In situ electrical resistance measurements of Al-Ge films in the TEM using a modified heating holder
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In situ electrical resistance measurements of Al-Ge films in the TEM using a modified heating holder M.A. Verheijen, J.J.T.M. Donkers1, J.F.P. Thomassen1, J.J. van den Broek1, R.A.F. van der Rijt1, M.J.J. Dona, C.M. Smit Philips CFT, Prof. Holstlaan 4, 5656 AA Eindhoven, the Netherlands 1
Philips Research, Prof. Holstlaan 4, 5656 AA Eindhoven, the Netherlands.
ABSTRACT
A TEM specimen holder has been developed for the measurement of the electrical resistance of a TEM sample as a function of temperature. A Philips TEM heating holder was modified for this purpose. This creates the opportunity to directly correlate changes in the resistance to microstructural changes as a function of temperature. The microstructure of Al-Ge films of several thicknesses has been studied in an in-situ annealing experiment and has been recorded on videotape, while simultaneously acquiring resistance data. These in-situ TEM studies confirm that the irreversible decrease in resistance of these films is caused by crystallisation. During this transition segregation occurs, resulting in crystalline Al and Ge phases. INTRODUCTION For the development of many materials, insight in the influence of the microstructure on the electrical properties is of utmost importance. In many cases, TEM investigations on these materials include in-situ annealing experiments to monitor changes as a function of temperature. In this way crystallisation phenomena and other phase transitions can be studied in-situ in the TEM. Correlating these changes in microstructure to changes in the electrical properties has always been difficult because of two reasons: (i) all electrical data have to be measured after or prior to the TEM work; (ii) in most experiments resistance and TEM studies have to be performed on separate samples.
In order to be able to measure the electrical resistance of thin (metal) films in-situ during TEM studies, a new TEM specimen heating holder has been developed that allows for measurement of the resistance of the sample as a function of temperature (the ‘RT-holder’). A custom Philips TEM heating holder was modified for this purpose. Below, the design of the specimen holder will be presented in short. Several materials already have been studied using the RT-holder. One of these experiments, the study on the crystallisation of thin Al-Ge films will be discussed to illustrate the possibilities of the technique. DESIGN OF THE RT-HOLDER
A Philips PW6592 TEM specimen heating holder has been altered to enable resistance measurements. The most radical changes to the original holder have made to the front end: the tip. Figure 1 shows an exploded-view drawing of this tip, indicating the most important parts. The four point electrical resistance measurement is performed using four additional feed-through CoNiFer1 wires. The back ends of these wires are fixed in an electrically isolating ceramic plate. The tips of the wires are laser-cut in a wedge shape. Thus, contact pins are obtained that both have mechanical strength and only small, well defined conta
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