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Microscope: Scanning Probe, Variable Temperature UHV

Quick Specs

  • Sample temperature range from 30 K to 1500 K
  • Characterization includes AES and LEED
  • Maximum scan area of 15 μm x 15 μm

The Omicron variable temperature ultra-high vacuum (UHV) scanning tunneling microscope (VTSTM) is designed to study the structure of both clean and adsorbate-covered solid surfaces. As a real space probe, emphasis is placed on examining defect structures and understanding their role in heterogeneous chemical processes. Sample temperatures during imaging can nominally range from 30 K to 1500 K. At low temperatures, even weakly bound adsorbates can be imaged due to the reduced thermal diffusion.

System Configuration and Operational Overview

Sample Preparation, Handling, and Characterization

The system is equipped with a sample load-lock for rapid introduction into the vacuum chamber. Samples may be radiatively heated up to 1200 K, and the manipulator can be modified to allow for electron-beam heating up to 2200 K. Sample-cleaning capabilities include ion sputtering and oxidative annealing, and surface characterization includes auger electron spectroscopy (AES) and low energy electron diffraction (LEED). Up to three evaporation sources can be mounted for metal- and oxide-film growth. Sample dimensions depend on which sample holder is used (see below). All work with these instruments must be performed in compliance with EMSL practices and permits.

Scanning Tunneling Microscope

The scanning tunneling microscope (STM) is an Omicron VTSTM with Scala Control Electronics. Substrates must be electrically conductive. Sample temperatures in the STM nominally can range from 30 K to 1500 K; however, the accessible temperature range is sample dependent.

Sample cooling in the STM is accomplished using a flow cryostat with a built-in heater. The range of the cryostat system is 30 K to 400 K, and the maximum sample size for use in the cryostat is 1 cm x 1 cm. Two specialized sample holders allow samples to be heated as well as cooled in the STM. The first holder has a built-in ceramic heater (Tmax ~750K), while the second allows for direct current heating of the sample (Tmax 1500 K, maximum heating current ~2 amps). The maximum sample size for these specialized holders is 9 mm x 3 mm.

The maximum scan area is 15 μm x 15 μm. The coarse motion control in lateral directions is 1 cm and allows for imaging over the entire surface. The system has capabilities for in situ tip transfer, and there is line-of-sight access to the sample in the STM for in situ optical and gas exposures. The control electronics allow for imaging, IV and IZ spectroscopy, and dual-bias imaging. The STM is computer controlled using a SPARC/UNIX system.

All Related Publications Related Publications

  1. Interaction of CO2 with Oxygen Adatoms on Rutile TiO2(110).
  2. The Release of Trapped Gases from Amorphous Solid Water Films: II. “Bottom-Up” Induced Desorption Pathways.
  3. The Release of Trapped Gases from Amorphous Solid Water Films: I. “Top-Down” Crystallization-Induced Crack Propagation Probed using the Molecular Volcano.
  4. Multiple Non-Thermal Reaction Steps for the Photooxidation CO to CO2 on Reduced TiO2(110).
  5. Characterization of the Active Surface Species Responsible for UV-Induced Desorption of O2 from the Rutile TiO2(110) Surface.

Related Research Highlights

  1. Novel method yields highly reactive, highly hydroxylated TiO2 surface (Water, Sun, Energy)
  2. ARRA-enabled upgrades enhance research capabilities (Imaging Oxygen Molecules Up Close)
  3. Itinerant electrons are vital in bonding oxygen to common oxide surface (Vacancies Needed)
  4. Alcohol Chemistry on Rutile TiO2(110): The Influence of Alkyl Substituents on Reactivity and Selectivity (On the Surface)
Dohnalek, Zdenek | , 509-371-6150