MAG*I*CAL™ TEM Calibration Specimen

Question of ISO 9000 type traceability

We at SPI Supplies have had many requests for persons asking this question and the original developers of the product have been negotiating with NIST to arrange for some form of certification for this sample because of the frequent requests for such clarification.

The developers of the Mag*I*Cal product, on June 26, 1998, made a posting on the Microscopy Listserver that included the following statement and we publish it here for the convenience of our would-be customers of this product:

The biggest problem for both us and NIST has been that the MAG*I*CAL sample is made from a single crystal of silicon, with the calibration marks being directly traceable to the silicon (111) lattice spacing. This spacing is directly observable on the sample itself through lattice imaging; i.e.: the sample is internally calibrated to a "God-traceable" standard, and NIST generally doesn't bother confirming intrinsic properties of materials. Certification auditors requiring NIST-traceable samples are generally most concerned about adequate paperwork, This recent communication with NIST gives us that paperwork, I believe, as NIST acknowledges the lattice spacings of silicon as being well characterized and documented, making the MAG*I*CAL sample a NIST-recognized sample. We'll be discussing the proper NIST term to use with the MAG*I*CAL sample when Rob Gettings gets back from a business trip in a couple of weeks.


The following is the full text of the letter from NIST that was published on the Microscopy Listserver on June 26, 1998 and we reprint this letter for the benefit of our prospective customers:

TEXT OF LETTER FROM ROBERT GETTINGS, NIST:

NIST
U.S. Department of Commerce
NATIONAL INSTITUTE FOR STANDARDS & TECHNOLOGY

Robert Gettings
Standard reference Materials Program
Bldg. 202, Rm. 212, Gaithersburg, MD 20899

June 23, 1998

Dear Mr. McCaffrey:

I am sending this communication in regards to your question concerning the calibration of Transmission Electron Microscopes (TEM) using silicon lattice spacings. NIST does not currently supply a standard for calibrating the magnification scale of TEM's, nor for the crystalline lattice spacings of silicon.

The crystalline lattice spacing is an intrinsic property of a material. For pure silicon, the spacing has been well characterized and documented by the scientific community. It is known to 6 decimal places, and can be obtained from the CRC handbook of Chemistry and Physics among other references.

Related work by NIST:

NIST is currently working on SRM 640c Silicon X-ray Diffraction Powder. This material, when finished will provide certified line positions traceable to the SI definition of length.

NIST is also working on a new standard, SRM1990, for the lattice spacing of single crystal ruby. The material will be in the form of a 0.15 mm sphere, and is expected to be complete by the end of this year.

Thank you for your interest in NIST standards.

Sincerely,
(signature)
Robert J. Gettings
Project Manager
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We, at SPI Supplies hope this information has been useful to those concern about the admissibility of the Mag*I*Cal TEM Calibration Sample from the perspective of ISO 9000 (or ISO Guide 25) type traceability.

Summary:
So having said all of that, the point is that there currently is no NIST- traceable standard for high-magnification TEM being manufactured for this purpose. The next best thing is the MAG*I*CAL TEM calibration sample, which is internally calibrated against the lattice spacing of silicon, a fundamental constant of nature. This statement has been used successfully in the past in fulfillment of the requirements for certification and traceability. The MAG*I*CAL sample allows magnification calibrations across the entire magnification range of TEMs, as well as the camera constant calibration and the image/diffraction pattern rotation calibration. But one must always remember that is not an "NIST-traceable standard". One might argue whether, in this instance, it really matters, but that is the kind of philosophical question we would prefer to avoid for now......

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