An instrument for direct measurements of sputtering related momentum transfer to targets J. Rutscher ⇑ , Th. Trottenberg, H. Kersten Institute of Experimental and Applied Physics, Christian-Albrechts-University of Kiel, D-24098 Kiel, Germany article info Article history: Received 30 November 2012 Received in revised form 27 February 2013 Available online 13 March 2013 Keyword: Sputtering abstract The article presents an instrument that measures sputtering related momentum transfer to a target. The instrument is operated in the beam of a broad-beam ion source and its main part is similar to a rotor of a wind mill. One component of the transferred momentum perpendicular to the beam is converted into a rotational movement of its rotor. This geometry makes the device sensitive to the momentum of sput- tered target atoms and reflected beam particles, but insensitive for the momentum of the impinging par- ticles itself. Exemplary measurements with argon ions in the energy range from 0.5 keV to 1.5 keV impinging onto copper targets at an incidence angle of 56° are presented. The results are compared with simulations based on the popular Monte-Carlo program TRIM and show a good agreement. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Sputtering became over the time an important method for the production of thin films. In the early seventies of the 20th century, magnetron sputtering was invented and is now the technique of choice for many industrial coating applications [1]. Sputtering be- came also the basis of several analytical techniques like secondary ion mass spectrometry [2] for the determination of the composi- tion of solid surfaces and thin films. However, there are also disad- vantageous aspects of sputtering. Grid erosion by sputtering is a crucial effect that determines the maintenance intervals for indus- trial broad-beam ion sources and the life expectancy of gridded ion thrusters for propulsion of space vehicles [3,4]. Sputtering is also a serious problem on the way to a future fusion reactor [5,6]. Driven by the wide application and occurrence of sputtering, the understanding of the underlying physics advanced, too. Impor- tant was the insight, that sputtering is the result of a series of atomic collisions initiated by each impacting particle rather than evaporation due to local heating [7–9]. Two of the important cor- roborative experiments in favor of the collision cascade concept were the measurements of the velocity of sputtered atoms by Ko- pitzki and Stier [10] and later of the velocity distribution by Thompson in a time-of-flight experiment [11]. The concept of col- lision cascades was at first applied in analytical models [12,13] and not much later in computer simulations. In the eighties, a large number of computer simulations for the stopping of ions in solids were published [14], most of them based on the binary collision approximation. A few of them have been maintained to this day. A popular Monte-Carlo program for amorphous targets is TRIM [15–17], today part of the program package SRIM. The program MARLOWE [18] can treat collision cascades in crystalline materials. In addition to the initial version of TRIM, which only treats projec- tiles, its extension TRIM.SP [19] also deals with sputtered target atoms. The simulation codes TRIDYN [20,21] and SDTrimSP [22], both based on TRIM.SP, allow a treatment of dynamically altering of the target composition due to implantation and collisional trans- port of target atoms. These computer programs can deliver espe- cially the angular distributions of number and energy of sputtered target atoms and recoiled particles. Comparisons between computer simulations and experiments are often done with respect to the sputtering yield, which is the most widely investigated quantity of sputtering [19,23–25]. How- ever, a wrong model can still output a correct integral quantity by chance or after tuning the input parameters, especially the surface binding energy. Therefore, more than one integral quantity is re- quired when improvements of the models are the aim of the com- parison. Techniques for the determination of angular distributions [26–29] and velocity or energy distributions [11,30–32] of sput- tered atoms, which allow a better comparison, require much more experimental effort. In this article, we present a novel and simple technique for the di- rect measurement of one component of the momentum transferred to a target by sputtered atoms and recoiled particles. Though the momentum is also an integral quantity, it differs from the sputtering yield mainly in that it is a vectorial quantity. Therefore, the method delivers additional information about sputtering, which can easily be compared with results of computer simulations. For simulation codes which are already proven with respect to sputtering 0168-583X/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nimb.2013.03.004 ⇑ Corresponding author. E-mail addresses: rutscher@physik.uni-kiel.de (J. Rutscher), trottenberg@physik. uni-kiel.de (Th. Trottenberg), kersten@physik.uni-kiel.de (H. Kersten). Nuclear Instruments and Methods in Physics Research B 301 (2013) 47–52 Contents lists available at SciVerse ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb