A millikelvin scanning tunneling microscope in ultra-high vacuum with adiabatic demagnetization refrigeration.

We present the design and performance of an ultra-high vacuum scanning tunneling microscope (STM) that uses adiabatic demagnetization of electron magnetic moments for controlling its operating temperature ranging between 30 mK and 1 K with an accuracy of up to 7 µK rms. At the same time, high magnetic fields of up to 8 T can be applied perpendicular to the sample surface. The time available for STM experiments at 50 mK is longer than 20 h, at 100 mK about 40 h. The single-shot adiabatic demagnetization refrigerator can be regenerated automatically within 7 h while keeping the STM temperature below 5 K. The whole setup is located in a vibrationally isolated, electromagnetically shielded laboratory with no mechanical pumping lines penetrating its isolation walls. The 1 K pot of the adiabatic demagnetization refrigeration cryostat can be operated silently for more than 20 days in a single-shot mode using a custom-built high-capacity cryopump. A high degree of vibrational decoupling together with the use of a specially designed minimalistic STM head provides outstanding mechanical stability, demonstrated by the tunneling current noise, STM imaging, and scanning tunneling spectroscopy measurements, all performed on an atomically clean Al(100) surface.

Low vibration laboratory with a single-stage vibration isolation for microscopy applications.

The construction and the vibrational performance of a low vibration laboratory for microscopy applications comprising a 100 ton floating foundation supported by passive pneumatic isolators (air springs), which rest themselves on a 200 ton solid base plate, are discussed. The optimization of the air spring system leads to a vibration level on the floating floor below that induced by an acceleration of 10 ng for most frequencies. Additional acoustic and electromagnetic isolation is accomplished by a room-in-room concept.

A nanopositioner for scanning probe microscopy: the KoalaDrive.

We present a new type of piezoelectric nanopositioner called KoalaDrive which can have a diameter less than 2.5 mm and a length smaller than 10 mm. The new operating principle provides a smooth travel sequence and avoids shaking which is intrinsic to nanopositioners based on inertial motion with sawtooth driving signals. In scanning probe microscopy, the KoalaDrive can be used for the coarse approach of the tip or sensor towards the sample. Inserting the KoalaDrive in a piezo tube for xyz-scanning integrates a complete scanning tunneling microscope (STM) inside a 4 mm outer diameter piezo tube of <10 mm length. The use of the KoalaDrive makes the scanning probe microscopy design ultracompact and accordingly leads to a high mechanical stability. The drive is UHV, low temperature, and magnetic field compatible. The compactness of the KoalaDrive allows building a multi-tip STM as small as a single tip STM.

Ultra compact multitip scanning tunneling microscope with a diameter of 50 mm.

We present a multitip scanning tunneling microscope (STM) where four independent STM units are integrated on a diameter of 50 mm. The coarse positioning of the tips is done under the control of an optical microscope or scanning electron microscopy in vacuum. The heart of this STM is a new type of piezoelectric coarse approach called KoalaDrive. The compactness of the KoalaDrive allows building a four-tip STM as small as a single-tip STM with a drift of less than 0.2 nm/min at room temperature and lowest resonance frequencies of 2.5 kHz (xy) and 5.5 kHz (z). We present as examples of the performance of the multitip STM four point measurements of silicide nanowires and graphene.