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Single crystal diamond wafers by heteroepitaxy

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Diamond offers a unique combination of extreme material properties. For many technological applications, single crystals with the highest crystal quality are required to profit from the ultimate potential of the material. For already more than two decades the Augsburg diamond group focuses on the exploration of heteroepitaxy by microwave plasma chemical vapor deposition (MWPCVD) as a promising concept towards diamond single crystals in wafer size. During this time iridium has been identified as the best template for epitaxial growth. The transition from highly oriented mosaic blocks to a real single crystal layer and the mechanisms of epitaxial nucleation have been studied in detail. In 2004, the multilayer structure Ir/YSZ/Si has been introduced as a substrate that is expected to fulfill the requirements for a robust technological solution to produce single crystal diamond wafers. The figure shows the different morphology of (a) polycrystalline films (b) highly oriented epitaxial diamond layers consisting of individual mosaic blocks (c) a heteroepitaxial layer on Ir.

Diamond mosaic crystals – the ultimate material for neutron monochromators

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Neutrons are a powerful tool to probe the properties of materials in solid state research. They are generated by nuclear fission in dedicated reactors or in modern spallation sources. The initially high energy neutrons have to be slowed down in different moderators from MeV to typically 1 - 1000 meV (corresponding to wavelengths λ of ~ 9 Å .... 0.3 Å). As a consequence, the whole generation process is energetically extremely inefficient and intensity is a primary issue for all experiments at neutrons sources. The neutrons that leave the moderators still have broad energy and wavelength distributions. To be useful for diffraction and scattering experiments they have to be monochromatized. This is typically done by Bragg reflection using mosaic crystals e.g. of Cu, Ge, HOPG with an angular spread of 0.2 – 0.8°. For neutrons with wavelengths around 1 Å calculations have shown that diamond should have the highest reflectivity outperforming all the other existing crystalline materials by a factor of 2-5.

We try to synthesize diamond mosaic crystals with (001) or (111) orientation having an appropriate mosaic spread, a thickness of 1 – 2 mm and lateral dimensions of 10 x 10 mm2 to 15 x 15 mm2. This work is performed in cooperation with and funded by the neutron sources ILL (Grenoble, France) and FRM2 (Munich).

Single crystal diamond detectors for particle physics

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There is a general trend in elementary particle physics at large accelerator centers like CERN (Genf) or FAIR (GSI, Darmstadt) towards a continuous increase in energies of the primary particles and in beam currents. Every progress on the accelerator side is accompanied by increasing demands on the detector side. Ideal detectors should (a) be fast, (b) collect all generated charge, (c) allow high spatial resolution, and (d) sustain high doses (radiation hardness). Diamond can basically fulfill all these requirements. In addition, due to its large band gap it doesn’t need cooling which represents a huge advantage compared to silicon.

We try to grow diamond samples of highest structural quality with areas of several square centimeters for application as timing and tracking devices at the new FAIR facility in Darmstadt.

Doping diamond for future high power high frequency electronics

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The key figures of merit qualify diamond as an ideal base material for high power high frequency electronic devices. In contrast to many other semiconductor materials doping by diffusion or ion implantation is impossible or it does not yield satisfying results, respectively. As a consequence, doping diamond is usually performed in-situ during growth. We study in-situ doping of diamond by using trimethyl boron as a precursor. We analyze in-situ the plasma emission, the growth rate and study ex-situ the B incorporation and the structural properties of the films. Finally, the electrochemical and electronic properties are studied and p-n structures are grown in cooperation with international partners form other institutes.

Chemical vapor deposition on metal/YSZ/Si – a route to wafer size graphene layers

Bilder_Diamond_Website_2014_05_02_graphene   The single crystal metal films which have been developed as substrates for heteroepitaxial diamond nucleation and growth represent also ideal substrates for the CVD of graphene layers. We have developed Ir(111), Rh(111), Ru(0001), Pt(111), Ni(111) and CuxN1-x(111) with single crystal structure on 4-inch YSZ/Si(111). We study graphene growth and the subsequent transfer to insulating substrates.