bNMR – TRIUMF

01 Overview
02 Research Track Record
03 How it Works
04 bNMR and TRIUMF Science

01 Overview

At TRIUMF’s unique bNMR (beta-detected Nuclear Magnetic Resonance) facility, scientists are using radioactive isotopes to take inside-out, atomic-level snapshots to guide the way to new materials and medicines.

bNMR (the Greek-letter b is pronounced ‘beta’) is a next-generation form of the better-known Nuclear Magnetic Resonance (NMR), one of the most important tools in science for characterizing substances. Both work by analyzing atomic-level magnetic fields, and the way that these fields change in certain conditions.

But bNMR is NMR on steroids. bNMR is a billion-times more sensitive.

The higher-resolution view bNMR provides is critical in the current search for superconductors and nanomaterials, and to better understand complex, biologically important molecules. For these materials, knowing a substance’s overall qualities isn’t enough. For example, scientists need to characterize the special electrical or magnetic properties at material surfaces, or at the metal ion binding sites around which biomolecules fold.

This is where bNMR excels.

02 Research Track Record

CMMS-bNMR Research Track Record: bNMR reveals nanoscale surface details in topological insulators

bNMR reveals nanoscale surface details in topological insulators: Wolfgang Pauli said, “God made the bulk; surfaces were invented by the devil”, a recognition of the fact that theories and experimental measurements of near-surface properties are very difficult. Surfaces may be difficult to study, but it is where much interesting physics arise. Topological insulators (TI) are materials where the bulk is an insulator but whose surface contains conducting states, which means that electrons can only move along the surface of the material. Topologically protected states could act as a source of spin-polarized electrons with properties relevant to spintronics applications including quantum computing. As published in the Proceedings of the National Academy of Sciences (2015) researchers at CMMS used bNMR spectroscopy as a nano-scale depth-resolved probe of magnetism and conductivity within about 10 nm of the free surface of (Bi,Sb)₂Te₃. This depth-dependent study of electronic and magnetic properties of TI epitaxial layers using implanted, spin-polarized ⁸Li⁺ ions reveals differences in the band structure between the near-surface and deeper into the bulk material.

CMMS-bNMR Research Track Record: Towards more data-dense hard drives:

bNMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface Hard drives use disks made of magnetic material to store information, and an electromagnet in the read/write head writes information to the disk by magnetizing small sections of the disk. Increasing the information on a hard drive requires shrinking the size of the magnetic sections and this means the near-surface regions are increasingly important. The prototypical antiferromagnet α-Fe₂O₃has a first-order transition known as the Morin transition at 260 K, where the orientation of antiferromagnetic order with respect to the crystal lattice undergoes an abrupt change. In this work the static spin orientation and dynamic spin correlations within nanometers from the surface of a single crystal was studied via the nuclear spin polarization of implanted ⁸Li ions and detected via bNMR spectroscopy. As reported in Physical Review Letters (2016), the experiment found that the Morin transition temperature was independent of depth from 1 to 100 nm from the free (110) surface but the fluctuations of the electronic spins are faster near the crystal surface and decay into the bulk over a characteristic length of 11(1) nm. The results suggest the magnetic order parameter undergoes a continuous gradient rather than a phase separation of bulk vs. surface magnetism. Whereas previous studies made use of nanoparticles to achieve sufficient near-surface volume fraction to extract a signal, β-NMR spectroscopy allowed a depth-resolved characterisation of the magnetic order parameter into a macroscopic single crystal of α-Fe₂O₃, differentiating free-surface and finite-size effects on magnetic order.

03 How it Works

bNMR wields incredible power to resolve materials at the atomic level by embedding polarized radioactive isotopes into a substance.

Beta decay (the beta in bNMR) is a form of radioactive decay in which an unstable nucleus becomes more stable by emitting a fast, high-energy electron: a beta particle. At TRIUMF, scientists produce rare isotopes, particularly lithium-8 (⁸Li) and magnesium 31 (³¹Mg), which decay and emit beta particles at just the right rate for collecting exquisite, atomic-level details.

In the bNMR facility, isotopes from the beam line are fired into a solid material, or proteins in water, at just the right energy to come to rest where they can provide information that’s of interest to researchers.

Since the isotopes are polarized, or all spinning in the same direction, the researchers know how the isotopes are oriented before they embed within the sample. Once at rest, each embedded isotope is affected by the magnetic characteristics of its local atomic environment, which also affects the emitted beta particle. The beta particle therefore carries a detailed characterization of the local magnetic fields within the substance, which is recorded by a beta particle detector.

This makes each beta particle equivalent to a photon of light that your camera detector would record in taking a picture. The result: An Instagram-worthy spectrogram, one prized by scientists because it provides critical, otherwise inaccessible information about the sample’s nanoscale structure and electromagnetic qualities.

bNMR’s high level of sensitivity comes from its combination of a high percentage of both isotope polarization and beta particle detection.

04 bNMR and TRIUMF Science

TRIUMF’s unique bNMR facility supports key research for TRIUMF scientists, collaborators and visiting users in the Centre for Molecular and Materials Science (CMMS) and in the Life Sciences division.

The bNMR facility is the product of the lab’s world-leading advanced isotope and accelerator science, technology, and multidisciplinary personnel, enabling the production of unique beam lines and spectrometers.

For both CMMS and TRIUMF life sciences researchers, the bNMR facility provides intense, highly polarized beams of rare isotopes with well-characterized beta-decay characteristics that act as sensitive probes of local conditions in target materials.

Centre for Molecular and Materials Science (CMMS)

At CMMS, bNMR is opening the door as never before to the localized study of the magnetic and electronic properties of ultra-thin films, nanostructures and interfaces. TRIUMF bNMR’s primary advantages for the study of condensed matter are:

The ability to adjust the beam energy in order to precisely control the implantation depth of the lithium-8 (⁸Li) probe in solids. TRIUMF researchers have demonstrated the ability to control the implantation depth to just 2.5 nanometres, or about 25-times the size of an atom. This makes bNMR an extremely sensitive probe of local condensed matter conditions, for example in developing next-generation batteries with increased storage capacity and reduced charging times.
TRIUMF scientists have demonstrated that the lab’s lithium-8 (⁸Li) bNMR facility can effectively measure novel detail about nano-level electromagnetic characteristics at surfaces and interfaces. This includes structure, phase transitions and barrier dynamics. This makes bNMR a powerful new tool for optimizing functionality in novel nanostructures, and identifying materials with localized novel magnetic or superconducting characteristics. This ability is particularly important with the further miniaturization of electronic components, such as transistors, where electronic and magnetic phenomena at surfaces and interfaces play a larger role in overall functionality.

Life Sciences

TRIUMF’s Life Sciences division researchers are pioneering the use of bNMR in characterizing the role of metal ions in biologically important biomolecules. Many biomolecules, including chlorophyll, RNA, insulin, or beta-amyloid have structures that fold around key metal ions, including Mg, Cu and Zn.

In bNMR, a radioactive metallic isotope is incorporated into a biomolecule’s structure to act as an incredibly sensitive built-in probe transmitting otherwise unattainable information. This is done through the beam implantation of radioactive metallic isotopes, including ³¹Mg, into solutions of target molecules.

TRIUMF’s bNMR offers the first opportunity to study localized structure and dynamics around metal ions in biomolecules. This major advance is facilitated by:

TRIUMF’s bNMR researchers have provided the proof-of-principle that beam embedded ³¹Mg isotopes become functionally bound in biological samples. This bNMR achievement opens a new scientific frontier in the detailed characterization of metal-ion related protein structure and dynamics.
The invention of TRIUMF’s new patented liquid-phase bNMR spectrometer optimized for the study of biological samples. The new bNMR spectrometer will provide an unprecedented quadrapole spectroscopic perspective on liquid samples at biologically relevant temperatures under vacuum conditions. In conjunction with the existing b-NMR spectrometers, the new spectrometer will provide for triple data-taking within one experiment.

To learn more, please visit the TRIUMF bNMR website.