In the materials science, bioengineering and nanotechnology sectors, where the use of highly sensitive instruments and equipment such as scanning probe microscopes (SPMs) is very common, even very low levels of vibration noise can impact the quality of data and images.
In SPM, a number of probes are used and the data obtained include conductivity, elemental composition, topography and others. For recording and measuring data precisely, a uniform distance must be maintained between the stage, probe and the detector.
As these methods are sensitive to environmental disturbance, SPMs need some form of vibration isolation. Active or passive vibration isolation systems are recommended for elimination of AFM noise based on a number of factors such as thermal fluctuations, application field and type of equipment.
Scanning Probe Microscopy (SPM)
In scanning probe microscopes (SPMs), a probe is scanned across the sample surface to obtain information. There are several probes used in SPM and the collected information takes a number of forms such as topography, elemental composition, conductivity depending on the type of probe used.
Scanning Tunneling Microscopy (STM)
This was the first kind of SPM developed. The first STM was developed by IBM researchers in 1981. An STM works by bringing an atomically sharp tip (normally tungsten) into close contact with the sample, then a bias voltage is applied to the tip generating a tunneling current. The tip is scanned across the surface and the level of current is compared to a reference level to obtain the sample surface topography. STM imaging can be performed in open air or in ultra-high vacuum chambers (UHV-STM).
With the help of the STM, researchers were able to see samples at resolutions that were not possible before. They could see and manipulate individual atoms. The development of the STM transformed the field of nanotechnology research. Not only did it offer novel capabilities by establishing certain basic concepts of SPM, STM proved to be the basis for a new microscopy field.
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Figure 1. STM installed on TS-150
Atomic Force Microscopy (AFM)
Atomic force microscopy (AFM) is the most widely used SPM technique. The operation of the AFM operates involves dragging an ultra-fine mechanical probe known as a tip across the surface of a sample.
Instead of actual contact with the sample, the tip comes close to the sample surface and interacts with atomic forces on the sample surface. The tip is fitted to a cantilever, which is deflected as the tip rasters across the sample surface. A laser is reflected off the cantilever back into the detector that collects information on movement of the probe and produces a sample image.
The resulting image offers an excellent view on the topography of the sample at a very high resolution level. Along with the original contact mode described several other operation modes have been developed including tapping mode, non- contact mode and force modulation.
Newer applications of AFM continue to be developed such as the use of AFM techniques for the diagnosis and investigation of cancer cells.
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Figure 2. Veeco MultiMode AFM on TS-140 Active Vibration Control System
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Figure 3. Comparison of AFM Performance with Active and Passive Isolation
Performance Comparison
The video below shows an AFM probe being imaged using interferometry. The tip is suspended in the air to determine how much noise reaches the probe. The video is taken determining the quality of application in the following conditions:
- Using an optical table
- Without vibration isolation
- Using a Herzan TS-150 active vibration isolation table
It can be noted that the noise reaching the probe is almost completely eliminated. This video was taken at a third floor lab at the University of Wisconsin-Madison, Materials Science Center.
Active vs. Passive Vibration Control for AFMs
Comparision of isolation techniques for AFM measurements
Other Types of SPM
Several new techniques have evolved from the SPM and include the following:
- Scanning Near-field Optical Microscopy (SNOM or NSOM) uses a tip with an aperture as an optical probe to provide images with excellent spatial resolution and spectroscopic information.
- Scanning ion conductance microscopy (SICM) determines ion currents and topography of samples using a charged pipette filled with electrolytes in a non- contact mode.
- SICM is especially useful for biological applications.
- Dip Pen Nanolithography (DPN) applies scanning probe techniques to lithography, using a cantilever and tip to deposit material onto a substrate.
Environmental Challenges
Scanning probe microscopy techniques are highly sensitive to environmental disturbances. This sensitivity is due to operating at very high precision levels and due to the instruments’ mechanical structure. In order to obtain precise data, it is required that the instrument maintains a uniform distance between the stage, probe and detector. Tiny AFM noise levels can also disturb the spatial relationship between the components and cause inaccurate data.
SPMs need some kind of vibration isolation. These are not massive instruments hence are easily excited by even normal environmental vibrations. Also due to their ease of use, SPMs are used in several environments from production environments to highly controlled research labs.
Certain SPMs make use of passive vibration control mechanisms such as air tables and bungee systems. Active vibration control is required in very high accuracy applications. Vibration measurement equipment must be used to find the right location of the instrument before installation.
It is not advisable to use an SPM in open air. It is required to have acoustic enclosures at sample level or around the complete testing setup.
Challenging SPM applications need high-performance soundproof hoods designed around the requirements of the particular instrument.
Other environmental challenges include controlling thermal fluctuation. AFM noise may occur due to electronic controls. SPMs which measure conductance and electrical properties of materials require isolation from stray electromagnetic interference (EMI).
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Figure 4. AFM image with visible noise
Typical Applications
Applications of vibration isolation solutions for AFM and SPM are:
- Bioengineering
- Data Storage
- Energy Research
- Failure Analysis
- Materials Science
- MEMS
- Semiconductor
About Herzan
Herzan provides high performance environmental solutions for precision research instruments. They include acoustic enclosures, vibration isolation systems, Faraday cages, and site survey tools. Herzan specializes in supporting nanotechnology research, but also offers solutions for product testing, in-vitro fertilization, and many other applications.
Herzan understands that every application and environment is different, so it collaborates with customers to create comprehensive integrated solutions that satisfy their unique demands.
Herzan was founded in 1992 by Ann Scanlan in Orange County, California. Originally, Herzan was established as an American subsidiary of Herz Company Ltd., a Japanese company specializing in vibration control. The name Herzan comes from the amalgamation of 'Herz' and 'Ann'.
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This information has been sourced, reviewed and adapted from materials provided by Herzan.
For more information on this source, please visit Herzan.