Time‐differential radio‐frequency muon spin resonance (TD‐RFμSR) technique at a pulsed muon beam

Longitudinal‐field μSR methods, e.g., radio‐frequency μ⁺ spin resonance (RFμSR), are well suited to investigate dynamic processes that destroy the phase coherence of the muon spin ensemble. Additional information on relaxation processes of the muon species under investigation is obtained from time‐differential (TD) data acquisition. In this paper we describe the set‐up of a TD‐RFμSR spectrometer installed at the ISIS pulsed muon facility at the Rutherford Appleton Laboratory (RAL, Chilton, UK). As an example, results of TD‐RFμSR measurements on muons in diamagnetic environment μ^d in a boron‐doped silicon sample under illumination at 55 K are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electrically active paramagnetic centres at Si-SiO2 interfaces

Spin-dependent resonance (SDR) measurements show several paramagnetic centres at silicon-oxide interfaces after room temperature oxide growth. The density of centres is about 10¹¹ cm^–2, and increases with the thickness of the oxide at a similar rate. Upon heating in N₂ in the range 100–400 K the signals reduce, but recover logarithmically with time upon standing in air. They are ascribed to hydrogen or hydrogen containing species which diffuse through the oxide to the interface.On leave at: Xerox, Palo Alto Research Center, Palo Alto, CA 94304, USA     

Paramagnetic Impurities in Graphene Oxide

We report on electron paramagnetic resonance and nuclear magnetic resonance study of graphene oxide produced by the Hummers method. We show that this compound reveals isolated Mn²⁺ ions, which originate from potassium permanganate used in the process of the sample preparation. These ions are likely anchored to the graphene oxide planes and contribute to the ¹H and ¹³C spin–lattice relaxation.     

Influence of gadolinium concentration on the EMR spectrum of Gd in zircon

Electron magnetic resonance (EMR) spectra of gadolinium-doped zircon (ZrSiO₄) powders have been studied at room temperature for gadolinium concentrations between 0.20 and 1.0 mol%. The results suggest that Gd³⁺ ions occupy substitutional sites in the zircon lattice, that the electron magnetic resonance linewidth increases with increasing gadolinium concentration and that the range of the exchange interaction between Gd³⁺ ions is about 1.17 nm, larger than that of the same ion in other host lattices, such as ceria (CeO₂), strontium oxide (SrO) and calcium oxide (CaO). The fact that the electron magnetic resonance linewidth of the Gd³⁺ ion in polycrystalline zircon increases, regularly and predictably, with Gd concentration, shows that the Gd³⁺ ion can be used as a probe to study, rapidly and non-destructively, the crystallinity and degradation of ZrSiO₄.     

Improved method to detect nitric oxide in biological systems

In this work an improved method is described for using organic solvent extracting to detect nitric oxide. The partition coefficients of the diethylthiocarbamate (DETC)-Fe²⁺ complex between different organic solvents and water, the signal intensity of the same NO trapping complex concentration in different organic solvents, and the extracting abilities of the organic solvents were determined. It was found that ethyl acetate was the optimal organic solvent. With ethyl acetate as extracting solvent, the (DETC)₂-Fe²⁺-NO complex was extracted from water phase to organic phase, and low concentration of nitric oxide in large volume could be detected by electron spin resonance (ESR) at room temperature. The ESR signal intensity had a good linear relationship with the concentration of nitric oxide, at a signal-to-noise ratio of 2. The detection threshold of this method was improved to lower than 50 nM, which was more sensitive than the usually used method. The (DETC)₂-Fe²⁺-NO complex was stable in the dark at 0–4°C, and there was little change after days. Nitric oxide produced by cardiomyocytes cultured in media and other biological systems was firstly detected with this method.     

pp annihilations into four-and five-pion final states in the T(2190) region

New data from a 600 000 picture exposure of the BNL 31 inch hydrogen bubble chamber to a separated antiproton beam have been analyzed to try to determine if the π⁺π^?π⁺π^? or π⁺π^?π⁺π^?π⁰ final states contribute any broad or narrow structure in the T(2190) region. The resonance channel fractions determined by maximum likelihood fits are all consistent with smooth behavior through the T-region and therefore there is no significant evidence that any of these resonance channels contributes to the broad bump in the total cross section. The errors on some of the fractions, however, limit the sensitivity to ～ 0.5 mb for enhancements in these channels.     

Europium-151 Mössbauer spectroscopic and XANES investigation of europium-exchanged Y-zeolite

Eu³⁺ in ca. 10 wt% europium-exchanged Y-zeolite is partially reduced by treatment in hydrogen at 600°C to Eu²⁺. The reduction of Eu³⁺ is more readily achieved in Y-zeolite than in europium(III) oxide. The discrepancy in the extent of reduction as revealed by¹⁵¹Eu Mössbauer spectroscopy and near edge X-ray absorption fine structure (XANES) is associated with any difference in the recoil free fractions of Eu²⁺ and Eu³⁺ which may exist at 298 K and the enhanced sensitivity of the XANES to changes in the europium oxidation state.     

Oxide aperture scaling effect on high-speed (>16 GHz) vertical-cavity surface-emitting lasers performance

High-speed, oxide-confined, polyimide-planarized 850 nm vertical-cavity surface-emitting lasers (VCSELs) with oxide aperture diameters of 9, 10, 12, 15, 20, and 30 μm have been fabricated and characterized. For a 9 μm oxide aperture diameter, the lasers exhibit a resonance frequency, a 3-dB modulation frequency, and a modulation current efficiency factor (MCEF) up to 12.4, 16.5 GHz, and 10.9 GHz/mA^1/2, respectively, at only 7.9 kA/cm². Threshold voltage and current were 1.45 V and 0.7 mA, respectively. It is demonstrated that increasing the resonance frequency with bias does not guarantee a higher modulation bandwidth. The influence of oxide aperture scaling effect on VCSEL performance is presented.     

Repolarization studies in amorphous and polycrystalline silicon

A procedure has been developed to extract qualitative and quantitative information on the muonium fractions, in particular the Mu^* fraction, in polycrystalline and amorphous materials from their longitudinal field repolarization curves. Preliminary results for amorphous silicon suggests that both the Mu^* and Mu^* fractions here are generally lower than in crystalline silicon at temperatures below 200K, but the Mu^* fraction may survive to room temperature in this disordered host.     

Magnetic resonances spectroscopy of nanosize particles La0.7Sr0.3MnO3

Using a co-precipitation method, perovskite-type manganese oxide La_0.7Sr_0.3MnO₃ nanoparticles (NPs) with particle size 12 nm were prepared. Detailed studies of both ⁵⁵Mn nuclear magnetic resonance and superparamagnetic resonance spectrum, completed by magnetic measurements, have been performed to obtain microscopic information on the local magnetic structure of the NP. Our results on nuclear dynamics provide direct evidence of formation of a magnetically dead layer, of the thickness ≈2 nm, at the particle surface. Temperature dependences of the magnetic resonance spectra have been measured to obtain information about complex magnetic properties of La_0.7Sr_0.3MnO₃ fine-particle ensembles. In particular, electron paramagnetic resonance spectrum at 300 K shows a relatively narrow sharp line, but as the temperature decreases to 5 K, the apparent resonance field decreases and the line width considerably increases. The low-temperature blocking of the NPs magnetic moments has been clearly observed in the electron paramagnetic resonances. The blocking temperature depends on the measuring frequency and for the ensemble of 12 nm NPs at 9.244 GHz has been evaluated as 110 K.     

Structural Properties of Cr<Superscript>3+</Superscript>-Doped Cadmium Oxide Nanopowders

The Cr³⁺-doped cadmium oxide nanopowder is prepared at room temperature by a mild and simple solution method. The prepared powder is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), optical, electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) techniques. The XRD powder pattern reveals the lattice structure and cell parameters are evaluated. The SEM image shows the stone-like morphology of the nanopowder. The optical absorption spectrum indicates the distorted octahedral site symmetry of Cr³⁺ ions. The crystal field Dq and interelectronic repulsion parameters B and C are evaluated. The EPR spectrum gives a resonance signal at g = 1.973 for Cr³⁺ ions. The FT-IR spectrum reveals the characteristic vibrations of cadmium oxide.     

Photodissociation effects on pulsed laser deposited silver oxide thin films: surface‐enhanced resonance Raman scattering

Temporal Raman scattering measurements with 488, 532 and 632 nm excitation wavelengths and normal Raman studies by varying the power (from 30 W/cm² to 2 MW/cm²) at 488 nm were performed on silver oxide thin films prepared by pulsed‐laser deposition. Initially, silver oxide Raman spectra were observed with all three excitation wavelengths. With further increase in time and power, silver oxide photodissociated into silver nanostructures. High‐intensity spectral lines were observed at 1336 ± 25 and 1596 ± 10 cm⁻¹ with 488 nm excitation. No spectral features were observed with 633 nm excitation. Surface‐enhanced resonance Raman scattering theory is used to explain the complex behavior in the intensity of the 1336/1596 cm⁻¹ lines with varying power of 488 nm excitation. Copyright © 2011 John Wiley & Sons, Ltd.     

The initial stages of deposition of Cu on ZnO(101&#x0304;0) and MgO(001) surfaces studied by electron energy loss spectroscopy

The copper deposition on single crystal ZnO(101&#x0304;0) and MgO(001) surfaces has been studied by electron energy loss spectroscopy (EELS) in UHV at room temperature. The initial deposited Cu (well below one monolayer) induces a loss peak at about 2 eV on both oxide surfaces and at 4.3 eV on the MgO(001) surface. Based upon heat treatment and oxidation experiments the 2 eV structure is assigned to the electronic resonance of Cu(I) from the Cu deposit on the oxide matrix substrates. On the basis of the experiments the colour-center-related loss peaks, at 2.6 eV for MgO(001) and at 1.9 eV for ZnO(101&#x0304;0), are believed to be due to electronic resonance of a V⁻_s center, and the metal ion vacancies are suggested to be active centers which interact with the submonolayer copper deposits. Finally, the electronic energy loss spectra from the Cu-covered oxide surfaces are discussed in the framework of electronic band structures.     

Work function, valence band and secondary ion intensity variations noted during the initial stages of SIMS depth profiling of Si and SiO2 by Cs

Work function, valence band and ²⁸Si⁻ secondary ion intensity variations from various Si substrates sputtered by 1 keV Cs⁺ at 60° were measured. Oxide free Si wafers and native oxide terminated wafers did not reveal any appreciable valence band variations close to the Fermi edge. Their work functions however, decreased substantially with an exponential trend noted between this and Si⁻ secondary ion intensities from the O free Si wafer. This is consistent with the electron tunneling model which assumes a resonance charge transfer process. Native oxide terminated wafers exhibited deviations from this exponential trend, while Si wafers with thicker oxides revealed the growth of sub-band features in the valence band spectra on sputtering with Cs⁺. These features, may partially, if not fully, explain the Cs⁺ induced enhancement effect noted on SiO₂ substrates where work function based models are not applicable.     

Influence of gadolinium concentration on the ESR spectrum of Gd in MgO

Electron spin resonance spectra of gadolinium-doped magnesium oxide have been studied at room temperature for Gd concentrations between 0.10 and 1.00 mol%. The results suggest that the range of the exchange interaction between Gd³⁺ ions is about 0.60 nm.     

Microscopic determination of band interaction in 154Gd and 164Er

Microscopic equations describing the direct coupling of the ground state band with the beta-, gamma- and K^π = 1⁺ (responsible for the RAL effect) rotational bands are solved and the interaction strengths are obtained using a Woods-Saxon potential and P + QQ residual forces. The calculated non-adiabatic characteristics are found to be in good agreement with experimental data and are compared to other theories.     

Auger electron spectroscopy and leed studies of adsorption isotherms: Xenon on (0001) graphite

The passivation mechanism and related natures of silicon surfaces with a very thin natural oxide film baked at low temperature and low pressure (≤ 600°C, 1–5 × 10^?6Torr) was studied principally by the measurement of ESR absorption. Two sorts of resonance lines, which are called the broad and the narrow line hereafter, were observed in the dark by vacuum baking after introducing air. Paramagnetic centers responsible for the broad line have a one-to-one correspondence to such surface states at the silicon-silicon oxide interface that have an electrically amphoteric nature. The narrow line with an intense g-anisotropy originated from trivalent silicons. These ESR lines interact very sensitively with atmospheric gases such as water and oxygen. In addition, light illumination induced two ESR lines different from those observed in the dark. The electron trapped at the surface state forms an intrinsic layer at the surface of n-type silicon. It has been confirmed by present ESR experiments and surface conductance measurements that the passivation effects of this surface to various atmospheric ambients such as water vapor results from the existence of an intrinsic layer at the surface of n-type silicon.     

Elektronenspinresonanz von Kaliumchlorid mit sauerstoffhaltigen Zusätzen

Single crystals of KCl with admixtures of KOH, KNO₃ and K₂CO₃ are grown in the air or in a nitrogen atmosphere and the electron spin resonance is studied at low temperatures. The crystals grown in the air show strong resonance signals of O ₂ ^? -ions. This oxide can be reduced to K₂O by introducing F-centers. After that the crystals contain O^?-ions and anion vacancies. By irradiation with ultraviolet light of longer wavelength F-centers are formed in these crystals. Then new resonance signals are found at temperatures below 30° K, which are ascribed to O^?-ions. The resonance lines show an angular variation with ag-tensor of axial symmetry. A hyperfine interaction with one of the surrounding potassium nuclei can be resolved. In KCl-crystals containing KNO₃ new resonances of nitrogen are found.     

Spin dynamics in oriented ferromagnetic nanowires Ge<Subscript>0.99</Subscript>Co<Subscript>0.01</Subscript>

The magnetic properties of one-dimensional oriented nanowires Ge_0.99Co_0.01 grown in pores of anodized aluminum oxide membranes are investigate using ferromagnetic resonance spectroscopy. The electron spin resonance signals of the magnetically ordered cobalt subsystem and the charge-carrier subsystem are identified. It is revealed that the anisotropy field at 4 K is equal to 400 Oe and aligned parallel to the nanowire axis. The transverse relaxation time of spin waves at 4 K is estimated to be ～10^?10 s. It is shown that the magnetic properties of nanowires are predominantly determined by the ferromagnetism of Co and GeCo alloy clusters.