Very Sharp Platinum Tips by Electrochemical Etching

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Very sharp platinum tips Martin Kupper 0830965Contents1 Introduction 32 State of the art 42.1 Electrochemical etching . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2 Tips for resistivity measurements. . . . . . . . . . . . . . . . . . . . . . 53 Experimental methods 73.1 Spot welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.2 Etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73.3 Annealing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.4 Micropolishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.5 Removing the oxide - ”reverse polishing” . . . . . . . . . . . . . . . . . 134 Tip properties 154.1 Elastic properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.2 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Very sharp platinum tips Martin Kupper 08309651 IntroductionThe tips used up to now to make electrical measurements in an SEM at the SEMlaboratory of the Institute of Solid State Physics [1], are industrially manufacturedtungsten tips (see Fig.1.1). To make electrical contact, the tip has to be pressed veryhard on the surface of the sample and because the tip is very sharp (about 500 nm)it bends. So the contact between the tip and the sample is not at the head of the tip,but somewhere behind. It is also not possible to say how big the contacting part ofthe tip is. So the aim of this project was to try and make very sharp Pt/Ir tips, testtheir elastic and electrical properties and test if these tips are more suitable for theelectrical measurements which are currently done at the SEM laboratory. The projectis based upon the paper Very sharp platinum tips for scanning tunneling microscopy[2].The produced tips have a sharp shape and are about 60 - 150 nm thick at theend. (See Figs.3.8 and 3.10) They also have good electrical properties, if the oxidelayer is being removed. It there is an oxide layer, however, there is then a problemin making contact with the sample. During the project it was not possible to makegood contact between a Pt/It tip and the silicon samples which were analyzed at thetime, but there was good contact between the tips. The resistivity was about 30 - 50 Ω.The elastic properties were not as bad as expected, but nor were they as good ashoped. After crashing on the surface the tip went back a bit, but it was bent (seeFig.3.7).Figure 1.1: An etched Pt/Ir tip (left picture), compared with an industrially manufacturedtungsten tip (right picture)3
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Page 5 and 6: 2 State of the art Martin Kupper 08
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Page 9 and 10: 3 Experimental methods Martin Kuppe
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Page 17 and 18: 4 Tip properties Martin Kupper 0830
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Very Sharp Platinum Tips by Electrochemical Etching

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