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Principle:
An intense, low energy, neutron beam illuminates the sample uniformly, producing initially monoenergetic charged
particles (i.e., H+, He2+) from exoergic nuclear reactions. These isotropically emitted particles lose energy in passing
through the sample. The energy which they retain upon leaving the sample surface is primarily dependent on the depth at
which the reaction took place. The depth profiles are obtained by the deconvolution of the measured charged particle energy
spectra. The number of charged particles observed at a particular energy is directly proportional to the concentration of the
nuclide at a particular depth.
Applications:
The technique provides quantitative depth profiles in solids for certain elements, such as He, Li, B, N, Cl, etc.
(see table below). It can be used to probe semiconductor samples, polymers, optoelectronic materials, metal alloys, and
most other solids. The analysis is nondestructive to samples, leaving only trace amounts of residual radioactivity. |
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| Sample Requirements: |
| The sample must be solid, or a liquid with very low volatility. It must present a flat, smooth surface with a
minimum area of at least a few mm2. Typical analysis area is a 2 cm diameter circle. Large samples up to 300 mm diameter
can be scanned. |
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| Quantitation: |
| Concentrations down to a few parts per million can be determined, depending on the element and the matrix.
Profiling to depths of a few tens of micrometers is obtained, with resolution in depth varying between a few nanometers
and a few tenths of a micrometer. Time for Analysis: Each run takes a few minutes to a few hours, depending on the nuclide,
sample, and the degree of quantitation desired. Limitations: The technique is applicable only to the elements listed in the
table. Also, as mentioned before, the sample must present a smooth surface and have a low vapor pressure. |
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| Recent applications: |
| In-situ Measurement of Lithium Movement in Thin Film Electrochromic Coatings |
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| Reference: |
"Neutron Depth Profiling: Overview and Description of NIST Facilities,"
R. G. Downing, G. P. Lamaze, J. K. Langland, and S. T Hwang. NIST Journal of Research 98 (1993) 109.
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| Contacts: |
George P. Lamaze, 301/975-6202, george.lamaze@nist.gov
See also http://www.ncnr.nist.gov/instruments/coldintr.html
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Last modified 21-July-2003 |
