Efficiency Of Decoupling Research Articles

Efficient heteronuclear decoupling by quenching rotary resonance in solid-state NMR

We propose a new scheme for heteronuclear decoupling designed for fast magic-angle spinning (MAS), dubbed phase-inverted supercycled sequence for attenuation of rotary resonance (PISSARRO). Its efficiency compares favourably with CW, TPPM, SPINAL and XiX decoupling methods at medium and high RF amplitudes, particularly under conditions where the efficiency of decoupling is affected by undesired rotary resonance effects.

Effect of quantum dot shape on dynamical dephasing suppression in exciton qubits under applied electric field

We investigate the efficiency of periodic dynamical decoupling of an exciton qubit confined in a self-assembled quantum dot in the presence of an applied electric field. The shape of the quantum dot is found to have a large effect on the excitonic dephasing. It is shown that dynamical suppression of dephasing, through a simple series of equally spaced bit flips, is most efficient for quantum dots that are close to spherical. In addition, compared to the no field case, the presence of an electric field increases the efficiency of the decoupling technique as the quantum dot becomes more oblate. Our calculations show that dephasing can be significantly suppressed in GaAs/AlAs quantum dots suitable for quantum information processing.

Bimodal Floquet description of heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance

A theoretical treatment of heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance is presented here based on bimodal Floquet theory. The conditions necessary for good heteronuclear decoupling are derived. An analysis of a few of the decoupling schemes implemented until date is presented with regard to satisfying such decoupling conditions and efficiency of decoupling. Resonance conditions for efficient heteronuclear dipolar decoupling are derived with and without the homonuclear (1)H-(1)H dipolar couplings and their influence on heteronuclear dipolar decoupling is pointed out. The analysis points to the superior efficiency of the newly introduced swept two-pulse phase-modulation (SW(f)-TPPM) sequence. It is shown that the experimental robustness of SW(f)-TPPM as compared to the original TPPM sequence results from an adiabatic sweeping of the modulation frequencies. Based on this finding alternative strategies are compared here. The theoretical findings are corroborated by both numerical simulations and representative experiments.

A simplified and efficient numerical model for charge injection in acoustic charge transport devices

A numerically efficient model for simulating electrical charge injection in acoustic charge transport (ACT) devices is developed. This model simplifies an existing charge injection model and is derived using the coupled set of semiconductor device equations. The present model increases the computational efficiency of decoupling and reducing the number of mathematical equations forming the charge injection model. A brief overview of the original model is presented. The assumptions leading to the decoupling and reduction of the device equations are described, as are differences between the two models. Results computed by the simplified model are shown and compared to the results from the original charge injection model and experimental measurement. The present model is able to examine 45 SAW wave positions and 163 contact voltages in 8 h on a 25 MHz PC in comparison to the previous model which simulated 59 wave positions and 164 contact voltages on an Hewlett-Packard 9000 series 500 minicomputer in 37 h. A substantial reduction in computation time is achieved. >

Composite decoupling in CPMAS of moderate-susceptibility materials

The limiting resolution of CPMAS has been discussed extensively (I, 2), with the conclusion that one of the factors affecting the resolution of 13C CPMAS spectra is the effect of the bulk magnetic susceptibility of the sample in distorting the magnetic field. We have investigated an indirect effect of this, that of the field distortion in spreading the proton resonance and thereby reducing the efficiency of decoupling. This effect will not be significant for diamagnetic materials, which have small negative values of the susceptibility x ( m 1 X lo-* m 3 / kg); however, paramagnetic constituents of heterogeneous samples, particularly those found in soils, will have positive values of x of the order of lo-100 X 10e8 m3/kg (3). These have been observed to broaden the resonance of free water in soil preparations to 5-10 kHz (4) and to severely distort magnetic resonance images in soils (5). Recently it has been shown that magnetic sieving will improve the quality of CPMAS spectra of soils (6). While this technique removes highly paramagnetic particles, it also is likely to change the organic composition of the soil. To investigate the effect moderate values of x will have on CPMAS spectra, we placed a standard material (hexamethylbenzene, or HMB) in two different hosts: 99.9% alumina (Johnson-Matthey, Hartfordshire, England) and vermiculite (Ernst Home Centers, Seattle, Washington). Vermiculite was chosen because it has a x typical of soil minerals ( = 15 X 1 O-* m 3 / kg (3)) and is readily available. The samples were prepared by adding 5 wt% HMB to each host material and mixing thoroughly. For HMB/alumina, this was done in a ceramic mortar, while for HMB/vermiculite the vermiculite was ground in a Wiley mill and passed through a 60 mesh screen prior to mixing, because the layered structure of vermiculite prevents grinding in a mortar. To each of these samples we applied several methods of decoupling at moderate RF field strength ( yl ): CW, COMARO-2 ( 7, 8) ALPHA-3 (9), and TREV (IO). For comparison purposes, we also applied the liquid heteronuclear decoupling sequence WALTZ16 ( II ) and solid-state homonuclear decoupling sequences MREV-8 (semi-windowless) and BLEW-48 ( 12) to the sample in vermiculite. All experiments were performed on a CXP-200 NMR spectrometer using an external pulse programmer (13) interfaced to the Aspect 2000 and a Bruker MAS probe with a 7 mm Doty Scientific (Columbia, South Carolina) spinner assembly; the spinning rate was about 2600 Hz in all cases. For both 13C and ‘H, the RF field strength was set to 4 1.7 kHz (6 ps 90” pulse). The pulse lengths and phases of the proton pulses were carefully adjusted using a small bulb of hexamethyldisiloxane, and the proton offset was set to