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Koala TetraProbe - Electrical characterization at the nanoscale

Ultra Compact Multi-Tip Scanning Probe Microscope / Nanoprober for electrical characterization at the nanoscale.

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The ultra compact Koala TetraProbe STM integrates four independent STM units within a diameter of 50 mm resulting in an unsurpassed mechanical stability, enabling atomic resolution imaging with each tip.

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Features:

  • Modular and compact design based on the KoalaDrive® nanopositioner
  • Each tip can be positioned independently
  • Tip coarse positioning with optical microscope/SEM control
  • Simultaneous tunneling and scanning with all four tips
  • Atomic resolution with each tip
  • Tip exchange and sample exchange in situ
  • Software controlled switching between current probe and voltage probe for each tip
  • Software allows virtually any possible "concerted" spectroscopic measurements involving the four tips and the sample
  • [Four tip STM/AFM combination] and low temperature version available

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Applications:

  • Local potential measurements on the nanoscale
  • Controlled nondestructive measurements in spectroscopy mode
  • Four point measurements with free positionable local probes on structured samples

[VIDEO]

Real time optical microscope movie of the positioning of the sample and four tips on a structured wafer. The structured rectangles have a size of 30 μm x 50 μm.

Specifications:

  • Outer diameter: 50 mm
  • Drift at room temperature: < 0.3 nm/min
  • Tip xyz coarse positioning: ±2 mm
  • Tip scan range at RT: 6 μm (xy), 1.5 μm (z)
  • Atomic resolution with each tip

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Sketch of two of the four modular units of the Koala TetraProbe. Each unit consists of a KoalaDrive used for the coarse tip approach towards the sample. The KoalaDrive is fixed to a plate (resting on three balls fixed to three tube piezo elements). The plate is moved according to the design of the beetle STM allowing for a coarse motion in the xy-directions. The xyz-scanning of the tip is also performed by these three piezo elements.

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SEM view of the tips. Tip shadows indicate the tip-sample distance

Results:

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Atomically resolved image of the Si(111)-7x7 surface







Surface conductivity determined by distance dependent four probe measurements:







The surface and step conductivities of the Si(111)-7x7 were measured. More information can be found in [Phys. Rev. Lett. 115 (2015) 066801].









The anisotropy of the surface conductance can be determined using rotated tip configurations (optical microscope view). More information can be found in [Phys. Rev. Lett. 115 (2015) 066801].










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Resistance / dopant profiling along freestanding GaAs nanowires:

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Resistance profile along a nanowire. More information can be found in Appl. [Phys. Lett. 103 , 143104 (2013)].







[VIDEO]

[BILD]

Movie of an STM tip moving along a GaAs nanowire measuring a four point probe resistance profile

[VIDEO]

[VIDEO]

Movie of an elastic bending of a GaAs nanowire (left). SEM zoom to nanowires (right).

Scanning tunneling potentiometry with a four tip STM:

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(left:) Potential map on a Si(111)-7x7 surface during current flow from top to bottom. (right:) Potential map of a Si(111)/Ag-sqrt3 with overlaid topography. More information can be found in [here].


Multiprobe measurements on Sb2Te3 nanowires.

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Potential measurements along a 2 μm long wire segment.


Multiprobe measurement on a freestanding topological insulator nanowire:

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Customer specific extensions, like for example optical fibers brought close to the tip/sample regions by a fiber positioner integrated in the TetraProbe system can be provided. A low temperature version of the TetraProbe system is available as well.

[Leaflet: Koala TetraProbe]

Some results are discussed this [application note]


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