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Maximizing standoff distance by direct placement of probe coils on magnet bodies, while maximizing signal-to-noise is critical to the successful application of unilateral NMR. Two types of radio frequency (rf) coils for linear array, unilateral magnets are described: "simple fringe" and "split fringe coils." These coils are designed to fully exploit the standoff distance of the unilateral magnet by placement directly on the magnet surface. Such placement fails for normal surface coils used for magnetic resonance due to eddy current induced shielding by the conductive magnet surface. The coil design strategy includes a rectangular cross section solenoid coil, either continuous or split in the center, mounted with the center axis of the coil parallel to the magnet surface. These geometries, when placed on a conducting surface, enhance the rf field produced in the sample region, outside of the solenoid coil. The spatial homogeneity of both rf coils are characterized using the ANSYS™ finite element modelling software. ANSYS™ modeled coil geometries led to homogeneous, surface displaced rf fields. These coils were then constructed and characterized with magnetic resonance imaging. Finally, two experiments that use these coils to perform large standoff relaxation measurements are described.

Low frequency nuclear magnetic resonance (NMR) is used to noninvasively and nondestructively detect spoiled tomato concentrate stored in >200 L metal-lined containers. It is shown that longitudinal and transverse NMR relaxation times change as the tomato concentrate spoils. A rapid, viscosity-dependent spoilage detection method that takes advantage of the inherent inhomogeneity in single-sided NMR instruments is proposed. Here, the effective transverse magnetization decay rate is used as a parameter to determine tomato concentrate spoilage. Three different low frequency, single-sided NMR instruments are described and compared to determine the optimum sensor for spoiled tomato concentrate detection in large-format, metal-lined, aseptic containers. The most effective NMR sensor for this application is temperature stable and has large magnetic field gradients and a homogeneous magnetic field region offset >0.5 cm from the magnet surface. PRACTICAL APPLICATION: This manuscript describes a noninvasive and nondestructive tomato concentrate spoilage detector for application to large-format, sealed, commercial storage bins.

Pollination-variant persimmon (Diospyros kaki) fruit exhibits two distinct phenotypes based upon pollination status. Pollinated fruit are seeded and develop flesh that is brown in color, nonastringent, delectable in taste and highly desirable, whereas non-pollinated fruit retain unseeded orange-color flesh that is astringent and virtually unpalatable. Growers face the problem that both types of flesh may be present in the same persimmon fruit, and external skin color is uniformly orange, regardless of the extent of astringency. Thus, in this work, the nondestructive measurement modalities of nuclear magnetic resonance (NMR) relaxometry and near-infrared (NIR) spectroscopy were investigated for their ability to screen pollination-variant persimmons for extent of nonastringent flesh. Fruit from a diverse sample set – including six cultivars stored for varying lengths of time and exhibiting an array of astringency levels – was subjected to the two nondestructive measurements and then evaluated destructively for astringency using a sequential blotting and visual sensory analysis approach. The sensory astringency score was then used as the response variable to construct partial least squares – discriminant analysis (PLS-DA) models from spectra from each modality on its own as well as for concatenated spectra, which combined the information from both modalities. These PLS-DA models performed well, showing a maximum misclassification rate of 33%. When the most market-relevant astringency threshold was used, NIR slightly outperformed NMR. When different astringency screening thresholds were considered, combining the two modalities did not consistently improve PLS-DA model performance. Thus, both modalities show promise for nondestructive characterization of the flesh of pollination-variant persimmons.

A low cost, portable, high volume, stainless steel pressure reactor is modified to easily perform magnetic resonance relaxometry at industrially relevant pressures. Unlike existing pressurization strategies common to nuclear magnetic resonance (NMR) spectroscopy, this approach is amenable to realistic samples that feature heterogeneity and have traditionally escaped NMR study at pressure. This pressure reactor/NMR probe combination is easily accommodated by most single-sided and other low magnetic field permanent magnet assemblies. The performance of the probe is demonstrated by accomplishing NMR relaxometry on polydimethylsiloxane at different pressures with two types of unilateral magnets.

Nuclear-magnetic resonance (NMR) spectra of CsCl and LaCl3 in D2O/H2O solutions were collected up to pressures of 1.9 GPa using a new NMR probe design that considerably extends the pressure range available for geochemical experiments. The longitudinal-relaxation times (T1) for 2H compare well with those reported in the previous studies of Lee et al. (1974), who examined lower pressures, and indicate that the probe functions properly. In some experiments, 133Cs and 1H NMR spectra could be taken on solutions to pressures well beyond the nominal freezing pressure of D2O or H2O to form Ice VI (near 0.9 GPa). Freezing to form the high-pressure ice is kinetically slow on an experimental time scale (minutes to hours). The data indicate that the electrolyte concentrations increase the freezing pressure of the solution. This result means that solution NMR spectra can be collected at pressures that are nearly twice the nominal freezing pressure of pure D2O or H2O. Pulsed-magnetic-field-gradient NMR methods are used to independently measure the self-diffusion coefficient of H2O in these solutions, which yields estimates of solution viscosity via the Stokes–Einstein relation. The increased viscosity accounts for the pressure variation of T1 values as rates of molecular tumbling are affected. Accounting for such changes is essential if NMR spectral line widths are used to infer pressure-enhanced rates of geochemical reactions, such as interconversion of aqueous complexes.

Nuclear spin relaxation rates of (2) H and (139) La in LaCl3 +(2) H2 O and La(ClO4 )3 +(2) H2 O solutions were determined as a function of pressure in order to demonstrate a new NMR probe designed for solution spectroscopy at geochemical pressures. The (2) H longitudinal relaxation rates (T1 ) vary linearly to 1.6 GPa, consistent with previous work at lower pressures. The (139) La T1 values vary both with solution chemistry and pressure, but converge with pressure, suggesting that the combined effects of increased viscosity and enhanced rates of ligand exchange control relaxation. This simple NMR probe design allows experiments on aqueous solutions to pressures corresponding roughly to those at the base of the Earth's continental crust.

Author(s): Augustine, MP; Ochoa, G; Casey, WH | Abstract: Recent theoretical advances and molecular-dynamic estimates of the dielectric constant of water have extended the HKF model for aqueous solution chemistry up to 6.0 gigapascals (GPa), which are conditions well beyond the capabilities of conventional NMR spectroscopy (Pan and others, 2013; Sverjensky and others, 2014, see also Wasserman and others, 1995). These developments provide strong motivation to design a simple NMR probe that allows experiments on solutions, at high resolution, to pressures of a few GPa (Pautler and others, 2014; Ochoa and others, 2015, 2016). Here we describe the performance of a compact NMR probe that can reach several GPa pressures. The probe is made by placing a solenoid microcoil inside of a standard piston-cylinder device used in solid-state physics. High pressures are achieved in the sample by applying force to a coaxial piston. Early designs of the probe, although useful, were limited in sample size to 10 to 15 L. Here we describe modifications that allow greatly improved resolution and sensitivity, including 1H-1H NMR correlation spectroscopy, on solutions at 2.8 GPa pressure. Sample sizes can be expanded if, instead of a standard NMR spectrometer that is built around a superconducting magnet, one employs a magnetic-resonance imaging (MRI) system that is built around a permanent magnet. The MRI systems can apply larger magnetic field gradients than conventional spectrometers, and thus have more robust shimming capability, which is needed because of the juxtaposition of different alloys in the pressure cell. More importantly, these systems can have magnetic fields that are oriented perpendicular to the magnet bore, which allows rotation of the coil within the axis of the pressure cell to increase sample volumes and pressure. Sensitivity is improved by replacing the traditional, but reduced-volume, closed sample container mounted in the center of the NMR detection coil with an open NMR coil that dangles freely in solution, thus making the sample solution itself the pressure-transmission fluid. The efficacy of these modifications are demonstrated by measuring 1H NMR spectra for ethyl alcohol and ethyl alcohol/methyl alcohol mixtures at pressures up to 2.8 GPa. Further developments are discussed that will allow geochemists to acquire aqueous solution NMR spectra at higher 3 to 4 GPa pressures.

The Dirac–Frenkel–Maclachlan (DFM) variation of parameters approach to approximately solving the time dependent Schrodinger equation is used to generate free precession and echo signals from the Bloch equations corrected for the effects of radiation damping and inhomogeneous broadening. Following a brief description of how the DFM method can be applied to the non-linear Bloch equations, two figures of merit designed to evaluate how a DFM optimized approximation compares with the exact solution is provided. This framework is used to optimize and evaluate the performance of six trial functions describing inhomogeneously broadened, radiation damped free precession and echo signals. The trial functions are then used to analyze the resolution enhancement and signal attenuation produced by pulse sequences that suppress radiation damping.

© 2016 American Chemical Society. Although doping is a cornerstone of the inorganic semiconductor industry, most devices using organic semiconductors (OSCs) make use of intrinsic (undoped) materials. Recent work on OSC doping has focused on the use of dopants to modify a material's physical properties, such as solubility, in addition to electronic and optical properties. However, if these effects are to be exploited in device manufacturing, a method for dedoping organic semiconductors is required. Here, we outline two chemical strategies for dedoping OSC films. In the first strategy, we use an electron donor (a tertiary amine) to act as competitive donor. This process is based on a thermodynamic equilibrium between ionization of the donor and OSC and results in only partial dedoping. In the second strategy, we use an electron donor that subsequently reacts with the p-type dopant to create a nondoping product molecule. Primary and secondary amines undergo a rapid addition reaction with the dopant molecule 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4TCNQ), with primary amines undergoing a further reaction eliminating HCN. Under optimized conditions, films of semiconducting polymer poly(3-hexylthiophene) (P3HT) dedoped with 1-propylamine (PA) reach as-cast fluorescence intensities within 5 s of exposure to the amine, eventually reaching 140% of the as-cast values. Field-effect mobilities similarly recover after dedoping. Quantitative fluorescence recovery is possible even in highly fluorescent polymers such as PFB, which are expected to be much more sensitive to residual dopants. Interestingly, treatment of undoped films with PA also yields increased fluorescence intensity and a reduction in conductivity of at least 2 orders of magnitude. These results indicate that the process quantitatively removes not only F4TCNQ but also intrinsic p-type impurities present in as-cast films. The dedoping strategies outlined in this article are generally applicable to other p- and n-type molecular dopants in OSC films.

The time dependent variation of parameters solution to the time dependent Schrödinger equation pioneered by Dirac, Frenkel, and McLachlan is described in terms useful for immediate application to complex time dependent problems in magnetic resonance. A benchmark comparison of the theory to one dimensional images and spin echo envelope signals in simple spatially varying magnetic fields with molecular diffusion is provided.

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Cavity ring-down spectroscopy is used to probe the optical absorption of the optical pseudo-two level system [Xe]4f(13) Yb(3+) in room temperature solution, a situation where the two-color pump-probe luminescence approach commonly used to study the other [Xe]4f(n) (2or = nor = 12) trivalent lanthanide ions fails. A 1m optical cavity constructed from two highly reflective mirrors is used to obtain ring-down signals as a function of wavelength from 1 mL samples contained in a quartz cuvette placed in the center of the cavity. Absorption spectra constructed from these signals characteristic of the (6)H(15/2)--(4)F(9/2) [Xe]4f(5) Dy(3+) and the (7)F(0)--(5)D(0) [Xe]4f(6) Eu(3+) transitions are presented and compared to the corresponding single pass absorption and two-color pump-probe luminescence spectra to obtain sensitivity estimates. Finally the spectrum for the (2)F(5/2)--(2)F(7/2) [Xe]4f(13) Yb(3+) transition for a model Yb(3+) complex in room temperature solution is obtained using cavity ring-down spectroscopy for the first time.

© The Royal Society of Chemistry 2016. Doping polymeric semiconductors often drastically reduces the solubility of the polymer, leading to difficulties in processing doped films. Here, we compare optical, electrical, and morphological properties of P3HT films doped with F4TCNQ, both from mixed solutions and using sequential solution processing with orthogonal solvents. We demonstrate that sequential doping occurs rapidly (

Water soluble silicon nanoparticles were prepared by the reaction of bromine terminated silicon nanoparticles with 3-(dimethylamino)propyl lithium and characterized with liquid and solid state nuclear magnetic resonance (NMR) and photoluminescence (PL) spectroscopies. The surface site dependent 29Si chemical shifts and the nuclear spin relaxation rates from an assortment of 1H–29Si heteronuclear solid state NMR experiments for the amine coated reaction product are consistent with both the 1H and 13C liquid state NMR results and routine transmission electron microscopy, ultra-violet/visible, and Fourier transform infrared measurements. PL was used to demonstrate the pH dependent solubility properties of the amine passivated silicon nanoparticles.

Air- and water-stable silicon nanocrystals were prepared by the bromine oxidation of porous silicon nanoparticles followed by reaction with n-butyllithium. Transmission electron microscopy suggests that the vigorous oxidation of porous silicon under reflux conditions removes the porous layer from the nanoparticle to expose a crystalline silicon core that can be passivated with organic ligands. A combination of infrared, ultraviolet/visible, and photoluminescence demonstrate the presence of small crystalline silicon particles and saturated hydrocarbon ligands, while solid- and liquid-state nuclear magnetic resonance spectroscopies establish that butyl ligands are localized on the nanocrystal surface. All of these analytical methods suggest that the product of this synthesis is stable in air and water indefinitely.

The Mg 2 Si x Ge 1 - x solid solution was prepared by heating stoichiometric amounts of elemental Mg, Si, and Ge in an argon atmosphere. Both microprobe and X-ray diffraction analysis of the reaction products suggest that homogeneous alloys can be made by heating the elements to 1200 °C, a temperature roughly 100 °C in excess of the melting temperatures for pure Mg 2 Si and Mg 2 Ge. 2 9 Si solid-state nuclear magnetic resonance was used to characterize the Mg 2 Si x Ge 1 - x solid solution. The 2 9 Si isotropic chemical shift changes consistent with the band gap in these materials while the line width increases with local disorder.

A nuclear magnetic resonance (NMR) probe and spectrometer capable of investigating full intact wine bottles is described and used to study a series of Cabernet Sauvignons with high resolution 1H NMR spectroscopy. Selected examples of full bottle 13C NMR spectra are also provided. The application of this full bottle NMR method to the measurement of acetic acid content, the detection of complex sugars, phenols, and trace elements in wine is discussed.

© 2015 American Chemical Society. Organic electronics promise to provide flexible, large-area circuitry such as photovoltaics, displays, and light emitting diodes that can be fabricated inexpensively from solutions. A major obstacle to this vision is that most conjugated organic materials are miscible, making solution-based fabrication of multilayer or micro- to nanoscale patterned films problematic. Here we demonstrate that the solubility of prototypical conductive polymer poly(3-hexylthiophene) (P3HT) can be reversibly "switched off" using high electron affinity molecular dopants, then later recovered with light or a suitable dedoping solution. Using this technique, we are able to stack mutually soluble materials and laterally pattern polymer films by evaporation or with light, achieving sub-micrometer, optically limited feature sizes. After forming these structures, the films can be dedoped without disrupting the patterned features; dedoped films have identical optical characteristics, charge carrier mobilities, and NMR spectra as as-cast P3HT films. This method greatly simplifies solution-based device fabrication, is easily adaptable to current manufacturing workflows, and is potentially generalizable to other classes of materials.

The hardware necessary for the electro-optic study of conducting polyelectrolyte solutions is frequently not commercially available or financially practical. The designs of an electrical rectangular pulse switch and polarity-reversing relay switch capable of producing 3 kV 5 A direct current pulses lasting longer than 100 μs are presented. As an example of the operation of this equipment, the electric birefringence of an aqueous solution of the Pseudomonas bacteriophage Pf1 in tris/EDTA buffer is presented.

The compounds Ca14AlP11, Ca14MnP11, and Eu14MnP11 have been synthesized and are isostructural to the Zintl compound, Ca14AlSb11. Eu14MnP11 is a ferromagnet showing colossal magnetoresistance at TC = 52 K, Ca14MnP11 shows paramagnetic behavior down to 5 K, and Ca14AlP11 is nonmagnetic. The formula unit for these Zintl compounds is A14MPn11 and comprises 14 A cations, a MPn4 tetrahedron, four isolated Pn anions, and a Pn3 linear unit. The central Pn of the Pn3 unit is believed to be positionally disordered, and it has been speculated that the disorder is static rather than dynamic. To address this issue, 31P solid-state NMR was applied to these new compounds to provide insight into the magnetic ordering and structural changes. The NMR chemical shift anisotropy and the dipolar coupling for the 31P nuclei as well as the quadrupolar coupling for the 27Al nucleus in the diamagnetic compound Ca14AlP11 provide structural details consistent with the Zintl structure. Wide-line 31P NMR and EPR were applied to the pa...

The nuclear magnetic resonance (NMR) spectra of the I=3/2 monovalent ions 23Na, 35Cl, 39K, and 79Br for NaCl and KBr dissolved into filamentous bacteriophage Pf1 solutions display line splittings and shifts consistent with an interaction between the nuclear spin and the electric field gradient produced by the Pf1 particles. The average electric field gradient and thus the spectral splitting for ions in the void space between magnetically aligned Pf1 particles is modeled using a numerical solution to the Poisson–Boltzmann equation. An NMR titration experiment in a 57 mg/mL Pf1 solution is used to determine the background Na+ ion concentration in solution as 32 mM which compares well with the 31.1 mM negative surface charge on Pf1.

The synthesis of silicon nanoclusters and their characterization by multinuclear solid-state nuclear magnetic resonance (NMR) is presented. A combination of 23Na, 29Si, and 13C magic angle spinning with and without cross polarization to 1H nuclei have been used to investigate the reaction of sodium silicide (NaSi) with silicon tetrachloride (SiCl4) followed by varying degrees of surface passivation. The 23Na and 29Si NMR spectra of NaSi distinguish the two crystallographically inequivalent sites for each, consistent with the crystal structure. This compound exhibits extreme diamagnetic chemical shifts for 29Si of −361 and −366 ppm. NaSi is reacted with SiCl4 in refluxing ethylene glycol dimethyl ether to produce both amorphous and crystalline Si nanoparticles with surfaces capped by chlorine. This reaction produces new 29Si resonances that survive subsequent capping and oxidation reactions. The 29Si NMR spectrum shows that the product is incompletely passivated with butyl groups and gives several peaks ly...

The measurement of residual dipolar and quadrupolar coupling constants in the liquid phase by using an electric field to destroy the isotropic nature of molecular tumbling is complicated by charge-induced turbulent motion. In many cases this motion is due to charge injection at electrode surfaces, an effect that leads to an apparent removal of electrically recovered anisotropic spectral splittings when measured from a spin-echo () envelope modulation produced by a train of radio frequency rf pulses. To understand this averaging, the effect of quadrupolar couplings and enhanced molecular diffusion on free-in- duction, spin-echo, and Carr Purcell signals is analytically determined in the special case of homogeneous rf pulses. Additional signal damping due to rf inhomogeneity and coupling constant heterogeneity is determined by numerically extending the kernel formalism intro- duced by Herzog and Hahn to understand spin diffusion in solids. Finally, the merit of the numerical approach is tested by comparison with analytical results for homogeneous rf pulses and experimental results for perdeuterated nitrobenzene involving inhomogeneous rf pulses and coupling heterogeneity. 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 171 189, 2001

High-resolution liquid- and solid-state 119Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C6H3-2,6-Trip2 (X = Cl, Cr(eta 5-C5H5)(CO)3, t-Bu, Sn(Me)2C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip2H3C6Sn-Sn(Me)2C6H3-2,6-Trip2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.

Molecular motion in the polar organic solvent nitrobenzene induced by an electric field is studied by magnetic resonance imaging. Rf pulse sequences that correlate images obtained at two different times under conditions of both continuous and pulsed electric fields are introduced. The resultant image correlation spectra indicate that the time scale of motion in a 9.6 kV/cm electric field is tens of milliseconds. Comparison of the results to an analytic solution for the Fokker-Planck probability function for one-dimensional bounded diffusion yields an electric field dependent effective diffusion coefficient for perdeuterated nitrobenzene of D = 1.08 x 10(-5) cm(2)/s + (3.33 x 10(-3) cm(4)/kV(2)s) E(2) at room temperature. Characteristics of this electroconvection and its consequences for combining multidimensional nuclear magnetic resonance with electrical orientation are also discussed.

Spontaneous radiation damping in nuclear magnetic resonance spectroscopy of sharp lines is commonly encountered in highly magnetized samples following magnetization inversion. The time delay for the maximum of the hyperbolic secant like signal to develop following inversion is measured and calculated. The distribution function of the measured delay times is Gaussian–Boltzmann and can be used to predict the sensitivity of both signal delay and phase to inversion errors.

Molecular alignment by an electric field is used to reintroduce quadrupolar couplings into the nuclear magnetic resonance spectrum of polar liquids. By interleaving a pulsed electric field with rf ...

A combination of stimulated Raman pumping and rotational Raman spectroscopy is used to accomplish the first measurement of the polarizability anisotropy γ11,13 (355 nm) for the S11 (1) transition in molecular hydrogen H2. Saturation of the Q01(1) transition connecting the |X1 Σ+ g, v = 0, J = 1 > state to the |X1 Σ+ g, v = 1, J = 1 > state in H2 by stimulated Raman pumping is the critical element in this experiment. The observed intensities of the rotational Raman lines for these states allow an estimate of γ11,13 (355 nm) as 0.358 ± 0.004 A3. A comparison of this value to that obtained from fundamental ab initio calculations in H2 also is possible for the first time.

Nonlinear evolution of the Landau-Lifshitz type can be exactly linearized. Special cases include the radiation-damped spin system and the superradiant system in the semiclassical regime, in the presence of time-varying driving fields. For these, the resultant linear system is simply that of a spin 1 / 2 particle, with the radiation damping rate, or superradiant characteristic time, manifested as an imaginary addition to the spin's resonance frequency. Consequently, methods from inverse scattering theory can be used to design driving fields. The behavior of these systems under stochastic excitation can be determined exactly.

There are several examples in the literature where effects of inhomoge- neous broadening on radiation damping of free precession signals have been described using a phenomenological 1 / T term in the Bloch equations. The inappropriate use of this 2 model is illustrated for specific cases. Correct signal shapes are predicted only when isochromat solutions of Bloch's equations are integrated over the spectrum of the inhomo

A study of radiation damping e ects in inhomogeneously broadened systems leads to an analytical theorem that relates the time integral area of the nuclear magnetic resonance signal to the tipping angle of the magnetization caused by the circuit generated reaction field. The theorem is applied to predict relative signal areas in examples of pulse sequences. In a few selected cases these predictions are also checked by experiment.

The heteronuclear J-coupling tensor between nearest neighbor ${}^{31}\mathrm{P}$ and ${}^{113}\mathrm{In}$ spins in undoped InP is investigated by means of ${}^{113}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{In}}}^{31}\mathrm{P}$ polarization transfer under rapid magic angle spinning (MAS). The scalar contribution can be measured directly and is found to have the value $|{J}^{\mathrm{iso}}{(}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In})|=(225\ifmmode\pm\else\textpm\fi{}10) \mathrm{Hz}.$ The principal value of the traceless anisotropic J-coupling tensor (pseudodipolar coupling) is determined to be ${J}^{\mathrm{aniso}}{(}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In})=2/3[{J}_{\ensuremath{\Vert}}{(}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In})\ensuremath{-}{J}_{\ensuremath{\perp}}{(}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In})]=(813\ifmmode\pm\else\textpm\fi{}50) $ or $(1733\ifmmode\pm\else\textpm\fi{}50) \mathrm{Hz},$ assuming axial symmetry with the principal axis parallel to the In-P bond. Our values deviate from those reported previously [M. Engelsberg and R. E. Norberg, Phys. Rev. B 5, 3395 (1972)] [based on a moment analysis of the ${}^{31}\mathrm{P}$ resonance $|{J}^{\mathrm{iso}}{(}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In})|=350 \mathrm{Hz}$ and ${J}^{\mathrm{aniso}}{(}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In})=1273 \mathrm{Hz}$], but confirm the postulate that the nearest neighbor ${}^{31}\mathrm{P}{\ensuremath{-}}^{113,115}\mathrm{In}$ magnetic dipolar and pseudodipolar interactions are of the same order of magnitude and partially cancel each other.

Effects of radiation damping on nuclear magnetic resonance (NMR) pulse transient echo and free induction decay (FID) signals in the presence of inhomogeneous magnetic fields are measured and analyzed. An analytical theorem serves as a guide for computer simulations that confirm the experimental results. In comparison to the two-component refocusing of magnetization vectors typically observed as a spin echo in the limit of negligible radiation damping, a two-pulse ﷿-﷿ sequence produces an echo where all three components of the magnetization vary and refocus. The analytical theorem is extended to describe echo properties of various two-pulse and stimulated three-pulse echo sequences. Multiple echoes occur for a class of two-pulse sequences. Multiple rf-pulses interleaved with pulsed magnetic field gradients and the design of multiple pulse sequences for spectroscopic applications are discussed.

The dc Superconducting QUantum Interference Device (SQUID) is a sensitive detector of magnetic flux, with a typical flux noise of the order 1 μΦ 0 Hz −1/2 at liquid helium temperatures. Here Φ 0 = ℏ /2 e is the flux quantum. In our NMR or NQR spectrometer, a niobium wire coil wrapped around the sample is coupled to a thin film superconducting coil deposited on the SQUID to form a flux transformer. With this untuned input circuit the SQUID measures the flux, rather than the rate of change of flux, and thus retains its high sensitivity down to arbitrarily low frequencies. This feature is exploited in a cw spectrometer that monitors the change in the static magnetization of a sample induced by radio frequency irradiation. Examples of this technique are the detection of NQR in 27 Al in sapphire and 11 B in boron nitride, and a level crossing technique to enhance the signal of 14 N in peptides. Research is now focused on a SQUID-based spectrometer for pulsed NQR and NMR, which has a bandwidth of 0–5 MHz. This spectrometer is used with spin-echo techniques to measure the NQR longitudinal and transverse relaxation times of 14 N in NH 4 ClO 4 , 63±6 ms and 22±2 ms, respectively. With the aid of two-frequency pulses to excite the 359 kHz and 714 kHz resonances in ruby simultaneously, it is possible to obtain a two-dimensional NQR spectrum. As a third example, the pulsed spectrometer is used to study NMR spectrum of 129 Xe after polarization with optically pumped Rb. The NMR line can be detected at frequencies as low as 200 Hz. At fields below about 2 mT the longitudinal relaxation time saturates at about 2000 s. Two recent experiments in other laboratories have extended these pulsed NMR techniques to higher temperatures and smaller samples. In the first, images were obtained of mineral oil floating on water at room temperature. In the second, a SQUID configured as a thin film gradiometer was used to detect NMR in a 50 μ m particle of 195 Pt at 6 mT and 4.2 K.

The polarization of 129 Xe gas by spin exchange with optically pumped Rb vapor is examined in high magnetic field. Measurements of the Rb–Xe velocity averaged spin exchange cross section 〈 σ v 〉 and the 129 Xe relaxation time in the absence of Rb, T 1 Xe , are discussed. Comparison of these high field results to low field literature values for 〈 σ v 〉 show that this parameter is essentially field independent. T 1 Xe is also found to be significantly longer in high field. On the basis of these observations, it is shown that production of large amounts of spin polarized 129 Xe gas can be made more efficient by high field operation.

Exploration of the theory for spin–cavity coupling in inhomogeneously broadened spin ensembles shows that all three components of magnetization can be refocused. The conventional spin echo generated by two components of magnetization is a special case of this three component refocusing in the limit of negligible radiation damping. We demonstrate this effect by an analytical theorem, numerical simulation, and experiment.

We describe the design and construction of a single-coil, two-channel probe for the detection of low-field magnetic resonance using dynamic nuclear polarization (DNP). The high-frequency channel of the probe, which is used to saturate the electron spins, is tuned to the electron Larmor frequency, 75 MHz at 2.7 mT, and matched to 50 Ω. Low-field, 1H nuclear magnetic resonance (NMR) is detected through the second, low-frequency channel at frequencies

Nuclear magnetic resonance (NMR) spectroscopy is used to track factory relevant tomato paste spoilage. It was found that spoilage in tomato paste test samples leads to longer spin lattice relaxation times T1 using a conventional low magnetic field NMR system. The increase in T1 value for contaminated samples over a five day room temperature exposure period prompted the work to be extended to the study of industry standard, 1,000 L, non-ferrous, metal-lined totes. NMR signals and T1 values were recovered from a large format container with a single-sided NMR sensor. The results of this work suggest that a handheld NMR device can be used to study tomato paste spoilage in factory process environments.

The phenomenon of multiple echoes following a two-pulse stimulated-echo experiment in highly polarized systems is reinvestigated and explained using the Bloch equations. A semiquantitative formalism based on the nuclear contributions to the magnetic susceptibility throughout a multiple-pulse sequence is outlined and used to understand the formation of the echoes. This theory is used to direct the design of phase-cycled and pulsed-field-gradient experiments to control the echo formation. The theory also suggests a means of indirectly detecting a heteronucleus contained in a different molecule. This kind of detection is accomplished by modifying the static magnetic field with a stimulated-echo experiment on one set of the spins. Heteronuclear experiments show that this classical semiquantitative formalism is a useful tool in the understanding of spin dynamics in highly polarized systems.

The polarization of 129Xe gas by spin exchange with optically pumped Rb vapor is investigated in high magnetic field. Operation in a high field provides added spectral dispersion via Zeeman shifts of the electronic transitions. This simplifies the physics of the pumping process in such a way as to make it more amenable to treatment with simple rate theory. A relationship between the steady state 129Xe polarization and the applied laser power is derived which agrees with experimental results. This theory serves as a guide to the manufacture of very high polarizations of 129Xe gas.

Solvent additives have been explored as a reliable way to control the morphology in bulkheterojunction (BHJ) layers for improved device performance. We show that the choice of solvent additives has direct implications on morphological evolution, i.e. poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) BHJ films processed with a small amount of 1,8-diiodooctane or 1-chloronaphthalene have more crystalline PCBM domains compared to crystalline P3HT domains, while the opposite is true for films cast with nitrobenzene additive and films cast purely from chlorobenzene. The BHJ film cross-links when annealed at 300 °C in the presence of 1,8-diiodooctane. Cross-linking is found to occur even in pristine P3HT and PCBM films annealed under similar conditions. NMR spectroscopy is presented as a viable technique for quantitative analysis of the amount of solvents left in the BHJ films before and after heat treatment. Despite differences in the ways the additives affect the morphology of the BHJ layer, device performance remained stable over 300 h for all additives tested. © 2013 Elsevier B.V.

A bivariate correlated Student distribution is applied to full wine bottle diamagnetic screening measurements. Previous work involving a limited number of rare wines indicated that like wines cluster in a plot of the first two principal component scores derived from a covariance matrix of the diamagnetic screening measurements. This study extends the approach to a much larger, statistically meaningful sixty bottle wine library where bivariate statistics are used to comment on the measured data. The full bottle diamagnetic screening of thirty-six identically labeled, sealed bottles of wine obtained from four different sources combined with principal component analysis data reduction followed by treatment with a bivariate distribution permit the effect of wine transport and storage to be observed. The usefulness and future success of the method towards the identification of counterfeit wines is mentioned.