Tethered AFM Offers Operators More Flexibility

Michael D. Wheeler

A researcher at the National Research Council of Canada has adapted a commercial atomic force microscope (AFM) to perform near-field scanning in a tethered mode. This could have a significant impact on testing photonic devices such as waveguides and ridge diode lasers that do not fit under conventional AFMs.
Several years ago, senior scientist Rod Taylor began converting an AFM from Digital Instruments Inc. to use in near-field scanning. Although the concept behind near-field scanning optical microscopy has been around for the better part of a century, only a select number of researchers have worked to develop the technology. Near-field scanning microscopes are similar to light microscopes but are far more sensitive.
Much of the hardware and software was interchangeable for both types of microscopes, Taylor realized. He made two major modifications: A signal access module was used to couple detected optical signals into the scanning probe microscope controller, and a near-field scanning probe was designed by bending a single-mode fiber and carefully shaping its tip.
This led to a hybrid device that could perform the high-resolution topographic measurements of an AFM and, by inserting a bent fiber probe, could perform high-resolution imaging and spectroscopy on surfaces.

Tethering cable
But there was a problem. The space underneath the microscope head was seriously restricted. Frequently the object under study simply wouldn't fit under the microscope head.
To address this, Taylor added a cable, attaching the microscope head to the rest of the microscope. This enabled the user to position the head at various angles and locations within a 1.5-m radius from the main body of the device. It also freed up valuable space and opened a wealth of testing possibilities.
Since he added the tethering cable, Taylor has used the near-field scanning option to perform optical beam scans of a ridge diode laser from telecommunications giant Nortel. Because of the size of the diode laser, this would not have been possible without tethering the probe.
"By tethering the microscope, it gives you incredible flexibility," said Taylor. He added that it enables users to perform both types of microscopy on a wide range of devices.
There are currently no plans to commercialize the device.