Nuclear Magnetic Resonance Studies of Deuterium in Silicon
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NUCLEAR MAGNETIC RESONANCE STUDIES OF DEUTERIUM IN SILICON KAREN CARR BUSTILLO*, EUGENE E. HALLER*, and JEFFREY A. REIMER** *Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720 USA **Department of Chemical Engineering, University of California, Berkeley, CA 94720 USA ABSTRACT We report nuclear magnetic resonance measurements of deuterons diffused into silicon powders. Deuterium spectra show a two-component lineshape corresponding to two distinct hydrogen sites. The component with a narrow Lorentzian lineshape is assigned to D2 molecules. The second component is a quadrupolar doublet powder pattern, and its characteristic splitting provides a value of the electric field gradient at the site of 5 the deuterium atom of 1.45x10 dyn/cm. We have observed the deuterium magnetic resonance signal in deuterated silicon powders and report a two-component lineshape: a narrow Lorentzian attributed to D2 molecules and a broadened 5 doublet with a measured electric field gradient of 1.45x10 dyn/cm. We find the ratio of doublet to Lorentzian sites is 2:1 for a heavily boron doped sample. The starting material was Czochralski grown silicon ([B] =ixl0 1 9 cm- 3 ) mechanically broken to particles with average dimensions of 45 to 63 jm. The particles were placed on silicon wafers which in turn were positioned on a graphite slab located 25 cm downstream of a 13.6 MHz inductively coupled D2 plasma. A second rf coil at 450 kHz heated the sample to 300 0 C as measured with a thermocouple embedded in the graphite. The long mean free path of deuterium atoms at 400 mTorr allows all sides of each particle to be exposed to deuterium. This was confirmed by performing secondary ion mass spectroscopy (SIMS) depth profiles on wafer pieces located both next to and underneath the particles. The similar results from both silicon slices demonstrate that atomic deuterium is able to reach the surface of each particle and effectively diffuse into the bulk even when covered by other particles. NMR experiments were performed at 4.3 Tesla (27.84 MHz for 2 H) and 9.4 Tesla (61.25 MHz for 2 H) using Fourier-transform pulse spectrometers. A quadrupolar echo pulse [1] sequence (90'x-tau-90'y-tau), which completely refocuses the quadrupolar interaction (doublet component) and results in refocusing approximately one half of the magnetization due to terms linear in Iz (Lorentzian component), was used for most data acquisition. A spin echo pulse [I] sequence (90°x-tau-180°y-tau), which completely refocuses the IZ component and minimizes the quadrupolar component, was used for elucidation of the chemical shift of the Lorentzian component. The 900 pulses had a duration of 7.2 gs at 27.84 MHz and 6.0 ls at 61.25 MHz, and corrections were made to all fits of the data to account for distortion due to inhomogeneous irradiation. [2] The Hamiltonian for the deuterium (spin I=l) quadrupolar nucleus in a strong magnetic field and in the presence of an Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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