Advertising feature Physics World  May 2017

Nano mechanisms – atomic-force microscopy

Queensgate Instruments specializes in delivering world-leading nano-positioning systems. Our nanomechanisms are piezo-driven and Queensgate has pioneered the use of capacitive sensors in high-performance stages and actuators, delivering the highest resolution, linearity of movement and dynamic performance.

Atomic-force microscopy (AFM) and scanning-force microscopy (SFM)
are types of scanning-probe microscopy (SPM) that scan a surface with a mechanical probe, achieving high resolutions.

AFM Scanners

High-performance piezoelectric stages are used in the specimen scanner of an AFM to provide sub-nanometre spacial resolution.

Queensgate provide high-precision, high-speed piezo actuators and flexure-driven stages using capacitive positioning sensors for use in “closed-loop AFM”. With options for travel ranges of 50, 100 and 200 µm, the XY stages provide market-leading positioning resolution; the 100 µm range provides resolution better than 0.25 nm. Finite element analysis of the flexure guidance mechanisms has reduced parasitic angular motions, providing the smoothest, most repeatable scan with greatly minimized out-of-plane motion.

Decoupling the Z axis by using a separately mounted Z stage will usually provide the best dynamic performance and range. For example, the NPS-X-25 operates over a closed-loop range of 25 µm, with a subnanometre resolution of better than 0.1 nm and resonant frequency of 6 KHz.

Where it is more convenient to use an integrated system, the hollow NPS-Z-15H stage integrates with the NPS-XY-100 stage to provide an optical taper right into the focal plane of the sample under test. This arrangement offers accurate travel over 100 μm of travel in the X & Y axes and over 15 μm travel in the Z axis.

All the stages and actuators use plug and play technology, allowing the stages to be swapped between controllers but maintain calibrated performance. For example, a controller can be replaced in an AFM instrument without disrupting the stages.

Stages are offered as standard in aluminium and superInvar. Aluminium stages provide faster response times, whilst SuperInvar provides the best metrological performance. SuperInvar (CTE 0.3ppm K-1, compared to aluminium at 23ppm K-1) minimizes thermal drift, which on a nanometre scale can be important. The SuperInvar stage has a unique isostatic mounting system, which ensures that stresses from the mounting system are properly relieved, and establishes the centre of the stage as the co-ordinate reference point.

The NPC-D-6000 Series controller is designed to control multiple Queensgate stages and actuators. Special features include:

  • USB and Ethernet interfaces. Analogue command and analogue position monitors.
  • Function playback, per channel, where a pre-programmed waveform can be downloaded into the controller and played back using trigger inputs via the USB, Ethernet or TTL inputs. This would be useful for raster scanning.
  • Programmable trigger output based on the function playback. The trigger points can be programmed at any point(s) within the function playback waveform.
  • In-position TTL signal, per channel, to indicate that the stage/actuator position is with a pre-programmed tolerance from the commanded position. This signal is also available via the USB and Ethernet interfaces.
  • Tuneable low pass and notch filters per channel for improved stability and reduced noise.
  • Synchronization, allowing multiple controllers to be used together.
  • Control algorithms allowing higher bandwidths to be achieved compared to conventional PID control.

Queensgate specialize in offering product solutions to meet individual customer requirements. We can advise on the best use of standard products and are specialists in delivering custom systems. Products are engineered to last, with many systems in continuous operation in excess of 20 years.

If you have a positioning application where you require a nanopositioning solution, please contact us.