The authors hereby retract the above article published in Applied Physics Letters (APL) because identical contents were published as a part of the overviewed conference proceedings.1 The corresponding author wishes to express deep regret in having submitted this APL manuscript without knowing publication of the conference proceedings. The authors apologize to the editors, the journal publishers, and the scientific community for this breach of the well-established protocol for scientific publications.

1.
A.
Inoue
,
H. M.
Kimura
, and
T.
Zhang
,
Mater. Sci. Eng., A
294–296
,
727
(
2000
).