An improved process for making nanocrystallites, commonly denoted quantum dots (QDs), is based on spray pyrolysis. Unlike the process used heretofore, the improved process is amenable to mass production of either passivated or non-passivated QDs, with computer control to ensure near uniformity of size

Banger, Kulbinder

Hepp, Aloysius

Jin, Michael H.

NASA Technical Reports Server

18 NASA Tech Briefs, August 2006
Producing Quantum Dots by Spray Pyrolysis 
Sizes of quantum dots are determined by sizes of sprayed drops. 
John H. Glenn Research Center, Cleveland, Ohio
An improved process for making
nanocrystallites, commonly denoted
quantum dots (QDs), is based on spray
pyrolysis. Unlike the process used hereto-
fore, the improved process is amenable
to mass production of either passivated
or non-passivated QDs, with computer
control to ensure near uniformity of size. 
The extraordinary optical properties
that make QDs useful can be tailored via
the chemical compositions and sizes of
the QDs.  Heretofore, QDs have been
made by in situ pyrolysis of molecular
reagents that contain all the elemental in-
gredients. In order to make all QDs in a
batch have the same or nearly the same
size, it is necessary to prevent nucleation
with adjacent QDs by passivating the sur-
faces of the QDs soon after they have
formed. Passivation is effected by use of a
passivating coordinating solvent/ligand
compound as one of the ingredients. This
compound both serves as a medium for
the formation of the QDs via pyrolysis
and readily coordinates to the surfaces
of the QDs, thereby preventing further
nucleation. Covering of the surfaces of
the QDs with the coordinating molecu-
lar groups is known in the art as cap-
ping. The capping groups 
can be organic or inorganic. The sol-
vent/ligand can be formulated to tailor
the surface properties of the QDs for a
specific application. For example, they
can be made hydrophilic or hydropho-
bic. Unfortunately, this in situ pyrolysis
process cannot readily be scaled up to
mass production, and the QDs pro-
duced exhibit excessive nonuniformity.
The improved process also includes py-
rolysis, but differs from the prior process
in the pyrolysis conditions and in the
manner in which the ingredients are pre-
pared for pyrolysis. In addition, one has
an option to form QDs of controlled size
without or with capping. Unlike in the
prior process, one does not rely on for-
mulation and pyrolysis process conditions
to cause the QDs to form spontaneously
in the desired size range. Instead, one
forces the QDs to form in a desired rela-
tively narrow size range by spraying a solu-
tion of QD-precursor material through an
ultrasonic nozzle to form drops of con-
trolled size. The average size of the drops
can be tailored via the surface tension
and density of the solution. Even more
conveniently, the average size can be tai-
lored via the frequency of ultrasonic agi-
tation. Experiments have shown that for a
given formulation, the average size is in-
versely proportional to frequency to the
2/3 power. 
The basic concept of the improved
process admits of variations. For exam-
ple, in a simple embodiment of the
process for making non-capped QDs, a
precursor solution is sprayed into a cold-
wall reactor that contains a substrate that
is electrically heated to the desired reac-
tion temperature (see figure). The drops
falling on the substrate become pyrolized
into QDs. In a slightly more complex ex-
ample, capped QDs are made by similar
spraying of a precursor solution into a
hot passivating solvent. 
This work was done by Kulbinder Banger,
Michael H. Jin, and Aloysius Hepp of Glenn
Research Center. Further information is
contained in a TSP (see page 1).
Inquiries concerning rights for the commer-
cial use of this invention should be addressed
to NASA Glenn Research Center, Commercial
Technology Office, Attn: Steve Fedor, Mail Stop
4–8, 21000 Brookpark Road, Cleveland, Ohio
44135. Refer to LEW-17444.
LEW-17444
ABPI
11-18-03 es
Argon
Supply
Syringe Pump
Containing
Precursor Solution
Ultrasonic
Nozzle
Outlet to
Cold Traps
APPARATUS FOR MAKING
UNCAPPED QUANTUM DOTS
Argon
Supply
Syringe Pump
Containing
Precursor Solution
Ultrasonic
Nozzle
APPARATUS FOR MAKING
CAPPED QUANTUM DOTS
To
Bubbler and
Traps
Hot Passivating
Solution
These Two Apparatuses serve to illustrate the basic principles of two variants of the spray-pyrolysis
process for making uncapped or capped QDs of controlled size. 
https://ntrs.nasa.gov/search.jsp?R=20110012952 2019-08-30T16:05:13+00:00Z


Producing Quantum Dots by Spray Pyrolysis

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