Improved method for minimizing vibrational motion transmitted by pumping lines

We present design and performance of a scanning tunneling microscope (STM) that operates at temperatures down to 10 mK providing ultimate energy resolution on the atomic scale. The STM is attached to a dilution refrigerator with direct access to an ultra high vacuum chamber allowing in situ sample preparation. High magnetic fields of up to 14 T perpendicular and up to 0.5 T parallel to the sample surface can be applied. Temperature sensors mounted directly at the tip and sample position verified the base temperature within a small error margin. Using a superconducting Al tip and a metallic Cu(111) sample, we determined an effective temperature of 38 ± 1 mK from the thermal broadening observed in the tunneling spectra. This results in an upper limit for the energy resolution of ΔE = 3.5 kBT = 11.4 ± 0.3 μeV. The stability between tip and sample is 4 pm at a temperature of 15 mK as demonstrated by topography measurements on a Cu(111) surface.

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“…12). 45 All pumps are placed in a separated acoustically shielded room. An overview of the complete setup is depicted in Fig.…”

Section: Implementation Of the Mk-stmmentioning

confidence: 99%

A 10 mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields

Assig

Etzkorn

Enders

et al. 2013

Review of Scientific Instruments

108

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“…To achieve the same effect on the much larger diameter (and thus much stiffer) still pumping line, a double gimbal based on the design of Ref. 13 (left inset of Fig. 2, manufactured by Energy Beams, Inc.) is used to bridge the gap between the lab floor and the plinth.…”

Section: Vibration Isolationmentioning

confidence: 99%

Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

Misra

Zhou

Drozdov

et al. 2013

Review of Scientific Instruments

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We describe the construction and performance of a scanning tunneling microscope (STM) capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically-resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of performance as typical machines with more modest refrigeration by measuring spectroscopic maps at base temperature both at zero field and in an applied magnetic field.PACS numbers: 07.79.Cz,07.79.Fc Scanning tunneling microscopy (STM), since its development almost 30 years ago, has become a powerful technique in condensed matter physics, providing not only structural information about surfaces, but also spectroscopic measurements of the electronic density of states at the atomic length scale. However, most instruments operate at temperatures above 1 K, limiting access to exotic electronic phases and quantum effects expected at lower temperatures, which are studied as a matter of routine by other techniques. Generally, very little spectroscopic information about the electronic density of states is known at dilution refrigerator temperatures, usually being limited to what can be learned using either point contact spectroscopy or planar tunnel junctions. Moreover, STM can make such measurements on the atomic length scale, allowing it to probe systems, such as single spins and atomic chains, which are not directly accessible any other way.While the integration of STM with a dilution refrigerator can be conceptually reduced to simply attaching the microscope to the end of a mixing chamber in lieu of some other cryogenic refrigerator, the technical requirements for sub-Angstrom positioning of an STM tip above an atomically clean surface are often at odds with those for cooling a sample to milli-Kelvin temperatures. For example, when attaching the microscope to the refrigerator, the former would favor the use of a soft mechanical joint using springs, which would isolate vibrations, while a) Electronic mail: yazdani@princeton.edu the latter would favor the use of a rigid mechanical joint with a metal rod, which would provide a strong thermal contact. Nevertheless, a number of STM instruments have been developed that cool the sample using a dilution refrigerator 1-8 . However, among these, few feature ultra-high vacuum (UHV...

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“…An established technique for the isolation of large pump lines was implemented in the dilution refrigerator. This vibration isolator consisted of cable-suspended bellows supported by double gimbals modeled after [1]. This design has the advantage of lowering the resonance frequency of the pump line to the point where vibration from most external sources is simply reflected.…”

Section: Optimizing Polarizationmentioning

confidence: 99%

Brute Force with a Gentle Touch: Vibration Isolation Techniques Used to Increase HD Target Polarization

Bade¹,

Caracappa²,

Kageya³

et al. 2003

AIP Conference Proceedings

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The performance of statically polarized high-field/low-temperature targets is a strong function of the base temperature during polarization. At the Laser-Electron Gamma Source (LEGS) facility, highly polarized Hydrogen Deuteride targets are created in a dilution refrigerator/15 tesla superconducting magnet system, and converted to a frozen spin state. This allows them to retain polarization when placed in a beam at a lower field (0.7 T) and higher temperature (1.3 K). An increase in temperature from the 0 T state to the 15 T state of the refrigerator suggested eddy currents were primarily responsible for heating of the cold finger. Vibration-isolation techniques have been developed to reduce the level of eddy currents due to vibration inside the polarizing field. These techniques reduced the amplitude of vibration due to the pumping system by two orders of magnitude and lowered the cold finger temperature with field energized from 17 mK to 12 mK. The potential gain in polarization is substantial.

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Improved method for minimizing vibrational motion transmitted by pumping lines

Cited by 13 publications

References 2 publications

A 10 mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields

A 10 mK scanning tunneling microscope operating in ultra high vacuum and high magnetic fields

Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields

Brute Force with a Gentle Touch: Vibration Isolation Techniques Used to Increase HD Target Polarization

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