The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation “sandwich method” (SSM) with a donor concentration of about 10 17cm-3 at T=10–40K. The donor electrons of the N donors substituting quasi-cubic “k1” and “k2” sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1 -1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1 -1 for the donor electrons of N substituting hexagonal (“h”) site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm -1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed

The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation “sandwich method” (SSM) with a donor concentration of about 10 17cm-3 at T=10–40K. The donor electrons of the N donors substituting quasi-cubic “k1” and “k2” sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1 -1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1 -1 for the donor electrons of N substituting hexagonal (“h”) site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm -1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed

The spin relaxation of nitrogen donors in 6H SiC crystals as studied by the electron spin echo method

We present the detailed study of the spin kinetics of the nitrogen (N) donor electrons in 6H SiC wafers grown by the Lely method and by the sublimation “sandwich method” (SSM) with a donor concentration of about 10 17cm-3 at T=10–40K. The donor electrons of the N donors substituting quasi-cubic “k1” and “k2” sites (Nk1,k2) in both types of the samples revealed the similar temperature dependence of the spin-lattice relaxation rate (T1 -1), which was described by the direct one-phonon and two-phonon processes induced by the acoustic phonons proportional to T and to T9, respectively. The character of the temperature dependence of the T1 -1 for the donor electrons of N substituting hexagonal (“h”) site (Nh) in both types of 6H SiC samples indicates that the donor electrons relax through the fast-relaxing centers by means of the cross-relaxation process. The observed enhancement of the phase memory relaxation rate (Tm -1) with the temperature increase for the Nh donors in both types of the samples, as well as for the Nk1,k2 donors in Lely grown 6H SiC, was explained by the growth of the free electron concentration with the temperature increase and their exchange scattering at the N donor centers. The observed significant shortening of the phase memory relaxation time Tm for the Nk1,k2 donors in the SSM grown sample with the temperature lowering is caused by hopping motion of the electrons between the occupied and unoccupied states of the N donors at Nh and Nk1,k2 sites. The impact of the N donor pairs, triads, distant donor pairs formed in n-type 6H SiC wafers on the spin relaxation times was discussed

Paramagnetic Properties of Fullerene-Derived Nanomaterials and Their Polymer Composites: Drastic Pumping Out Effect

Abstract The evolution of paramagnetic properties of the fullerene soot (FS), fullerene black (FB), and their polymer composites Phenylon C-2/FS, FB has been studied using the electron paramagnetic resonance (EPR) method. For the first time, a drastic growth of the EPR signals in the FB, FS, and composite samples was observed under pumping out at temperatures T = 20 ÷ 300 °C, which is attributed to the interaction between carbon defects and adsorbed gas molecules, mainly oxygen. It is shown that the ensemble of paramagnetic centers in the FB, FS, and the composite is heterogeneous. This ensemble consists of three spin subsystems 1, 2, and 3 related with different structural elements. The subsystems give three corresponding contributions, L 1, L 2 and L 3, into the overall contour of the EPR signal. The most intensive and broad signal L 3 is caused by 2D electrons from the surface of carbon flakes. Theoretical calculations of the L 3 signal line shape were carried out, and the decay rate of the integral intensity has been obtained for each component L 1, L 2, and L 3 after the contact of the sample with the ambient air. The signal decay process in the bulk composite samples is much slower due to their low gas permeability at room temperature (RT)

Luminescent and Optically Detected Magnetic Resonance Studies of CdS/PVA Nanocomposite

A series of solid nanocomposites containing CdS nanoparticles in polymeric matrix with varied conditions on the interface particle/polymer was fabricated and studied by photoluminescence (PL) and optically detected magnetic resonance (ODMR) methods. The results revealed interface-related features in both PL and ODMR spectra. The revealed paramagnetic centers are concluded to be involved in the processes of photo-excited carriers relaxation.Funding Agencies|Volkswagen Foundation; Swedish Institute via Visby program; National Academy of Science of Ukraine [26/17-H]</p