X-ray Diffraction Facility

Offering a number of distinct advantages for materials research, this facility houses four X-ray diffraction instruments, including an automated powder diffractometer, a small-angle X-ray scattering (SAXS) instrument, a general area detector diffraction system (GADDS), and a real-time Laue instrument. All types of materials, including polymers, clays, metals, and ceramics can be analyzed. Samples can be in powdered, single crystal, thin film, or bulk form. Little or no sample preparation is usually needed. X-ray techniques are completely nondestructive.

	Manager Dr. Maura Weathers 607.255.2295 msw11@cornell.edu	Faculty Advisor Prof. Emmanuel Giannelis, MS&E epg2@cornell.edu
	Main Location: 1158 and 1102 Snee Hall

Instrumentation

Theta-Theta Diffractometer, Scintag, Inc.
Standard powder analysis; high-temperature diffraction; polycrystalline thin film analysis.

Nanostar System, Bruker-Axs
Small angle X-Ray scattering; resolution of d-spacings up to ~40 nm.

General Area Detector Diffraction System (GADDS), Bruker-Axs
Standard powder analysis and texture analysis in transmission or reflection.

The varying intensities along the arcs in this GADDS image indicate a preferred orientation in a Cu film deposited on a Si substrate.

Back Reflection Laue, Multiwire Ltd.
Crystal orientation.

Information Obtained from X-ray Diffraction

Phase Identification
This is the most widely used application of X-ray diffraction. Most materials have a diffraction pattern "fingerprint." The material is identified by comparing its pattern with a database that consists of more than 250,000 diffraction patterns for inorganic and organic materials.

Crystal Orientation
For research involving single crystals, the orientation of the crystal is extremely important. Crystals have different properties along different crystallographic directions. The orientation of a surface relative to a primary crystallographic direction can be determined to within 0.2°.

Structural Information
Crystal structure can be determined using a structural refinement program on a standard powder diffraction scan. A shortcut is to compare the diffraction scan with data included in the ICDD PDF database. When a scan is matched with an entry in the database, the crystal system and the space group information is provided.

Quantification of Phases
If a sample contains more than one phase, the percentage of each phase can be determined by comparing the diffraction peaks associated with the individual phases.

Texture
The powder samples that are commonly analyzed in the facility have crystallites that are randomly oriented. If a sample has a nonrandom distribution of crystallites, it has a preferred orientation or texture, which can be determined using the GADDS diffractometer. The extent to which a material deviates from random can be quantified by collecting multiple data frames on the GADDS instrument and compiling the information to create a pole figure. Researchers can use this technique on bulk samples, including polymers, or on thin films, in transmission or reflection.

Crystallinity and Crystallite Size
Crystallite sizes up to ~1500 Å can be measured from the broadening of diffraction peaks as calculated by the Scherrer equation. The fractional crystallinity in a mixed amorphous/crystalline material can be determined.

Small-Angle X-ray Scattering (SAXS)
Analysis of the large chain spacings in many polymers requires a detector-to-sample distance much greater than that of a normal diffractometer. Our Nanostar instrument has a detector-to-sample distance of 62.5 cm and uses a two-dimensional detector to analyze lattice spacings and strain in polymers.

Small-angle scattering from intercalated clay in a polymer. The scattering is the result of spacing between clay particles, on the order of 10-40 nm. Symmetric scattering in the left image is from an unstrained sample; asymmetric scattering in the right image is from strained sample.