Arbeitsgruppe Prof. Hillebrands

Molecular beam epitaxy (MBE)

The Molecular Beam Epitaxy (MBE) technique involves highly controlled evaporation of materials in an ultra-high vacuum chamber (pressure in the low 10-11 mbar region). This deposition from the vapor phase can lead to single crystal film growth. For this reason MBE possesses a dominant role in the world of nanotechnology regarding fabrication of materials for high performance applications.

Our group operates two molecular beam epitaxy growth clusters. Both systems are equipped with tools for cleaning the substrates, for controlling the evaporation from the sources and the film deposition, for in-situ structural and chemical characterization, as well as sample storage.

The first cluster is called MDA (Multidepositionsanlage). The MDA has been heavily loaded this year with the growth of magnetic structures. The growth chamber contains two Knudsen cells, and one electron gun with 5 crucibles that are used to heat and evaporate the materials. The growth procedure is controlled in-situ by a quartz crystal. Additionally in-situ Low-Energy Electron Diffraction (LEED) and Auger analytics can be performed. Furthermore, the linear construction of the sample holder reduces the total time for sample preparation largely.

Our second cluster, called MBE, contains two Knudsen cells, and one electron gun with 5 crucibles. The growth procedure is also controlled in-situ by a quartz crystal. One of the great advantages of our MBE system is the capability to control the in-situ growth by means of Reflection of High-Energy Electron Diffraction (RHEED). The characteristics of the RHEED technique is not to interfere with the deposition. This renders it as a unique tool for real-time structural characterization of the sample during the growth process and enables the control of the growth procedure at the atomic level. Using the MBE, there is also an option for Low-Energy Electron Diffraction (LEED) and Auger spectroscopy.

In addition to the aforementioned techniques and linked to the MBE, an scanning tunneling microscope (STM) set-up is used for in-situ atomic probing. This further increases the capabilities of our MBE chamber. STM is a unique tool for surface investigation of the evaporated samples. Also, the cluster includes a load chamber for inserting samples into the vacuum and into the preparation chamber. The latter is used for cleaning the samples since there is the possibility to heat the samples up to 800° C. Furthermore, there is an option for optical coatings. The ionization chamber is equipped with a fine-focus noble gas keV ion source. A transfer chamber connects all the parts of the growth cluster while a repository chamber is also available. The MBE chamber has another unique feature: that of in-situ magnetic characterization with Brillouin light scattering (BLS) spectroscopy and Kerr effect magnetometry. The applied magnetic field can reach 1.2 T. There is an option for the implementation of a cryostat.

The MBE evaporation technique offers unique advantages for the fabrication of patterned samples. The good control of the film growth and the directionality of the beam renders MBE suitable to grow materials on patterned masks. Patterned samples of very high quality can be produced either with pre- or post treatment techniques.

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