XY Loop Control of Scanning Electron Microscopes

ADwin-Gold II Real-Time Systems for Precise Control

When working with high-tech lab equipment such as scanning electron microscopes, users need instantaneous feedback to achieve high precision and real-time control. For these applications, ADwin measurement and control systems can provide an XY Loop control on scanning microscopes. These systems achieve high-speed control independent of a PC. In our latest Apps Note, CAS DataLoggers gives a brief overview of relevant ADwin features and capabilities.

Real-Time Control of Magnetic Coils

In physics applications, scanning electron microscopes (SEM) use a focused electron beam to generate highly detailed images of samples at the nanometer level. These samples are generally mounted rigidly on a specimen holder called a specimen stub. The electron beam passes through a pair of magnetic scanning coils which deflect its path in the x and y axes so that it scans over a rectangular area of the sample surface at the atomic level. Part of the beam is absorbed by the material being scanned (about 10-20% of the electrons are reflected off the surface, aka ‘secondary electrons’). In this way, the beam’s position is combined with the detected signal from the secondary electrons to produce a topographical 3D image of the surface.

The ADwin-Gold-II is a portable data acquisition system suitable for control of all types of scanning microscopes including atomic force microscopes, raster tunneling, focused ion beam, and other types. The ADwin-Gold-II controls the electron beam’s movement using its own Analog Outputs 1 and 2. ADwin can achieve 10-20 millisecond (ms) precision here or even 50ms if needed. Data is in the form of an analog value (aka the feedback). With a sample rate of 100kHz aggregate, to 1.25 MHz per channel, ADwin has tightly-coupled analog and digital Input/Outputs.

ADwin provides the necessary XY loop control to reflect the electron beam by supplying a varying current to the focus coil enabling the beam go deeper or higher. This intelligent adaptive deflection with feedback measurement allows for a precise XY scan of the surface.

Unique to ADwin systems, TiCo is a local processor with a real-time operating system running independently from the Windows CPU. The TiCo-1 is clocked to 20ns (nanosecond) response time, more than sufficient for these applications.

ADwin automation systems feature all the benefits of direct software connection with Windows without the risk of OS lockups and crashes, since the onboard DSP operates independently of the OS. ADwin control systems are available in multiple form factors including Plug-in boards, Encased stand-alone systems with USB or Ethernet interfaces, and Modular rack-mounted systems.

Users are free to develop their own applications with a full set of available drivers provide for full integration with other applications and programming languages. ADwin proves an interface library for all of the most common GUI and development packages (VB, VC, LabView, etc.)

ADBasic Programming Language

Users develop their code in the ADwin ADBasic programming language. ADbasic optimizes and compiles program code with a mouse-click. After being loaded on the ADwin system, the real-time processes execute fully independently. ADbasic contains the functions to access all I/Os as well as functions for floating-point operations, process control, and communication with the PC. ADlog also contains standard functions e.g. for closed-loop controllers, filtering, function generators etc. which leads to a fast program implementation.

Users can also display real-time data graphically or numerically, to visualize process sequencing, or to set input values via potentiometers, sliders or push buttons. ADtools also displays the current status of ADwin system resources. ADwin can also be bundled with Kalliste’, a visualization tool convenient for control and automation processes. With this software it’s easy to drag and drop, create dials/knobs, view dashboards etc. Kalliste’ works well with many other applications including Microsoft Excel.