In-situ thermal compensation

To characterize the variable temperature capabilities of a specific VT-SPM, one not only has to specify the thermal drift (drift after temperature stabilization) but also the thermal shift, which is the shift of the image during temperature changes. A small thermal shift parameter allows the operator to image the exact same atoms or terraces while the temperature is changed.

A unique feature of the LPM VT-STM is that when the temperature is ramped, thermal expansion of the sample is restricted to a small unidirectional, reversible lateral shift. Drifts during temperature ramping are much lower than with alternative designs and a specific area can thus be brought back into view over a large temperature range. This means that the operator can keep an atomic size feature in view while the temperature is changed over a range of ~300 K.

A measurement of the lateral thermal shift is shown below, where we swept the temperature in 10 minutes from 440 K to 457 K and back to 440 K while monitoring the x and y shift. The data clearly shows that the maximum shift is 200 nm, which is about 5% of the total scan range. Therefore using drift/shift correction procedures, one can easily follow the image during the temperature sweep.

A small perpendicular thermal shift parameter allows the operator to sweep the temperature over a large range without the need to reposition the probe-sample distance by means of the coarse approach motor. We have been rapidly sweeping (‘flashing’) the temperature over 1000 K while the LPM VT-STM kept on scanning the surface. In the graph below, the temperature sweep is 73 K, showing a net shift of 30 nm after 2 minutes.

Thermal specifications

  • Thermal drift: <15 nm/min (X,Y) and 0.05 nm/min (Z)
  • Thermal shift:<15 nm/K (X,Y) and 100 nm (Z, 10% of full range)

Additional information and documentation

Get a pdf-brochure on this topic here.

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