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www.us-tech.com
July, 2021 Scanning Atoms with the Tip of a Needle T
he atomic force microscope (AFM) is an important tool in materials science and used for mechanical scanning of sur-
faces. The forces acting between the atoms of the surface and the tip of a nanoscopic needle are measured and calculated giving resolu- tions in the order of fractions of a nanometer. Now, the University of Newcastle in
Australia is improving and simplifying these complex machines, so that a wider use in lab- oratories worldwide will be possible. In this sophisticated research, an eight-channel Spectrum digitizerNETBOX provides the high precision needed to push the evolution of AFMs. The AFM, invented in 1985, became a
vital tool used by laboratories around the world involved in surface chemistry. Its out- standing resolution means that this instru- ment can reveal more detail than conven- tional light-based microscopes by a factor of more than 1,000. And, unlike other advanced systems such as electron microscopes, it can image samples in situ. This, along with the ability to perform topographical imaging and force measurements, makes AFMs well suit- ed for the study of soft biological materials, polymers, nanostructures and various other materials.
Atomic Force Microscopy At the University of Newcastle, Dr.
Michael Ruppert and his team are improving the key elements of AFM systems. The aim is to simplify operation as well as to enhance the overall performance of these microscopes.
By Oliver Rovini, Chief Technology Officer, Spectrum Instrumentation At the core of the instrument is a micro-
The precision mechatronics lab at the
University’s school of electrical engineering and computing brings together expertise in nanotechnology, mechatronics, microelectro- mechanical systems (MEMS), and low-noise electronic design to create unique solutions that can reduce an AFM’s system complexity and cost. An AFM typically creates a topographical
image by scanning a cantilever/tip across a sample surface. A laser beam and position-
cantilever that interacts with the sample and provides the “physical link” to measuring nanomechanical properties. While cantilever microfabrication technology has continuously advanced over the years, the overall design has remained largely unchanged — a passive rectangular cantilever has been adopted as the industry wide standard. Consequently, conventional cantilever
instrumentation requires external piezo- acoustic excitation as well as an external opti- cal deflection sensor. Both components are not optimal for trends in multifrequency AFM technology which can extend the imaging information beyond the topography to a range of nano-mechanical properties, including sample stiffness, elasticity and adhesiveness. In contrast, active cantilevers with inte-
grated actuation and sensing on the chip level provide several distinct advantages over a conventional cantilever including the absence of structural modes of the mounting system, the possibility of downscaling, sin- gle-chip AFM implementations, paralleliza- tion to cantilever arrays as well as the absence of optical interference.
Dr. Michael Ruppert aligns a custom active cantilever in a modified AFM.
sensitive photodiode detector is then used to determine small changes in cantilever deflec- tion. Signals from the detector need to be acquired and analyzed to determine any topo- logical height changes on the sample’s surface to create a three-dimensional topography.
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Improving AFM Systems Dr. Ruppert and his coworkers have
recently published a number of papers that propose novel, integrated cantilever designs to improve AFM performance, simplify oper- ation and drastically reduce the footprint
and equipment costs. The papers discuss top- Continued on next page
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