Volume 02 Issue 10-2022
41
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
02
I
SSUE
10
Pages:
41-45
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
OCLC
–
1121105677
METADATA
IF
–
5.582
Publisher:
Oscar Publishing Services
Servi
ABSTRACT
Study of the adsorption nature, emission - adsorption parameters of La, Sm, Gd films on the surface of the sharp
monocrystal of the molybdenum alloy - rhenium CCC and GPU structure and the establishment of general laws and
regulations of the adsorption nature of these rare earth metals.
KEYWORDS
Adsorption; rare earth metals; emission paramets; exit operation; desorption heat; acute single crystal.
INTRODUCTION
Interest in the study of films of rare earth metals
on the surface of refractory metals is associated
with the search for new highly efficient film
substrates for thermionic emitters. Studies of the
films of these metals on the surface of the faces of
metallic single crystals made it possible to
establish a relationship between the variable
valence of some rare earth metals on the surface
Research Article
EMISSION AND ADSORPTION PARAMETERS OF RARE EARTH METAL
FILMS ON THE SURFACE OF MOLYBDENUM - RHENIUM ALLOY SINGLE
CRYSTAL
Submission Date:
October 10, 2022,
Accepted Date:
October 15, 2022,
Published Date:
October 30, 2022
Crossref doi:
https://doi.org/10.37547/ajast/Volume02Issue10-07
Tulametov Makhmudjan Akhmedovich
Senior Lecturer, Department of Physics and Electrical Engineering, Tashkent Institute of Chemical Technology,
Tashkent, Uzbekistan
Bozorov Ismoil Tukhtaevich
Senior Lecturer, Department of Physics and Electrical Engineering, Tashkent Institute of Chemical Technology,
Tashkent, Uzbekistan
Journal
Website:
https://theusajournals.
com/index.php/ajast
Copyright:
Original
content from this work
may be used under the
terms of the creative
commons
attributes
4.0 licence.
Volume 02 Issue 10-2022
42
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
02
I
SSUE
10
Pages:
41-45
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
OCLC
–
1121105677
METADATA
IF
–
5.582
Publisher:
Oscar Publishing Services
Servi
of their own and foreign substrates with the
structure of the surface film. Features of the
electronic structure of rare earth metals - the
filling of the inner 4f - shell with an increase in the
atomic number of elements in the series of
lanthanides - are responsible for their interaction
one after another and the atoms of the substrate.
Establishing the nature of this connection can be
facilitated by the study of the novelty of atoms of
rare earth metals on various adsorbents. To date,
sufficiently detailed studies of the surface of rare
earth metal atoms on the surface of single crystals
of the BCC (div-centered cubic) structure have
been carried out and the general nature of
adsorption on these crystals has been established,
regardless of the individual properties of each of
the rare earth metal elements [1-4].
The conclusion of the determining role of this
commonality is the nature of the electronic
structure of rare earth metals is given and verified
by experiments on the adsorption of various
representatives of rare earth metals on the
surface of single crystals of the HCP(hexagonal
close-packed) structure. The use of field electron
microscopy makes it possible, in relatively simple
experiments, to study the crystal structure of a
single crystal - an adsorbent of the adsorption
density of foreign atoms over its surface. In this
case, it is possible to study the nature of the
rearrangement of the crystal surface under the
influence of temperature and electric field, i.e. the
conditions for studying the adsorption of foreign
atoms under identical vacuum conditions on
modified single-crystal surfaces are provided.
The research carried out represents an important
role for the physics of surface phenomena, since
the mechanism of adsorption bonds of a group of
chemical elements
–
lantonoids is studied.
The thermionic parameters of the polycrystalline
wire of molybdenum-rhenium alloy were
measured in the work. The method of field
electron microscopy established the transition of
a single crystal of the molybdenum-rhenium alloy
from the BCC to the HCP structure. The
dependence of the work function of the surface of
a molybdenum - rhenium single crystal on the
degree of coating with La, Sm, Gd films was
studied. The heat of desorption of various rare-
earth metals from the surface of a molybdenum-
rhenium single crystal has been measured.
Studying the temperature regime of crystal
rearrangement, it was experimentally established
that after heating in a vacuum above 2000 K, a
pointed single crystal is rearranged in a BCC
lattice - in HCP. Thanks to this, it was possible to
conduct a study of films of rare earth metals on
one material in two crystalline modifications.
The distribution of the adsorbate with optimal
coverage on the surface of the BCC crystal for all
rare-earth metals studied is the same as for pure
refractory BCC metals W, Mo. The regions (111)
and (112) make the main contribution to the
emission. Films of atoms of rare earth metals at
the optimal degree of coverage of a single crystal
of BCC structure are predominantly adsorbed on
loose faces, saturating dangling bonds.
The dependence of the work function on the
degree of coverage has a normal yield with a
minimum at optimal coverage, conditionally
taken as θ = 1. It should be borne in mind that
Volume 02 Issue 10-2022
43
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
02
I
SSUE
10
Pages:
41-45
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
OCLC
–
1121105677
METADATA
IF
–
5.582
Publisher:
Oscar Publishing Services
Servi
although in these experiments the total current
from the surface of a single crystal was measured,
the actual obtained values of the minimum work
function characterize the faces (111) and (116),
which under these conditions make the main
contribution to the total current. For the same
reason, the values of the heat of desorption of
rare-earth metal (REM) atoms from the surface of
a molybdenum-rhenium crystal characterize the
binding energy with the same loose faces. Table 1
shows the average values of the work function at
optimal coverage (eφmin), in a thick layer (eφt.s)
and the value of the heat of desorption (qdec) in
the range of coverage degrees 0.8<θ<1.
An emission-microscopic study of the adsorption
of La, Sm, Gd on the surface of a pointed HCP, a
molybdenum-rhenium alloy crystal, showed that
the anisotropy of an equilibrium submonolayer
coating is qualitatively general for all rare-earth
metals studied and does not depend on the
orientation of the axis of a pointed single crystal.
At low degrees of coverage of adatoms of rare
earth metals (θ<0.5), the contrast of the emission
image increases compared to a clean surface due
to the preferential activation of faces with low
work function. With the optimal degree of
coverage, the main emitting faces in all cases
studied are the (1120) and (1010) type faces.
Since under these conditions, the overwhelming
part of the emission current comes from these
faces, the results of measurements of the work
function and the heat of evaporation characterize
these faces.
Table 1
Emission-adsorption parameters of REM adatoms on the surface of a BCC crystal of molybdenum-
rhenium alloy (in EV)
Molybdenum-rhenium
Tungsten
REM
eφ
min
eφ
т.с
q
дес
q
субл
q
дес
La
2,5
2,7
5,8
4.47
5,8
Sm
2,4
2,5
5,2
2,13
3,8
Gd
2,9
3,1
5,3
4,15
5.1
Measurements in the device with a oscillating tip were performed during adsorption and desorption of Gd
and Sm from the (111), (100) type faces of a molybdenum
–
rhenium alloy single crystal and after
rearranging the tip of the same tip into an HCP structure. Table 2 shows the measurements of the work
Volume 02 Issue 10-2022
44
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
02
I
SSUE
10
Pages:
41-45
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
OCLC
–
1121105677
METADATA
IF
–
5.582
Publisher:
Oscar Publishing Services
Servi
funct
ion on the faces at optimal (eφmin) coating in a thick layer (eφt.s), as well as the heat of desorption
in the region of change in the degree of coverage from optimal to 0.8 optimal.
Table 2
Emission-adsorption parameters of Gd and Sm films on the faces of BCC and HCP crystals of
molybdenum-rhenium alloy
REM
BCC
HCP
edge
eφ
min
q
дес
Грань
eφ
min
q
дес
Gd
(111)
3,1
5,1
(1231)
3,3
5,1
(100)
2,1
5,0
(1120)
2,6
5,1
Sm
(111)
2,87
4,5
(1231)
2,9
4,8
(100)
2,2
4,9
(1120)
2,5
4,9
The greatest decrease in the work function during the
adsorption of rare earth metals on a BCC crystal of an
alloy of molybdenum - rhenium is observed on loose
faces (111), (116) on the same faces, the heat of
desorption of atoms of rare earth metals is the highest.
The same trend takes place during the adsorption of
rare earth metals on the faces of HCP crystals of the
molybdenum-rhenium alloy.
The results of measuring the parameters from the
surface of the (111) faces of the BCC crystal and (1120)
HCP crystal, given in Table 2, are in good agreement
with the results of measuring the parameters of the Sm
–
Gd films from the surface of the entire crystal,
because the emission of electrons from these faces
makes the main contribution to the total emission with
optimal coverage.
The results of the experiments performed indicate that
the
anisotropy
of
adsorption
of
various
representatives of the group of rare earth metals on
the surface of an HCP crystal is determined by the
common structure of the electron shells of these
elements and does not depend either on the chemical
nature of the adsorbate or on the individual physical
properties of the element of rare earth metals.
CONCLUSION
In conclusion, we can draw the following conclusions:
Pointed monocrystals from an alloy of molybdenum -
rhenium can be in BCC and HCP structures;
Adsorption of rare-earth metals on the surface of a BCC
molybdenum-rhenium alloy crystal with optimal
Volume 02 Issue 10-2022
45
American Journal Of Applied Science And Technology
(ISSN
–
2771-2745)
VOLUME
02
I
SSUE
10
Pages:
41-45
SJIF
I
MPACT
FACTOR
(2021:
5.
705
)
(2022:
5.
705
)
OCLC
–
1121105677
METADATA
IF
–
5.582
Publisher:
Oscar Publishing Services
Servi
coverage, adsorption occurs on faces of the (111) and
(112) types, as well as on pure BCC metals;
Predominantly, adsorption occurs on the faces of the
HCP crystal with a relatively high value of the specific
surface energy.
REFERENCES
1.
Utamuradova Sh.B., Daliev Kh.S., Daliev Sh.Kh.,
Faizullaev K.M. Vliyanie atomov khroma i
zheleza na protsessy defektoobrazovaniya v
kremnii. // Prikladnaya fizika, (Rossiya), 2019,
№6, S.90
-
95 (№3 Scopus).
2.
Utamuradova Sh.B., Faizullaev K.M. Rol'
termoobrabotki v formirovanii defektov v
kremnii s primes'yu kobal'ta. // Fizika
poluprovodnikov i mikroelektronika, 2019, №3,
S.9-
15 (01.00.00; №16).
3.
Utamuradova
Sh.B.,
Yusupova
Sh.A.,
Fayzullaev K.M. Impurity-impurity interaction
in silicon doped with manganese and nickel. //
Euroasian Journal of Semiconductors Science
and Engineering, 2020, №6, pp.11
-15.
4.
Pleshkov V.A. etc. / Surface 1991, No. 4 p. 34.
