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Energy-resolved mass spectroscopy studies during the deposition of TiC films by ion plating under different magnetic fields
ARTICLE IN PRESS
Vacuum 80 (2005) 184–188 www.elsevier.com/locate/vacuum
Energy-resolved mass spectroscopy studies during the deposition of TiC films by ion plating under different magnetic fields M. Macˇeka,b,, M. Misˇ inac, M. Cˇekadaa, P. Panjana a
Faculty of Electrical Engineering, University of Ljubljana, Trzˇasˇka 25, 1000 Ljubljana, Slovenia b Jozˇef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia c Institute of Physics, Academy of Sciences, Na Slovance 2, 18040 Prague 8, Czech Republic
Abstract The energy-resolved mass spectroscopy studies during the discharge in an Ar+C2H2 gas mixture in a triode ionplating system revealed two different working regions. At strong magnetic fields (IcX15 A, BX7 mT), the spectra show a high degree of Ti ionisation accompanied by almost complete acetylene dissociation. The main ionised species besides + 12 + þ þ Ar+ are Ti+, Ti2+, Hþ 13 , ArH and C . The intensity of hydrocarbon ions CH15 and C2 H15 is very low. At weak magnetic fields (Ico12.5 A, Bo5:8 mT), the evaporation (and consequently ionisation) of Ti is low, but the plasma is + þ þ rich in hydrocarbon radicals. The most intense of them is the parent ion C2 Hþ 2 followed by C , CH3 and C2 H3 ions. Carefully adjusting the magnetic field, arc current and partial pressure of reactive gases, different plasmas rich in Ti ions or different hydrocarbon ions and even pure carbon ions can be obtained. r 2005 Published by Elsevier Ltd. Keywords: Energy-resolved mass spectroscopy; Ar–C2H2 plasma; Ion plating; TIC
1. Introduction Hard coatings based on transition metal nitrides MN (M ¼ Ti, Cr, etc.) are nowadays widely accepted as protective layers [1]. Less attention has been dedicated to transition metal carbides or Corresponding author. Tel.: +386 1 4768 356; fax: +386 1 4264 644. E-mail address: [email protected] (M. Macˇek).
0042-207X/$ - see front matter r 2005 Published by Elsevier Ltd. doi:10.1016/j.vacuum.2005.08.011
to ternary metallic carbonitrides [2–5] in spite of their interesting tribological properties. The common precursors used for the deposition of metallic carbides are the lower hydrocarbons such as methane (CH4) and acetylene (C2H2). Coatings deposited in hydrocarbon atmospheres contain a considerable amount of hydrogen. At higher hydrocarbon pressures and/or low evaporation rates, excess C atoms are incorporated in the form of amorphous hydrocarbon inclusions or,
ARTICLE IN PRESS M. Macˇek et al. / Vacuum 80 (2005) 184–188
even, amorphous hydrocarbon coatings doped with the metal (0–30 at%) [6] can be deposited. In our previous investigations, we performed energy-resolved mass spectroscopy studies during TiN, TiC and TiCN deposition [7,8]. In these studies, we focused our attention on the effect of arc current and reactive atmosphere in a triode ion-plating apparatus (Balzers BAI–730). It was found that the degree of ionisation in this system under standard conditions is very high. In this paper, we focused our attention on the effects of the magnetic field on the energy and mass spectra during TiC deposition.
185
with the substrates [8]. An important problem arises because the spectrometer is partially immersed in the vessel with a relatively strong magnetic field. Since it is very difficult to protect the whole spectrometer from the effect of the magnetic field, we performed a calibration, measuring the effect of the magnetic field on the spectra of neutrals. As we expected, only light ions with m/q less than 12 amu are strongly affected. All our results for the integrals of ion intensities and energy distributions are corrected for the effect of the magnetic field (but not for the quadrupole transmission factor). The mass spectra presented are as measured.
2. Experimental details 3. Results and discussion The energy-resolved mass spectroscopy of the ion flux was performed during the deposition of TiC films in the commercial Balzers BAI 730 triode ion-plating system. This system uses a filament-based ionisation chamber, which forms a low-voltage arc expanding into the reaction chamber. A more detailed description of the system can be found elsewhere [9]. TiC plating was done under the following conditions: arc current I arc ¼ 190 A, substrate voltage U B ¼ 125 V, argon pressure pAr ¼ 0:15 Pa (argon flow FAr 90 cm3/min), total pressure measured by ionisation gauge ptot ¼ 0:28 Pa (estimated partial pressure of C2H2 ¼ 0.08 Pa at FC2 H2 ¼ 85 cm3 = min) and current in both coils I c ¼ 15 A which corresponds to a magnetic field of 7 mT measured at the centre of the vessel. The temperature during deposition was 400–450 1C. The working gas mixture comprised Ar (499.999% purity) and acetylene (499.95%). The gas flow was measured by mass flow controllers (MFC) calibrated to the particular gas. The flow was adjusted automatically so that the total pressure, as measured by an ionisation gauge, was constant during the deposition. Since the ion gauge calibration is gas sensitive, appropriate correction factors were used as described elsewhere [7,8]. Energy and mass distributions of positive ions were measured using the energy and mass analyser (Balzers PPM421) with a floating orifice aligned
The energy distribution of ions is a strong function of magnetic field in the chamber. In Fig. 1, the energy distribution for a weak (a, I c ¼ 10 A) and strong magnetic (b, I c ¼ 15 A) field are presented. As can be seen, the distribution for the strong field is narrower than for the weak field and is sharply peaked at about 40 V. There are no ions with energy below 30 V but the distribution has a high-energy tail. Especially Ti+ and Ti2+ ions are sharply distributed, while Ar+ ions have a plateau between 40 and 60 V. For the weak field, the distribution is spread over 20–80 V with a maximum at about 55 V. Ti ions have a step in their distribution at about 35 V as seen previously; they basically follow the distribution for a strong magnetic field, but the intensity is lower. The same step is evident also for the 12C+ ion. On the other hand, the energy distributions for H+, Ar+ and the parent C2 Hþ 2 ions spread over the entire range of measured energies. The ion mass spectra for weak (I c ¼ 10 A) and strong (I c ¼ 15 A) magnetic fields are compared in Fig. 2. During the deposition under the strong magnetic field (Fig. 2b), the spectrum is similar to those we reported earlier [7,8]. The mass spectrum under a strong field reveals typical features of the plasma in the BAI 730 ion-plating apparatus. A high degree of ionisation is notable for the evaporated Ti, highlighted by the fact that the
ARTICLE IN PRESS M. Macˇek et al. / Vacuum 80 (2005) 184–188
186
+
40
Ar
48
+
Ti
+
ion flux [counts / s]
++
+ Hx
104
103
102
Ar
Ar
++
+
ArH
105
+
+
CHx
104
C2Hx
++ +
Ti
{
ion flux [counts / s]
Ti
C
C2H2
105
106
++
48
12 +
H2
103 102 101
(a)
101 10
20
30
60
12 + 40
Ar
70
48
++
+
48
+
Ti
104
103
Ar
30
50
60
++
Ar
++
Ti
105
40
12 +
+
Ti
+
C
104 103 102 101 0
102
(b)
10
(b)
10
20
30
40
50
60
m/q
Fig. 2. Comparison of the ion mass spectra measured during TiC deposition at (a) I coil ¼ 10 A and (b) I coil ¼ 15 A.
101 20
30
40
50
60
70
80
stopping potential [V]
Fig. 1. Energy spectra of the most significant ions during TiC deposition in Ar+C2H2 plasma at (a) I coil ¼ 10 A and (b) I coil ¼ 15 A.
intensities of the doubly charged Ti2+ ions observed at the mass-to-charge ratios from 23–25 are of the same order of magnitude as that of the singly charged Ti+ ions (peaks at m/q ¼ 46–50 amu).1 The spectrum contains also many other peaks due to the complicated cracking pattern of the C2H2 molecule. The most intense non-Ti peak is at the mass number m=q ¼ 41 amu, which belongs to the hydrogenated argon ion ArH+, followed by the hydrogen peaks at m=q ¼ 123 amu. The hydrocarbon ion intensities are relatively low compared with argon and Ti. The most intense peak is the carbon peak at m=q ¼ 12 amu (C+ or C2þ 2 ), while the hydrocarbon peaks 1
20
106
80
Ti
C
++
C2H2
105
ion flux [counts / s]
50
10
{
+ H2
40
ion flux [counts / s]
(a)
0
Note the Iarc is only 190 A instead of the standard 200 A.
þ CHþ n¼15 and C2 Hn¼15 have an order of magnitude lower intensities, with the parent ion C2 Hþ 2 (m=q ¼ 26 amu) being the most intense of these. However, it must be noted that the peaks at m=q ¼ + 24 and 25 amu (C+ 2 , C2H , respectively), which may be present, could not be distinguished because of the strong contribution of the 48,50Ti2+ isotope ions at these mass numbers. On the basis of our previous spectroscopic studies performed during CrC ion plating [10], we believe that they are of a lower intensity than the parent C2 Hþ 2 ion. It is necessary to point out again that the mass spectra are not corrected for the effect of the magnetic field. It was already mentioned in Section 2 that hydrogen peaks are underestimated (at I c ¼ 15 A) by about 5–10 times compared with the peaks with mass number m/q412 amu, which are more or less insensitive to the magnetic field. Consequently, the intensities of the hydrogen peaks with m=q ¼ 123 amu are comparable to the intensity of the hydrogenated argon ion.
ARTICLE IN PRESS M. Macˇek et al. / Vacuum 80 (2005) 184–188
The mass spectra in Fig. 2a (low magnetic field) are quite different from the spectra discussed above. Obviously, the intensity of Ti+ ions is much lower due to the lower evaporation rate obtained with the unfocused electron beam. Also, the very intense Ti2+ ion is either not present or it is masked by the group of C2 Hþ x ions. On the other hand, ions belonging to the þ CHþ x (x ¼ 025, m=q ¼ 12217 amu) and C2 Hx (m=q ¼ 24229 amu) groups are much more intense. The most intense of them is the parent ion + þ þ C 2 Hþ 2 followed by the C , CH3 and C2 H3 , whose intensities are only slightly lower than the intensity of the parent acetylene ion. The intensities of C x Hþ y ions are lower than the intensity of the 40 Ar+ ion and the same as the intensity of the doubly charged Ar ion (m=q ¼ 20 amu). Intensities of Hþ 13 ions are relatively strong and are in between the intensities of 40Ar2+ and 40Ar+ ions. Dissociation of acetylene under a high arc current and a weak magnetic field is not so effective as in strong field conditions when the acetylene is almost decomposed into its constituents. The main constituents are now hydrocarbon groups. In Fig. 3, the sums of the intensities over the mass number pertinent to various elements are plotted as a function of the coil current. The intensities were obtained by integrating the energy distribution, and the summing was performed over mass numbers with weights corresponding to the
integral intensity [counts / s]
ΣH ΣC Σ Ar
106
Σ Ti Σ
105
104
10
15
20
25
Icoil [A] Fig. 3. Sum of the integral ion flux densities as a function of the coil current in the Ar+C2H2 plasma.
187
number of atoms in the pertinent molecular species. From Fig. 3 we see that there are two regions. For coil currents ranging from 15–20 A, there is a region with high Ti evaporation and ionisation. The intensity of hydrocarbon ions is low and the most intense of carbon-containing species is pure 12C+ ions. On the other hand, the intensity of hydrogen is comparable to the Ar ion intensity. For coil currents below 12.5 A, there is an another region where the intensity of Ti ions is much lower, but the intensities of the whole family of acetylene dissociation products are significantly higher. It is evident from the mass spectra in Fig. 2a that for a weak field a whole family of hydrocarbons is present, and not only carbon and hydrogen as in the case for a strong field.
4. Conclusions The energy-resolved mass spectroscopy studies during a discharge in an Ar+C2H2 gas mixture in a triode ion-plating system revealed two different working regions. At strong magnetic fields (I c X15 A), the spectra show a high degree of Ti ionisation accompanied by almost complete acetylene dissociation. The main ionised species besides Ar+ are Ti+, Ti2+, + Hþ and 12C+. The intensity of hydro13 , ArH þ carbon ions CHþ 15 and C2 H15 is very low. At weak magnetic fields ðI c o12:5 A), the evaporation (and consequently ionisation) of Ti is low. The plasma is rich in hydrocarbon species. The most intense of them is the parent ion C2 Hþ 2 þ ions followed by the C+, CHþ 3 and C2 H3 ions. The mass distribution is qualitatively similar to that measured during the deposition of TiC under a strong magnetic field and low arc current, but the overall intensity is higher by an order of magnitude. By carefully adjusting the magnetic field, arc current and partial pressure of reactive gases, different plasmas rich in Ti ions or different hydrocarbon ions and even pure carbon ion can be obtained. Therefore, a wide range of conditions can be selected for the deposition of TiC coatings with hydrocarbon inclusions or even hydrocarbon coatings doped with Ti.
ARTICLE IN PRESS 188
M. Macˇek et al. / Vacuum 80 (2005) 184–188
Acknowledgements This work was supported by the Ministry of Education, Science and Sports of the Republic of Slovenia and partly sponsored in the scope of the bilateral Slovene–Czech project. References [1] Hedenqvist P, Bromark M, Olsson M, Hogmark S, Bergmann E. Surf Coat Technol 1994;63:115–22. [2] Sundgren J-E, Johansson B-O, Karlsson S-E. Thin Solid Films 1983;105:353–66.
[3] Yao SH, Su YL. Wear 1997;212:85. [4] Wilson A, Matthews A, Housed J, Turner R, Garside B. Surf Coat Technol 1993;62:600. [5] Ertu¨rk E, Knotek O, Burgmer W, Prengel H-G, Heuvel H-J, Dederichs HG, et al. Surf Coat Technol 1991; 46:39. [6] Su YL, Kao WH. Surf Coat Technol 2001;137:293. [7] Macˇek M, Misˇ ina M, Cˇekada M, Panjan P. Surf Coat Technol 2003;174–175:943. [8] Macˇek M, Cˇekada M. Surf Coat Technol 2004; 180–181:2. [9] Macˇek M, Navinsˇ ek B, Panjan P, Kadlec S. Surf Coat Technol 2001;135:208. [10] Macˇek M, Cˇekada M, Misˇ ina M. Czech J Phys 2000;50(Suppl S3):403.
Vacuum 80 (2005) 184–188 www.elsevier.com/locate/vacuum
Energy-resolved mass spectroscopy studies during the deposition of TiC films by ion plating under different magnetic fields M. Macˇeka,b,, M. Misˇ inac, M. Cˇekadaa, P. Panjana a
Faculty of Electrical Engineering, University of Ljubljana, Trzˇasˇka 25, 1000 Ljubljana, Slovenia b Jozˇef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia c Institute of Physics, Academy of Sciences, Na Slovance 2, 18040 Prague 8, Czech Republic
Abstract The energy-resolved mass spectroscopy studies during the discharge in an Ar+C2H2 gas mixture in a triode ionplating system revealed two different working regions. At strong magnetic fields (IcX15 A, BX7 mT), the spectra show a high degree of Ti ionisation accompanied by almost complete acetylene dissociation. The main ionised species besides + 12 + þ þ Ar+ are Ti+, Ti2+, Hþ 13 , ArH and C . The intensity of hydrocarbon ions CH15 and C2 H15 is very low. At weak magnetic fields (Ico12.5 A, Bo5:8 mT), the evaporation (and consequently ionisation) of Ti is low, but the plasma is + þ þ rich in hydrocarbon radicals. The most intense of them is the parent ion C2 Hþ 2 followed by C , CH3 and C2 H3 ions. Carefully adjusting the magnetic field, arc current and partial pressure of reactive gases, different plasmas rich in Ti ions or different hydrocarbon ions and even pure carbon ions can be obtained. r 2005 Published by Elsevier Ltd. Keywords: Energy-resolved mass spectroscopy; Ar–C2H2 plasma; Ion plating; TIC
1. Introduction Hard coatings based on transition metal nitrides MN (M ¼ Ti, Cr, etc.) are nowadays widely accepted as protective layers [1]. Less attention has been dedicated to transition metal carbides or Corresponding author. Tel.: +386 1 4768 356; fax: +386 1 4264 644. E-mail address: [email protected] (M. Macˇek).
0042-207X/$ - see front matter r 2005 Published by Elsevier Ltd. doi:10.1016/j.vacuum.2005.08.011
to ternary metallic carbonitrides [2–5] in spite of their interesting tribological properties. The common precursors used for the deposition of metallic carbides are the lower hydrocarbons such as methane (CH4) and acetylene (C2H2). Coatings deposited in hydrocarbon atmospheres contain a considerable amount of hydrogen. At higher hydrocarbon pressures and/or low evaporation rates, excess C atoms are incorporated in the form of amorphous hydrocarbon inclusions or,
ARTICLE IN PRESS M. Macˇek et al. / Vacuum 80 (2005) 184–188
even, amorphous hydrocarbon coatings doped with the metal (0–30 at%) [6] can be deposited. In our previous investigations, we performed energy-resolved mass spectroscopy studies during TiN, TiC and TiCN deposition [7,8]. In these studies, we focused our attention on the effect of arc current and reactive atmosphere in a triode ion-plating apparatus (Balzers BAI–730). It was found that the degree of ionisation in this system under standard conditions is very high. In this paper, we focused our attention on the effects of the magnetic field on the energy and mass spectra during TiC deposition.
185
with the substrates [8]. An important problem arises because the spectrometer is partially immersed in the vessel with a relatively strong magnetic field. Since it is very difficult to protect the whole spectrometer from the effect of the magnetic field, we performed a calibration, measuring the effect of the magnetic field on the spectra of neutrals. As we expected, only light ions with m/q less than 12 amu are strongly affected. All our results for the integrals of ion intensities and energy distributions are corrected for the effect of the magnetic field (but not for the quadrupole transmission factor). The mass spectra presented are as measured.
2. Experimental details 3. Results and discussion The energy-resolved mass spectroscopy of the ion flux was performed during the deposition of TiC films in the commercial Balzers BAI 730 triode ion-plating system. This system uses a filament-based ionisation chamber, which forms a low-voltage arc expanding into the reaction chamber. A more detailed description of the system can be found elsewhere [9]. TiC plating was done under the following conditions: arc current I arc ¼ 190 A, substrate voltage U B ¼ 125 V, argon pressure pAr ¼ 0:15 Pa (argon flow FAr 90 cm3/min), total pressure measured by ionisation gauge ptot ¼ 0:28 Pa (estimated partial pressure of C2H2 ¼ 0.08 Pa at FC2 H2 ¼ 85 cm3 = min) and current in both coils I c ¼ 15 A which corresponds to a magnetic field of 7 mT measured at the centre of the vessel. The temperature during deposition was 400–450 1C. The working gas mixture comprised Ar (499.999% purity) and acetylene (499.95%). The gas flow was measured by mass flow controllers (MFC) calibrated to the particular gas. The flow was adjusted automatically so that the total pressure, as measured by an ionisation gauge, was constant during the deposition. Since the ion gauge calibration is gas sensitive, appropriate correction factors were used as described elsewhere [7,8]. Energy and mass distributions of positive ions were measured using the energy and mass analyser (Balzers PPM421) with a floating orifice aligned
The energy distribution of ions is a strong function of magnetic field in the chamber. In Fig. 1, the energy distribution for a weak (a, I c ¼ 10 A) and strong magnetic (b, I c ¼ 15 A) field are presented. As can be seen, the distribution for the strong field is narrower than for the weak field and is sharply peaked at about 40 V. There are no ions with energy below 30 V but the distribution has a high-energy tail. Especially Ti+ and Ti2+ ions are sharply distributed, while Ar+ ions have a plateau between 40 and 60 V. For the weak field, the distribution is spread over 20–80 V with a maximum at about 55 V. Ti ions have a step in their distribution at about 35 V as seen previously; they basically follow the distribution for a strong magnetic field, but the intensity is lower. The same step is evident also for the 12C+ ion. On the other hand, the energy distributions for H+, Ar+ and the parent C2 Hþ 2 ions spread over the entire range of measured energies. The ion mass spectra for weak (I c ¼ 10 A) and strong (I c ¼ 15 A) magnetic fields are compared in Fig. 2. During the deposition under the strong magnetic field (Fig. 2b), the spectrum is similar to those we reported earlier [7,8]. The mass spectrum under a strong field reveals typical features of the plasma in the BAI 730 ion-plating apparatus. A high degree of ionisation is notable for the evaporated Ti, highlighted by the fact that the
ARTICLE IN PRESS M. Macˇek et al. / Vacuum 80 (2005) 184–188
186
+
40
Ar
48
+
Ti
+
ion flux [counts / s]
++
+ Hx
104
103
102
Ar
Ar
++
+
ArH
105
+
+
CHx
104
C2Hx
++ +
Ti
{
ion flux [counts / s]
Ti
C
C2H2
105
106
++
48
12 +
H2
103 102 101
(a)
101 10
20
30
60
12 + 40
Ar
70
48
++
+
48
+
Ti
104
103
Ar
30
50
60
++
Ar
++
Ti
105
40
12 +
+
Ti
+
C
104 103 102 101 0
102
(b)
10
(b)
10
20
30
40
50
60
m/q
Fig. 2. Comparison of the ion mass spectra measured during TiC deposition at (a) I coil ¼ 10 A and (b) I coil ¼ 15 A.
101 20
30
40
50
60
70
80
stopping potential [V]
Fig. 1. Energy spectra of the most significant ions during TiC deposition in Ar+C2H2 plasma at (a) I coil ¼ 10 A and (b) I coil ¼ 15 A.
intensities of the doubly charged Ti2+ ions observed at the mass-to-charge ratios from 23–25 are of the same order of magnitude as that of the singly charged Ti+ ions (peaks at m/q ¼ 46–50 amu).1 The spectrum contains also many other peaks due to the complicated cracking pattern of the C2H2 molecule. The most intense non-Ti peak is at the mass number m=q ¼ 41 amu, which belongs to the hydrogenated argon ion ArH+, followed by the hydrogen peaks at m=q ¼ 123 amu. The hydrocarbon ion intensities are relatively low compared with argon and Ti. The most intense peak is the carbon peak at m=q ¼ 12 amu (C+ or C2þ 2 ), while the hydrocarbon peaks 1
20
106
80
Ti
C
++
C2H2
105
ion flux [counts / s]
50
10
{
+ H2
40
ion flux [counts / s]
(a)
0
Note the Iarc is only 190 A instead of the standard 200 A.
þ CHþ n¼15 and C2 Hn¼15 have an order of magnitude lower intensities, with the parent ion C2 Hþ 2 (m=q ¼ 26 amu) being the most intense of these. However, it must be noted that the peaks at m=q ¼ + 24 and 25 amu (C+ 2 , C2H , respectively), which may be present, could not be distinguished because of the strong contribution of the 48,50Ti2+ isotope ions at these mass numbers. On the basis of our previous spectroscopic studies performed during CrC ion plating [10], we believe that they are of a lower intensity than the parent C2 Hþ 2 ion. It is necessary to point out again that the mass spectra are not corrected for the effect of the magnetic field. It was already mentioned in Section 2 that hydrogen peaks are underestimated (at I c ¼ 15 A) by about 5–10 times compared with the peaks with mass number m/q412 amu, which are more or less insensitive to the magnetic field. Consequently, the intensities of the hydrogen peaks with m=q ¼ 123 amu are comparable to the intensity of the hydrogenated argon ion.
ARTICLE IN PRESS M. Macˇek et al. / Vacuum 80 (2005) 184–188
The mass spectra in Fig. 2a (low magnetic field) are quite different from the spectra discussed above. Obviously, the intensity of Ti+ ions is much lower due to the lower evaporation rate obtained with the unfocused electron beam. Also, the very intense Ti2+ ion is either not present or it is masked by the group of C2 Hþ x ions. On the other hand, ions belonging to the þ CHþ x (x ¼ 025, m=q ¼ 12217 amu) and C2 Hx (m=q ¼ 24229 amu) groups are much more intense. The most intense of them is the parent ion + þ þ C 2 Hþ 2 followed by the C , CH3 and C2 H3 , whose intensities are only slightly lower than the intensity of the parent acetylene ion. The intensities of C x Hþ y ions are lower than the intensity of the 40 Ar+ ion and the same as the intensity of the doubly charged Ar ion (m=q ¼ 20 amu). Intensities of Hþ 13 ions are relatively strong and are in between the intensities of 40Ar2+ and 40Ar+ ions. Dissociation of acetylene under a high arc current and a weak magnetic field is not so effective as in strong field conditions when the acetylene is almost decomposed into its constituents. The main constituents are now hydrocarbon groups. In Fig. 3, the sums of the intensities over the mass number pertinent to various elements are plotted as a function of the coil current. The intensities were obtained by integrating the energy distribution, and the summing was performed over mass numbers with weights corresponding to the
integral intensity [counts / s]
ΣH ΣC Σ Ar
106
Σ Ti Σ
105
104
10
15
20
25
Icoil [A] Fig. 3. Sum of the integral ion flux densities as a function of the coil current in the Ar+C2H2 plasma.
187
number of atoms in the pertinent molecular species. From Fig. 3 we see that there are two regions. For coil currents ranging from 15–20 A, there is a region with high Ti evaporation and ionisation. The intensity of hydrocarbon ions is low and the most intense of carbon-containing species is pure 12C+ ions. On the other hand, the intensity of hydrogen is comparable to the Ar ion intensity. For coil currents below 12.5 A, there is an another region where the intensity of Ti ions is much lower, but the intensities of the whole family of acetylene dissociation products are significantly higher. It is evident from the mass spectra in Fig. 2a that for a weak field a whole family of hydrocarbons is present, and not only carbon and hydrogen as in the case for a strong field.
4. Conclusions The energy-resolved mass spectroscopy studies during a discharge in an Ar+C2H2 gas mixture in a triode ion-plating system revealed two different working regions. At strong magnetic fields (I c X15 A), the spectra show a high degree of Ti ionisation accompanied by almost complete acetylene dissociation. The main ionised species besides Ar+ are Ti+, Ti2+, + Hþ and 12C+. The intensity of hydro13 , ArH þ carbon ions CHþ 15 and C2 H15 is very low. At weak magnetic fields ðI c o12:5 A), the evaporation (and consequently ionisation) of Ti is low. The plasma is rich in hydrocarbon species. The most intense of them is the parent ion C2 Hþ 2 þ ions followed by the C+, CHþ 3 and C2 H3 ions. The mass distribution is qualitatively similar to that measured during the deposition of TiC under a strong magnetic field and low arc current, but the overall intensity is higher by an order of magnitude. By carefully adjusting the magnetic field, arc current and partial pressure of reactive gases, different plasmas rich in Ti ions or different hydrocarbon ions and even pure carbon ion can be obtained. Therefore, a wide range of conditions can be selected for the deposition of TiC coatings with hydrocarbon inclusions or even hydrocarbon coatings doped with Ti.
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Acknowledgements This work was supported by the Ministry of Education, Science and Sports of the Republic of Slovenia and partly sponsored in the scope of the bilateral Slovene–Czech project. References [1] Hedenqvist P, Bromark M, Olsson M, Hogmark S, Bergmann E. Surf Coat Technol 1994;63:115–22. [2] Sundgren J-E, Johansson B-O, Karlsson S-E. Thin Solid Films 1983;105:353–66.
[3] Yao SH, Su YL. Wear 1997;212:85. [4] Wilson A, Matthews A, Housed J, Turner R, Garside B. Surf Coat Technol 1993;62:600. [5] Ertu¨rk E, Knotek O, Burgmer W, Prengel H-G, Heuvel H-J, Dederichs HG, et al. Surf Coat Technol 1991; 46:39. [6] Su YL, Kao WH. Surf Coat Technol 2001;137:293. [7] Macˇek M, Misˇ ina M, Cˇekada M, Panjan P. Surf Coat Technol 2003;174–175:943. [8] Macˇek M, Cˇekada M. Surf Coat Technol 2004; 180–181:2. [9] Macˇek M, Navinsˇ ek B, Panjan P, Kadlec S. Surf Coat Technol 2001;135:208. [10] Macˇek M, Cˇekada M, Misˇ ina M. Czech J Phys 2000;50(Suppl S3):403.