Porous silicon structure studied by nuclear magnetic resonance

1997 ◽  
Vol 70 (2) ◽  
pp. 191-193 ◽  
Author(s):  
D. Petit ◽  
J.-N. Chazalviel ◽  
F. Ozanam ◽  
F. Devreux
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Porous Silicon ◽  
Silicon Structure ◽  
Nuclear Magnetic

Characterization of Porous Silicon by Solid-State Nuclear Magnetic Resonance

1996 ◽  
Vol 100 (50) ◽  
pp. 19653-19658 ◽  
Author(s):  
W. K. Chang ◽  
M. Y. Liao ◽  
K. K. Gleason
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Solid State ◽  
Magnetic Resonance ◽  
Porous Silicon ◽  
Nuclear Magnetic

Nuclear Magnetic Resonance (NMR) of Porous Silicon

1996 ◽  
Vol 452 ◽  
Author(s):  
W. K. Chang ◽  
M. Y. Liao ◽  
K. K. Gleason
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Porous Silicon ◽  
Crystalline Silicon ◽  
Bulk Single Crystal ◽  
Hydrogenated Silicon ◽  
Low Temperature Annealing ◽  
Amorphous Hydrogenated Silicon ◽  
Silicon Nanocrystallites ◽  
Nuclear Magnetic

AbstractPorous silicon (PS) was characterized by 1H, 19F and 29Si solid-state nuclear magnetic resonance (NMR). On freshly prepared samples, hydrogen contents were between 3 × 1014 and 3 × 1015 per cm2 of PS surface area, while fluorine concentrations were below the detection limit. Cross-polarization (CP) was used to selectively observe the 29Si near the hydrogen passivation. The features of the 29Si NMR spectra are assigned as (O)2(Si)Si-H (-50 ppm), (O)3Si-H (-84 ppm), (Si)3Si-H (-91 ppm), (Si)2Si-H2 (-102 ppm) and (O)4Si (-109 ppm). Changes resulting from low temperature annealing in air and an HF soak were observed by both NMR and infrared spectroscopy. The 29Si NMR line widths for PS fall between those for crystalline silicon and those for amorphous hydrogenated silicon films (a-Si:H), suggesting disorder near the PS surface is intermediate between these extremes. However, comparison of the isotropie chemical shift values shows that the bonding in the disordered regions of PS differs from that found in a-Si:H. In addition, the sharp 29Si NMR resonance observed in the bulk single crystal starting material can not be resolved in the spectra of PS. Thus, well-ordered silicon nanocrystallites in the PS are either several bond-lengths removed from hydrogen or comprise only a small fraction of the PS layer.

An emerging technology: Nuclear magnetic resonance microscopy

1988 ◽  
Vol 46 ◽  
pp. 1000-1001
Author(s):  
M.J. Hennessy ◽  
E. Kwok
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Times ◽  
Basic Research ◽  
Local Environment ◽  
Magnetic Resonance Images ◽  
Nmr Microscopy ◽  
Mri Scans ◽  
Temperature Relaxation ◽  
Nuclear Magnetic

Much progress in nuclear magnetic resonance microscope has been made in the last few years as a result of improved instrumentation and techniques being made available through basic research in magnetic resonance imaging (MRI) technologies for medicine. Nuclear magnetic resonance (NMR) was first observed in the hydrogen nucleus in water by Bloch, Purcell and Pound over 40 years ago. Today, in medicine, virtually all commercial MRI scans are made of water bound in tissue. This is also true for NMR microscopy, which has focussed mainly on biological applications. The reason water is the favored molecule for NMR is because water is,the most abundant molecule in biology. It is also the most NMR sensitive having the largest nuclear magnetic moment and having reasonable room temperature relaxation times (from 10 ms to 3 sec). The contrast seen in magnetic resonance images is due mostly to distribution of water relaxation times in sample which are extremely sensitive to the local environment.

Nuclear magnetic resonance microscopy

1989 ◽  
Vol 47 ◽  
pp. 828-829
Author(s):  
Paul C. Lauterbur
Keyword(s):  
Magnetic Field ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Signal To Noise ◽  
Field Gradients ◽  
Useful Signal ◽  
Magnetic Field Gradients ◽  
Observation Times ◽  
Nuclear Magnetic

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

Sign in / Sign up

Export Citation Format

Share Document