Experiment Principles and Applications of a Scanning Tunneling Microscope (STM)

Topics covered:

- STM and tunneling effect

- Hexagonal structures

- Sub-nanometer scale imaging

- Piezoelectric devices

- Local density of states (LDOS)

- Constant height mode

- Constant current mode

Principles and objectives:

Approaching a very sharp metallic tip to an electrically conductive sample by applying an electric field leads to a current between the tip and the sample without any mechanical contact. This so-called tunneling current is used to

study the electronic topography at the sub-nanometer scale of a freshly prepared graphite surface (HOPG). By scanning the tip line by line on the surface, the graphite atoms and hexagonal structure are then imaged.

The different tasks are:

- Prepare a Pt-Ir tip and the oriented pyrolytic graphite sample (HOPG) and approach the tip to the sample.

- Study the topography of the layers and the height of the steps between neighboring layers in constant current mode.

- Visualize the arrangement of graphite atoms by optimizing tunneling and scanning parameters.

- Interpret the structure by analyzing angles and distances between atoms and atomic rows and using the 2D and 3D graphite model.

- Measure and compare images in constant height and constant current modes.

Comments:

Observe atoms in minutes. Custom-designed system for use in teaching laboratories.

The microscope consists of a single compact and portable instrument, no additional equipment is needed. Isolated from vibrations for better and reproducible results. Can be used for both atomic resolution imaging and spectroscopy. Possibility to perform additional experiments

with a gold sample.

- Compact eff and tunnel microscope - STM - Tools needed for tip preparation - Pt-Ir wire for tips: length 30 cm, diam. 0.25 mm - Samples: graphite (HOPG), gold film (111), and 4 sample holders - Power supply (100-240 V, 50/60 Hz), USB cable - Interactive teaching and learning software