Low Temperature UHV STM and AFM Technology

At a Glance

  • Low Temperature Operation at T < 5 K
  • Lowest Thermal Drift & Highest Stability
  • Ultimate STM/STS/IETS Performance
  • Leading QPlus AFM Technology
  • Variable Temperature Operation
  • Guided 3D Coarse Positioning
  • Fast Cool Down
  • Safe & Quick Sample/Tip Exchange
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Why low temperature SPM?

15 years after market introduction of our LT STM (in 1996), the importance of dedicated low temperature SPM techniques in a wide range of active scientific fields is still unbroken. Imaging and spectroscopy of molecules, atom manipulation, graphene, semiconductors and superconductors are only a few examples where research takes great advantage of low temperature SPM.

The reduced mobility of adsorbates at low temperatures allows the detailed analysis of the diffusion behavior and interactions between individual species on the surface. In addition, the internal structure of molecules can be investigated since lateral or rotational motion is 'frozen'. Beyond that, tunnelling is more stable due to less diffusion at the STM tip.

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The second generation of the LT STM

The second generation of the LT STM with extended LHe and LN2 hold time, extremely low drift and highest stability offers ideal performance at 5 K and meets the trend in research towards sophisticated experiments with extremely long measurement times.

The creation and investigation of nanostructures, molecules or atomic structures on insulating surfaces pushes AFM as a complementary imaging and spectroscopy technique to STM. The QPlus AFM technology has successfully been integrated without compromising on the proven STM/STS performance.

The combination of QPlus AFM and STM has a tremendous potential for a range of applications, including AFM-based single molecule manipulation on insulating surfaces and single molecule force probing.

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The LT STM stage

The LT STM stage has been designed for ultimate STM and AFM performance. It employs a very efficient damping system based on the combination of spring suspension and eddy current damping.

This, together with the very rigid scan head design, ensures excellent vibration isolation with a stability in the picometer range. While maintaining its unique performance level, the LT STM has been continuously improved for additional functionality and flexibility.

Some examples for the experimental customization possible with the LT STM are: pre-fitted tapped holes at all optical axes and the cryostat bottom, an optional capillary for integration of glass fibers and optional lens holders.

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QPlus Sensor

The QPlus sensor allows for atomic resolution non-contact AFM while maintaining the user-friendliness and known performance level of the LT STM. Benchmark measurements on single crystal NaCl(100), KBr(001), Si(111)7x7 and Au(111) prove that resolution is competitive with the best cantilever-based AFM results. Atomic resolution in genuine df feedback and at temperatures of below 6K can be maintained with oscillation amplitudes below 100 pm. All measurements and NaCl amd KBr have been carried out on single crystalline samples to fundamentally prove the AFM performance.

The ease of use of the QPlus sensor now makes atomic resolution AFM a routine experiment. The sensor employs a quartz tuning fork for force detection in non-contact AFM operation. One prong of the tuning fork is fixed, while the SPM probe tip is mounted to the second prong. It thus acts as a quartz lever transforming its oscillation into an electrical signal as a result of the piezoelectric effect. The feedback signal is based on the frequency shift originating from the tipsample force interaction. A dedicated and unique preamplification technique ensures distance control based on the pure AFM signal.

Wet-chemically etched tungsten tips are employed for QPlus AFM to enable its simultaneous or alternative use as a high-resolution STM probe. The ability to simultaneously monitor frequency shift and tunnelling current and to freely select one or both as the feedback signal strongly enhances experimental flexibility and opens up a variety of new experiments. 

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