A MEMS-based atomic force microscope developed by engineers at UT Dallas is about 1 square centimeter in size (top center). Here it is attached to a small printed circuit board that contains circuitry, sensors and other miniaturized components that control the movement and other aspects of the device. Credit: The University of Texas at Dallas
A new microscope has shrunk both in size and in cost.
Researchers at The University of Texas at Dallas have created an atomic force microscope on a chip using a microelectromechanical systems (MEMS) approach.
The microscope is about one square centimeter in size and is attached to a small printed circuit board, about half the size of a credit card, which contains circuitry, sensors and other miniaturized components that control the movement and other aspects of the device.
“A standard atomic force microscope is a large, bulky instrument, with multiple control loops, electronics and amplifiers,” Reza Moheimani, Ph.D., a professor of mechanical engineering at UT Dallas, said in a statement. “We have managed to miniaturize all of the electromechanical components down onto a single small chip.”
Anthony Fowler, Ph.D., a research scientist in Moheimani’s Laboratory for Dynamics and Control of Nanosystems and one of the article’s co-authors, explained the new approach to creating the microscope.
“A classic example of MEMS technology are the accelerometers and gyroscopes found in smartphones,” Fowler said in a statement. “These used to be big, expensive, mechanical devices but using MEMS technology, accelerometers have shrunk down onto a single chip, which can be manufactured for just a few dollars apiece.”
An atomic force microscope (AFM) is a scientific tool that is used to create detailed three-dimensional images of the surfaces of materials, down to the nanometer scale—that’s roughly on the scale of individual molecules.
The basic AFM design consists of a tiny cantilever that has a sharp tip attached to one end and as the apparatus scans back and forth across the surface of a sample or the sample moves under it, the interactive forces between the sample and the tip cause the cantilever to move up and down as the tip follows the contours of the surface.
Those movements then are translated into an image.
“An AFM is a microscope that ‘sees’ a surface kind of the way a visually impaired person might, by touching. You can get a resolution that is well beyond what an optical microscope can achieve,” Moheimani said. “It can capture features that are very, very small.”
Conventional AFMs operate in various modes, with some being able to map out a sample’s features by maintain a constant force as the probe tip drags across the surface, while others do so by maintaining a constant distance between the two.
“The problem with using a constant height approach is that the tip is applying varying forces on a sample all the time, which can damage a sample that is very soft,” Fowler said. “Or, if you are scanning a very hard surface, you could wear down the tip.”
When MEMS-based AFM operates in “tapping mode” the cantilever and tip oscillate up and down perpendicular to the sample and the tip alternatively contacts then lifts off from the surface.
When the probe moves back and forth across a sample material, a feedback loop maintains the height of the oscillation, which ultimately creates an image.
“In tapping mode, as the oscillating cantilever moves across the surface topography, the amplitude of the oscillation wants to change as it interacts with sample,” Mohammad Maroufi, Ph.D., a research associate in mechanical engineering and co-author of the paper, said in a statement. “This device creates an image by maintaining the amplitude of oscillation.”
Conventional AFMs require lasers and other large components to operate, their use can be limited and they are also expensive.
However, by reducing the size and the cost, researchers could expand the AFMs’ utility beyond current scientific applications.
“For example, the semiconductor industry might benefit from these small devices, in particular companies that manufacture the silicon wafers from which computer chips are made,” Moheimani said. “With our technology, you might have an array of AFMs to characterize the wafer’s surface to find micro-faults before the product is shipped out.
“This is one of those technologies where, as they say, ‘If you build it, they will come.’ We anticipate finding many applications as the technology matures,” Moheimani added.
