Supplemental Information
1) Preparation of samples
The V2O5 nanoribbons were grown by a thermal deposition method. A clean piece of
vanadium foil (Lesker, 99.8 %) was heated at 660C for four hours under ambient
conditions. The nanoribbons were collected on Si or quartz substrates which were
covered on the foil without using of catalyst. A representative dark-field optical image
of the as-grown samples is shown in Figure S1a. The selected-area electron
diffraction (SAED) pattern in Fig. S1b reveals that the ribbons have a
single-crystalline structure and the growth direction is along [011]. Furthermore,
high-resolution transmission electron microscope (HRTEM) images from different
positions of sample demonstrate the uniformity along the nanoribbon.
Divanadium pentoxide (V2O5), which exhibits highly anisotropic electronic and
optical properties, can be an outstanding candidate for optoelectronic applications.
The active waveguide properties on the V2O5 nanoribbons have been studied in our
previous work.1 An example of this waveguiding is shown in Figure S1c, where a
V2O5 nanoribbon was excited by a 532 nm laser focused at the middle, right and left
ends of the sample. It can be seen that the light travels along the ribbon and emerges
at the ends. In addition, we found that the Raman signals also exhibit pronounced
waveguide effect, suggesting that these nanostructures may be potentially useful for
novel sub-wavelength optoelectronic devices.
For optical studies, the nanoribbons were dispersed onto a glass substrate after being
removed from their growth substrates by ultrasonic agitation in acetone. As shown in
Fig. S1d, the Raman spectrum of the sample corresponds well to the characteristic
modes of crystalline V2O5.2 (The spectrum is taken from body of sample and no
analyzer is used in this case.)
2) Polarization-dependent Raman and the Raman tensor analysis
Polarization-dependent Raman measurements on individual V2O5 nanoribbons were
investigated in backscattered configuration by WITEC CRM200 confocal system,
together with a high-resolution piezoelectric stage. A laser beam (λ=532 nm) was
focused down with a 100× (N. A. =0.95) objective. And the polarized Raman spectra
were acquired at room temperature by rotating a linear polarization analyzer in the
collection optical path while excitation polarization was maintained. Nanoribbons
were aligned to be parallel to the polarization of the incident laser (as shown in
Figure S2). The Porto notation will be used to indicate the polarization configuration
in which each spectrum was taken. For example, the symbol Z  XY  Z represents
that the laser light is incident from the Z direction with the X polarization, while the
scattered signal is collected with the Y polarization in the opposite Z direction. In fact,
all images generated using the same phonon modes, exhibit nearly identical patterns.
t
According to the group-theoretical treatment, the Raman tensors ( R ) of V2O5 with
orthorhombic symmetry D2h are as follows:
a


t

, t

R  Ag   
b  R  B1g    d


c 


d


, t

 R  B2 g   

e


e




where a, b, c, d, and e are components of the Raman tensors.3 The observed Raman
t 2
scattering intensity is given by S  A eˆ s  R eˆ l , where A is the constant and êl ,s
represent unit vectors of the incident (l) and scattered (s) light, respectively. In the
mentioned backscattering configuration, the incoming and scattered vectors are given
by
 0 


êl   cos   and ês   sin
 sin  


cos  sin  
where  is the angle between a primary axis such as <011> direction and the
radiated electric field, and  is the cross angle between <010> and <011> directions
in the (100) plane. So the Raman intensity as a function of  will be given by
S  Ag   cos 2  , S  B1g   sin 2  , S  B2 g   sin 2  .
3) The polarized Raman-active waveguide effect on V2O5 nanoribbons
To demonstrate the optical propagation effect on V2O5 nanoribbons, we have explored
the spectral variation of polarized Raman-active waveguide emission using a WITEC
CRM200 Raman system. Experimental details of this technique are presented in ref 1.
The excitation laser was focused onto the body with about 10 μm distance away from
the tip of sample. The waveguided signals were captured at the tip of nanoribbon from
the opposite side of excitation. An analyzer was inserted into the collection path. In
this regard, the polarized properties of waveguided photons can be investigated.
Figure S1: (a) Dark-field image of an as-grown sample. (b) TEM of a single
crystalline nanoribbon. (c) Photoluminescence images of the nanoribbon show
promising waveguiding properties. As highlighted by the green circles, the exciting
laser spot was focused at the middle, right and left ends, respectively. (d) Typical
Raman scattering spectrum of the sample.
Figure S2: Experimental setup for polarized Raman experiments on individual
nanoribbons
References
1
B. Yan, L.
Liao, Y. M. You, X. J.
Xu, Z. Zheng, Z. X. Shen, J.
Ma, L. M.
Tong, and T.
Yu, Adv. Mater. 21, 2436 (2009).
2
E. Husson L. Abello, Y. Repelin, G. Lucazeau, Spectrochim. Acta A 39, 641 (1983).
3
R. Loudon, Adv. Phys. 50, 813 (2001).