10. Appendix

688 Appendix D
The “TOPO” and related Method of Growing Nanocrystals
This technique starts with solutions in tri-n-octyl-phosphine oxide (TOPO)
of the desired chemical species for forming the semiconductor, such as Cd
and Se compounds (or precursors) to produce CdSe. After reacting to form
CdSe the size of the resultant nanocrystals is limited due to capping by TOPO
molecules. The size of the almost spherical nanocrystals can be controlled to
certain extent by selecting the temperature of the reagents and by performing
further size sorting afterwards. This method can produce large quantities
of nanocrystals with size spread of 5% for industrial application. Core-shell
nanocrystals have also been successfully grown. The discovery of many other
chemical agents to replace TOPO has greatly broadened the choice of nanostructured
semiconductor which can be grown by this technique.
C. B. Murray, D. J. Norris and M. G. Bawendi: Synthesis and Characterization
of Nearly Monodisperse CdE (E=S, Se, Te) Semiconductor Nanocrystallites.
J. Am. Chem. Soc. 115, 8706–8715 (1993).
J. E. B. Katari, V. L. Colvin and A. P. Alivisatos: X-ray Photoelectron spectroscopy
of CdSe nanocrystals with applications to studies of the nanocrystal
surface. J. Phys. Chem. 98, 4109–4117 (1994).
K. Hashizume, M. Matsubayashi, M. Vacha1 and T. Tani: Individual mesoscopic
structures studied with sub-micrometer optical detection techniques:
CdSe nanocrystals capped with TOPO and ZnS-overcoated system. J. of Luminescence,
98, 49–56 (2002).
J.-Yu Zhang and W. W. Yu: Formation of CdTe nanostructures with dot, rod,
and tetrapod shapes. Appl. Phys. Lett. 89, 123108 (2006).
P. Dagtepe, V. Chikan, J. Jasinski and V. J. Leppert: Quantized growth of
CdTe quantum dots; observation of magic-sized CdTe quantum dots. J. Phys.
Chem. C, 111, 14977–83 (2007).
N. O. V. Plank, H. J. Snaith, C. Ducati, J. S. Bendall, L. Schmidt-Mende and
M. E. Welland: A simple low temperature synthesis route for ZnO-MgO
core-shell nanowires. Nanotechnology, 19, 465603–465610 (2008).
Growth Of Nanocrystals In Glass
In the middle ages stained glass was fabricated by dissolving metals in molten
glass following by quenching and annealing to form metallic nanocrystals. Today
this method can be used to produce nanocrystals of semiconductors embedded
in a glass matrix. First the semiconductor is dissolved in the molten
glass which is then quenched to room temperature. By annealing, the dispersed
semiconductor molecules or atoms coalesce into nanocrystals which are
approximately spherical. This method is inexpensive and can produce industrial
size glass containing semiconductor nanocrystals for optical applications
(neutral density filters, color filters in photography are some examples). A
variation of this method involves implanting ions into the glass and then heat-