The research today deals with microscopically small parts often even with dimensions in the range of a few nanometers. The tools react particularly sensitive to disturbances. Therefore, protected laboratories in which such disturbances are reduced, are needed. The fields can be reduced by using two techniques: passive shielding or active cancellation. If the combination of both techniques is used we call them "Low Field Rooms™".
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VISTEC E-beam writer, Athen
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OMICRON Spin SEM, Lausanne
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JEOL JSM 7001, Prag
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FEI Nova NANOSEM, Zürich
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FEI Tecnai, Gatersleben
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Electron microscopy facilities
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Rooms for electron microscopes have to be protected from magnetic interference fields when external interference fields affect the operation of the microscopes. The supplier/manufacturer of microscopes therefore defines the appropriate limit values. In addition to active compensation systems the interference fields can also be reduced with room shields.
Interference fields such as the ones caused by railway systems, trams, high voltage power lines, but also building internal sources can be reduced effectively with room shields.
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Practical example
The REM-laboratory of a customer had to be moved. The magnetic field strength were measured at several locations in question. Finally a room had to be chosen, in which the magnetic field strength exceeded the interference boundary of the REM. The customer tested various field reduction solutions and went for a passive shielding solution. This solution was chosen in particular, because once the passive room shielding is mounted, no further maintenance is required. The new location was surrounded by “in-house” interference sources such as an electric cable channel in the aisle in front of the laboratory, a power rail on the wall and an induction furnace in the rear adjacent production area.
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Layout with sources of interference
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Sources of interference |
Room shielding finished
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Set up laboratory
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The active magnetic compensation system MACS™ was developed specifically to reduce low-frequency magnetic fields to the lowest possible values. With the MACS™ interference limits of electron microscopes can be fulfilled or magnetic field interferences in bio magnetic examination rooms, EEG/EKG/EMG, can be prevented. The MACS™ is used if the environment has to be as free as possible from low-frequency magnetic fields, be it for experiments or measurements.
The MACS™ compensates low-frequency magnetic fields such as the ones caused in real time by vehicles, elevators, railway, electrical equipment or other sources of interference. Interference fields are measured with a sensitive sensor and actively compensated by counter fields.
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Active compensation system MACS™ | Compensation comparison “On” / “ Off” |
Initial situation:
A new scanning electron microscope Carl Zeiss SEM Supra 55VP was installed in a laboratory in Vienna. Because of disruptions during the microscopy work, magnetic field measurements were carried out. These measurements have shown that the DC magnetic fields were outside the specifications. The source was the tram that passes by the building.
Solution:
In order to guarantee trouble-free operation a magnetic field compensation system has been installed. This allowed to reduce the interference fields in the room well below the specific values.
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Supra 55VP with active compensation system | Measured values compensation “OFF and compensation “ON” |
Initial situation:
A new FEI TEM, Titan 80-300 was installed in a laboratory in Bern. After commissioning it was established, that the quality of the image doesn’t meet the expectations. With appropriate magnetic field measurements the disturbing influence of a nearby power distribution, which was not in operation at the time of the room measurements, could be evidenced.
Solution:
To eliminate the interference fields, an active compensation system has been installed. The problem of middle field sources is that the gradient at the location of the microscope is high and the fields are inhomogeneous. It is not easy to properly solve such situations with compensation systems. The aim of these being to compensate a maximum possible volume. In situations with a high gradient, however this is only possible to a limited extent.
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Position of the electrical distribution |
Red: Magnetic field sensor
White: Compensation coils |
Field strengths with compensation “OFF” and “ON” |
Initial situation:
An electron beam lithography device Electro Beam Writer RAITH 150 TWO has to be installed in a research center. Preliminary magnetic field measurements have revealed that the field strengths at the site of the lithography device are beyond the device specifications. With measurements it was found that the main power lines of the building are embedded in a channel in the floor. The channel crossed the room on the entire length.
Solution:
A magnetic field compensation system has been installed, to be able to use the lithography device in this room anyway. With the compensation, the field strengths could be reduced far enough to meet the specifications. The interference-free operation is therefore guaranteed.
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Cable channel in the floor of the microscopy room | E-Beam writer Raith 150 two |
Initial situation:
In a University in Cologne a Philips CM 10 TEM has to be installed in one room and a LEO 430i REM in the room next to it. The devices are moved from an old building into new laboratories. To eliminate the interferences of the nearby railway line (16,7Hz) and the tram (DC), compensation systems have to be installed in both laboratories. If two compensation systems are being installed right next to each other, special points have to be considered, otherwise the systems would interfere with each other.
Solution:
In order for the compensation systems not to influence each other, certain minimum dimensions between the Helmholtz coils of the two systems and the sensors must be fulfilled. Initial measure is to place the two microscopes as far apart from each other as possible. The coil cage in one room was reduced so that the coils aren’t directly next to each other. The coils were relocated to about 1m off the wall into the inside of the room. This allowed to maintain the distance between the souelen-coils and the coil sensors.
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Ground plan of the two adjacent laboratories | Philips CM 10 TEM with sensor | LEO 430i REM with sensor |
Initial situation:
After the commissioning of a Jeol SEM JSM 6490 in a laboratory in Jena, significant disorders were apparent during the recording. Measurements have shown that these failures were cause by the ceiling mounted power cable. A transfer of the cable was not possible.
Solution:
Due to the very limited space and the unusual geometry of the microscopy room the customer decided to go with a freestanding frame construction made of GFK. On request of the customer, the construction of the frame was painted traffic red. The design should be an eye-catcher.
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Frame construction made of GFK profiles | Mounting of the sensor holder on the ceiling |
![]() “Low field room”, Binnig and Rohner Nano Technology Center, Rueschlikon
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In the Binnig and Rohner Nano Technology Centre, Rueschlikon, a combination of a mu-metal shielded room and active compensation system, specially designed for the Nano Technology Center, has been developed. This solution was successfully installed in the research laboratories
Requirements for “Low Field Rooms™” for the electromagnetic induction:
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