A mode of pulse biasing of DLC coating deposition is theoretically investigated. In this mode a deposited
ion flow of plasma with energy of E0 (20 200) eV is modified by superimposing of pulse potential
~ 1000 V. It was shown that intrinsic stress in a DLC coating can be decreased in several times without of
essential decrease of sp3-bonded carbon concentration compared with DLC made in stationary mode deposition
at E0 ion energy. A method of optimization of pulse mode parameters is proposed which is based on
analysis of location of thermoelastic peaks of ions on phase P, T-diagram of carbon.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3539

Kalinichenko, A.I.

Strel'nitskij, V.E.

Vasyliev, V.V.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 4, 04PITSE07(3pp) (2012)   2304-1862/2012/1(4)04PITSE07(3) 04PITSE07-1  2012 Sumy State University Characteristics of DLC Coating Prepared by Pulse Biasing:  Analysis in Model of Thermoelastic Peak of Ion   V.V. Vasyliev, A.I.  Kalinichenko, V.E.  Strel‟nitskij  National Science Center “Kharkov Institute of Physics and Technology”,  61108, Akademicheskaya, 1, Kharkov Ukraine  (Received 19 June 2012; published online 24 August 2012)  A mode of pulse biasing of DLC coating deposition is theoretically investigated. In this mode a deposit-ed ion flow of plasma with energy of E0  (20  200) eV is modified by superimposing of pulse potential ~ 1000 V. It was shown that intrinsic stress in a DLC coating can be decreased in several times without of essential decrease of sp3-bonded carbon concentration compared with DLC made in stationary mode depo-sition at E0 ion energy. A method of optimization of pulse mode parameters is proposed which is based on analysis of location of thermoelastic peaks of ions on phase P, T-diagram of carbon.   Keywords: DLC coating, Plasma-based ion deposition, Pulse mode deposition, Intrinsic stress, Phase P,T-diagram of carbon, Non-local thermoelastic peak of ion.   PACS numbers: 52.77.Dq, 81.15.Jj   1. INTRODUCTION   Tetrahedral amorphous carbon (ta-C) formation at deposition of low-energy C+ ions is directly connected with subsurface phenomena occuring near the ion tra-jectory in carbon target [1]. Different aspects of ta-C formation at ion implantation were explained with con-cept of a thermal spike of ion that is a small nanome-ter-sized region where implanted ion energy contains [2-5]. Particularly, a model of ta-C formation at im-plantation of ions with energy from 25 to 1000 eV in carbon target was proposed in [4, 5]. According to this model, ta-C forms as a result of short-time coaction of high temperature and pressure in non-local thermoe-lastic peak (NTP) containing thermalized phonon loss of ion energy. The pressure in the peak consists of a thermoelastic component, a deformational one due to additional introduced volume and an intrinsic stress appearing in the coating at the ion bombardment. As it was shown experimentally and theoretically [1, 2, 5], intrinsic stress value varies depending on energy of deposited ions and substrate temperature in the range from ~10 GPa to 0.5 GPa when the ion energy E varies from 25 eV to 1000 eV. The compression stresses stimulate a dense phase formation but on the other hand they can lead to splitting of coating and its de-tachment from substrate [2].  Therefore, elaboration of deposition methods to de-crease intrinsic stress without appreciable degradation of physical and mechanical properties of coatings is the highly actual problem. One of working methods ensur-ing intrinsic stress decrease is the plasma immersion ion implantation in a pulse biasing mode [6,7]. In this case stationary deposition of ions with energy E0  (20–200) eV alternates with pulse bombardment by ions with considerably high energies E  1000 eV. The goal of this work is the analysis of thermody-namic conditions of carbon coating formation in pulse biasing mode to determine influence of ion deposition parameters, i.e. duration and frequency of pulses as well as ion energy in pulses, on carbon coating charac-teristics. 2. METHOD OF ANALYSIS AND CALCULATION   Calculations of radius R(t, E), temperature T(t,E) and pressure in NTP of C+ ion in ta-C depending on ion energy E and time t from moment of origination gave an opportunity to build NTP trajectories of C+ ions of different energies on phase P,T- diagram of carbon [4, 5]. Location of P, T- trajectory relatively to bounda-ry “diamond - graphite” was accepted as the main test of possibility of ta-C production in the ion NTP.  Fig. 1 displays the initial locations of NTPs of C+ ions with different energies in an unstressed ta-C ma-trix (symbols ◊). As can be seen in Fig. 1, only the ion peaks with minimal energies E  25 eV lie in the area of diamond stability. According to accepted supposition only ions with these energies produce sp3-bond carbon effectively.  GRAPHITE05101520  P,GPaT, К1000 2000 3000DIAMOND1   -  25 eV2   - 50 eV3   - 75 eV4  - 100 eV6  - 300 eV 7 - 500 eV5  - 150 eV 8 - 1000 eV1234567821345678  Fig. 1 –  Initial localization of C  NTPs of different energies in carbon matrix on phase P,T-diagram of carbon. The symbols ◊ correspond to case of unstressed target; symbols ♦ show peak locations subject to intrinsic stress appearing at deposition of ions of different energies in stationary mode  As it was noted in INTRODUCTION, a compressive stress (E) appears in coating at deposition of ions with energy E. The expression for (E) was obtained in [5] using NTP model of implanted ion:  V.V. VASYLIEV, A.I.  KALINICHENKO, V.E.  STREL’NITSKIJ PROC. NAP 1, 04PITSE07 (2012)  04PITSE07-2  1 2( )1 ( ) ( )YEM EE BR j w Es r= × ×- P + , (1)  where R is the flux density of deposited atoms, j is the flux density of bombarding ions, M is the atom mass, r is the mass density of a coating material, and B is the numerical constant. The number of thermoactivated transitions w(E)  in  NTP  with  migration  energy  of  de-fects U = 0,3 eV depends on temperature and is deter-mined subject to decrease of defects due to migration:   ( ) ( ) ( )( )tn tn-- - ò= ò, , 000, ,0 00, ,Utk T E TBcBUt e dk T t E Tw E T n V t E e dt ,    Here n0 is the bulk concentration of atoms, n is the De-bye’s frequency for carbon, tc = – R2/4k – is the effective time of cooling, k - is the thermal diffusivity of a target material, kB is the Boltzmann constant. Temperature in NTP is determined from Debye’s formula for energy of solid as a root of equation [4]:   ( ) ( )h q qræ öæ ö= - ç ÷ç ÷è ø è ø00E ETD T DC V t T T,   where C is the high-temperature limit of heat capacity, h(E) is the fraction of phonon energy loss of C+ ion with energy E in carbon target, and   ( ) = -ò33031xzz dzD xx e.  Eq. (1) is a modification of known Davis’es formula [2]. It takes into account nonlocality of ion energy loss, sub-strate temperature T0 and  dependence  of  thermal  ca-pacity on temperature. NTP volume is determined by expression [4]:  ( ) ( ) ( ) ( ) ( )pé ùê ú= + -ê úë û33 22 1, , ,3 2 3 8L E L EV E t R E t R E t ,  where L(E)  is  the  average  projective  range  of  C+ ion. Functions L(E) and h(E) are calculated by TRIM2000 [8]. Fig. 2 displays dependence of compressive stress in deposited ta-C coating on energy of C+ ions calculated by Eq. (1) (stationary mode of deposition) [5]. Substrate temperature T0 is equal to 300°K. Analogous depend-ence was obtained in [2] assuming that U = 3 eV. Subject to these stresses, NTPs of C+ ions on phase diagram  occupy  places  shown  by  symbols  ♦ in  Fig.  1.  The initial locations of peaks shifted in the direction of diamond stability area, the ion energy range producing sp3-bond carbon increases considerably (from 25 eV up to ~250 eV) [5]. In pulse biasing mode a coating is produced by ions of two different energies. It is known that in stationary mode C+ ions of low energies E0 £ 100 eV produce ta-C coating with maximal concentration of sp3–bonds [1, 2]. However low-energy ions generate maximal compres-sive stresses s0 = (8 – 10) GPa. The purpose of “high-energy” pulses is to reduce intrinsic stresses in coating. Deposition of C+ ions with energies E ~ 1000 eV leads to generation of considerably lower stresses s ≤ 1 GPa [1,2]. However, it forms mainly sp2-bond carbon because thermodynamic conditions appearing in NTPs of C+ ions with such energy are favourable for its production [5].  02468200 400 600 800 1000E, eVs(E),GPa  Fig. 2 – Compressive  stress  in  ta-C  coating  vs.  energy  of  C+ ion (stationary mode of deposition)   Intrinsic stress sp(f,E) which generates in the coat-ing in pulse biasing mode is determined by additive effect of ions of two different energies:   ( ) ( ) ( ) ( )s s s= + - 0, 1p p pf E ft E ft E , (2)  Expression (2) is true when the following conditions are satisfied: 1) applicability of NTP model; 2) establishing of stationary intrinsic stress during pulse time; 3) in-dependence of activation energy of defect migration on pressure.  Fulfilment of these conditions permits to use func-tion s(E) shown in Fig. 2 [5, 9]. It is obviously that intrinsic stress value lies in the range s(E) < sp < s0. Dependence of intrinsic stress sp in carbon coating deposited in pulse mode on pulse-repetition frequency f is shown in Fig. 3. Calculation data adduce for three different energies of ions in the “high-energy” pulse at E0 = 25 eV. Assuming E0 = 25 eV, E = 1000 eV, we find that in-trinsic stress changes in rather wide range 0.5 GPa < sp < 8.6 GPa depending on pulse-repetition frequency f.  Arising  intrinsic  stress  leads  to  ‘rising’  of  NTP of ‘high-energy’ ion and to ‘lowering’ of NTP of ‘low-energy’ ion on phase P, T- diagram  of  carbon  at  arbitrary frequency f from allowed range 0 £ f £ 1/tp. So, Fig. 4 shows location of NTPs of ions with energies 25 eV and 1000 eV in unstressed matrix (symbols ◊), in stressed matrix at deposition of ions of specified ener-gies in stationary mode (symbols ♦), in stressed matrix at deposition of ions in pulse mode (symbols ▲). Char-acteristics of the pulse mode are the following tp = 5 ms; E0 = 25 eV; f  = 24 kHz; E = 1000 eV. Fig. 4 shows that NTP location of ‘low-energy’ ion of 25 eV changed insignificantly as compared with sta-tionary mode and it stays in the area of diamond stabil-ity. On the contrary, NTP of ‘high-energy’ ion has con-siderably risen in the area of higher pressures passing from the area of graphite stability to the one of dia-mond stability. For this reason, deposited ions of high-energy fraction have to produce sp3-bond carbon as ‘low-energy’ ions. In this case, the use of pulse mode  CHARACTERISTICS OF DLC COATING PREPARED BY … PROC. NAP 1, 04PITSE07 (2012)  04PITSE07-3 decreases insignificantly effectiveness of generation of sp3-bond carbon coating as compared with deposition of ions of ‘low’ energy E0 = 25 eV.  50 100034567  s ,GPa123t = 5 mspf, kHz15012p  Fig. 3 – Dependence of intrinsic stress sp  on pulse-repetition frequency f. Energy of ions in pulse is equal to 200 eV, 400 eV and 1000 eV (curves1, 2, 3, correspondingly)  010201000 2000 3000  P,GPaT, КDIAMONDGRAPHITEE =25 eVE=1 keVf = 24 kHzt    = 5 msp0  Fig. 4 – Initial points and trajectories of NTPs of C+ ions with energies 25 eV and 1000 eV in carbon matrix on phase P,T-diagram of carbon in cases of unstressed target (◊); in station-ary mode of deposition (♦); in pulse mode with repetition fre-quency f = 24 kHz (▲)  Intrinsic stress in deposited coating decreases when repetition frequency f of ‘high-energy’ pulses increases (see Fig. 3). Due to this regularity we can reduce resid-ual stress in the coating at insignificant decrease of effectiveness of generation of sp3-bond carbon. At that a necessary condition is that initial locations of the ion NTPs and their trajectories in phase P,T – diagram of carbon do not go beyond area of diamond stability. The extreme case that corresponds to minimal residual stress spmin = 3,2 GPa is reached at fm = 132 kHz (see Fig. 5). Further increase of repetition frequency of ‘high-energy’ pulses leads to shift of NTP trajectory down into the area of graphite stability. It causes decrease of effectiveness of generation of sp3-bond carbon that leads to considerable decrease of hardness and modulus of elasticity of coating. The use of pulse mode of DLC coatings deposition permits to reduce residual stress in coating more than in 2.5 times as compared with deposition of ions with energy E0 = (20 ¸ 200) eV in stationary mode when high residual stress s occurs (up to ~ 10  GPa). At that effec-tiveness of sp3-bond carbon formation does not decrease considerably.  010201000 2000 3000  P,GPaT, КDIAMONDGRAPHITEE=25 eVE=1 keVf  = 132 kHzt  = 5 mspm  Fig. 5 – Initial points and trajectories of NTPs of C+ ions with energies  25  eV  and  1000  eV  in  carbon  matrix  on  phase  P,T-diagram of carbon in cases of unstressed target (◊); in station-ary mode of deposition (♦); in pulse mode with repetition fre-quency f = 132 kHz (▲)  3. CONCLUSIONS   1. The use of pulse biasing mode of DLC coating deposition permits to reduce considerably (in several times) residual stress and to maintain effectiveness of sp3-bond carbon formation as compared with deposi-tion of ions with energies E0 = (20 ¸ 200) eV in station-ary mode. 2. Analysis of location of C+ ion NTPs on phase P,T-diagram of carbon permits to chose optimal character-istics of pulse mode deposition ensuring sp3-bond car-bon generation in NTPs of both ‘low-energy’ and ‘high-energy’ ions.   REFERENCES  1. J. Robertson, Mater. Sci. Eng. R37, 129 (2002). 2. C.A. Davis, Thin Solid Films 226, 30 (1993). 3. J. Robertson, Diam. Relat. Mater. 2, 984 (1993). 4. A.I. Kalinichenko, S.S. Perepelkin, V.E. Strel’nitskij, Di-am. Relat. Mater. 15, 365 (2006). 5. A.I. Kalinichenko, S.S. Perepelkin, V.E. Strel’nitskij, Di-am. Relat. Mater. 19, 996 (2010). 6. D. Sheeja, B.K. Tay, L.J. Yu, S.P. Lau, J.Y. Sze, C.K. Cheong, Thin Solid Films 420–421, 62 (2002). 7. Y.B. Zhang, S.P. Lau, D. Sheeja, B.K. Tay, Surf. Coat. Tech. 195, 338, (2005). 8. F. Ziegler J, J.P. Biersack, U. Littmark. The Stopping and Range of Ions in Solids. New York: Pergamon Press, 1996. 9. A.I. Kalinichenko, S.S. Perepelkin, V.E. Strel’nitskij, Prob-lems of atomic science and technology, series: “Physics of radiation damages and radiation material science” No 6, 116(2007). 

Characteristics of DLC Coating Prepared by Pulse Biasing: Analysis in Model of Thermoelastic Peak of Ion

Abstract

Similar works

Full text

Available Versions

Electronic Sumy State University Institutional Repository