Direct evidence for off-centering of Mn impurity in SrTiO<Subscript>3</Subscript>

Mn-doped SrTiO₃ samples (3% Mn) with different deviations from stoichiometry have been investigated using XAFS spectroscopy. It was shown the under various preparation conditions manganese atoms can sub-stitute A and B sites of the perovskite structure and are in them in different charge states. Impurity Mn⁴⁺ ions that substitute Ti sites occupy on-center position in the lattice, whereas Mn²⁺ ions that substitute Sr sites are off-center and are displaced from the lattice sites by a distance of 0.32Å.     

Ferromagnetism in Mn-doped ZnO due to impurity bands

We have prepared quasi-homoepitaxial Zn_0.95Mn_0.05O-films on ZnO substrates by pulsed laser deposition. The thin films were characterized by in situ RHEED during growth, X-ray diffraction and reflectometry, as well as transmission electron microscopy (TEM). The magnetic properties have been analyzed by SQUID magnetometry and by measuring the anomalous Hall effect. By varying the growth conditions (substrate temperature: 200–600 ^∘C, deposition atmospheres: Ar, O₂) a different concentration of impurities has been generated. Our results show that the films are electron doped and exhibit a ferromagnetic coupling that depends on the impurity concentration.     

Direct evidence for conduction pathways in a solid electrolyte

The emission of silver ions from the apex of an amorphous electrolyte tip has been investigated by field ion microscopy. The ion emission patterns show discrete nanometer-sized spots. We present evidence that they represent the termination of bulk ion conduction pathways at the solid-vacuum interface. The analysis of the signals from individual emission sites suggests the existence of a network of such pathways in the solid. Auto- and cross-correlation measurements of the currents from individual sites provide quantitative information on the microscopic dynamics of charge transport in solid electrolytes as well as on the lateral extent of the pathway network.     

Experimental evidence for electron-hole liquid in ZnO

Measurements of optical gain in ZnO have been performed as a function of excitation intensity and temperature. The results are interpreted in terms of formation of an electron-hole liquid at temperatures below 70K. The liquid has a binding energy of 22 meV and a low temperature density of 0.98 × 10¹⁸cm^-3.     

Lattice location of implanted As in ZnO

Radioactive ⁷³As ions were implanted into a ZnO single crystal at room temperature with 60 keV up to a fluence of 2×10¹³ cm⁻². Subsequently, the angular emission channeling patterns of emitted conversion electrons were recorded by means of a position-sensitive detector in the as-implanted state and following annealing up to 900 C, and were compared to simulated emission yields for a variety of different lattice sites. We find that As does not occupy substitutional O sites, but mainly occupies the substitutional Zn sites. The fraction of As on O sites was at most a few per cent. Arsenic in ZnO is thus an interesting example of an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system. Possible consequences with respect to the role of arsenic as a p-type dopant in ZnO are being discussed.     

Experimental evidence for the existence of biexcitons in ZnO

For the first time resonant two-photon Raman scattering via biexcitons in highly excited ZnO is reported. The existence of biexcitons is thus shown. Their binding energy is determined to be (20 ± 1) meV.     

Submillimeter EPR evidence for the As antisite defect in GaAs

A new EPR spectrum has been observed in semi-insulating GaAs with a submillimeter laser magnetic resonance spectrometer. The spectrum is isotropic with g = 2.04 ± 0.01 at $\text{υ}\text{?}\text{= 11.236}\text{cm}{}^{\mathrm{-I}}$. The hyperfine interaction parameter | A | ($\text{[ =}\text{3}\text{2}$) is 0.090 ± 0.001 cm^-1. The spectrum is attributed to the As antisite defect in GaAs and the parameters are compatible with the P antisite defect in GaP.     

Magnetism in C- or N-doped MgO and ZnO: a density-functional study of impurity pairs

It is shown that substitution of C or N for O recently proposed as a way to create ferromagnetism in otherwise nonmagnetic oxide insulators is curtailed by formation of impurity pairs, and the resultant C2 spin=1 dimers as well as the isoelectronic N2(2+) interact antiferromagnetically in p-type MgO. For C-doped ZnO, however, we demonstrate using the Heyd-Scuseria-Ernzerhof hybrid functional that a resonance of the spin-polarized C2 ppπ* states with the host conduction band results in a long-range ferromagnetic interaction. Magnetism of open-shell impurity molecules is proposed as a possible route to d(0)-ferromagnetism in oxide spintronic materials.     

Direct evidence for homonuclear bonds in amorphous SiC

The Raman Spectra of carbon-deficient sputtered amorphous SiC films contain an intense band centered at 1442 cm^?1. This band is attributed to the presence of C-C bonds. Similarly a peak at ～508 cm^?1 is attributed to Si-Si bonds. The depolarization spectrum was found to be constant at $\text{?(Δ}\text{v}\text{?}\text{) = 0.32 ± 0.03}$ for $\text{0 < Δ}\text{v}\text{?}\text{< 1800}\text{cm}{}^{\mathrm{?1}}$. Our results indicate a degree of compositional disorder which prevents an identification of the observed like-atom bonds with those predicted by a modified Polk model.     

Control of doping by impurity Cchemical potentials: predictions for p-type ZnO.

Theoretical work has so far focused on the role of host-element chemical potentials in determining defect formation energies that control doping levels in semiconductors. Here, we report on our analysis of the role of the dopant-impurity chemical potential, which depends on the source gas. We present first-principles total-energy calculations that demonstrate a wide variation in the possible effective chemical potential of N. We account in detail for the recent puzzling observations of doping ZnO using N2 and N2O and predict that the use of dilute NO or NO2 gas would resolve the long-standing problem of achieving p-type ZnO.     

Thermoluminescence in ZrO2 with impurity of ZnO induced by UV radiation

ZrO₂ pellets doped by ZnO after 302 nm UV irradiation have been studied for ThermoLuminescent (TL) glow. The TL peak at 90°C for the 1100°C sintered ZrO₂ pellet shifted to 85°C with intensity increased three times for the 1% ZnO doped ZrO₂ sintered at 1100°C. The peak intensity at 210°C for the doped one is only one tenth of the undoped one. The emission spectra of thermoluminescence for undoped and ZnO-doped ZrO₂ revealed that the effect of ZnO doping is to increase the number of luminescent centers. The trapping center associated to the 90°C TL peak is explained by the similar model as that of Kirsh et al. For the case of 210°C TL peak, we have proposed two different models of trapping centers; one is the Zr⁴⁺ in an asymmetrical oxygen arrangement, and the other is the defect complex formed from an oxygen vacancy and an anion.     

Effect of impurity scattering on superconductivity in K2Cr3As3

Impurity scattering in a superconductor may serve as an important probe for the nature of superconducting pairing state. Here we report the impurity effect on superconducting transition temperature T c in the newly discovered Cr-based superconductor K₂Cr₃As₃.The resistivity measurements show that the crystals prepared using high-purity Cr metal（99.99%） have an electron mean free path much larger than the superconducting coherence length. For the crystals prepared using impure Cr that contains various nonmagnetic impurities, however, the T c decreases significantly, in accordance with the generalized Abrikosov-Gor’kov pair-breaking theory. This finding supports a non-s-wave superconductivity in K₂Cr₃As₃.     

Direct evidence for W exchange in charmed meson decay

Using the ARGUS detector at DORIS II, we have observed a signal of 36.7±8.0 events in the decay channel D⁰→K_s⁰φ. In the same data sample, we have observed the well established decay D⁰→K_s⁰π⁺π^?, and find the ratio, $\text{Br(D)}{}^0\text{→}\text{K}{}_{\mathrm{<mtext>s</mtext>}}{}^0\text{φ)}\text{Br(D)}{}^0\text{→}\text{K}{}_{\mathrm{<mtext>s</mtext>}}{}^0\text{π}{}^{\mathrm{+}}\text{π}{}^{\mathrm{?}}\text{)}$, to be 0.186±0.052. The substantial value of (0.99±0.32±0.17)% then derived for the branching ratio for $\text{D}{}^0\text{→}\text{K}{}^0\text{φ}$ gives direct evidence that W exchange contributes D⁰ decay.     

Bit-number cumulants as a correlation measure of self-generated oscillations in a semiconductor model for low-temperature impurity breakdown

A semiconductor model for self-generated, coupled oscillations in the regime of lowtemperature impurity breakdown is used to show that the bit-number cumulants of the invariant density of a dynamic system represent a measure for internal correlations between certain subsystems of this system. The bit-number cumulants appear to be an appropriate measure for linear as well as for nonlinear correlations.     

Direct evidence for dia‐ and paramagnetic domains in beryllium

The first spectroscopic evidence for dia‐ and paramagnetic domains (Condon domains) in beryllium metal is presented. The domains, detected by the splitting of the μSR line, arise and disappear periodically in each de Haas–van Alphen cycle as the field \bf H, normal to the single crystal Be plate and parallel to its [0001] axis, is tuned near \bf H_0\approx 2.7\ T. The intensity of the lines in the doublet reflect the ratio of dia‐ to paramagnetic regions. For the difference in induction within the domains we obtain \Delta B\approx 30\mbox--40\ G in the investigated field range at T=0.8 K. This revised version was published online in July 2006 with corrections to the Cover Date.