The Cross-Sectional Structure of Vanadium Oxide Nanotubes Studied
by Transmission Electron Microscopy and Electron Spectroscopic Imaging
Frank Krumeich, Hans-Joachim Muhr, Markus Niederberger, Fabian Bieri, and Reinhard Nesper*
ZuÈrich/Switzerland, Laboratory of Inorganic Chemistry, ETH ZuÈrich
Received May 22nd, 2000.
Dedicated to Professor JuÈrgen Felsche on the Occasion of his 60
th
Birthday
Abstract. Vanadium oxide nanotubes (VO
x
-NTs) are easily
accessible in pure form from vanadium(V) alkoxides and
amines by a sol-gel reaction and a subsequent hydrothermal
treatment. The wall structure of VO
x
-NTs containing hexa-
decylamine or dodecylamine as the structure-directing tem-
plate has been characterised by transmission electron micro-
scopy (TEM). A standard method for preparing TEM
specimens was modified in order to investigate the cross-sec-
tional structure of the tubes. The elemental distribution in
the layered structure inside the tube walls has been visu-
alised by electron spectroscopic imaging: vanadium oxide
builds up the layers that appear with dark contrast in the
TEM images while carbon, i. e., the organic template, is pre-
sent in between. The bent VO
x
layers inside the tube walls
are preferentially scrolls rather than concentric cylinders.
Moreover, some tubes are formed by a combination of both
types. The layer structure inside the tube walls is frequently
disordered, and several types of defects appear.
Keywords: Vanadium oxide; Nanotubes; Cross-sectional
structure; Transmission electron microscopy; Electron spec-
troscopic imaging
Querschnitte von Vanadiumoxid-Nanoro
È
hren und ihre Charakterisierung
mittels Transmissions-Elektronenmikroskopie und elektronenspektroskopischer
Abbildung
Inhaltsu
È
bersicht. Vanadiumoxid-NanoroÈhren (VO
x
-NTs)
sind aus Vanadium(V)-Alkoxiden und Aminen durch eine
Sol-Gel Reaktion und eine anschliessende hydrothermale
Umsetzung leicht in reiner Form zu erhalten. Die Wand-
struktur von VO
x
-NTs, die entweder Hexadecylamin oder
Dodecylamin als Struktur-dirigierendes Templat enthaÈlt,
wurde mittels Transmissionselektronenmikroskopie (TEM)
charakterisiert. FuÈ r die Untersuchung des RoÈ hrenquer-
schnitts wurde eine Standardmethode fuÈ r die PraÈparation
von TEM-Proben modifiziert. Die elektronenspektroskopi-
schen Abbildungen zeigen die Elementverteilung in den
Schichten der RoÈ hrenwand: Die in den TEM-Aufnahmen
mit dunklem Kontrast erscheinenden Schichten enthalten
Vanadiumoxid, waÈhrend das organische Templat dazwischen
eingebaut ist. Die RoÈhrenwaÈnde bestehen oft aus gerollten
VO
x
-Schichten; geschlossene, konzentrische RoÈhren sind da-
gegen selten. Einige RoÈ hren stellen Kombinationen dieser
beiden Grundtypen dar. In der Schichtstruktur der WaÈnde
treten haÈufig verschiedene Arten von Defekten auf.
Introduction
Starting in 1991 with Iijima's discovery of carbon na-
notubes by transmission electron microscopy [1], this
method has made an immense impact on detection
and characterisation of related tubular structures in
various other systems like dichalcogenides (e. g.,
MoS
2
,WS
2
[2±4]), NiCl
2
[5], TiO
2
[6, 7] and modified
vanadium oxides [8±13]. By far most of these investi-
gations have been performed with the electron beam
perpendicular to the tube axis. This longitudinal pro-
jection allows for an investigation of the tube mor-
phology and of the wall structure. In carbon nano-
tubes, for example, defects were detected [14], and
structural models as well as a growth mechanism were
proposed on the basis of thereby obtained TEM re-
sults [15]. However, in order to characterise the struc-
ture of the tubes comprehensively, especially with re-
spect to an unambiguous discrimination between
scrolls of layers and cylindrical layer arrangements, re-
spectively, the examination along the tube axis is in-
dispensable. For this purpose, cross-sectional prepara-
tion methods for TEM specimens have to be applied.
In the case of carbon nanotubes, the projection of
choice was achieved by embedding tube bundles with
a common orientation in a resin and then cutting thin
slices perpendicular to the tube axes by ultramicro-
2208 Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000 0044±2313/00/6262208±2216 $ 17.50+.50/0 Z. Anorg. Allg. Chem. 2000, 626, 2208±2216
* Prof. Dr. Reinhard Nesper,
Laboratory of Inorganic Chemistry,
Swiss Federal Institute of Technology (ETH),
UniversitaÈtstrasse 6,
CH-8092 ZuÈrich, Switzerland,
e-mail: nesper@inorg.chem.ethz.ch