ASC500
Scanning Probe Microscope Controller
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The ASC500 is a modular and flexible digital SPM controller which combines state-of-the-art hardware with innovative software architecture, offering superior performance and unprecedented variety of control concepts. The ASC500 controller was developed with the goal to never be the limiting factor in any SPM experiment. All desirable functions and high-end specifications for conducting the experiment of your choice in AFM, MFM, CFM, SNOM, STM, and many more are available.

FEATURES


Scan Engine
The ASC500 uses a dedicated hardware with a 5 MHz scan generator to create the voltages necessary for the raster motion. The 16 bits of the xy outputs are always automatically mapped to the actual scan field, yielding a virtually unlimited bit resolution. Further features are:

- hardware rotation of the field of view,
- hardware slope and drift compensation,
- fully software integrated control,
- LabVIEW™ interface, and
- optional adjustment of scan parameters via ASC-iBox.

Z controller
The z scanner output is controlled by a digital PI algorithm with a bandwidth of 50 kHz. The z output DAC has a resolution of 18 bit, yielding a 4 pm resolution on a 1 µm scan range. This resolution can be increased to a theoretical value of 60 am by limiting the control range. Further features are:

- highly versatile; all channels can be used as control inputs,
- physical units of P/I gain,
- setpoint modulation for P/I fine tuning,
- inversion of feedback gain, and
- inversion of output polarity.

Digital/analog converters (DAC/ADC)
The outstanding input and output capabilities of the ASC500 are the key to highest precision measurements. Its analog-digital converters use state-of-the-art hardware with lowest possible noise. On-board preamplifiers and switchable lowpass filtering allow for maximum signal-to-noise ratio. The high frequency in- and output section of the ASC500 allows for sophisticated measurement concepts as bimodal AFM or advanced Kelvin Probe techniques. Additional features include:

- oversampling and offset compensation,
- analog modulation inputs for the most important channels,
- 6 ADC inputs with 400 kS/s, 18bit,
- 2 high frequency ADC inputs with 50 MS/s, 16bit,
- 4 DAC outputs with 200kS/s, 16bit, and
- software defineable transfer functions.

Q Control
The ASC500 provides full control over the Q factor of any driven lever system by means of electronic Q control. The natural Q factor of the lever can be varied by typically more than one order of magnitude in each direction. Benefits are:

- to gain sensitivity due to increased Q factor,
- to gain scan speed in ultra high Q setups by reducing the Q factor, and
- to use well-known room temperature scan parameters also for low temperature
experiments with help of Q reduction.

PLL
A fully digital phase locked loop is implemented into the ASC500. It uses the high frequency inputs/outputs with 50 MHz bandwidth. A high-speed Lock-in demodulator and two PI control loops are used to control the amplitude of an oscillator and to follow the resonance shifts. The frequency resolution is below 0.2 µHz in a range of 1 kHz up to 2 MHz. Therefore, it is possible to

- gain access to direct measurement of force gradients by means of measuring
(delta)f, and to
- have a clear PLL concept with graphical interface and to access to all data
streams in the PLL chain.

Spectroscopy
The ASC500 features advanced spectroscopy techniques such as z spectroscopy and bias voltage spectroscopy. These measurements are supported by an internal Lock-in and a limiter functionality which drastically reduces the likelihood of a tip crash. Spectroscopy measurements can be automatically triggered on line, grid, or point-by-point paths. Combinations of spectroscopies can be defined in action lists.

Measurement Modes
STM: constant height (with tilt correction), constant current
AFM: contact mode, amplitude modulation, frequency modulation (PLL), Kelvin Probe, bimodal AFM, scanning gate microscopy SGM
MFM: constant height (with tilt correction), dual pass mode
CFM: constant height, step scan mode for increased scan ranges

LabVIEW™ control
The new LabVIEW™ interface provides full control over all ASC500 functions. Benefits are:

- measurement automatization,
- user definable experiments, and
- easy implementation with 3rd party instrumentation.

Data Processing
Collection of data is the most important task in every experiment. The ASC500 was built to give the user every possibility to view, process, and save all data streams. Data can be visualized in 1D, 2D, or 3D displays. Furthermore, the ASC500 features are:

- real-time FFT calculation and background filtering,
- full control over all raw and processed data,
- global snapshot functionality: a user definable collection of data can be saved with only one mouse click, and
- saving of parameters in a text file.