Vibrational modes at the Si/SiO₂ interface detected by pulse electron spin resonance

Electron spin relaxation mechanisms for dangling bonds (P_b centers) at the Si/SiO₂ interface in silicon nanowires produced by metal assisted chemical etching have been investigated by pulse electron spin resonance. The increased interface area in the nanowires provides the signal to noise ratio required to detect non-exponential decay of spin magnetization The spin-lattice relaxation rates are reported in the temperature range 4-300 K and the experimentally observed temperature dependence is explained in terms of the excess vibrational modes which manifest as tunneling two level systems (TTLSs) giving rise to the so called “boson peak” of the amorphous interface. The experiment together with a theory of the spin relaxation mechanism which involves TTLSs provide a novel method to address the boson peak and other issues related to the role of the TTLSs in determining noise and decoherence in qubits and other sensitive devices.