Working during an experiment with Dr. Joonkon Kim in ERDA-TOF Beamline

ERDA-TOF system working during an experiment with Dr. Joonkon Kim

Tipical ERDA-TOF spectrum

ERDA-TOF spectrum of a LiNbO3 sample where 6Li and 7Li isotopes are perfectly resolved with a 20 MeV I4+ beam.

Responsible scientist: Andrés Redondo Cubero

The Time-of-flight (ToF) beamline at CMAM is located at the 10˚ port of the switching magnet. It is specifically designed for Elastic Recoil Detection Analysis (ERDA) with heavy ion beams, such as 35Cl, 79Br, 127I or 197Au. This line allows the mass-resolved depth profiling of light elements (Z<14) thanks to the simultaneous detection of both the recoil energy and the time of flight.

The optics of the beam line includes two sets of four independent slits to control the beam spot and divergence. A beam profile monitor and a Faraday cup are used for diagnostics. An additional transmission Faraday cup is placed before the scattering chamber to monitor the current during the measurement. The sample holder is prepared to store up to 12 samples, controlled by means of a 3-axis goniometer.

The ToF telescope, placed at 40˚ scattering angle, is based on the Jyväskylä design and hosts two time stations (separated 456 mm). When a particle crosses every time station, a fast electronic signal is generated. This signal is used to feed a GHz amplifier and timing discriminator connected to a time-to-amplitude converter. Thus, a pulse proportional to the start-stop delay is generated. The particle energy is detected using a large-area Si detector placed 869 mm away from the sample.

Both time and energy signals are digitilized and recorded in a multiparameter analyzer that selects the coincidence events. The energy signal is used for mass separation while the time signal is used for the depth profiling analysis due to its better resolution.
ERDA-ToF is a powerful technique for the detection of common impurities (e.g., H, C, N and O) and for the isotopic identification of light species (e.g., 6Li and 7Li ). However, the method is not limited to these elements and allow the depth profiling of a wide range of atoms, including heavy ones, with similar sensitivity (0.1%) and depth resolution (few nm). In most practical cases the maximum depth of analysis is 500 nm. The mass resolution is 1 atomic mass unit for most of the interesting elements.

Recent publications related with ERDA-ToF beamline: