Investigations of reconstruction of passivation layer on stainless steel surface using AFM-based techniques

Continuous development of stainless steel technology forced by the increase in the growing demands on the operating parameters of various stainless steel alloys, is the motivation for implementation of research for understanding the complexity of electrochemical processes ongoing on the surface of a material during various technological processes and during exploitation of the finished components. In this paper, the use of atomic force microscopy (AFM) is presented as a tool for observation of reconstruction process of passivation layers on the surface of previously electropolished stainless steel. For this purpose, a technique called nanoscratching was used, in which scratches are made on the surface of a material by means of diamond scanning probe, which violates the continuity of the passivation layer. Then, the dynamics of the process of reconstruction of that layer was assessed using continuous imaging of the scratched area in AFM semicontact mode. Studies of this type can be used to evaluate the impact of various factors on the spontaneous reconstruction of the passivation layer as well as possible susceptibility of the material on the course of corrosion processes initiated as a result of mechanical defects arising during operation of the material. By using the AFM, it was possible to observe changes in the depth of scratches with a subnanometer resolution. Obtained results proved that the presented AFM application allowed observation of the dynamics of passivation layer reconstruction process in a quantitative fashion, therefore it seems to be a very useful tool in the investigation of the impact of various conditions on this phenomenon. The results showed that changes in surface modification were occurring in a continuous manner. Changing dynamics of said process was presented. It should be underlined that no such experiments have been reported so far.

COMPLEX AFM ANALYSIS WITH RASTER SPRING IMAGING MODE

The new Raster Spring Imaging Mode is developed to study soft and bad – fixed objects in AFM. The normal and lateral force between tip and sample is minimized. We discuss the principle of operation, main features and its prospect for specific applications. Experimental results revealed advantages with regard to other techniques like contact or semicontact mode. The silicon structure measurements with Raster Spring Imaging Mode allow to obtain information of elastic and adhesion properties without losing sight of good topography image.

Micro/Nano-Tribological Behavior of Octadecyltrichlorosilane on Silicon as a Coating for MEMS

Despite progresses achieved in the technology of MEMS, the tribological problem continues being an unresolved matter. Wear and stick-slip phenomena are many times the origin of failure of these devices. The application of self-assembled monolayers (SAMs) in liquid phase seems to be a solution to this problems. SAMs of octadecyltrichlorosilane (CH3(CH2)17SiCl3, OTS) were attached to Si(100) oxidized in liquid phase. Contact angle measurements were used for characterizing the grade of hydrophobicity. The topography of the coating was obtained with an Atomic Force Microscopy (AFM) in semicontact mode. The images showed the presence of particles related to the polymerization of the precursor molecule during the formation process of the SAMs. Creating the film of lubricant in vapour phase would avoid this undesirable effect. Tribological tests were carried out with a microtribometer in linear reciprocating movement with a ball of 2 mm of diameter (100Cr6 and Si3N4) and load of some milinewtons. Results were compared with those obtained for silicon oxidized without any coating. The coefficient of friction (COF) and wear (substrate and ball) were studied under different test conditions.