Long-Lived States of Magnetically Equivalent Spins Populated by Dissolution-DNP and Revealed by Enzymatic Reactions

Hyperpolarization by dissolution dynamic nuclear polarization (D-DNP) offers a way of enhancing NMR signals by up to five orders of magnitude in metabolites and other small molecules. Nevertheless, the lifetime of hyperpolarization is inexorably limited, as it decays toward thermal equilibrium with the nuclear spin-lattice relaxation time. This lifetime can be extended by storing the hyperpolarization in the form of long-lived states (LLS) that are immune to most dominant relaxation mechanisms. Levitt and co-workers have shown how LLS can be prepared for a pair of inequivalent spins by D-DNP. Here, we demonstrate that this approach can also be applied to magnetically equivalent pairs of spins such as the two protons of fumarate, which can have very long LLS lifetimes. As in the case of para-hydrogen, these hyperpolarized equivalent LLS (HELLS) are not magnetically active. However, a chemical reaction such as the enzymatic conversion of fumarate into malate can break the magnetic equivalence and reveal intense NMR signals.

Quantum dynamics in individual surface spins

Tobias Bilgeri

This thesis presents a combined experimental and theoretical study of the classical and quantum magnetization dynamics in single magnetic adatoms and molecules, and on the classical and quantum coherent control thereof. First, a detailed description of the methods and in particular electron spin resonance scanning tunneling spectroscopy is given. Next, we give a detailed account of how to experimentally update a standard scanning tunneling microscope for such experiments, which ultimately lead us to set up the world's second microscope with such capabilities. Subsequently, we show how we iteratively improved the setup, and how we were able to achieve a transmission of radiofrequency voltages to the tunneling junction with almost no additional losses beyond the intrinsic limitations of the materials used, a great improvement compared to most setups presently in use.Afterwards, we apply this technique to the metal-organic complex iron phthalocyanine. On MgO, we find it to form a spin-1/2 system, and we demonstrate quantum coherent control thereof, and investigate the magnetic interaction between surface-adsorbed molecules. Furthermore, we use this technique to experimentally demonstrate the magnetic stability of Dy adatoms on MgO. We find that this system, by several metrics, represents the worlds most stable single atom magnet discovered thus far. Using the capability of scanning tunneling microscopes to perform atomic manipulation, we ensemble atomically precise Dy nanostructures. By classically controlling the magnetic orientation of the Dy atoms, we are thus able to store information long-term in single adatoms and nanostructures even in absence of an external field, and create nanomagnets and local magnetic fields with unprecedented precision and stability.Finally, we investigate the magnetic properties of Ho/MgO. Depending on the precise adsorption site and charge configuration, we find either long lifetimes in the case of top-site 4f10 Ho, which was recently discovered as world's first single atom magnet, or fast sub-barrier relaxation due to strongly mixed quantum states. Using a novel theoretical approach, we are able to disentangle the different contributions of the individual species measured in ensemble-averaging X-ray absorption studies, and lift the discrepancies between previous X-ray and scanning tunneling microscopy based studies on Ho/MgO. By theoretically describing the perturbing effects of the experimental probes driving the spin degree of freedom out of thermal equilibrium, we are able to explain the measured dynamics in good agreement with the experimental data.

EPFL2021

Electrospray Ion Beam Deposition of Complex Non-Volatile Molecules

Gordon Rinke

The rational synthesis of novel materials requires the control over the arrangement of matter in order to meet the desired properties for applications and devices. Ultimately, control means to define the place of each atom and determine its chemical state, as well as being able to confirm the result in a measurement. Control at the atomic level can be achieved with scanning tunneling microscopy (STM), both in imaging and atomic manipulation. The latter, however, can never be used in meso- or even macroscopic material synthesis. Self-ordering phenomena determines atomic control in material synthesis as well, observed for instance in protein folding or in molecular beam epitaxy (MBE) technology. In both cases the atomically determined arrangement of the atoms in the structure is controlled only by environmental parameters that steer the self-ordering phenomena. In this thesis I show that electrospray ion beam deposition (ES-IBD) or ion soft-landing is a material processing technique, which combines and even extends the level of control offered by MBE. It is demonstrated that a vast range of complex organic materials including peptides and proteins is now available to ultrapure vacuum processing and moreover completely novel schemes of controlling self-ordering processes are provided. In-situ STM is applied to investigate the structure formation of complex molecules deposited by ES-IBD on well-defined, clean, and atomically flat surfaces in ultrahigh vacuum at the greatest detail. This allows us to explore the novel control features that are intrinsic to the ES-IBD deposition process like online coverage monitoring, deposition energy control, and mass-selection to select charge states or reactive species. The molecules studied here include organic molecular salts, dye molecules, reactive polymer building blocks, and finally peptides and proteins. Crystalline layer-by-layer as well as island growth was observed and revealed the equivalence to conventional MBE growth. On the basis of these deposition experiments the crucial influence of clusters in the ion beam for high material flux was discovered. Furthermore, it was found that the chemical state of the molecule is a key factor for the deposition result as chemical reactions can be induced or the self-assembly behavior can be altered. Alongside the capability to handle also extremely reactive molecules, the feasibility to control chemical reactions occurring as a result of an external stimulus to a specifically selected reactive species is demonstrated. Employing the control parameters that are specific to ES-IBD like charge state selection and deposition energy to complex biomolecules opens up new perspectives for vacuum deposition. In addition to the self-assembly governed by the molecule-substrate and molecule-molecule interaction, it was possible to actively steer the structure formation of proteins by influencing their stiffness and their reactivity through their charge state as well as by the deposition energy, parameters intrinsic to the ES-IBD method. Hence, electrospray ion beam deposition is indeed a tool to prepare well defined surface coatings at highest level of control and complexity. To be relevant for industrial applications, the performance of the system has to be further improved, most importantly in terms of deposition rate. In general, ES-IBD enables new approaches for the growth of functional coatings but also serving as perfect sample preparation tool for the characterization of complex molecules on the atomic scale by scanning probe or more general surface science methods.

EPFL2013

Hyperpolarization of Deuterated Metabolites via Remote Cross-Polarization and Dissolution Dynamic Nuclear Polarization

Geoffrey Bodenhausen, Aurélien Bornet, Sami Jannin, Jonas Milani, Basile Vuichoud

In deuterated molecules such as [1-C-13]pyruvate-d(3), the nuclear spin polarization of C-13 nuclei can be enhanced by combining Hartmann-Hahn cross-polarization (CP) at low temperatures (1.2 K) with dissolution dynamic nuclear polarization (D-DNP). The polarization is transferred from remote solvent protons to the C-13 spins of interest. This allows one not only to slightly reduce build-up times but also to increase polarization levels and extend the lifetimes T-1(C-13) of the enhanced C-13 polarization during and after transfer from the polarizer to the NMR or MRI system. This extends time scales over which metabolic processes and chemical reactions can be monitored.