Nuclear magnetic resonance (NMR) is a powerful scientific tool used in medical imaging and in probing the chemical structure of molecules and compounds. New research from Brown University shows a technique that helps adapt NMR to study the physical properties of thin films, two-dimensional nanomaterials and exotic states of matter.
NMR involves applying a strong magnetic field to sample and then zapping it with pulses of radio waves. The magnetic field aligns the magnetic moments, or "spins," of atomic nuclei within the sample. The radio waves will flip the spins of certain nuclei in the opposite direction, depending on the frequency of the waves. Scientists can use the signal associated of spin flips at different frequencies to create images or to determine a sample's molecular structure.
"NMR is a very useful technique, but the signal you get is very weak," said Vesna Mitrovic, an associate professor of physics and the senior author of the research, which is published in Review of Scientific Instruments. "To get a usable signal, you need to detect a lot of spins, which means you need a lot of material, relatively speaking. So much of the work we're doing now in physics is with thin films that are part of small devices or materials that have tiny crystals with odd shapes, and it's really difficult to get an NMR signal in those cases."
Part of the problem has to do with the geometry of the probe used to deliver the radio pulses and detect the associated signal. It's usually a solenoid, a cylindrical coil of wire inside of which the sample is placed. The NMR signal is strongest when a sample takes up most of the space available inside the cylinder. But if the sample is small compared to the volume of the cylinder -- as thin films and nanomaterials would be -- the signal weakens to nearly nothing.
But for the past few years, Mitrovic's lab at Brown has been using flat NMR coils for a variety of experiments aimed at exploring exotic materials and strange states of matter. Flat coils can be placed directly on or very close to a sample, and as a result they don't suffer from the signal loss of a solenoid. These types of NMR coils have been around for years and used for some specific applications in NMR imaging, Mitrovic says, but they've not been used in quite the same way as her lab has been using them.
For this latest research, Mitrovic and her colleagues showed that flat coils are not only useful in boosting NMR signal, but that different geometries of flat coils can maximize signal for samples of different shapes and in different types of experiments.
For instance, in experiments using thin-films of the semiconductor indium phosphate, the researchers showed that very small samples yield the most signal when placed at the center of flat, circular coil. For larger samples, and for experiments in which it is important to vary the orientation of the external magnetic field, a meander-line shape (a line that makes a series of right-angle turns) worked best.
The ability to get a signal at varying magnetic field orientations is important, Mitrovic says. "There are exotic materials and interesting physical states that can only be probed with certain magnetic field orientations," she said. "So knowing how to optimize our probe for that is really helpful."
Another advantage to flat coils is it gives experimenters access to their sample, as opposed to having it caged inside a solenoid.
"Many of the states we're interested in are induced by manipulating the sample -- applying an electric current to it or applying a stress to it," Mitrovic said. "The flat coils make it much easier to be able to do those manipulations."
Mitrovic hopes the guidance this research provides in how to optimize flat coils will be useful to other physicists interested in using NMR to investigate exotic materials and states of matter.
Mitrovic's co-authors were Wencong Liu and Lu Lu, both from the Brown. The research was supported by a grant from the National Science Foundation (DMR-1608760).
Kevin Stacey | EurekAlert!
Breaking bad metals with neutrons
16.01.2018 | DOE/Argonne National Laboratory
White graphene makes ceramics multifunctional
16.01.2018 | Rice University
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
17.01.2018 | Ecology, The Environment and Conservation
17.01.2018 | Physics and Astronomy
17.01.2018 | Awards Funding