Angstrom Scale Research Articles

Hard X-Ray Free Electron Lasers: How They Work, Photon Characteristics Important to Biology and Possibilities for the Future

Accelerator based photon sources have played a key role in the understanding of protein structures at the atomic scale. The next generation of these sources, free electron lasers, now operate with Angstrom scale wavelengths and open unique opportunities for biophysics. How these lasers work, the photon properties they yield and a look toward future upgrades will be discussed using LCLS, the world's first operating hard x-ray free electron laser as an example.

CoFe2O4−TiO2 and CoFe2O4−ZnO Thin Film Nanostructures Elaborated from Colloidal Chemistry and Atomic Layer Deposition

CoFe(2)O(4)-TiO(2) and CoFe(2)O(4)-ZnO nanoparticles/film composites were prepared from directed assembly of colloidal CoFe(2)O(4) in a Langmuir-Blodgett monolayer and atomic layer deposition (ALD) of an oxide (TiO(2) or ZnO). The combination of these two methods permits the use of well-defined nanoparticles from colloidal chemistry, their assembly on a large scale, and the control over the interface between a ferrimagnetic material (CoFe(2)O(4)) and a semiconductor (TiO(2) or ZnO). Using this approach, architectures can be assembled with a precise control from the Angstrom scale (ALD) to the micrometer scale (Langmuir-Blodgett film). The resulting heterostructures present well-calibrated thicknesses. Electron microscopy and magnetic measurement studies give evidence that the size of the nanoparticles and their intrinsic magnetic properties are not altered by the various steps involved in the synthesis process. Therefore, the approach is suitable to obtain a layered composite with a quasi-monodisperse layer of ferrimagnetic nanoparticles embedded in an ultrathin film of semiconducting material.

Nanoscale characterization of martensite structures in copper based shape memory alloys

Martensitic transformations are first order displacive transitions and occur in the materials on cooling from high temperature. Shape memory effect is an unusual property exhibited by certain alloy systems, and leads to martensitic transition. Copper-based alloys exhibit this property in beta phase field which possess simple bcc- structures, austenite structure at high-temperatures. As temperature is lowered the austenite undergoes martensitic transition following two ordering reactions, and structural changes in nanoscale govern this transition. Atomic movements are also confined to interatomic lengths in sub-μm or angstrom scale in martensitic transformation. The formation of the layered structures in copper based alloys consists of shears and shear mechanism. Martensitic transformations occur in a few steps with the cooperative movement of atoms less than interatomic distances by means of lattice invariant shears on a {110} - type plane of austenite matrix which is basal plane or stacking plane of martensite. The lattice invariant shears occurs, in two opposite directions, <110> -type directions on the {110}-type plane. These shears gives rise to the formation of layered structure.

Probing structures of nanomaterials using advanced electron microscopy methods, including aberration‐corrected electron microscopy at the angstrom scale

Structural and compositional studies of nanomaterials of technological importance have been carried out using advanced electron microscopy methods, including aberration-corrected transmission electron microscopy (AC-TEM), AC-high angle annular dark field scanning TEM (AC-HAADF-STEM), AC-energy filtered TEM, electron-stimulated energy dispersive spectroscopy in the AC-(S)TEM and high-resolution TEM (HRTEM) with scanning tunneling microscopy (STM) holder. The AC-EM data reveal improvements in resolution and minimization in image delocalization. A JEOL 2200FS double-AC field emission gun TEM/STEM operating at 200 kV in the Nanocentre at the University of York has been used to image single metal atoms on crystalline supports in catalysts, grain boundaries in nanotwinned metals, and nanostructures of tetrapods. Joule heating studies using HRTEM integrated with an STM holder reveal in situ crystallization and edge reconstruction in graphene. Real-time in situ AC-HAADF-STEM studies at elevated temperatures are described. Dynamic in-column energy filtering in an AC environment provides an integral new approach to perform dynamic in situ studies with aberration correction. The new results presented here open up striking new opportunities for atomic scale studies of nanomaterials and indicate future development directions.

New Flexible Toolbox for Nanomechanical Measurements with Extreme Precision and at Very High Frequencies

We show that the principally two-dimensional (2D) scanning tunneling microscope (STM) can be used for imaging of 1D micrometer high free-standing nanowires. We can then determine nanowire megahertz resonance frequencies, image their top-view 2D resonance shapes, and investigate axial stress on the nanoscale. Importantly, we demonstrate the extreme sensitivity of electron tunneling even at very high frequencies by measuring resonances at hundreds of megahertz with a precision far below the angstrom scale.

Atomistic study of the thermodynamic equilibrium of nano-sized helium cavities in βSiC

The estimation of the number of inert gas atoms contained at equilibrium in microscale bubbles in a solid usually relies on a well-known formula equilibrating the internal pressure of He to the surface energy of the bubble. This approach evidences a strong variation with temperature of He content for a given bubble. At the opposite, at the Angstrom scale, ab initio calculations for He contained in vacancy assemblies neglect temperature effects. In this work, empirical potential molecular dynamics simulations are used to study, in the case of helium inserted in cubic silicon carbide, the variation of the He content of sub-nanoscale cavities with temperature. To do so free energy for He atoms inserted in cavities made of a few vacancies (up to 29) are calculated. One then evidences the existence of a sub-surface segregation in interstitial sites close to the surface of the cavity. The variation of the He content with temperature is observed to be negligible at the nanoscale, thus validating the ab initio approach.

TRNA Stabilization by Modified Nucleotides

Post-transcriptional ribonucleotide modification is a phenomenon best studied in tRNA, where it occurs most frequently and in great chemical diversity. This paper reviews the intrinsic network of modifications in the structural core of the tRNA, which governs structural flexibility and rigidity to fine-tune the molecule to peak performance and to regulate its steady-state level. Structural effects of RNA modifications range from nanometer-scale rearrangements to subtle restrictions of conformational space on the angstrom scale. Structural stabilization resulting from nucleotide modification results in increased thermal stability and translates into protection against unspecific degradation by bases and nucleases. Several mechanisms of specific degradation of hypomodified tRNA, which were only recently discovered, provide a link between structural and metabolic stability.

Deriving principles of microbiology by multiscaling laws of molecular physics

It has long been an objective of the physical sciences to derive principles of biology from the laws of physics. At the angstrom scale for processes evolving on timescales of 10(-14) s, many systems can be characterized in terms of atomic vibrations and collisions. In contrast, biological systems display dramatic transformations including self-assembly and reorganization from one cell phenotype to another as the microenvironment changes. We have developed a framework for understanding the emergence of living systems from the underlying atomic chaos.

Insights in High-Temperature Superconductivity from the Study of Films and Heterostructures Synthesized by Molecular Beam Epitaxy

Using molecular beam epitaxy, we synthesize atomically smooth thin films, multilayers and superlattices of cuprate high-temperature superconductors (HTS). Such heterostructures enable novel experiments that probe the basic physics of HTS. For example, we have established that HTS and antiferromagnetic phases separate on Angstrom scale, while the pseudo-gap state apparently mixes with HTS over an anomalously large length scale (“Giant Proximity Effect”). Here, we briefly review our most recent experiments on such films and superlattices. The new results include an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations and the discovery of interface HTS.

Design and performance of a practical variable-temperature scanning tunneling potentiometry system

We have constructed a scanning tunneling potentiometry system capable of simultaneously mapping the transport-related electrochemical potential of a biased sample along with its surface topography. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit--the Johnson noise of the scanning tunneling microscope (STM) tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining angstrom scale STM imaging, all at scan sizes of up to 15 microm. A millimeter-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. By performing studies of several model systems, we discuss the implications of various types of surface morphology for potentiometric measurements.

Carbon-13 Cross-Polarization Magic-Angle-Spinning Nuclear Magnetic Resonance Investigation of the Interactions between Maleic Anhydride Grafted Polypropylene and Wood Polymers

The chemical interactions between maleic anhydride grafted polypropylene (MAPP) and wood were studied with solid-state carbon-13 cross-polarization magic-angle-spinning nuclear magnetic resonance ((13)C CPMAS NMR) spectroscopy. MAPP was synthesized with 100% (13)C enrichment at the C(1) and C(4) carbons to allow detection of the [1,4-(13)C(2)]MAPP functional groups and was melt blended with cellulose, lignin, and maple wood. In the cellulose/MAPP blend, changes in (13)C CPMAS NMR corrected signal intensities for the anhydride and dicarboxylic maleic acid functionalities suggested that esterification may have occurred predominantly from the more numerous diacid carbons. A single proton longitudinal relaxation in the rotating frame, (H)T(1rho), for the MAPP and the cellulose carbons in the blend suggested that they were spin coupled, i.e., homogeneous on a 10-200 Angstrom scale. Esterification was also suggested in the lignin/MAPP blend. Furthermore, the more significant changes in the intensities of the carbonyl signals and (H)T(1rho) values suggested that lignin may be more reactive to MAPP than cellulose. Finally, when maple was melt blended with MAPP, the same trends in the (13)C CP-MAS NMR spectra and (H)T(1rho) behavior were observed as when MAPP was blended with cellulose or lignin. This study therefore clarifies that during melt compounding of wood with MAPP, esterification occurs with wood polymers, preferentially with lignin. Understanding the interactions of MAPP with wood is of significance for the development of natural-fiber-reinforced thermoplastic composites.

Amplifying a Tiny Optical Effect

How do you measure a transverse shift of a light beam to within a nanometer? Recently, physicists predicted (1) that light could experience such a shift similar to what happens to electrical currents in semiconductors through the spin Hall effect (2–4). On page 787 of this issue, Hosten and Kwiat (5) use “weak measurement,” a controversial procedure from the foundations of quantum mechanics, to amplify this spin Hall effect in light (SHEL) rather than detecting it directly. In their experiment, they boost the tiny shift by a factor of 10,000, detecting it for the first time and characterizing it at the angstrom scale. This realizes one of the long-standing promises of weak measurement and demonstrates its potential in precision measurements.

Control of Interfacial Structure for Granular Type Perpendicular Magnetic Recording Media

For realizing perpendicular magnetic recording media (PRM) for hard disk drive (HDD), precisely controlled fabrication technology with angstrom scale according to the required properties is essential from material, processes, and physical view point. PRM presently consist of three functional parts; a soft magnetic underlayer (SUL), a nonmagnetic intermediate layer, and a recording layer (RL). The control of domain structure through interlayer coupling induced by RKKY-like interaction in SUL and narrower size distribution of the magnetic particles with magnetically decoupling in recording layer are indispensable for advanced PRM with high signal to noise ratio and thermal stability. In this paper, structure and magnetic properties for SUL and RL in a real fabricated PRM is discussed in connection with sputtering process parameters and also target materials.

Preparation of heterogeneous catalysts

The preparation of heterogeneous catalysts has been for many years a dynamic field of sub-nanotechnology and remains so nowadays. The approach to preparation must be examined in function of the specific demands concerning (i) activity and (ii) selectivity, that both depend on the arrangement of atoms at a scale smaller than 0.02 nm. Adequate access of reactants to the surface must be provided. Most catalysts are used in the form of pellets or cylinders obtained by pressing, extrusion or other techniques. This implies a control of texture at dimension scales extending from a fraction of a nanometer to several millimetres (and sometimes more). A third demand (iii) is resistance to ageing. In particular, stability at relatively high temperatures is necessary. The strategy adopted in the majority of cases is to start from a material that is homogeneous in composition at the Angstrom scale, generally a liquid or a solid of complex composition, frequently amorphous. A general objective is to locate the different constituting atoms at precise positions. The main difficulty is to transform the starting precursor into a highly porous solid without segregation of different elements that would produce tiny parts with different properties. The specific approach to catalyst preparation is based on the general concepts used for controlling the reactivity of solids. Typical methods of general use will be examined. Chemical bonds of practically any kind can retain the elements constituting the future catalyst at the position they have in the precursor. The so-called 'citrate process' and its variants are of wide application. More elaborate approaches start from molecules or polymers associating the necessary elements.

Surface-hydrophilic and protein-resistant silicone elastomers prepared by hydrosilylation of vinyl poly(ethylene glycol) on hydrosilanes-poly(dimethylsiloxane) surfaces

Poly(ethylene glycol) (PEG) was grafted on the hydrophobic poly(dimethylsiloxane) (PDMS) surface as a hydrophilic outmost monolayer for potential applications such as biomaterials, microfluidics, and anti-fouling coatings. A two component sylgard 184 PDMS (part A of poly(hydrogen methyl siloxane) (PMHS) and part B of poly(methyl vinyl siloxane) (PMVS)) was vulcanized in an off-ratio of, A/B > 1/10, where excess Si–H species exist in the elastomer. An allyl PEG took the hydrosilylation reaction with the surface Si–H groups, catalyzed by the Speier's or Karstedt's catalyst, and resulted a hydrophilic and anti-fouling surface. Atomic Force Microscopy (AFM) observations revealed a well uniform surface with a surface height variation at angstrom scale. Bovine Serum (BS), Bovine Serum Albumin (BSA), Lysozyme (Lys), and Rb IgG/FITC were used to evaluate the protein adsorption on PEG-coated PDMS surface by means of the well-established ATR-FTIR and fluorescence scanner. Results indicated that the PEG monolayer was efficient in reducing the adsorption of proteins.

Combining Atomic Layer Deposition with a Template-Assisted Approach To Fabricate Size-Reduced Nanowire Arrays on Substrates and Their Electrochemical Characterization

We report a combinational method to fabricate well-aligned size-reduced gold nanowire (Au NW) arrays on a Si substrate over large areas (>1.5 cm2). In this method, we employ a SiO2 atomic layer deposition (ALD) technique to reduce the pores of a porous anodic alumina (PAA) template which serves as a template for the electrodeposition of Au NW arrays and is directly integrated on the Si substrate. Unlike conventional method that simultaneously reduces the pore size and the interpore spacing by decreasing the applied potential during PAA anodization, our method allows for independently tuning these parameters. By using the ALD-reduced PAA template, we can fabricate the size-reduced Au NW arrays directly on the Si substrate with the average diameter reduced from ∼79 to ∼33 nm while their nanowire density and interwire spacing remain constant. The ALD technique enables the fine-tuning of the pore size or the nanowire diameter at an angstrom scale. Electrochemical characterization of the size-reduced Au NW arrays as nanoelectrodes is performed. The double-layer charging current (noise of the nanoelectrodes) decreases with the reduction of the nanowire diameter. Our method could be used to fabricate nanowire arrays with large spacing and small diameters via high voltage anodization and subsequent ALD reduction on the PAA template. This type of nanowire arrays might have potential applications in electrochemical and field-emission devices.

Novel, uniform nanostructured catalytic membranes

Nanostructured membrane structures have been fabricated by a combination of anodic aluminum oxidation (AAO) and atomic layer deposition (ALD) for use as platforms for the synthesis of highly uniform heterogeneous catalysts. The ALD method makes it possible to control pore diameters on the Angstrom scale even when the overall pore diameter is 10’s to 100’s of nanometers. AAO membranes imbedded in an aluminum sealing ring have been tested for flow properties and found to follow Knudsen diffusion behavior. Vanadia-coated membranes have been tested for the catalytic oxidative dehydrogenation of cyclohexane and show improved selectivity at the same conversion compared to conventional powdered alumina supported vanadia catalysts.

Spectroscopic study on the zinc-contaminated soils for the determination of zinc speciation

The purpose of this paper reported the zinc species in the highly contaminated soils from metallurgical area around Erh-Jen River in the southern of Taiwan. FTIR and XPS were used to investigate the zinc species in the contaminated soils. Through a FTIR analysis, appreciable of zinc bound by organic matter was found and their bonding structure consisted of antisymmetric and symmetric stretchings, Zn–HS sym and Zn–HS asym. With XPS analysis, the Angstrom scale depth scan was surveyed for investigation the zinc speciation. No signal of zinc was detected in the depth of 900 Å for the larger particle contaminated soils whereas the detectable signal of zinc was determined in the XPS experiment. With further regression and fitting results, the major zinc species presented in the surface of larger and fine particle contaminated soils consisted of reductive and oxidative zinc species. In the deeper depth of contaminated soils, an inverse spinel zinc ferrite was found in the case of larger particle soil. No inverse spinel zinc ferrite was detected in the case of fine particle soil and could be attributed to the relatively small particle size.

Nonequilibrium state of self-organized protein nanostructures

Early experiments (1988–2004) on drying out an open (far from equilibrium) colloid protein-water system in vitro at a sufficiently high rate of water evaporation allowed us to reveal for the first time the nonequilibrium state of protein during its self-organization. Thus, an experimental model of protein in vitro, which is to some extent reminiscent of its behavior in vivo, is realized. Based on these findings, we discuss the role of the nonequilibrium liquid-crystal state of protein at its self-organization in the living organism. The emphasis is on the information content of protein and phase transitions in it, as well as on the properties of the aqueous adenosine triphosphate(ATP)-adenosine diphosphate (ADP) system with regard to the rate of water removal. A hypothesis is put forward that the ATP-ADP system serves to accomplish a special mechanism of vital importance providing cyclic self-organization of protein in the high-energy state. It is hoped that an in-depth study of this state will form the basis for further advances in the science of protein not only in the equilibrium state (on the angstrom scale) but also in the nonequilibrium state from the nano-to macroscale.

An Angstrom Scale Interaction between Plasma Membrane ATP-Gated P2X2and α4β2Nicotinic Channels Measured with Fluorescence Resonance Energy Transfer and Total Internal Reflection Fluorescence Microscopy

Structurally distinct nicotinic and P2X channels interact functionally, such that coactivation results in cross-inhibition of one or both channel types. It is hypothesized, but not yet proven, that nicotinic and P2X channels interact at the plasma membrane. Here, we show that plasma membrane alpha4beta2 nicotinic and P2X2 channels form a molecular scale partnership and also influence each other when coactivated, resulting in nonadditive cross-inhibitory responses. Total internal reflection fluorescence and fluorescence resonance energy transfer microscopy between fluorescently labeled P2X2 and alpha4beta2 nicotinic channels demonstrated close spatial arrangement of the channels in human embryonic kidney cells and in hippocampal neuron membranes. The data suggest that P2X2 and alpha4beta2 channels may form a dimer, with the channels approximately 80 A apart. The measurements also show that P2X2 subunits interact specifically and robustly with the beta2 subunits in alpha4beta2 channels. The data provide direct evidence for the close spatial apposition of full-length P2X2 and alpha4beta2 channels within 100 nm of the plasma membrane of living cells.