  Diamond has superlative material properties for a broad range of quantum and
electronic technologies. However, heteroepitaxial growth of single crystal
diamond remains limited, impeding integration and evolution of diamond-based
technologies. Here, we directly bond single-crystal diamond membranes to a wide
variety of materials including silicon, fused silica, sapphire, thermal oxide,
and lithium niobate. Our bonding process combines customized membrane
synthesis, transfer, and dry surface functionalization, allowing for minimal
contamination while providing pathways for near unity yield and scalability. We
generate bonded crystalline membranes with thickness as low as 10 nm, sub-nm
interfacial regions, and nanometer-scale thickness variability over 200 by 200
$\mu m^2$ areas. We measure spin coherence times $T_2$ for nitrogen-vacancy
centers in bonded membranes of up to 623(21) $\mu$s, suitable for advanced
quantum applications. We demonstrate multiple methods for integrating high
quality factor nanophotonic cavities with the diamond heterostructures,
highlighting the platform versatility in quantum photonic applications.
Furthermore, we show that our ultra-thin diamond membranes are compatible with
total internal reflection fluorescence (TIRF) microscopy, which enables
interfacing coherent diamond quantum sensors with living cells while rejecting
unwanted background luminescence. The processes demonstrated herein provide a
full toolkit to synthesize heterogeneous diamond-based hybrid systems for
quantum and electronic technologies.
