgB₂ powder (99%; Sigma-Aldrich, St. Louis, MO, USA) were purchased to use MgB₂ thin film deposition. Acetonitrile (99.5% (JIS Special grade), FUJIFILM Wako Pure Chemical Industries Ltd., Osaka, Japan), a cation-exchange resin (15JS-HG⋅DRY, Organo Corp., Tokyo, Japan) and formic acid (Kanto Chemical Co., Inc., Tokyo, Japan) were purchased for ion-exchange treatment.
A pulsed laser ablation device (PLFD-221-1R, Freedom Ltd., Kawasaki, Japan) was used for PLD. X-ray diffractometer (Smartlab, Rigaku Corporation, Tokyo, Japan), laser microscope (LEXT OLS5100, Olympus Corporation, Tokyo, Japan), TOF-SIMS 5-100-AD (ION-TOF GmbH, Germany), FT/IR-6100 (JASCO, Co., Ltd., Tokyo, Japan), atomic force microscope (SPM-9700, Shimadzu Corp., Kyoto, Japan) and scanning electron microscope (JEM-2010F, JEOL, Ltd., Tokyo, Japan) were used for characterization of prepared films.

Exfoliation was carried out by suspending 450 mg of MgB₂ powder (–100 mesh size, Sigma Aldrich, purity ≥96%) in 150 ml water and exposing to ultrasonication using a 1 inch probe ultrasonicator (Sonic Vibracell-VC505, 500 watt, 20 kHz) for 30 minutes (amplitude: 30%, 10 sec on/off pulse). The resultant dark black suspension was allowed to stand for 24 hours. A distinct phase separation was observed as top phase (lighter in appearance) and bottom phase (darker in appearance). Without disturbing the sediments, decantation was carried out to separate the top phase. This top phase was exposed to two cycles of centrifugation at 1500 rpm for 45 minutes to pellet out any heavier particulate residues (Eppendorf centrifuge-5430R). After each centrifugation, top half of the dispersion was collected for further investigation.