Neon in carbon nanopores: wetting, growth mechanisms and cluster structures
Low-temperature high-energy (50 keV) electron diffraction study of size-dependent structures and growth mechanisms of neon samples in multiporous «amorphous» carbon films is presented. Electron diffractograms were analyzed on the basis of the assumption that there exists the cluster size distribut...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
2007
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irk-123456789-1217772017-06-17T03:03:07Z Neon in carbon nanopores: wetting, growth mechanisms and cluster structures Krainyukova, N.V. Classical Cryocrystals Low-temperature high-energy (50 keV) electron diffraction study of size-dependent structures and growth mechanisms of neon samples in multiporous «amorphous» carbon films is presented. Electron diffractograms were analyzed on the basis of the assumption that there exists the cluster size distribution in deposits formed in substrate and multi-shell structures such as icosahedra, decahedra, fcc and hcp were probed for different sizes up to approximately 3·10⁴ atoms. The analysis was based on the comparison of precise experimental and calculated diffracted intensities with the help of the R (reliability) — factor minimization procedure. Highly reproducible discrete distribution functions of sizes and structures were found. The time-dependent evolution of diffractograms at earlier stages of growth was revealed. Initially distinct diffraction peaks gradually «disappeared» although the total electron beam absorption evidenced that deposited neon was preserved in the porous substrate. We ascribed this effect to diffusion-like gas penetration from larger to smaller pores which resulted in a highly dispersed or even disordered substance. Evidently, clusters initially grown during deposition were later soaked by a sponge-like substrate due to capillary forces. 2007 Article Neon in carbon nanopores: wetting, growth mechanisms and cluster structures / N.V. Krainyukova // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 747-751. — Бібліогр.: 25 назв. — англ. 0132-6414 PACS: 61.14.–x; 61.46.–w; 67.70.+n; 81.05.Rm; 81.05.Uw http://dspace.nbuv.gov.ua/handle/123456789/121777 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| topic |
Classical Cryocrystals Classical Cryocrystals |
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Classical Cryocrystals Classical Cryocrystals Krainyukova, N.V. Neon in carbon nanopores: wetting, growth mechanisms and cluster structures Физика низких температур |
| description |
Low-temperature high-energy (50 keV) electron diffraction study of size-dependent structures and
growth mechanisms of neon samples in multiporous «amorphous» carbon films is presented. Electron
diffractograms were analyzed on the basis of the assumption that there exists the cluster size distribution in
deposits formed in substrate and multi-shell structures such as icosahedra, decahedra, fcc and hcp were
probed for different sizes up to approximately 3·10⁴ atoms. The analysis was based on the comparison of
precise experimental and calculated diffracted intensities with the help of the R (reliability) — factor
minimization procedure. Highly reproducible discrete distribution functions of sizes and structures were
found. The time-dependent evolution of diffractograms at earlier stages of growth was revealed. Initially
distinct diffraction peaks gradually «disappeared» although the total electron beam absorption evidenced
that deposited neon was preserved in the porous substrate. We ascribed this effect to diffusion-like gas penetration
from larger to smaller pores which resulted in a highly dispersed or even disordered substance. Evidently,
clusters initially grown during deposition were later soaked by a sponge-like substrate due to capillary
forces. |
| format |
Article |
| author |
Krainyukova, N.V. |
| author_facet |
Krainyukova, N.V. |
| author_sort |
Krainyukova, N.V. |
| title |
Neon in carbon nanopores: wetting, growth mechanisms and cluster structures |
| title_short |
Neon in carbon nanopores: wetting, growth mechanisms and cluster structures |
| title_full |
Neon in carbon nanopores: wetting, growth mechanisms and cluster structures |
| title_fullStr |
Neon in carbon nanopores: wetting, growth mechanisms and cluster structures |
| title_full_unstemmed |
Neon in carbon nanopores: wetting, growth mechanisms and cluster structures |
| title_sort |
neon in carbon nanopores: wetting, growth mechanisms and cluster structures |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2007 |
| topic_facet |
Classical Cryocrystals |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121777 |
| citation_txt |
Neon in carbon nanopores: wetting, growth mechanisms
and cluster structures / N.V. Krainyukova // Физика низких температур. — 2007. — Т. 33, № 6-7. — С. 747-751. — Бібліогр.: 25 назв. — англ. |
| series |
Физика низких температур |
| work_keys_str_mv |
AT krainyukovanv neonincarbonnanoporeswettinggrowthmechanismsandclusterstructures |
| first_indexed |
2025-07-08T20:30:29Z |
| last_indexed |
2025-07-08T20:30:29Z |
| _version_ |
1837112103729627136 |
| fulltext |
Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7, p. 747–751
Neon in carbon nanopores: wetting, growth mechanisms
and cluster structures
N.V. Krainyukova
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine
47 Lenin Ave., Kharkov 61103, Ukraine
Email: ninakrai@yahoo.com
krainyukova@ilt.kharkov.ua
Received October 20, 2006
Low-temperature high-energy (50 keV) electron diffraction study of size-dependent structures and
growth mechanisms of neon samples in multiporous «amorphous» carbon films is presented. Electron
diffractograms were analyzed on the basis of the assumption that there exists the cluster size distribution in
deposits formed in substrate and multi-shell structures such as icosahedra, decahedra, fcc and hcp were
probed for different sizes up to approximately 3·10
4
atoms. The analysis was based on the comparison of
precise experimental and calculated diffracted intensities with the help of the R (reliability) — factor
minimization procedure. Highly reproducible discrete distribution functions of sizes and structures were
found. The time-dependent evolution of diffractograms at earlier stages of growth was revealed. Initially
distinct diffraction peaks gradually «disappeared» although the total electron beam absorption evidenced
that deposited neon was preserved in the porous substrate. We ascribed this effect to diffusion-like gas pene-
tration from larger to smaller pores which resulted in a highly dispersed or even disordered substance. Evi-
dently, clusters initially grown during deposition were later soaked by a sponge-like substrate due to capil-
lary forces.
PACS: 61.14.–x Electron diffraction and scattering;
61.46.–w Nanoscale materials;
67.70.+n Films (including physical adsorption);
81.05.Rm Porous materials; granular materials;
81.05.Uw Carbon, diamond, graphite.
Keywords: carbon nanopores, electron diffraction.
Introduction
According to the Stranski–Krastanov growth scheme,
which was expected to be operative for the noble gas clus-
ter formation on a flat substrate [1], an intermediate layer
between the surface and clusters forms first and then no-
ble gas islands grow above. This growth mode owes to the
stronger atomic interaction between noble gas atoms and
the substrate compared to the interaction between adsor-
bate atoms themselves. Although theoretical studies of
relevant growing processes demonstrated a reduced wet-
ting [2] of adsorbate layers and no equilibrium between
the intermediate layer and the islands [3], the electron mi-
croscopy observation [4] of the time delay for the cluster
growth on graphite was ascribed to the intermediate layer
formation.
In the field of nanostructural carbon-based materials
with drastically different structures and properties, which
is rapidly developing during the last two decades, a vari-
ety of growth schemes can be presumed with numerous
opportunities of applications. The so-called schwartzites
[5,6] formed by negatively curved graphitic sheets are
permitted by interconnected channels and can be consid-
ered as a porous matrix, which may be filled with differ-
ent substances under certain conditions. Clusters grown
inside pores obey the growth mechanisms typical of con-
fined geometry and demonstrate the absolute prevalence
of structures with the five-fold symmetry [7–9]. Such
structures were earlier observed in essentially different
experiments [7–21] with the only one common feature,
i.e., the limited number of interacting atoms during growth.
© N.V. Krainyukova, 2007
Experimental details and analysis method
The so-called «amorphous» [5] carbon films filled
with solidified neon by gas deposition onto the substrate
cooled down to liquid helium temperature were studied in
high-energy (50 keV) electron diffraction experiments.
Neon was precooled to a liquid nitrogen temperature be-
fore deposition and was studied at 6 K. During deposi-
tion, carbon films were evacuated from backside inside
the electron diffraction column to facilitate gas penetra-
tion into substrate. The effective thickness � of deposits
characterized the total amount of condensed materials
and the pore filling. All diffraction data were collected in
the form of numerical files.
Porous carbon films were produced from vacuum sub-
limated graphite (by means of the electric current heating
of thin carbon rods of approximately 1 mm or thinner in
diameters, the arc discharge avoided) by deposition onto
a cleaved NaCl single crystal surface. Salt sublayers were
dissolved in water; carbon films were put onto the copper
mesh (with a high-thermal conductivity and transparent
for electrons) by means of the floating of carbon films.
Prepared in such way, the carbon films were evacuated
during several hours (or even days) before gas deposition.
Basically the applied procedure was typical of the prepa-
ration of «amorphous» carbon films, which are widely
used in electron microscopy and diffraction as supporting
substrates mainly because of the absence of distinct dif-
fraction peaks from such films superimposed on lines of
the material deposited upon substrates. However, it was
noticed [5,8,9] that carbon films prepared in such a way
also exhibit several important features, which character-
ize them as a porous matrix with very fine channels. One
of them is the absence of the (broad) peak corresponding
to distances between basal planes of graphite [8] (see also
Fig. 1) while other characteristic peaks were observed
and evidenced (allowing for the radial distribution func-
tions [5,8]) in favor of negatively curved graphitic sheets
forming the porous matrix. Several independent observa-
tions confirmed the essential difference of such substrates
from (e.g.) polycrystalline aluminum films. Simulta-
neously deposited gases onto these two substrates formed
samples, which demonstrated (as compared with each
other) the diffraction traces with low for the Al substrate
and high for carbon films backgrounds, with thin and dis-
tinct peaks on Al and wide lines onto carbon, in numerous
experiments deposits on carbon noticeably evolved with
time. These differences increase at higher temperatures
and for lighter gases, for instance it was rather difficult to
observe distinct diffraction peaks from the hydrogens de-
posited onto carbon films (in particular, because these
peaks gradually disappeared) while on polycrystalline Al
films all peaks were distinctly observable.
Diffractograms (Fig. 1) were analyzed using simula-
tions, which were made in a similar way as described pre-
748 Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7
N.V. Krainyukova
2 4 6 8
exp
calc
90 s
60 s
40 s
carbon substrate
Ne 6 K
Is
3
Fig. 1. Experimental diffractograms from Ne samples recorded
for different deposition time intervals tdep. Closest traces are
separated from each other by black and gray colors. The expe-
rimental diffractogram (exp) for tdep = 60 s is superimposed
with the calculated one (calc). The diffractogram (lowest)
from the carbon film is shown.
ico dec
fcc hcp
Fig. 2. Examples of model-clusters used in the simulations of
diffraction patterns: icosahedra (ico), decahedra (dec), fcc and
hcp clusters.
viously [7–9], i.e., on the basis of the assumption of a
wide variety of possible structures and sizes of clusters
(Fig. 2). We included in our analysis single crystals such
as cube-octahedra and hcp clusters as well as multiply
twinned particles (MTPs) with five-fold symmetry, i.e.,
noncrystallographic multishell icosahedra (ico) [22] and
Mark’s decahedra (dec) [23], with initially from one up to
20 shells for every structural type. The diffracted inten-
sity (per atom) for each cluster k comprising Nk atoms was
calculated using the Debye formulas:
I s
f s S s
t
f
N
u S
sr
k
k
k
calc, ( )
( )
exp ( )
sin
�
�
�
�
� �� �
�2 4
2
2 2
1
2 � ij
ij k
sr
�
�
�
�
� .
Here the fraction t of atoms was assumed not to be bonded
to the cluster. The summation in the interference function
runs in the cluster k over all pairs of atoms i > j, se-
parated by the distance rij; the Debye–Waller factor
exp ( )�� �u Sk
2 2 allows for mean-square atomic displace-
ments � �u k
2 ; f s( ) is the elastic atomic scattering factor
for electrons; S s( ) is the incoherent x-ray scattering fac-
tor. The superposition of diffracted intensities Icalc from
different clusters k with their relative weights wk, i.e.,
Icalc = �wkIcalc,k, was compared with the experimental in-
tensities Iexp using the reliability factor R in the form R =
= ��Iexp – Icalc����Iexp + Icalc), where the summation was
taken over approximately 300–400 points along the ex-
perimental and calculated diffraction patterns with the
equidistant step of ~ 0.015 �
–1
in s = 4� sin(�)/� (� is the
diffraction angle and � is the wavelength of electrons).
The values wk were involved in the total analysis as nearly
independent variables [7–9]. The total �wk of all relative
weights is equal to 1.
Results and discussion
Neon gas was condensed on substrate by small por-
tions and diffractograms (Fig. 1) were recorded after ev-
ery next portion deposited. The carbon substrate
contribution was measured before deposition and ac-
counted for in the analysis. The relevant distribution
functions over structures and sizes are shown in Fig. 3.
They demonstrate a highly reproducible discrete charac-
ter, which was nearly independent of the effective deposit
thickness and implies the self-selection in sizes and struc-
tures that may characterize the porous matrix. Clusters
with the five-fold symmetry (MTPs) prevail and basically
appear in the size intervals predicted in the theory
[11,24], i.e., icosahedra for small sizes while decahedra
for largest formations. Only three typical sizes were ob-
served and can be ascribed to micro- and mesopores ac-
cording to the classification [6] because in the wide class
of nanostructured carbon-based materials carbon sheet
curvatures and structural arrangements range from
nanometers up to several hundred nanometers. The small-
est cluster size (about 13–55 atoms) was earlier ascribed
[9] to some characteristic structural motif, which forms
inside carbon films under the preparation conditions and
is preserved even under the film annealing. The next in
size pores presumably belong to some kind of large de-
fects (~40–50 �) inside films while the largest clusters
evidently grow above substrate in essentially open geom-
etry that makes it possible to use these films as supporting
substrates in numerous electron microscopy and electron
diffraction experiments. Several experimental facts de-
scribed below confirm our classification.
At earlier growth stages we observed only two types of
sizes (Fig. 3), namely, the smallest and the largest ones as
well as a time evolution of the diffraction patterns and re-
levant distributions (Fig. 4). The contribution of the larg-
est clusters rapidly decreases in a few minutes by several
percents while the number of atoms in smallest clusters
grows up. We conclude that the substance directly depos-
ited on substrate in the form of large clusters later pene-
trate in smaller pores due to diffusion-like processes. Ab-
sence of intermediate sizes in this stage confirms our
Neon in carbon nanopores: wetting, growth mechanisms and cluster structures
Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7 749
0
0,2
0,4
N
1/3
60 s
0
0,2
0,4
tdep
tdep
tdep
20 s
10 20 300
0,2
0,4
ico
dec
hcp
120 s
w
N
w
N
w
N
Fig. 3. Distribution functions of Ne clusters over sizes and
structures found on the basis of the analysis of experimental
diffractograms. The inset shows the structure identifications.
previous assumption concerning large defects inside
films because otherwise all sizes would be visible at the
beginning. Moreover, smaller sizes also decrease, possi-
bly due to cluster splitting into smaller formations owing
to the interaction through pore walls. As we will see be-
low, with growing amount of the deposited material a
highly disordered matter forms, which does not belong to
any clusters. This observation implies that smaller voids
can form inside substrate and are filled at later growth
stages with deposited atoms because the potential barriers
delay penetration into these positions. Really, our method
allows the description not only of the clusters contribu-
tion into the resulting diffraction pattern but also the esti-
mation of the total amount t (see the formula given in the
previous section) of the part of atoms not bonded with
clusters. In Fig. 5 one can see the evolution of this compo-
nent depending on the effective thickness of the deposited
material. We express here the effective thickness by
means of the ratio of the total amount of deposited neon
atoms NNe to the total number of carbon atoms NC partici-
pating in the scattering process, with allowance for their
different scattering abilities. In contrast with the antici-
pated Stranski–Krastanov growth scheme, which pre-
sumes the disordered layer formation before the cluster
growth, we see no contribution from the atoms not bon-
ded with clusters at earlier growth stages, i.e., clusters
grow first. The roughness of inner walls in porous materi-
als was presumed [25] to be the reason, which may reduce
wetting because of bending energy «penalty» in adsorbate
layers picked up by wall roughness. But at the later stages
the disordered component appears and increases with fill-
ing. Hence, our previous conclusion concerning the diffu-
sion- like penetration of atoms into ever smaller voids is
basically the most reasonable. In addition, we can empha-
size also the possible role of the «effective pressure» aris-
ing in larger pores and «pushing» atoms in the smaller
ones.
Summary
According to the Stranski–Krastanov growth scheme,
noble gases deposited on substrates first form an interme-
diate disordered layer between the substrate and the crys-
talline phase, which later grows above this layer. Our
work does not support this scenario in application to the
porous carbon substrate. The crystalline phase appears
first in the form of clusters, then due to the diffusion pro-
cesses the smaller clusters grow inside substrate pores
and at last the disordered component appears at latter
growth stages, filling the smallest voids inside substrate
in positions, where no crystalline phase can exist.
The distribution functions in cluster structures and
sizes calculated on the basis of the diffraction pattern ana-
lysis demonstrate the unique similarity; they are nearly
independent of the deposit effective thickness and pre-
sumably characterize the porous carbon matrix. Thus, in
line with our previous observations [7–9], the discrete
character of micro- and mesopores presumably induces
the found self-selection in cluster sizes. The distribution
functions exhibit for all objects under study absolute
prevalence of MTPs, i.e., clusters with the five-fold sym-
metry. Comparison with the energy calculations made for
different structures showed that both ico and dec clusters
were basically found in the size intervals predicted by
theory.
750 Fizika Nizkikh Temperatur, 2007, v. 33, Nos. 6/7
N.V. Krainyukova
0 10 20 30
0
0,2
0,4
ico
dec
in 4 min
0 10 20 30
0
0,2
0,4
w
N
w
N
N
1/3
Fig. 4. Time evolution of distribution functions at earlier
stages of the film growth: � = 15 �, tdep = 20 s.
0.5 1.0 1.5 2.0 2.50
0.2
0.4
0.6
t
N /NNe C
Fig. 5. Dependence of the disordered fraction t on the film filling.
The highly reproducible discrete distribution func-
tions characterize our method as a good application to the
pore medium description. Finally we should conclude
that the method suggested in this and our previous similar
works [7–9] can also be used in the analysis of a wide
group of objects, which obey the growth mechanisms typ-
ical of confined geometry.
The author is grateful to V.G. Manzhelii, M.A. Strzhe-
mechny, V.V. Khmelenko, V.A. Apkarian, J.-P. Galaup,
and V. Kiryukhin for fruitful discussion of the problem,
she is also greatly indebted to B.W. van de Waal for nu-
merous valuable comments and also for the software pro-
vided for cluster modelling.
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