Low Electric Field Gradient Research Articles

Manipulation and diagnosis of femtosecond relativistic electron bunch using terahertz-driven resonators

Using strong electromagnetic fields generated by lasers to interact with electrons for precise diagnosis and manipulation of electron beams represents a recent focal point in accelerator technology. This approach surpasses the limitations of conventional RF technology, such as low electric field gradients and timing jitters, effectively enhancing the accuracy of ultrafast electron beam diagnostics and manipulations. As demands for precision continue to rise, the precise diagnosis of crucial parameters of ultrafast electron beams remains challenging. This study delves into the electromagnetic behavior of THz-driven devices and proposes an all-optical method utilizing single-cycle THz radiation to compress and characterize a 3 MeV electron beam. Particle tracking simulations demonstrate an astonishing compression effect, reducing the bunch length from 54.0 fs to 4.3 fs, and achieving sub-femtosecond bunch length measurement resolution. Moreover, when combined with an orthogonal THz streak camera, this method shows even greater potential in multi-bunch scenarios.

Pseudo-gap in RuGa3: A microscopic point of view

We report a detailed study of the nature of the RuGa3in-gap states by means of precision microscopic methods: nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR), and pump-probe spectroscopy. We observe a pronounced splitting of 69Ga nuclear spin-lattice relaxation curves below ∼40 K and between 70 and 145 K, although the corresponding NQR lines remain narrow over the entire temperature range under study. The slow relaxing component behaves like a typical phonon-induced relaxation way, while the fast relaxing one demonstrates signatures of paramagnetic (below ∼40 K) and activation (between 70 and 145 K) mechanisms. Moreover, additional Ga’ and Ga’’ positions with anomalously low electric field gradient were revealed for the first time for IrIn3-type structure gallides, which stay almost unchanged, at least up to 77 K. The observed microscopic features are accompanied with in-gap states saturation or depleting, which is seen as the resistivity mechanism crossover at ∼180 K and electron localization below 145 K evidenced by pump-probe spectroscopy. Based on our experimental results, we associate this pseudo-gap like behavior with inhomogeneously distributed electronic density defects, which manifest at both micro- (nuclear spin and phonon dynamics) and macroscale (bulk transport properties such as resistivity).

Crystallographic and Computational Characterisation of the Potential PET Tracer 1,4,7‐Triazacyclononane‐1,4,7‐tri(methylenephosphonato)gallium(III)

AbstractThe macrocyclic chelator 1,4,7‐triazacyclononane‐1,4,7‐tri(methylenephosphonic acid) (H6NOTP) has shown significant promise for use in positron emission tomography with the positron‐emitting radionuclide 68Ga3+. We report the X‐ray crystal structure of the neutral complex 1,4,7‐triazacyclononane‐1,4,7‐tri(methylenephosphonato)gallium(III) ([Ga(H3NOTP)]), which crystallised in the centrosymmetric space group P21/n. The coordination geometry of the Ga3+ ion is distorted octahedral with three macrocyclic amine N donor atoms and three singly deprotonated phosphonato O donor atoms. Two discrete enantiomers, Δ(λλλ)‐SSS and Λ(δδδ)‐RRR, are present as a racemate within the unit cell. Intermolecular hydrogen bonds between phosphonic acid groups of adjacent complexes form a two‐dimensional sheet network. Density functional theory (DFT) calculations supported the observation of complexes with low electric field gradient values with slight but significant deviations from ideal octahedral geometry. The DFT calculations were also used to investigate the influence of intermolecular interactions and ligand protonation states on the coordination environment and surface charge distribution.

Ion mobility spectrometer—field asymmetric ion mobility spectrometer-mass spectrometry

Since the development of electrospray ionization (ESI) for ion mobility spectrometry mass spectrometry (IMMS), IMMS have been extensively applied for characterization of gas-phase bio-molecules. Conventional ion mobility spectrometry (IMS), defined as drift tube IMS (DT-IMS), is typically a stacked ring design that utilizes a low electric field gradient. Field asymmetric ion mobility spectrometry (FAIMS) is a newer version of IMS, however, the geometry of the system is significantly different than DT-IMS and data are collected using a much higher electric field. Here we report construction of a novel ambient pressure dual gate DT-IMS coupled with a FAIMS system and then coupled to a quadrupole ion trap mass spectrometer (QITMS) to form a hybrid three-dimensional separation instrument, DT-IMS-FAIMS-QITMS. The DT-IMS was operated at ~3 Townsend (electric field/number density (E/N) or (Td)) and was coupled in series with a FAIMS, operated at ~80 Td. Ions were mobility-selected by the dual gate DT-IMS into the FAIMS and from the FAIMS the ions were detected by the QITMS for as either MS or MSn. The system was evaluated using cocaine as an analytical standard and tested for the application of separating three isomeric tri-peptides: tyrosine-glycine-tryptophan (YGW), tryptophan-glycine-tyrosine (WGY) and tyrosine-tryptophan-glycine (YWG). All three tri-peptides were separated in the DT-IMS dimension and each had one mobility peak. The samples were partially separated in the FAIMS dimension but two conformation peaks were detected for the YWG sample while YGW and WGY produced only one peak. Ion validation was achieved for all three samples using QITMS.

Negative Dielectrophoretic Patterning with Colloidal Particles and Encapsulation into a Hydrogel

Microparticle patterns have been fabricated on a nonconductive glass substrate and a conductive indium tin oxide (ITO) substrate using negative dielectrophoresis (n-DEP). The patterned microparticles on the substrate were immobilized by covalent bonding or embedded into polymer sheets or strings. The patterning device consisted of an ITO interdigitated microband array (IDA) electrode as the template, a glass or ITO substrate, and a polyester film (10-microm thickness) as the spacer. A suspension of 2-microm-diameter polystyrene particles was introduced into the device between the upper IDA and the bottom glass or ITO support. An ac electrical signal (typically 20 Vpp, 3 MHz) was then applied to the IDA, resulting in the formation of line patterns with low electric field gradient regions on the bottom support. When the glass substrate was used as the bottom support, the particles aligned under the microband electrodes of the IDA within 5 s because the aligned areas on the support were regions with the weakest electric field; however, for the ITO support, the particles were directed to the regions under the electrode gap and aligned on the support because these regions had the weakest electric field. The width of the particle lines could be roughly controlled by regulating the initial concentration of the suspended particles. The particles forming the line and grid patterns with single-particle widths were immobilized by using a cross-linking reaction between the amino groups on the aligned particles and N-hydroxysuccinimide-activated ester on the glass substrate activated by succinimidyl 4-(p-maleimidophenyl)-butyrate (SMPB). The patterned particles were also embedded in a photoreactive hydrogel polymer. A prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA) was used as the suspension medium to maintain the particle patterns in the polymerized hydrogel sheet and string following photopolymerization. The hydrogel sheets with particle patterns were fabricated by ultraviolet (UV) irradiation through the ITO-IDA template for 120 s. Hydrogel strings with the aligned particles were fabricated by using a conductive ITO support and a Pt-IDA template. Pt-IDA was used as a template as well as a photomask to block UV transmission. The present procedure affords extremely simple, rapid, and highly reproducible fabrication of particle arrays. The reusability of the template IDA electrode is also a substantial advantage over previous methods.

Dielectrophoresis with application to boiling heat transfer in microgravity. I. Numerical analysis

This article presents a numerical analysis for the use of a dielectrophoretic (DEP) force on vapor bubbles to sustain nucleate boiling heat transfer in space where the gravity-driven buoyancy force is absent. The analytic and numerical solution procedures for the DEP force are outlined for an infinite-plate and a finite-plate electrode geometry, respectively. A simple analysis is presented that describes the limits on the magnitude of the DEP force. A comparison is made between the DEP forces produced near the edges of the finite-plate electrodes (where there is a relatively high-gradient electric field) to the forces produced between the electrodes and away from the edges (where there is a relatively low-gradient electric field). The predicted DEP forces are then used to study the effectiveness of bubble transport for both high and low electric-field gradients in microgravity. To effectively maintain boiling in space with the DEP force, a knowledge of the electric field is required which addresses both the DEP force strength and the DEP force spatial distribution in order to appropriately balance between the short-distance vapor bubble detachment needs and the long-distance bubble transport requirements.

Dielectrophoresis with application to boiling heat transfer in microgravity. II. Experimental investigation

The objective of this paper is to analyze experimentally the feasibility of utilizing the dielectrophoretic (DEP) force to sustain boiling in space where the gravity-driven buoyancy force is absent. First, a bubble trajectory experiment is present to determine the magnitude of the DEP force produced at the edge of two diverging-plate electrodes to the highly nonuniform electric field. The results showed that the DEP forces measured experimentally are equal to those predicted in Part I to within 10%–15%. Second, the bubble detachment diameter and frequency of bubbles generated with a gold-film, single-bubble heater were measured in microgravity so that the masking effect of gravity could be eliminated. In particular, a comparison is made between the DEP forces produced with a relatively high-electric-field gradient at the edge of two flat-plate electrodes to the DEP forces produced with the relatively low electric-field gradient between two diverging-plate electrodes. It was discovered that the bubble detachment diameter and frequency could be reduced to a single curve by plotting the data against effective gravity ratio [g(b,e)] due to the dielectrophoretic forces. In this way, the normalized bubble diameter at the time of breakoff from the heated surface was found to vary inversely as the effective gravity ratio to the 1/2 power.

Tetrachloro- and Tetrabromostibonium(V) Cations: Raman and (19)F, (121)Sb, and (123)Sb NMR Spectroscopic Characterization and X-ray Crystal Structures of SbCl(4)(+)Sb(OTeF(5))(6)(-) and SbBr(4)(+)Sb(OTeF(5))(6)(-).

The stable salts, SbCl(4)(+)Sb(OTeF(5))(6)(-) and SbBr(4)(+)Sb(OTeF(5))(6)(-), have been prepared by oxidation of Sb(OTeF(5))(3) with Cl(2) and Br(2), respectively. The SbBr(4)(+) cation is reported for the first time and is only the second example of a tetrahalostibonium(V) cation. The SbCl(4)(+) cation had been previously characterized as the Sb(2)F(11)(-), Sb(2)Cl(2)F(9)(-), and Sb(2)Cl(0.5)F(10.5)(-) salts. Both Sb(OTeF(5))(6)(-) salts have been characterized in the solid state by low-temperature Raman spectroscopy and X-ray crystallography. Owing to the weakly coordinating nature of the Sb(OTeF(5))(6)(-) anion, both salts are readily soluble in SO(2)ClF and have been characterized in solution by (121)Sb, (123)Sb, and (19)F NMR spectroscopy. The tetrahedral environments around the Sb atoms of the cations result in low electric field gradients at the quadrupolar (121)Sb and (123)Sb nuclei and correspondingly long relaxation times, allowing the first solution NMR characterization of a tetrahalocation of the heavy pnicogens. The following crystal structures are reported: SbCl(4)(+)Sb(OTeF(5))(6)(-), trigonal system, space group P&thremacr;, a = 10.022(1) Å, c = 18.995(4) Å, V = 1652.3(6) Å(3), D(calc) = 3.652 g cm(-)(3), Z = 2, R(1) = 0.0461; SbBr(4)(+)Sb(OTeF(5))(6)(-), trigonal system, space group P&thremacr;, a = 10.206(1) Å, c = 19.297(3) Å, V = 1740.9(5) Å(3), D(calc) = 3.806 g cm(-)(3), Z = 2, R(1) = 0.0425. The crystal structures of both Sb(OTeF(5))(6)(-) salts are similar and reveal considerably weaker interactions between anion and cation than in previously known SbCl(4)(+) salts. Both cations are undistorted tetrahedra with bond lengths of 2.221(3) Å for SbCl(4)(+) and 2.385(2) Å for SbBr(4)(+). The Raman spectra are consistent with undistorted SbX(4)(+) tetrahedra and have been assigned under T(d)() point symmetry. Trends within groups 15 and 17 are noted among the general valence force constants of the PI(4)(+), AsF(4)(+), AsBr(4)(+), AsI(4)(+), SbCl(4)(+) and SbBr(4)(+) cations, which have been calculated for the first time, and the previously determined force constants for NF(4)(+), NCl(4)(+), PF(4)(+), PCl(4)(+), PBr(4)(+), and AsCl(4)(+), which have been recalculated for the P and As cations in the present study. The SbCl(4)(+) salt is stable in SO(2)ClF solution, whereas the SbBr(4)(+) salt decomposes slowly in SO(2)ClF at room temperature and rapidly in the presence of Br(-) ion and in CH(3)CN solution at low temperatures. The major products of the decompositions are SbBr(2)(+)Sb(OTeF(5))(6)(-), as an adduct with CH(3)CN in CH(3)CN solvent, and Br(2).

SQUID-NQR of nitrogen-14 in amino acids and small peptides

We present a technique for the study of nuclear quadrupole resonance of 14N interacting with low electric field gradients as found, for example, in amino acids. A superconducting quantum interference device (SQUID) is used to detect directly small NMR signals via cross relaxation of the 14N polarization to adjacent proton spins, eliminating the need for field cycling. When one nitrogen quadrupolar transition matches the proton Zeeman splitting, the remaining two quadrupolar transitions can be observed by sweeping a saturating rf field through resonance. In addition, signal enhancement by simultaneous excitation of two nitrogen resonances helps to identify connected transitions.

Arrangements of ligands giving low electric field gradients

The rules for predicting arrangements of point charges which give zero electric field gradient at a point are summarized. It is then shown that in an axially symmetric group of charges, it is quite a straightforward matter to calculate the position of the zero-EFG point and that the tetrahedron and octahedron are only special cases of an infinite set of possibilities. These concepts are applied to a number of molecules which contain a quadrupolar nucleus in an apparently irregular environment but which give a narrow nuclear resonance, and it is shown that in such cases it may be possible to place quite strict limits upon the directions in which the electronic charge is concentrated and which portion of the bond is effective in generating field gradients. The results obtained support Gordy's contention that only the electronic density near the nucleus in question is effective.

Multinuclear magnetic resonance study of organomercury fulminates. The structure of mercury fulminate in solution

Abstract1H, 13C, 14N and 199Hg NMR data were obtained for organomercury fulminates, RHgCNO (R  Me, Ph, CNO). The relatively slow relaxation processes effective for the quadrupolar nitrogen muclei of these compounds allow the detection of 199Hg14N scalar coupling constants. This feature is ascribed to the presence of low electric field gradients around the 14N nucleus, owing to the presence of the mercury atom. In mercury fulminate, the 199Hg nucleus appears to be coupled with two equivalent 14N nuclei, thus indicating the existence of a covalent structure Hg(CNO)2 in solution.

TDPAC measurements on phase transition and hydrogen up-take in C15 laves phases

Intermetallic compounds with C15 structure are studied by TDPAC in the search for changes in the electric field gradient (EFG) on181Ta probes due to martensitic phase transition and hydrogen absorption. The residual low EFG of the cubic phase of HfV2, ZrV2 and Hf5Zr5V2 is distinctly increased in the low temperature modification. Hydrogen does not affect the distribution of probe sites, but influences the features of the martensitic transition. In TaV2 the sites with low EFG are split into an unperturbed and a strongly perturbed fraction.