1/f noise and two-level systems in MBE-grown Al thin films

Aluminum thin films play a critical role in electronic and quantum devices, where two-level systems (TLSs) can limit performance. Molecular beam epitaxy (MBE) offers a promising route to reduce TLS densities in Al films. We investigated the energy distribution of TLS densities, g(E), in 10-nm-thick MBE-grown and electron-beam-evaporated Al films via 1/f noise measurements from 80 to 360 K.  At 300 K, the MBE-grown films exhibited noise magnitudes about three times lower than those of the evaporated films, corresponding to roughly an order-of-magnitude reduction in g(E). These results indicate that the observed 1/f noise originates from thermally activated TLSs associated with grain boundaries, consistent with previously established observations [1].