Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1994-04-19
1996-10-22
Dougherty, Thomas M.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310316, 310369, H01L 4109
Patent
active
055680046
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an electromechanical positioning device for exactly placing a tip means, particularly the tip of a needle-like probe, into a space of atomic order at the surface of a sample, said device comprising a piezo-tube having electrodes to be connected to variable voltages for the generation of movement actions of said tip means.
A positioning device of this kind, constructed as a piezo-mechanical device for positioning a tip means in a scanning tunneling microscope, is known from Review Sci. Inst. 63(1), January 1992, pp. 263-264. In the device disclosed therein a support carrying a sample to be investigated is frictionally mounted in a piezo-tube. Drawbacks of these devices are a comparatively complex construction, a comparatively high weight, their bulkiness, and the use of two different methods of movement for coarse and for fine positioning.
A further moving device for positioning a sample to be analysed in the range of atomic order, particularly in a scanning tunneling microscope (STM), is disclosed in DE 36 10 540 A1. According to this prior art the sample is placed on three piezo-holders having electrodes to be connected to variable voltages for the generation of positioning actions of said tip means. The distance between tip and sample can only be varied fine, that means in the range of the piezo-expansions. Coarse positioning actions with this moving device are only possible laterally, say transverse to the movement of the sample relative to the tip means.
A still further electromechanical positioning device, say micromanipulator, is disclosed in DE 38 22 504 A1. The micromanipulator comprises piezo-holders for carrying and moving the respective sample. For micromovements the holders are piezo-electficaily adjustable. For respective macromovements at least one of the holders comprise a socket, which is piezo-electrically deformable, whereby in the socket a bolt is mounted to be frictionally movable in said piezo-holder responsive to variable voltages to be applied to the holder. Thus the sample can be placed coarsely into a starting position for the required fine placing in relation to the tip of a needle-like probe or the like.
It is an object of the invention to mitigate the drawbacks of the known electromechanical positioning devices. It is a further object to design the device so that no movements of the sample are required to position--say bring closer to or move away from, respectively--the tip means or the like into the space of atomic order at the surface of the sample. The new device shall be constructed so that practically no mechanical vibrations, no thermal drifts can happen and no respective damping systems are required.
The solution according to the invention is characterized in that said tip means is connected to a low-mass support means, said support means is mounted to be frictionally movable in a direction vertical to the surface of the sample in said piezo-tube, and said piezo-tube comprises means for generating and transmitting electrically controllable movement actions to said support means in response to said variable voltages. Improvements and further developements of the invention are stated in the sub-claims.
Since the device in accordance with the invention comprises a single electro-mechanical drive for coarse as well as for fine positioning of the probe, the device can be comparatively small and of low weight, and is electrically controllable in a simple manner in that coarse and fine positioning can be realised automatically in a single action using only different control signals.
In a preferred embodiment the low-mass support is mounted in a friction holder under such a friction that, owing to its mass, it does not follow comparatively rapid longitudinal movements of the friction holder but it does follow comparatively slow movements of said holder. Such an embodiment enables coarse positioning of the moving-tip relative to the sample, preferably with a stepwise movement of the moving-tip owing to the comparatively slow movement of the holder and int
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