Ion Beam Assisted Deposition of Si-Diamond-Like Carbon Coatings on Large Area Substrates
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diffusion pump oil). The diffusion pump oil precursor was evaporated through seven, 3 mm diameter, closely packed nozzles (multinozzle container) arranged in a hexagonal pattern. The distance between the apertures was fixed at approximately 5mm according to a mathematical model [1], developed at AR, of the spatial distribution of film deposition from nozzles and apertures onto inclined substrates. This model has been used to predict the appropriate source spacing to obtain uniform deposition thickness across even larger area substrates. The substrates were initially cleaned in methanol and acetone and then sputter-cleaned with a 40 keV Ar÷ beam(40 WAlcm.' for 10 min.). A watercooled sample stage maintained the temperature of the substrates during deposition close to room temperature. The base pressure was 2 x 10-6 Torr and the deposition was carried out at 3x 10 Torr pressure. The oil temperatures, monitored by a thermocouple, used for the film deposition were 115 *C, a substantial evaporation temperature decrease from all other previous works, and 130 *C. The substrate was inclined at 450 with respect to both the horizontal ion beam and the vertical flow direction of the vaporized oil. A shutter was placed above the oil container to start and stop the oil deposition. The growing film surface was continuously bombarded by a slowly oscillating (1 Hz) ribbon (0.02 m x 0.20 m) Ar+ion beam at 40 keV. Typical depositions lasted from 120 to 380 minutes. Thepeak ion current density in the ribbon beam was varied from 83 pA cm. 2 to 270 p-A cm. (Table I) as read by a Faraday cup. The thickness and the microhardness of the films were measured along the rectilinear surface coordinates of the substrate with the aid of a Dektak II profilometer. The microhardness of the coatings were also measured along the rectilinear surface coordinates using a Knoop microhardness tester. A ball-on disk tribometer (Implant Sciences ISC-200) with a 1/2" diameter AISI 52100 high chrome steel ball under 1 N load was used to determine the unlubricated sliding coefficient of friction. TABLE I. Deposition Parameters, Thickness, Microhardness, Deposition Rate and Adhesion of Si-DLC Coatings Produced at 40 keV. Oil Ion Beam (Ar÷) Thickness Evaporation Current Density (nm) Temperature (pA/cm 2)
Microhardness (MPa)
Deposition Rate (nm/min.)
Adhesion
(00) 115
145
542
15,410
1.505
Excellent
115
228
904
5,000
3.78
Poor (Porous)
130
100
1,087
8,080
2.86
Excellent
130
130
1,482
5,880
4.12
Excellent
130
153
1,587
10,920
4.41
Excellent
130
184
1,574
5,040
13.12
Excellent
130
195
1,372
7,960
5.72
Excellent
130
255
1,159
8,920
3.73
Excellent
570
EXPERIMENTAL RESULTS Adhesion and Film Thickness Distribution The film thickness depended upon the evaporation temperature and ion current density. The film thicknesses were varied from 542 to 1590 nm, depending on the deposition time. At 115 °C oil evaporation temperature the film deposition rate increased with increasing ion current density (Table I). While the depos
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