  A strongly correlated Mott first-order metal-insulator transition (MIT) (or
Jump) not accompanied by the structural phase transition (SPT) was clearly
revealed in VO_2, (New J. Phys. 6 (1004) 52, Appl. Phys. Lett. 86 (2005)
242101, Physica B 369 (2005) 76). In order to re-confirm the MIT for a
VO_2-based device with a narrow width of 3 micrmeter and a length of 20
micrometer such as a rod (Fig. A), both phonon peaks (Fig. B) by a micro-Raman
scattering with a laser beam of about 5 micrometer and the MIT with jump in I-V
curve (Fig. C) were simultaneously measured. A device like a rod has less
inhomogeneity. The current was restricted for measurements. The phonon peaks of
monoclinic exist even after the abrupt jump, and disappear in over 10 mA. The
jump was changed to negative differential resistance type during Raman
measurement after the jump. The high current causes a Joule heat which arises
from the SPT near 68^oC from monoclinic to tetragonal. The clean film surface
without a breakdown damage after several measurements was taken by a
micro-photograph camera (Fig. A). The MIT (jump) occurs prior to the SPT and
not affected by the SPT as evidence of electron-phonon interaction. Thus VO_2
is a Mott insulator not Peierls insulator.
