Previously, it was not a very difficult task to decide where to locate one’s scanning probe microscope it was mostly placed in the basement where ambient vibration is considerably reduced. Of late, with nanotechnology applications growing at an exponential rate, engineers and scientists are placing their equipment in several locations where vibration noise is considerably high. Interferometers, scanning probe microscopes and stylus profilers are being placed in locations that pose a serious challenge to vibration isolation.
Furthermore, in an attempt to maintain nano-equipment costs as low as possible by cutting out the peripherals, many academics and industries are not adequately providing for vibration isolation on the ultra-sensitive nano- equipment that they are putting into their facilities.
With any type of nano-instrument or microscope, even a high-powered optical microscope, one needs to put noise isolation or fuzzy and diffused imaging or no image at all resulting in reduced operability of a facility's nano- equipment.
Different Types of Vibration Isolators
Vibration isolators are absolutely essential, however people are not actually focused on that while purchasing an instrument such as an atomic force microscope (AFM). The bigger transmission electron microscopes and scanning electron microscopes are different as one is dealing with a highly expensive piece of gear that may technically need all sorts of mechanical isolation in order to work properly.
For smaller instruments such as laser interferometers, white light interferometers, atomic force microscopes and stylus profilers, there are problems with site preparation. As instrumentation becomes more and more complicated and measurements are done at a very small level there is a dire need for effective isolation.
The vibrations are normally very subtle. One may not actually feel the vibrations, this may cause considerable disturbance and noise to an interferometer or AFM. A lot of things may cause noise, it is not originating from a single spot. Every building makes the noise. Based on how high up off the ground or the age of the building, there will be a constant vibration. In the building itself, there are things that will create more vibrations such as the ventilation and heating systems, pumps that are not isolated properly and elevators. These mechanical devices cause considerable vibration in the building and based on how far away the instruments are from it, they may or may not be adversely affected.
The equipment may be impacted by vibrations from wind, traffic, construction and other elements external to the building. These external and internal impacts cause low-frequency vibrations that raise havoc with nano-instrumentation.
It is essential to have an absolutely stable surface for resting the instrument. If not, the vibration transferred to the mechanical structure of the instrument will cause vertical noise.
Since the 1960s air tables have been used for mechanical noise isolation. Basically cans of air, they are still the most popular isolators used. However air tables at resonant frequencies at 2 to 2.5 Hz can only handle vibrations down to about 8 to 10 Hz, not quite low enough for optimum performance with modern nano-equipment.
Air tables are an ineffective isolation solution for clarity purposes in interferometers and scanning probe microscopes. The air systems had been adequate up until a few years ago when better isolation was required.
Active isolation makes use of electronics to sense the motion, and then puts in equal amounts of motion electronically to compensate, effectively canceling out the unwanted motion. Their efficiency is fine for application with the latest nanotechnology, as they can start isolating as low as 0.7 Hz, quite sufficient for isolating the lower frequencies that are so damaging to image clarity with SPMs and interferometers.
Negative-Stiffness Vibration Isolators
Presently, negative-stiffness vibration isolation systems have become a growing choice for nanotechnology applications as shown in Figure 1. They are not only a highly workable vibration solution, however their cost is considerably less-up to one-third the price of active systems making it an economical solution to cost-conscious administrators.
Figure 1. Minus-K vibration isolator
These isolation systems enable vibration-sensitive instruments, such as scanning probe microscopes, micro-hardness testers and scanning electron microscopes to operate in severe vibration environments, such as upper floors of buildings and clean rooms. The images and data produced are many times better than those achievable with pneumatic isolators.
Negative-stiffness isolators make use of an innovative and completely mechanical concept in low-frequency vibration isolation. A stiff spring provides vertical motion isolation supporting a weight load combined with a negative- stiffness mechanism (NSM). Without impacting the static load supporting capability of the spring, the net vertical stiffness is made very low.
Enhanced vibration isolation correlates directly to enhanced instrument performance. While trying to measure atomic scale features, mechanically stable support structures arc critically important.
Benefits offered by negative-stiffness isolators are truly unique to the field of nanotechnology. The transmissibility of a negative-stiffness isolator, the vibration that transmits through the isolator as measured as a function of floor vibrations, which is substantially improved over air or active isolation systems.
Even though active isolation systems have no resonance, their transmissibility does not roll off as fast as negative-stiffness isolators. At seismic and building frequencies, the transmissibility of active isolators can be 10X greater than negative-stiffness isolators. Air isolators have the added disadvantage that their 2 to 2-1/2 Hz resonance affects a significant loss in isolation capability below about 5 Hz. Negative-stiffness isolators are clearly the most efficient choice for probe microscopes.
About Minus K Technology
Minus K® Technology, Inc. was founded in 1993 to develop, manufacture and market state-of-the-art vibration isolation products based on patented negative-stiffness technology. Minus K® is based in the Los Angeles area.
The Minus K® products, formerly sold under the trade name Nano-K®, represent an important enabling technology. By reducing building and floor vibrations to unprecedented levels these systems enable vibration sensitive instruments and equipment to perform at unprecedented levels.
They are used in a broad spectrum of applications including nanotechnology, biological sciences, semiconductors, materials research, zero-g simulation of spacecraft, and high-end audio.
Minus K® is an OEM supplier to leading manufactures of scanning probe microscopes, micro-hardness testers and other vibration-sensitive instruments and equipment. Minus K® customers include private companies and more than 200 leading universities and government laboratories in 43 countries.
Dr. David L. Platus is President and Founder and is the principal inventor of the technology. He earned a B.S. and a Ph.D. in Engineering from UCLA, and a diploma from the Oak Ridge School of (Nuclear) Reactor Technology. Prior to founding Minus K® Technology he worked in the nuclear, aerospace and defense industries conducting and directing analysis and design projects in structural-mechanical systems. He became an independent consultant in 1988. Dr. Platus holds over 20 patents related to shock and vibration isolation.
This information has been sourced, reviewed and adapted from materials provided by Minus K Technology.
For more information on this source, please visit Minus K Technology.