Friday, February 13, 2009Volume 9, Issue 1
New X-Ray Diffraction Instrument in MCL Spins Off Technology from Large Hadron Collider
It doesn’t get much more cutting edge than the technology incorporated into the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Switzerland, the world’s largest particle physics laboratory. Though meltdown of a supermagnet in September, 2008, has delayed the scientists’ efforts to understand the nature of gravity and dark energy, one LHC program, known as the Medipex2 collaboration, has developed a pixel read-out chip that has spun off new technologies in various fields. One of these, known as the PIXcel detector, manufactured by PANalytical, Inc., has landed in MCL’s Powder X-Ray Diffraction Lab inside a new PANalytical X’Pert Pro MPD diffractometer, overseen by Materials Characterization Laboratory research assistant Nichole Wonderling.
This new diffractometer has Wonderling excited as she lists its improvements over the lab’s previous generation XRD:
- Speed -- The PIXcel detector consists of a high spatial, high contrast- resolving complementary metal oxide semiconductor (CMOS) pixel read-out chip combined with a semi-conductor sensor that converts x-rays into detectable electric signals. Working in single photon counting mode, with 65,000 pixels, each of which is 55 microns square with its own individual readout circuitry, the PIXcel is the primary speed-enhancing component of the diffractometer. Capable of 25 million counts per second per pixel, and with a 95% count rate linearity, data collection times are reduced to a fraction of what is required with a conventional x-ray diffractometer. A major advantage of this speed is the capability to do time-resolved, in situ studies of phase changes that occur quickly, such as at high temperature with an Anton-Paar HTK-16 high temperature chamber. The HTK-16 is a strip heater style temperature
chamber that can be used from room temperature up to 1600⁰ C in air, vacuum, or inert gas atmospheres. It is equipped with a stage height adjustment module for compensation of sample displacement with increasing temperature due to thermal expansion of the sample stage. - Resolution -- The PIXcel gives a resolution far superior to earlier diffractometers. Typical FWHM for NIST reference materials is less than 1/3 that seen on the lab’s conventional diffractometers. This high resolution makes it possible to collect data that were not previously obtainable by x-ray diffraction and makes the X’Pert Pro MPD a viable option for some applications that previously demanded synchrotron sources to obtain the needed resolution.
- Flexibility -- The new XRD also benefits from PANalytical technology known as Pre-Fix optics which makes the process of switching optics a simple, highly reproducible procedure. Where formerly it could take hours to change from one configuration to another, now it can generally be done in minutes. In addition, the system is equipped with a sample changer that holds up to 15 samples, allowing unattended data collection and extending the hours of instrument operation. “It is essentially a robot that can be programmed to run samples overnight, but it is a dream come true for weary grad students with high numbers of samples that would otherwise have to sit by the instrument through the night,” Wonderling says.
- Enhanced thin film measurement capability -- With the addition of a parabolic mirror capable of converting a divergent beam from a line focus source into a quasi-monochromatic and quasi-parallel beam of high intensity to the incident side of the diffractometer, the X’Pert Pro MPD is enabling Penn State researchers to investigate thinner, less crystalline films using grazing incidence Diffractometry (GIXRD). According to Wonderling, “We are able to see diffraction patterns for materials we could never see before.”
Bryan Gauntt, a graduate student in Elizabeth Dickey’s group, agrees. He is part of a team of researchers trying to make better thin films for un-cooled infrared sensors for night vision binoculars and other infrared applications. Gauntt is working on thin films of vanadium oxide, a material used in uncooled infrared detectors due to a large temperature dependent change in the electrical resistivity. Using transmission electron microscopy, he found evidence of crystallinity via electron diffraction, so he knew there was a crystalline phase present in many of the films. When he first looked at his films using a conventional powder diffractometer, in grazing incidence geometry, all films appeared to be amorphous, not what he was expecting or hoping for. Even the two dimensional detector on the Rigaku D-Max Pro, another diffractometer operated by MCL, was unable to collect enough of the poorly scattered x-rays to allow adequate phase identification.
“At that point I was pretty convinced I couldn’t use XRD to obtain crystallographic information from these films,” he admits, “I was really hoping to because XRD is less invasive, and you usually don’t have to do any sample prep, which can inadvertently alter the structure you are trying to observe. The other diffractometers on campus are incredible machines, and I’ve successfully used most of them with samples that show more long-range order. These samples now are particularly difficult because they lack the extensive long-range order that results in strong, coherent diffraction. It wasn’t until Nichole got this PANalytical machine with the PIXcel detector that we were able to get any kind of useful information from x-ray diffraction experiments. It’s been really helpful to know that the nano-crystals I observed using the TEM are characteristic of the sample as a whole and not just the area I happened to be looking at with the TEM. It’s a first level screening of what these samples may look like crystallographically, and it allows me to quickly determine if the samples are worth studying with the TEM.”
For Wonderling, the addition of the diffractometer to the lab is a wonderful complement to MCL’s already vast line-up of x-ray characterization equipment. From powder diffraction to micro-diffraction to high-resolution diffraction and more, researchers needing x-ray diffraction services in most any shape or form can have their needs met by one of the instruments the facility offers.
Stop by the X-ray Diffraction Lab in the MRL Building or contact Nichole Wonderling (nmw10@psu.edu) to find out how the new PANalytical XRD can benefit your research.
