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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/226334416
Copper and Copper Oxide NanoparticleFormation by Chemical Vapor Nucleation From
Copper (II) Acetylacetonate
ARTICLE in JOURNAL OF NANOPARTICLE RESEARCH · NOVEMBER 2001
Impact Factor: 2.18 · DOI: 10.1023/A:1012508407420
CITATIONS
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213
5 AUTHORS, INCLUDING:
Albert G Nasibulin
Skolkovo Institute of Science and Technology
241 PUBLICATIONS 3,991 CITATIONS
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Igor Altman
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letting you access and read them immediately.
Available from: Albert G Nasibulin
Retrieved on: 06 March 2016
https://www.researchgate.net/?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_1https://www.researchgate.net/profile/Igor_Altman?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_7https://www.researchgate.net/profile/Igor_Altman?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_5https://www.researchgate.net/profile/Igor_Altman?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_4https://www.researchgate.net/profile/Albert_Nasibulin?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_7https://www.researchgate.net/institution/Skolkovo_Institute_of_Science_and_Technology?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_6https://www.researchgate.net/profile/Albert_Nasibulin?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_5https://www.researchgate.net/profile/Albert_Nasibulin?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_4https://www.researchgate.net/?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_1https://www.researchgate.net/publication/226334416_Copper_and_Copper_Oxide_Nanoparticle_Formation_by_Chemical_Vapor_Nucleation_From_Copper_II_Acetylacetonate?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_3https://www.researchgate.net/publication/226334416_Copper_and_Copper_Oxide_Nanoparticle_Formation_by_Chemical_Vapor_Nucleation_From_Copper_II_Acetylacetonate?enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2&el=1_x_2
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Journal of Nanoparticle Research 3: 385–400, 2001.© 2001 Kluwer Academic Publishers. Printed in the Netherlands .
Copper and copper oxide nanoparticle formation by chemical vapornucleation from copper (II) acetylacetonate
Albert G. Nasibulin1, P. Petri Ahonen1, Olivier Richard1, Esko I. Kauppinen1,∗ and Igor S. Altman21VTT Chemical Technology, Aerosol Technology Group, P.O. Box 1401, FIN-02044 VTT, Finland;2 Institute of Combustion & Advanced Technologies, Odessa National University, Dvoryanskaya 2,
Odessa, 65026, Ukraine; ∗ Author for correspondence (Tel.:+358 9 456 6165; Fax:+358 9 456 7021; E-mail: [email protected])
Received 22 January 2001; accepted in revised form 20 June 2001
Key words: Cu, Cu2O, nanoparticle, copper acetylacetonate, thermal vapor decomposition, chemical nucleation
Abstract
Crystalline nanometer-size copper and copper (I) oxide particle formation was studied by thermal decomposition of
copper acetylacetonate Cu(acac)2 vapor using a vertical flow reactor at ambient nitrogen pressure. The experiments
were performed in the precursor vapor pressure range of P prec = 0.06 to 44 Pa at furnace temperatures of 431.5◦C,596.0◦C, and 705.0◦C. Agglomerates of primary particles were formed at P prec > 0.1 Pa at all temperatures. At431.5◦C the number mean size of the primary particles increased from Dp = 3.7 nm (with geometric standarddeviation σ g
=1.42) to Dp
=7.2 nm (σ g
=1.33) with the increasing precursor vapor particle pressure from 1.8 to
16 Pa. At 705.0◦C the primary particle size decreased from Dp = 24.0 nm (σ g = 1.57) to Dp = 7.6 nm (σ g = 1.54),respectively.
At furnace temperatures of 431.5◦C and 596.0◦C only crystalline copper particles were produced. At 705.0◦C thecrystalline product of the decomposition depended on the precursor vapor pressure: copper particles were formed
at P prec > 10 Pa, copper (I) oxide at P prec ≤ 1 Pa, and a mixture of the metal and its oxide at intermediate vaporpressures. A kinetic restriction on copper particle growth was shown, which leads to the main role of Cu 2 molecule
participation in the particle formation. The formation of copper (I) oxide particles occurs due to the surface reaction
of the decomposition products (mainly carbon dioxide). For the explanation of the experimental results, a model is
proposed to build a semiempirical phase diagram of the precursor decomposition products.
Introduction
Copper and copper oxide particles are of significanttechnological interest. Applications for copper pow-
der include bronze self-lubricating bearings, conduc-
tive epoxys, metal-bonded abrasive wheels and cutting
tools, and braking systems. Ultra-fine copper particles
are a base for developing technologies such as metal
injection molding as well as for electronics, ceram-
ics and for thick/thin-film applications. Copper oxides
have applications in thin-film oxygen pressure sensors,
as a binder in pastes for thick-film microelectronic
circuits, as a p-type semiconductor and they exhibit
luminescence (Majumdar et al., 1996; Holzschuh &
Suhr, 1990).The importance of producing copper and copper
oxide particles is exemplified by applications such as
high surface area catalysts that are used in diverse
chemical processes, for example, the water-gas shift
reaction (Campbell et al., 1987), the butanol dehydro-
genation reaction (Shiau & Tsai, 1997) and the car-
bon monoxide oxidation (Van der Meijden, 1981; Du
et al., 1997). Copper-based catalysts are used as a key
intermediate in the industrial synthesis of methanol
https://www.researchgate.net/publication/223211557_CuZnO0001_and_ZnOxCu111_Model_catalysts_for_methanol_synthesis?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/223211557_CuZnO0001_and_ZnOxCu111_Model_catalysts_for_methanol_synthesis?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2
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(Klier, 1982; Campbell et al., 1987; Yurieva et al.,
1993; Klenov et al., 1998), which is promising as
an environmentally friendly fuel for the power indus-
try. In addition, copper and copper-based materials
have applications as catalysts in traditional and new
organic syntheses, for example, the condensation of
aromatic halides, known as Ullmann reaction (Dhas
et al., 1998), synthesis of cyclic amines from amino-
alcohols and their alkyl derivatives (Hammerschmidt
et al., 1986; Kijenski et al., 1989), synthesis of methy-
lamines (Gredig et al., 1997), thermal cracking of plas-
tics and many others (Kijenski et al., 1984; Runeberg
et al., 1985; Vultier et al., 1987; Pereia et al., 1994;
Shannon et al., 1996). Copper has been also identi-
fied as a good catalyst for the combustion of methane
(Tijburg, 1989) and selective oxidation of hydrocar-
bons (Adams & Jennings, 1964; Voge & Adams,
1967).
Thus, studies of the formation of copper and cop-
per oxide particles are important. Accordingly, it has
been a subject of much research during thelast decades.
Copper and copper oxide particle formation have
been studied by solution reaction: reduction of cop-
per (II) acetate in ethanol (Ayaappan et al., 1997)
and in water and 2-ethoxyethanol using hydrazine
(Huang et al., 1997), the reaction of copper (II)
chloride with organolithium compounds (Takahashi
et al., 1988), reduction of copper dodecylsulfate bysodium borohydrate (Lisieski et al., 1996), by using
reverse micelles (Lisieski & Pileni, 1993; 1995),
thermal and sonochemical reductions of copper (II)
hydrazine carboxylate (Dhas et al., 1998), chem-
ical deposition in two-phase system octane–water
(Vorobyova et al., 1997), by means of electrolysis
(Folmanis & Uglov, 1991; Kirchheim et al., 1991;
Pietrikova & Kapusanska, 1991) and others (Herley
et al., 1989). Ding et al. (1996) prepared copper
nanoparticles by a mechanochemical process and
studied the influence of milling conditions on par-
ticle structure and size. Nanocrystalline copper was
prepared by consolidation of mechanically milledpowder by Weins et al. (1997). Copper oxide for-
mation was studied via oxidation of copper par-
ticles (Kaito et al., 1973; 1993; Kellerson et al.,
1995).
Much work has been devoted to the investigation of
aerosol formation of copper or its oxide particles by
physical methods, including molecular beams (Bowles
et al., 1981), direct laser vaporization (Moini andEyler,
1988), by using gas evaporation (Kashu et al., 1974;
Peoples et al., 1988; Xu et al., 1992), sputtering
(Haas & Birringer, 1992), melting in a cryogenic
liquid (Champion & Bigot, 1996) and others (Long
& Petford-Long, 1986; Girardin & Maurer, 1990;
Bouland et al., 1992).Another anda very attractive way
to obtain aerosol particles is via the chemical route.
This method might be the least expensive for aerosol
particle formation under controlled conditions. Little
work has been devoted to copper and its oxide for-
mation by chemical vapor nucleation. Majumdar et al.
(1996) generated CuO powder by spray-pyrolysis from
Cu(NO3)2 solution. Daroczi et al. (1998) studied the
production of copper and iron nanocomposites by ther-
mal decomposition of copper–ferrocyanide in an open
vertical tube. The obvious advantage of the chemical
vapor nucleation method is the possibility to produce
nanosized particles at relatively low temperatures and
ambient pressure.
The current work is devoted to the investigation
of copper and copper oxide particle formation from
metal–organic compound, copper (II) acetylacetonate
(Cu(acac)2). A suitable equilibrium vapor pressure
(P = 13.1Pa at t = 150.0◦C) and a convenientdecomposition temperature (t dec = 286◦C) were thereasons for the choice of this precursor. The selection
of this metal–organic substance was also based on its
popularity as a precursor for chemical vapor deposi-
tion processes (e.g., Pelletier et al., 1991; Pauleau &Fasasi, 1991; Gerfin et al., 1993; Marzouk et al., 1994;
Hammadi et al., 1995; Maruyama & Shirai, 1995) and
on the knowledge of decomposition reaction kinetics
(Tsyganova et al., 1992). The goals of the investigation
are to produce copper and/or copper oxide nanoparti-
cles at ambient pressure and at a temperature as low
as possible, to characterize the obtained nanoparticles
synthesized with various reactor conditions, and to
discuss nanoparticle formation based on experimental
results.
Experimental
Materials
For this study copper (II) acetylacetonate, Cu(acac)2,
(Aldrich Chemical Company, 97%) has been used as
a precursor. The decomposition of Cu(acac)2 vapor
leads to the formation of copper vapor that is supersat-
urated at the experimental conditions. The Cu(acac)2
https://www.researchgate.net/publication/231678344_Synthesis_Characterization_and_Nonlinear_Optical_Properties_of_Copper_Nanoparticles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231655678_Control_of_the_Shape_and_the_Size_of_Copper_Metallic_Particles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231435324_Synthesis_of_Copper_Metallic_Clusters_Using_Reverse_Micelles_as_Microreactors?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/248543000_Low-frequency_internal_friction_studies_of_nanocrystalline_copper?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/250337194_Production_of_Fe_and_Cu_Nanocrystalline_Particles_by_Thermal_Decomposition_of_Ferr-_and_Copper-Cyanides?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231435324_Synthesis_of_Copper_Metallic_Clusters_Using_Reverse_Micelles_as_Microreactors?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231678344_Synthesis_Characterization_and_Nonlinear_Optical_Properties_of_Copper_Nanoparticles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/231655678_Control_of_the_Shape_and_the_Size_of_Copper_Metallic_Particles?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/248543000_Low-frequency_internal_friction_studies_of_nanocrystalline_copper?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/250337194_Production_of_Fe_and_Cu_Nanocrystalline_Particles_by_Thermal_Decomposition_of_Ferr-_and_Copper-Cyanides?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2
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decomposition reaction can be presented as
CH3
HC Cu CH
CH3 CH3
CH3
O O
O O ∆T
38.0
Cu+CuO+H2C CH2(CO)
36.0 22.3
O
+ CO2 + H3C C CH3
3.2 0.3
O
+ H2O + H3C C C2H5, (1)
where numbers below the decomposition reaction
products indicate molar percentage fraction of thegaseous reaction products which were measured using
mass-spectrometry analysis by Tsyganova et al. (1992).
Such reaction products indicate significant destruc-
tion of the ligand, acetylacetone, which is possibly
formed on the initial stage of the thermal decomposi-
tion. The Cu(acac)2 vapor decomposition was studied
using the manometric method in static conditions in
clear ampoules at 290–335◦C and at initial pressures of 98–173 hPa (Tsyganova et al., 1992).
In our study two sources of nitrogen (AGA,
99.9 vol.% and 99.999 vol.%) have been used as a
carrier gases. Inert nitrogen was used in order to pre-
vent the additional reoxidation of the formed cop-
per vapor by atmospheric oxygen. The compaction of
Cu(acac)2 powder in a saturatorand hence,blockingthe
flow were prevented by mixing the powder with inert
chromatographic carrier, silicon dioxide, SiO2 (Balzers
Materials, 99.9%) with a grain size of 0.2–0.7 mm.
Experimental methods
A vertical laminar flow reactor for experimental inves-
tigation of Cu(acac)2 decomposition under controlled
conditions was designed and constructed (Figure 1).
The experimental device consistedof a saturator,a lam-inator, and a furnace. The saturator and the lamina-
tor consisted of a stainless steel tube with an internal
diameter of 22 mm. A removable cartridge, to hold the
mixture of Cu(acac)2 powder and the chromatographic
carrier, was inserted inside the tube. An absolute filter
(Munktell, MK 360) was used to clean the vapor–gas
flow downstream of the saturator. The saturation mix-
ture and the filter were retained on a stainless steel net.
In order to laminarize the flow and to avoid turbulence
of the flow proceeding from small diameter to large
one after the saturator a laminator has been used. It was
constructed as a cylindrical cone in the junction part.
Between the laminator and the furnace, a Teflon ther-
moinsulator was used. A ceramic tube, with external
and internal diameters of 28 and 22 mm, respectively,
inserted inside the furnace (Entech, Sweden) has been
used as a reactor.
The flow of pure filtered nitrogen carrier gas was
supplied from a high-pressure cylinder to the satura-
tor. Then the gas passed through the heated Cu(acac) 2powder and the vapor saturation by the precursor was
reached. Inside the laminator, a steady state lami-
nar flow was established. Then the vapor–gas mix-
ture entered to the furnace where the temperature
is maintained higher than the Cu(acac)2 decompo-
sition temperature. The formation of supersaturated
copper vapor, as a result of the precursor decomposi-
tion reaction, led to the nucleation process and further
growth of particles via condensation, coalescence, and
agglomeration processes.
The flow rate of the gas-carrier was measured by
a flow meter (DC-2, BIOS) and was referred to the
standard condition (t = 25◦C, P = 101325 Pa).Temperatures were measured by nichrome–nickelther-
mocouples (K-type) which had been calibrated with an
accuracy of 0.1◦C by using an oil bath and thermoresis-
tors calibrated against the Finnish National Standard.The aerosol number size distributions in the range of
3–200 nm were measured by a differential mobility
analyzer (DMA) system consisting of a charger, a clas-
sifier (Winklmayr et al., 1991, modified Hauke, length
of 11 cm), a condensation particle counter (CPC, TSI
3027), and a supporting software. A sheath flow rate
for DMA system was maintained at Qsh = 14.5 lpm.The morphology, the primary particle size, and the
crystallinity of the particles were investigated with
a field emission scanning electron microscope (Leo
Gemini DSM982) and a field emission transmission
electron microscope (Philips CM200 FEG), respec-
tively. An electrostatic precipitator (Combination elec-trostatic precipitator, InTox Products, Albuquerque,
NM, USA) was used to collect the aerosol particles
on a carbon-coated copper grid (SPI Holey Carbon
Grid). Electron diffraction patterns of the particles
were used for determination of the crystalline phase.
The samples for X-ray diffraction (XRD, Philips MPD
1880 powder X-ray diffractometer) spectrometry were
collected on silver filter disks (Millpore AG4502500,
45 µ m pore) and studied with Cu Kα (λ = 0.154 nm)
https://www.researchgate.net/publication/222309681_A_New_Electromobility_Spectrometer_for_the_Measurement_of_Aerosol_Size_Distribution_in_the_Size_Range_From_1_to_1000?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/222309681_A_New_Electromobility_Spectrometer_for_the_Measurement_of_Aerosol_Size_Distribution_in_the_Size_Range_From_1_to_1000?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2
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Figure 1. Schematic presentation of the experimental setup.
radiation. A Mettler Toledo TA8000 system equipped
with TGA850 thermobalance was used for thermo-
gravimetric analysis (TGA) of the samples under
flowing nitrogen atmosphere with the heating rate of
10◦C/min for sample sizes of approximately 3 mg.Inside the reactor a known temperature gradient
was maintained, which gives the possibility to deter-
mine the location where the decomposition of the pre-
cursor occurs. Tsyganova et al. (1992) reported that
the Cu(acac)2 vapor decomposition was a first-order
rate reaction. The rate constant of this reaction can
be calculated by using the Arrhenius equation k =k0 exp (−Ea/RT), where the pre-exponential factor isk0 = 3.02×107 s−1, the activation energy is Ea =115.4 kJ/mole, andR is the universal gas constant. It is
obvious that most of the copper acetylacetonate vapor
thermolysis occurs in the vicinity of the highest tem-
perature zone in the furnace. In Figure 2 the depen-
dence of temperature and the rate constant of Cu(acac)2decomposition reaction inside the reactor are shown.
On the basis of data presented in Figure 2, the decom-
position of the metal–organic precursor occurs at loca-
tion x = 255 ± 12 mm, and at the temperature of t = 431.5± 0.5◦C.
Determination of Cu(acac)2vapor concentration
It is known that the vaporization rate of the solid
precursor changes with time due to decreasing sur-
face area of the powder (Chou & Tsai, 1994;
https://www.researchgate.net/publication/256362839_Dynamic_evaporation_behaviour_of_diketonate_compounds_of_yttrium_copper_and_barium?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2https://www.researchgate.net/publication/256362839_Dynamic_evaporation_behaviour_of_diketonate_compounds_of_yttrium_copper_and_barium?el=1_x_8&enrichId=rgreq-bf4c1784-6c58-4384-a595-ed7c6d8c135e&enrichSource=Y292ZXJQYWdlOzIyNjMzNDQxNjtBUzo5NzAzNTkxMDkwOTk1NkAxNDAwMTQ2NTcyNDI2
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Figure 2. The dependence of temperature and the rate constant of Cu(acac)2 decomposition reaction inside the reactor.
Figure 3. The dependence of the evaporation rate at different conditions.
Kodas & Hampden-Smith, 1999). Certainly, the vapor
pressure of the precursor is a crucial factor in the
decomposition reaction. It can be a reason for the irre-
producibility of the experimental results and, as it will
be found out later, it is even the reason for a change of
decomposition reaction products. Therefore, studies of
gas flow saturation by Cu(acac)2 vapor are necessary.
The usage of the removable cartridge (Figure 1)
allows determining of the saturation degree of the car-
rier gas flow by Cu(acac)2 vapor. If the flow rate of
the gas and the mass difference of the cartridge with
Cu(acac)2 powder in a certain time interval are known,
it is possible to calculatethe evaporationrate andhence,
the vapor pressure of the metal–organic compound at
the entrance of the reactor. From Figure 3 it can be seen
that the evaporation rate decreases with experimental
time. The gas saturation by Cu(acac)2 vapor decreases
very rapidly at a saturatortemperatureof t sat = 190.0◦Cand at a flow rate of Q = 2000 cm3 /min. Because of high gas velocity, the saturation time is too short to heat
the carrier gas in the upper part of the saturator. The
observation of saturator mixture color showed that the
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precursor was consumed in the lower part where gas
temperature reached the saturator temperature. At the
flow rate of Q = 330 cm3 /min and at t sat = 170◦C,the evaporation decreases less rapidly and depends on
the decrease of the powder surface area. Decreasing
the saturator temperature down to 150◦C leads to thesignificant decrease of the evaporation rate dependence
on time. Four days of continuous operation using the
flow rate of Q = 330 cm3 /min revealed that a signif-icant change in the results (concentration and number
size distribution of agglomerated particles) was found
only after the first 24 h period.
The effect of the composition of the copper acety-
lacetonate and silicon dioxide mixture on the evapora-
tion rate was also investigated. Variation of the mass
ratio of Cu(acac)2 and SiO2 from 1:3 to 1:150 did
not significantly affect on the precursor vapor pres-
sure at the entrance to the reactor. The influence of
using a small precursor fraction (1 : 150 relation) was
found only after about 7 h because of the exhaustion
of Cu(acac)2 material, while duration of an experi-
ment was only about 30–40 min. During the follow-
ing experiments only newly prepared powder mixtures
consistingof 4 g (1.53×10−2 mole) of copper(II) acety-lacetonate and 16 g (0.27 mole) of silicon dioxide have
been used as the saturator mixture.
The dependence of vapor pressure, as determined
from the cartridge mass difference, on the satura-tor temperature at Q = 330 cm3 /min is presented inFigure 4. Also, a fitted curve and literature data of
Figure 4. The dependence of the precursor vapor pressure on the saturator temperature.
Cu(acac)2 equilibrium vapor pressure (Teghil et al.,
1981; Tonneau et al., 1995) are shown. From the figure,
a difference between the literature data and our results
can be seen. It is necessary to note that the measured
saturator temperature does not coincide with the pow-
der temperature inside the saturator and has been used
only as a reference temperatureduring the experiments.
The main crucial experimental parameter is the pre-
cursor concentration, which has been determined after
each experiment. Thus, during our experiments, well-
controlled parameters of the setup regarding the con-
tents of vapor–gas phase have been maintained.
Results and discussion
Experimental results
Experiments on particle formation were carried out at
two fixed temperature profiles inside the furnace. One
of these profiles is shown in Figure 2. Experiments
were also performed with a similar temperature profile
with a temperature maximum at t = 705.0 ± 0.5◦C,where this condition was valid at x = 255 ± 15 mm.In the following section, we refer to those temperature
profiles as 431.5◦C and 705.0◦C.First, experiments on the influence of residence
time (flow rate) on particle number size distribu-tions were carried out. At the furnace temperature of
t furn = 431.5◦C, at flow rates higher than 400 cm3 /min,
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Figure 5. Number particle size distributions at the different flow rates.
a bimodal particle size distribution was measured
(Figure 5). SEM and TEM micrographs showed two
kindsof particles – smallagglomerated copper particles
and needle-like particles of Cu(acac)2. Thus, the mode
with the smaller mean size is connected to copper par-
ticle formation and the second one is due to nucleationof undecomposed Cu(acac)2 vapors downstream of the
furnace. The variation of the flow rates at the furnace
temperature of 705.0◦C showed that the optimum flowratewasabout330 cm3 /min. The choice of this flow rate
was determined by the concentration range of the con-
densation particle counter (1–105 particles/cm3)andby
reasonable time of a sample collection for XRD anal-
ysis. Hereafter, only experimental results obtained at
the flow rate of Q = 330 cm3 /min are presented.TEM micrographs of the nanoparticles synthesized
at reactor temperature of 431.5◦C and at the precur-sor vapor pressures of P prec
= 1.8 and P prec
= 16Pa
are presented in Figure 6. As one can see, the primaryaerosol particles are fairly monodisperse and the size
of the particles increases with increasing saturator tem-
perature. In the same figure, the electron diffraction
patterns of the agglomerated particles are presented.
The electron diffraction ring pattern simulations per-
formed for copper fits with the experimental results.
These results have been confirmed by XRD analysis.
TGAshowed that at thefurnace temperature of 431.5◦Cthe decomposition of the precursor was not complete.
At the furnace temperature of 431.5◦C only 20% of Cu(acac)2 was thermolyzed. The remaining undecom-
posed Cu(acac)2 forms a layer around copper particles
that can be seen on the TEM images (Figure 6). It is
worth noting that the electron diffraction ring pattern
enclosed in Figure 6(a) is not so clear as the othersdue to the large amount of amorphous unreacted pre-
cursor. Microdiffraction patterns for this experimental
condition have been also performed in order to deter-
mine unambiguously that the particles presented in
Figure 6(a) are crystalline copper.
TEM results for the nanoparticles synthesized
at 705.0◦C and at the precursor vapor pressures of P prec = 1.8 and P prec = 16 Pa are presented in Figure 7.With these conditions, the size of the primary par-
ticles decreases with increasing the vapor pressure
of the precursor, that is, there is an inverse situation
compared to the preceding samples synthesized at
the furnace temperature of t furn = 431.5◦C. Electrondiffraction patterns of the agglomerated particles pro-
duced at the furnace temperature of t furn = 705.0◦Cindicate the presence of crystalline copper particles
at the vapor pressure of P prec = 16 Pa and copperoxide (Cu2O, cuprite) particles at the vapor pressure
of P prec = 1.8 Pa. In Figure 8 XRD diffractograms of the particles collected on a silver filter are shown. The
variation of the crystalline phase with changing the
precursor vapor pressure can be seen. At the vapor
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Figure 6 . Transmissionelectron microscopyimages and electron
diffraction patterns of particles produced at the precursor vapor
pressure of P prec = 1.8 Pa (a) and P prec = 16 Pa (b). The furnacetemperature is 431.5◦C.
pressure of P prec = 1.8 Pa and P prec = 6 Pa, a mixtureof crystalline copper and copper (I) oxide particles
was synthesized and at higher saturator temperatures
only copper particles were formed.
The additional experiments of XRD phase identi-
fication were carried out at the intermediate furnace
temperature of t furn = 596.0◦C. At the precursor vaporpressures of P prec = 6 and 44 Pa only copper crystallineproduct was found.
The effect of the experimental conditions on product
compositions is presented in Table 1. As one can see
from Table 1, the dependence of the decomposition
Figure 7 . Transmissionelectron microscopyimages and electron
diffraction patterns of particles produced at the precursor vapor
pressure of P prec = 1.8 Pa (a) and P prec = 16 Pa (b). The furnacetemperature is 705.0◦C.
product on theprecursor vaporpressureis revealed only
at highest experimental temperature of t furn =705.0◦C.
The possible reasons of this phenomenon are examined
in the discussion part of the article.
In an attempt to reduce agglomeration, the aerosol
flow was diluted by excess nitrogen flow immedi-
ately downstream of the furnace. The particle num-
ber size distribution was not significantly changed,
indicating that agglomeration of the particles occurred
inside the furnace. Another way to avoid the for-
mation of the agglomerated particles is to decrease
the number concentration of the primary particles by
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Figure 8. XRD spectra of particles synthesized at the furnace temperature of 705.0◦C and collected on the silver filter.
Table 1. List of experimental conditions, corresponding
crystalline product compositions, and methods used for the
phase identification
Furnace Vapor pressure Crystalline Method
temperature, ◦C of precursor, Pa products
431.5 0.15–44 Cu XRD, ED
596.0 6–44 Cu XRD
705.0 0.06–1.0 Cu2O ED
705.0 1.8–10 Cu/Cu2O XRD, ED
705.0 16–44 Cu XRD, ED
decreasing the Cu(acac)2 vapor pressure. In Figure 9
and Figure 10 the number size distribution of the
produced particles at different saturator temperatures
of t furn = 431.5◦C and t furn = 705.0◦C are presented. Itis known that the area limited by the curve determines
the particle number concentration. At t furn = 431.5◦Cthe concentration grows smoothly when the satura-
tor temperature increases, but at t furn = 705.0◦C the
change of the concentration is not smooth. This is
probably in connection with the formation of different
decomposition products.
At precursor vapor pressures below 0.1 Pa, single
crystalline individual particles are formed, the forma-
tion of agglomerated particles is observed at higher
vapor pressures. In Figure 11, TEM micrograph of
copper (I) oxide nanoparticle that was produced at
the furnace temperature of 705.0◦C and at the vaporpressure of P prec = 0.04 Pa is presented. This high
resolution picture shows the possibility to produce
single crystalline individual nanoparticles.
Discussion
The size distribution of primary particles obtained
from TEM micrographs is presented in Figure 12. At
431.5◦C the number mean size of the primary particlesis increased from Dp = 3.7 (with geometric standarddeviation of σ g = 1.42) to Dp = 7.2nm (σ g = 1.33)with increasing precursor vapor pressure from 1.8 to
16 Pa. At t furn = 705.0◦C, the primary particle sizeis decreased from Dp = 24.0 n m (σ g = 1.57) toDp = 7.6 nm (σ g = 1.54), respectively. At the fur-nace temperature of t furn = 431.5◦C, increasing thevapor pressure increased the size of the primary par-
ticles, but at t furn = 705.0◦C an inverse situation wasobserved. Apparently, it is connected with the dif-
ferent products of the precursor decomposition. The
diameter of the primary copper (I) oxide particles
(t furn = 705.0◦C, P prec = 1.8 Pa) is about three timeslarger than that of the copper particles (t furn = 705.0◦C,P prec = 16 Pa). The qualitative explanation of the pri-mary size dependence on the crystalline products can
be obtained from the consideration of physical proper-
ties of these compounds. It is known that the sintering
rate, which controls the size of primary particles,
is dependent on the self-diffusion coefficient of the
elements contained in the substance: with the larger
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Figure 9. Number size distributions of agglomerated particles at the furnace temperature of t furn = 431.5◦C.
Figure 10. Number size distributions of agglomerated particles at the furnace temperature of t furn = 705.0◦C.
coefficient the sintering rate is enhanced and the size
of primary particles becomes larger. According to the
literature data (Smithells & Brandes, 1983; Kofstad,
1972), the self-diffusion coefficients of copper atoms
are 1.9×10−12 cm2 /s in pure crystalline copper and1.5×10−10 cm2 /s in crystalline copper (I) oxide attemperature t = 705◦C. The almost two orders of magnitude of difference in the diffusion coefficients
is most likely the reason for the formation of such a
different size of copper and copper (I) oxide primary
particles.
As it was found, the product of the decomposition
reaction depended on the precursor vapor pressure only
at t furn = 705.0◦C: copper particles were formed atthe higher vapor pressures (P prec > 10 Pa), copper (I)
oxide particles at the pressures of P prec < 1 Pa, and a
mixture of Cu and Cu2O was formed at the interme-
diate vapor pressures. At the furnace temperatures of
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431.5◦C and 596◦C, only copper particles were formed(Table 1). At the first glance, the revealed dependence
of oxygen content in particles upon the precursor pres-
sure seems to be anomalous. Indeed the formation of
Figure 11. High resolution transmission electron micrograph of
Cu2O particle produced at the furnace temperature of 705.0 ◦Cand at the vapor pressure of P prec = 0.04 Pa.
Figure 12. Particle number size distributions of primary particles.
primary particles can be presented by two sequential
steps. At the first stage, small clusters are formed by
means of homogeneous nucleation process, and sec-
ondly, the particles grow because of a coalescence of
the clusters and vapor condensation on the particles.
Increasing the precursor pressure leads to the increase
of the oxygen-containing gas pressure in the system
and its participation in these two stages. The presence
of oxygen in the particles with increasing the precur-
sor pressure at least cannot vanish. Let us demonstrate
that this prima facie consideration is incorrect for the
explanation of the experimental results.
A few possible reasons for the change of decom-
position products were examined. The first reason
could be the presence of impurities in the carrier
gas. The appearance of the copper (I) oxide in the
crystalline products occurs at the precursor vapor
pressure of 10 Pa, which corresponds to a concen-
tration of 2.6×1015 molecules/cm3. Meanwhile, themaximum concentration of admixtures in the nitrogen
carrier gas sample is about 2.5×1016 molecules/cm3,that is, the concentration of the main component in
the reaction is of the same order or less than the
impurity concentration. In order to check this hypoth-
esis, the nitrogen gas cylinder was changed to a
liquid nitrogen tank to obtain ultra-pure carrier gas
(99.999 vol.% with maximum oxygen concentration
of 8.1×1013
molecules/cm3
). Decreasing the content of admixtures by two orders of magnitude did not change
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the product of the Cu(acac)2 decomposition. Moreover,
the results by Tonneau et al. (1995) and Hammadi et al.
(1995) on chemical vapor deposition are also contrary
to this assumption. They showed that when the vapor
mole fractions of oxygen and Cu(acac)2 were about
the same, only crystalline copper was formed. Accord-
ingly, the presence of impurities in the gas-carrier is
not likely to be the reason for the different products of
the reaction.
Another possible reason is connected with the kinet-
ics of the decomposition. It is well known that chang-
ing the gas phase concentration of the reactant can
lead to the change of the decomposition mechanism
(Kondrat’ev, 1964). For example, at lower precur-
sor concentrations a unimolecular decomposition can
occur and as a result of the decomposition Cu 2O is
formed. Increasing the vapor pressure leads to the
increase in the probability of collisions of two or more
molecules during the Cu(acac)2 thermolysis reaction,
which leads to the decomposition product of pure
copper. However, in order to form Cu2O molecule
it is necessary to have two precursor molecules, but
for copper formation only one precursor molecule
is needed. Thus, this explanation is correct for the
inverse behavior. Moreover, it is hard to believe that
switching the mechanism from a unimolecular to a col-
lision reaction can occur in a such small vapor pres-
sure range. Therefore, the explanation of switching thedecomposition mechanism does not seem to be justi-
fied for the elucidation of the variation of the reaction
products.
Also, a possible reason of the condensed product
variation may be related to the kinetics of particle
formation. Then the explanation of the phenomena is
possible only in the case of any second-order reac-
tion. Indeed, the ratio of partial pressures of all species
formed in the first-order reactions is the same at all pre-
cursor pressures. Thereby, the relative role of different
gaseous species in the condensed particle growth can-
not depend on the precursor pressure. The possible rea-
son for the crystalline product change is the existenceof a secondary reaction. We assume that this reaction
is a formation of copper dimers that are quite stable at
the experimental conditions (Petrov, 1986):
2Cu(g)⇔ Cu2(g). (2)
In order to explain the revealed transition between the
crystalline products let us consider the mechanism of
the formation of different condensed substances from
gas phase in detail.
It is worth noting that there is a restriction prohibit-
ing the growth of copper particles from gas via single
Cu atom adsorption on thecluster surface. Thephysical
fundamentals of such restrictions for different mate-
rials are discussed by Altman et al. (2001). They are
based on the mechanism of energy transfer during a
phase transition. The energy release during Cu atom
condensation is about 3.5 eV, and this energy has to
be dissipated directly during the adsorption. There are
two possible ways for this process: an electron exci-
tation and a phonon creation. Since this energy value
is large compared to a typical Debye energy value
(0.05 eV), only the electron excitation for energy dis-
sipation is left. However, the energy band structure of
copper contains the sp-band gap (Knoesel et al., 1998).
The value of the sp-band gap energy at the experimen-
tal conditions is about 4.6–4.7 eV. The existence of this
gap leads to impossibility of the direct energy dissi-
pation from an adsorbing copper atom and to a pro-
hibition of the atom condensation as a consequence.
The energy release for Cu2 molecule condensation is
about 5 eV, which is larger than the copper energy
gap. Therefore, this process becomes feasible and the
growth of the particles is made possible by conden-
sation of Cu2 molecules. Then the reason of the crys-
talline product change can be understood. Indeed, due
to the second-order reaction (2), the Cu2 partial pres-
sure increases with the precursor pressure as its secondpower instead of all other gas partial pressures. Thus,
since the condensation of Cu2 molecules determines
the copper particle formation, the relative role of this
process increases with increasing precursor pressure
faster when compared to other processes.
The secondquestionto be discussedis thepossibility
of copper (I) oxide formation. Because of low reagent
concentration, the variety of possible pathways can be
limited by bimolecular reactions. In this case, the only
way of copper (I) oxide formation is the reaction on the
surface of a growing oxide particle:
Cu2 + CO2 ⇔ Cu2O(s)+ CO. (3)It is obvious that this reaction should be activated.
Let us propose the physical model of the transition.
The formation of copper (I) oxide particle occurs if the
flux of CO2 molecules (with an energy larger than the
barrier Eo) j CO2 on a particle surface is larger than
the flux of Cu2 molecules j Cu2 , in the opposite case
copper particle formation occurs. Thereby, transition
between the two products might occur due to the vari-
ation of these two fluxes. At a given temperature of T
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the fluxes may be defined as
j Cu2 =P Cu2
2πmCu2kBT ,
j CO2
= P CO2 2πmCO2kBT
exp
− EokBT
,
(4)
where mCu2 and mCO2 are masses of Cu2 and CO2molecules, respectively, and kB is Boltzmann’s con-
stant. It is obvious that the copper particle growth
leads to the exhaustion of the copper vapor and to the
decrease of relative value of j Cu2 flow. The initial ratio
of j Cu2 and j CO2 flows is more than unity (in case of
pure copper formation), but at the end of the precursor
decomposition this ratio becomes smaller (in case of copper (I) oxide formation). That is why there is a tran-
sition region instead of the sharp border between the
different crystalline products. The absence of copper (I)
oxide (atP prec > 10 Pa) most likely means that the ratio
of amount of the oxide to pure copper is less than the
relative sensitivity f of XRD phase identification. In
this case, at the precursor pressure of P prec = 16 Pa, thecopper (I) oxide particles are formed only at the end of
the precursor decomposition, where the j Cu2 / j CO2 flux
ratio becomes smaller than unity due to the exhaustion
of copper vapor and an accumulation of the decompo-
sition products (carbon dioxide). In order to obtain the
characteristic value of the precursor pressure where thetransition between products occurs, let us consider the
final location of the decomposition. The partial pres-
sure of carbon dioxide can be written as
P CO2 = 2P prec, (5)
where the factor 2 is obtained on the basis of
mass-spectrometry results of gaseous decomposition
products (Tsyganova et al., 1992). The copper vapor
pressure at the end of the decomposition, when
copper (I) oxide starts to be formed, can be written by
taking into account the copper exhaustion and phase
identification sensitivity f :
P Cu = fP prec. (6)
The partial vapor pressureP Cu2 canbefoundusingequi-
librium constant Kp of the reaction (2):
P Cu2 = KpP 2Cu. (7)
Combining Eqs. (4)–(7) with the condition j Cu2 =j CO2 , the expression for the boundary precursor
pressure P ∗prec (the transition pressure of Cu2O productidentification) can be written as
KpfP ∗
prec
2√ mCu2
=2P ∗
prec√ mCO2
exp
− EokBT
. (8)
Based on the experimental data of the disappearance
of copper (I) oxide phase (P ∗prec = 16Pa at t furn =
705.0◦C) andthermodynamic data (Kp = 1.84Pa−1),atthe sensitivity of f = 0.01, the value of the energy bar-rier for reaction (3) is Eo = 0.595 eV (57.3 kJ/mole).This value seems to be realistic. Then, it is easy to
show that the boundary pressure of copper (I) oxide
formation with mole fraction of less than 0.01 may be
calculated as
P ∗prec =const
Kpexp
− EokBT
, (9)
where const = 3.4 × 104. The semiempirical temper-ature dependence of the boundary pressure obtained
on the basis of Eq. (9) is presented in Figure 13. The
area on the diagram above the boundary pressure line
is related to the region of the absence of copper oxide
products. As one can see the proposed semiempirical
phase diagram is in agreement with the experimen-
tal results of the current work. The boundary pressure
P ∗prec decreases by decreasing the furnace temperature.That is why at lower temperatures (t furn = 431.5◦C atP prec = 0.06 to 44 Pa and t furn = 596◦C at P prec =16–44 Pa) only pure copper particles in the final prod-
uct of Cu(acac)2 decomposition were obtained. It is
worth noting that the diagram could be useful for the
Figure 13. The phase diagram of Cu(acac)2 decomposition crys-
talline products. Marks ‘’ and ‘’ correspond to the exper-
imentally determined copper and copper (I) oxide products,
respectively.
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Figure 14. The schematic presentation of copper and copper (I)oxide particle formation by the Cu(acac)2 vapor decomposition.
prediction of the product of the precursor vapor decom-
position at other experimental conditions. The pro-
posed approach for the building of the decomposition
product phase diagram can be used for other experi-
mental systems with chemical reactions.
Figure 14 summarizes our viewpoint of the main
stages occurring inside the furnace at 705.0◦C during
the precursor decomposition and copper and copper (I)
oxide particle formation. After the Cu(acac)2 vapor
evaporation and heating the vapor up to a high enough
temperature, the formation of copper vapor anddecom-
position products, as a result of Cu(acac)2 decompo-
sition reaction, occurs inside the furnace. The next
important stage is the formation of gaseous copper
dimers that participate in nucleation and condensa-
tion processes. Formation of copper (I) oxide particles
occurs at low precursor vapor pressures due to the sur-
face reaction of Cu2 vapor and the products of the
decomposition (mainly, carbon dioxide). The last stage
is theagglomeration process of theformedprimary par-
ticles, which exist at the precursor vapor pressure of
P prec ≥
0.1Pa.
Conclusion
For this study, a vertical laminar flow reactor has been
constructed and tested for the investigation of nanopar-
ticle formation via chemical vapor nucleation. It has
been shown that crystalline nanometer-size copper and
copper oxide particles can be produced by thermal
vapor decomposition of a metal–organic precursor,
Cu(acac)2, at relatively low temperatures. Individual
primary particles are formed at the precursor vapor
pressure of P prec < 0.1 Pa. At higher vapor pressures,
particles form aggregates. At t furn = 431.5◦C, the num-ber mean size of the primary particles increased from
Dp = 3.7 nm (with geometric standard deviation of σ g = 1.42) to Dp = 7.2nm (σ g = 1.33) with increas-ing precursor vapor particle pressure from 1.8 to 16 Pa.
At t furn = 705.0◦C, the primary particle size decreasedfrom Dp = 24.0 n m (σ g = 1.57) to Dp = 7.6 nm(σ g = 1.54), respectively.
At the furnace temperaturesof 431.5◦C and 596.0◦C,only crystalline copper particles were produced. At the
furnace temperature of t furn = 705.0◦C, the product of the decomposition reaction depended on the precursor
vapor pressure: copper particles were formed at vapor
pressures higher than 10 Pa, copper (I) oxide at pres-
sures lower than 1 Pa, and a mixture of the metal and
its oxide at intermediate vapor pressures. For the expla-
nation of the obtained results, the kinetic restriction on
copper particle growth was proposed. It leads to the
mainrole ofa Cu2 molecule participation in the particle
formation. The formation of copper (I) oxide particles
occurs due to the surface reaction of the decomposition
products of which carbon dioxide is the most impor-
tant. For the explanation of the experimental results,
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a model is proposed to build a semiempirical phase dia-
gram of the precursor decomposition crystalline prod-
ucts. The phase diagram, showing the boundary of the
appearance of copper (I) oxide, is in agreement with
the experimental results.
Acknowledgements
This work has been supported by TEKES, Finland
and VTT Chemical Technology via the MATRA
research program. Mr. P. Räisanen, Dr. M. Ritala and
Prof. M. Leskelä are gratefully acknowledged for help
during the XRD analyses and Mr. Timo Hatanpää
for carrying out TGA analysis. The authors thank
Dr. J.K. Jokiniemi, Dr. P.V. Pikhitsa, Dr. V. Mikheevand Prof. T. Ward for fruitful discussions and Dr.
D.P. Brown for discussions and proofreading the
manuscript.
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