CreaTec STM/AFM Electronics
The STM electronics are based on a digital design. A DSP (digital signal processor) controls the scanning parallel (x, y) to the surface as well as the tip/sample separation. All scanning/feedback parameters are fully controlled through the STM program. An additional high voltage amplifier and a current preamplifier complement the electronics. There are options to read data from external devices, too.
The heart of the STM electronics is a DSP (TMS320C6657 with 16GFLOPS @1GHz) by Texas Instruments. It is integrated into a commercial Single Board Computer (SBC) and connects to a Windows operated PC via ethernet (1GB/s). The DSP is electronically decoupled from the analog I/O board, which provides 6 D/A outputs (20bit, 50kHz), 4 A/D inputs (18bit, 50kHz) and 32 digital I/O ports. 4 analog output channels are used to control the piezo-voltages (x, y, z) and the sample bias voltage. One input channel records the tunneling current, the others may be used to read other signals (e.g. dI/dV from an external lock-in-amplifier).
Another analogue I/O board (clocked at 500kHz) is used to operate a PLL for qPlus sensors. It's operated by another core of the same DSP too.
CreaTec High-Voltage Amplifier
The three piezo voltages (x, y, z) are amplified by a selectable factor of 1, 3, 10 or 30 to the dual voltage bipolar output. An offset voltage or a modulation voltage may be added to any channel by a potentiometer and via separate inputs. The maximum output voltage is ±200 V. An interface to the DSP board allows reading the gain settings into the STM program to set the appropriate scaling in the images.
Any I/V-converter with the desired specifications can be used with the STM program, but it should be externally gain switchable to exploit the manipulation techniques implemented in the software. We supply the Femto DLPCA-200 (gain: 103–1011 V/A, bandwidth: 500k–1200 Hz).
The STM software can be controlled via OLE/COM from other windows programs. Some other devices like the Data Logger Agilent 34970 or the Lock-In-Amplifier SR830 are read from the STM-software via the GPIB-interface or RS-232.