Optically detected magnetic resonance of crystalline AgCl

The intrinsic ODMR spectrum of AgCl is due to holes trapped at tetragonally distorted Ag⁺ sites, recombining with electrons trapped at unidentified substitutional sites which are similarly distorted. Bromide ions induced characteristic changes in the spectrum.     

Optically detected magnetic resonance of Mn-related excitations in (Cd,Mn)Te quantum wells

Optically detected magnetic resonance (ODMR) was applied to reveal the exchange interaction effects between Mn²⁺ ions and confined holes in (Cd,Mn)Te quantum wells with 2D hole gas. Two anisotropic ODMR signals with different angular variations were found and ascribed to isolated manganese ions and to exchange-coupled complexes consisting of manganese and holes. It is shown that calculations on the basis of spin Hamiltonian for these systems are in agreement with the experimental data.     

电阻式核磁共振测量的最新进展

电阻式核磁共振(RDNMR)测量是1988年由德国马普所的von Klitzing研究小组针对GaAs二维电子气中少量核自旋的探测而提出的一种具有超高灵敏度的实验技术. 目前, RDNMR已经成为研究单层或双层GaAs二维电子气核自旋和电子自旋特性的重要手段. 由于为实现电阻式核磁共振测量所建立的动态核极化方法强烈依赖于GaAs特有的材料属性, 至今这一技术一直没有扩展应用到其他半导体低维系统中. 最近,本研究小组发展了一种动态核极化新方法,成功实现了对典型窄带半导体锑化铟(InSb) 二维电子气的电阻式核磁共振测量.本文在介绍电阻式核磁共振测量工作原理及已建立的典型动态核极化方法的基础上,着重讨论所提出的动态核极化新方法的机理、 实验结果以及对今后研究的展望.     

Self-diffusion in plastic crystalline perfluorocyclohexane studied by nuclear magnetic resonance

Polarized Mandelstam-Brillouin scattering data in isomeric pentanols (normal-pentanol and 2-methyl-2-butanol) are presented. Hypersonic velocity ν_s and absorption α/f ² are measured as a function of temperature in the liquid phase. The experimental results indicate, for both the alcohols, a shear relaxation phenomenon in the GHz region. The shear relaxation times τ_s and the shear moduli G _∞, evaluated in the framework of visco-elastic theories, show a temperature dependence characteristic of strongly associated liquids in n-pentanol, whereas a more molecular behaviour is evidenced for 2-methyl-2-butanol.     

Optically detected nuclear magnetic resonance in amorphous silicon related materials

Optically detected nuclear magnetic resonance (ODNMR) measurements have been carried out for a-Si:H samples with different hydrogen content and for a-Si_xN_1−x:H (x = 0.01 and 0.05). We have observed for the first time the ODNMR signal of hydrogen. The ODNMR spectrum is decomposed into two Lorentzians with different widths (FWHM) which arise from the dipole-dipole interactions of a trapped hole with its nearby and distant H¹ nuclei, respectively. The trapping site of the hole is discussed based on the experimental results.     

Optically detected magnetic resonance of the zinc vacancy in ZnS

Optical detection of magnetic resonance (ODMR) is reported for the single negative charge state, V_Zn^?, of the isolated zinc vacancy in ZnS. Produced by 2.5 MeV electron irradiation, it is detected in a distant donor-acceptor (DA) pair luminescent band at 570 nm in which the vacancy acts as the acceptor. Excitation and emission spectral dependences of the V_Zn^? ODMR signals are analyzed in terms of a configurational coordinate model. We conclude that the double acceptor level (V_Zn⁼/V_Zn^?) is located ～1.1 eV from the valence band edge and that the trigonal Jahn-Teller relaxation energy for the V_Zn^? state is ～0.5 eV.     

Optically detected magnetic resonance from a complex donor in CdS

A new optically-detected magnetic resonance at g = 1.885 for H|c, associated with a broad emission band at 2.17 eV, has been observed. The 2.17 eV band is attributed to donor-acceptor recombination involving a complex double donor, and the optically-detected magnetic resonance effect to spin-dependent electron transfer from a shallow donor to the complex donor.     

Neonatal auditory activation detected by functional magnetic resonance imaging

The objective of this study was to detect auditory cortical activation in non-sedated neonates employing functional magnetic resonance imaging (fMRI). Using echo-planar functional brain imaging, subjects were presented with a frequency-modulated pure tone; the BOLD signal response was mapped in 5 mm-thick slices running parallel to the superior temporal gyrus. Twenty healthy neonates (13 term, 7 preterm) at term and 4 adult control subjects. Blood oxygen level-dependent (BOLD) signal in response to auditory stimulus was detected in all 4 adults and in 14 of the 20 neonates. FMRI studies of adult subjects demonstrated increased signal in the superior temporal regions during auditory stimulation. In contrast, signal decreases were detected during auditory stimulation in 9 of 14 newborns with BOLD response. fMRI can be used to detect brain activation with auditory stimulation in human infants.     

Optically detected nuclear magnetic resonance at the sub-micron scale

Nuclear magnetic resonance is arguably one of the most powerful techniques available today to characterize diverse systems. However, the low sensitivity of the standard detection method constrains the applicability of this technique to samples having effective dimensions not less than a few microns. Here, we propose a novel scheme and device for the indirect detection of the nuclear spin signal at a submicroscopic scale. This approach--for which the name Dipolar Field Microscopy is suggested--is based on the manipulation of the long-range nuclear dipolar interaction created between the sample and a semiconductor tip located close to its surface. After a preparation interval, the local magnetization of the sample is used to modulate the nuclear magnetization in the semiconductor tip, which, in turn is determined by an optical inspection. Based on results previously reported, it is shown that, in principle, images and/or localized high-resolution spectra of the sample can be retrieved with spatial resolution proportional to the size of the tip.     

Luminescence fatigue and optically detected magnetic resonance in amorphous silicon-hydrogen alloys

Fatigue of the luminescence in amorphous SiH alloys has been investigated as a function of dangling bond density and of hydrogen content at 2 K. Optically detected magnetic resonance measurements have also been carried out to elucidate the origin of the fatigue effect for those samples.     

An optically detected magnetic resonance study of manganese-doped silver chloride

ODMR spectra have been observed in manganese-doped AgCl crystals and precipitates at low temperatures. During crystal growth from the melt or during annealing some of the Mn²⁺ is converted to Mn³⁺, which is an electron trap. The low-temperature luminescence is interpretated as recombination between self-trapped holes and [Mn²⁺nV_Ag] donors.     

Zero-field optical detected magnetic resonance of [70]-fullerene

The phosphorescence spectrum of [70]-fullerene in a glassy toluene matrix has been investigated at 77, 4.2 and 1.2 K. At 77 K, only one decay time (47.0 ms) has been observed while at 4.2 and 1.2 K two decay times (46.7, 5.6 ms and 46.6, 24.2 ms, respectively) were recorded. The zero field splitting parameters |D|=0.00489(25) cm^?1 and |E|=0.00135(7) cm^?1 were measured at 1.2 K using a pulsed ODMR technique.     

Investigation of electronic transitions in semiconductors with pulsed electrically detected magnetic resonance

A short review is given on pulsed electrically detected magnetic resonance (pulsed EDMR), a highly sensitive method for the investigation of spin-dependent transport and recombination mechanisms in semiconductors. Pulsed EDMR is based on the transient detection of spin-dependent recombination in a coherent time domain by means of the photoconductivity response after the application of a short electron spin resonance (ESR) pulse. Pulsed EDMR is about 8 to 9 orders of magnitude more sensitive than ESR and highly selective and it gives access to quantitative information such as transition probabilities for the electronic states involved. The theoretical and experimental foundations of the time-domain measurement of spin-dependent charge carrier recombination with pulsed EDMR are given and experimental results are discussed.