Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
Preparation of zinc nitride (Zn 3 N 2 ) nanopowders and their optical properties.
Waheed S. Khan * , Chuanbao Cao
Research Center of Materials Science, Beijing Institute of Technology, Beijing 100081, P. R. China
Abstract- Zinc nitride (Zn 3 N 2 ) nanopowders were prepared by nitridation of aqueous ammonia treated zinc precursor under ammonia
gas reaction (150 sccm) at 600 o C for 120 minutes inside horizontal tube (HT) furnace. The as-prepared product was characterized by
XRD, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). Using Scherrer formula, particles size of
nanopowders was found to be 40-50 nm. Room temperature photoluminescence (PL) spectrum exhibited a broad ultraviolet (UV)
emission band at 389 nm corresponding to near band edge emission of zinc nitride. These studies indicated the potential of the zinc nitride
for applications in the UV-light emitting devices.
Over the past few years, zinc nitride (Zn 3 N 2 ) has attracted
much research focus due to its n-type conduction, high
electron mobility of about 100 cm 2 V -1 s -1 at room
temperature [1], wide band gap of 3.2 eV [2-3] and its use as
channel layer in TTFTs [4]. The other most important aspect
associated with zinc nitride is its conversion into p-type ZnO
[5]. The band gap of zinc nitride has been a controversial
issue as it has no single agreed value but different values
ranging from 0.9 eV [6] to 3.2 eV [2]. One main reason of
this variation is different preparative routes of zinc nitride.
Practical applications of Zn 3 N 2 demand the resolution of this
controversy. It is comparatively a new material and
researchers have started exploring its electronic, optical and
electrical properties since 1993. Most of the stress on zinc
nitride work has been on its thin film/polycrystalline structure
and few reports can be found on nanostructured zinc nitride
[3, 7].
In the present work, we report the synthesis,
characterization and optical properties of Zn 3 N 2. About 2
gram zinc powder (99.9%) mixed with aqueous ammonia was
loaded in alumina boat and shifted to the centre of the
horizontal tube (HT) furnace. The precursor was heated at
600 o C for 2h under NH 3 gas flow of 150 sccm. A black color
product was obtained in the boat on cooling to room
temperature. The crystal structure and phase purity were
tested by XRD analysis. All the diffraction peaks in XRD
spectrum of black powder were indexed to the cubic
structured zinc nitride (Zn 2 N 3 ) with lattice parameter a=0.976
nm matching very well with that given in JCPDS data (Card
No. 035-0762). No other phase like Zn, ZnO was observed in
the product. The particle size of zinc nitride nanopowders
was calculated by using Scherrer‘s equation with the help of
XRD data. Energy dispersive x-ray spectroscopy (EDS)
exhibited the presence of zinc and nitrogen in the product. A
small peak of oxygen was also observed in EDS possibly due
to the inclusion of oxygen on the surface while measurement
procedure.
Figure (a) presents SEM image of a particular portion of zinc
nitride product prepared at 600 o C under ammonia gas flow
for 120 minutes. From SEM micrographs, it can be clearly
observed that zinc nitride consists of nanoparticles with
average dimensions much less than 100 nm which is very
close to the values calculated by Scherrer formula.
Room temperature PL emission spectrum of Zn 3 N 2
nanopowders measured at an excitation wavelength of 325
nm using Xe lamp source is shown in Figure (b). The
spectrum exhibits a very prominent and broad peak at 389 nm
in ultraviolet (UV) region which corresponds to band gap of
Zn 3 N 2 . This value is very close to the reported values of 3.2
eV [2, 3] estimated by PL spectra. The UV band at 389 nm
Figure: (a) SEM image of zinc nitride nanopowders. (b) Room
temperature PL spectrum of Zn 3 N 2 product.
riginates from near band-edge transition of cubic zinc nitride
[3] and can possibly be attributed to the excitonic emission
caused by radiative recombination of electrons and holes [8].
The absence of the emission bands in the visible region
indicate the non-existence of defects and hence purity of the
product. PL investigations of zinc nitride nanopowders
demonstrate the promise of the material for UV-light emitting
devices.
In conclusion, we have successfully synthesized Zn 3 N 2
nanopowders via nitridation of aqueous ammonia mixed zinc
source at 600 o C for 2 hours. The structural, compositional
and morphological characterizations were performed by
XRD, EDS and SEM tests. The room temperature PL studies
of zinc nitride exhibited a broad emission UV band
corresponding to the band gap of the product. This feature
indicates the promise of the zinc nitride for applications in
UV-light emitting devices.
This work was supported by National Natural Science
Foundation of China ((20471007). We are thankful to Higher
Education Commission (HEC) Pakistan for providing
financial support for presenting this paper in the 6th
Nanoscience and Nanotechnology Conference (NanoTR6-
2010) held in Turkey.
*Corresponding author: waheedskhan@yahoo.com
[1] Futsuhara, M., Yoshioka, K. and Takai, O., Futsuhara, M., 1998.
Thin Solid Films 322: 274 .
[2] Kuriyama, K., Takahashi, Y., Sunohara, F.,1993. Phys. Rev. B
48: 2781.
[3] Zong, F., et al., 2005. Appl. Phys. Lett. 87: 233104.
[4] Aperathitis, E., et al., 2009. Thin Solid Films 518: 1036.
[5] Kambilafka, V., et al., 2007. Superlattices Microstruct. 42: 55.
[6] Paniconi, G., et al., 2008. J. Solid State Chem. 181: 158.
[7] Waheed S. Khan, Chuanbao Cao, 2010. J. Crys. Growth (In
press).
[8] Kaminska, E., et al., 2005. Phys. Status Solidi (c) 2: 1119.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 228