Mapping Polar Distortions using Nanobeam Electron Diffraction and a Cepstral Approach.

Measuring local polar ordering is key to understanding ferroelectricity in thin films, especially for systems with small domains or significant disorder. Scanning nanobeam electron diffraction (NBED) provides an effective local probe of lattice parameters, local fields, polarization directions, and charge densities, which can be analyzed using a relatively low beam dose over large fields of view. However, quantitatively extracting the magnitudes and directions of polarization vectors from NBED remains challenging.

Extended q-Range X-Ray Scattering Reveals High-Resolution Structural Details of Biomacromolecules in Aqueous Solutions.

We communicate a feasibility study for high-resolution structural characterization of biomacromolecules in aqueous solution from X-ray scattering experiments measured over a range of scattering vectors (q) that is approximately two orders of magnitude wider than used previously for such systems. Scattering data with such an extended q-range enables the recovery of the underlying real-space atomic pair distribution function, which facilitates structure determination. We demonstrate the potential of this method for biomacromolecules using several types of cyclodextrins (CD) as model systems.

Dielectric Relaxation, Local Structure and Lattice Dynamics in Mn-Doped Potassium Tantalate Ceramics.

Alkaline niobate and tantalate perovskites have attracted attention as polar dielectrics for electronics and telecommunications. Here, we studied the polar behaviour, lattice dynamics, and local structure in conventionally processed KMnTaO ceramics using a combination of variable-temperature dielectric and Raman spectroscopies, and X-ray absorption fine structure (XAFS) measurements, respectively. Mn doping induces a low-frequency dielectric relaxation in KTaO (KT), which follows the Arrhenius law with an activation energy ≈ 105 meV and the characteristic relaxation time ≈ 4.

Tuning between Proper and Hybrid-Improper Mechanisms for Polar Behavior in Cs TiNbO Dion-Jacobson Phases.

The Dion-Jacobson (DJ) family of perovskite-related materials have recently attracted interest due to their polar structures and properties, resulting from hybrid-improper mechanisms for ferroelectricity in = 2 systems and from proper mechanisms in = 3 CsBiTiNbO. We report here a combined experimental and computational study on analogous = 3 Cs TiNbO ( = La, Nd) materials. Density functional theory calculations reveal the shallow energy landscape in these systems and give an understanding of the competing structural models suggested by neutron and electron diffraction studies.

Materials Research & Measurement Needs for Ceramics Additive Manufacturing.

We report on a recent workshop dedicated to additive manufacturing (AM) of ceramics that was held at the National Institute of Standards and Technology (NIST) in November 2019. This two-day all-invited meeting brought together experts from industry, government agencies and academia to review the state of the field and identify the most pressing applied materials research and metrology issues which, if addressed, could accelerate the incorporation of AM methods into commercial ceramic manufacturing. Besides the AM technologies, the discussions included consideration of the necessary post-processing steps.

Time-of-flight neutron total scattering with applied electric fields: and studies of ferroelectric materials.

Characterizing the structural response of functional materials (e.g., piezoelectrics and ferroelectrics) to electric fields is key for the creation of structure-property relationships.

Synthesis, Structure, and Electrical Properties of the Single Crystal BaCuAs.

Single crystals of clathrate-I BaCuAs have been synthesized and their structure and electronic properties determined using synchrotron-based X-ray diffraction and first-principles calculations. The structure is confirmed to be Pm3̅ n (No. 223), with lattice parameter a = 10.

Comparison of convergent beam electron diffraction and annular bright field atomic imaging for GaN polarity determination.

A comparison of two electron microscopy techniques used to determine the polarity of GaN nanowires is presented. The techniques are convergent beam electron diffraction (CBED) in TEM mode and annular bright field (ABF) imaging in aberration corrected STEM mode. Both measurements were made at nominally the same locations on a variety of GaN nanowires.

Structural studies of LiMnNiCoO electrode material.

A pristine Li-rich layered electrode material with composition LiMnNiCoO was characterized by X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy to determine whether it is a coherent mixture of monoclinic 2 LiMO and trigonal [Formula: see text] LiMO phases or a solid solution of the monoclinic phase. Contradictory results have been previously reported which can be attributed to the complexity and structural similarity of the monoclinic and trigonal phases. We resolved this uncertainty by combining diffraction and imaging techniques that probe complimentary length scales.

Use of Bayesian Inference in Crystallographic Structure Refinement via Full Diffraction Profile Analysis.

A Bayesian inference method for refining crystallographic structures is presented. The distribution of model parameters is stochastically sampled using Markov chain Monte Carlo. Posterior probability distributions are constructed for all model parameters to properly quantify uncertainty by appropriately modeling the heteroskedasticity and correlation of the error structure.

Stochastic behavior of nanoscale dielectric wall buckling.

The random buckling patterns of nanoscale dielectric walls are analyzed using a nonlinear multi-scale stochastic method that combines experimental measurements with simulations. The dielectric walls, approximately 200 nm tall and 20 nm wide, consist of compliant, low dielectric constant (low-) fins capped with stiff, compressively stressed TiN lines that provide the driving force for buckling. The deflections of the buckled lines exhibit sinusoidal pseudoperiodicity with amplitude fluctuation and phase decorrelation arising from stochastic variations in wall geometry, properties, and stress state at length scales shorter than the characteristic deflection wavelength of about 1000 nm.

Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics.

The atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres.

Nanoscale Buckling of Ultrathin Low-k Dielectric Lines during Hard-Mask Patterning.

Commonly known in macroscale mechanics, buckling phenomena are now also encountered in the nanoscale world as revealed in today's cutting-edge fabrication of microelectronics. The description of nanoscale buckling requires precise dimensional and elastic moduli measurements, as well as a thorough understanding of the relationships between stresses in the system and the ensuing morphologies. Here, we analyze quantitatively the buckling mechanics of organosilicate fins that are capped with hard masks in the process of lithographic formation of deep interconnects.

H2 evolution at Si-based metal-insulator-semiconductor photoelectrodes enhanced by inversion channel charge collection and H spillover.

Photoelectrochemical (PEC) water splitting represents a promising route for renewable production of hydrogen, but trade-offs between photoelectrode stability and efficiency have greatly limited the performance of PEC devices. In this work, we employ a metal-insulator-semiconductor (MIS) photoelectrode architecture that allows for stable and efficient water splitting using narrow bandgap semiconductors. Substantial improvement in the performance of Si-based MIS photocathodes is demonstrated through a combination of a high-quality thermal SiO2 layer and the use of bilayer metal catalysts.

Reverse Monte Carlo refinements of local displacive order in perovskites: AgNbO3 case study.

Reverse Monte Carlo refinements with combined input from neutron/x-ray total scattering and extended x-ray absorption fine structure (EXAFS) were applied to analyze local atomic displacements in perovskite-related AgNbO(3). This compound exhibits complex displacive order-disorder behavior that determines the unique dielectric properties of AgNbO(3)-based ceramics. Our results revealed that the total scattering and EXAFS data collected from polycrystalline samples were insufficient to reproduce the correlated local Nb displacements which are evident from the diffuse scattering observed in electron diffraction.

Tapering control of Si nanowires grown from SiCl₄ at reduced pressure.

Device applications of tapered Si nanowire (SiNW) arrays require reliable technological approaches for fabricating nanowires with controlled shape and orientation. In this study, we systematically explore effects of growth conditions on tapering of Si nanowires grown by chemical vapor deposition (CVD) at reduced pressure from SiCl(4) precursor. Tapering of SiNWs is governed by the interplay between the catalyzed vapor-liquid-solid (VLS) and uncatalyzed vapor-solid (VS) growth mechanisms.

Workshop on Measurement Needs for Local-Structure Determination in Inorganic Materials.

The functional responses (e.g., dielectric, magnetic, catalytic, etc.

The problem with determining atomic structure at the nanoscale.

Emerging complex functional materials often have atomic order limited to the nanoscale. Examples include nanoparticles, species encapsulated in mesoporous hosts, and bulk crystals with intrinsic nanoscale order. The powerful methods that we have for solving the atomic structure of bulk crystals fail for such materials.