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TEM-SPM FORIN-SITU PROBING OF ELECTRICAL AND MECHANICAL PROPERTIES

D. Erts2, H. Olin1, E. Olsson1 and K. Svensson1

1Physics and Eng. Physics, Chalmers Univ. of Techn., SE-412 96 Göteborg, Sweden2Institute of Chemical Physics, University of Latvia, LV-1586 Riga, Latvia

TEM-SPM is a combination of the scanning probe microscope (SPM) and thetransmission electron microscope (TEM) for in-situ probing of electrical andmechanical properties. Today, two scanning probe techniques are used for in-situ TEMexperiments, the scanning tunneling microscope (STM) and the atomic forcemicroscope (AFM).

Since the first TEM-STM introduced by Spence1, the technique has increasingly beenused during the last years, notably by the groups of Takayanagi2 and Kizuka3. TheTEM-STM has been used in a number of applications, for example in carbonnanotubes7,8, gold nanowires2, and gold point contacts3,9. The TEM-AFM4,5 is a newmember of the TEM-SPM family, enabling mechanical properties to be studied on alocal scale. Another new method for probing hardness is in-situ nanoindentation6.

It is important to note that in TEM-SPM the SPM-tip is not primarily used for imaging,instead it is used as a local probe, and the selection of measuring point is guided byTEM imaging. In addition to more standard TEM microscopy and analysis, the TEMgives crucial information of tip-sample distance, tip and sample shape andmicrostructure, contact area size, etc. The TEM gives essential information that islacking and thus hampering standard SPM experiments. The SPM-part allows in-situprobing of electrical and mechanical properties, making the TEM a powerful dynamicexperimental tool.

Our TEM-SPM (Nanofactory Instruments) is based on a piezo-electric tube (with adiameter of 3 mm), which is used both for fine motion (10 pm step, 10 µm range) aswell as for rough motion by inertial sliding (1 µm step, 1 mm range), leading to a verycompact and low noise design (Fig. 1). The SPM is incorporated into a side entryholder. The investigations were carried out using a Philips CM200 Super TWIN FEG.

Here, we present two examples from our work: 1) electron transport in gold pointcontacts9 and 2) force interactions using the TEM-AFM5. In Fig 2 TEM images of in-situ created gold point contacts are shown. It was only for the thinnest wires that theelectron transport was ballistic, for thicker ones, the transport became more and morediffusive. By measuring the conductance with the TEM-STM and the contact radius byTEM imaging, the electron mean free path was calculated, and surprisingly, it was anorder of magnitude lower than the bulk value (4 nm here).

Fig. 3a shows a TEM image of an AFM-cantilever above a gold sample. The full forceinteraction cycle was studied (Fig. 3b), from approaching with van der Waalsinteractions, the jump-in-contact, adhesion, and jump-off-contact. In addition, TEMimaging enables contact radius and plastic versus elastic deformation to be determined. 9

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Figure 1. TEM-SPM. Tip holder (1), sapphire ball (2), sliding rods (3), piezo tube (5).Figure 2. a) TEM images of a single atom wide contact between two gold tips. b) Theconductance follows a radius squared dependence. The straight line describes theballistic case.Figure 3. a) TEM image of a gold coated AFM-tip above a gold sample. b) The fullforce-distance curve. Jump-in-contact (b), adhesion (b-c-d), and jump-off-contact (d-e).

References1. Spence, J.C.H. (1988) Ultramicroscopy 25, 165.2. Ohnishi, H., Kondo, Y., and Takayanagi, K. (1998) Nature 395, 780.3. Kizuka, T. (1998) Phys. Rev. Lett. 81, 4448.4. Kizuka, T., Ohmi, H., Sumi, T., Kumazawa, K., Degushi, S., Naruse, M., Fujisawa,

S., Sasaki, S., Yabe, A., and Enomoto, Y. (2001) Jpn. J. Appl. Phys. 40, L170.5. Erts, D., Lõhmus, A., Lõhmus, R., Olin, H., Pokropivny, A.V., Ryen, L. and

Svensson, K. (2002) Appl. Surf. Sci. in press.6. Minor, A.M., Stach, E.A. and Morris, J.W. (2001) Appl. Phys. Lett. 79, 1625.7. Poncharal, P., Wang, Z.L., Ugarte, D., and de Heer, W.A. (1999) Science 283, 1513.8. Cumings, J. and Zettl, A. (2000) Science 289, 602.9. Erts, D., Olin, H, Ryen, L, Olsson, E, and Thölen, A. (2000) Phys. Rev. B61, 12725.

email: hakan.olin@fy.chalmers.se