Doping of Diamond by Co-Implantation with Dopant Atoms and Carbon

In this Rapid Communication, we propose a mechanism for electric dipole active spin resonance caused by spin-dependent electric polarization in a quantum spin gapped system. This proposal was successfully confirmed by high-frequency electron spin resonance (ESR) measurements of the quantum spin dimer system ${\mathrm{KCuCl}}_{3}$. ESR measurements by an illuminating linearly polarized electromagnetic wave reveal that the optical transition between the singlet and triplet states in ${\mathrm{KCuCl}}_{3}$ is driven by an ac electric field. The selection rule of the observed transition agrees with the calculation by taking into account spin-dependent electric polarization. We suggest that spin-dependent electric polarization is effective in achieving fast control of quantum spins by an ac electric field.

While most polymers are good insulators, some of them known as conducting polymers show remarkable electrical conductivities upon doping with electron donors or acceptors. The electrical conductivity is generally known to be governed by the one-dimensional diffusion of the chargecarrying solitons or polarons, and the main charge transfer mechanism in conjugated conducting polymers is known to be the intrachain diffusion and interchain hopping of polarons and/or bipolarons. Electron paramagnetic resonance (EPR) is a powerful tool for spin dynamics, and have been employed to study various conducting polymers as they can sensitively reflect the spin carrier motions and interactions. In conjugated conducting polymers like poly[2buthoxy-5-methoxy-1,4-phenylenevinylene] (PBMPV) where the charge carriers are polarons and bipolarons, the EPR intensity is proportional to the density of the spincarrying polarons (spin 1=2, charge e). A pair of polarons can form spinless singlet bipolarons (spin 0, charge 2e), which are energetically more stable. The spin-carrying polarons can give rise to EPR signals, whereas the spinless singlet bipolarons cannot make EPR transitions. Thus EPR can serve as a sensitive probe of spin carriers in the conducting polymers. PBMPV is a derivative of the conjugated PPV (polyphenylenevinylene) polymer. It can be easily doped to controllable degrees of doping and provides a unique opportunity to systematically study the doping as well as conductivity dependence of various properties including the dopant kinetics and spin/charge dynamics. Recently, we have reported a critical behavior associated with the delocalization of the charge-carrier wave function in a series of I2-doped PBMPV conducting polymers by means of nuclear magnetic resonance (NMR) measurements. In this work, we have investigated the charge/spin dynamics in the same series of samples by means of EPR measurements. While there have been some indirect indications of bipolaron formation in some electrochemically synthesized conducting polymers through the EPR and susceptibility measurements, this quantitative and systematic work is believed to represent a comprehensive observation of the collective critical behavior of bipolaron formation and spin–charge carrier delocalization in an iodine-doped conjugated polymer system. The PBMPV conducting polymer samples were prepared by thermal elimination of polyelectrolyte precursor polymer films and iodine-doping, and the iodine concentration was determined from the weight gain after doping. While the doped PBMPV samples are known to have inherent inhomogeneities, relatively thick good quality samples have been obtained according to visual inspection. The electrical conductivity was measured by the standard four-in-lineprobe method. The room temperature EPR measurements were made at 9.4 GHz using an X-band spectrometer, and the magnetic susceptibilities were obtained by doubleintegrating the differential lineshapes. The room temperature electrical conductivity was measured as a function of the degree of I2-doping, and the conductivity displayed a characteristic increase with the doping. A rapid increase of the electrical conductivity was noticed around the dopings of pc1 1⁄4 10 3 I3 /RU (repeating unit) and pc2 1⁄4 10 1 I3 /RU, which can be attributed to the dynamics governing the charge conduction mechanism. Figure 1 shows the doping degree dependence of the spinto-charge ratio obtained from the spin susceptibility, assuming that the charge density is the same as the dopant density per repeating unit of the polymer. Figure 1 displays an initial decrease of the spin-to-charge ratio until it reaches a minimum of less than 10 2 around pc2, which can readily be attributed to the polaron–bipolaron recombination. It is also interesting to note the spin-to-charge ratio minimum, followed by an increase of the ratio, which may be explained by the dissociation of some of the spinless bipolarons to polarons. Figure 2 shows the EPR lineshapes for samples with various degrees of doping. It is also worth noting the abrupt increase of the peak-to-peak EPR linewidth, in Fig. 3, at the same doping degrees where the spin-to-charge ratio shows a minimum, which indicates that they arise from the same spin dynamics. The abrupt increase in the EPR linewidth at pc2 appears to be a lifetime broadening, i.e., line broadening due to the lifetime shortening, arising from the delocalization of the spin/charge-carrier wavefunctions at the percolation threshold. Thus, EPR is shown to reflect sensitively the spin dynamics in our systems. Figure 4 shows the temperature dependencies of the EPR spin susceptibility and the linewidth for a heavily doped sample with p 1⁄4 3 10 . The spin susceptibility undergoes a decrease with decreasing temperature before showing a typical Curie behavior below a critical temperature around which the linewidth shows a characteristic peak. This

INTRODUCTION

We have developed a means to perform "on the fly" electron spin resonance (ESR) measurements of NBTI defect generation. The approach permits ESR measurements to be performed during NBTI stress void of any recovery contamination. We demonstrate that elevated temperature (100°C) and modest negative polarity oxide electric field (<5MV/cm) generates ESR spectra of E' oxide defects. (These defects are holes trapped in oxygen vacancies.) When similar measurements are made at elevated temperature and no oxide bias, E' center spectra are not observed. When ESR measurements are made with identical negative oxide bias at room temperature, E' center spectra are not observed. Furthermore, we demonstrate that the NBTI induced E' center spectrum disappears, a recovery phenomena, when the NBTI stressing condition is removed. These observations indicate that NBTI is triggered by inversion layer hole capture at an E' precursor site (an oxygen vacancy) which then leads to the depassivation of nearby interface states (P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> centers).

Temperature dependence of the electron paramagnetic resonance of unhydrogenated carbon nitride

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

EPR characterization of defects in monoclinic powders of ZrO 2 and HfO 2

EPR study of several Cr3+ centres in K2MgCl4 single crystal

International audience

The paper is concerned with the fracture toughness and microfractures of a sheet molding compound polyester composite at room and low temperatures. Fracture toughness tests were performed by using compact tension specimens of the composite at room temperature and liquid nitrogen temperature, 77K. Acoustic emission signals were monitored during the fracture toughness tests. The microscopic observation of the fractured surfaces and the spectrum analysis of the acoustic emission signals were made in order to obtain a reasonable explanation of the fracture mechanism. The results are summarized as follows:(1) The load-crack mouth displacement curves at liquid nitrogen and room temperatures became nonlinear at about the same load level and the maximum load observed at liquid nitrogen temperature increased by about three times that observed at room temperature. The acoustic emission activity for the specimen tested at liquid nitrogen temperature was higher than that at room temperature.(2) The fracture toughness KAE at liquid nitrogen temperature, obtained as the stress intensity factor which corresponds to the onset of abrupt increase of the accumulated acoustic emission energy, was extremely larger than that at room temperature.(3) At room temperature the fracture toughness KAE was in good agreement with the fracture toughness KQ obtained by the 5% offset procedure of ASTM E399, and at liquid nitrogen temperature KAE was larger than KQ.(4) From the microscopic observation, it was found that the fracture of a sheet molding compound composite accompanies the microfractures of four types, i.e. fiber breakage, fiber debonding, resin cracking and delamination.(5) The spectrum analysis indicated that the acoustic emission signals could be classified into three types for the specimens tested at room temperature and four types for the specimens tested at liquid nitrogen temperature. An attempt was made to assign each type of the frequency spectra to the microfracture, and the fracture mechanism of the SMC composite was discussed.

Hexagonal molybdenite (MoS2) is one of the most promising two-dimensional (2D) semiconductors, known with n-type and p-type conduction, with possible applications in electronic, opto-electronic, and spintronic devices. In this work, highly pure geological samples of 2H-MoS2 were investigated by temperature-dependent electron paramagnetic resonance (EPR) and Hall effect measurements. The low-temperature (&amp;lt;55 K) EPR spectra were consistently explained as holes (S = 1/2) trapped on shallow As acceptors on sulfur sites leading to a four-line hyperfine-split spectrum (75As: I = 3/2, 100%) in axial symmetry and with a concentration of 5(1) ppm (∼2 × 1017 cm−3). Electrical measurements indicate p-type conduction with a free carrier concentration of about 5 × 1017 cm−3 at room temperature and an ionization energy of 52 meV associated with the shallow As acceptors, which is consistent with the ionization energy determined from the hydrogenic model of shallow acceptors in 2H-MoS2. These values are in strong contrast to the unrealistic value of 0.7 meV reported in the literature obtained from the analysis of temperature-dependent EPR measurements. Possible explanations are related to temperature-dependent spin-lattice relaxation effects, affecting strongly EPR line intensities and making impossible their use in obtaining the ionization energy.

THz electron spin resonance (ESR) measurement has been a powerful means to study novel magnetic systems because of the advantages of high spectral resolution, ESR measurement beyond the zero-field splitting or the magnetic phase transition. Therefore, we have been developing this THz ESR system since 1988, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic field, the high pressure, the low temperature and the micro-mechanically detected ESR. Recent new developments, especially focusing on the high pressure THz ESR, will be shown.

Due to the advantages of high spectral resolution, ESR measurement beyond the zero field splitting or the magnetic phase transition, THz electron spin resonance (ESR) measurement has been a powerful means to study novel magnetic systems. We have been developing this THz ESR system since 1988, and we are now extending to the multi-extreme THz ESR. Here the multi-extreme corresponds to the high magnetic field, the high pressure, the low temperature and the micro-mechanically detected ESR. Recent new developments, and the application of the high pressure THz ESR will be shown.

THz electron spin resonance (ESR) measurement has been a powerful means to study magnetic systems due to the advantages of high spectral resolution, ESR measurement beyond the zero field splitting or the magnetic phase transition. We have been developing this THz ESR system, and we are now extending our developments to the multi-extreme THz ESR. Here the multi-extreme includes the high magnetic field, the high pressure, the low temperature and the micro-cantilever ESR. Using these advantages of THz ESR, we have studied perfect kagome lattice antiferromagnet Cr-jarosite, which has attracted much attention in the field of magnetism recently.

Electrical, magnetic, and EPR studies of the quaternary chalcogenides Cu 2AIIBIVX4 prepared by iodine transport