Supplementary for APL paper
Large photoresponse of Cu:TCNQ nanowire arrays formed as
aligned nanobridges.
Rabaya Basori,1,a) K. Das,1 Prashant Kumar,2 K.S.Narayan,2 A. K. Raychaudhuri1,a)
1
Theme Unit of Excellence on Nano Device Technology, S.N. Bose National Centre for Basic
Sciences, Salt Lake, Kolkata-700098, India
2
Jawaharlal Nehru Center for Advanced Scientific Research, Jakkur Bangalore-560 064,
India
Fabrication of device for nanobridge formation:
To integrate an ensemble of one-dimensional nanostructure system on a chip, a commercial
Si wafer with 300nm thick SiO2 layer was used as a substrate. Desired pattern was transferred
on a substrate using electron beam lithography, followed by metal deposition (Au deposition
on top of Cu) and lift-off. During Au deposition, substrate was intentionally kept at an angle
so as to cover the sidewall of one Cu electrode. So, nanowire growth occurs only from
uncovered Cu film which makes the growth unidirectional. Schematic representation of
whole process is shown below along with SEM image of actual nanobridge device. Figure
S1.(f) clearly shows the electrode from where growth starts.
Figure S1: (a) Resist coated Si/SiO2 substrate for doing e- beam lithography. (b) After
electron-beam writing of specific pattern and developing. (c) Cu evaporation keeping sample
normal with Cu source and then Au evaporation keeping substrate at an angle to wholly cover
Cu film only in one electrode . (d) After lift-off with acetone. (e) Growth of CuTCNQ
nanowire bridging the electrodes. (f) SEM image of CuTCNQ nanowire.
Structural characterization of the nanowires: As grown nanowires were characterized by
Electron Microscopy (SEM) (Quanta 200), X-Ray Diffraction measurements (MiniFlex II),
Fourier Transform Infra-red Spectroscopy (JASCO, FT/IR 6300) and Raman Spectroscopy.
Figure S2: SEM image of CuTCNQ nanowire showing nanowires of different diameter
X-ray diffraction: Figure S3 shows the XRD pattern of the Cu:TCNQ nanowire grown Cu
film on Si/SiO2 substrate and the intense feature in low angle region confirmed about Phase I
structure of nanowires. The X-RD pattern led to the tetragonal cell with a = b = 11.2524 Å, c
=3.9501Å, and V = 500.16 Å3.
Figure S2: X-RD diffraction pattern of Cu:TCNQ nanowires showing Phase I in structure.
Raman spectroscopy: A Micro-Raman spectrum of CuTCNQ nanowire was taken C=C-H
bending, C-CN stretching and C=C ring stretching mode of which was at around 1202, 1376
and 1601 cm-1 whereas for neutral TCNQ it was at 1207, 1451 and 1598 cm-1 as shown in
figure S4. The C-CN stretching mode is shifted from 1451 cm-1 (neutral TCNQ) to 1376 cm-1
(CuTCNQ) through the formation of CuTCNQ complex by means of the redox reaction
between Cu and TCNQ. In this case, the degree of charge transfer (CT) is estimated near
about 1.0. This means almost complete CT has occurred between Cu and TCNQ in CuTCNQ
nanowire.
Figure S4: Raman spectroscopy result of CuTCNQ and TCNQ