Angstrom Level Research Articles

Probing bonding and electronic structure at atomic resolution with spectroscopic imaging

Abstract

Location and distribution of inorganic material in a low ash yield, subbituminous coal

Previous studies of mineral matter in low ash yield, low rank coals have suggested that much of the inorganic material is present as organically bound elements rather than as discrete minerals. This study investigates the location and occurrence of this inorganic material to the angstrom level using non-invasive small angle scattering techniques. Microstructural analysis conducted on matrix and vitrain samples, collected from the subbituminous coals of the Huntly coalfield, found that the inorganic material is located in the 12.5 A < r < 125 A size range. This was consistent for all samples, irrespective of seam or location. As there was greater influence on X-ray scattering curves seen in the vitrain samples than the matrix samples, it is suggested that the inorganic material is located within the structured vitrinite tissues, likely originating from the original plant material rather than being precipitated post deposition. The fitting of microstructural models to the scattering curves suggests that the inorganic material exists as inorganic shells or coatings.

Modeling mechanical properties of an epoxy using particle dynamics, as parameterized through molecular modeling

The current paper successively applies molecular modeling and mesoscale modeling to scale mechanical models from an atomistic angstrom level to a sub-micron level and determine modulus, stress/strain behavior and defect formation in an epoxy and epoxy–copper interface. The results will show that molecular modeling may be applied directly to parameterize the bead properties used in the mesoscale model, which scale to the physical properties so could provide a means to understand interface behavior linked directly back to molecular origins.

Synchrotron Small Angle X-Ray Scattering Quantitatively Detects Angstrom Level Changes in the Average Radius of Taxol-Stabilized Microtubules Decorated with the Microtubule-Associated-Protein Tau

With the emerging proteomics era the scientific community is beginning the daunting task of understanding the structures and functions of a large number of self-assembling proteins. Here, our study was concerned with the effect of the microtubule-associated-protein (MAP) tau on the assembled structure of taxol-stabilized microtubules. Significantly, the synchrotron small angle x-ray scattering (SAXS) technique is able to quantitatively detect angstrom level changes in the average diameter of the microtubules modeled as a simple hollow nanotube with a fixed wall thickness. We show that the electrostatic binding of MAP tau isoforms to taxol-stabilized MTs leads to a controlled increase in the average radius of microtubules with increasing coverage of tau on the MT surface. The increase in the average diameter results from an increase in the distribution of protofilament numbers in MTs upon binding of MAP tau.

Nano-Platelet Structure of Clay Materials Observed by Atomic Force Microscope

In this study, we investigated the nano-platelet structures of original and organically modified montmorillonite clays. Atomic force microscope observation gave accurate width and thickness of the nano-platelet clays. The organically modified clays could not be homogeneously dispersed even in organic solvent. Ultrasonication of the solution resulted in the destruction of the layered structure of the clays. In contrast, the supernatant solution before ultrasonication contained the mono-layered nano-platelets of the organically modified clays whose surface was rough in the angstrom level due to the adsorbed molecules.

Angstrom analysis with dynamic in-situ aberration corrected electron microscopy

Following the pioneering development of atomic resolution in-situ environmental TEM (ETEM) for direct probing of gas-solid reactions, recent developments are presented of dynamic real time in-situ studies at the Angstrom level in an aberration corrected electron microscope. The in-situ data from Pt-Pd nanoparticles on carbon with the corresponding FFT/optical diffractogram (OD) illustrate an achieved resolution of < 0.11 nm at 500 °C and higher, in a double aberration corrected JEOL 2200 FS TEM/STEM employing a wider gap objective pole piece and gas tolerant TMP column pumping system. Direct observations of dynamic biofuel catalysts under controlled calcinations conditions and quantified with catalytic reactivity and physico-chemical studies show the benefits in-situ aberration correction in unveiling the evolution of surface active sites necessary for the development efficient heterogeneous catalysts. The new results open up opportunities for dynamic studies of materials in an aberration corrected environment and direct future development activities.

Double aberration-corrected TEM/STEM of tungstated zirconia nanocatalysts for the synthesis of paracetamol

We report highly active tungstated zirconia nanocatalysts for the synthesis of paracetamol by Beckmann rearrangement of 4-hydroxyacetophenone oxime. Double aberration-corrected (2AC)-TEM/STEM studies were performed in a JEOL 2200FS FEG TEM/STEM at the 1 Angstrom (1 Å = 0.1 nanometer) level. Observations at close to zero defocus were carried out using the AC-TEM as well as AC-STEM including high angle annular dark field (HAADF) imaging, from the same areas of the catalyst crystallites. The studies from the same areas have revealed the location and the nanostructure of the polytungstate species (clusters) and the nanograins of zirconia. The AC (S)TEM was crucial to observe the nanostructure and location of polytungstate clusters on the zirconia grains. Polytungstate clusters as small as 0.5 nm have been identified using the HAADF-STEM. The nanostructures of the catalyst and the W surface density have been correlated with paracetamol reaction studies. The results demonstrate the nature of active sites and high activity of the tungstated zirconia nanocatalyst, which is an environmentally clean alternative to the current homogeneous process.

High-Resolution Dual-Trap Optical Tweezers with Differential Detection: An Introduction: Figure 1.

Optical traps or "optical tweezers" have become an indispensable tool in understanding fundamental biological processes. The ability to manipulate and probe individual molecules or molecular complexes has led to a new, more refined understanding of the mechanical properties of the fundamental building blocks of the cell, and of the mechanism by which molecular machines function. The field has seen a steady stream of technological advances that have greatly refined the technique. One major effort has been in developing methods to resolve motions at the angstrom level--the fundamental length scale for many biological processes. This drive has only recently come to fruition with the advent of high-resolution optical trapping techniques that can now detect movements on the scale of a single base pair of DNA, 3.4 A. Here we briefly review the basic concepts and components of optical traps and the single-molecule experiments in which they are used.

Advances in atomic resolution in situ environmental transmission electron microscopy and 1Å aberration corrected in situ electron microscopy

Advances in atomic resolution in situ environmental transmission electron microscopy for direct probing of gas-solid reactions, including at very high temperatures (approximately 2000 degrees C) are described. In addition, recent developments of dynamic real time in situ studies at the Angstrom level using a hot stage in an aberration corrected environment are presented. In situ data from Pt/Pd nanoparticles on carbon with the corresponding FFT/optical diffractogram illustrate an achieved resolution of 0.11 nm at 500 degrees C and higher in a double aberration corrected TEM/STEM instrument employing a wider gap objective pole piece. The new results open up opportunities for dynamic studies of materials in an aberration corrected environment.

Steps in the History of Mudstone Investigations—A Timeline, 1556 Through 2007

In 1556, Agricola published the first detailed description of a mudstone posthumously, but it was not until 1747 that one of them (a black shale) was formally defined by William Hooson. A review of the world literature since Hooson's time shows a slow, steady activity in the study of mudstones in the 1800s, a sharp break to more frequent activity in the early 1920s, a decline during World War II, followed by a return to the pre-war level, but then followed in the 1990s by a possible decrease in activity.The trends are similar for both conceptual advances and for new techniques. The break in the 1920s was led by new technologies that expanded observations down to the angstrom level with X-ray diffraction and up to the formation scale with down-hole geophysical logging and seismic reflection. A comparison with a similar compilation for igneous and metamorphic rocks shows the same three phases—early slow phase, intermediate rapid phase punctuated by the Second World War, final slower phase—but in the case of the crystalline rocks, the rapid phase begins much earlier, in the 1880s. We suggest that the common techniques of that time—the petrographic microscope and wet chemistry—were well suited to the investigation of crystalline rocks, but the breakthrough for mudstones had to wait for new technologies.

Optical micromanipulation

Optical micromanipulation has engendered some major studies across all of the natural sciences at the mesoscopic scale. Though over thirty-five years old, the field is finding new applications and has lost none of its dynamic or innovative character: a trapped object presents a system that enables a calibrated minuscule force (piconewtons or less) to be exerted at will, enabling precision displacements right down to the angstrom level to be observed. The study of the motion of single biological molecular motors has been revolutionised and new studies in the physical sciences have been realised. From the chemistry and microfluidic viewpoint, optical forces may remotely actuate micro-components and perform micro-reactions. Overall, optical traps are becoming a key part of a wider "optical toolkit". We present a tutorial review of this technique, its fundamental principles and a flavour of some of the recent advances made.

Study and Application of a Linear Frequency−Thickness Relation for Surface-Initiated Atom Transfer Radical Polymerization in a Quartz Crystal Microbalance

A linear frequency-thickness (F-T) relation was established for surface-initiated atom transfer radical polymerization (SI-ATRP) in a quartz crystal microbalance (QCM). This quantitative F-T relation is monomer dependent but independent of polymerization rate, initiator and polymer density. With this F-T relation and the online monitoring capacity, QCM was successfully applied to study the kinetics of SI-ATRP mechanisms. QCM was also demonstrated to be useful in controlling film thickness at the angstrom level, which is critical in nanofabrication.

WITHIN TREE VARIATION OF LIGNIN, EXTRACTIVES, AND MICROFIBRIL ANGLE COUPLED WITH THE THEORETICAL AND NEAR INFRARED MODELING OF MICROFIBRIL ANGLE

A theoretical model was built predicting the relationship between microfibril angle and lignin content at the Angstrom (Å) level. Both theoretical and statistical examination of experimental data supports a square root transformation of lignin to predict microfibril angle. The experimental material used came from 10 longleaf pine (Pinus palustris) trees. Klason lignin (n=70), microfibril angle (n=70), and extractives (n=100) were measured and reported at different ring numbers and heights. All three traits were strongly influenced by ring age from pith while microfibril angle and extractives exhibited more of a height effect than lignin. As such, the multivariate response of the three traits were different in the axial direction than the radial direction supporting that care needs to be taken when defining juvenile wood within the tree. The root mean square error of calibration (RMSEC) for microfibril angle of the theoretical model (RMSEC = 9.8) was almost as low as the least squares regression model (RMSEC = 9.35). Microfibril angle calibrations were also built from NIR absorbance and showed a strong likeness to theoretical and experimental models (RMSEC = 9.0). As a result, theoretical and experimental work provided evidence that lignin content played a significant role in how NIR absorbance relates to microfibril angle. Additionally, the large variation in extractives content coupled with sampling procedure proved important when developing NIR based calibration equations for lignin and microfibril angle.

Self-calibrating hybrid wavelength, polarization, and time-multiplexed heterodyne interferometers for Angstrom precision measurements

Propose here unique wavelength and hybrid wavelength-polarization and wavelength-polarization-time-multiplexed heterodyne optical interferometers using an internal self-referencing scheme enabling Angstrom level sensitivity optical path-length measurements. As a first step, a proof-of-concept wavelength multiplexed scanning heterodyne interferometer is built to test the surface quality of a test mirror, demonstrating ±100 A profile variations with a 0.9 A accuracy. The hybrid wavelength-polarization and wavelength-polarization-time-multiplexed interferometers can be used to form spectrally coded distributed sensors.

Precision polarization multiplexed heterodyne acousto-optic interferometric sensor

Proposed and demonstrated is an angstrom level optical path length (OPL) detection sensitivity polarization multiplexed heterodyne acousto-optic interferometric sensor. Because both the phase-coded and the reference rf signals in the design are generated by the same optics, the heterodyne detected rf signals generated contain correlated phase noise characteristics that essentially cancel out during the mixing process in the rf domain. Hence, the proposed four-beam design leads to a super stability OPL sensor with angstrom level experimentally demonstrated measurement stability. A proof-of-concept experiment measures the voltage-dependent phase change due to the refractive index change of a liquid crystal sensor chip.

Polymer Imprint Lithography with Molecular-Scale Resolution

We show that small diameter, single-walled carbon nanotubes can serve as templates for performing polymer imprint lithography with feature sizes as small as 2 nm − comparable to the size of an individual molecule. The angstrom level uniformity in the critical dimensions of the features provided by this unusual type of template provides a unique ability to investigate systematically the resolution of imprint lithography at this molecular scale. Collective results of experiments with several polymer formulations for the molds and the molded materials suggest that the density of cross-links is an important molecular parameter that influences the ultimate resolution in this process. Optimized materials enable reliable, repetitive patterning in this single nanometer range.

Nanocoating individual cohesive boron nitride particles in a fluidized bed by ALD

Experiments are conducted with alumina (Al 2 O 3 ) deposition on a wide size range of hexagonal boron nitride (BN) platelet-like particles. Successful deposition of alumina films on these particles, with film thickness controllable at the Angstrom level, is observed based upon TEM imaging, ICP-AES, particle size distributions, and surface area analysis. While fluidizing, fine BN particles aggregate in the bed. The aggregates are the entities fluidizing, not the primary particles. However, individual particles are coated using Atomic Layer Deposition (ALD), not aggregates. Since ALD is a surface chemistry phenomenon, the films grow uniformly on every primary particle. BN particles are small platelets with different functional groups on the basal planes and edge planes. A small exposure to reagents [2.5×10 6 Langmuir (L) per reagent per cycle], will only coat the edge planes of uncoated BN particles. A larger dose of 1×10 8 L will coat the entire uncoated BN particle (edge and basal planes). After 10 ALD cycles of the 1×10 8 L dose, the exposures can be reduced to 1×10 6 L as the film is then growing on alumina and not BN. Peel strength data indicate that adhesion between the coated particles and a cured epoxy in a filled composite is ∼25% stronger than that of uncoated particles and the epoxy. The overall thermal conductivity drops ∼17% for an identical filler loading as expected due to the additional thermal resistance added by the film. However, the viscosity of an epoxy resin loaded with coated BN is as much as five times lower than that of the resin loaded with the same amount of uncoated BN. These results indicate that the loading of Al 2 O 3 nanocoated BN particles in an epoxy matrix can be substantially increased relative to that of uncoated particles. The thermal conductivity of the more highly filled composite will be increased without adversely impacting filled resin viscosity or the peel strength of the cured material. This is the first reported study indicating that cohesive primary particles that fluidize as aggregates in a fluidized bed can be individually coated with a nano-thick ceramic film using ALD.

Nanocoating individual cohesive boron nitride particles in a fluidized bed by ALD

Experiments are conducted with alumina (Al 2O 3) deposition on a wide size range of hexagonal boron nitride (BN) platelet-like particles. Successful deposition of alumina films on these particles, with film thickness controllable at the Angstrom level, is observed based upon TEM imaging, ICP-AES, particle size distributions, and surface area analysis. While fluidizing, fine BN particles aggregate in the bed. The aggregates are the entities fluidizing, not the primary particles. However, individual particles are coated using Atomic Layer Deposition (ALD), not aggregates. Since ALD is a surface chemistry phenomenon, the films grow uniformly on every primary particle. BN particles are small platelets with different functional groups on the basal planes and edge planes. A small exposure to reagents [2.5×10 6 Langmuir (L) per reagent per cycle], will only coat the edge planes of uncoated BN particles. A larger dose of 1×10 8 L will coat the entire uncoated BN particle (edge and basal planes). After 10 ALD cycles of the 1×10 8 L dose, the exposures can be reduced to 1×10 6 L as the film is then growing on alumina and not BN. Peel strength data indicate that adhesion between the coated particles and a cured epoxy in a filled composite is ∼25% stronger than that of uncoated particles and the epoxy. The overall thermal conductivity drops ∼17% for an identical filler loading as expected due to the additional thermal resistance added by the film. However, the viscosity of an epoxy resin loaded with coated BN is as much as five times lower than that of the resin loaded with the same amount of uncoated BN. These results indicate that the loading of Al 2O 3 nanocoated BN particles in an epoxy matrix can be substantially increased relative to that of uncoated particles. The thermal conductivity of the more highly filled composite will be increased without adversely impacting filled resin viscosity or the peel strength of the cured material. This is the first reported study indicating that cohesive primary particles that fluidize as aggregates in a fluidized bed can be individually coated with a nano-thick ceramic film using ALD.

Patterned Adsorption of Protein onto a Carbohydrate Monolayer Immobilized on Si

We propose a technique for fabricating a carbohydrate-terminated monolayer (CM) surface, which is extremely flat at the angstrom level. The CM was immobilized onto a Si surface by Si−C covalent bond. Specific adsorption of the protein molecule from a contacting solution was observed on the CM area of a patterned CM substrate surface, while its nonspecific adsorption was observed on the Si−O area.

Short-range wetting at liquid gallium-bismuth alloy surfaces: X-ray measurements and square-gradient theory

We present an x-ray reflectivity study of wetting at the free surface of the binary liquid metal gallium-bismuth (Ga-Bi) in the region where the bulk phase separates into Bi-rich and Ga-rich liquid phases. The measurements reveal the evolution of the microscopic structure of wetting films of the Bi-rich, low-surface-tension phase along different paths in the bulk phase diagram. A balance between the surface potential preferring the Bi-rich phase and the gravitational potential which favors the Ga-rich phase at the surface pins the interface of the two demixed liquid metallic phases close to the free surface. This enables us to resolve it on an Angstrom level and to apply a mean-field, square gradient model extended by thermally activated capillary waves as dominant thermal fluctuations. The sole free parameter of the gradient model, i.e. the so-called influence parameter, $\kappa$, is determined from our measurements. Relying on a calculation of the liquid/liquid interfacial tension that makes it possible to distinguish between intrinsic and capillary wave contributions to the interfacial structure we estimate that fluctuations affect the observed short-range, complete wetting phenomena only marginally. A critical wetting transition that should be sensitive to thermal fluctuations seems to be absent in this binary metallic alloy.