Cleaving crystals in a vacuum chamber is a simple method for obtaining
atomically flat and clean surfaces for materials that have a preferential
cleaving plane. Most in-situ cleavers use parallel cutting edges that are
applied from two sides on the sample. We found in ambient experiments that
diagonal cutting pliers, where the cleavage force is introduced in a single
point instead of a line work very well also for hard materials. Here, we
incorporate the diagonal cutting plier principle in a design compatible with
ultra-high vacuum requirements. We show optical microscopy (mm scale) and
atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with
this device.Comment: 7 pages, 3 figures Submitted to Review of Scientific Instruments
  (2005

A. Renner

Eberhart M. E.

F. J. Giessibl

Kim Y. -C.

M. Schmid

English

arXiv

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Device for
                    in situ

Schmid, Martina

Renner, A.

Giessibl, Franz Josef

Online-Publikationserver Augsburg

Device for in situ cleaving of hard crystals

OPUS Augsburg

Cleaving crystals in a vacuum chamber is a simple method for obtaining atomically flat and clean surfaces for materials with a preferential cleaving plane. Most in situ cleavers use parallel cutting edges that are applied from two sides on the sample. We found in ambient experiments that diagonal cutting pliers, where the cleavage force is introduced in a single point instead of a line, work very well also for hard materials. Here, we incorporate the diagonal cutting plier principle in a design compatible with ultrahigh-vacuum requirements. We show optical microscopy (millimeter scale) and atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with this device

Schmid, Martin

Renner, Andreas

Giessibl, Franz J.

University of Regensburg Publication Server

arXiv:cond-mat/0511325v1  [cond-mat.mtrl-sci]  14 Nov 2005APS/123-QEDDevice for in-situ cleaving of hard crystalsM. Schmid,∗ A. Renner, and F. J. GiessiblUniversita¨t Augsburg, Institute of Physics,Electronic Correlations and Magnetism, Experimentalphysik VI,Universita¨tsstrasse 1, D-86135 Augsburg, Germany.(Dated: Submitted to Review of Scientific Instruments, originally received May 31 2005, revision 2)AbstractCleaving crystals in a vacuum chamber is a simple method for obtaining atomically flat and cleansurfaces for materials that have a preferential cleaving plane. Most in-situ cleavers use parallelcutting edges that are applied from two sides on the sample. We found in ambient experimentsthat diagonal cutting pliers, where the cleavage force is introduced in a single point instead of a linework very well also for hard materials. Here, we incorporate the diagonal cutting plier principlein a design compatible with ultra-high vacuum requirements. We show optical microscopy (mmscale) and atomic force microscopy (atomic scale) images of NiO(001) surfaces cleaved with thisdevice.∗Electronic address: martina.schmid@physik.uni-augsburg.de1I. INTRODUCTIONSurface science relies on the availability of atomically clean and well-defined surfaces.Cleaving a crystal in an ultra-high vacuum environment is a simple means to provide cleanand atomically flat surfaces. Existing implementations of cleavers use a spring-loaded bladethat moves towards an anvil [1, 2, 3] with parallel edges, an anvil with one blade thatpresses against the sample that is to be cleaved [4, 5, 6] or a device that pushes the sampleagainst an obstruction [7, 8, 9]. Other techniques use one blade that is introduced fromone side of the vacuum chamber with a wobble-stick type feedthrough hitting a sample thatis countered by a fixed or movable anvil [10]. Cleaving crystals in situ is relatively simplefor soft materials, such as alkali halides. However, cleaving hard materials as NiO is moredifficult. We could successfully cleave a strip cut from a NiO wafer with a cross section ofroughly 2mm by 0.6mm with the techniques described in references [7, 8, 9]. However, inparticular on hard samples, the sample areas close to the crystal boundaries show very poorsurface quality and it is desirable to provide cleavage faces with greater lateral dimensionsto obtain good quality surface areas. We found in ambient experiments that cleaving NiOwith a razor blade that touches the sample along a line is rather difficult, while cleaving itwith a wire cutter is simple and requires little force even for large cross sections. In a wirecutter, the cleavage force is introduced in a single spot. This highly localized stress fieldis known to facilitate cleaving [11]. We therefore aimed to incorporate this principle in avacuum compatible form, shown in the next section.II. EXPERIMENTAL IMPLEMENTATIONOur cleaver (see Fig. 1 (a)) sits on a single CF 35 flange that holds a rotary feedthrough ca-pable of transmitting a torque of 10Nm mounted on a CF16 flange. The rotary feedthroughconnects to an axle that has the cleavage knife mounted to it at its end. The CF35 flangehas a pipe with venting holes welded to it, holding an anvil at its end and housing a ballbearing that supports the axle. Because the knife edge is not parallel to the surface whenthe crystal is not cleaved yet, the cleavage force is applied at a well-defined point (see Fig.1 (b)), facilitating the cleavage process and usually resulting in fairly flat cleavage planes.When the knife edge is touching the crystal along its whole length, as done in many previous2cleavage designs, the cleavage can start at multiple points that are on different parallel crys-tal planes (see Fig. 1 (c)). The rotating blade and the steady anvil resemble the two cuttingblades of a wire cutter. In the present cleaver, the blade is made of stainless steel, but itcould also be manufactured from hardened steel or other hard materials such as tungstencarbide. The blade angles are chosen such that once the cleave is initiated, the blade pushesthe sample backwards and the blade does not scratch over the freshly cleaved surface (Fig.1(c)). The maximum force that can be applied to the initial point of contact between knifeand sample is given by the length of the arm and the maximal torque rating of the rotaryfeedthrough. In our setup, it is approximately 1 kN.III. RESULTSFigure 2 shows an optical microscopy image of a typical cleavage plane. The steplinesclearly merge into the point where the initial cleaving force was applied. The cleavage processis shown in real time for soft (KBr) and hard (NiO) materials by two movies, online availableat www.xxx.yyy. The advantage of a large cleavage area is that high-quality surface areas aremore likely to be found. In most experiments, it is not possible to obtain atomic resolutionover the whole surface area (see caption Fig. 2). Debris on surfaces is especially harmful forscanning probe microscopy studies, because the radii of the probe tips are often large andeven small pieces of debris on otherwise perfectly flat and clean surfaces can prevent the tipapex from reaching the flat surface, because other tip sections may make contact with thedebris before the apex reaches the sample.With the cleaver shown in Fig. 1, we could easily cleave cross sections on the order of 2 by4mm2 and we could find surfaces that are clean enough to allow atomic resolution by AFMin approximately 9 out of 10 cleavage trials. Figure 3 shows typical atomic force microscopyimages of an in situ cleaved NiO(001) surface that was produced with this device.Because the cleaver can be mounted on a single flange, it is very compact. As it uses onlya single rotary feedthrough and few other parts, it is easy to build and quite cost effective.3IV. ACKNOWLEDGMENTSWe thank Jochen Mannhart for support and useful suggestions, Marilyn Gleyzes forassistance with preparing the mechanical drawings, Rainer Pa¨tzold for machining the secondversion of the cleaver and Michael Reichling for helpful comments. This work is supportedby the Bundesministerium fu¨r Bildung und Forschung (project EKM13N6918).[1] C. A. Pela, J. X. De Oliveira, Z. P. De Arguello, Rev. Sci. Instrum. 44, 1406 (1973).[2] A. P. Janssen, A. Chambers, Journal of Physics E: Scientific Instruments 7, 425 (1974).[3] T. Angot, J. Suzanne, J. Y. Hoarau, Rev. Sci. Instrum. 62, 1865 (1991).[4] B. Dupoisson, P. Dumas, A. Steinbrunn, J. C. Colson, Journal of Physics E: Scientific Instru-ments 9, 266 (1976).[5] R. Carr, Rev. Sci. Instrum. 59, 989 (1988).[6] J. T. Yates, Experimental Innovations in Surface Science (Springer Berlin Heidelberg NewYork, 1998).[7] F. J. Giessibl, Ph.D. thesis, Ludwig-Maximilians-Universita¨t Mu¨nchen, Germany (1991).[8] M. Otha, Y. Sugawara, S. Morita, N. Nagaoka, S. Mishima, T. Okada, J. Vac. Sci. Technol.B 12, 1705 (1994).[9] Y.-C. Kim, M. J. Nopwakowski, D. N. Seidmann, Rev. Sci. Instrum. 67, 1992 (1996).[10] M. Reichling, private communication.[11] Mark E. Eberhart, Why things break (Harmony Books, New York, 2003).4FIG. 1: (a) Perspective view of the single-flange cleaver. It consists essentially of three parts: arotary feedthrough, an axle holding the cleavage knife that is connected to the rotary feedthroughand a tube with venting holes that has the anvil welded to it. (b) Cleaving a crystal using thewire cutter principle results in a well-defined point where the cleave is initiated. In contrast toa cleaver where the blade is applied parallel to the side faces of the crystal sample to be cleaved(c), the wire cutter principle does not require perfect alignment between the cutting edge and theintended cleavage direction. (d) Schematic view of the blade with cutting angle φcut and clearanceangle φclear in the initial phase of cleavage. In our setup, φcut ≈ 42◦ and φclear ≈ −6◦. (e,f) Thenegative clearance angle ensures that the cleavage plane remains unscathed when the blade slidesover the sample surface after the cleave (see also online movies). The sample holder is movablealong a line perpendicular to the cleavage plane, enabling the sample to move backwards (whitearrow in (e) and (f)).5FIG. 2: Optical microscopic view of the cleaved NiO(001) surface. Cleavage was initiated on thetop left corner of the sample. The central region of the cleavage plane has a rather good surfacequality, while the sections close to the boundaries are more rugged and are sometimes covered withdebris.6FIG. 3: Atomic force microscopy images of the cleaved NiO(001) surface. NiO(001) has a rocksaltstructure with a cubic lattice constant of a0 = 417 pm and natural step heights of integer multiplesof a0/2. (a) Image size 1µm×1µm, showing atomic steps with heights of a0/2 and a0. At the top,the NiO crystal is 3 unit cells higher at the right edge than at the left, and at the bottom, theleft edge is 3 unit cells higher than the right edge. The misorientation angle of the actual cleavageplane with respect to the ideal (001) plane is thus on the order of 3 a0/1µmrad = 0.07◦. The imageshows that the (001) surfaces are not ideal – a few screw dislocations are present (arrows). (b)Atomic resolution image (size 1.5 nm×1.5 nm). Images of this quality could only be obtained onsurface areas that are flat and free of debris for fairly large areas. The larger the area of a cleavedsurface, the more likely it is possible to find such good surface areas.7

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Device for in-situ cleaving of hard crystals

Device for in-situ cleaving of hard crystals

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