SPMagic: a Custom AFM Design Service

Author(s):
M. Adami - ELBATECH

Industry:
Electronics, Research, Industrial Controls/ Devices/ Systems, Imaging Equipment

Products:
LabWindows/CVI, M Series Devices, Multifunction DAQ, DAQCard-6036E, PCI-6036E, PCI-6014

The Challenge:
The market of Atomic Force Microscopy (AFM) systems shows a wide offer of general purpose equipments, featuring a broad range of inspection techniques with a base cost over 100 K€. The goal of the application was to lower this economic threshold, introducing on the market highly targeted low cost instruments.

The Solution:
The net separation of the instrument components into distinct blocks allowed to apply optimized design patterns for each of them, ensuring an high level of flexibility. The adoption of National Instruments products both in hardware and software components made easier the process of integration of single pieces into the final product. Atomic Force Microscopy (AFM) is a flexible imaging technique, based on a simple concept, with a wide range of possible applications. The typical AFM systems present on the market are general purpose instruments, with a monolithic design (at most expansible with few add-ons), resulting in high costs and poor specificity. On the contrary, having the possibility to customize mechanics and electronics for particular needs can result in lower cost instruments with highly dedicated measuring features.

The Atomic Force Microscopy (AFM) measuring technique is based on an elastic micron-sized cantilever, with a sharp tip on the top, scanned over the sample, allowing to image the surface with nanometric resolution. Based on this simple working principle, reminding of the macroscopic mechanical profilometers or feeler pins, AFM is a really flexible tool, able to image samples ranging from nanostructured materials (nanotechnology) to living cells (biotechnology). Switching from one context to another is clearly a matter of designing the proper measuring head, but also it is fundamental to optimize the control logic and to develop a dedicated software interface to the machine.
Instead of proposing only a rigid product to the customer, the aim of ElbaTech is to offer the full AFM design service, reflecting the application needs into the implementation details. SPMagic is thus an “open” system, to such an extent that different experimental set-ups are just a matter of combining the available blocks and signals.
In order to gain the desired level of flexibility in the whole AFM system, it is necessary to apply the key concepts of modularity and extensibility to the design of all the three fundamental components of an AFM system:

1) the mechanical head
2) an electronic controller performing synchronous AD/DA conversions and implementing Real-Time operations (such as a feedback ring on the actuator);
3) a software interface for data inspection and parameters setting.

Mechanical Head
The main constraints in designing an AFM mechanical head are related to the required sample access (optical and mechanical) and scanning area. In particular, the core component of the head is a piezo positioning system devoted to scanning the sample under the tip. The XYZ extensions of the actuator have to be selected in connection to the sample under study: for protein studies in liquid, for example, a scanning range of 10 x 10 x 3 µm could be enough, whereas for material studies it could be interesting to image areas as large as 200 µm. The task of designing the mechanical head has been carried out in collaboration with two partners: the Complex Systems Institute of the National Research Council (ISC-CNR) and the Italian representative of PiezoSystem Jena, Micos Italia. The result of the research activity carried out in this context is presented in figure 1. This set-up allows for housing different piezo flexures by PiezoSystem Jena, thus offering the possibility to change the scanning features in a broad range, both using commercial or OEM products.

Controller
The AFM controller proposed by ElbaTech has been designed in an open architecture, so that all signals can be accessed and conditioned through BNC connectors, as shown in Figure 2. But the requirement of flexibility means also changing sampling rate and resolution of AD/DA conversions following the customer's needs. With this aim, it has been fundamental not to design a dedicated hardware for signal acquisition, but to rely on NI Multifunction DAQ boards. These, in fact, embed in one single solution the AD/DA block, a basic digital interface and at least a couple of counters, thus lowering the external electronics needed to complete a full-power AFM controller. Thanks to NI-DAQ drivers, SPMagic supports different E-series boards, and is now upgrading to M-series boards driven by NI-DAQmx drivers.

Software Interface
Requirements of modularity and adaptability are clearly more simply fulfilled in software than in hardware components. Nevertheless the user interface has to take into account for the specificity of the AFM application: being a microscopy technique, the user should be able not only to “see” the surface topography of the sample, but also to perform advanced image processing operations. Using the National Instruments RAD tool LabWindows/CVI, it was possible to develop a software interface strongly integrated in the data acquisition environment, featuring reach GUI widgets and analysis functions. Figure 3 shows a screenshot of the application running on Windows XP pro. Other versions exists for Windows based operating systems (2003, 2000, NT).

Conclusions
The presented project is an example of high-level integration of NI products into instruments at the boundary between the industrial and the research fields. Embedding a multifunction card in a product is obviously feasible only when the overall target is of the high-end range, as in this case. The product is, in fact, a real microscope capable of enhancing the resolution up to the nanometre scale. This requires a PC and therefore allows for an integrated PCI card. Moving some or most of the basic functionalities to this card is a clever way to simplify the external electronics and using the NI visual development suite brings to the simplified realization of the consequent user interface needed.

Author Information:
For more information on this Case Study, contact:
M. Adami
ELBATECH
Tel: +39 (0)565 901002
adami@elbatech.com

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