For example, adhesive wear occurs frequently during tribo-test under aqueous condition.

1. Case 2. Penetration into film Case 1. Reaction at surface F1 F1 F1 F2 substrate substrate substrate substrate = > : Initial residual stress : added force : film thickness Residual Stress of a-C:H Film in Humid Environment • Young-Jin Lee1), 2), Tae-Young Kim1),Kwang-Ryeol Lee1), In-Sang Yang2) • Future Technology Research Division, Korea Institute of Science & Technology, Korea 2) Department of Physics, Ewha Womans University, Korea Result & Discussion a-C:H film has excellent physical and chemical properties such as high hardness, low friction, high wear resistance and chemical inertness. Various applications ranging from data storage to bio-materials have been investigated. Increase in the residual stress with humidity change from 20% to 90%. Max. 16MPa Immediate and reversible change of the residual stress with humidity change. Increase in the residual stress with humidity change from 20% to 90% Max. 12MPa Immediate and reversible change of the residual stress with humidity change. Critical issue of a-C:H film for bio-application : Film delamination is enhanced in humid and aqueous environment. For example, adhesive wear occurs frequently during tribo-test under aqueous condition. Observations • Residual stress of a-C:H film exhibits a humidity dependence, which is related to the atomic bond structure of the film. • In polymeric and graphitic film, the compressive residual stress increases as the humidity increases. • The residual stress of diamond-like film is independent of the humidity. • The change of the residual stress is immediate and reversible with humidity variation. Tribo-test of a-C:H film in aqueous environment T. Ohana at al. Diamond Rel. Mater., 13 (2004) 1500 Residual stress is independent of the humidity in the range from from 20% to 90% Max. 0 MPa • Purposes of the Present Work • To check the possibility that the residual stress of a-C:H film is dependent on the humidity. • To characterize the humidity dependence of residual stress of a-C:H film of various atomic bond structures. The Role of Water Molecules in the Change of Stress The role of water molecules can be found by the relationship between the film thickness and variation of stress. Stress Measurement with Humid Change • In situ stress measurement : kMOS (k-space Multi-beam Optical Sensing) • Humidity control : 10~90% in air (±5%) step control. • Temperature : room temperature (19~26°C) • Measurement time : about 600sec for each step. • Resolution of kMOS : maximum 4km in radius (In this system 1MPa) Film Deposition • r.f. PACVD (13.56 MHz) • Precursor Gas : C6H6, CH4 • Deposition Pressure : 1.33 Pa • Bias Voltage : -100V ~ -500V • Substrate : • P-type (100) Si-wafer 525㎛ • P-type (100) Si-wafer 200㎛ (5×50㎜) • Film Thickness : 500㎚ In polymeric films, the variation of stress with humidity decreases as the film thickness increases. “Case 1. Reaction at surface” is predominant. In the case of polymeric a-C:H film, for all thickness additional surface force caused by water molecule is Film Characterization 9.4±1.4 Nm-1 Residual Stress Raman spectroscopy C6H6 CH4 Conclusions • The most significant result of the present work is to show that theresidual stress of a-C:H film is dependent on the humidity, which is related to the atomic bond structure of the film. • The humidity dependence of the residual stress is due to the interfacial reaction with water molecule. 1) Immediate and reversible change with humidity variation 2) Change of the residual stress is inversely proportional to the film thickness • Humidity dependence of the residual stress could be controlled by either changing the atomic bond structure or a simple surface treatment. From the residual stress and Raman spectroscopy, C6H6 -100V Polymeric film CH4 –150V Diamond-like film CH4 –500V Graphitic film