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5PHYSICAL SCIENCES
ELECTRICAL AND OPTICAL PROPERTIES OF RHENIUM COVERED BY GRAPHITE MONO
LAYER
Orujov A.,
Assoc. Prof. phD Rustamova S.
Master degree Baku State University
Abstract
The study of the electrophysical properties of the Re-C system by the catalytic dissociation of CsCl molecules and thermionic emission by TEE methods shows that a graphite monolayer is formed on the rhenium layer when the rhenium layer is heated to benzene vapors and saturated with carbon atoms to T< 1800 K and then lowers the temperature. As an example, 50x1,5x0,02 mm3 rhenium layer (the layer is polycrystalline) was used. Recrystalli-zation of rhenium layer at T = 2300-2400 K is obtained after heating for several hours at alternating current. After heating, the recrystallized rhenium layer becomes homogeneous in terms of output (no anomalousSchottky effect is observed).
Keywords: graphite, output, thermoelectron emission, surface ionization, diffusion, mass spectrometry
We used layer-shaped materials to study the elec-trophysical properties of the Rh-C, Re-C system. The output of the recrystallized rhenium layer was determined by the surface ionization method (TEE) of the difficult ionizing element - indium. Both methods of determining the output give almost the same results. At the beginning, the resistance of the recrystallized rhenium layer was R0 c = 0,29 Ohm. After the Re (1010) surface was taken, T = 1600 K heated layer was stored in P # = 2.10-5 Torr pressurized benzene vapors. The decomposition of benzene occurs as follows CsH5^6C+6H, hydrogens combine with volumetric oxygen, form water vapor and are absorbed by the pump. In order to obtain a graphite monolayer on the surface of rhenium, as in the case of polycrystalline rhenium layer, the carbon atoms obtained by the decomposition of benzene molecules on the surface of the heated rhenium layer diffuse into the volume of rhenium until the concentration of carbon atoms increases, dissolves at a given temperature, and then a graphite monolayer forms on
the surface of Re (1010) (Fig. 1). This process continues « 30-40 minutes. To obtain a carbon monolayer on rhenium, a graphite monolayer on rhenium in the interval
T = 1600-1800 K was obtained by releasing C6H6
benzene vapor as a pressure of 3.10-2 Torr from a special gas discharge system (Fig.2). The production of carbon monolayer was determined based on the increase in thermoelectric emission current and surface ionization of CsCl molecules. Calculations based on known currents and temperatures show that the output decreases from 5.1 eV to 4.5 eV, and in particular the ion current of Cs atoms resulting from the dissociation of CsCl molecules decreases sharply. It was determined that the ionization coefficient on the surface of Re-C was reduced by about a thousand times. Figure 10 shows one of the numerous dependencies of the thermoelectron emission current of the sample at a constant temperature T = 1600K, the surface ionization
ion I+ currents of I , CsCl and KI molecules in the benzene vapor of the layer (Pc H =2 10-5 Torr).
Figure 1. Model offormation of graphite monolayer on the surface of rhenium
Figure 2. Time dependence of ion (1; 2) and electron currents (3) when the Re layer is stored in benzene vapor
P
- 2 ■ 10-5 Torr, T = 1600K.
In this case, the resistance of the rhenium layer was recorded to increase from the value at room
temperature from R20°c = 0,29 Ohm to 0.46 Ohm. It
is known that the characteristic features of the formation of a graphite monolayer in metals (Ir, Rh, Re) are a decrease in the dissociation coefficient of CsCl molecules on a clean surface from 1 to ~10-3 ^ 10-5 (for Me - C) and a change in the output of the metal (~ 4.5
eV).We used this feature of the Me-C system in the study of Re-C.When the temperature of the sample is increased from the graphite extraction (dissolution) temperature (5-10) K, the surface of the rhenium is cleared of the graphite monolayer, as well as the carbon atoms are dissolved in the volume of rhenium.The output of the Re-C layered system was determined by the surface ionization of
Figure 4. Temperature dependence of the ionization current of the CsCl molecule on the surface of rhenium coated with a graphite
monolayer .
Figure.3. Richardson graph for graphite monolayer rhenium (1010)
CsCl molecules and the TEE method according to the temperature dependence of ionic and electron currents according to the Sax-Langmur and Richardson formulas (Figures 3 and 4).The value of the output gave practically the same result for both methods (e^ = 4.5 eV), which corresponds to the output Re (1010) -C [10].After saturating the volume of rhenium with carbon atoms at a constant temperature to a certain limit, as in the case of polycrystalline rhenium wire, the surface of rhenium is cleared of graphite when the temperature of the rhenium layer increases by AT = 20 ^ 30 K.In this case, the carbon atoms on the surface either enter the volume of rhenium or are desorbed from the surface. After these processes, at a certain incandescent current greater than Ti = 1600K, the TEE current from the clean surface decreased slightly compared to carbon diffusion. After these processes, at a certain incandescent current greater than T1 = 1600K, the TEE current from the clean surface decreased slightly compared to carbon diffusion.This decrease can be explained by an increase in the integrated emission capacity of the Re-C system.Since the resistance of carbon to the rhenium increases significantly as a result of its diffusion, the strength released at a given heat must increase.The decrease in rhenium temperature can be found by comparing TEE currents from a clean surface before and after the diffusion of carbon from the Richardson formula.The determination of the working function of the Re layer showed that the output function of rhenium does not change as a result of carbon diffusion; the facet (1010) is not rearranged.The change in integrated radiation emission can be estimated by comparing two values of filament current corresponding to the same temperature (i.e., same TEE current) from Re before and after carbon diffusion.As the current at high temperature is released mainly in the form of radiation, we can write it like this:
W = 12 R = sTOT4, (1)
therefore we obtain from the condition T = const
£
-TL - . Rl
R
(2)
here, a is Stefan-Boltzmann constants r ande T are I and I arethe corresponding integral black radiation coefficients,and R and R are the currents for
heating the layer, and the electrical resistance of the layer after diffusion and before diffusion. When rhenium was saturated with carbon in benzene vapor at a pressure of Pc6 h6 = 5 10-5 Torr, the resistance of rhenium R20°C increased from 0.29 Ohm to 0.52 Ohm, and respectively, R1 / R0 = 1.79.Then, knowing that I1/ I0 = 1.01, we can find pure rhenium at T = 1600K for Re (1010) -C.The temperature dependence of the TEE and SI currents of CsCl molecules with decreasing temperature of the carbon-saturated rhenium layer at T<1800 K was characteristic for the corresponding temperature dependences on the surface of the metal-graphite monolay system.On the other hand, it is known that the concentration of the limiting solubility depends on the temperature and should decrease as T decreases.Then the question occurs about the escape of "excess" carbon atoms with a decrease in rhenium temperature.When the temperature of the rhenium layer is lowered, it is necessary to consider the need to remove the "excess" carbon atoms from the Re-C system, since the volumetric phase transition of carbon atoms saturated with carbon atoms does not occur.
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REFERENCES: 1. Orujov A.K. Adsorption and desorption of samarium atoms on the surface of iridium and iridium coated with a monolayer of graphite. Journal "Physics of Metals and Metal Science". Yekaterinburg, 2009, volume 109, issue 1, p.58-62
2. Orujov A.K. Modification of the physical properties of iridium with a surface monolayer graphite film due to intense diffusion of potassium atoms. Journal "Physics of Metals and Metal Science". Yekaterinburg, 2011, volume 111, no. 6, p. 626-627.
3. Fomenko F.S. Emission properties of materials. Kyiv, NaukovaDumka, 1981, p.338
