E. Di Mauro

EPR of Cu2+ Doped in NH4Br: Orthorhombic centre

Abstract Cu2+-doped ammonium bromide, grown in acidic solution (pH ≈ 0), has been studied by electron paramagnetic resonance in the range 294-77 K. A new Cu2+ centre has been found with spin Hamiltonian parameters almost constant with temperature. At 294K, gx = 2.313 ± 0.005, gy = 2.144 ± 0.005, gz = 2.046 ± 0.005, Ax = 162 ± 3, Ay = 0 ± 5, Az = 13 ± 3, A′x = 0 ± 2 and A′y = 78 ± 3 (A is given in units of 10−4 cm−1). A model with Cu2+ ion at the centre of a Br− square, with two adjacent vacancies at the NH4+ sites, is proposed.

EPR of Mn2+ doped in Zn(BF4)26H2O

Abstract EPR of Mn 2+ doped (∼ 1%) in single crystal of zinc fluoroborate hexahydrate has been studied between 94 and 353 K. Angular variation study of the spectra indicated that the crystal field distortion has a trigonal symmetry along the crystallographic c -axis. The D distortion parameter has two linear regions in its thermal variation. It varies above 200 K as D = (149 + 0.107 T ) G and below 150 K as xz D = (127 + 0.228 T ) G . A “knee”-like curve links these two linear regions confirming an anomaly observed in a previous work at 181 K due to a phase transition. Other spin Hamiltonian parameters are g = 2.000 ± 0.001, a = (8.9 ± 1.5) G , A = (97.9 ± 0.9) G and B = (97.0 ± 0.9) G . They are constant with temperature.

Multifrequency (X-band to W-band) CW EPR of the organic free radical in petroleum asphaltene

Petroleum of Arabian and Colombian origin was studied by electron paramagnetic resonance (EPR) spectroscopy at X- (9 GHz), Q- (34 GHz) and W-bands (94 GHz). The experiments were performed at room temperature (about 300 K) and at 77 K (W-band only). The asymmetry in the lines corresponding to free radicals was observed more intensely in the W-band spectra. The values of the line width ΔH in the spectra increased linearly with the microwave frequency utilized in the EPR experiments. A mathematical simulation of the free radical signal for the EPR spectra in three bands with a set of parameters corresponding to a single species was attempted, but this was not exactly coincident with the experimental signals, suggesting that the hyperfine interaction of the unpaired electron with its neighborhood corresponds to more than one species of radical in the molecular structure of the petroleum asphaltene.

Investigation of optical properties of interfaces between heavily doped Al0.48In0.52As:Si and InP (Fe) substrates by photoreflectance analysis

A set of heavily doped Al0.48In0.52As samples grown by molecular beam epitaxy on InP (Fe) substrates was investigated using the photoreflectance (PR) technique. The spectra at 300 K are characterized by a transition in the vicinity of the InP energy gap, followed by strongly damped Franz–Keldysh oscillations (FKOs) which do not appear when the spectra are obtained at 77 K. The builtin electric field estimated from FKOs shows a small doping dependence but is substantially affected by the inclusion of a thin layer of AlxGayIn1−x−yAs (x≡0.22) at the interface between InP (Fe) and AlInAs:Si. In order to explain these results, a model based on the discontinuity of the energy bands in the InP/AlInAs and InP/AlGaInAs/AlInAs systems and also on the matching of the Fermi levels between the different materials is suggested.