Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
1999-06-10
2001-12-04
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
Reexamination Certificate
active
06326787
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to nuclear magnetic resonance (NMR), particularly to the use of NMR for the analysis of thin planar or curved layer and surface layer geometries, and more particularly to a sensor using a miniaturized meanderline surface coil for NMR analysis of contact layers, non-destructive depth profiling to films, or imaging thin multilayers in a 3-D sense. The invention enables high resolution NMR of the chemistry and physics of surface layers, or layered materials, without the interference of signals from the bulk material.
The nuclear magnetic resonance (NMR) and the magnetic resonance imaging (MRI) technologies are well known. NMR and MRI are normally considered to be bulk techniques for examining short range structure and dynamics in liquid and solid materials. Surface NMR has been observed for absorbed species and surfaces of high surface area powders. Optically detected NMR and surface NMR with polarized atomic beams have sufficient sensitivity to detect signals from flat surfaces but are of low resolution, limited to relaxation studies, and not found widespread use due to their complexities. For the most part, magnetic resonance experiments are usually carried out in the presence of a spatially uniform static DC (direct current) magnetic fields and a spatially uniform radio frequency (RF) excitation fields. In the case of NMR, particle diffusion measurements are generally carried out by applying an inhomogeneous static field rather than using an inhomogeneous RF field. An RF excitation, with a wave vector periodically varying across the plane of the surface of a sample, may be generated by a periodic meanderline.
A meanderline is a zig-zag or serpentine array of parallel conductors of mutual separation, and has been used for several years as an electromagnetic acoustic transducer and has RF magnetic field characteristics which are well understood. Meanderlines have been used for excitation of bulk and surface spin waves in ferromagnets, see S. A. Bogacz, et al. “New Techniques For Excitation of Bulk and Surface Spin Waves in Ferromagnets,” J. App. Phys. 58(5), Sep. 1, 1985, and to search for nuclear acoustic resonance effects on surface waves in films, see R. G. Spulak, Jr., “Detection of Alpher-Rubin attenuation and a search for nuclear acoustic resonance of surface waves in tantalum films,” Phys. Rev. B, 40(9), Sep. 15, 1989. Also, a meanderline surface coil has been utilized in detecting
14
N pure nuclear quadrupole resonance (NQR) signals in large thin-layer samples or in regions near the surface of bulk samples while avoiding interfering signals from interior regions. See M. L. Buess, et al., “NQR Detection Using a Meanderline Surface Coil,” J. Magn. Resonance 92, 348 (1991), and the meanderline coil thereof, which demonstrated its use for observation of zero-field pure NQR in large samples such as 100 cc of Na
14
NO
2
at 3.6 MHz, and the meanderline thereof is illustrated and will be discussed hereinafter with respect to
FIGS. 1 and 2
.
In the present invention, the meanderline surface coil, such as shown in
FIGS. 1 and 2
, has been miniaturized to small planar (or cylindrically curved) samples and applied to the much more useful NMR technique by determining the unique configurations in an external magnetic field which produce the uniform orthogonal RF pulses and allow the magic angle spinning required for high-resolution spectroscopy. Thus, the miniaturized sensor coil of this invention extends the capabilities of NMR to provide analysis of thin planar (or curved) samples and surface layer geometries.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a miniaturized meanderline surface coil for analysis of thin layers and surface layer geometries.
A further object of the invention is to provide a meanderline surface coil which extends the capabilities of nuclear magnetic resonance (NMR).
Another object of the invention is to provide a thin-layer NMR technique using a stationary meanderline coil in a series-resonant, or parallel resonant circuit.
Another object of the invention is to provide a flat meanderline coil geometry which has about the same detection sensitivity as a solenoidal coil, but is specifically tailored to examine planar layers.
Another object of the invention is to provide a miniaturized meanderline surface coil geometry in an external magnetic field which produces the uniform orthogonal RF pulses.
Another object of the invention is to provide a meanderline configuration comprising the magic angle spinning required for high-resolution NMR spectroscopy.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves NMR of thin layers using a miniaturized meanderline surface coil. The miniature sensor coil, a meanderline surface coil, of this invention extends the capabilities of NMR to provide analysis of thin planar (or curved) surfaces and surface layer geometries. The miniaturized meanderline coil allows standard, pulsed NMR techniques to be used to examine thin layers, extending NMRs utility to many problems of modern interest. For example, the miniature coil can be used to examine contact layers, provide non-destructive depth profiles into films, or image multiple layers in a 3-D sense, as well as for use in high resolution NMR techniques of magic angle, 54.74°, spinning, and thus can be used to quantify the bonding and electronic structure in layered materials, or to observe the chemistry associated with aging coatings. The sensitivity is increased for ultra-thin films by using miniature meanderlines generated by photolithography. Reducing the spacing between the meanderline and sample plane also enhances the sensitivity. Tilting the meanderline and sample relative to the magnetic field allows this spacing to be reduced while maintaining planar uniformity of the RF and detection sensitivity. High speed spinning of the meanderline and sample about an axis parallel to the elements and tilted at the magic angle will average many of the NMR line-broadening interactions and produce high resolution solid-state NMR spectra.
REFERENCES:
patent: 5365171 (1994-11-01), Buess et al.
Bogacz, S.A., et al. “New Techniques For Excitation of Bulk and Surface Spin Waves in Ferromagnets,” J. App. Phys. 58(5), pp. 1935-1942, Sep. 1, 1985.
Buess, M.L., et al., “NQR Detection Using a Meanderline Surface Coil,” J. Magn. Resonance (92), pp. 348-362 (1991).
Spulak, Jr., R.G., “Detection of Alpher-Rubin attenuation and a search for nuclear acoustic resonance of surface waves in tantalum films,” Phys. Rev. B, 40(9), pp. 6052-6057, Sep. 15, 1989.
Carnahan L. E.
Evans T. P.
Sandia National Laboratories
Vargas Dixomara
Williams Hezron
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