In 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.
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.
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).
Applications of vibration isolation solutions for AFM and SPM are:
- Data Storage
- Energy Research
- Failure Analysis
- Materials Science