Tramea base configuration

The system handles 128 live signals in real-time: Up to 48 outputs, up to 24 inputs with the remaining signals being user configurable internal signals. Up to 24 signals can be acquired simultaneously with up to 8 additional signals streamed to disk at up to full ADC speed. The base configuration offers 8 inputs and 8 outputs and can be flexibly expanded with additional TSC or TSO signal interfaces.

This very large number of live signals can not only be monitored, but also all signals are displayed as real world numbers in floating- point representation, with assigned SI units for immediate quantitative results, without the need of additional calibrations during data analysis.

All signals can be inspected with the FFT spectrum analyzer, dual-channel oscilloscope, signal charts, and history panels. Such fully digital and integrated software instruments are much more efficient in use, less invasive, better in performance, and lower in cost than their external counterparts.

The ability to digitally route live signals to software instruments during active measurements without any negative impact on signal quality is truly invaluable when optimizing the experimental set-up, eliminating disturbances and thus improving the quality of scientific results.

The signal frontend of the base configuration, the Nanonis TSC, uses the latest advances in AD/DA conversion technology, in combination with sophisticated digital filtering, oversampling, and dithering techniques, to provide the highest resolution.

All outputs of the TSC and TSO use 20-bit resolution DACs with 1-ppm precision, the best available on the market. just a few years ago, similar performance on multiple outputs would have been impossible to realize. The patented hrDAC™ technology turns these state-of-the-art converters into real 22-bit devices, which in a traditional approach would fill a rack with single-channel instruments and cost ten times as much.

Measurements requiring very small modulations with large offsets are thus possible without the need for drift- and error-inducing analog circuits or external mixers or attenuators. The impressive dynamic range also eliminates the need for switching gains.

When experiments involve energies of a few μeV, high resolution alone is not the only pre- requisite for a measurement interface: Low noise is of utmost importance, and the TSC delivers impressive performance on both inputs and outputs. The noise floor of the TSC and TSO lies below 25 nV/√Hz with an output voltage range of ±10 V. Despite its large bandwidth of 40 kHz, the output noise does not exceed 10 μV RMS at a measurement bandwidth of 300 kHz, meaning that the noise contribution of the SC5 is irrelevant in experimental situations.

Scanning probe microscopes require very stable signals over long measurement times. For this reason, the TSC5 and TSO are equipped with a custom temperature-stabilized, high precision voltage reference. The reference has a very low inherent noise and drift. Temperature stabilization combined with thermal decouplingallows reduction of the temperature coefficient to below 3 μV/°C and output drift to below 1.5 μV in 12 hours at 0 V.

In contrast to broadband noise, which can be easily filtered, 1/f noise cannot be eliminated and becomes an issue for experiments requiring signals to be very stable. The outputs of the TSC and TSO have been designed keeping this in mind, leading to a noise level below 750 nV peak- peak (0.1 – 10 Hz, ±10 V range), or about 2²³ times smaller than the maximum output signal.

A custom-designed input stage allows acquisition of the weakest analog signals, without compromises in dynamic range. The signals are digitized at an early stage with 18-bit AD converters running at 1 MS/s and then processed in the digital domain. Adaptive over- sampling is used to always obtain the best signal-to-noise ratio for a given data acquisition rate.

Intelligent adaptive oversampling adds an additional degree of intelligence to data acquisition: Measurement speed can be adapted automatically to the actual value and required quality of the input signal. This results in faster measurements for intervals where no interesting input signal is expected (e.g. just noise) and in higher quality data for the measurement ranges of interest. Instead of guessing integration times, the system automatically determines the optimal value for each measurement point based on signal noise and amplitude.

For even smaller signals, for direct measurements of high-resistance samples, for true differential measurements or simply for extremely small signals, the newly developed MCVA5 voltage amplifier is the ideal frontend to the SC5. It provides staggering 10 TΩ input impedance (to GND), an input spectral noise below 4 nV/√Hz (single-ended at 1 kHz and gain 100), over 120 dB of common-mode rejection and over 500 kHz bandwidth at any gain setting. Remote control is provided for gain (1, 10, 100, 1000), coupling (DC, AC) and input mode (A, A-B).

The preamplifier is seamlessly integrated into the Nanonis software meaning that all calibrations are automatically adjusted when the gain is switched. The design ensures exceptional low-frequency performance resulting in a noise density below 11 nV/√Hz at 1 Hz and 0.1-10 Hz noise of only 25 nV rms (gain 100, single-ended).

The user interface is the crucial part of the measurement system when recording of high quality data in a short time is required. The growing complexity of quantum transport measurements requires control and visualization of a large number of parameters in real-time. At the same time, sensitive samples do not tolerate user errors, meaning that the user interface should ensure that no sample can be damaged by erroneous user inputs.

To ensure that the user is not overwhelmed by the resulting experimental complexity, the user interface is designed based on the typical measurement workflow, with all functions accessible but with the option to only display the relevant ones. A streamlined design ensures that the software is easy to use and that even inexperienced users can work more productively and safely.

More details about the software can be found in the Tramea software page

Competitive advantage in research is often based on the modification of an instrument that allows the researcher to perform experiments in a way nobody else has done before. This is where the built-in API steps in: to give you the building blocks to design your own experiment. It is used to automate experiments, sequences, calibration routines and experimental procedures. Polling of parameters and signals at high rates allows for supervision and alarm settings, and many other features. The user can program in any programming language able to write to and read from a TCP port on the host PC, including Python, Matlab or C++, using a generic script format.

For users preferring an easier start in experiment programming, or users which are used to a LabVIEW programming environment, the LabVIEW programming interface add-on module is the ideal API choice. The LabVIEW programming interface adds the ease of use and debugging options of LabVIEW and consists of libraries to access the controls and functions of the graphical user interface. With the LabVIEW interface the Nanonis SPM Control System provides full access to all the features provided with LabVIEW: graphs, database access, convenient data handling, TCP/ IP, GPIB, RS232, USB access to other instruments, signal analysis functions and much more.

For experiments where exact timing is crucial, the scripting add-on module becomes the ideal tool for customization: Scripts are executed on the real- time system in a time-deterministic manner, improving the time response by a factor of 100 compared to the programming interface. Logic functions can be implemented with the use of FOR loops and IF conditions, for example for real-time feedback. Triggering over TTL lines directly from the real-time system is ideal for fast synchronization with external equipment.