Electron Diffraction Methods Research Articles

Sensitive Electrochemical Sensing Properties for Cyanide Detection Using Polyaniline/Cu-Vanadate Nanobelt-modified Electrode

Background: Cyanide is a toxic anion and may be discarded into the water environment, which is a serious threat to human beings and the environment. Hence, it is essential to explore a facile, sensitive method for cyanide detection. Polyaniline/Cu vanadate nanobelts serve as electrode materials for sensitive cyanide determination. Methods: Polyaniline/Cu vanadate nanobelts were obtained by a simple route using polyaniline, Cu vanadate nanobelts. The polyaniline/Cu vanadate nanobelts were measured via electron microscopy, diffraction, infrared spectrum, and electrochemical methods. Results: Amorphous polyaniline nanoparticles with a particle size of about 100 nm were attached firmly to the surface of Cu vanadate nanobelts. Electrochemical sensing properties for cyanide detection were analyzed using a cyclic voltammetry technique using the nanobelts-modified electrode. The cyclic voltammograms (CV) peaks centered at +0.64 V and +0.54 V were observed using the polyaniline/Cu vanadate nanobelts in 0.1 M KCl solution with 2 mM cyanide. The proposed composite nanobelt-modified electrode possessed the detection range and detection limit of 0.001-2 mM and 0.22 μM, respectively. Conclusion: Polyaniline greatly enhances the electro-catalytic performance of the Cu vanadate nanobelt-modified electrode for cyanide detection.

Yttrium iron garnet single-crystal particles - a simple and effective synthesis

Abstract Yttrium iron garnet (YIG) is a ferrimagnetic material which found applications in magnetics, electronics and optics. For those applications, a monocrystalline structure is often required. Although effective methods to grow large YIG single crystals exist, fabricating such structures in a powder form can be challenging. Here, we show a simple procedure to obtain large quantities of monocrystalline Y3Fe5O12 particles based on the precipitation synthesis. The average size of the single crystals was evaluated to be 149(6) nm. The morphology of the particles was analysed using SEM, TEM, DLS and nitrogen adsorption techniques. The material was tested for its structural properties with the use of XRD and electron diffraction methods. The chemical composition was investigated using FTIR, EDS and Raman spectroscopy. Finally, the thermal characteristics were analysed using TGA, while magnetic properties were tested with the use of the SQUID magnetometry. The obtained results are in good agreement with the theoretical values.

Gold Tripyrrindione: Redox Chemistry and Reactivity with Dichloromethane.

The identification of ligands that stabilize Au(III) centers has led to the isolation of complexes for applications in catalysis, gold-based therapeutics, and functional materials. Herein, we report the coordination of gold by tripyrrin-1,14-dione, a linear tripyrrole with the scaffold of naturally occurring metabolites of porphyrin-based protein cofactors (e.g., heme). Tripyrrindione H3TD2 binds Au(III) as a trianionic tridentate ligand to form square planar complex [Au(TD2)(H2O)], which features an adventitious aqua ligand. Two reversible ligand-based oxidations of this complex allow access to the other known redox states of the tripyrrindione framework. Conversely, (spectro)electrochemical measurements and DFT analysis indicate that the reduction of the complex is likely metal-based. The chemical reduction of [Au(TD2)(H2O)] leads to a reactive species that utilizes dichloromethane in the formation of a cyclometalated organo-Au(III) complex. Both the aqua and the organometallic Au(III) complexes were characterized in the solid state by microcrystal electron diffraction (MicroED) methods, which were critical for the analysis of the microcrystalline sample of the organo-gold species. Overall, this study illustrates the synthesis of Au(III) tripyrrindione as well as its redox profile and reactivity leading to gold alkylation chemistry.

Topochemical Polymerization at Diacetylene Metal-Organic Framework Thin Films for Tuning Nonlinear Optics.

Developing the topochemical polymerization of metal-organic frameworks (MOFs) is of pronounced significance for expanding their functionalities but is still a challenge on third-order nonlinear optics (NLO). Here, we report diacetylene MOF (CAS-1-3) films prepared using a stepwise deposition method and film structural transformation approach, featuring dynamic structural diversity. The MOF structures were determined by the three-dimensional electron diffraction (3D ED) method from nanocrystals collected from the films, which provides a reliable strategy for determining the precise structure of unknown MOF films. We demonstrate the well-aligned diacetylene groups in the MOFs can promote topological polymerization to produce a highly conjugated system under thermal stimulation. As a result, the three MOF films have distinct NLO properties: the CAS-1 film exhibits saturable absorption (SA) while CAS-2 and CAS-3 films exhibit reverse saturable absorption (RSA). Interestingly, due to the topochemical polymerization of the MOF films, a transition from SA to RSA response was observed with increasing temperatures, and the optical limiting effect was significantly enhanced (∼46 times). This study provides a new strategy for preparing NLO materials and thermally regulation of nonlinear optics.

Study of Crystallography and Reciprocal Space of Higher Oxides of Lanthanides Using Electron and Neutron Diffraction

Abstract: This study explains uses electron and neutron diffraction techniques to study the crystallography and reciprocal space of higher oxides of lanthanides. The significance of crystallography in comprehending the geometric configuration and bonding of atoms in solids is discussed at the outset of the study. The comprehensive analysis of the crystal structures using accelerated electrons and neutrons highlights the tremendous penetration power of these particles. While neutron diffraction is concerned with plane incidence waves and their scattered counterparts, electron diffraction is concerned with electron generation pulsed by a laser.Important findings show how experimental data may be used to validate Bragg's equation and show how scattering angles, interplanar distance, and order of wavelength are related. To display the relationship between electron energy and electron radiation per electron volt, energy distribution curves are displayed. Additionally, several crystal systems, such as hexagonal, monoclinic, and cubic face-centered structures, are revealed by structural investigation of higher oxides of lanthanides, such as terbium dioxide (Tb2O3).The talk emphasizes how, in contrast to other elements in the series, lanthanides have special qualities that enable them to produce higher oxides with oxidation states greater than +3. The outcomes highlights the improved precision and in-depth structural insights that come from combining electron and neutron diffraction methods. This opens the door for more studies in the crystallography of complicated materials in the future.

Experimental molecular structures in the gas phase at the upper size limit: The case of Si6Tip6.

Currently, the largest (ramax = 19.9Å) and by far the most complicated (234 atoms, C1 symmetry, 696 independent geometrical parameters, and 27 261 interatomic terms) experimental molecular structure of a cage-type Si6Tip6 (Tip = 2,4,6-iPr3C6H2) isomer has been investigated in the gas phase by the electron diffraction method (Tav = 645K) supplemented with theoretical simulations. A detailed analysis of the current possibilities for experimentally investigating large molecular structures is performed. A series of density functional theory approximations and the role of dispersion interactions have been benchmarked using the obtained data. Based on the refined geometry of Si6Tip6, various quantum-chemical methods have been applied for the investigation of the electronic structure of its Si6 core. In particular, natural bond orbital, quantum theory of atoms in molecules, interacting quantum atoms, fractional occupation number weighted density, and complete active space self-consistent field (CASSCF) methods were utilized. The diradical character of the molecule has been assessed by the UHF and CASSCF approximations. The problem of bonding between the hemispheroidal silicon atoms has been investigated.

Ultrafast Picometer-Resolved Molecular Structure Imaging by Laser-Induced High-Order Harmonics.

Real-time visualization of molecular transformations is a captivating yet challenging frontier of ultrafast optical science and physical chemistry. While ultrafast x-ray and electron diffraction methods can achieve the needed subangstrom spatial resolution, their temporal resolution is still limited to hundreds of femtoseconds, much longer than the few femtoseconds required to probe real-time molecular dynamics. Here, we show that high-order harmonics generated by intense femtosecond lasers can be used to image molecules with few-ten-attosecond temporal resolution and few-picometer spatial resolution. This is achieved by exploiting the sensitive dependence of molecular recombination dipole moment to the geometry of the molecule at the time of harmonic emission. In a proof-of-principle experiment, we have applied this high-harmonic structure imaging (HHSI) method to monitor the structural rearrangement in NH_{3}, ND_{3}, and N_{2} from one to a few femtoseconds after the molecule is ionized by an intense laser. Our findings establish HHSI as an effective approach to resolve molecular dynamics with unprecedented spatiotemporal resolution, which can be extended to trace photochemical reactions in the future.

Structural, spectroscopic and improved photoelectrochemical properties of TiO2/C composites with anatase/brookite matrix, prepared by air-thermolysis of microspherical titanium glycolate

X-ray powder diffraction, Raman spectroscopy, HRTEM, electron diffraction and differential thermal analysis methods were used to study structural and spectroscopic properties and thermal stability of the products obtained by air-thermolysis of Ti-glycolate in the temperature range 300–450°С. TiO2/C composites were obtained, which have anatase/brookite matrix with a variable degree of crystallinity and contain different contents of brookite and free polymeric-like carbon with COO− groups. It was found that the residual content of carbonaceous component and the intensity of exothermal decomposition of Ti-glycolate have an effect on the formation of brookite-rich TiO2 matrix. Correlations between the phase composition and the free carbon content suggest that during crystallization brookite/carbon nanoparticles are more stable than anatase/carbon nanoparticles. PEC tests demonstrated that the composite photoanode, which has the greatest degree of crystallinity, the optimal carbon content and is most enriched with brookite, exhibits the greatest incident photon-to-current conversion efficiency (IPCE), and its IPCE peak value is twice as great as the IPCE peak value for Degussa P25. The increased IPCE value is associated with the preferable formation of carbon/brookite/anatase heterostructures. The carbon component has an optical gap of approx. 1.1 eV, and at the optimal contents it ensures efficient photogeneration and transfer of electrons into the conduction band of brookite and then into the conduction band of anatase. HRTEM study demonstrated the formation of such heterostructure with anatase/brookite heterojunction.

Radiation-enhanced crystallization of amorphous Nb2O5 films according to TEM with in situ video recording

Amorphous films are formed on substrates at room temperature in the process of anodic oxidation of niobium foil. The studies were carried out using methods of electron diffraction and “in situ” transmission electron microscopy (TEM) with video recording of structural changes. It was found that electron beam irradiation of the film with a dose rate (4–7)·104 e−/Å2·s inside the column of the electron microscope causes its layer polymorphous crystallization (LPC) with the formation of Nb2O5 crystals with hexagonal lattice. The dimensionless parameter of the relative crystallization length δ0≈ 5000 − 7000. The dependence on time of the crystal diameter is described by a power function with exponents of 1.55, 1.1 and 1.3. According to this the dependence of the fraction of the crystalline phase on time is described by a power function with exponents of 3.1, 2.2 and 2.6. This non-quadratic nature is explained with the formation of a domain superstructure in the low-temperature modification of α-Nb2O5 and phenomenon of polyamorphism in amorphous films.

Comprehensive Study of Equilibrium Structure of Trans-Azobenzene: Gas Electron Diffraction and Quantum Chemical Calculations

The geometrical re parameters of trans-azobenzene (E-AB) free molecule were refined by gas electron diffraction (GED) method using available experimental data obtained previously by S. Konaka and coworkers. Structural analysis was carried out by various techniques. First of all, these included the widely used molecular orbital constrained gas electron diffraction method and regularization method. The results of the refinements using different models were also compared—a semirigid model, three variants of one-dimensional dynamic models, and a two-dimensional pseudoconformer model. Several descriptions have been used due to the fact that E-AB has a shallow potential energy surface along the rotation coordinates of phenyl groups. Despite this, it turned out that the semirigid model is suitable for use for E-AB and allows good agreement with experimental data to be achieved. According to the results of GED structural analysis, coupled with the results of DLPNO-CCSD(T0) calculations, E-AB has a planar structure. Based only on GED data, it is impossible to unambiguously determine the rotational angle of the phenyl group due to the facts that (i) with rotation over a wide range of angles, the bonded distances in the molecule change insignificantly and (ii) potential function in a structural analysis within a dynamic model is not determined with the necessary accuracy. This work also examines the sensitivity of the GED method to structural changes caused by trans-cis isomerization. The paper also analyzes the applicability of different variants of density functional theory (DFT) calculations in GED structural analysis using E-AB as an example. There are not enough similar methodological works in the literature. This experimental and methodological information is especially important and relevant for planning and implementing GED experiments and corresponding processing of the results for azobenzene derivatives, in which the conformer and isomeric diversity are even more complicated due to the presence of different substituents.

Crystal structures of two new high-pressure oxynitrides with composition SnGe4N4O4, from single-crystal electron diffraction.

SnGe4N4O4 was synthesized at high pressure (16 and 20 GPa) and high temperature (1200 and 1500°C) in a large-volume press. Powder X-ray diffraction experiments using synchrotron radiation indicate that the derived samples are mixtures of known and unknown phases. However, the powder X-ray diffraction patterns are not sufficient for structural characterization. Transmission electron microscopy studies reveal crystals of several hundreds of nanometres in size with different chemical composition. Among them, crystals of a previously unknown phase with stoichiometry SnGe4N4O4 were detected and investigated using automated diffraction tomography (ADT), a three-dimensional electron diffraction method. Via ADT, the crystal structure could be determined from single nanocrystals in space group P63mc, exhibiting a nolanite-type structure. This was confirmed by density functional theory calculations and atomic resolution scanning transmission electron microscopy images. In one of the syntheses runs a rhombohedral 6R polytype of SnGe4N4O4 could be found together with the nolanite-type SnGe4N4O4. The structure of this polymorph was solved as well using ADT.

Absolute structure determination of Berkecoumarin by X-ray and electron diffraction.

X-ray and electron diffraction methods independently identify the S-enantiomer of Berkecoumarin [systematic name: (S)-8-hydroxy-3-(2-hydroxypropyl)-6-methoxy-2H-chromen-2-one]. Isolated from Berkeley Pit Lake Penicillium sp., Berkecoumarin is a natural product with a light-atom composition (C13H14O5) that challenges in-house absolute structure determination by anomalous scattering. This study further demonstrates the utility of dynamical refinement of electron-diffraction data for absolute structure determination.

Molecular structure of 2,5,9,12-tetraethylbenzo[f]quinolino[3,4-b][1,7]naphthyridine-6,8(5H,9H)-dione in gas phase from electron diffraction method supported by theoretical calculations

The semi-experimental molecular structure of 2,5,9,12-tetraethylbenzo[f]quinolino[3,4-b][1,7]naphthyridine-6,8(5H,9H)-dione has been determined using the gas electron diffraction method in combination with the quantum chemical calculations. It was compared to X-ray diffraction data known from literature. Close to planar configuration of the frame is found to be undistorted.Conformational analysis revealed a set of isoenergetic conformers of the compound, the intramolecular interactions were characterized with the use of AIM and NCI approaches. Mean vibrational amplitudes (uij,h1) and anharmonic vibrational corrections (rij,e-rij,a) were calculated for the experimental temperature of 606 K using the quadratic and cubic force constant fields.

Facile Synthesis of Stable Nanosized Silver Clusters in Plasma Discharge Under Ultrasonic Cavitation

This work is devoted to the study of plasma-chemical processes determined by the combination of the effect of thermally nonequilibrium, low-temperature plasma and intensive ultrasonic vibrations in the regime of intensive cavitation on liquid-phase media. This method for the realization of plasma-chemical transformations has been proven to be of significant interest and to have advantages for the creation of new nano-sized materials with special properties because it allows for varying the electrophysical and acoustic characteristics of the process when carrying out plasma-chemical reactions and fusion reactions. In this work, a novel facile technique for the synthesis of nanosized silver clusters in plasma discharge under ultrasonic cavitation is reported. Such a type of plasma involves the simultaneous effect of high-intensity cavitation and steady electric discharge in a liquid phase between electrodes of desired material. As a result, stable tiny silver nanoclusters with around a 1-nm size and a relatively narrow particle size distribution were obtained using toluene as a liquid medium. The nanoclusters were characterized with dynamic light scattering, transmission electron microscopy, electron diffraction, and optical methods. The results confirmed the formation of nanoclusters with an absorbance peak around 300 nm and the absence of 400-nm peaks typical for silver nanoparticles. Fluorescence tests allowed for establishing the amorphous structure of the synthesized nanoclusters occupying the intermediate position between few-atom nanoclusters and nanoparticles. The nanoclusters obtained were proven to be stable for more than 3 months. The experiments also revealed the possibility of performing high-temperature plasma-chemical reactions that can be applied in fusion technology.

Nanoscale Energy Transport Dynamics across Nonbonded Solid-Molecule Interfaces and in Molecular Thin Films.

Thermal conductance across a solid-solid interface requires an atomic- or molecular-level understanding, especially when a system is in a non-equilibrium state and/or consists of nanosized materials with prominent differences in structures, properties, and vibrational behaviors. Here, we report the lattice dynamics of graphite-supported molecular thin films of ethanol, whose layers exhibit in-plane hydrogen-bonded chains and out-of-plane van der Waals stacking with clear structural anisotropy. The direct structure-probing method of ultrafast electron diffraction reveals a surprising temperature difference of more than 400 K at pico- to sub-nanosecond times across the graphite-ethanol interface, yet the temporal behavior signifies a reasonably large thermal boundary conductance. This apparent conflict in a non-equilibrium condition can be resolved by considering the coupling of out-of-plane motions, instead of the commonly used temperature-based model, at transient times for energy transport across the interface separated by van der Waals interactions with mismatched unit sizes and no strong bonds. The importance of spatiotemporally resolved structural dynamics at the atomic or molecular level is emphasized.

The Equilibrium Molecular Structure of Cyclic (Alkyl)(Amino) Carbene Copper(I) Chloride via Gas-Phase Electron Diffraction and Quantum Chemical Calculations.

Copper-centered carbene-metal-halides (CMHs) with cyclic (alkyl)(amino) carbenes (CAACs) are bright phosphorescent emitters and key precursors in the synthesis of the highly promising class of the materials carbene-metal-amides (CMAs) operating via thermally activated delayed fluorescence (TADF). Aiming to reveal the molecular geometry for CMH phosphors in the absence of the intermolecular contacts, we report here the equilibrium molecular structure of the (CAAC)Cu(I)Cl (1) molecule in the gas-phase. We demonstrate that linear geometry around a copper atom shows no distortions in the ground state. The structure of complex 1 has been determined using the electron diffraction method, supported by quantum chemical calculations with RI-MP2/def2-QZVPP level of theory and compared with the crystal structure determined by X-ray diffraction analysis. Mean vibrational amplitudes, uij,h1, and anharmonic vibrational corrections (rij,e • rij,a) were calculated for experimental temperature T = 20 °C, using quadratic and cubic force constants, respectively. The quantum theory of atoms in molecules (QTAIM) and natural bond order (NBO) analysis of wave function at MN15/def2TZVP level of theory revealed two Cu…H, three H…H, and one three-center H…H…H bond paths with bond critical points. NBO analysis also revealed three-center, four-electron hyperbonds, (3c4e), [π(N-C) nπ(Cu) ↔ nπ(N) π(N-Cu)], or [N-C: Cu ↔ N: C-Cu] and nπ(Cu) → π(C-N)* hyperconjugation, that is the delocalization of the lone electron pair of Cu atom into the antibonding orbital of C-N bond.

Carbon nanoparticle identification using transmission electron microscopy methods in biological samples

Carbon nanoparticles are a common type of nanoparticles, the identification of which in biological samples is associated with great difficulties. It is demonstrated that the use of standard transmission electron microscopy in combination with the electron diffraction method is a reliable and relevant tool for the carbon nanoparticles identification in biological samples.

Preparation and study of B and P doped SiNTs

The unique properties of silicon nanotubes (SiNTs) are expected to provide them with a very wide range of application potential in nanoelectronic devices, lithium-ion batteries, sensors, field-effect transistors, magnetic nanodevices, hydrogen reservoirs, optoelectronic devices, field emission display devices, and quantum computers, and they are a new one-dimensional nanomaterial with a wide range of applications in the future. Although researchers have already prepared SiNTs in the laboratory, there are not many research reports on SiNTs, especially the preparation of B and P doped SiNTs and analysis based on spectroscopic techniques. Our research group used silicon sources (SiO2 and Si) that had not been previously reported or catalyzed by the rare earth element lanthanum (La). The optimal experimental conditions for the preparation of SiNTs, as well as the doping preparation and study of B and P, were explored by thermal evaporation. Finally, SEM, Raman spectroscopy, selected area electron diffraction, HRTEM, XRD, PL spectroscopy, and other characterization methods were performed on the experimental samples. The experimental results show that 1280 °C was the best experimental temperature for the preparation of SiNTs. Under experimental conditions of 1280 °C, doping of B favored the synthesis of silicon nanowires and SiNTs, and the number of products generated was from least to most: no added B2O3 < 0.1 g B2O3 < 0.2 g B2O3 < 0.3 g B2O3 < 0.4 g B2O3. Under the experimental conditions of 1280 °C, when the amount of doped B2O3 is large (2.2 g), a “needle” structure product is generated. Under experimental conditions of 1400 °C, when the ratio of doped P to the original material is 1:9, a new material that has not been previously reported is generated. Through relevant research and the findings of this paper, it is hoped that it can be helpful for the future research and application of SiNTs.

Thermal Instability of Gold Thin Films

The disintegration of a continuous metallic thin film leads to the formation of isolated islands, which can be used for the preparation of plasmonic structures. The transformation mechanism is driven by a thermally accelerated diffusion that leads to the minimalization of surface free energy in the system. In this paper, we report the results of our study on the disintegration of gold thin film and the formation of nanoislands on silicon substrates, both pure and with native silicon dioxide film. To study the processes leading to the formation of gold nanostructures and to investigate the effect of the oxide layer on silicon diffusion, metallic film with a thickness of 3 nm was deposited by molecular beam epitaxy (MBE) technique on both pure and oxidized silicon substrates. Transformation of the thin film was observed by low-energy electron microscopy (LEEM) and a scanning electron microscope (SEM), while the nanostructures formed were observed by atomic force microscope (AFM) method. Structural investigations were performed by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS) methods. Our experiments confirmed a strong correlation between the formation of nanoislands and the presence of native oxide on silicon substrates.

Effect of a phosphorus modifier on the behavior of palladium catalysts in direct synthesis of hydrogen peroxide

The behavior of palladium-phosphorus catalysts deposited on a Na-ZSM-5 zeolite support, in the direct synthesis of hydrogen peroxide under mild conditions has been studied. It was found that elemental phosphorus exerts a promoting effect on the activity and selectivity of Pd catalysts for synthesizing H2O2. A direct relationship between the P:Pd ratio (in the range P:Pd = 0: 1.0) and the activity of the catalysts is shown. The influence of phosphorus on the properties of palladium catalysts in side reactions: decomposition and hydrogenation of H2O2 is considered. The chemical and phase composition of Pd-P particles was studied by ICP, HRTEM, electron diffraction, and XRD methods. The modifying effect of phosphorus on the properties of Pd catalysts in the direct synthesis of H2O2 is associated with the formation of solid solutions between palladium and phosphorus, an increase in the dispersion, and the surface roughness of Pd-P particles.