How quality control of everyday products with AFM creates competitive advantages
(Nanowerk Spotlight – Application Note) Many of today’s high-tech products rely on nano-level functional structures, and in products such as mobile phones, integrated circuits and glasses they have already become commonplace. But with increasing demands on products and their quality, tiny structures and the ability to evaluate them are also becoming decisive factors for the production of everyday products.
The experience of a ball-point pen maker shows how atomic force microscopy enables highly accurate quality control during manufacturing, eliminating entire production steps in the process. Everyone has had to contend with scratchy or messy ball-point pens, but not everyone knows that often this malfunction is the result of a manufacturing error: smooth writing depends largely on the roughness of the sphere at the tip of the pen. Its roughness needs to lie in a well-defined interval: too rough, and the pen leaks; too smooth, and it scratches and fails to transport enough ink. The roughness of this little sphere thus becomes the decisive quality indicator of the entire writing apparatus.
In the past, the surface of these spheres could only be checked by making an entire pen around them and testing them in use, a costly process that can be eliminated if the maker opts instead for reliable quality control at the nano-level.
This AFM image shows the topography of a ball-point pen tip. The color scale represents height information. (Image: Nanosurf)
Measuring Inter-Atomic Forces
The atomic force microscope (AFM) belongs to the family of scanning probe microscopes and finds its main use in the inspection of topographical surface features. To achieve its high resolution, it relies on the ability to sense minute inter-atomic forces between the surface and its probe. As it measures, it gently traces its probe – a microscopic needle fixed to a flexible cantilever – right along the surface topography, line by line, in a defined raster pattern. Surface features of varying height cause a varying deflection in the cantilever, which is measured with optical sensors and indicates the inter-atomic forces at play between the probe needle and the surface. The controlling software samples data at predefined locations and collates them to a 3D mathematical representation of the surface. This representation can be visualized as a photo-like height image that allows an immediate understanding of the sample surface.
A New Era
One drawback of this high-resolution microscopy used to be its technical complexity. Only highly qualified specialists have to date been able to make use of this important method. The Nanosurf Nanite AFM ushers in a new era of atomic force microscopy. Lauded with the Swiss Technology Award 2007 in the category “inventing the future”, this little AFM exhibits an array of interesting functions and features. Its ease of use, which allows even lay-persons to obtain high-resolution surface information, and its reasonable price make it particularly interesting for small and medium enterprises.
A further advantage is the automation of the measurement process down to serial measurements without operator presence, which results in a simultaneous gain of productivity and reduction of work. Moreover – and here is where the Nanite takes a step into a new dimension – it can be customized to the relevant measuring needs and requirements. The Nanite system platform offers the possibility of adapting the whole measurement process – sample holders, measurement routines, and measurement evaluations – to the individual customer’s wishes.
Spheres with different diameters rest in predefined positions on this customized sample holder.
Everything Revolves Around the Ball
But how exactly was the Nanite used to control quality in the case of the aforementioned ball-point pen sphere production? First, a dedicated sample holder was built, which holds 20 spheres in well-defined positions and can be repositioned so precisely that the sphere positions need only be entered into the software once.
Next, a measurement procedure suited to the task had to be developed. In the present case, the AFM measures two perpendicular lines on the sphere. From these, the software calculates the sphere’s highest point, centered on which the AFM images its surface.
Finally, crucial measurement parameters such as measurement speed, sensitivity and image size are determined and stored. The reporting software then performs a fully automated analysis, which furnishes the roughness representative of a million spheres. This analysis shows if the production lot in question meets the requirements of the maker, who is now no longer forced to produce an entire test series, because he has reliable evidence of the component quality prior to the next manufacturing steps.
The Nanite system for automated AFM measurements consist of the translation stage and its controller (below) and the AFM and its controller (above).
High-Tech Microscopes on the Shop Floor: New Tools for New Perspectives
With the advent of affordable and easy-to-use atomic force microscopes like the Nanite, the versatile tool previously reserved for research and development is now also available for prototype and series manufacturing in small and medium enterprises. Just like with other technologies, only time will tell which areas in which industries will benefit the most from quick and easy digital surface analysis at the nano-level, but it takes no fortune teller to see an array of potential savings and quality gains.
Many groups that currently use comparatively inaccurate profilometers, which are also limited in their data treatment possibilities, will find that atomic force microscopes offer a new insight into the nano-world, which remains hidden from their current instrumentation. Harkening back to the management rule: “You can’t manage what you can’t measure”, the eagle-eye AFM offers the basic conditions for a new and improved product understanding, better cost efficiency, higher quality, and, as a result, better products.