Pd(III) Mott–Hubbard Compounds - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 48

Fig. 4.14 STM images of (a) [Ni(chxn) 2 Br]Br 2 and (b) [Pd(chxn) 2 Br]Br 2 in the bc plane
(200 200 ˚ ). The image was acquired with a sample bias ( V s ) of +1.3 V and +1.0 V for Ni
and Pd chains, respectively. The white arrow shows the 1D chain direction

Fig. 4.15 Diagram of the band structure of (a) [Ni(chxn) 2 Br]Br 2 and (b) [Pd(chxn) 2 Br]Br 2

current is observed from the Fermi energy level ( E F ) of the tip to the conduction band
of the sample. In other words, in the image of [Ni(chxn) 2 Br]Br 2 , a tunnel current from
E F to the UHd z 2 band of Ni(III) was observed, whereas that from E F to the d z 2 band of
Pd(IV) was observed in the image of [Pd(chxn) 2 Br]Br 2 , which causes the twofold
periodicity along the 1D chain observed in the STM image.
Then, we carried out STM measurements on the mixed metal complexes
[Ni 1 x Pd x (chxn) 2 Br]Br 2 to determine their local valence structures. Figure 4.16
shows STM images of the complexes with x ¼

(a) 0.70, (b) 0.80, (c) 0.86, and (d)

200 ˚ 2 . The image of the x ¼

0.95 in an area of 200 0.70 complex was similar to

that of [Ni(chxn) 2 Br]Br 2 with almost no twofold periodicity. This result shows that
the x ¼ 0.80

complex, on the other hand, twofold periodicity was observed in several areas,
which we attributed to CDW states.

0.70 complex is in a Mott-Hubbard state. In the image of the x ¼