Yasuhiro HASEGAWA (Saitama Univ., Japan)

Jeudi 21 Septembre à 14 h 00
Amphi Holweck, Esc. C
1er étage

Title : Study on fabrication of single crystal bismuth nanowire and
measurement of its thermoelectric properties utilizing nano-processing

Abstract :
Bismuth nanowire with utilizing a quartz template was
fabricated by applying liquid-phase high pressure injection method.
The Seebeck coefficient and resistivity of bismuth nanowires which had
several hundred nanometers diameter were measured in this study.
Temperature dependencies of the Seebeck coefficient and resistivity
varied widely from that of bulk single crystalline bismuth. The
resistivity and Seebeck coefficient were calculated by considering the
mean free path limitation at the boundary of the bismuth nanowire to
describe experimental result. The total resistivity and Seebeck
coefficient were calculated with assuming crystal orientation for the
wire longitudinal direction. As a result of the calculation, I
concluded that thermoelectric properties of the bismuth nanowire
strongly depend on not only wire diameter but also the crystal
orientation ; therefore, the crystal orientation is significant factor
in order to evaluate physical properties of the bismuth
nanowire.
Furthermore, how to make electrical contact to sides of the
bismuth nanowire for electrical properties measurement is
investigated. It was reported that naked surface of bismuth nanowire
is likely to oxidize, and elimination of the oxide layer was very
important process in order to get ohmic contact. On the other hand, we
have successfully fabricated an individual bismuth nanowire completely
covered with quartz, preventing its oxidation ; however, it was
difficult to attach electrodes on the side surface of the nanowire due
to its covering quartz. I attempted the electrical contact to nanowire
by utilizing polishing and focused ion beam processing. One side of
the quartz template was removed by polishing process without ex-
posing the nanowire into the air, and rest part of the quartz that
covers the nanowire is locally removed by focused ion beam processing
to expose surfaces of the nanowire. The carbon thin film was deposited
on the wire surface in situ to make the
electrical contact with preventing its oxidation. Four electrodes were
successfully fabricated and the resistivity was measured with
4-terminal method. Furthermore, Hall measurement for nanowire is also
attempting utilizing the electrode fabrication technique by focused
ion beam.

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