Could you explain the significance of your article to the non-specialist?

Friction occurs when 2 surfaces in contact are moved with respect to each other. This phenomenon, first scientifically described by Leonardo da Vinci, is well known to everybody and economically extremely important: Improved attention to friction and wear would save developed countries more than 1% of their gross national product. A better understanding of the processes leading to the corresponding energy losses on an atomic scale is possible with the atomic force microscope. Quite often friction occurs between surfaces which are "wet", and therefore electrochemistry is involved. This article describes for the first time the influence of potential and adsorbates on friction forces under electrochemical conditions.

What has motivated you to conduct this work?

In the past, most fundamental experiments were done under UHV conditions. Besides the practical importance of friction under electrochemical conditions, a further advantage of friction measurements at well defined electrode surfaces is that adsorbate layers can often be quickly deposited and desorbed again simply by varying the electrode potential. This fast reversibility of the systems allows an easy control of artifacts, which in the case of AFM or FFM measurements could originate from irreversible changes of the AFM-tip.

Where do you see this work developing in the future?

Other adsorbate systems with different adsorption strengths will have to be studied in order to substantiate the proposed model of energy dissipation due to desorption and readsorption. This could lead to trends that may be correlated with the physical properties of the adlayer like surface energy or point of zero charge (pzc). In particular organic adsorbates will be studied because they could serve as a model for organic lubricants. Due to the anisotropy of single crystalline surfaces, friction also should depend on the scan direction, in particular for surfaces with a low surface symmetry, e.g. Au(110). This, together with the influence of monoatomic steps and atomic roughness in general, has to be elucidated.

Are there any particular challenges facing future research in this area?

A particular challenge is to elucidate the role of the tip on the friction results. We will use different tip materials, and also use metallized tips, in order to separate different effects on friction. Also the anisotropy of friction and the influence of steps on friction forces are of great interest. Further challenges in future research are the following questions: 1. Can tribological measurements under electrochemical conditions help to understand faster and better the role of monolayers and adsorbates on friction effects in general? 2. Is there a chance that friction force measurements will help in gaining additional information on the double layer structure, the mobility or stiffness of adsorbate layers? 3. Will the transition from friction to wear be dependent on potential and adsorbates?