Instrumentation

 

Ultra-high vacuum (UHV) low-temperature (LT) scanning tunneling microscopes (STM), which operate at or close to the liquid helium (LHe) temperature allow imaging of conducting surfaces and adsorbates with atomic resolution and with a spectroscopy, localized to single atoms (STS). In case of sufficiently stable systems it is possible to resolve the internal structure of individual molecules. By applying appropriate tunneling parameters to the STM tip, it is possible to examine the local structure and properties, but also to manipulate individual atoms and molecules in a controlled manner and to construct in this way artificial nanostructures. A very important and unique aspect is the ability of the instrument to perform electronic and vibronic spectroscopies on individual adsorbates, which enables in addition to the local structural studies also chemical identification on an atomic scale. The junction between the scanning STM tip and the surface of the sample represents a tiny chemical "reactor" in which chemical bonds can be created and broken, offering for the time a controlled chemical design of individual molecules.

 

 

UHV room-temperature STM-1 from Omicron

 

The first scanning tunneling microscope was installed in our lab in year 1991. It was an ultra-high vacuum (UHV) STM-1 from Omicron. The microscopy is known for its high stability and is after over 25 years still produced.

 stm         STM 1         NbSe2 image with RT STM

The microscope is still functional but is not used by our group anymore.

 

UHV low-temperature STM 1

 

First low-temperature UHV STM system was homemade and put into operation in 2006. The microscope is based on a Besocke- (Beetle-) type STM head and electronics from Createc. It is cooled by a rather small 4L helium bath cryostat and the working temperature is about 7 K. The instrument was continuously improved in the past and it offers in its present form excellent mechanical and electronic stability.

  UHV LT STM 1 system            head           manipulaton

 

 

UHV low-temperature STM 2

 

Second low-temperature microscope is modified Createc beetle-type STM. It is cooled by a larger custom-made 8L helium bath cryostat from CryoVac. The base temperature is below 5K and the helium cooled manipulator enables cooling of the sample close to LHe temperatures. The system offers standard apparatus for sample preparation (annealing, sputtering, evaporation, LEED/AES). Currently we are using the system to experiment with high frequency (RF) signal detection.

  createc stm      lt stm2 system
    

 

 

UHV Joule-Thomson low-temperature STM

 

Our newest microscope is a Specs Joule-Thomson UHV STM with base temperature of about 1K. The hold time for liquid helium is more than 100 hours which allows us to run experiments over long time. We use Nanonis SPM controller package to operate the microscope. The UHV system with base pressure in 10-11 mbar region is equipped with a wide choice of in-situ surface preparation techniques (ion gun, anneling stage, knudsen evaporators and effusion cell) and chemical (Auger electron spectroscopy (AES) and structural (low-energy electron diffraction (LEED)) characterization of the examined surfaces.

  1     3

 

 

Other equipment

 

UHV suitcase

UHV suitcase with base pressure 10-11 mbar allows us to transfer samples between different UHV systems. The aim is to connect different preparation (PLD, MBE) and analytical systems (XPS, 4-probe STM) with our STMs.

 UHVsuitcase

 

Helium liquefier

Liquid helium is used to cool the STMs down to 4 Kelvin or even lower to improve their stability, reduce noise, improve energy resolution and to be able to observe low-temperature phenomena. However, liquid helium is expensive so one needs to recycle helium gas and liquefy it for re-use. Our institute has a central recovery system and an Air Liquid liquefier with capacity of over 40 L per hour.

 IMG 20160531    kompresor

 

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