The choice of silicon nanostructures for CH₄ detection: ab-initio calculation
The paper focuses on the ab initio theoretical study of the silicon nanostructures’ sensitivity to adsorption of CH₄ molecules. The electronic properties of porous silicon, silicon nanoclusters in a vacuum, silicon nanowires, and nanoscale silicon film are examined. The analysis of results shows tha...
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| Cite this: | The choice of silicon nanostructures for CH₄ detection: ab-initio calculation / R.M. Balabai, P.V. Merzlikin // Наносистеми, наноматеріали, нанотехнології: Зб. наук. пр. — К.: РВВ ІМФ, 2014. — Т. 12, № 4. — С. 743-750. — Бібліогр.: 13 назв. — англ. |
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Balabai, R.M. Merzlikin, P.V. 2018-07-13T08:56:08Z 2018-07-13T08:56:08Z 2014 The choice of silicon nanostructures for CH₄ detection: ab-initio calculation / R.M. Balabai, P.V. Merzlikin // Наносистеми, наноматеріали, нанотехнології: Зб. наук. пр. — К.: РВВ ІМФ, 2014. — Т. 12, № 4. — С. 743-750. — Бібліогр.: 13 назв. — англ. 1816-5230 PACS: 07.07.Df, 68.43.Bc, 68.47.Fg, 71.15.-m, 73.20.-r, 73.22.Dj, 82.47.Rs https://nasplib.isofts.kiev.ua/handle/123456789/140654 The paper focuses on the ab initio theoretical study of the silicon nanostructures’ sensitivity to adsorption of CH₄ molecules. The electronic properties of porous silicon, silicon nanoclusters in a vacuum, silicon nanowires, and nanoscale silicon film are examined. The analysis of results shows that silicon nanofilm is most sensitive to CH₄ adsorption as compared with nanoclusters, nanowires, and porous silicon. Роботу присвячено теоретичному дослідженню методами з перших принципів чутливости кремнійових наноструктур щодо адсорбції молекул CH₄. Вивчалися електронні властивості наступних наноструктур: пористий кремній, нанокластери кремнію у вакуумі, кремнійові нанодроти та наномасштабна плівка. Аналіз результатів показує, що нанорозмірна кремнійова плівка найбільш чутлива до процесу адсорбції в порівнянні з іншими досліджуваними об’єктами. Работа посвящена теоретическому исследованию методами из первых принципов чувствительности кремниевых наноструктур к адсорбции молекул CH₄. Изучались электронные свойства таких наноструктур: пористый кремний, нанокластеры кремния в вакууме, кремниевые нанопроволоки и наномасштабная плёнка. Анализ результатов показывает, что наноразмерная кремниевая плёнка наиболее чувствительна к процессу адсорбции по сравнению с другими исследуемыми объектами. en Інститут металофізики ім. Г.В. Курдюмова НАН України Наносистеми, наноматеріали, нанотехнології The choice of silicon nanostructures for CH₄ detection: ab-initio calculation Article published earlier |
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The choice of silicon nanostructures for CH₄ detection: ab-initio calculation |
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The choice of silicon nanostructures for CH₄ detection: ab-initio calculation Balabai, R.M. Merzlikin, P.V. |
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The choice of silicon nanostructures for CH₄ detection: ab-initio calculation |
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The choice of silicon nanostructures for CH₄ detection: ab-initio calculation |
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The choice of silicon nanostructures for CH₄ detection: ab-initio calculation |
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The choice of silicon nanostructures for CH₄ detection: ab-initio calculation |
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choice of silicon nanostructures for ch₄ detection: ab-initio calculation |
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Balabai, R.M. Merzlikin, P.V. |
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Balabai, R.M. Merzlikin, P.V. |
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Наносистеми, наноматеріали, нанотехнології |
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Інститут металофізики ім. Г.В. Курдюмова НАН України |
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The paper focuses on the ab initio theoretical study of the silicon nanostructures’ sensitivity to adsorption of CH₄ molecules. The electronic properties of porous silicon, silicon nanoclusters in a vacuum, silicon nanowires, and nanoscale silicon film are examined. The analysis of results shows that silicon nanofilm is most sensitive to CH₄ adsorption as compared with nanoclusters, nanowires, and porous silicon.
Роботу присвячено теоретичному дослідженню методами з перших принципів чутливости кремнійових наноструктур щодо адсорбції молекул CH₄. Вивчалися електронні властивості наступних наноструктур: пористий кремній, нанокластери кремнію у вакуумі, кремнійові нанодроти та наномасштабна плівка. Аналіз результатів показує, що нанорозмірна кремнійова плівка найбільш чутлива до процесу адсорбції в порівнянні з іншими досліджуваними об’єктами.
Работа посвящена теоретическому исследованию методами из первых принципов чувствительности кремниевых наноструктур к адсорбции молекул CH₄. Изучались электронные свойства таких наноструктур: пористый кремний, нанокластеры кремния в вакууме, кремниевые нанопроволоки и наномасштабная плёнка. Анализ результатов показывает, что наноразмерная кремниевая плёнка наиболее чувствительна к процессу адсорбции по сравнению с другими исследуемыми объектами.
|
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1816-5230 |
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https://nasplib.isofts.kiev.ua/handle/123456789/140654 |
| citation_txt |
The choice of silicon nanostructures for CH₄ detection: ab-initio calculation / R.M. Balabai, P.V. Merzlikin // Наносистеми, наноматеріали, нанотехнології: Зб. наук. пр. — К.: РВВ ІМФ, 2014. — Т. 12, № 4. — С. 743-750. — Бібліогр.: 13 назв. — англ. |
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| fulltext |
743
PACS numbers: 07.07.Df, 68.43.Bc, 68.47.Fg, 71.15.-m, 73.20.-r, 73.22.Dj, 82.47.Rs
The Choice of Silicon Nanostructures for CH4 Detection:
Ab Initio Calculation
R. M. Balabai and P. V. Merzlikin
Kryvyi Rih Pedagogical Institute SHEI ‘Kryvyi Rih National University’,
54 Gagarin Ave.,
50086 Kryvyi Rih, Ukraine
The paper focuses on the ab initio theoretical study of the silicon nanostruc-
tures’ sensitivity to adsorption of CH4 molecules. The electronic properties of
porous silicon, silicon nanoclusters in a vacuum, silicon nanowires, and na-
noscale silicon film are examined. The analysis of results shows that silicon
nanofilm is most sensitive to CH4 adsorption as compared with nanoclusters,
nanowires, and porous silicon.
Роботу присвячено теоретичному дослідженню методами з перших прин-
ципів чутливости кремнійових наноструктур щодо адсорбції молекул
CH4. Вивчалися електронні властивості наступних наноструктур: порис-
тий кремній, нанокластери кремнію у вакуумі, кремнійові нанодроти та
наномасштабна плівка. Аналіз результатів показує, що нанорозмірна
кремнійова плівка найбільш чутлива до процесу адсорбції в порівнянні з
іншими досліджуваними об’єктами.
Работа посвящена теоретическому исследованию методами из первых
принципов чувствительности кремниевых наноструктур к адсорбции мо-
лекул CH4. Изучались электронные свойства таких наноструктур: пори-
стый кремний, нанокластеры кремния в вакууме, кремниевые нанопро-
волоки и наномасштабная плёнка. Анализ результатов показывает, что
наноразмерная кремниевая плёнка наиболее чувствительна к процессу
адсорбции по сравнению с другими исследуемыми объектами.
Key words: silicon, nanostructure, CH4 molecules, ab initio calculations.
(Received 17 July, 2014)
1. INTRODUCTION
Gas sensors are widely used in various fields of human activity. In par-
Наносистеми, наноматеріали, нанотехнології
Nanosystems, Nanomaterials, Nanotechnologies
2014, т. 12, № 4, сс. 743–750
2014 ІÌÔ (Іíñòèòóò ìåòàëîôіçèêè
іì. Ã. Â. Êóðäþìîâà ÍÀÍ Óêðàїíи)
Надруковано в Óкраїні.
Ôотокопіювання дозволено
тільки відповідно до ліцензії
744 R. M. BALABAI and P. V. MERZLIKIN
ticular, the harmful gases (such as CH4, CO2, NO2 and others) sensors
are in large demand. There are observed trends in reduction of gas sen-
sors and searching for new materials to create them.
Thus, much attention is devoted to the sensory properties of carbon
nanostructures—nanotubes and graphene [1, 2, 3]. The authors of [1]
experimentally documented the changing of electrical resistance of the
examined nanotubes after adsorption of CH4 and CO2 gas molecules. It
has been noted that this sensor has good sensitivity and short response
time. However, after CO2 adsorption, the sensor has not been fully re-
covered. The authors explain the change in conductivity by the shift of
the valence band of nanotubes, which leads to appearing of the p-type
semiconductor.
The authors of [2] experimentally investigated the sensory proper-
ties of graphene on the adsorption of vapours of ethanol, methanol,
chloroform and other gases. In addition to changes in electrical re-
sistance (which is different for different gases by value and by sign),
the shift of the noise spectra of graphene has been observed. Therefore,
by fixing these two options, one can achieve a high selectivity of single-
transistor graphene sensor and use it to define a wide range of gases.
In Ref. [3], the sensory properties of nanopatterned graphene on ad-
sorption of NO2 have been experimentally examined. The nanopat-
terned samples showed sensitivities for NO2 of more than one order of
magnitude higher than for non-patterned graphene. The NO2 concen-
trations as low as 300 ppt. were detected with an ultimate detection
limit of tens of ppt.
Another area of research covers the sensory properties of nanocrys-
talline oxides ZnO, SnO2, In2O3, TiO2 and its composites [4, 5].
Thus, in Ref. [4], it has been experimentally demonstrated the role
of quantum dots of SnO2 in detecting low concentrations of methane
(CH4) at a relatively low temperature of 150C with high response
(S3.5%) and response time below 1 min. These SnO2 nanoparticles
exhibited a strong sensing response to CH4 in comparison to the an-
nealed sample.
The paper [5] experimentally investigates the sensory properties of
ZnO nanoparticles on atmospheric gases N2, O2 and CO2. In addition to
changing the electrical conductivity, the changes of examined material
photoluminescence under the influence of gases were observed. It has
been detected relationship between air pressure and photolumines-
cence.
Two-dimensional semiconductors are also interesting for gas sens-
ing [6, 7]. In Ref. [6], it has been investigated the sorption ability of
Ge20Se80 thin films applied as active layers of quartz crystal microbal-
ance (QCM) for NO2 gas sensing. It has been experimentally demon-
strated that the introduced gas molecules interact electrostatically
with the chalcogen atoms of the host material and initiate some degree
THE CHOICE OF SILICON NANOSTRUCTURES FOR CH4 DETECTION 745
of structural changes in it.
Authors of [7] investigated the role of quantum confinement on the
performance of H2 sensors based on two-dimensional InAs membranes.
They found the strong thickness dependence, with 100 enhance-
ment in the sensor response as the thickness is reduced from 48 to 8
nm.
Other promising materials for the construction of gas sensors are
nanowires. In paper [8], the analysis of researches in this area, the
classification of sensor materials, the methods of synthesis and com-
parison of sensory properties are given. This group of materials can be
divided into nanowires of metal oxides, polymer nanowires, metal nan-
owires and silicon nanowires.
Silicon-based gas sensors are of great interest because they may be
easily integrated to electronic circuits [8].
Thus, we can distinguish the following main lines of gas sensors evo-
lution: reduction of the size, the transition to the nanoscale and in-
creasing of selectivity and sensitivity. In addition to the empirical se-
lection of sensor parameters, theoretical studies are effective for bet-
ter understanding the nature of sensory properties, and may indicate
directions for improving gas sensor.
2. MODELS AND METHODS OF CALCULATION
The aim of this work was the ab initio theoretical study of the silicon
nanostructures sensitivity to adsorption of CH4 molecules. All calcula-
tions were performed using the author’s source code [9], which imple-
ments the Car–Parrinello quantum-mechanical dynamics, the density
functional theory with local density approximation [10, 11], and norm-
conserving ab initio pseudopotential of Bachelet–Hamann–Schlüter
[12].
The ground states of the electron-nuclear systems were detected by
means of the self-consistent solution of the Kohn–Sham equations, be-
cause electronic variables only were determined with the atomic cores
fixed. Following Kohn–Sham approach, electronic density was written
down in terms of occupied orthonormal one-particle wave functions:
2
( ) ( )
i
i
n r r . (1)
The point on the surface of potential energy in the Born–
Oppenheimer approximation was determined as a minimum energy
functional with regard to the wave functions:
2
* 2
{ },{ },{ } ( ) ( ) { ( )},{ },{ }
2
i j i i j
i
E R d U n R
m
r r r r , (2)
746 R. M. BALABAI and P. V. MERZLIKIN
where { }
j
R are coordinates of atomic cores; { }
are any external in-
fluences on the system.
In the generally accepted formulation, minimization of the energy
functional (2) with respect to one-particle orbitals with additional or-
thonormal constraint on the one-particle orbitals ( )
i
r results in the
Kohn–Sham one-particle equations:
2
2
( ) ( )
2 ( )
i i i
U
m n
r r
r
. (3)
The distribution of electrons along the energy zones for -state was
found by means of numerical calculation of derivative
0
lim
E
N E
(where N is a number of the allowed states for the E interval of en-
ergy). The one-particle energy spectrum was obtained from calculation
of the eigenvalues of the Kohn–Sham matrix. In accordance with ide-
ology of the electronic density functional, the occupied states at abso-
lute zero temperature were defined (states of valence zone and states in
the gap zone, which are related to the defects). It allowed defining po-
sition of Fermi level, based on the last occupied state, their number be-
ing half the number of electrons (due to ignoring the spin of the elec-
tron). Attention should be paid to the fact that the -point for super-
lattice calculations has the meaning of the Baldereschi mean-value
point [13], which represents all vectors in the Brillouin zone.
3. RESULTS OF CALCULATION AND THEIR DISCUSSION
The atomic basis of the unit cell, which reproduces artificial transla-
tional symmetry of the system, consisted of 64 silicon atoms. By set-
ting the different vacuum gap widths in the directions of the coordi-
nate axes, various nanostructures of silicon were simulated: porous
silicon, silicon nanoclusters in a vacuum, silicon nanowires and na-
noscale silicon film. Coordinates of the atomic basis have not been op-
timized. We investigated the changes in the electronic structure of
these materials after the adsorption of CH4 molecules.
Figure 1 shows the partial valence electrons density distribution in
the studied systems for a range of 0.7–0.8 of the maximum value. For
all of nanostructures, the rearrangement of the electronic density af-
ter the gas molecules adsorption may be seen. The appearance of charge
jumper between molecules and silicon nanostructures is observed. The
analysis of the intensities of these interactions shows that silicon nan-
ofilm is the most sensitive to the adsorption process; in this case, the
highest values of the electron density are located around the adsorbed
molecule. One can also observe the influence of the molecule to the dis-
tribution of electronic density inside the nanostructure.
THE CHOICE OF SILICON NANOSTRUCTURES FOR CH4 DETECTION 747
For example, in nanoclusters (see Fig. 1) in the absence of adsorbed
molecules, the electronic distribution was symmetric with respect to
the centre of the cluster, but, after the adsorption, it takes asymmetric
Fig. 1. The valence-electrons’ density distribution in different examined
nanostructures. The valence electrons density in the range of 0.7–0.8 of its
maximum value is shown.
748 R. M. BALABAI and P. V. MERZLIKIN
shapes’ stretched in the direction of the adsorbed molecules.
Fig. 2. Density of states for -point of Brillouin zone for different examined
nanostructures. The x-axis shows energy in atomic units. The y-axis shows
number of states.
THE CHOICE OF SILICON NANOSTRUCTURES FOR CH4 DETECTION 749
A similar internal reorganization of the electronic density is ob-
served for nanowires.
The valence-electrons’ density of allowed states in the energy range
is shown in Fig. 2. The low-populated states (states occupied by one
electron) at the bottom of the energy range are states of the molecule
CH4, and the states in the upper part of the range belong to the silicon
nanostructures. The analysis of these distributions shows that, with
such graph resolution, it is difficult to determine the details of the
changes in the part of the range, corresponding to silicon nanostruc-
tures. Nevertheless, it can be detected that the most of the spectrum is
concentrated near the Fermi level (i.e., the right boundary of the ener-
gy range of occupied states). Moreover, this effect is most emphasized
for the porous silicon and silicon nanofilm.
The distribution of low-populated states in the lower part of energy
range is different for different types of nanostructures. This may indi-
cate that the adsorption of the molecule occurs either by physical or by
chemical way. In addition, looking to the degree of changes in the elec-
tronic structure, we assume that the adsorption on silicon nanoclusters
and nanowires is carried out by physical principles and on porous sili-
con—by chemical principles.
Therefore, nanoscale silicon film is most sensitive to the adsorption
process: its electronic spectrum changes most significantly. The ex-
pansion of occupied-states’ range and the emergence of local states at
the top of the energy range of occupied states are observed. The chang-
es of a similar nature, but less noticeable, are present in other exam-
ined nanostructures. The observed transformations of the electronic
spectrum, leading to a conductivity-type changing of silicon
nanostructures, may be used for the construction of gas sensors.
4. CONCLUSIONS
Ab initio calculations show that silicon nanostructures change their
electronic properties because of gas molecules adsorption, which leads
to change of the material conductivity. These changes are most inten-
sive in silicon nanofilm compared to nanoclusters, nanowires and po-
rous silicon. Thus, nanoscale silicon films may be used to construct
CH4 sensors. The still actual issue is studying the selectivity of this
type of sensors.
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750 R. M. BALABAI and P. V. MERZLIKIN
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8. Y. Dan, eprint arXiv:0804.4828 (2008).
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