APPLIED PHYSICS LETTERS 87, 093105 ͑2005͒
a͒
Klemens Hitzbleck, Hartmut Wiggers, and Paul Roth
Institut für Verbrennung und Gasdynamik, Universität Duisburg-Essen, 47057 Duisburg, Germany
͑
Received 22 February 2005; accepted 28 June 2005; published online 22 August 2005͒
Indium nanoparticles were synthesized in a microwave flow reactor by thermal decomposition of
trimethylindium. The particles were extracted from the gas phase by molecular beam sampling,
deflected in an electric field, and deposited on a semiconductor surface. The size of the deposited
particles was selected by adjusting the deflection voltage. The geometric standard deviation of the
size-selected particles was found to be smaller than 10%. The deposition method is compatible with
Nanosized materials have properties that differ from the
corresponding bulk behavior, making them attractive for new
applications in materials science and nano electronics.
the synthesis of charged nanoparticles and a particle mass
spectrometer ͑PMS͒ described by Hospital and Roth for the
1
–3
4–7
16
particle deposition.
As a result of the nanoscaled dimensions, quantum effects
are becoming important, opening new applications, particu-
larly with regard to semiconductor technology, e.g., quantum
dots in semiconductor structures. An established method to
generate such structures is the self-organized growth of
The solid precursor TMIn was vaporized and mixed with
argon in an online mixing device similar to well-established
techniques used for MOVPE. The precursor concentration
was varied between 200 and 500 ppm. A molecular beam
sampling system, located downstream the plasma zone, was
used to extract particles from the reactive zone for PMS
analysis and surface deposition. A glass nozzle helps to form
a free-jet by directing a sample from the low pressure par-
8
quantum dots by the Stranski–Krastanov mode. This
method is based on epitaxial distension and works for certain
material combinations determined by atomic structure and
size. It has been successfully applied for a lot of quantum dot
ticle formation region into
a
vacuum chamber ͑p
9
−3
=
10 mbar͒. The supersonic expansion into the free-
devices, for instance quantum dot lasers. Nevertheless, the
Stranski–Krastanov growth is limited in terms of material,
size, and deposition density of quantum dots. A possibility to
overcome these restrictions is the deposition ͑and subsequent
embedding͒ of pre-produced nanoparticles within a semicon-
ductor structure. To this purpose, several deposition methods
molecular regime leads to a rapid decrease in temperature,
which suppresses further chemical and physical processes
almost completely. The center of the free-jet is then extracted
by a skimmer and propagates as a particle loaded molecular
beam into the analysis chamber ͑p=10− mbar͒, where PMS
analysis and particle deposition is performed.
The principle of the PMS is based on the behavior of
charged particles in an electric field. The particle loaded mo-
lecular beam is directed through a deflection capacitor which
separates charged particles according to their mass, velocity,
and charge. Particles from the deflected molecular beam can
pass an aperture and are detected, if their properties fulfill the
following condition:
6
1
0
are possible, but with respect to purity and surface compo-
sition, particles from gas phase synthesis are preferred com-
pared to materials from wet synthesis with surface active
11
additives.
A lot of groups deal with size separation by means of
low pressure operating differential mobility analysis
1
2,13
͑DMA͒.
This system has been successfully applied for
high deposition rates at an operating pressure of a few mbar.
Nevertheless, DMA technology is not compatible in pressure
with metal organic vapor phase epitaxy ͑MOVPE͒ and metal
organic chemical vapor deposition ͑MOCVD͒, since an ad-
ditional pressure stage is necessary while the deposition rate
drops. There are a couple of methods available, consisting of
low pressure particle formation combined with high vacuum
2
Kmv = n eU ,
͑1͒
e
D
where K is a geometric constant, n the number of elemen-
e
tary charges e per particle, U the deflection voltage, m the
D
particle mass, and v the particle velocity. Figure 1 shows a
schematic drawing of the analysis chamber. Our laboratory-
made system consists of a deflection capacitor ͑copper,
11
extraction. Several of these methods have been applied for
size selected deposition, but usually these methods suffer
from the disadvantage that they produce comparatively low
particle concentration. This paper focuses on a method that is
compatible in pressure and purity with epitaxial conditions
7
0 mm long, separation distance 20 mm͒, and a 5 mm aper-
ture 300 mm downstream. The particles passing the aperture
slit can either be counted by a Faraday cup or are sampled on
a surface. TEM grids and substrates can be positioned by
means of an adjustable holder in the particle beam. A me-
chanical shutter allows a time-controlled deposition of par-
ticles on a substrate.
7
and enables high deposition rates of up to 10 size-selected
particles/s with very narrow size distribution. Details of the
1
4,15
experimental setup have been reported elsewhere,
but it
is composed of a low pressure microwave plasma reactor for
The geometry of the PMS is optimized to measure par-
ticles in the size range of 2 to 15 nm. According to Fuchs’
1
7
a͒Author to whom correspondence should be addressed; electronic mail:
equation, the probability to synthesize single charged par-
ticle is 32% in case of particles with a diameter of 15 nm,
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Hitzbleck, Klemens
