Photonic crystals in biology

P
P
P,P
Poster Session, Tuesday, June 15
Theme A1 - B702
Structural and Optical Characteristics of CdSe Quantum Dots
1
2
1
1
1
M.R. KarimP P, A.K. TürkoluP
PN. AtmacaP P, N. YavariniaP P, and UHilmi ÜnlüUP P*
1
PIstanbul Technical University, Department of Physics, Maslak 34469, Istanbul, Turkey
2
PTUBITAK UME, Optik Grubu Lab, PK.54, Gebze, Kocaeli, Turkey
Abstract-CdSe quantum dots (QDs) were prepared by a vacuum heating method in which the particle size was controlled mainly by changing
different reaction temperatures. The synthesis CdSe QDs were characterized with UV-Vis absorption spectroscopy, atomic force microscopy
(AFM) and transmission electron microscopy (TEM). The quantum dots sizes at the first excitonic absorption peak increase with increasing
temperatures. The diameters of resulting CdSe QDs were about 4-5 nm with narrow size distribution both UV-Vis absorption spectra and TEM
results.
CdSe quantum dots are probably the most extensively
investigated object among chemically grown semiconductor
nanoparticles since the introduction of the “size quantization
effect” in the earlier eighties [1-2]. Semiconductors (II-VI)
have attracted considerable attention to understand the size
dependence of their optical properties and various applications
such as biological sensors, laser diodes, solar cells [3].
The CdSe nanocrystals were synthesized by using
modifications of R. He and H. Gu’s method [4]. 0.69g
cadmium acetate and 2.5 mL oleic acid were dissolved with 10
mL phenyl ether in three neck flask. The reaction mixture was
heated 140 °C. under stirring and continuous nitrogen flow,
and then the mixture was cooled. 3 mL 1M TOPSe was added
to mixture, rapidly, heated to 155 °C.-180 °C. and 1-25 min.
The purposed method was done 1 mL aliquot crude solution
was washed with methanol and isolated by centrifugation.
After fine isolation of growth CdSe, the precipitation was
5.2
5
Figure 2. AFM image of CdSe quantum dots at 160 °C.
grown at 160 °C. for 1 minute. The mean particle diameter is
around 4 nm, in good agreement with Figure 1.
4.8
10 Min
20 Min
15 Min
5 Min
Size (nm)
4.6
4.4
1 Min
4.2
4
3.8
155 160 165 170 175 180
Temparature (°C)
Figure 1. Size effect at the first peak absorption of CdSe QDs
dissolved with different volume of hexane.
The reaction process was monitored by UV-Vis absorption
with aliquots taken from different time and temperature. Fig. 1
shows that nanoparticle size increases with increasing
temperature.
Atomic force microscopy (AFM) allows imaging of
description of size and shape of the particles in solutions. At
higher reaction temperature larger particles were obtained.
High temperature results high rate attaching and larger particle
size and quick growth of the particle (Figure 2).
The diameter and narrow size distribution of the crude CdSe
QDs were determined by TEM. A representative example was
presented in Figure 3, for a sample of CdSe quantum dots
Figure 3. TEM image of CdSe quantum dots at 160 °C
In summary, TEM and AFM results revealed that CdSe
quantum dots were well-ordered crystallized with average
particle sizes 4-5 nm, which accords well with UV-Vis
spectrum results.
The authors would like to acknowledge the financial support
provided by TUBITAK under Grant No.TBAG-105T463.
*Corresponding author: HThunlu@itu.edu.trT
[1] Rossetti, R., Nakahara, S. & Brus, L. E. J. chem. Phys. 79, 1086
(1983)
[2] Al. L. Efros, A.L. Efros. sov; Phys. Semiconducd., 16, 772(1982)
[3] A. P. Alivisatos, Science 271, 933 (1996).
[4] T R. He, H. Gu, Colloids and Surfaces A: Physicochem.
Eng.Aspects, 272 (2006) 111-116.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 285