Nano-ruler sets very small marks
The new ruler is in the form of a multilayer thin silicon chip of 25 square millimeters (just under an inch). Each has a measured and certified by NIST for the separation and angles of the crystal planes of silicon atoms in the crystal base.
X-ray diffraction work by sending X rays through a crystal, which can be anything from a wafer used to make microchips to a sample of an unknown protein crystal and observing the patterns made by X-rays as diffraction of electrons in the crystal. The space, the angles and the intensity of the lines tell a crystallographer pattern formation on the relative positions of atoms in the crystal, as well as something about the quality of the crystal, the nature of chemical bonds and more. It is one of the workhorse techniques of materials science and engineering. The version of precision, high resolution X-ray diffraction, can be used to determine the thickness, the crystal structure, embedded tension and orientation of thin films used in advanced semiconductor and nanotechnology devices.
Formally NIST Standard Reference Material (SRM) 2000, “Standard for calibration of high resolution X-ray diffraction,” the new ruler crystallographers gives a well-known glass sample for calibration of precision instruments. This was made possible by the development of a unique diffractometer in parallel beam measurements performed at NIST traceable to international measurement standards and is believed to be more accurate angle measurement device of its kind in the world. The instrument can measure the angle of NIST with an accuracy better than an arc second, 1 / 3600 of a degree. “Our accuracy is in fact the angle on the diameter of a quarter if you’re looking at it from two miles away,” explains NIST materials scientist Donald Windover, “The accuracy is better, about the size of the Washington’s nose. ”
Because the lattice values of SRM 2000-space, inclination, orientation, are traceable to SI units, the new material offers an absolute reference for calibration of high precision. Details are available at https://www-s.nist.gov/srmors/view_detail.cfm?srm=2000.