Materials Sciences and Engineering Research Highlights

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Tuning Electronic Structures through Strain

A 3D representation of magnetoelastoresistance

Diffraction paradox reveals perfection in graphene

A broad diffraction component observed in electron diffraction of graphene reveals the degree of structural perfection. The broadening is due to electron confinement within the graphene layer, with single layer precision over the mesoscale.

$(top) 2-d diffraction pattern of graphene grown on SiC shows sharp spots on a very broad background around the (00) and G(10) spots. (bottom) 1-d scan of the (00) spot along [12 ̅10] shows the broad component with unusually large FWHM that unexpectedly correlates to forming a highly uniform film.$

Competing orders and role of fluctuations in FeSe

Above a critical pressure associated with the onset of magnetic order, superconducting and magnetic fluctuations exist over a wide temperature range above their respective bulk transition temperatures. Superconductivity in FeSe under pressure is bulk and competes with magnetism; measurements reveal fluctuations of superconductivity and magnetism likely due to their competing nature similar to other high-Tc superconductors.

Temperature-pressure phase diagram of FeSe from specific heat measurements.

Probing the Microstructure of Poly(Cyclosilane)

The microstructure of poly(cyclosilane) was determined by 29Si solid-state NMR spectroscopy and density-functional theory calculations. The NMR and DFT calculation structure determination protocol will be useful to resolve the molecular structure of silicon-based materials, enabling structure-function relationships to be established.

(Left) Simplified polymeric microstructures of poly(cyclosilane) consisting of a trans (blue) and cis (red) diastereomer with chair and twisted-boat cyclosilanering conformations. (Right, Top) Natural abundance 2D 29Si double-quantum-single-quantum homonuclear correlation NMR spectrum. (Right, Bottom) Comparison of the experimental and DFT calculated 29Si NMR spectra for both diastereomers

Phase diagram of the van der Waals ferromagnet VI3 under pressure

Van der Waals (vdW) materials are versatile systems for the study of magnetism in low dimensions. Motivated by the potential tunability of the new vdW ferromagnet VI3, a microscopic and thermodynamic study on bulk single crystals were performed under hydrostatic pressure using new techniques developed at Ames Laboratory.

The Surface Structure of Semiconductor Nanoparticles Revealed

By mixing precipitated nanoparticles (NP) with boron nitride (BN) a 9-fold improvement in DNP NMR sensitivity was realized compared to established DNP protocols. This new protocol enables challenging 2D NMR experiments that reveal the structure and connectivity of atoms in a variety of semiconductor NP systems.

(Top) Schematic structure of a semiconductor nanoparticle showing the crystalline core region, the surface region and capping ligands. (Lower) The impregnated powder procedure described in this work yields 9-fold better DNP NMR sensitivity than the previously described impregnated support procedure.

Direct imaging of unstained DNA origami

DNA origami was deposited and directly imaged using scattering transmission electron microscopy, with spatial resolution adequate for detecting key nanometer-scale structural details. This work presents proof-of-concept results demonstrating that electron microscopy can be used to resolve key elements of DNA-based structures without the use of staining protocols.

Tailor Plasmons in Pentacene/Graphene Heterostructures with Interlayer Electron Transfer

Van der Waals (vdW) heterostructures, which are produced by the precise assemblies of varieties of two-dimensional (2D) materials, have demonstrated many novel properties and functionalities. Here we report a nanoplasmonic study of vdW heterostructures that were produced by depositing ordered molecular layers of pentacene on top of graphene.

Dynamic Nuclear Polarization Using Radicals Created by γ-Irradiation

γ-irradiation induced the formation of stable radicals that were used to polarize 29Si and 1H spins in inorganic and organic solids by dynamic nuclear polarization (DNP). γ-irradiation will enable magic angle spinning (MAS) DNP experiments on previously inaccessible non-porous inorganic solids and insoluble polymers.

Interplay between magnetism and superconductivity probed by controlled disorder

Introducing disorder through electron irradiation simultaneously suppresses the magnetic and superconducting transition temperatures. The effects of non-magnetic disorder reveals the non-trivial influence of non-magnetic disorder on coupled superconductivity and magnetism in iron based superconductors.